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HT/dedicated listening room sizes


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Hey artto, I was wondering if you'd chime in here sometime. I know we've been around the "Golden Rule" about room size before, I'm just trying to make the most of the space I have to work with. A couple questions..

As I recall, the ratios end up with an 8:5 aspect ratio, correct? In that case, with a 20' length, I should be ok with a 12.5' width. How will the 8' ceiling height figure into the sound of that size room?

If I can't meet the ideal 1:1.29:1.56, and the "Half Room Principle", which would leave me a 20x25 or 10x12.5, which is either too big or too small, would angling/flaring the outward walls as they move away from the main speakers reduce the node problem? If so, how much flare would be needed to acheive any kind of appreciable results?

Would it be of any benefit to have the height of the room change from one end to the other? Since this is still in the drawing stages, I could "grow" the room height by 12-18 inches as it progresses out from the main speakers. Keep the floor flat, angle the ceiling? I'd prefer the flat floor, but that may not be in my best interests, you tell me. The front end height could be an issue, especially since I am 6'4", but then again, I don't know that I would spend a lot of time up in the front of the room.

It just struck me funny that I'm talking about essentially a horn loaded room, in a forum created by a company founded by a man who saw the intrinsic values of a horn when it comes to sound reproduction. HMMmmmmmmmm.........

Another thought b4 I hit Submit... does it matter what length you're using first in your calculations? As I reread this, I saw I had both 12.5 and 25 as acceptable for wall sizes, but upon reflection, I see that it simply moves the short wall to the the long wall, so forget this paragraph. 9.gif

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No problem. What I'd suggest as an alteration to your floor plan:

Cut back about 6" from the exterior wall on the one side, and build your HT room walls to about 8" from the ceiling. That way this becomes an almost totally freestanding room. Use drop ceiling throughout the storage and HT room area. Use Owens Corning 703 panels in the drop ceiling framework, with 6" of plain fiberglass between it and the hard ceiling. Install homemade bass traps in the corners, and checkerboard that 703 on the walls. That will kill your noise bleed to the upstairs, and still give you the great room sound.

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Griff... If I read you right, you're suggesting I build a false wall away from the cement exterior walls? Wouldn't I be better off with the solidity of the cement rather than building something out of wood? At this point, looking at the above floor plan, I could conceviably put concrete along one of the long walls in the room too, though it may cost more than the Misses is willing to absorb for my indulgances. The forms aren't THAT expensive, and once they're out with the pump truck a few more yards of concrete is almosts free, but...I'll have to look into it. If I knew for sure what I wanted for wall length, spacing, etc., I could probably have em build the whole room out of concrete for not a lot in the big scheme of the house costs, but then again, every $500 the Misses sees as a stove, fridge, portion of a tile entry, an arch over a window, etc.

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On 3/8/2004 8:29:22 PM Champagne taste beer budget wrote:

Griff... If I read you right, you're suggesting I build a false wall away from the cement exterior walls? Wouldn't I be better off with the solidity of the cement rather than building something out of wood? At this point, looking at the above floor plan, I could conceviably put concrete along one of the long walls in the room too, though it may cost more than the Misses is willing to absorb for my indulgances. The forms aren't THAT expensive, and once they're out with the pump truck a few more yards of concrete is almosts free, but...I'll have to look into it. If I knew for sure what I wanted for wall length, spacing, etc., I could probably have em build the whole room out of concrete for not a lot in the big scheme of the house costs, but then again, every $500 the Misses sees as a stove, fridge, portion of a tile entry, an arch over a window, etc.

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I am suggesting exactly that. It's not the wall that absorbs sound - it's the air that dissipates what the insulation fails to absorb. Hence, the false walls plus the 8" of insulation on the ceiling, including 2" of 703 rigid fiberglass.

Re: your earlier question...

I've always ordered it from my local hardware guys (don't bother with Lowe's - you'll get dumb looks in response) as Owens Corning 703 rigid fiberglass. Somehow I suspect those panels you're referring to are just overpriced repackaged versions of this basic industrial insulation.

