Room treatments 101: where to start?

[PrestonTom]

Folks,

I am bit embarrassed to confess this since I actually work in audio.

I will be finishing up a kitchen re-model, which of course has taken 3 times as long to complete then as I predicted. Which leaves me time for my next project: Serious (or semi-serious) sound treatments for my listening room.

I live in a raised ranch and use the living room as my listening room (K-Horns with 2-channel music & no eye toward home theater). The room is limited by 8 ft ceilings but measures 12 ft deep by 19 ft wide. The width spills open to a front entry stairwell, and a hallway. The depth spills open to a wide kitchen entrance with a cutout (window) between the rooms. There are enough complications so that a simple geometric model will not work. But the good news is that the space is not terribly small.

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

My dilemma is the measurement issue. Naively, one could use some long-term signals (flat noise or warble-tones) and measure long-term frequency response. This could tell me about standing waves. This frequency domain approach is attractive since it is straight forward and easily implemented ( I can borrow some of the equipment from work). However, the disadvantage of a frequency domain approach is that a highly reverberant room can also generate a sound field with a uniform SPL (room modes are densely spaced). Such a reverberant room can sound terrible (believe me I used to work with these).

What about the time domain? There are ways to measure this also but what about the treatment? One can diffuse, trap, and absorb much of the sound but then what are you left with? An anechoic chamber describes this extreme. Believe me you would not want this for your room. It is a rather dead environment (believe me again, I used to work in one). Again you would decrease the echoes and reverberation (at least at some parts of the spectrum), but the frequency response of the Speaker-Room system would not be flat.

The other aspect is sound deadening (making the room quiet & decreasing room-to-room transmission). This is difficult to achieve since the room already exists (this is NOT new construction) and this is also an "open" floor plan (which allows it to be a "larger" room).

Where does one start? I assume I will re-read my time domain measurement handbooks, borrow a microphone and spectrum analyzer and check out some DIY projects on fabricating sound absorbers, sound diffusers, and bass traps. And by the way, the treatments will require some aesthetic design criteria (you guys have girlfriends and wives so I don't need to explain this...).

Your thoughts please (and this should be an ongoing dialog),

-Tom

[WMcD]

I'm starting to work on a similar project. It is my thought that a combination of polycylinders and sound abosorbing panels made from thermal insulation are the way to go and can be dressed up as artistic wall hangings.

My project got stalled because of work issues . . . my source of money for the hobby. Dang.

If you look at Art's room and some other designs they are just fully populated by polys. OTOH, PWK suggested ten percent or so. I don't know. I do observe that acoustics driven by a Sony tap-tune radio in my enclosed bathtub are bad until I open the door to remove 20 percent of a hard surface. Such is amature science.

You should buy The Master Handbook of Acoustics by Everest. D-Man has a not quite high opinion of the book. (Shhhh, D-Man is very opinionated, but otherwise okay. Just don't tell him I said so.) For me, the book is a gold mine.

In my view the issues are how to measure to find out what is wrong, and then physical room treatment to solve the problems.

One figure of merit for a room is the RT-60 decay. It is the amount of time it takes a given frequency room resonance to decay by 60 dB. The theory is that this should be relatively constant across the frequency band. I believe no one thinks this is the sole measurement to trust, but it is an important first one which can be measured..

The MHoA shows an example were there is a long decay of a bass freq. Then a Helmhotz resonantor is used to "trap" it. It looks good on paper.

There is are a few measurment soft ware packages out there to do an RT-60 measurement. One is a free ware, which I'll have to find at the office, and post, I got the lead from this BBS (it costs to turn on the complete package). Praxis (Liberty Instruments) and LMS also do this.

Here, happily, we don't need a calibrated microphone because we're looking at time to decay by 60 dB. We don't need a flat microphone.

I had intended to work on the project and then show the fruits of my genius. Ego. Perhaps we should colaborate.

I will add that I have a little problem with the Handbook in that it shows the merits of polycylinders, which are workable, and then gushes about RPG, which I think are too complicated for home builders. I think the advantages of less than RPG are damned with faint praise (sp).

