# Generic Advice on Accoustics



## JCD (Apr 20, 2006)

I thought I'd throw this out there for the experts and pro's in accoustics..

Assume we have a rectangular room with a carpeted floor and a typical height ceiling. I'd like to keep the advice as generic as possible, but if you need a dimension for the room, how about 10x15.

If I want to address the accoustics in the room properly, please answer the following:

1) Where would you put the front speakers, on the short or long wall?
2) What treatments would you use first and where would they be placed?
3) What treatments would you use second and where would they be placed?
4) What treatments would you use third and where would they be placed?
5) Etc
6) Would any of the answers change if it were simply a 2 channel system?

Mostly what I'd like to get at is if someone were on a limited budget, how could they get the best accoustics from a room.

JCD


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## bpape (Sep 14, 2006)

1. Speakers should be on the short wall firing down the long dimension. Exact placement would depend on factors including screen size, screen type, # and placement of seating, etc.

2,3,4. Don't know that you can really say any one thing is a priority over another. I think it depends on budget, quantity discounts, DIY or not, etc. If I had to get pinned down, I'd say:
- Side wall refleciton points and in between speakers on the front wall
- Bass control in the room corners, probably front corners first to do some double duty for SBIR and front wall reflection control
- Balance of Front Wall
- Scattered targeted absorbtion throughout the rest of the space.

6. Yes. In a pure 2 channel room, you'd not have the front wall as dead nor would you have as much in the rear half of the room. Target decay times for 2 channel duties are higher for the same room than they are for HT or multi-channel music duties.

Bryan


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## chasw98 (Apr 20, 2006)

I've seen Bryan give very good advice on many occasions, so I would listen to him. My thoughts would be:
01) Do the mirror trick and use absorption on the first reflection points on the side walls.
02) Look into some form of diffusion for the rear wall. (A bookcase with different sized books can some times work effectively).
03) Take care of the first reflection points on the ceiling.
04) Bass traps. You can rarely have enough. I mean true bass traps that will absorb the deep stuff, usually very expensive and bulky even doing it DIY.

All of these suggestions do not include any WAF problems, but in reality you usually have to compromise. If you are serious about it, measure, measure, measure, both before and after and at different listening positions. What may sound good at the sweet spot might not sound very good 2 seats over or behind. Back in my day, everyone strove to build an LEDE (Live End Dead End) room and as time has gone on the buzz words are now RFZ (Reflection Free Zone). These are types of environments you would find in studios more than home theaters but the concepts hold true in general. Do some googling on DIY absorption or acoustics and start getting some ideas. It can be done quite effectively and relatively inexpensively if you put your mind to it.

Chuck


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## bpape (Sep 14, 2006)

Very true on the seat to seat variations. That's one of the things that properly treating a room will help to overcome. You'll find after appropriate decay control and sufficient bass absorbtion, your response variation from seat to seat will be much less than it was before.

Bryan


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## JCD (Apr 20, 2006)

Thanks for the insights.

I have a basic understanding of how to treat a room. I assumed the side reflections (using mirror trick) was the place to start, but was unsure what location/type would be next best step. I knew about the LEDE concept, but wasn't familiar with the RFZ. 

In my particular situation, I have a small garage that I will partition a listening room in. Backround, it's a tiny single car garage that I plan on cutting off the back area for storage and leaving the center as a listening room and the front as a work area. When I built my speakers, I bought 6 (8?) sheets of an OC703 equivelent. I'm trying to think of a way to best use those sheets in my room. Eventually, I'll probably get more, but thought I'd go slow for various reasons. 

Oh, and the garage is mine, so no WAF to consider.

JCD


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## Wayne A. Pflughaupt (Apr 13, 2006)

I think you’re going for 2-channel in there, right? 

Yes, the mirror trick has its uses, but I think most people don’t use it correctly. The problem is that sound from speakers is not narrowly focused like what you’ll visually see with the mirror. Once you find the exact reflection point, I don’t see how it can do much good to simply throw some absorption up on the wall there a foot or two square. Speakers generate considerable high frequency energy 20 degrees or more off-axis. So basically, at the so-called reflection point, that’s merely the “epicenter” of the radiant soundfield. I would think you’d need to treat at least several feet in all directions from that point if it’s going to have any effect at all. Maybe Bryan can comment... 









