Room treatments 101: where to start?

[westcott]

Dr. Who,

Wouldn't saying that you should listen to your room first before making changes been a lot shorter????

Ha Ha Ha

I have read some interesting material that focused on how human hearing becomes accustomed to what it hears over a relatively short period of time. Our brain has a tendency to filter out a great deal of information as we listen to something over time.

For example, you have x brand of speakers and you have had them for some time. You listen to them on a regular basis yet you never notice that one of the drivers have failed due to slow deterioration.

This may sound far fetched but you would be surprised what one can get accustomed to hearing and all objectivity is lost.

I believe this, in a round about way, supports what Dr. Who was saying. Your taste for music or sound is influenced a great deal more by desensitivity over time than quality of sound.

[DrWho]

Wouldn't saying that you should listen to your

room first before making changes been a lot shorter????

[][][]

Actually, saying that you should listen to your MUSIC first to decide what might need to be attenuated

would have been much shorter. To stress the point: the music decides

what needs to be attenuated. Typically, same genre music is all

recorded in the same methods so there will be common themes amongst

studios that can be specifically addressed in the playback system.

Btw, the male to female ratio is so bad in the ECE (electrical and

computer engineering) college that we're not allowed to put our gender

down for teacher reviews (because there are at most 3 girls in every

class), or pretty much anything that is supposed to be anonymous. The

other 70% of the classes are filled with Asian students that don't

speak a lick of english....yet they do so amazingly well in the

classes. They don't know how to ask where a bus goes, but they can

program and solve nasty word problems like it was basic addition.

This may sound far fetched but you would be surprised what one

can get accustomed to hearing and all objectivity is lost.

How bout a more dramatic example....when mixing live concerts, it seems

the guitar player in every band is always asking for more of himself in

the monitors. Just to prove they're "deaf", when they ask for more

sometimes I will actually turn down the guitar level (especially when I

know their guitar is more than loud enough)...the best part is they

will thank me for making the change and claim that it sounds much

better!!! There are times where I'll even turn it off completely and

they still thank me for the change! What happens is they are expecting

to hear the guitar being louder and subconciously trust that I'm not

mischevious...once they think a change has been made they change the

focus of their hearing to their guitar. Now that they're actually

listening to the guitar, they determine they can now hear it (which

would only be coming from thier acoustic guitar itself or their amp if

they're playing electric) and then just assume that it was turned up.

We as humans hear whatever we want to hear....the trick is being able

to choose how you're hearing...Bands that I mix with often enough start

to catch on after a while (or they overhear me talking about it), which

is a good thing because it causes them to have an ounce of doubt and

they double think what they hear. After a while they start to actually

ask for the correct things in the monitors and from then on I never

have to worry about them being stupid. I have to be careful though that

I'm rock solid on the FOH mix though so that they continue to ask me

back. My goal everytime is to make them sound better than they ever

have before (which has been pretty easy to do cuz most of the bands I

mix with never have had real sound guys before) []

I've mentioned it a few times on the forum, but when mixing a live show

(especially when you're rushed to setup in 15 minutes) you always start

off with critical ears and listen for the major flaws and start working

down the list of things to do. On one occasion I was working the board

so hard trying to make things sound good (after the show was already

started) and a good friend of mine who has "good ears" stepped over and

pushed me away from the board. I asked what was up and he told me to

shut up and listen to the music...without my critical ears. It was

unreal how the mix instantly transformed into one of my best mixes

ever, and all it took was listening differently! Ever since I keep a

notecard on the mixer that says "shut up and listen" to remind myself

to just shut up and enjoy the concert instead of trying to wring every

last ounce of goodness out of the band. I think in the end the concerts

end up going smoother too and I enjoy myself a lot more. The card

serves a dual purpose for when people in the audience come up asking

for me to change things...I can just point to the card [H]

And here I go again blabbing on and on and this time I have no excuse because I'm at home from school now.

so room acoustics...lol. Since it hasn't been mentioned, I think the

best bargain for acoustical treatment right now can be found at

"foambymail"

http://www.foambymail.com/

The same company also sells on ebay under the name "Foam-Factory-Inc"

http://stores.ebay.com/Foam-Factory-Inc_Acoustic-Sound-Proofing-Foam_W0QQcolZ4QQdirZ1QQftidZ2QQtZkm

This is the exact same material as what auralex uses, but costs way

less because you are buying direct from the factory. I believe they are

pretty lineant in changing things around in the $100 packages (to them

it's all the same, just a different cut).

So far I know Michael Hurd and Michael Colter have purchased a package

and I can't believe how much stuff you get. The package has enough to

do about 75% of all your acoustical treatments (and you'll probably

have a lot left over too). DEFINETLY something to look into, or even to

look at splitting with a friend.

[TheSoundBroker]

Starting with the bass is a good idea...and the most frustrating of all

things to deal with. The deeper the frequency your acoustical problem

resides at, the bigger and more expensive it is to treat acoustically.

The best one can hope for (if aesthetics are an issue) is to hope for

well defined peaks. Well definined peaks can be tuned at the listening

position with a Parametric EQ (like a BFD). Not the best solution but

probably easier on the eyes than a tuned helmholz resonator or big

freaking DIY bass trap. From about 80hz on up, acoustic treatment gets

easier (and electronic tuning gets harder!).

