[Jon L]

Room acoustics has been of interest to me lately.  Since I had to move my audio into a smaller upstairs den, I definitely noticed a lot more echo and reflections.  The old handclap test sounded pretty bad with some nasty upper-midrange glare/ring.  

I put up some stuffed animals (for real) on the 2 upper corners, which helped.  I still needed first-reflection treatment badly since I was getting a lot of upper-mid ringing.

Well, I bought some 2" pyramid acoustic foams (I didn't want to make low-mids too lean with 3-4" foams), 4'x6'.  I put one on each side wall.

Now the sound is smooth as honey, no peaks or ringing in upper-mids.  It really IS a drastic difference since the side walls were pretty close to my speakers.  However, I am now missing some of the liveliness and sparkle that I love.  I actually had to toe in my speakers quite a bit more, which makes things less overdamped but not quite as lively as I'd like still.

What's the best approach at this point, to retain the smoothness while not giving up transients, decay, and liveliness?  

1)  Try cutting my foam into 2'x6' and reduce foam space?
2)  Get some diffusors instead for side walls
3)  Get one of those cylinders that has half reflective, half absorptive surface and tune.

[Rob Babcock]

I've been wondering if it might work to cover some of the foam with a fairly tight weave fabric?  My thinking is that it'd make them reflective of high freqs but still absorptive at the lower treble and midrange.  There'd be no way of knowing just how much except by trying it.

[Ethan Winer]

Jon,

> I am now missing some of the liveliness and sparkle that I love ... What's the best approach at this point, to retain the smoothness while not giving up transients, decay, and liveliness? <

Yes, a room can definitely have too much absorption, especially if the material is effective only at mid and high frequencies like the thin foam you have. The problem is the room becomes to dead sounding, yet is still boomy and muddy in the bass range. The best solution is broadband absorption that works down to at least 100 Hz. If it absorbs even lower, all the better.

For a good overview of acoustic treatment see the Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

I'll also mention that it's probably not possible to have too much absorption at low frequencies, below about 300 Hz. You really need all the damping you can get down there.

--Ethan

[John Casler]

Room acoustics has been of interest to me lately.  Since I had to move my audio into a smaller upstairs den, I definitely noticed a lot more echo and reflections.  The old handclap test sounded pretty bad with some nasty upper-midrange glare/ring.  

I put up some stuffed animals (for real) on the 2 upper corners, which helped.  I still needed first-reflection treatment badly since I was getting a lot of upper-mid ringing.

Well, I bought some 2" pyramid acoustic foams (I didn't want to make low-mids to ...

Jon,

I think acoustic room treatment will likley become as hot a topic as speakers, since it can have a more dramatic effect on shaping sound than just about any other component (except the speakers).

That said, I have to ask the question:  What "room generated" sound do we want to hear?

If the true goal is to hear what is on the recording, then anything "created" after the recording (as in room sound) will not be true to the original.

So aside from few ear/brain spatial effects, room sound is damaging (IMO)

Sounds simple, but we have to determine what is sonic direction and delivery, and what is "room sound", or sounds created by the room that "change" the original recording.

What is sound direction or delivery?  Well when we visit the low frequencies, room boundaries play a large role in "directing" the bass frequencies to us.  Bass notes travel along the floor, walls and ceiling to reach us.

In this aspect, the room boundaries are almost an extension of the speaker.  If you can imagine a corner loaded sub as using the corner just like a horn speaker uses the horn it all becomes clear.

Mids and Highs however, are another story.  As the frequencies become higher, the resulting reflections become more damaging to the "real" sound of the recording.

While many might contend that it is desirable to have some reflection or diffusion, I would say that that (to my ears and preferences) that reflected and diffused sound is like adding diffused and reflected light in a HT.

In the best theaters, the ideal is to block any an all light possible, so that the vision of the room is taken out of the equation, and you are transported to the reality of what is on film.

Also the diffused and reflected light "destroys" black levels, by washing them out.

Same thing happens in "Sound".  

If you have diffused, dispersed and reflected sound bouning around and filling the room, then the sonic "black levels" are also not as good.

Also these "room created" sounds cause you to "hear the room" just like turning a light on in a theater casues you to "see the room".