Regards,
Wayne


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## chasw98 (Apr 20, 2006)

I agree with Wayne. The mirror trick is just a good starting or localizing point. And it can extend left & right, and up & down!


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## alan monro (May 9, 2006)

JCD , Do not get confused about the general acoustic treatment of a room nightmare. It is very simple to understand.The following statement may upset a lot of readers due to their misinformed knowledge.The best acoustics a person can wish , Is out doors in a open field ,no reverberation,no room distortions . Seeing that is not practical to listen to music etc. in that perfect infinite sized room we have to compromise.The solution is to absorb ALL reflections from the speakers as the sound is bounced around the room. To come even close to this one needs to have heavy couches carpet with heavy underfelt, thick scatter rugs ,ALL walls coated with sound absorbancy,heavy drapes and the whole ceiling also treated. The only reverberation that you will hear is the engineered ones or the natural ones ie, reverberation from the hall where the recording was made.So, getting back to your enquiry. First , heavy scatter rugs.Second, heavy window drapes.Third ,heavy drapes around walls etc. good luck , kind regards alan.


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## bpape (Sep 14, 2006)

Sorry Alan but I'd disagree on how to get there. Your assertion of being outside being a perfect environment is close - but unfortunately almost all speakers are designed with room gain in mind and accounted for. If you have ever listened in an anechoic chamber which is pretty close to no room gain, you'd realize quickly that it's not a pleasant thing to listen to. I'm not 'upset' with your comments but feel I need to clarify a few things. 

If one treated a room as you suggested, it would be very overly dead and bordering on uncomfortable to be in. I've been in several rooms that were treated this way and they were in fact uncomfortable. And more importantly, the reason I was there was because after doing this, the owner had a mess on his hands and didn't like the sound at all so he hired me to come 'fix it'. The first thing we normally do is pull down all the curtains, all the treatment on the wall, all the treatment on the ceiling and then measure the room and see what it's actually doing based on a mic position in the appropriate seating position(s). 

A studio control room is relatively dead and is about as close as you'll get to what you describe. However, those rooms are also set up to listen in the nearfield which is almost never what is done in a home 2 channel or home theater room. Treating a room for farfield listening is a whole different game. And just to be clear, treating for 2 channel vs multi-channel is another whole different set of design goals.

Also, using tons of drapes and carpet and having all the walls covered with relatively thin material will unbalance the absorbtion curve by giving you tons of absorbtion from 1kHz up and almost zero below that. It also ignores treating things like SBIR issues. In fact, hanging thin absorbers spaced from the wall can actually act like a very narrow filter absorber based on the wavelength related to the distance from the wall. If you really want to closely replicate the great outdoors, you'd build a series of tuned bass absorbers and cover the rest of the room in diffusion (which would be huge to diffuse lower frequencies) - not to mention the fact that the absorbtion of people and furniture compared to the room volume vs. being outside makes this impossible. 1 single person in 1 stuffed chair emulates the absorbtion outdoor absorbtion of air volume of of approximately 1 square mile!

Every room has a target decay time curve based on usage (HT, Multi-channel music, 2 channel music, studio live room, studio control room, classroom, etc.) and volume. Covering ALL wall surfaces and the whole ceiling as well as having carpet will yield a very skewed frequency AND decay time response curve that will be too dead in relation to the target up high yet still uncontrolled on the bottom end. Leaving a room uncontrolled on the bottom ignores trying to smooth bass response from seat to seat and also leaves symptoms such as dialog intelligibility issues in a home theater environment.

As for reflection points, yes. There is considerable energy off axis. However, most of that will bounce at least a couple of times before it would hit your ear and is therefore outside the definition of 'early' reflections. However, if you map out the points from 3 front speakers to 2-3 front seats, you'll find that you'll have 6-9 points on each side wall - some of which are relatively close in proximity. Also, you don't want to lock your listener's head into a vice so treating an area can certainly help and is generally called for.