I sell the Auralex Sonoflat panels and they are the best looking

of the foam panel solutions and do work pretty well. The guys from

Foambymail don't have anything similar in aesthetics (probably a

trademark thing). One thing you want to do on them (or any other wide

bandwidth panel) is space them off the wall (yes, they are fire rated). Spacing them 2" off the

wall extends their bandwidth quite a bit and can lead to some pretty

cool looking visual effects if you use a combination of

spaced/non-spaced panels.

You can also go the DIY route with semi-rigid fiberglass and acoustic

material. Sounds like it can save you some $$...until you price

semi-rigid fiberglass and acoustic material. Sonoflats are also good

because if you rent or plan to move...they are easy to take down. They

are also easy to move around when you are playing with things...which

you will do...a lot...obsessively in fact once you get into

acoustics...god help you.

Make sure anything you put on the wall is fire code rated. This is NOT an option!

Oh, and ETF is cool!

[PrestonTom]

Soundbroker,

I am not sure what you mean by seeking "well defined peaks".

As for the low bass problems, I am uneasy with using an equalizer (for various reasons). My space may be large enough to use some sort of bass trap or Helmholtz resonators. I agree with your view about the aesthetics issue, but may be I can get clever and figure out a way to disguise things. As for the higher frequencies, I am also toying with foam along with the idea of fabricating some RPG panels, this may or may not be do-able or aesthetic.

Right now things are on hold till I get finished with the carpentry in my kitchen and get an affordable measurement rig. My measurement equipment at work is no longer an option.

Good luck,

-Tom

[damonrpayne]

I second (or third, or whatever) the recommendation to get the Master Handbook of Acoustics. I just got a copy for xmas and shall have plenty of time to read and digest before I can start my room project.

[sfogg]

Tom,

""As for the low bass problems, I am uneasy with using an equalizer (for various reasons)."

Might I ask why? IME well placed (and that is the key) parametric EQ can work very well in the minimum phase bass range.

Shawn

[artto]

Folks,

First question: When Artto and others first tackled their environments, what was the first step. As a scientist, I am inclined to do some subjective evaluation about what I like and don't like and then follow this up with some physical/acoustic measurements before starting

-Tom

I'll probably follow up with other answers but to answer your first question: First the bad news. I bought this house (a raised ranch) when I was relatively young (26) (and certainly didn't expect to say here this long, but, as I'm sure you know, life has it's own way of changing things). I started off by selecting a house that had reasonably good possibilities to build an "ultimate" listening room that could specifically support Klipschorns. I had already been planning this while I was still in college, long before I had Khorns.

The criteria were 1. It had to have at least two full corners across one wall. 2. It had to be capable of construction with "correct" proportions to minimize frequency response anomolies due to room modes. 3. I needed to be able to isolate it and reduce sound transmision (in or out) to a minimum which meant the "space" needed to be unfinished so I could perform the necessary construction isolation techniques myself.

Everything else was added later, and optimized though experimentation. I might also mention, that even with my background in architecture and music, and after all the "planning" that preceded construction and installation, the early incarnation of this space (the one pictured in my avatar) came out nothing like it was planned, kind of like what happened to Lincoln Center. You must use your ears.

[JeffDurbin]

You might want to take a look at this before you spend the money on ETF.

http://www.avsforum.com/avs-vb/showthread.php?t=529224

[PrestonTom]

Tom, ""As for the low bass problems, I am uneasy with using an equalizer (for various reasons)." Might I ask why? IME well placed (and that is the key) parametric EQ can work very well in the minimum phase bass range. Shawn

Shawn,

A few reasons on why I hesitate using an equalizer.

First, the setups I have seen using EQ for correcting room problems have not been satisfactory. You may have had/seen better results, I have not.

Second, I am concerned about putting extra things in the signal chain. The K-Horns are very revealing of any noise, distortion, hiss & hum. So it gets risky ( I am interested in as clean a signal as possible).

Third, I don't feel an EQ will clean up reverberation problems, it will only attenuate them. Actually it can make matters worse since a narrow band filter will, for physical reasons, cause the waveform to "ring" and loose its attack. Although, at a low frequency this may not be a severe problem.

There are cases where an EQ is advantageous. Certainly for correcting coloration form the speakers themselves or perhaps "correcting" some problems inherent in the original recording.

Good Luck,

-Tom

[strutter]

for those that don't have the time or equipment check this out.

http://www.rivesaudio.com/services/servframe2.html

they also have ETF software package for $150.

[sfogg]

"The K-Horns are very revealing of any noise, distortion, hiss &

hum. So it gets risky ( I am interested in as clean a signal as

possible)."

You do have to be careful there but that can be done. It is a matter of

tradeoffs since not correcting the problems your room is going to

impart on the playback has its own downsides as well.

"Third, I don't feel an EQ will clean up reverberation problems, it will only attenuate them."