Now I know that many get used to these "sonic reflections" and call them "air" and in some cases they create a "sonic mirage" of a larger soundstage, but never the less they are not in the recording.

It is like the artist sent you a tape and you use it to create what "you" want in your room.

And I should make it perfectly clear, that doing so is perfectly correct, since the enjoyment of the hobby is to find the "sound" that "YOU" like.

So what does this then mean to you when you go to "acoustically treat" your space?

1) use the room to "direct' the bass.
2) try to eliminate all first reflections
3) if possible reduce or eliminate "all" mid/high reflections from the frontal portion of the room
4) diffusion can be valuable at the sides and rear (LEDE) to allow the ear to aquire a "spatial perception"
5) as much as you can "treat" all "intersecting" boundaries.

As far as #5.  Keep in mind that sound will travel until it hits something or disperses completely (since it expands like ripples from a stone thrown into a pond)

When it hits something it is diffused, reflected, or absorbed.  Generally a little of all three, but it is also "channeled" or directed.  That is, depending on the angle, it will be bounce off the object or surface and have a tendency to "flow" along the boundary.

The lower the frequency and larger the wave form (bass) the more this takes place but it happens with all frequencies.

This is the principle that the "ear horn" (pre electronic hearing aid) the "megaphone", the "horn speaker", and most "concert shells"  are based on, since it works both ways.

Even the ear itself is a "sonic collector" that channels the sounds to the tympanic membrane.

As music plays around your room, it bounces back and forth and "collects" in "all" intersecting room boundaries.

Just stand in the corners of your room sometime a play a few loud cuts to see what I mean (the bass is to die for)

Well these collection zones don't sit by quietly, they spew out many bad cajangles of sonic horrors and "NO" good things.    That is why you will find that "taming" these will generally help your sound quite a bit.  That is why much of the acoustic treatment focuses on reducing the affects of the sonic garbage collectors and distributors .... the corners.

Back in 1982 or so before I knew what a Live End Dead End room was, I had a house with a spare bedroom and a large bathroom.

In that bathroom, I took about 6 blankets and hung them in a tent leaving the back open and then took a Rotel CDP, an NAD integrated amp and some KEF 303 speakers and placed them inside the tent, and sat down to listen.

It was unbeleivable.  So much so that I actually made drawings and plans for a "sound booth" that one could DIY and put an "isolated" audiophile listening booth in the attic, garage, or wherever and disturb no one and hear non-room created music.

But I got busy and forgot about it.

But in any event, I hope some of that rambling above offered some stimulation of information you can or could use.

Plus, as you know, you are always welcome to stop by and see what I have done here for ideas. (thank goodness, I'm single)

[8thnerve]

What's the best approach at this point, to retain the smoothness while not giving up transients, decay, and liveliness? ...

We believe that the only way to maintain proper high frequency balance in the room, AND retain a realistic soundstage, the front surface (the part facing the room) MUST be reflective.  Otherwise, not only do you overattenuate high frequencies, but you create surfaces in the room that return sound area differently than the rest of the wall surfaces, creating what I refer to as black holes.  This is the single most destructive thing that can be done to your soundstage after of course no treatment at all.

People talk a lot about no reflection is the best reflection.  Well, theoretically that may be true, but that is impossible to achieve at any cost unless you A. make a true anechoic chamber or B. have no wall boundaries at all (i.e. outside).  Incidentally, these are not pleasant places to listen to music.  Otherwise, I firmly believe that the benefits of treating any space with only absorption are far outweighed by the consequences. Most people forget that 99.9% of all music we listen to is done in a room.  We are used to hearing the room interact with our music.  When you hear a concert, you hear the space it is in.  When recording live or in a studio, you generally hear much more of the space of the room than the mic does in the case of a live event, and studios are usually heavily overdamped, again resulting in less room sound.  I think that in order for us to hear music that sounds natural to us, we NEED the room to contribute.  So focus instead on how to reduce the distorted sound and balance the room instead of fighting with it.

So here is the short answer to your short question.  Glue some foil to the front surface of the foam.  Keep it as flat as possible.  Your mid to high frequency sparkle will be back, the echo will still be attenuated and your soundstage should get much better.