Everyone here has read my posts on this before. Basically, I think that all home type rooms are so bad that any treatment is for the better. But, of course we should get scientific.

Send me some e-mail. I'll send you some info. PM and e-mail here does not allow attachments.

Things on the BBS here have changed. It used to be that you couldn't post the work "treatment". I tried. The internal words of eatme got censored. I did a spell check word search. The word treatment is the only one in which eatme appears. Smile.

Best,

Gil

[PrestonTom]

Gil,

Thanks for your thoughts and I will certainly keep everyone posted (I think our solutions will be of interest to everyone).

As a starting point RT-60 decay times (I remember them as the "Sabine decays") are probably a good starting point. Although trying to keep them uniform across frequency will be tricky (trivial at high frequencies and requiring heroic efforts at low frequencies). This will be a blast getting back into this topic again.

A number of years ago I was the technical point of contact when our lab was renovating the anechoic chamber and reverberant rooms in our suite of laboratories. I am certainly familiar with Everest's Book. There was another more technical book by Kruttoff (?) on room acoustics. It was older but provided a solid technical background.

My goal is toward some workable solutions that are flexible, visually pleasing (at least not annoying), appropriate for others to borrow, and will not entirely alienate my girlfriend.

I will begin in earnest sometime in Jan (once my kitchen renovation is finished).

Good Luck,

-Tom

[DrWho]

The goal of the RT60 is NOT to have a uniform time of delay for each

frequency. I'll see if I can dig it up as there is an ideal curve that

someone somewhere determined was the most natural sounding (I think it

involved running around and measuring all the subjectively considered

great acoustical environments so there will be some fudging involved).

If you're serious about measuring and experimenting with the time

domain, then you need to get yourself an ETF. If you have a computer

that you can bring into the room, then I would suggest buying some

software (there is one that only costs $200 or so, I'll see if I can

find the link...some guys on the forum have it) and then you would need

to purchase a calibrated mic. The mic ECM8000? from Behringer only

costs $50 and then you would need to purchase a $50 mixer (cheapest

mic-pre out there). You then run the signal into your computer and

you'll have a very insane measuring system. There is also free software

out there that will do RTA measurements (I have a nice shareware

program I can send you) and then of course there is always "Spectrum

Lab" - which will do waterfalls and some other stuff. I just got it and

haven't figured it out yet, but formica seems to know his way around

the program...so I nominate him to help you with it [] So for $300

you're talking about an intense measuring system, which sounds like

something you are more than capable of understanding and something you

would enjoy playing with too.

The first place to start however is with the bass response. The bass is

very important to what is percieved as the midrange and the typical

bass treatment will also have other higher frequency side effects (like

diffusion and absorbtion at frequencies other than the low ones). The

idea behind the typical bass trap is to absorb at many frequencies,

which will have a larger impact on the room modes, but will also affect

non-problem frequencies. So if you're very serious about this project

and have the measuring tools available, then you might look into

Helmholtz radiators and start getting very frequency specific. But keep

in mind that the more specific you get, the narrower the target

listening area becomes...so you need to determine how big the listening

position is.

Once the bass is roughly tuned in (don't fine tune it right away) then

you really need to look at the early reflection points. With khorns I

think your best bet is to address the cieling first, by getting lots of

diffusion up there. When measuring in the time domain, you should be

able to notice certain lengths of time that are causing you

problems....you can then translate this into a distance using the speed

of sound and then hopefully you can find some attribute in the room

that could be causing the problem...

I think one of the first things you'll notice is that the khorn is not

time-aligned. I dunno why people seem to be rejecting the concept

lately, but I'll name drop and mention that Roy Delgado claims that

time-alignment is an essential ingredient. [] You will only be able

to align in the horizontal and depth plains, which leaves some issues

in the vertical plane, but these can be minimized with steep crossover

slopes and probably even some room treatments as well (afterall, the

only vertical issues that could be a problem would be with the

indirect/reflected sound). I know you wanted to talk about "room

acoustics", but I feel the issue of time-alignment is very closely

related and needs to be dealt with before you go treating them

room.....because later on down the road if you decide to time-align,

you will probably notice a need to change around some things. And since

you're strictly 2-channel the overall cost shouldn't be too

much...'all' you need is 2 more amps and the processing unit.

