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Clean Sheet Approach for a DIY Multi-Channel + General Use System

Fredygump

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Nov 3, 2022
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My perception is that the setup of most home audio systems is dictated by fairly arbitrary constraints, things like the height of the TV stand, the height of the left and right speaker, and our cultural knowledge of what such a system is supposed to look like. So we have a left and right with tweeter near center line of the TV, and a center channel below the TV.

So the first question should be, is the "normal" configuration an optimal system, or can it be improved?

Next question: If we throw out all the pre-made furniture, and if we are use DIY speakers that can be made any way we like, what theory would give the best possible results for audio quality? My particular interest is arranging the left, center, and right channels relative to a TV. And the hope is that the resulting arrangement would be equally suited for stereo and multi-channel. The intent is to use it for stereo, movies, and atmos music.

Anecdotally Ethan Winer has shared his home theater setup, where he uses active studio monitors all placed at equal height, with a projection screen above the center channel. Is this acoustically superior? Or does it really not matter what height speakers are?

For context about my specific thought process, my speakers-in-progress were designed with the horns matching the vertical center line of my TV (65"). It seems ideal for stereo, which is where I've been at for awhile now. But if I add a center channel either above or below the TV, the horn center is approx 24" above or below the horns on the right or left. I think this might become noticeable.

At this point I can change anything. The height of the TV, the height of the speakers, the location of the horns within the speaker cabinet, the design of the center channel and the expected location of the center channel. So I'm just in search of a theory to guide my design.
 
My first advice would be to get rid of the TV, and replace it with an acoustically transparent projection screen and projector. It allows you to place the center channel at ear height, you can use the same speakers on all channels, and avoid a compromised vertical center speaker. The center is the most important channel, so don’t compromise there! Next - a truckload of good subwoofers….

I’ve done the same as you’re thinking of - build a system for everything; stereo music, surround and atmos music, and home theatre. Watching movies with a truly great hifi sound system is really something. They put a lot of work into movie sound design these days, and some movies sounds extremely good in my opinion.
 

This is sort of the gold standard but it only works for projectors with acoustically transparent screens.

The other consideration would be strategies like the Meyer Ultra Reflex which is intended to work with large format LED displays.



This is supposed to be patented, but patent holders go after commercial infringement not hobbyists doing this on their own.

Going above and below the screen will depend on where your speaker is relative to screen and how far you sit away.

Products from Sony, Yamaha, and Trinnov allow you to utilize the front height speakers in combination with an under-TV center to provide a phantom image that is closer to a projector/transparent screen. I don’t care what the diffraction risks are — it really works well.

Along those lines, my argument is that the center under the TV is less ideal if you are running a processor that lacks the center lift approach. Since dialogue is coming from the center, and people’s heads are usually mid frame or above, you really should be putting the center channel ABOVE the TV.

This is how Skywalker Sound sets up their nearfield setups. Speaker above, inverted to get the tweeter closer to the screen.

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My first advice would be to get rid of the TV, and replace it with an acoustically transparent projection screen and projector. It allows you to place the center channel at ear height, you can use the same speakers on all channels, and avoid a compromised vertical center speaker. The center is the most important channel, so don’t compromise there! Next - a truckload of good subwoofers….

I’ve done the same as you’re thinking of - build a system for everything; stereo music, surround and atmos music, and home theatre. Watching movies with a truly great hifi sound system is really something. They put a lot of work into movie sound design these days, and some movies sounds extremely good in my opinion.

As a general design philosophy, it sounds like you're willing to sacrifice some video quality in favor of "perfect" audio alignment?

I like the idea of big speakers for all channels, but I'm not sure I want to give up the image quality of a good TV. I have a 65" Sony OLED, and I am a fan of the overall picture quality and it's ability to reproduce perfect blacks.

I had a projector in my living room some years ago. It wasn't acoustically transparent, though. I used a gray paint designed to improve contrast when there was ambient light, and it worked ok. But it was not close to an LCD, let alone an OLED, atleast not in day time. While I suspect screen technology has improved since then, this strategy will have to wait until I can build the dream home....
 
Products from Sony, Yamaha, and Trinnov allow you to utilize the front height speakers in combination with an under-TV center to provide a phantom image that is closer to a projector/transparent screen. I don’t care what the diffraction risks are — it really works well.

Along those lines, my argument is that the center under the TV is less ideal if you are running a processor that lacks the center lift approach. Since dialogue is coming from the center, and people’s heads are usually mid frame or above, you really should be putting the center channel ABOVE the TV.

This is how Skywalker Sound sets up their nearfield setups. Speaker above, inverted to get the tweeter closer to the screen.