[John Casler]

We believe that the only way to maintain proper high frequency balance in the room, AND retain a realistic soundstage, the front surface (the part facing the room) MUST be reflective.  Otherwise, not only do you overattenuate high frequencies, but you create surfaces in the room that return sound area differently than the rest of the wall surfaces, creating what I refer to as black holes.  This is the single most destructive thing that can be done to your soundstage after of course no treatment at all.

P ...

Hi Eighth,

Not to be contentious, but I wasn't aware that you suggested a "reflective" front wall

I have a "very" damped (two layers of 3" acoustic wedge foam) front wall and the soundstage is incredible.  The frequency balance is very realistic with no "overattenuation" of highs.

The suggestion that the front wall "MUST be reflective", flies in the face of just about every thing I have read and every great system I have heard.

I would be interested in how and why you think creating short range reflection can contribute to the original sound.

you create surfaces in the room that return sound area differently than the rest of the wall surfaces, creating what I refer to as black holes.

I am also interested in what is meant here.  All room surfaces "return" sound differently, based on angular intersection of the soundwaves, surface texture and shape, and distance from the source.  I always thought the idea was to ameliorate the most destructive of these.

I would like to know what is meant by "black holes"

In the listening environment, there will be sections between instruments and performers that "should" be black.  Filling this in with reflected sound seems counter productive to the reality of the presentation?

Most people forget that 99.9% of all music we listen to is done in a room. We are used to hearing the room interact with our music. When you hear a concert, you hear the space it is in.

Are you saying that using the room surfaces of a 12 x 15 room can produce the same sound as a concert hall or even club which is much larger?  Delay and decay times in these very different sized environments cannot be "created" in room by any simple method I know.

How is this possible?

When recording live or in a studio, you generally hear much more of the space of the room than the mic does in the case of a live event, and studios are usually heavily overdamped, again resulting in less room sound. I think that in order for us to hear music that sounds natural to us, we NEED the room to contribute. So focus instead on how to reduce the distorted sound and balance the room instead of fighting with it.

I agree that "sound preference"  is ultimatley the most satisfying result we seek, but I might take issue that "creating" rather than "recreating" is a good thing, "IF" our goal is to hear what the original sounded like.

I would contend that there is no way using any "primary" reflections can contribute to the original signal.  I do think that "live end" reflections that are well diffused/dispersed can offer a type of non-harmful spatial awareness.

While various set ups can certainly make a system sound "good", I think what I am looking for here is for it to sound "true" to the original.  Hope you don't mind me questioning your suggestions, but I am always interested in learning what, how and why

[BrunoB]

... Not to be contentious, but I wasn't aware that you suggested a "reflective" front wall  

I have a "very" damped (two layers of 3" acoustic wedge foam) front wall and the soundstage is incredible. The frequency balance is very realistic with no "overattenuation" of highs.
...

I second John on this: the more foam I put betwen the two front speakers, the better the soundstage is. I have a much better imaging and  focus. I love the effect for classical music.  Also, sound adsorption improves micro, macrodynamics and intelligibility. The latter makes it  easier to hear the reverberation of the concert hall.  
However, not everyone likes this type of sound, some prefer a soundstage where all instruments are more blended. In this case, I would suggest to diffuse the sound as best possible on the front wall. In my humble opinon, a reflective wall is the worse of the three situations.


Bruno

[8thnerve]

Not to be contentious, but I wasn't aware that you suggested a "reflective" front wall

I don't.  I suggest a reflective front surface on all acoustic products.  I would never cover an entire wall with acoustic treatments, only the areas that cause sound distortion.

I have a "very" damped (two layers of 3" acoustic wedge foam) front wall and the soundstage is incredible. The frequency balance is very realistic with no "overattenuation" of highs.

I generally don't like to make absolute statements, but saying that 3" of foam results in no overattenuation of highs, is well, physically impossible.  If the end result in your room is a balanced frequency spectrum well up to and beyond 20KHz, then those tweeters are running REALLY hot.  What RTA did you use to get these figures?  If you are judging by ear, it makes sense that you would think there is no overattenuation, because what most people consider highs (based on what they can hear) is actually only 7KHz to about 12KHz.  16KHz + are not exactly heard, although we do perceive them.

the soundstage is incredible

I also believe that the soundstage that we achieve is incredible.  Having used LEDE rooms, I believe that our approach is FAR superior in terms of soundstage width, depth, height, and natural musical representation.  Unfortunately, all of this is subjective.  I have also found that most people think their soundstage is incredible when it is the best they have ever acheived.  But as soon as it is improved...  You see what I mean.  You always have that shock of, I can't believe there were things that I was missing.