Well that's enough for now...it'll be fun watching this project unfold.

[westcott]

I realize I will probably receive a lot of grief over some of the statements I am going to make but here it goes.

I would start with the floor.

I know that this may sound oversimplified, but once the floor is laid, there usually is no going back. Just adding carpet is not going to be the end all solution if you are serious about your sound. It would take a 4" shag to be as effective as other solutions and I doubt that will meet the WAF.

Second, IMO, an open floor plan like yours can be a very forgiving environement in many ways and I tend to prefer a large, open area for music listening. A lot of problems are caused by overloading a closed room. An open architecture greatly reduces these issues. On the other hand, you will need some serious power and speakers to ovecome this in an open architecture.

I have also found that most books and software are geared toward speakers that are not of the horn design. I find that horn loaded speakers have some unique atrributes when it comes to room interaction.

Their directionality reduces side wall interactions, especially in an open floor plan.

I find that it is much easier to manage bass frequencies to ovecome the "holes" created by your floor plan.

The second area I would address first is your primary and secondary reflection points on the side walls. I have found that my room sound better when I move the sound absorbtion panels further towards the center of the side walls due to the more directional design. Line of sight (mirror method) was not the ideal placement with my speakers. The areas behind your speakers are also a great place to start.

After that, I would set up your system, place your speakers and furniture, listen to your system, and then decide if you have problems that need to be addressed. Bass traps are an easy way to address acoustics, but as you mentioned, WAF is a big concern. Dr. Who was been very helpful in helping me assess my situation and I am very pleased with the direction I am heading. This is a shared room so WAF was a primary force in the decision making process. I still have work to do but just having the floors installed has made a huge difference.

[Zealot125]

I was just pondering that kind of stuff the other day. Allow me to propose a question. Can one use a nice directional microphone (cardioid?) to gather data in a frequency domain and they apply a reverse fourier transform in order to convert the data into a time domain? If this will work, I can write a program to do the math, unless there is one readily availible (and free). Would that be the way to go to really analyze things in a time domain, or am I mising something?

[PrestonTom]

Westcott,

I appreciate your comments about the floor. But I am stuck on this one. The house is already built. The floors are hardwood. Currently there is an area carpet with a pad underneath. I will have to work with this (also the floor can not be raised since I only have an 8ft ceiling).

I also agree about the open floor plan being forgiving. I am banking on the various openings (to kitchen, hall, front entry) to alleviate some of the "building up" of the low frequencies. This also gives some nice asymmetries.

I am also sympathetic to your comment about the about the uniqueness of horns. I do, and will continue to, have my horns positioned so the listening chair is at a 45 deg with each horn. Your right in pointing out the advantage of direct to reverberant energy in this configuration. It also has the advantage of a flatter freq response since the listener is on-axis with the speaker and minimizing any off-axis frequency response drop off (I think this is sometimes forgotten about by many folks). The other, and more obscure, advantage to the 45 deg placement, is that the listening sweetspot is enlarged (left-to-right). I won't go into here, but for anyone interested there is a nice pictorial description in one of the Dope from Hope issues.

Good Luck,

-Tom

[formica]

see my post below... [:$]

[PrestonTom]

Zealot,

You are posing a rather tough question actually. The choice of microphone is not as important since ultimately you will be making repeated measures throughout the space. If there were no boundaries, then the SPL would drop off at a rate of -6dB per doubling of distance. This in fact is part of the ANSI standard for measuring the low frequency cut off of an anechoic chamber. One can play this trick also to get a sense (spectrally) of the standing waves in a room.

The problem with using Freq domain approach (i.e., Fourier) is that it does not really tell you about echoes, only their results via standing waves and room modes. Inverting the FFT to go back to the time domain is tricky, since the algorithm assumes that the signal started a very long time ago and will contnue for a very long time. So the time information you get is the ongoing phase of the constituent cosines - if they were continuous. With a transient signal, the algorithm, in effect, asumes the transient is simply repeated indefinitely. There will be various

nobs" of the machine to apply various windows or filters; however, these must be used with some underlying knowledge of what is being done inernally. In this regard, many folks using an FFT & applying various windows are unintentionally filtering or smearing the signal.

