High Performance Music and Home Theater Design Thread [Archive]

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Bruce H.

10-26-2018, 12:10 AM

Hi Guys,

I asked in another thread and it would seem there are a few folks here that would enjoy a discussion about achieving great sound in their homes. For those that missed it here's my background and where the focus will be in this thread...

I was an early adopter of Dolby surround when it was in it's infancy in the early 90's, trained in theater design and in the connection between sound reproduction, human hearing and room acoustics, an active member of the Consumer Electronics Designers and Installers Association (CEDIA) for many years, and have designed and built many media rooms and home theaters professionally.

My passion has always been the pursuit of faithfully and convincingly reproduced stereo and surround music and movie sound tracks. While the selection of equipment and surround sound formats has grown, and there's widespread availability of both technical information and businesses to design and install complete systems, achieving high performance sound is just as challenging today as in the early days. The last 20+ years of speaker, amplifiers, pre-amp, surround decoder and software playback system development hasn't really improved anything because the main limiting factor to the Holy Grail of reproduced audio hasn't been the equipment, it's in the acoustical nature of the rooms themselves. and the placement of speakers, listeners and acoustical treatment within them.

It's pretty easy to achieve a large and high quality picture image, high enough volume and deep enough bass to cause PTSD, and an ultra-plush theater decor, but accurately reproduced sound is the most difficult to achieve. That may not be a concern or priority for most, but for a discerning listener sub-par results can be very disappointing and frustrating. The problem can be compounded by a room that's been optimized for movie soundtracks when then used to listen to music in stereo or surround. Sometimes a room can be optimized for both...and sometimes for neither. It's good to know how suitable a room will be for the intended use, and to consider a better space possibly, and what can then be done to ensure best results.

I'd like to break down key factors affecting reproduced sound quality into two areas, the frequency domain and the time domain.

Frequency Domain

We ideally hear sound in the range of about 20 hz to 20,000 hz, with deep bass notes closer to the 20 HZ end of the scale and very highest notes above 10k hz. As we age our hearing degrades and we may only hear as high as 10,000 hz or so, if that. But most importantly is the range of the human voice and most instruments which are in the area of up to 4000 hz or so, and that's the range we need to be most concerned with. It's no coincidence that human hearing has developed to be most sensitive in this range. This is largely how we know and can recognize voices. If voices are reproduced inaccurately through speakers it's because the frequency response of the sound reaching our ears has been tonally altered by the interaction of the speakers sound with the room's walls, floor and ceiling, aka "room boundaries". Most speaker are able to reproduce fairly tonally accurate sound in the absence of any room boundaries, but in our rooms those surfaces amplify and reduce certain frequencies and change the sound.

I've never met most actors and singers but I know they sound a lot different through my Viper's radio than my home music/theater room where the frequency response of sound reproduced and heard in the room has been carefully calibrated to be tonally accurate. It's important to note the distinction between the sound that your speakers reproduce and the sound that you hear. The two are very different, and the reason is the effect that the room has on what we hear! You've no doubt experience that with the sound of your own voice when talking in acoustically different areas...perhaps in your home theater that has a lot of sound absorption.

We'll be discussing the effect of the room on your systems sound reproduction and figuring out how we can make it so the room doesn't degrade sound quality, and how it can maybe even enhance it!

Time Domain

We largely determine the direction of sound we hear by the difference in the timing that each ear hears it. Sound coming from our right side arrives at our right ear before it arrives at our left ear because that ear is closer and our ear and brain are so highly tuned that they can tell the difference, even small differences. If sound arrives at both ears at the same time, they can tell if it's centered in front or behind us. When we sit dead centered between our stereo speakers listening to music part of what we hear unfortunately is the speaker's sound reflecting off the floor almost immediately, off the ceiling immediately after that, and then off the side walls after that again. And not only does the right speaker's sound bounce off the right side wall but it also bounces off the left wall to further mess up what we call "imaging". A system with good imaging is able to fairly accurately place sounds around our room as existed in the space where it was recorded, or according to how the recording engineer intended it to sound. A system with poor imaging also degrades the intelligibility of dialogue which makes it harder to make out what is being said in movie soundtracks. This loss of "detail" through poor imaging also degrades the sound of music recordings. And we'll be discussing how to ensure that your subwoofer isn't degrading your system's tonal accuracy, imaging and detail.

Our ears hear quite a blurred sound and we lose some important directional cues if we don't do something about it. If we listen to well-recorded music it's really nice to get a sense of where the singers and instruments are located across the stage ("called sound stage"). Recordings also often contain the reflected sounds of the recording venue, perhaps a studio, performing venue, or maybe the outdoors. When these "spacial cues" are accurately reproduced we get a sense of the size and acoustical nature of recording space.