It is interesting that they keep the left and right tweeters centered to the monitor. Does this mean they don't think it matters? Or does it just mean he is a humble audio designer who can do his job well enough without the perfection of an Atmos mastering studio?

The physical alignment of those near field speakers would be about the same as if I slapped a center channel above my TV. I have been leaning towards mounting the center above the TV. The horns on my speakers are already somewhat above ear level, but that is not a problem since they have well controlled directivity.

The "does it actually matter" part is important. It would annoy me to create fancy speakers, just to realize that I overlooked some important design consideration. But at the same time, I don't want to work too hard on things that don't make a huge difference.

Would there be a way to quantify the height relationship? Like if you draw a line from the tweeter of the left or right, through the tweeter of the center, how many degrees from vertical is ideal? I think it is agreed that we are less sensitive to positions in space vertically than horizontally, but is there a way to how much of a height difference is required before we identify the sound as coming from a higher or lower location?
 
Using a projector with ambient light or in a room that isn’t black like a bat cave (like my room) isn’t really going to work. I also have a 120” screen, which used to be impossible or very expensive with a TV.

But yeah - to me perfect sound is more important than the image since I use my setup mostly for listening to music.
 
The "does it actually matter" part is important. It would annoy me to create fancy speakers, just to realize that I overlooked some important design consideration. But at the same time, I don't want to work too hard on things that don't make a huge difference.

Would there be a way to quantify the height relationship? Like if you draw a line from the tweeter of the left or right, through the tweeter of the center, how many degrees from vertical is ideal? I think it is agreed that we are less sensitive to positions in space vertically than horizontally, but is there a way to how much of a height difference is required before we identify the sound as coming from a higher or lower location?
R&D is your friend. :)

There are studies that say that in laboratory conditions, auditory localization limits are around 1° horizontal and 5° vertical. Other studies say those limits are wider. But you are not in laboratory conditions and you will see and know where your speakers are.

Therefore I suggest doing some research and development; four identical loudspeakers arranged as left, right, and two centers separated vertically. Select some content and see if you any preferences between the two center heights. Do some blind comparisons where you don't know which of the centers is active. You can use cheap little full range drivers in a simple box, or a mock-up or your finished design. The point is to construct an experiment that will satisfy those questions for you.
 
R&D is your friend. :)
Of course! But I like to soak up as much information as possible, trying to reconcile the different theories. I find that understanding the reasoning for various approaches can be informative.

There are studies that say that in laboratory conditions, auditory localization limits are around 1° horizontal and 5° vertical. Other studies say those limits are wider. But you are not in laboratory conditions and you will see and know where your speakers are.
Interesting. I briefly looked for info like this, but the studies were all locked behind pay walls!

Using a projector with ambient light or in a room that isn’t black like a bat cave (like my room) isn’t really going to work.

This may not be so clear cut. I started doing some new research on projection screens and projectors, and it appears the tech has advanced quite a lot! As an example, I found this comparison video of different screen. I'm not sure if these screen technologies are offered in acoustically transparent varieties, but the fresnel version seems surprisingly good. And I think all of these out perform the gray screen I had.

 
About the complete system design---

I built true full range speakers inspired by the Genelec W371A (More like the 8381A, but those didn't exist when I started), and I think they are an ultimate stereo speaker. They are 4 way active speakers, and external subwoofer(s) are not needed because the subwoofers are built into the speakers. So everything you could want, as long as you want two obelisks in your room!

But 4-way active obelisk speakers are not practical for a full surround system!

Alternate theory:

I have seen people who promote the theory that all the surround speakers should be the same, so they match. And they would use the full range of the speaker instead of crossing to a sub at 100hz.

Given this theory, I could reduce my speakers to a 3-way design by removing the subwoofer section. Then they'd have an f3 of ~45hz.

(I'm using 12" pro audio coaxials, and they barely extend down to 120hz. [Edit: this is based on a dramatic increase in distortion when the crossover is lowered below 120hz (48db/ octave), sealed enclosure. I could add a port to hit the 80 or 100hz crossover, but a review/test of the driver showed the increase in distortion I'm avoiding moves up to ~300hz when ported. Maybe it is not a problem, but I've been sticking to the dogmatic ideal of sealed enclosures for everthing but the subwoofers.] So I can't cross them directly to a subwoofer without adding a woofer to bridge the gap, and I haven't found a different 12" coaxial that would do much better down to 100hz in a sealed enclosure.

Multiple subs:

The goal is the best performance possible, so we have to consider multiple sub implementation. Normally we would have speakers plus subwoofers.

From my experience so far, it seems like the problems with room modes are happening from ~50hz to ~120hz. I've heard discussions about how the structure of a building often acts as an absorber of lower frequency sound, and I think I have observed the same. So if I have multiple speakers that extend down to 45hz, do I need multiple subwoofers for "best" performance?