Basically, with a many approaches (including FFT), you are either going to get spectral precision or temporal precision, but not both. In fact this headache is why waveform analysis using wavelets is so attractive, since you can get around some of this uncertainity. Alas, I am about to go off on a very different tangent .... I'll stop.

You really need the time-domain measures. Even a simple one like looking at the output on a scope (with the right test signal) will give some very solid clues about where the dominant reflections are coming from and also a ore macro vies of decay times etc. Although this can be a tedius process.

Good Luck,

-Tom

[PrestonTom]

Dr Who,

Thanks for your thoughts.

You are absolutely correct regarding the conundrum: On a continuum where the endpoints are either an anechoic chamber (no echoes or reverberation) or conversely to a reverberant room (where echoes are maximixed, yet the SPL is relatively uniform thought out the space): where do you want to be? That is a good question. There are certainly answers when it comes to concert hall acoustical design. But I am not trying to impose an additional concert hall on to what was originally recorded.

On your other thought on the time-alignment. Yes this is a tangent to the question, but there is an interesting relation to room setup issue. Basically, and simplistically, the bass bin effectively needs both to be in a corner yet at the same time about 6ft "in front" of the top section. This difference in propagation delay, would effectively re-align the drivers having different path lengths. I am ignoring the comparably slight difference in path length between the mid and the tweeter.

How to solve this. Well I can't have a corner "in front" of the top section. However, one could have the bass bin on the floor and position the top section in the corner but substantially elevated toward the ceiling (and angled downward).

My rough calculation, to create an extra 6ft (or about 6ms), would require the top section to be elevated by about 17 ft above the floor.

No, I only have an 8ft ceiling. So I can not do this trick. But consider this for a moment. It does not require any outboard equipment (no added distortion in the signal path), no extra amplifiers. What could be simpler! Does anyone have barn?

Good Luck,

Tom

[Jeff Matthews]

Where to start? Mostly starts with a stereo.

Where it ends? Usually never.... especially if you've gone so far as to worry about 6ms time-delays, etc. If you are into that kind of detail, you are into research labs. The research will never end. I suggest to find a way to do that on somebody else's nickel. []

[WMcD]

I thought DrWho was objecting to a lot of stuff that I left out. Actually, I think he is saying that some room freq response is perceived as being nicer. I wouldn't be surprized. There are studies that speakers with non flat responses I wasn't cringing at that.

Stuff I left out was:

Basically we start with an assumption that the acoustic energy is in the form of a echo off surfaces which absorb sound, or fail to reflect. And there are repeated echos. Lets call that 50 percent absorption. So an echo is 0.50, 0.25, 0,125 etc.

That is an exponential decay. We can write an equation using an exponent (time) to predict the levels. It is the same as our exponential horns which double in area every X distance down the horn. Of course the area halfs if we go the other way.

The decay in sound pressure at a given frequency is often displayed on a logarithimic scale. Logs and exponents are inverse functions of each other. Therefore, there is a straight line indicating decay.

But sometimes the decay measured does not result in a straight line. This shows something very odd. Some items and rooms vary in absorbance depending on sound intensity, at that frequency. I thought the good Dr. was calling me to task on that.

Remember, this is at a given frequency. It can vary with frequency and is part of the puzzle. The not straight line response changes with frequency.

In contrast, we see amps and speakers spec-ed to say response is plus or minus 3 dB and here is the curve. What we don't see is any spec saying that frequency response changes with level. The only exception is the review of the K-Horn where Richard Heyser has a comment on cresendo response. The KHorn was very good.

Now I feel better.

Gil

.

[SCOOTERDOG]

Speaking of

room treatments. I have looked at the Auralex sonoflat panels for quite

some time now. Here is the info on the product.