So that's a brief preview of what I want to cover, and why mastering these two areas is critical to being able to accurately reproduce music and movie sound tracks at home. It should be pointed out that reproducing impressive sound quality doesn't necessarily require you to spend a lot of money on modifications to your room, and that no amount spent on modifications to the room will compensate for not adhering to the basics we'll be discussing.

I'd like some of you to post a picture of your music or movie room taken from the back looking forward to show your listening seat, the main speakers, and the front and side walls next to them. We'll discuss that layout, how it affects the sound you hear, and whether there might be a tweak to significantly improve sound quality.

Bruce

Bruce H.

10-28-2018, 12:17 PM

Avoiding room sound issues is a lot easier than dealing with them

When you understand how much a room’s walls, floor and ceiling affect the ability to accurately reproduce music and movie sound tracks you’ll want to know what to look for when scouting out the best area in your home, and what challenges you may still have to face. And if you’re shopping for a new home you’ll be armed with what to look for if planning for great sound!

The easiest ways to avoid the vast majority of issues is to set up your system in as large a room or area as possible, and to avoid one with issues related to its design and construction. But that of course isn’t always possible. I’ll note whether issues are in the frequency or time domain as their possible treatment method can be quite different. Where one can be somewhat improved with the common use of electronic room equalization the other cannot. I’ll also refer to a “room” and an “area” because you can choose to set up a system in a dedicated theater/music room or in a larger multi-use area of the home, both with important considerations.

Size matters, and the benefits of a larger room or area are many…

If your main left and right front speakers are a few feet away from the side and front end wall then the tone of their sound won’t be degraded by the reflections of sound between the speakers and the walls that cancel some frequencies and amplify others. This is a frequency domain issue called the Boundary Effect. And keeping those speakers a few feet away from the side walls also addresses the time domain issue of “imaging” involving the direct sound reflection from the speaker to your ear off those walls. If your room isn’t wide enough for this spacing there are acoustical room treatment$ that can help.

All rooms with parallel walls have Room Modes, also known as standing waves. This is frequency domain issue whereby some very audible lower frequencies within the critical vocal range are cancelled and others amplified when they bounce back and forth between those parallel walls. The affected frequencies are determined by the distance between parallel boundaries, so you want to ensure that the the room’s height, width or length are not the same as another, or even a multiple of one of them. So no square rooms or rectangles that are 8’ high, 16’ wide and 24’ long for instance. When the walls are further apart the audibility of the affected frequencies becomes less. But even more importantly is the improvement in the lowest frequency range that is reproduced by the subwoofer speaker(s). Walls that are further apart allow for both smoother and deeper bass frequency response.

Room/area design, shape and construction matters…

Where I noted issues related to the sound from speakers reflecting off of nearby and parallel walls, ceilings and floors, reflections broken up by non-parallel and irregular surfaces can have real benefits. That room or area with the cathedral or coffered ceiling might be good, or the one with the irregular shaped floor plan. Where a dedicated home theater is often set-up in a rectangular room for practical reasons, separation from others to avoid disturbances, and predictable acoustical properties, you might be able to consider other areas also, including a media room concept where the space could include a variety of uses like a lounge with fireplace and windows with a view and suitable coverings, bar, games table, exercise equipment, office/computer desk, etc. Dedicated theaters are easiest to make dark for best picture quality, quiet for undisturbed enjoyment, and acoustically designed and treated for incredible movie sound, a system set up in a larger space can have equally impressive results and other advantage$!

Where the sound quality in most rooms will be heavily affected by room modes and reflections, they can be partially addressed by acoustical room treatments, the most common being sound absorption products. And the actual construction of room’s structure affects room modes and reflections at low frequencies below what most acoustic treatments can. You can actually feel the room’s structure absorbing sound. Whenever there are deep bass notes played in a movie sound effect or musical passage the floor actually flexes and you feel your chair shake. The walls also flex as does the ceiling. As these flex they absorb a range of low and deep bass frequencies that caused them to flex, and that absorption reduces the severity of some of the room modes that cause the uneven and annoying bass response. The floor of a room generally absorbs the lowest notes best, unless it’s made of concrete and doesn’t flex at all (warning!). Since deep bass notes bouncing around the room are very hard to absorb by any other means, they linger longer, and mask the detail of more subtle sounds being reproduced. Movie fans may be more tolerant of the trade-off between deep bass sound effects and detail but that can be a real problem for discerning music lovers.

The structures of floors, ceilings, and walls are all constructed of different size, length and spaced joists, rafters and studs, and are covered by plywood, sheet rock and other materials, all with different resonating (sound absorbing) frequencies which is good to cover more of the range of bass issues. A conventional rectangular shaped room would generally have fewer differences in construction and frequency absorption as opposed to an area that is more varied. Even windows flex and absorb frequencies according to their size and shape. All of these flexing structural room components are types of diaphragmic absorbers, and are invaluable at taming low frequencies problems.