The suggestion that the front wall "MUST be reflective", flies in the face of just about every thing I have read and every great system I have heard.

I don't want to stick on this point, but acoustics is a young science.  Remember, the sun used to rotate around the earth, the earth used to be flat, and the number zero was so rejected that people were burned at the stake for suggesting its existance.

All room surfaces "return" sound differently, based on angular intersection of the soundwaves, surface texture and shape, and distance from the source.

Technically all your points are true, but they are important for different reasons.  Sound is not light, it is only similar in that it can represented as a waveform.  Light is point source based, and it is a discrete particle, a photon.  Photons, for the most part, travel in straight lines and reflect off of surfaces based on angle of incidence.  Sound is not a particle, it is simply a constantly equalizing difference in sound pressure from one molecule to the next.  Its behavior is wildy different from light, and I think the mistaken relating of the two is one of the main impediments to the acoustic sciences.  Sound "travels" as a spherically radiating ripple in all directions.  When it interacts with a wall, it does reflect back, but not like light in any way other than the fact that it does in fact, come back.  A wall does not help the air molecules equalize their pressure nearly as much as, well, air.  This causes the air molecules to try and equalize with the air molecules that it just equalized with back toward the room.  Confused yet?  At any rate, the wall causes many things to happen.  Laminar flow, the tendency for the wall surface to sympathetically vibrate with the sound wave, the combination of the returning sound waves with the incoming ones, all contribute to the sound that eventually hits our ears.  However, flat wall reflections are not that important to a optimum audio system as far as I am concerned.  Corners are where all the damage occurs.  This is where the interaction between incoming and outgoing sound waves are significantly impacted by the decreased area of equalization available to the air returning from the corners.  Sorry if that is obtuse, but it is not a compact subject and as I mentioned before, there is much more to learn.

I agree that "sound preference" is ultimatley the most satisfying result we seek, but I might take issue that "creating" rather than "recreating" is a good thing, "IF" our goal is to hear what the original sounded like.

I have to say, I think this is one of the biggest foibles of hi-fi today.  Living in Nashville, I have been to many, many recording studios.  Trust me, you don't want to hear the original.  The goal of an engineer is NOT to capture the original performance, it is to create music from a collection of samples, played out of context, without the rest of the band.  Now don't point out to me the exceptions, I know they exist.  I am talking about 99% of all the music available.  There are live recordings which are exciting, but again, it will never be the same sound as being there, barely close, especially since if you were there, you'd be listening to them through PA equipment that is far inferior to any decent hi-fi system.  The one thing that is important in my view is communicating that which the artist is intending in the first place, the music.  Take any artist, and have him or her play for you in a garage, on a stage in front of 50,000 people, or in a dead studio, and you'll still be hearing his music.  This somehow eludes most hi-fi systems that I have heard.  There is some essence to the music that we have not yet definitively identified.  People think they know what it is, Avantgarde thinks it's about infinite dynamic ability, Naim thinks it's about incredible pace and rythym, most think it's about absolute detail of what is happening.  The only thing I am sure of is that is not just one thing.

And to really answer your question, reflection is not creating, it is part of listening to music in a room.  I would argue that creating different surfaces for the sound to interact with by having more or less absorptive areas for the air molecules to interact with creates much more artifacts than letting the wall do what it is going to do anyway, without mucking it up.

Again, acoustics is a very young science, with very few absolutes, although many people are happy to make it all absolute.  Whatever works for you I say.  But I am interested in finding the actual truth, no matter how much that flies in the face of current theories or how little they are opposed.

And John, I didn't find your post contentious at all.  Discussion groups are for discussing.  If everyone believed the same thing, this place would be pretty boring, not to mention redundant.  I hope you do not feel my post contentious either.

[Hantra]

Corners are where all the damage occurs. This is where the interaction between incoming and outgoing sound waves are significantly impacted by the decreased area of equalization available to the air returning from the corners.