Auralex SonoFlat

Panels are 2" x 2' x 2' panels made of Auralex's industry-leading

Studiofoam and offer great absorption of mid to high frequencies. The

edges are beveled, contributing to an elegant look not normally associated

with acoustic foam. The panels can be installed easily and arranged in

a multitude of attractive patterns.

Now I don't know what the so called Studiofoam is but it would seem to

me you could get some 2" thick styrafoam and put a bezel on the sides

just like they do. Granted it looks as if the foam has the color mixed

in. I would think you could spray the panels or cover them in fabric.

Lowes has 4x8 sheets of this 2" styrafoam, you could get 8 2x2 out of

one sheet. I wonder how much difference there would be in the acoustic

properties.

Has anyone done a diy project like this? If so I would like to here your thoughts.

For the cost of 30 bucks a sheet it would be worth the experiment.

scooter

[formica]

If you're serious about measuring and experimenting

with the time domain, then you need to get yourself an ETF.

The beauty of it is that it'll do "time-energy" plots ... taking the

guess work of finding the actual trouble frequency. Definitely easier

to interpret than RT60...

http://www.etfacoustic.com

It runs 150$ for the basic package... but an additional 150$ will get

you additional LF tools and ambient room noise reduction plug in.

It'll work with the RS SPL for the lower frequencies, but

accuracy goes up with a measurement mic (like the one Mike mentioned)

(there is one that only costs $200 or so, I'll see

if I can find the link...some guys on the forum have it)

I'm figuring you are referring to TrueRTA... which actually runs 100$

for the 1/24 octave version.? It's actually simpler and more

intuitive to use than ETF, but less flexible. I haven't

experimented with it, but I don't believe it'll give you a Time energy

plot.

http://www.trueaudio.com

then of course there is always "Spectrum Lab" -

which will do waterfalls and some other stuff. I just got it and

haven't figured it out yet, but formica seems to know his way around

the program...

I'm relatively new to it too... but as far as I know it'll produce a

coloured graph of the soundcards "line level input"... whatever you may

be pluging into it. I've been basically using it to plot a CD's

the sonic content directly. I have not used it for room

measurement.

You can check out the "Bass extension requirements for 2 channel music?" thread to see what they look like.

The first place to start however is with the bass

response. The bass is very important to what is percieved as the

midrange and the typical bass treatment will also have other higher

frequency side effects (like diffusion and absorbtion at frequencies

other than the low ones).

I second the proposition of attacking the bass frequencies first.

It's kinda like starting at the foundations, and moving your way

up. With no subwoofer, I'd look into placing bass traps in the

corners which measure with the highest peaks. This may not have

the highest WAF, but perhaps sticking with purchased units (like the

Auralex and competitors) may soften the blow?

BTW, attached is an low frequency "energy time" graph of my current

living room... could you guess what my problem frequency(s) is?

ROb

[formica]

Now I don't know what the so called Studiofoam

is but it would seem to me you could get some 2" thick styrafoam and

put a bezel on the sides just like they do. .... I wonder how much

difference there would be in the acoustic properties.

Unfortunately "Styrofoam" is a closed cell polystyrene insulation...

compared to the open cell type used in acoustics. You'd need to

find a product that absorbs water (a sign it's open celled) for it to

work.[]

ROb

[SCOOTERDOG]

Yes your right, The stuff at home depot is closed cell. I did find some open cell styrofoam that is 1.5" thick and comes in 2x3 sheets. Plus if it's open cell you wouldn't want to paint it as that would close it up. You could cover it with acoustic fabric so it has the WAF. It runs about 6 bucks for a 2x3 sheet. I guess I'm wondering what the big difference would be between off the shelf open cell styrofoam and the Auralex open cell panels are, other then the color is in the foam.

Any thoughts on this?

scooter

[PrestonTom]

Just a few thoughts on the open cell foam treatment. My experience is with the stuff distributed by Sonex.

First, there is an out gassing. So when it first installed, you will smell the organic compounds. Some are sensitive to this, others are not and it will not last forever.

Second, some of it is paintable. It will slightly change the absorbtion coefficient (but not drastically).