Choosing or building the perfect room

Forget it, perfect doesn’t exist! Not possible! Most homes don’t have an available room or area that’s large enough! Your wife is likely to threaten divorce if you even think about turning her stylish great room or master bedroom suite into a dark theater. Your basement may be humogous but the ceiling is a little on the low side, the floor is concrete, the furnace is noisy, and you’ll need a stair lift or elevator to get down there and back up again in a few years! And getting a subwoofer the size and weight of a small car down there won’t be easy either.

But the good news is you don’t have to have a perfect room to have great sound…and it doesn’t necessarily have to cost a lot if you know what you’re doing and can get the most important elements right! You can probably still use all of your existing sound equipment, it might even sound a lot better when you change a few things around, and if you do get the upgrade itch you’ll know where you need to focus your efforts!

Let me know if you're with me so far, and any questions or comments you have. I'm also interested in hearing what audible issues you realize that you are actually experiencing. Then we'll get into the specifics of analyzing a room to determine the best placement of listener/viewer, speakers, screen, and essential acoustical treatments.

Bruce

Bruce H.

10-29-2018, 08:55 AM

While there's no shortage of theater design advice available with a few clicks, the ultimate goal here is in the title of this thread, to also achieve high performance music reproduction. The reality today is that many do their critical music listening in rooms designed for home theater, often designed by professionals trained to do just that, and that generally seriously compromises the ability to reproduce music very well. It is often possible to do a brilliant job of both, and if you get certain details right the audible difference is night and day.

IndyRon

11-04-2018, 08:38 PM

Bruce, most of the purists would argue that a compromise is the best you can hope for. I personally put my emphasis on multichannel immersive reproduction as it pertains to movies. The 2 channel rooms are often treated differently. Of course the 2 channel guys also subscribe to the idea that even the power cords must be multi thousand dollar units.

A subject that I’d enjoy hearing your opinion on is in regard to high end power conditioners...

Bruce H.

11-05-2018, 12:28 AM

Hey Ron, how's the new theater coming along?

In order to achieve a dedicated theater room that involves little compromise to either movies or music the design needs to focus on the requirements for both. A theater can be designed and sound optimized with the "money seat" in more positions within the room than the ideal location for optimized music listening. If you can set up the room seating and main front speaker locations so one of the movie seats is in the ideal music listening position then there's no compromise necessary. Acoustical treatments can then be done to optimize for accuracy of all content played through them, movies or music. And then the blend of diffusion and absorption around the rest of the room can be done to satisfy the needs of surround sound while being careful not to make music reproduction suffer.

Creating an immersive movie viewing experience is relatively easy with multi-channel speakers and placement of discrete surround channel sounds all around the room, and that is more integral to that goal than the ability of the system to reproduce music with accurate detail and sound stage. But if your goal is to do both then that is often possible if approached accordingly.

I've never subscribed to the belief that high end cables sound better than merely decent quality ones. While some with golden ears may think they can hear subtle differences in cables... everybody can hear the difference listening to music in a room set up nicely for that. But whether your thing is music, movies or both, having a good room or area to set it up in has a big impact on the results. I'm afraid I'm not the one to discuss power conditioners with, but I'm sure there's a pretty lively discussion about them on-line!

It seems there's quite a lack of interest in this thread topic.

mjorgensen

11-05-2018, 01:47 PM

I don't think there is a lack of interest Bruce it's like anything it needs pictures!

Bruce H.

11-05-2018, 02:03 PM

Maybe that's it, Mark. What I'll do is take some pictures of my room in order to explain some of the techniques used to optimize a set-up for both uses.

Bruce H.

11-06-2018, 06:53 PM

I don't think there is a lack of interest Bruce it's like anything it needs pictures!

Okay, here's some pics of my setup. This is a fairly large 3rd floor loft that's somewhat divided into areas for movies/TV/music, exercise, crafts, daybed, and there's also a 4 pc bath and an HVAC room. The room isn't complete, with some changes to seating, furnishing and decor yet to come.

Front center
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Front right
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Front left
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Left side
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Rear
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Bruce H.

11-06-2018, 06:56 PM

100" electric screen

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Floor plan of the entire loft area. Note the location of the point marked with a circled "R".

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Deb and I were looking for a renovated Victorian era home three years ago, and when we found the one we really liked it just happened to have this open loft area and I knew exactly what I would use it for. It's a 2 1/2 storey home with this being the 3rd floor, 44" high knee walls around most of the perimeter, with sloped walls above that up to the ceiling. There's a window in a niche area with a daybed seen extending off in the front left pic, another in a niche at the rear left, an exercise area behind the wood room divider at the rear with a skylight, bathroom with skylight and a furnace room in the rear right, staircase on the right side with open railing to the 2nd floor, and a skylight hidden behind the front screen wall cabinetry. The floor has sound batts that deaden sound from the bedrooms below.