Not only that, but John G. McKendrick way back in 1896 gave a lecture in Glasgow that pretty much spelled out that when two waveforms collide, the resultant waveform is the sum of those two.  This almost always results in a waveform that is inharmonic with regard to either of the original waves.

My guess is that Casler just hasn't experienced playback in a good room that has been treated well, and not overly so.

[Rob Babcock]

But wouldn't 2 layers of 3" foam start to offer some broadband absorption?  Sure it'll suck up some treble, but 6" of foam is gonna start to absorb down into the lower midrange and upper bass.  Won't it?

[_scotty_]

Both John and 8thnerve may be right in their assertions depending on the loudspeakers radiation pattern and its location in the room. What 8th nerve may advocating is a more even spectral decay in the treated room.The empirical test for the effectiveness of any room treatment,is an assesment of speech intellegibility and flatness of response at the listening position.
My preference has been for LEDE type rooms based on the loudspeakers
I have heard.  If a precise recreation of the original waveform as captured by the microphone is to reach the ear the rooms contribution has to minimised. To many people LEDE rooms sound strange and people may become uncomfortable in them due to unfamiliarity. Most people cannot dedicate
a room solely to listening to music or home theatre and a LEDE room
is not the most aesthetically pleasing sight visually. I think 8thnerve's approach reflects a modification of sound treatment practices based on real world considerations and what level of decor alteration a customer
will accept to achieve an improvement in sound reproduction quality.
I will have to admit I don't understand how a sound wave impinging on a wall and causing a tympanic surface to resonate and reradiate a sound wave equates to laminar flow. A walls contribution to reradiation in this manner, and at what frequency it occured, could be easily measured with an accelerometer placed on the wall. My 2bits,Scotty

[Hantra]

But wouldn't 2 layers of 3" foam start to offer some broadband absorption?  Sure it'll suck up some treble, but 6" of foam is gonna start to absorb down into the lower midrange and upper bass.  Won't it?

Rob:  

Let's say that you would get 5% broadband absoprtion from 3" of foam at all frequencies.  How is that different from just taking an old Kenwood EQ and pushing the knobs down 5%?  Seems to counter our principals here, doesn't it?

[Rob Babcock]

Well, Hantra, I think your Kenwood EQ probably wouldn't acheive the same goal without distorions at other freqs (regardless of the Q of equalization there's always interaction at other frequencies, at least analog EQ), and of course a passive solution like foam will reduce noise where an active one, like an EQ, will add it.  And EQ won't affect the reverberant envelope of a room at all- its domain is freqency, not time.

An essential part of the problem is that I've never heard someone playing a trumpet in one foot away from the back wall in a 10' X 15' room, and I doubt anyone would want to.  But in a great many systems, that's what we get, with the speakers places very close to room boundaries.  Music is usually played back in a room far smaller than you'd ever hear it played in (I'm assuming for a moment we're talking about "real" music).  No speaker no matter how expensive nor amp no matter how well made can compensate for this.

I think the best room sound would be no room sound.  But as alluded to earlier, that isn't practical.  But if I want to hear a large orchestra as it sounds in the space it was recorded in, I can't see any way to do that in a small room without treating reflections and addressing the fact that the room surfaces are much closer than they'd be in real life.

In essence your pulling out your old Kenwood EQ when you swap cables and amps looking for just the right sound.  But I think you have to have the room right first.

I'm not really clear what you are disagreeing with- is it using absorption or using acoustic treatments at all?  If absorption, please understand I'm not advocating treating every room surface with absorption.  In this context I mean only LEDE.

[Hantra]

An essential part of the problem is that I've never heard someone playing a trumpet in one foot away from the back wall in a 10' X 15' room

There is no system in the world that can accurately simulate this.  

I am not really advocating anything.  I am just against overdamping a room.

[Rob Babcock]

You're right, on both counts.  Like Nathan said, it's not an exact science.  Of course what's overdamped to you might be just right for John Casler or not damped enough for me.

I sure don't claim to know, either.  If I had the answers I wouldn't have needed to start this Circle!

But I do have some opinions:

1.  It's not just a matter of bright or dull, in a freq sense.  The live & dead we talk about are more based on reverberant time.  There are some published numbers about what's supposed to constitute a good reverberant time for listening.  In a larger room diffraction is often sufficient.  But in a small room you almost always need some absorption.