Third, some of this stuff will release some nasty stuff if a flame is held to it - it smolders. Different brands may have different properties.

This last point raises another issue with room treatment. If you suspend stuff from the ceiling or on the wall. It will usually work better (absorb more sound and down to lower frequencies). But let me caution, that this also raises the red flag on fire issues. Suspended flammable material is not always and leaving an air gap behind it makes it even worse. It is something to keep in mind.

Good Luck,

-Tom

[DrWho]

Rob, were you using a calibrated mic for that frequency sweep? And will the program measure lower than 20Hz?

Since you posted a pic, I wanted to comment on the problem frequency (around 40Hz) and how it's affecting other frequencies (particularly that first octave harmonic around 80Hz). When reading these graphs, you are looking for two things: a flat response at 0ms (the shape of the back of the graph, aka the direct sound) and then similar decay rates across every frequency. In a perfect reproduction system in an anechoic chamber, we would expect to see a flat line across the back, and a vertical decay rate. We most certainly don't want to see that 40Hz note ringing on for so long. Likewise, we don't want to see a very steep decay rate either because that sounds most unnatural (mostly because no recording is capable of storing all the acoustical cues, not to mention the system is unable to reproduce the acoustical cues of your own breathing and sounds from isnide the room) and which is why we must avoid solely using absorbtion to obtain a flat response (because it makes the decay rate too fast). In fact, this brings up an interesting concept in that the sound of our room must sound pleasing (must sound like you're in a room), while also not coloring the music. Also, no recording is capable of capturing all the acoustical cues either...

In this case, I would argue that the best treatment to begin with would be a helmholtz radiator at the end of the room who's dimension might correspond to the 40Hz problem (28 feet). I'm not familiar with Rob's room, but I would bet this would be a tangential mode (going from the floor corner to the cieling corner diagnally opposite) simply because I don't think he has a room with a 28foot depth []

Anyways, the whole point I'm trying to get to is that treating the 40Hz problem will more than likely fix the 80Hz problem and all subsequent harmonics...so in a way, we must start with the lower frequencies.

Also, what speakers were being used in the test? It would be most valuable to take all the speakers in the system outdoors and run the same sweeps to get an idea of what the speaker is doing...it would be "incorrect" to compensate for a speaker resonation by further dampening the room at that frequency (you should fix speaker problems with the speaker, not the room...for the same reason we don't fix room problems with the speaker).

And to stress one very important point....the more "correct" you make your system, the more and more you must rely on the fact that the studio recording your music was also in a good environment. In other words, exceeding the resolution of the studio would be pointless (which is why crappy recordings sound decent on crappy systems, whereas crappy recordings sound rather awful on good systems....the flaws in the system no longer mask the flaws in the recording). And this is also why there is so much subjectivism with measurements....basically the text book ideal for everything would place 100% of the emphasis on the recording studio - and since nobody listens to all the same music, and all music isn't recorded perfectly, then we must adapt the text book ideal of our listening room to conform to the flaws in the recording studio. To portray a very simple example, let's say our playback system/room is identical in every way to the recording studio making our music, except the studio has the subwoofer 6dB too quiet. This means the recording will be 6dB too loud at those frequencies because the engineer will mix it to sound good in the room. When we playback the recording on our flat system it will seem like our sub is 6dB too loud because the recording is 6dB too loud and we dialed in our system to have a perfectly flat response. So though the text book ideal states that we should be perfectly flat, we must set that aside and realize that reducing our sub at home by 6dB will result in a true flat response (making up for a flaw in the recording studio). Sadly we do not know precisely what flaw was occuring in the studio (and chances are it's a much much more complex issue), so in the end we must trust our ears and use the measurements as only a reference point, to get an idea of where possible problem frequencies might be.

So instead of blindly foraging forward and correcting what the measurements say is wrong, we must instead listen to the music and decide ahead of time what seems to be lacking in the music. We then take some measurements and look to see if any possible explanation exists. We then go and find what tools (treatments) are available for the possible problems, pick one and then finally listen again to see if the problem is no longer there. I cannot emphasize enough that we must first start and end with listening to the music. I must admit that I like being a gear head and getting into all the technicals of everything, but it's all pointless if I forget to enjoy the music. In fact, it is quite interesting that all the flaws in the system seem to just go away when you're actually enjoying yourself.