Bryan


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## alan monro (May 9, 2006)

Brien, In response to your reply regarding JVC's query and my unbiased advice to him. First of all you say " most speakers are designed with room gain accounted for' By room gain you mean multiple echo,s That's a new one on me.To every ones understanding Primary' Speakers are designed for the flattest frequency response ,lowest distortion,highest power and to a price.The exception is for example Klipshhorns that are designed to sit in corners and use the adjacent walls as an extension of their Basshorn and as such increase the bass efficiancy.For the life of me i can not say being outside "with no room gain" is unpleasant,that is exactly as being in a room that is "dead"(no echo's).Lets face it 'all we want to hear from speakers are :-the frequencies coming from them thats all. NO ECHO'S no distortions from the room.Kind regards alan. Have to go Brien , Thirsty work wrighting this ,time for a beer


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## bpape (Sep 14, 2006)

Hi Alan. 

Your description of design GOALS of speakers are very correct. However, in order to get that to translate into a pleasant sounding speaker a designer must consider room gain (specifically in the bottom end).

As for anechoic and 'outside' being the same - sorry to say they're not. Anechoic is just that - no echoes through the use of heavy, heavy absorbtion and tons of large diffusion. It also has an extremely low noise floor. Outside has one absorber - air. Also, outside has a relatively high noise floor which severly restricts dynamic range. Ever heard an outside concert capable of an 80db dynamic range? Nope.

However, don't confuse damped with quiet - two very different things. One can have a room that is not overdamped and is still very quiet. On the contrary, I can have a room that is way overdamped but not at all quiet in terms of noise floor.

Hey, being a seller of acoustic materials, you'd think I'd WANT what you said to be true - cover every surface and make the room completely dead. We'd sell a lot more don't ya think?  It'd be easy enough to prove that thin absorbers won't handle the full range and the effects of same.

Bryan

Bryan


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## Ethan Winer (Jul 21, 2006)

Guys,

Interesting thread. And _of course_ I have some opinions to share. :laugh:

> By room gain you mean multiple echos <

"Room gain" is a colloquial expression that means the room resonates at certain frequencies related to its dimensions. By extension, the resonances yield higher SPL levels at those frequencies for the same amount of input power. So while technically the resonances are related to "echoes" (reflections really), I don't think it's accurate to refer to room gain as being the same as echoes.

It's also important to distinguish between over-damping a room at mid and high frequencies, which is what creates an unnatural effect, and having plenty of bass trapping to offset all the problems that come with room resonances. So I'd say that outdoors is indeed the perfect environment for bass, but probably not for frequencies above around 300 Hz. Then again, I've heard outdoor concerts that sounded great. So go figure. That's the wonderful thing about room acoustics - it's 100 percent science, but there's an additional 20 percent for taste and personal preference. :dizzy:

BTW, I found it _really difficult_ to avoid using 100 smileys. This forum has hands-down the largest and best collection I've seen anywhere! :jump:

--Ethan


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## Ethan Winer (Jul 21, 2006)

Bryan,

> almost all speakers are designed with room gain in mind and accounted for. <

How could that be? Every room has multiple resonances at different frequencies, so how could a speaker be "designed" to take advantage of resonances whose frequencies are unknown? It seems to me that all speakers aim to be as flat as possible - once they're in a room the chips will fall where they may, so to speak.

--Ethan


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## brucek (Apr 11, 2006)

> As for anechoic and 'outside' being the same - sorry to say they're not.


Anyone who's had the privilege of standing in an anechoic chamber will never say that outside is the same as anechoic. 

It's probably one of the strangest experiences you could ever have. Stand face to face with someone and speak - no problem. Turn your heads 45 degrees and speak again. You can hardly hear each other. Very strange........ The worst thing is listening to the unbelievable silence and the deafening ringing in your own ears. 

A true anechoic chamber is a wonder to behold for sure. It's interior is covered in immense wedges of foam, deep enough to absorb the entire hearing spectrum. The walls are very thick and the entire structure is floated on a set of springs to complete the isolation. If you ever have the opportunity to "get a ride" in one, take it. You'll never confuse it with being outside again.

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

What, Ethan, you’re only going to visit us once every two months? 


> How could that be? Every room has multiple resonances at different frequencies, so how could a speaker be "designed" to take advantage of resonances whose frequencies are unknown?


Apparently reality is stranger than speculation! This is from Axiom Audio’s website:

“*Look at a Bookshelf System* if you are considering a home theater for apartment-sized living rooms and bedrooms as well as dens.”