This leads me to a crazy thought--what about a single band pass subwoofer from ~10hz to 45hz? I haven't seen anyone use a band pass subwoofer for home theater. It's like a dirty word, but I'm not sure how else I could get sub and infrasonics to cover all possible LFE, without an unreasonably large enclosure. (I'm thinking the TV stand is the bandpass sub)

Antithesis:

The prevailing theory is to use small speakers for surrounds, because big speakers are expensive and don't fit with existing furniture? And these speakers are designed as 2-ways that extend down to ~80hz for the convenience of crossing them directly to a subwoofer.

I have also been toying with a 2 way design (woofer/ horn/ woofer) that would create worryingly "normal" multichannel system. With them I'd keep the obelisk speakers as-is, using their built-in subwoofers. No external subs would be needed (seriously!).

Details, if anyone is playing along, the "obelisk" speakers have B&C 12fhx76 (60x40 degree horn) coaxials. The little surround speakers I'm toying with would be Ciare PR614 horn (60x40 degree) w/ 2x 6" mid bass woofers. So in theory they would be a pretty good match to the coaxials, and the mid-bass woofers would cross at 100hz.


Anyway, I'd love to hear some feedback/ analysis of the above. What is your guiding acoustic theory?
 
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My perception is that the setup of most home audio systems is dictated by fairly arbitrary constraints, things like the height of the TV stand, the height of the left and right speaker, and our cultural knowledge of what such a system is supposed to look like. So we have a left and right with tweeter near center line of the TV, and a center channel below the TV.

So the first question should be, is the "normal" configuration an optimal system, or can it be improved?
This is definitely not an optimal solution. Optimal (video + audio) is still 3 identical front speakers at the same elevation either behind acoustically transparent screen (big-screen home-cinema) or with a direct-view screen such that the TV is either mounted as low as possible and the center speaker's tweeter directly above that. L-R can be at the same elevation as the centre or slightly below (about 30cm before multichannel music sounds 'off' - remember - a phantom center also appears slightly elevated so a centre speaker slightly above L-R speakers sounds 'familiar').
Or all speakers below the TV and the TV is higher than optimal. Low profile coaxials are a blessing in this scenario.
 
Low profile coaxials are a blessing in this scenario.
Which coaxials do you mean?

My original concept was going to use the same 12" coaxials for all channels. But later on I realized that using the 12" coax puts the center of the horn ~10" above or below the TV. (And they don't work down to 100hz!) I thought that was too much offset, which sent me the path of coming up with an alternative speaker design that is compatible with my main speakers, the Ciare PR 614 horn + 2 midbass woofers. That design puts the center of the horn ~4" from the top or bottom of the TV.

Then I thought I could use this "compact" 2-way center channel design for all the surrounds...but the idea of using big speakers that extend down another octave is something I'm curious about.
 
At this point I can change anything. The height of the TV, the height of the speakers, the location of the horns within the speaker cabinet, the design of the center channel and the expected location of the center channel.
If you can place a horn+midwoofer vertically below the screen, then do it (or inverted and above the screen). Coaxial, even a 12" would be shorter. If you would like to listen to multichannel music, make all front speakers identical. And place them at identical elevation. Center can be slightly above LR (the 5-degree rule mentioned above).
Next question: If we throw out all the pre-made furniture, and if we are use DIY speakers that can be made any way we like, what theory would give the best possible results for audio quality?
Best solution would be speakers and TV flush mounted behind a false wall to eliminate front wall SBIR effects. Or make speakers on-wall with a shallow and wide cabinet and laarge round-over. For example like Revel Gem2.
 
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Best solution would be speakers and TV flush mounted behind a false wall
I forgot about this technique. The aesthetic is great for a dedicated home theater. From a technical point of view, wouldn't soffit mounted speakers on a rigid wall be better still?

It seems you are choosing a theory of controlling unwanted room interactions by placing all speakers near or flush with the walls? I guess it is not uncommon to have in-wall speakers or speakers designed to butt up against a wall as you suggest. But I always thought people did this for aesthetic reasons or because of space limitations?

Atleast at this point in time, I am heading down the path of narrow directivity/ controlled directivity speakers, which should eliminate SBIR issues.
 
While I suspect screen technology has improved since then, this strategy will have to wait until I can build the dream home....
Right... There is no way to project black... ;)

I have seen people who promote the theory that all the surround speakers should be the same, so they match. And they would use the full range of the speaker instead of crossing to a sub at 100hz.
"Ideally" all of the speakers are full-range (except the sub) and the sub(s) ONLY used for the "point one" LFE channel. But for most people that's not practical and it becomes less practical as you add more surround channels.
 