That's not to say that a crappy system will sound better than or equally as good as a good one; quite the contrary actually. We can however maximize the enjoyment of our current (hopefully best sounding) system that we own by simply training ourselves to listen to the music instead of the system. However, being able to listen to the system is a most important skill as it allows one to decide how to improve upon the system (I like to call them "music ears" and "critical ears" respectively).

So....as you embark on your project, keep in mind that all the "ideal theories" that we throw around are merely ways of thinking about problems and it will be up to you to decide how to apply them to your very specific situation...and even up to you to decide what sounds best.

I did want to mention this and didn't know where to put it so here it goes at the end of the post....humans for some reason seem to be very keen on hearing resonating sounds. The science that goes behind the construction of musical instruments and determining ahead of time what will sound the best involves looking at the timbre of the instrument. The timbre is merely the natural resonations that the instrument makes as each note/combination of notes is played. By changing dimensions and locations of all the parts, we can change the harmonic structure such that resonations are occuring at different frequencies. It is interesting to note that 1/1000 of an octave shifts are extremely audible when it comes to timbre (even though it still sounds like the same note).

This logic can be applied to anything that deals with hearing...including room acoustics.

This concept can also be taken a step further, but begins to sound very elitist so I don't mention it very often (for fear of rubbing off that way). I have come across research though that takes the "instrument timbre" concept a step further to discuss the visual aspects of a room too. The sensory location in our brain is quite complex and it is interesting to note that there is overlaps between taste, sight, sound, feeling, etc etc....In fact, there are some people that are unable to distinguish the difference between taste and color. The same is true for sight and sound and the end conclusion is that the "visual resonation" of the room is such that it can vastly affect how one hears sounds in the room too. Some of the research goes on to suggest that the reason for the whole WAF factor has to do with the fact that most women aren't exposed to a "harsh work environment" everyday which means they haven't become numbed to these "harsh resonations." (btw, please don't mistake this as a sexist comment as it is by no means intended to be taken that way....in fact, the opposite occurs when the woman works and the man stays at home). Anyways, the goal of this kind of research is an exploration into the differences between classes of people and why people trend towards different things. In other words, it is blatantly obvious that just about everyone in this hobby finds something that looks better to also be better sounding...and there seems to be a trend correlated to the way we percieve things.

So all this to say....requiring that the room look acceptable is entirely an acceptable goal and even has scientific backing based on the way we has humans interpret our senses...and those who are more "refined" are simply more susceptible to such issues (I like to equate "refined" with "restricted").

Well I'm done babbling now and don't know why I'm talking about all this anymore so I think I'll just stop (oh the joys of being stuck in the lab inbetween classes with nothing better to do) []

(edit: wow, this is one fricken long post! might be my longest actually)

[dbflash]

Read this. It's been posted many times in the past, but it may help you to get started.

http://www.acoustics101.com/

Danny

[formica]

Rob, were you using a calibrated mic for that

frequency sweep? And will the program measure lower than 20Hz?

That test was actually done with the RS SPL meter, and "typical"

correction factors... so you have to take 0ms FR loosely.

Those were taken using a desktop in an adjoining room with long

cables. I had numerous problems getting accurate measurements on

the laptop because of poor control drivers. It was/is USB

data flow problems due to shared resources...

Anyways, the whole point I'm trying to get to is

that treating the 40Hz problem will more than likely fix the 80Hz

problem and all subsequent harmonics...so in a way, we must start with

the lower frequencies.

That's what I was figuring too. Given I'm moving most of the

equipment to a dedicated room, I'll retest after the dust settles.

Also, what speakers were being used in the test? It

would be most valuable to take all the speakers in the system outdoors

and run the same sweeps to get an idea of what the speaker is doing...

I believe it was Cornwalls and a DIY sub in the corner. I currently rearranged the room with Klipschorns.

this is one fricken long post!

You must have a lot of time and few women between those labs!! []

ROb