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Before anyone gets too excited about that Owens-Corning 703 or 705 rigid fiberglass......I've called OC inquiring about these products. They didn't seem to know too much about them & suggested that they were discontinued. I'm an architect. So I can tell you I was in touch with the 'professional' customer service department. I also tried to get pricing & availability thru a local professional building supply company. Same result......nothing.

For what its worth.....Ethan Winer http://www.ethanwiner.com/acoustics.html#big%20waves says he has inventory on both (a few months ago....I spoke with him). He says he can still get it. And I agree with him that it seems most of the customer service & sales folks at OC are somewhat inept.

However, other than Ethan, all I've been told from building suppliers & OC is that the fiberglass products are (or have been) phased out, being replaced by foam products.

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I am in the same boat, trying to locate 703/705 in my area

after constant calling to the hd pro sales desk I said to h**l with them, they responed back with; must order 10 sheets as mimun. But by them I had posted the a question on ethans froum & proaudio froums where can i locate 703/705 in the philly area?? got a couple of good leades that i am going to be running down tomorrow and i will get back to you. one reply suggested to looking for rigid fiber glass manfactures and to drop the o/c model. hopefully this will pan out.

much thanks to you griff for posting the atricle and link to ethans froum last week.

hope this helps

peace

yendor

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On 3/8/2004 11:44:32 PM YENDOR wrote:

I am in the same boat, trying to locate 703/705 in my area

after constant calling to the hd pro sales desk I said to h**l with them, they responed back with; must order 10 sheets as mimun. But by them I had posted the a question on ethans froum & proaudio froums where can i locate 703/705 in the philly area?? got a couple of good leades that i am going to be running down tomorrow and i will get back to you. one reply suggested to looking for rigid fiber glass manfactures and to drop the o/c model. hopefully this will pan out.

much thanks to you griff for posting the atricle and link to ethans froum last week.

hope this helps

peace

yendor

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Remember that the sheets are only 2'x4' - so 10 sheets really isn't all that many.

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On 3/8/2004 9:26:53 PM artto wrote:

I'm an architect....

I also tried to get pricing & availability thru a local professional building supply company. Same result......nothing.

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Must be why you didn't get a price... 3.gif2.gif The 703 is still available here... just checked with a supplier we use and the OC-703 in 3" is 2000$/mft2 (canadian) and about 2wks delivery. There is a minimum order.

later...

Rob

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On 3/9/2004 10:37:12 AM Champagne taste beer budget wrote:

OK, I understand about the dead space and it's acoustical properties, and the need for the insulating panels, but I'm not quite ready to start searching out material yet, I still need to get the room layout figured out. Any thoughts on the flared walls/ceiling idea?

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Flared walls are OK, but only if you position your fronts in the narrowest side of the room.

A flared ceiling is a waste of time and effort. Not worth the potential benefits vs. a drop-ceiling as I described above.

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Champaign, yes, a length to width ratio of 8:5 is the goal.

Ive found that if the width/length ratio is reasonable, you can apply the half-room principal to the ceiling height. In other words an 8 ceiling would be 1/2 the height of a 16 ceiling. So you can substitute 16 for the 8 dimension. Keep in mind this is not ideal & will not produce the same results as having the proper ceiling height. But it is still better than having a ceiling height dimension that is totally out of whack. If you run the dimensions on a room mode calculator youll see which modes are affected by the vertical dimension, and by how much. It would be something like, if 16 were substituted for the 8 ceiling dimension in a 25 x 20 room, you might expect that the number of modes would be reduced by one half (8 = 1/2 of 16)

I should make mention at this point that the objective is to have as many modes as possible, not fewer. More modes, but with a closer average mode (frequency/Hz) spacing.

In the above example, this is indeed approximately the case. The 25 x 20 x 8 room has 67 modes (below 150Hz) with an average mode spacing of 1.3Hz. The 25 x 20 x16 room has 117 modes with an average spacing of 0.6Hz. This will produce a much smoother low-end response.