From a technical point of view, wouldn't soffit mounted speakers on a rigid wall be better still?
You can incorporate invisible absorption and diffusion in a false wall. (it can be a high frequency reflector/bass absorber (with plastic sheet and fabric covering), or membrane absorber with resilient-channel + gypsum board or 'diffusion' with wooden slats covering) without compromising sound transmission to nearby rooms. Just don't build a massive caulked wall with large airgap to mitigate the 'triple leaf effect'.
But I always thought people did this for aesthetic reasons or because of space limitations?
If your TV is against the wall, bringing speakers >1m to the room is (to lower SBIR efffects below crossover) ugly. We are talking acoustic advantages plus aesthetics. Win-win.
I am heading down the path of narrow directivity/ controlled directivity speakers, which should eliminate SBIR issues.
Unless it's an ~1m midbass horn or a large baffle speaker, or Allison-style driver arrangement, it wont. You need size for 100-400Hz issues.
 
"Ideally" all of the speakers are full-range (except the sub) and the sub(s) ONLY used for the "point one" LFE channel.

I'm surprised by how few examples there are of this! But then, I've almost exclusively seen boom-hiss systems for the last 30 years.

By full range, do you mean 20hz to 20khz? If so, that is a tall order.

I know the theory for why crossing from a small speaker to a sub at ~100hz is supposed to be ok.

And I have observed that when I do a sweep of my rear firing subs, I see a marked drop off above 50hz...but flat response below. So it seems to me that 50hz and above is still somewhat directional, even if in theory we can't pinpoint it's location.

This leads me to conclude that extension down to ~45hz for surrounds is all that is needed?

In my lengthy post above I then went on to theorize about a single large bandpass sub tuned for ~12-45hz, instead of the traditional ported sub from 20-100hz.

I also mentioned a theory that "multiple subwoofers" are effective in a range from ~50hz to 120hz, because below that most structures become bass absorbers, reducing issues with room modes at those lowest frequencies.

All this leads me to a theory that if the surrounds extend down to ~50hz, only a single sub is needed. I'm curious if this theory stands up to scrutiny!
 
Unless it's an ~1m midbass horn or a large baffle speaker, or Allison-style driver arrangement, it wont. You need size for 100-400Hz issues.

My understanding is that room modes take over at ~500hz, so I would have to be convinced that 1) there is a problem needing to be solved, and 2) that any technique, like directivity or flush mounting, would fix that problem.

I did experiment with cardiod bass using my speakers, since everyone was convinced they are cardiod speakers, and the short story is that I couldn't improve the sound or measurements by using cardiod bass techniques. However, I was able to make very nice null patterns, which confirmed that I would have had a cardiod pattern, if I were in half space.
 
It seems you are choosing a theory of controlling unwanted room interactions by placing all speakers near or flush with the walls? I guess it is not uncommon to have in-wall speakers or speakers designed to butt up against a wall as you suggest. But I always thought people did this for aesthetic reasons or because of space limitations?
Aesthetics and space are advantages of in-walls, and probably why most people choose them, but certainly aren't the only advantage. Eliminating front-wall SBIR and baffle-step are big advantages that people often don't consider. Been a couple of threads lately where people are chasing down dips in the 100-200Hz range that's likely due to SBIR which would almost certainly be solved by changing to in-wall speakers (though of course I realize not everyone can do it for various reasons even if they want to). New system in my new home is going to be in-walls across the front, looking forward to the results.
Atleast at this point in time, I am heading down the path of narrow directivity/ controlled directivity speakers, which should eliminate SBIR issues.
Yeah, cardioid or other means of controlling directivity is another path, though from what I've seen it is generally costlier and comes with other disadvantages (cardioid designs often suffer from elevated distortion at lower frequencies). Whether you deal with those trade-offs or the trade-offs of in-walls, it seems to be worthwhile.
 
Been a couple of threads lately where people are chasing down dips in the 100-200Hz range that's likely due to SBIR
That is a fair point, but to be honest, things like that don't bother me. In room frequency response is never remotely flat. I can guarantee you that I would never walk into a room, hear some music, and say, "I think there is a dip at 150hz!"

But I have thought about soffit mounting speakers. I've sketched ideas for it while drawing up potential house floor plans. But that isn't the direction I want to go.
 
Another data point:

This is an interview done at Dolby, in one of their (music?) studios. They have Genelec "The Ones" + W371A for left, center, and right. And then "small" speakers for other channels.

I will probably do something similar, as in 3 large speakers across the front, and smaller frequencies with a higher crossover for the other channels.

The W371A is the inspiration for my speaker design. I'm currently thinking about making a version of my speakers that is shorter and fits under a TV, but keeps the large front woofer, rear ported subwoofer.
 
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