What criteria are important when choosing an area for your theater and music use?

-Separation from the rest of the home so as not to disturb others...or have them disturb you. A dedicated room with a door and maybe soundproofing is a popular solution for many families. That's what we did when we had kids still living at home but now it's just the two of us, and this area is already pretty well separated from most other areas.

-Control of lighting is important to picture quality. Window coverings can take care of that. The locations of our windows and skylights didn't require any special treatment.

-Room size large enough to accommodate the seating capacity that you need, and in such a way that everyone has an unobstructed view of the screen.

The more technically informed hobbyist likely also knows that room size and shape, the position of speakers and viewers/listeners, and the room's acoustical considerations affect sound quality, but likely don't appreciate the dramatic impact that all three make, how to avoid the most serious issues, or how to effectively deal with them. Those will be the focus of this thread. Much of it will seem like a review of what can be read in magazines and on A/V forums, or learned from theater designers, but I'm betting everyone will pickup a useful tip or two to improve their room's sound quality, and explain the audio issues they're experiencing.

The audio issues that many will be experiencing will be related to the accuracy and quality of deep bass, uneven frequency response, poor imaging, and movie dialogue with compromised intelligibility. I'll refer to these specific issues as I discuss the room's size, shape, seating and speaker positions, and room acoustics.

Bruce H.

11-06-2018, 08:19 PM

1. Room size and shape

Some sounds from your speakers reflects off of walls, ceilings and floors (aka room boundaries) like a pool ball, and others rebound back and forth between the parallel ones, which are typically front and back walls, between side walls, and floor and ceiling. The rebounding ones, which are notes in the low and very low frequency range, are notes at numerous frequencies that are dramatically increased in intensity and others that are reduced, making reproduced sound very noticeably inaccurate and often quite annoying. The affected notes are those with wavelengths that correspond to the distance between parallel boundaries. These affected frequencies are known as "Room Modes", and they can be rather easily calculated for any box shaped room.

I don't want to get too far into the weeds at this point, but suffice it say that the negative impact of room modes on sound quality can be minimized by planning a new room's dimensions carefully, and also by making it as large as possible. An example of a room shape that would have serious issues would be a square room where the front/back wall modes and the side/side wall modes would be at the same frequencies, thereby making each one even more severe. Any new room designed with parallel walls will have room modes, but the proportions of the room can be such that there's at least a less destructive distribution of them throughout the room.

Room modes are particularly important as they are very difficult to satisfactorily resolve with acoustical treatments.

2. Seating and speaker position

One goal should be to sit somewhere in the room where the negative effects of room modes is minimal. In decreasing order of severity, room modes typically are the worst close to corners of the room, near to walls, and in the center of a room. In a rectangular room the most even low frequency response is 38% of the room's length back from the front wall, or from the rear wall. You can use this as a guide, but in practice there are a number of reasons that may not work in your room, like sitting a suitable distance back from the viewing screen if it's location is restricted by other factors. Try to avoid the worst seating locations if you can and we'll discuss later the partial remedies that might help with those nasty room modes.

The speaker's sound interacts with the room in various ways, not only causing the room modes at low frequencies, but also causing something called "speaker boundary interference response", aka "boundary effect" for short. This involves speaker sound that directly reflects back off of a side wall next to the speaker and either cancels or increases certain frequencies based on their wavelength and distance from the wall. This also happens between speaker and back wall, and speaker and ceiling. At this point you may be thinking it's easier to just sell all your gear and find a new hobby but stay with me for a while!

Higher frequencies are reproduced by mid-range speakers and tweeters, and those frequencies are more directional. Those aren't going to reflect off the wall and back to the speaker directly when it's pointing into the listening area, and even less if the speaker is slightly toed in towards the middle of the room where the critical listening seat (aka "money seat") has been carefully positioned. The frequency range that is directed all around the speaker that we are concerned with here goes up to maybe around 500 hz, beyond that they are too directional to radiate to the side wall directly beside the speaker. This boundary effect can be dramatically reduced by positioning your main front speakers very close to the front wall or out several feet from it, and the same for side walls. This is because of the wavelength of the range of frequencies reproduced by the main speakers, most typically in the range of 50 hz and above in a subwoofer/sat configuration with a cross-over setting of 80 hz. The lower frequencies are more often reproduced by a separate subwoofer and it's position is more flexible than main speakers that need to flank a screen or be ideally positioned in relation to the "money seat".