Read how the EQ systems from both Lexicon and Meridian work. They both

perform their analysis in the time domain and specifically target the

points that ring longest in the room instead of the more common

approach of targeting flat amplitude response.. They both reduce

ringing audibly and measurably. And because of their methods of

measurement it means the correction is valid for far more then one

point in the room.

" Although, at a low frequency this may not be a severe problem. "

Room problems in the bass range are minimum phase problems. Correcting

them through EQ will actually correct the phase distortions from the

room too.

Shawn

[travisc]

you guys are trying to give me a headache and its working. http://www.hometheaterhifi.com/volume_11_4/feature-article-acoustic-treatment-methods-and-materials-12-2004.html

I found this, I dont know what to make of it

question, will 12" sana tubes from home depot help at all\

anyone got a link to this line if thought diy diffusers?

I get lost way to quick, any links for beginner/ignoramus room treatment 101?

[travisc]

http://www.allchurchsound.com/ACS/edart/sono1.html

[DrWho]

Sono Tubes are "acoustic absorbers" - know how a glass bottle makes a tone when you blow across the top? And how the tone changes depending on how much drink is left in the bottle? (aka, the depth of the tube). Sono Tubes are the same thing....they naturally resonate at a particular frequency and the trick is to make the sound in the room excite the tube, which will then become out of phase. And since out of phase signals cancel, you effectively achieve cancellation at the tuning frequency of the sono tube. Placement is of course very critical because they must be located in positions where acoustic build up of that particular frequency is occuring.

Helmholtz radiators work on the same premis as well...the surface sympathetically vibrates at a certain frequency, which will then be out of phase with the sound triggering it, thus yielding cancellation. Due to the large face of the HR's, they are less position sensitive. They also don't take up that much room, but tuning can be a major pain.

Corner "bass traps" work on a different principle where the acoustical energy hitting the panel gets turned into heat. (The foam absorbs the sound wave). This approach works over a much larger bandwidth and is the least position sensitive. Their downsize is they must be huge to be effective at low frequencies. In fact, an absorbtive panel needs to be larger than 1/4 wavelength for the sound to be effectively attenuated (basically not just go through and "not see" the panel). Note that these panels become more effective when mounted on walls because the sound travels through them twice (thus extending their effectiveness down an octave).

All forms of diffusion work on the premise of redirecting/spreading out reflections so that the reflected sound must travel further before reaching the listener (thus reducing the output). Diffusion is cool because it extends the reverberant nature of the room. Again, these panels follow the 1/4 wavelength rule (but don't necesarily benefit from wall/corner mounting).

After the bass issues, the second most annoying acoustical issue of normal listening environments is the unnatural reverb: slap-back echo which is due to having huge spans of parallel surfaces (our room are usually rectangular), and the decay time (how long frequencies resonate in the room - all frequencies will resonate for a bit, but usually there will be 4 or 5 such frequencies that dominate the rest). The easiest way to correct slap-back is to add diffusion throughout the room, but one must be careful to also implement some absorbtion so as to keep the room from getting too "live" (aka too long of a reverberation time across all the frequencies). At the same time, one must avoid using too much absorbtion so as to keep the room from getting too "dead" (aka too short of a reverberation time). It is important to note that every type of 'acoustic treatment' has both diffusive and absorbtive properties, both of which need to be taken into account (even though one might be listed as "absorbtion" or "diffusion"). In fact, one of the reasons I like to start with bass traps is because they have very strong diffusive and absorbtive properties at the higher frequencies too.

I have found that room resonations are best dealt with the "resonation treatments" (sono tubes and HR's). They just have a more natural effect than trying to use absorbtion to deal with them. I believe it has to do with the fact that the room resonations typically have a loose harmonic relationship, which is also present in the treatments. That means just one or two HR's are needed to knock out the majority of the resonation problems. These treatments however are not very effective at broadband solutions (like attenuating the "live" and "dead" sound of the room).

Btw, I just wanted to mention that all the treatments are very position sensitive so don't be misled by my relative comparisons.

Also, I wanted to mention that people that put absorbtion behind the speakers to reduce the audibility of cabinet vibrations should also consider coating the rear and sides of the speaker itself with absorbtion too. For the same reason absorbtion works on the walls, having absorbtion on the speaker itself will reduce the amplitude of these sounds.

In all things remember that the reflected sound is part of the music and that all treatments are frequency specifi - so make sure you don't go destroying the tonal balance by using too much of an identical treatment. (aka, variation is a good thing). Too many people get carried away and destroy their sound by not keeping their ears on the big picture. When doing things by ear, you need to anticipate the change in sound you hope to achieve so that you don't get lulled into thinking something that sounds different sounds better when in fact it usually sounds worse. It just takes you a few weeks/months/years to realize it. Also, add one panel at a time so that you can hear the difference each piece of the puzzle makes - that way, after you are using a lot more, you can better tweak your sound (because you can better anticipate the changes you want to achieve).

[Joe Auwen]

How would lining the sidewalls with bookcases & books effect the absortion/reflections in a room?

[DrWho]

I've seen it done on a few occasions and I've always felt that the bookshelf trick worked better on the rear walls. On the side walls it kinda makes the sound congested (probably because it really eats up the width of the room). Don't forget to stagger the books in the bookshelf