John Sayers' Recording Studio Design Forum Archive

I am getting ready to build my gobos Friday and am in the "gathering materials" stage. I am going to the fabric store to pick out the covering for the insulation when the question ran through my head.

I know from reading that people shun use of carpet damn near everywhere in studios. The reason for this I think is because hearing the word "Carpet" is probably associated with some pad then thats it. But in theory, what would be the drawbacks of using carpet as a facing over the insulation ILO just fabric for deadening? It seems that it would work just as fine, if not better in the aspect of not messing up the insulation behind it.

For me I am leaving an airgap behind the insulation which means the insulation would be pretty weak if one of my kids were to say, push on the front cloth. Not that carpet would be the saviour but maybe just a little stronger.

Thoughts?

Ron

Because carpet is an Uneven absorber. You want the cloth to allow the sound pass through and let the insul do the absorbing as it is a more even absorption.

Bryan Giles

So does that mean that carpet will reflect? My thoughts were that it would absorb what it does and the rest would pass through into the insul. Seems to me that if it does unevenly absorb, it would be irrelevant. <assuming it DOES'NT reflect>

I'm not trying to argue, only to understand.

Ron

Hey no offense taken. Arguments are good for finding solutions. In programming you code an argument to find a solution

Anyway, the carpet is mainly a high end absorber. the goal is to get even absorption of all frequencies with the materials you use to absorb.

Carpet is just a poor choice. I am not sure of the math, but using carpet as your cover will unevenly increase your Hi frequency absoprtion. You want it to be smooth and even absorption. As close to it as you can get. Hence our recomendations for 703 and mineral wool. More even absorption from these materials. Traps as much bottm as they do top end dependnign on the thickness.

Ever use auralex on the walls of a vocal booth and find that your top end is gone but the bass is still boomy? Well welcome to carpet. Same effects.

Stick with cloth. You'll be happier in the long run.

Bryan Giles

I am an ex-Auralex user. The John L Sayers forum became my 12 step program to better acoustics. LOL

I'm not so sure carpet would be a bad idea for gobo covers - I hadn't thought about this before, but hear me out - it might be an interesting experiment.

First, all the specs you see for absorption on carpet seem to be based on a solid backing, such as concrete or at least a solid floor. I've yet to see E-400 mounting listed for absorption figures on carpet (this is where the sample is mounted 400 mm away from a solid backing) - all the specs I see for similar types of carpet show increasing absorption clear down to 250 or even 125 hZ as the pile gets thicker. This tells me that maybe the lack of low absorption is due to the lack of depth of the material, and that if we instead backed the carpet with a more uniform ABSORBER instead of backing it with a uniform REFLECTOR, that things would change drastically.

Ron, if you're up to an experiment I'd say give it a try. My only reservation would be to suggest that you do it in such a way that if it doesn't work, you can remove the carpet without destroying the rest of the project.

The only way I know of to actually COMPARE results of this would be to build two IDENTICAL gobo's, one with a carpet cover and one with other cloth, and actually MEASURE the results in a controlled experiment.

The simpler way is to remember a saying that usually works better than anything else - "If it SOUNDS good, it IS good" -

So, if you're up for a small gamble, go for it Ron - you never know til you hear it for yourself, and it's not a $40,000 studio you're risking, it's a $50 gobo that can be re-done if it doesn't work... Steve

Actually Steve, it shouldn't be an issue at all. The way I was planning on building it,<see below> was to add the cloth cover screwed into the front. So it won't be a big deal at all the try the carpet first. Worst case senario, I unscrew the carpet, and put up the cloth. AND... since I was doing two sides I can do one with the cloth, and the other carpet.

The problem will be I can't measure the result. All I can do is listen, since I have no sort of measuring equipment. Not to mention I have damn near virgin ears to this stuff. So I'm not sure on how to test it.

Ron

<I'm starting the woodwork tomorrow>

Cool looking design Ron - as far as testing, do you use a computer for recording? what software do you have? It's possible that you have more available to you than you may realize... Steve

I do use a computer. I use Cubase SX. I also have an Audiophile 24/96, a few condensor mics, few more dynamics, RNP/RNC, mixer and more. I suppose if you helped me set up a controled type of enviroment, I could whip out two wavs < one of each> for someone else <you?> to test.

Let me know your thoughts.

Ron

Ron, don't have Cubase or Nuendo, I use Samplitude and Sound Forge for audio, Cake for MIDI stuff.

If either of your proggies will generate either white or pink noise, that would be the simplest test. You could set up one of your speakers, a mic (preferably the flattest response, most directional one you have) and the gobo - it would take 3 different tests, two of which were identical except for which cover material is used, and the third as a control.