And speaking of which, audiophiles mostly agree that the ideal positions of main left and right speakers and the money seat is in the form of an equilateral triangle, with the distance between left and right speaker being the same distance as each speaker to that prime listening seat. That position relationship is called "The Golden Rule" and has the effect of optimizing stereo imaging and maximizing the ratio of pure direct sound from the speaker relative to reflected sound from the room boundaries and objects within the room. As sound reflects off of objects and surfaces some frequencies will be absorbed and the reflected sound will be tonally distorted. Reflected sound also takes a longer path before it reaches our ears, arriving shortly after the direct sound. Too much reflected sound can blur and degrade the stereo imaging in a variety of ways.

3. Room acoustics

The size, shape, structural construction, finishing materials and everything within a room determine how sounds will sound in a room. An empty room with all glass walls and a tile floor will sound entirely different from a living room with heavy drapery, thick broadloom and over-stuffed sofas. Years ago as a hobbyist I had a problem with my movie room where I could never get the sound right when playing music in stereo. The bass was always off on one side of the room and that was affecting the stereo image. I swapped and reversed everything I could, even setting it all up at the opposite end of the room, but the bass was always weaker on the side of the room opposite the fireplace. Was bass leaking out around the door on the one side of the room, or up the fireplace on the other? One day I had been painting the room and moved the sofa from one side of the room to the other. I took a break and sat down to listen to some music. Well what so you know, the weak bass had suddenly shifted to the other side of the room! The position of the bass absorbing sofa was enough to make a very noticeable change to the sound in the room! And that's when I became interested (okay, obsessed) with acoustics, and how we hear and perceive sound.

Walls, ceilings and floors built on studs, rafters and joists will absorb a range of low bass frequencies, their finished surfaces affecting the absorbed frequencies. A wall covered with a double layer of 1/2" sheetrock absorbs lower frequencies than one covered with a single 3/8" layer. A plywood floor built on joists 12 feet long will absorb differently than one on 16 footers. These are examples of low frequency diaphramic absorbers.

Most carpet, stuffed furniture and acoustical room treatments made of sound absorbing materials affect mid and higher frequencies much more than lower ones. The more tonally accurate sounding rooms will have benefited from sound absorption across a very broad range, and not concentrated on a narrow range. Covering large expanses of walls in a home theater with sound panels affecting the same range of frequencies can throw off the tonal balance of the room.

Reflective surfaces in a room are also important as they help provide a more natural ambiance and add life to a room that would otherwise sound dead. The reflective, or reverberant, nature of a room can be both heard and measured. Reverberation is a measure of the time it takes sounds in a room to be absorbed, and can dramatically vary by frequency. As an example, a deep bass note is very difficult to absorb in some rooms and that makes it linger in the room, slowly dying down as it's absorbed. As it lingers it masks other sounds and makes them inaudible...not good. High frequencies are easily absorbed by almost everything in the room, even thin air. It's all too easy to absorb too much of the high frequencies as you attempt to tackle lower and mid-range frequencies. A room considered optimized for music is generally considered to be more reverberant than one optimized for surround sound movies, but the acoustics in a room can be designed to be adjustable to be optimize for both as desired. And a larger room can be set up to work equally well for both without any changes to acoustical treatments.

The design of acoustics for music rooms and theater involves understanding and dealing with room modes that will exist, constructive and destructive direct and early speaker reflections, and room reverberation.

Bruce H.

11-06-2018, 08:21 PM

Making the room design and layout decisions

I had already made the decision to use an existing room and not build a new one. Many here will have decided the same as opposed to building a new room from scratch. This is how I was able to make that decision and then make the key seating and main speaker placement decisions that would determine everything else that would follow.

Room layout showing "money seat" and main speakers
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Room size and shape. Large rooms will generally have a smoother and flatter low frequency response because there will be many more room modes, which you might think would be a bad thing, but is actually better. This is because you can more easily hear room modes causing distinct and excessively loud notes at say 32 and 64 hz than you can if they are numerous and more evenly distributed like say 16, 24, 32, 40, 64, and 78. When planning the build of a new room you can ensure a more even distribution of room modes by calculating and optimizing them with a favorable room size and shape. In a nut shell, room modes formed between parallel walls occur starting at lowest (fundamental) frequency and every multiple of it, and calculated as 1/2 the speed of sound divided by distance. Given the speed of sound at sea level is about 1125 ft/sec, the fundamental frequency in a room 37 ft long would be 1125 / (2 X 37) which rounds off to 15 hz, and with it's multiples creates modes at 15, 30, 45, 90, 135 and so on. A room 17 ft long has fewer modes at 33, 66, 99, 132 and so on, and fewer can be more troublesome to deal with. A full room mode analysis would calculate modes out to 300 hz where they are no longer a factor, and for the other "axial modes" occurring between the parallel side walls and floors and ceilings. The advantage of building a new room is that you can play with room dimensions to create a room with an even distribution of modes, thereby making them much less detectable, and often at least partially treatable with acoustical treatment and sparing use of electronic equalization. A room like mine is tough to calculate all modes as the room isn't perfectly uniform and rectangular, but jogs in and out and half of the wall height is sloped and not parallel. Good luck calculating that, but a room this size and shape is likely to produce a fairly even distribution of room modes.