2.  Many treatments that work at mid and upper freqs don't do anything to change the volume or RT of the bass freqs.

3.  Bass response is much more difficult to get right, especially in a small room.

4.  A mix of treatments and parametric EQ is often necessary for the low end.  And tradeoffs of EQ above 120 hz are rarely worth it.

I'll readily admit these points might be incorrect, but that's what my experiences up til now have taught me.  But I'm anxious to learn more.  

[8thnerve]

But wouldn't 2 layers of 3" foam start to offer some broadband absorption?  Sure it'll suck up some treble, but 6" of foam is gonna start to absorb down into the lower midrange and upper bass.  Won't it?

Yes but the absorption coefficients would be significantly non-linear.  You can't absorb more mid frequencies without absorbing more treble frequencies with foam.  Although some foam does this better than others.

[8thnerve]

Both John and 8thnerve may be right in their assertions depending on the loudspeakers radiation pattern and its location in the room. What 8th nerve may advocating is a more even spectral decay in the treated room.The empirical test for the effectiveness of any room treatment,is an assesment of speech intellegibility and flatness of response at the listening position.

Agreed.  Since many of our products are in multi-purpose spaces like gymnasiums, church sanctuaries, and even courtrooms, speech intelligibility is key, and a good indicator of overall sound quality.  There is standardization for this as well, it is called the Speech Intelligibility Index.  This is a more rigorous testing process than simple RT-60 calculations.

And for anyone that thinks we are advocating echo, we are not.  With our products installed, echo is virtually eliminated, the RT-60 measurements show a fairly consistent 1.2-1.6, and perhaps most importantly, actual sounds (not from speakers) come from their point of origin.  For instance, one of our customers (you know who you are) explained it very well.  He said that when he would walk through the room outside his listening room, he could hear his footsteps echoing throughout the room; and as he walked into his listening room (same floor surface) the sound of his footsteps were just as loud, but now they were coming from his feet.  The point is, our brain/ears are good at telling use where sound comes from even when there are wall reflections, it is the distorted sound coming from the 90 degree angles that confuse our sense of placement, and define the "character" of the room.  I don't think it is feasible to remove the sound of the room, but we can remove its character.

[Rob Babcock]

Sure, I agree.  I never meant to imply it would absorb all freqs the same.  I believe foams absorption drops with frequency, for the most part.  Since we probably can't come up with a substance with linear absorption at all freqs I can see why one would be tempted not to bother with absorption at all- but there's no part of the reproduction chain that attains linearity anyway.  Given small rooms I think the benefits are worth it.

Don't get me wrong, I'm trying to champion foam!  Just saying there's probably advantages and disadvantages to most types of treatments.

At any rate, the only way to really change the reverberant time of a room is to 1) have some absorption or 2) to make it larger.  Or am I missing something?  Treating the point of first reflection will improve sound, I know, but I'm talking total RT.

BTW, anyone can feel free to let me know if I'm off base.  This is the type of discussion we can learn from.

[8thnerve]

At any rate, the only way to really change the reverberant time of a room is to 1) have some absorption or 2) to make it larger. Or am I missing something? Treating the point of first reflection will improve sound, I know, but I'm talking total RT.

I hope no one thinks that we are advocating the use of NO absorption.  I said in the original post that I believe that the FRONT of any acoustic product should be reflective.  The rest of the product must be very absorptive.  And if any of you don't understand how the product can possibly do any good if only the sides and back, which is against the wall, are absorbing anything, turn on your system and put your ear closer and closer to the wall.  You will notice a significant increase in SPLs.  Almost all of the trouble sound in a room is found within the first inch and a half from the wall surface.

The key is knowing where to use absorption.

[Rob Babcock]

Ooops.  I totally forgot that.   I do remember from your website that the front side reflects and the rest absorbs- you even mention that the hard side is supposed to face out.  "My bad," as they say!

I don't want to seem like I'm trying to be argumentative or ragging on you guys @ 8th Nerve.  Every bit of feedback I've heard on your products is positive.  I'm just trying to understand a little better why stuff works.

Certainly it's a more elegant solution to use a bit of absorption in key areas (eg corners) than just covering entire walls with it & tackling it in a brute force way.