However, moving down to the 12.5 x 10 x 8 room yields only 20 modes with an average spacing of 5.1Hz! This will produce a very bumpy response. Some bass frequencies will sound awesome (exaggerated) while others are substantially reduced due to cancellations. And even worse, because of the smaller dimensions, the modes primarily affected extend to much higher frequencies than they do in the larger room.

If you make the room irregular (ie: flared walls), how much you need to flare or angle them will be, again, dependent on the room size. The smaller the room, the more it would benefit by increasing the depth or angle of the flare. The larger the room gets, the less important this is because the wavelengths are not equal to or shorter than the dimensions of the room, so there is little or no reinforcement of certain frequencies from room boundaries.

I dont think I would sacrifice ceiling height just to get an angle on it. If you can get the angle without reducing the ceiling heights much below 8 then by all means do.

What speakers are you using? Flaring the walls with Khorns presents its own set of opportunities, AND, potential problems.

Griff.thanks for that OC link.

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On 3/9/2004 5:42:56 PM artto wrote:

Champaign, yes, a length to width ratio of 8:5 is the goal.

I’ve found that if the width/length ratio is reasonable, you can apply the ‘half-room principal’ to the ceiling height. In other words an 8’ ceiling would be 1/2 the height of a 16’ ceiling. So you can substitute 16’ for the 8’ dimension. Keep in mind this is not ideal & will not produce the same results as having the proper ceiling height. But it is still better than having a ceiling height dimension that is totally out of whack. If you run the dimensions on a room mode calculator you’ll see which modes are affected by the vertical dimension, and by how much. It would be something like, if 16’ were substituted for the 8’ ceiling dimension in a 25’ x 20’ room, you might expect that the number of modes would be reduced by one half (8 = 1/2 of 16)

I should make mention at this point that the objective is to have as many modes as possible, not fewer. More modes, but with a closer average mode (frequency/Hz) spacing.

In the above example, this is indeed approximately the case. The 25 x 20’ x 8’ room has 67 modes (below 150Hz) with an average mode spacing of 1.3Hz. The 25 x 20 x16 room has 117 modes with an average spacing of 0.6Hz. This will produce a much smoother low-end response.

However, moving down to the 12.5’ x 10’ x 8’ room yields only 20 modes with an average spacing of 5.1Hz! This will produce a very bumpy response. Some bass frequencies will sound awesome (exaggerated) while others are substantially reduced due to cancellations. And even worse, because of the smaller dimensions, the modes primarily affected extend to much higher frequencies than they do in the larger room.

If you make the room irregular (ie: flared walls), how much you need to flare or angle them will be, again, dependent on the room size. The smaller the room, the more it would benefit by increasing the depth or angle of the flare. The larger the room gets, the less important this is because the wavelengths are not equal to or shorter than the dimensions of the room, so there is little or no reinforcement of certain frequencies from room boundaries.

I don’t think I would sacrifice ceiling height just to get an angle on it. If you can get the angle without reducing the ceiling heights much below 8’ then by all means do.

What speakers are you using? Flaring the walls with Khorns presents its own set of opportunities, AND, potential problems.

Griff….thanks for that OC link.

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No prob. The height issue is exactly why I laid out the drop-ceiling concept. It creates a "virtual" high ceiling by removing the hard surface. The rest of your discussion (room modes, etc) can all be solved with room correction.

I know several engineers who set up the acoustic correction in their control rooms by positioning their speakers, then using mirrors to line up the reflection points, then using those points to line up secondary reflection points, and some even tritiary. Net result is that they placed their absorption panels precisely where they needed to be for maximum effect. No reflection = no room effect. The best part? By taking this extra effort, they get a room that's very much alive and responsive, but doesn't interfere with the accuracy of the system.

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Yes, Griff, thanks for that link. I've been exploring it and trying to play with the ModeCalculator this afternoon, but this dang job has been getting in the way. Very good info there. I obviously need to read more in it, I was under the impression that the fewer the modes, the better. Thanks for clarifying that for me, artto.

The flared walls idea is out. Possible to do, but why if not needed? Same with the ceiling, a flat 8' is fine with me.