Seating and speaker locations. I could predict the optimum "money seat" location using the 38% room mode guideline mentioned in post #10, and noted this reference point on the plan with the circled "R". This is the distance back from an end wall where there should be the most even deep bass produced by the subwoofer and the lower reaches of the main speakers. Placing main speakers at the end of the room that was widest would minimize the effects of sound reflecting off the sidewalls and that viewing screen position would also allow for a good placement of the number and types of seating we wanted to use. It's also best to not place the main speakers equal distance from the side walls, which wasn't even an option in my room. I identified the overall seating area for listening and viewing and drew a center line to use for orienting everything. The "R" reference point was then used to locate the left and right main speakers according to the "Golden Rule" mentioned in post #10. You'll notice I actually used a seating position just slightly ahead of the "R" and the speaker measured placement according to that. This was a small compromise to place the second row seating also in the "sweet spot" and to use a technique of having the speakers intersecting point about 16" behind the ears rather than at the ears. You'll also notice that the speakers are pointed at the "R" just behind my head, pointing them at my ears instead of the center of my head. This is a modified Golden Rule approach said to further improve imaging. However, placing the speakers 4 feet or so from the back wall wasn't ideal because of the boundary effect that I'll discuss shortly.

The following layout shows a wood "baffle wall" that was constructed directly behind the main speakers and also houses the electric projection screen, and other speakers and room treatments that we'll discuss soon. The cabinetry's real purpose is to eliminate destructive reflections between the main speakers and the front wall behind them which were cancelling certain bass notes (aka "bass suckouts") that are directed full circle around a speaker, and which were very audible in the male vocal range. Placing a speaker against the wall eliminates the wall problem. In my case wall placement wasn't a good option. But by placing this reflective surface directly behind the speakers only shorter wavelength frequencies could be affected, leaving all bass notes unaffected. And since the higher frequencies are too directional to be directed backwards at all then we didn't need to worry about them at all!

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I found a couple of articles that discuss and illustrate rather well what I've covered regarding the 38% guide to help avoid room mode problems affecting bass, the Golden Rule for positioning main speakers and the listener, and the "Boundary Effect" (aka SBIR, Speaker Boundary Interference Response). If you can apply those in your room then you're well on your way to incredible 2 channel and multi channel sound! They discuss recording studio control rooms and listening rooms, but the principles are mostly the same.

http://arqen.com/acoustics-101/room-setup-speaker-placement/

http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

You'll also notice on the room layout that I've added the position of the 4 surround speakers and subwoofer that make up my 7.1 system, the second row and sofa seating, side wall and ceiling "early reflection" absorbers, deep bass sound absorption behind the screen wall, diffuser/room divider unit behind the seating area, and some diffusion created by furnishings. The pattern of dashed lines drawn outwards from the main speakers to the absorber panels are then extended into the room to show the approximate area of the room where early reflections will have been effectively treated. I forgot to show the center channel speaker but it is right in the middle between the main speakers and you can see it in the pictures of the room in post #8.

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Side surrounds (LS, RS) are located just behind the front row seats and pretty much directly to the sides of the second row seats. This follows within widely accepted recommended placement areas. They are mounted at ear level, and at that height mostly because above that level the wall is sloped and would have looked awkward. They are of the dipole type which are designed to spread their sound over a broader area than a monopole speaker, and in doing so helps masks its exact location in an effort to reproduce the sound of an array of speakers used in commercial theaters. This is a THX specification for home use and there's a lively debate by enthusiasts over which type of speaker is best. I've mostly used dipoles in the past and always found them to create a convincing surround sound effect when used correctly. I've also placed various furnishings around these speakers to promote enhanced diffusion of the sound field.

Rear surrounds (LR, RR) are mounted high on a cabinet designed as a sound diffuser (also used as a room divider for the gym behind it) to enhance the spaciousness of the sound field behind the listeners. They are also dipoles, but a design that is a little more directional than the side surrounds. I like to explain the surround speaker goals using the example of trying to reproduce the sound of a rain storm heard in a movie soundtrack. If the origin of the sound of rain can be easily localized at the speaker's location the rain sounds will seem to be coming through open windows rather than you standing outside in the middle of the rain storm itself. This surround pattern is also effective over a fairly large seating area. And when there are discrete sounds that are supposed to be localized around the room they still are. The diffuser unit is designed to scatter incoming sound over a broad range of frequencies to further enhance the envelopment of surround sound.