“*Look at a Tower System* if you are considering using a home theater in larger rooms or 'great rooms' with vaulted ceilings, which require the higher volume output capability and bass extension of floorstanding main speakers...”

Regards,
Wayne


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## Ethan Winer (Jul 21, 2006)

Hi Wayne,

> What, Ethan, you’re only going to visit us once every two months?  <

Actually, I sort of forgot about this forum after I first visited some time ago, though I do know about JohnPM's REW section. Then the other day I got an email from (I presume) the forum owners asking me to come visit again, so here I am!

> Apparently reality is stranger than speculation! This is from Axiom Audio’s website <

I read that very differently. Not that any company's marketing and ad copy would ever sway my opinion! 

I agree that larger rooms require speakers capable of higher output capability. I disagree that smaller rooms won't benefit from "bass extension." I mean, why wouldn't you want to hear the full frequency range regardless of the room you're in?

--Ethan


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## Sonnie (Apr 11, 2006)

Ethan Winer said:


> Actually, I sort of forgot about this forum after I first visited some time ago, though I do know about JohnPM's REW section. Then the other day I got an email from (I presume) the forum owners asking me to come visit again, so here I am!


Forgot about us... :nono: that's why we sent you a wake-up call... :boxer: 

:whistling:



brucek said:


> The worst thing is listening to the unbelievable silence and the deafening ringing in your own ears.


Tinnitis maybe?

Btw... very interesting description of an anechoic chamber... I'd like to visit one some day... other than the ringing in my ears part (yes, I have it!)


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## alan monro (May 9, 2006)

Brucek,Gooday, I thought top manufactures of speakers tested their spkrs in the anechoic chambers as "they" consider the chambers a typical room with no walls,no echos, and when it is raining they they wont get their "smokes "wet. Kind regards alan


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## Ethan Winer (Jul 21, 2006)

Sonnie,

> that's why we sent you a wake-up call... <

And thanks for that. Here come some more of those fabulous smileys:

:T :bigsmile: :jump: :heartbeat:  :laugh:

--Ethan


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## brucek (Apr 11, 2006)

> I thought top manufactures of speakers tested their spkrs in the anechoic chambers as "they" consider the chambers a typical room


No, they test speakers in anechoic chambers to remove any room effects, such that they can reveal the speakers true response. This keeps an apples to apples comparison between manufacturers.

brucek


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## bpape (Sep 14, 2006)

Exactly. They want to see what the speakers will really do without any room interaction.

As for keeping room gain in mind when designing Ethan, they have to. Yes - every room will be different in terms of modal issues. However, the entire spectrum does get some gain. Take an amplifier and a speaker of your choice and measure the speaker spectrum at 1W input in an anechoic chamber. Then measure it again with 1W outside. Then 1 last time in a room at 1W. You'll find that the overall average level will differ between the 3 situations even though it's the same system, same speakers, same power applied, etc. 

Some speakers even count on the walls for their 'effects' - think Bose, think Martin Logain, think any speaker tha has a bass driver close to the floor to extend apparent 'in room' response.

The trick is to get the room ISSUES ironed out and still allow it to function in harmony with the speaker as designed. If I can get the room peaks and nulls smoothed but keep the gain, then I've done part of my job

Specific manufacturers even spec how far from the front wall the speakers should be placed. Why? To get the SBIR to HELP the response in certain areas. It's not pretty but it's real.

Bryan


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## Ethan Winer (Jul 21, 2006)

Bryan,

> the entire spectrum does get some gain. <

Gotcha, that makes sense.

--Ethan


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## Glenn Kuras (Sep 7, 2006)

Good to see you here Ethan. It is always a pleasure to have your knowledge in a forum, so please put this on your "every day" list. If for nothing else but the cool smilies you can use. raying: :dontknow: :joke: :scared: 

Glenn


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## drf (Oct 22, 2006)

brucek said:


> No, they test speakers in anechoic chambers to remove any room effects, such that they can reveal the speakers true response. This keeps an apples to apples comparison between manufacturers.
> 
> brucek



hi guy's, first actual post!! :bigsmile: Another reason (just in case anyone didn't already guess) why
manufactures use an anechoic chamber to measure speakers, is so pro-sound installers can weigh up a speakers suitability to a particular application with a certain amount of accuracy.


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