All three tests should have the mic and speaker at the same height, which should be NOT at any height that divides evenly into the total ceiling height by any number up to 6 or 7 (measure the ceiling height in inches, divide that # by 2, 3, 4, etc, write those values down and STAY AWAY from them for your test height)

Test one should be just the mic and speaker, using the point on the speaker baffle that is equidistant from the center of the woofer and the center of the tweeter as the reference height - the mic should be at this same height, and both speaker and mic should not change height for all tests. Point the mic directly at the speaker, head on at a distance of 3 feet, with no other objects closer to either than at least 9 feet. Record at either 16 bit 44.1, or 16 bit 48 kHz for all tests. Record 15-20 seconds of your noise source for each test. Make sure the level is constant between tests - -3 to -5 dB will ensure no clipping but with enough signal level for analysis. The main thing is that all files are recorded at the same 16/44 or 16/48 setting, and at the same record level.

Test two and three should be identical to each other, except for which covering is on the gobo. Don't change height of either the speaker or the mic for ANY of the three tests.

Aren't experiments fun?

Seriously, if this sounds like a lot of work it IS - if you're pressed for time don't bother. If you're curious and can spare the time, it will be an interesting project that may enlighten all of us.

If your software doesn't have noise generating capabilities, you can download the virtual Minirator free here (thanks, Ethan)

http://www.realtraps.com/nti_minirator.exe

If you decide to go ahead with this, let me know and we can arrange for file transfers later... Steve

Well, it sounded like very interesting up until the "with no other objects closer to either than at least 9 feet". I don't have anywhere I could do this, not until the new studio is done. Everything else I think I can handle.

A stupid question though. You said set the speaker and mic three feet apart in test one. Then test two and three were about the gobo. Where do I put it?
It seems that for the testing purposes I would want to leave off the plywood backing and let the line of sight be speaker>cloth>insulation>mic and just let the sound pass through. Is this correct?

Sorry that I don't know anything about this, I told you man I want to do it but you have to assume I'm in first grade with the directions.

Ron

Can you say,"Sorry, the dumbass forgot to post the drawing"? - Well, maybe it'll make more sense if I remember this time -

And what you want is for each test to use the gobo as a "reflector", so you can record what gets reflected back to the mic.

The 9 feet bit is just to keep other objects in the room from having an effect on the sound path - if you can't get that much, just keep the test objects as far away from other walls (and free-standing objects) as you can.

Now, help me chant; Post the drawing, dumbass, Post the drawing, dumbass,....

All right, I got it now. Thanks for the pic, it helped.

I'll have to go and pick up some carpet to use, then I'll build those bastards hopefully within the week.

Sounds like a fun.


Ron

DOH!

So uh.... When you buy 1x6's of pine your really getting 3/4"x5 1/2" boards?!?!! When you buy 4" mineral its actually almost 5"!??!

I guess these bits of info are common knowledge for ppl w/ experience in woodworking and insulating, but I got a nice eyeroll from the guy at Home Depot when I complained. Unfortunately I made my plans based on the signs for the available materials while walking through Home Depot. So now it won't work.

I have a background in software development and finance, I just don't know this stuff! I guess I'm going to have to re-think this little project and lose the air gap. <since I don't have enough depth> I'm sure it will be fine, I was just planning ahead for other uses one day.

Just thought I would share. I guess its good to learn this now before I start my studio huh!

Ron

Hey, kinda fun (in a twisted sort of way) getting into new worlds, huh?

Sorry, I didn't realize you were that new to building - you're right, it's wierd. The older you are, the wierder it gets - a "2x4", at least in this country, actually started out being 2" x 4" - you used to be able to buy "rough" 2x4's, which actually WERE the size they claimed - then, the mills figured out that they could "smooth them out for you", and by being careful with saw kerf widths, etc, could get a few extra "2x4's" out of a log, by surfacing all 4 sides to 1-5/8" x 3-5/8", and just pretend that the board was 2" x 4" before they planed the surfaces. (It really didn't take that much difference to smooth out the board, but...)

Over the years, it's progressed to where now a 2x4 is really 1.5" x 3.5", and other framing lumber is similar. It's not even THAT simple, because as you go up in width they "steal" even MORE from you, til 2x8's are only 7-1/4" wide, etc -

Just to complicate things more, there's plywood and other sheet goods - these are made in even increments of feet, like 4 x 8 feet, 4 x 12 feet - they actually ARE the size they say. But, you used to be able to buy 3/4" plywood and it really WAS 3/4" - now, they sell you 11/32" stuff when you ask for 3/4", charge you more, etc -

Now, you get into hardwoods and furniture stuff - all rules change again... for one thing, 4/4 thickness is really 1", and you can buy 5/4 stock, which is actually 1-1/4", etc...

Bottom line - you're right, you need a tape measure and a notebook to keep track of all the REAL sizes of materials these days, especially if it's critical.

BTW, nails are the same way any more - used to be, you could buy 16 penny nails and they were 3-1/2" long. Now, they're tending to sell what they call "16 short", which are really 14 penny by old measure. Where will it stop? Probably when houses start falling down because the materials arent strong enough or thick enough -

Thanks for the info..

I'll be sure to do just that when hunting for materials next time: Carry a tape measure and notebook!!

Ron