Subwoofer is located very close to the front wall and to the right of center near the right main speaker. The front wall location energizes all of the room's length axial modes to provide the smoothest possible frequency response. If it were moved into the room it would start to stimulate some modes and not others, thereby making the bass response uneven and peaky sounding. I also tried moving the sub back and forth along the front wall and found this location to provide the smoothest response at the money seat and other seating as well. In the front right corner also worked particularly well but rear panel access and aesthetics considerations dictated its final location. It uses 2 18" drivers mounted vertically which has the effect of smoothing the axial room mode between ceiling and floor.

The "money seat" is used for listening to music, and more and more for movie viewing as opposed to the second row seat directly behind it that I was always more comfortable with in regards to screen size. I typically don't like the feeling of sitting too close to the screen but I seem to be getting over that sensation! The front seats are rather low and the second row is a taller style used in commercial theaters. Taller guests can sit in the 2nd row and have an unobstructed view of the screen. The sofa on the left side is there because Deb prefers to lay on a sofa to watch movies. She somehow manages to defy the theater seating law that states if the viewer is over 40 years of age and it's after 8 pm that they will surely fall asleep if they get horizontal!

Early reflection absorbers are needed on the side walls and ceiling positioned where sound from the two main speakers reflects off those surfaces to your ears. These sounds arrive at your ears a millisecond after the direct speaker sound to your ears and has the effect of blurring the imaging of well-recorded music and degrades the intelligibility of dialogue in a movie sound track...not good. They also cause "comb filtering" which is the amplifying and cancelling of certain frequencies as the direct and reflected sound waves combine at the listening position...not good either. I used a mirror held flat to the side walls and ceiling and my wife sitting in the 5 primary seats to locate all the places on the walls and ceilings where she could see the speakers reflected in the mirror. I marked those spots with painter's tape and then built my absorbers to a size that would cover all of those dozens of points. Note that the entire seating area is treated by two wall panels 36" X 64" and one ceiling panel 36" X 60". The difference they made to imaging and on-screen dialogue intelligibility was very obvious. The absorption material used needs to be effective over the frequency range of the reflections and be positioned out from the wall at that frequencies 1/4 wave length. This 1/4 wavelength is the part of the sound wave with the highest velocity (think of the wave oscillating up and down, peak to valley) and sound absorption material works on the basis of friction believe it or not, absorbing the oscillating sound energy. I made them out of 1"X4" wood covered with cloth and filled with 4" sound batts. Wall hung and spaced 1" out from the wall to extend their effectiveness to frequencies as low as possible while trying to maintaining an acceptable appearance!

I filled the area behind the front screen wall with Roxul Safe N Sound batts, floor to ceiling, 2 ft deep, 11 feet wide. That's the massive amount necessary for a friction type absorber to work on deep bass notes with such long wavelength, and it made a very audible improvement to the tightness and accuracy of deeper bass notes. That works in conjunction with the construction of the room that uses many different dimensions of wood covered in sheathing in the floor, ceiling and walls, each of them absorbing at different frequencies. Those are "diaphramic absorbers", absorbing the sound waves "pressure" (instead of velocity) and are the most effective at absorbing deep bass frequencies. This is a good time to note that covering entire walls with 4" sound batts will do nothing to absorb deeper bass notes, but will absorb all the mid and high frequency notes. And deep bass needs to be absorbed because otherwise it will bounce back and forth too long and mask important sounds.

Decay time (or reverberation time) of sounds reproduced in a room is the measure of how reflective or absorptive the room is. It's the difference between the sound of the glass walled room I mentioned earlier as opposed to a room with heavy drapes and over stuffed furniture. A room that is ideal for music is generally considered to be a little more reflective than an ideal room for surround sound use. I can't say I'm a huge believer in that as a hard and fast rule as there are other factors that influence the end results even more, and I feel that the distribution of absorption and diffusion is the key. You'll notice that I used a minimum of absorption panels, just enough to cover the early reflection points on the walls and ceilings, and placed all of the deeper bass absorption behind a reflective and diffuse screen wall where only the deep bass could be absorbed and none of the mids and highs. An option I'd prefer if more absorption was required to lower the decay time would be to have absorption panels that could be used for movies and covered with a removable diffusion panel when listening to music...make your room convertible to optimize for both if you find the need. But in my experience I prefer a room set up to optimize for music because that difference is so audible, as opposed to theater use where any slight difference in decay time is lost in the action.

So there you have it, the most important room design elements to account for when aiming for high performance sound reproduction at home. I didn't discuss speaker and A/V products, and there's a vast array available to choose from and many review sources. Much of my own system would be considered high-end, some of it's 20 years old, mains, sub and projector are almost new, but it really is "the room" that makes the jump to extraordinary sound quality!

I hope you enjoyed the read and I'd be happy to further explain any parts of it in more detail.

Bruce

IndyRon

11-07-2018, 11:57 AM

Looking good Bruce. My project is coming along. I’ll post some pics of the current progress soon. With a theater it’s a 2-fold challege. First is to isolate the room acoustically from the rest of the house and keep the sounds inside. Second is to optimize reflections, decay, absorption where appropriate.