When this room is initially completed, I doubt I'll have moved up from the current KG4's, but I DO expect to be the proud papa of a pair of Khorns at some point in my life, so planning ahead now. I did find a pair of LaScalas on eBay about 60 miles from me, but with the upcoming construction, not much chance of that happening till the house is up. I've been threatening the Misses with a new boat once the house is finished, she is starting to swallow that 25-30K bill, so hopefully a pair of classic horns for 15-2000 won't be too much for her to handle. I have access to a 10' fully enclosed trailer that would haul them nicely, so a trip like some of the other board members have made wouldn't be out of the question.

I did contact a buddy that works at a lumber yard re the OC 703 panels, he said that they were only available to larger commercial installers, that he couldn't even order it, but that it was available. Haven't pursued it further than that, but do have a couple local companies in mind that would be the type to have access to it.

Just want to let you guys know how much I appreciate your opinions and experience. I'm sure all the answers I am looking for are available on the web somewhere, but it sure is nice to have people around that you can just ask something and get a complete, informed reply. I'm sure that, with your help, I'll have the best sounding room for miles once it's finished. Best of all, it will be one that I designed and built myself. (With a little help from my friends.)1.gif

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Griff, I think you might be misunderstanding what I said. Room correction, as you put it, cannot make up for lousy room proportions or lack of size. Room modes are predominantly affecting the lower frequencies. Putting some absorption in the right places is going to primarily affect middle to upper frequencies. In order to have significant impact at lower frequencies the absorption materials need to be quite large & deep. A 2x2 panel, or even 2x4 is not going to do it. The largest polycylindrical panels in my room are 4x8. You really need a size that is at least 1/4, preferably 1/2 of the wavelength for it to be effective.

Therefore, a panel with an 8 dimension would have some absorption & diffusion effect down to at least 70Hz (16 wavelength). The diagonal dimension of a 4x8 panel is a little less than 9 which takes you down to 63Hz. Frequencies lower than 70Hz get very difficult to control even in a room the size of mine. Room proportions & non-parallel surfaces is the only way. Thats why even good sounding auditoriums, as large as they are, still have many non-parallel & diffusive surfaces.

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On 3/9/2004 6:57:56 PM artto wrote:

Griff, I think you might be misunderstanding what I said. Room correction, as you put it, cannot make up for lousy room proportions or lack of size. Room modes are predominantly affecting the lower frequencies. Putting some absorption in the right places is going to primarily affect middle to upper frequencies. In order to have significant impact at lower frequencies the absorption materials need to be quite large & deep. A 2x2 panel, or even 2x4 is not going to do it. The largest polycylindrical panels in my room are 4x8. You really need a size that is at least 1/4, preferably 1/2 of the wavelength for it to be effective.

Therefore, a panel with an 8 dimension would have some absorption & diffusion effect down to at least 70Hz (16 wavelength). The diagonal dimension of a 4x8 panel is a little less than 9 which takes you down to 63Hz. Frequencies lower than 70Hz get very difficult to control even in a room the size of mine. Room proportions & non-parallel surfaces is the only way. Thats why even good sounding auditoriums, as large as they are, still have many non-parallel & diffusive surfaces.

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That's what bass traps are for. Bass traps make up lack of width via depth and airspace.

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Most bass traps dont have (certified) very low frequency bass attenuation because their longest dimension usually dictates it, and test samples are limited in size. Itll help but it involves experimenting and there is no magic cure.

Even optimising your dimensions before building will help reduce the need for treatment... but real life performance rarely matches design predictions. Wall rigidity plays a role in the defining the apparent acoustic dimension of the room, but it is rarely factored in. (pliable walls will make the room appear acoustically larger versus its actual measured dimensions)

What does this all mean? Try your best to chose a reasonable room ratio, and expect to use some treatment to perfect it when your done. 4.gif

Rob

PS: you should get your contractor to purchase the K-horns as part of the home as built in speakers... theyll blend in very discreetly into the mortgage payments. 2.gif

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