Bruce H.

11-09-2018, 04:27 PM

Guys,

I've just completed the outline of key room design and layout considerations for high performance music and surround sound at home and edited it all into posts 8-11 to keep it concise and easy to read.

While the first step to the Holy Grail of sound is getting the room right so it can support it, the next steps involve measuring, calibrating and tweaking the system to perform its best. Integrating the sound from your subwoofer and main speakers can be a bit of a challenge and likely make the biggest impact, speaker and any EQ settings in your surround sound processor the easiest, and tweaking the frequency response with an electronic equalizer the most time consuming. Some processors use a built-in and auto calibrating EQ program by Audyssey or others, or you might have a separate EQ. But an EQ of some sort is required if you want to have an accurate sounding system. The attention to room details I've discussed above gets your room to the point where an EQ can get you the rest of the way to your sound goals, but an EQ is only able to address some sound problems, not all. Here's a link that discusses what a room correction equalizer can't do, which is why you need to get the room set up well first...

https://www.hifizine.com/2010/09/the-three-acoustical-issues-a-room-correction-product-can%E2%80%99t-actually-correct/

I've been using a cool Real Time Analyzer phone app for taking room frequency response measurements. I think it costs about $10 bucks and I also bought a calibrated phone mic for higher accuracy than the phone's built-in microphone. Works great and you can easily see where you have frequency response problems and then monitor various changes to speaker position and aim, subwoofer rear panel settings, processor speaker and EQ settings, room acoustical treatments and fine tuning with a separate equalizer.

https://sites.google.com/site/bofinit/audiotool

Hope all this inspires you to take a look at ways you might be able to improve your enjoyment of your systems...and if you live in northern area, to help pass the winter!

Bruce

BigBadViper

11-13-2018, 08:45 PM

Bruce H.

11-13-2018, 11:10 PM

Are you going to elevate your second row of chairs. The view from there looks like it would be horrible. The front chairs don't look all that comfortable. The room doesn't look like a great shape for a home theater. I know what you are doing with the diffusers and stuff. But you will have sound bouncing all over the place.

We have a 120" purpose built theater and we never go in there, maybe 3 times in 2 years. It will seat 8 normally but with bean bags we can fit 12-15. We use the 65" in our bedroom all the time.

No need to raise the second row seating as sight lines are actually quite good and the front seats can easily shift a bit if necessary, and have on occasion. If this were a dedicated theater I'd have probably used a riser for the second row, but it isn't, and I wanted to avoid a riser for this room, choosing instead to vary the height of the seats. Front tub chairs are actually very comfortable with pillows for lower back comfort (not shown).

The irregular shape is actually very good for sound quality as it breaks up room modes to provide a smoother room frequency response. Sound bouncing all around is essential to creating the desired reverberation time and an enveloping surround sound field to the sides and rear of the room. You really only need to absorb early side wall and ceiling reflections in a larger space along with any other absorption necessary to ensure balanced absorption across the spectrum (ie. so you aren't just sucking out the highs for instance thereby making the room sound dull). The sound quality is outstanding to even the most critical audiophile ears...and I've had a few of them audition the room.

Your comment about hardly ever using your dedicated theater is quite common and unfortunate. When a system is integrated into a comfortable space that's a bit more central to other activities it's more likely to get used more often, and maybe to enjoy the system for listening to music when doing other things. That's more the media room concept rather than a dedicated theater, and in our case we can enjoy our system when watching our nightly TV shows, while exercising, doing crafts or hobbies, playing cards with friends at the games table, etc. If we added a fireplace it would be even better! I have a bar, fridge, coffee maker, microwave, pop corn machine, etc. We use the room and the system every day.

BigBadViper

11-13-2018, 11:27 PM

Your comment about hardly ever using your dedicated theater is quite common and unfortunate. When a system is integrated into a comfortable space that's a bit more central to other activities it's more likely to get used more often, and maybe to enjoy the system for listening to music when doing other things. That's more the media room concept rather than a dedicated theater, and in our case we can enjoy our system when watching our nightly TV shows, while exercising, doing crafts or hobbies, playing cards with friends at the games table, etc. If we added a fireplace it would be even better! I have a bar, fridge, coffee maker, microwave, pop corn machine, etc. We use the room and the system every day.

I hope you do use it. We have so many dedicated rooms for different stuff and we hardly use any of them. Game room. Pool Room, Theater. We have the popcorn machines, cotton candy, snow cone. We have a 24 zone speaker system throughout the house and hardly use that.

For me the quality of the sound doesn't matter too much as everything rings like tinnitus.

I can't tell the difference between 1080, 4K, 8K, Heck I can barely read a document any more.

IndyRon

11-14-2018, 01:54 PM