Limp mass membrane material

Posted: Sun Jul 06, 2008 12:14 pm

Hi all,

I'll try to keep it short so you can skip this intro if you want to get to the question. I've always had trouble with my mixes, after putting a 'corrective' eq on the master bus recently I realized it's not my ears or ability. I used some commercial tracks and made them sound 'good' with an eq. Mixed as I usually do (with the eq on) and turned it off at mixdown and it was pretty damn close to what I wanted/expected.
I've really tried reading EVEYTHING I can find on acoustics, I do alot of forum surfing and gone thru EWhiner's site. I've done alot of treatment on my room, installed lots of trapping (I physically can't fit anymore in) and I'm still nowhere near. So I'm looking to modify/improve what I already have. My current corner traps are broadband devices, absorbing all highs mids and lows. Further research has led me to think about facing my corner traps with a "limp mass membrane" which will give back some hi's and help with the lows.

THIS IS WHERE I'VE HIT A DEAD END, people are very secretive about this 'magic' membrane

Now the way I understand it is, the thicker and denser the facing (bonded) material the lower the frequency of the trap. One line of thought has got me thinking I should sparymount some card to the insulation, reflecting highs and letting thru alot of mid and all lows.
The other way I'm going is to look for some heavy 1.5 dense rubber (like a doormat) which would make my corner traps low low traps.

Any thoughts or comments or advice gratefully recieved

Looking forward to your responses

S

Posted: Sun Jul 06, 2008 12:49 pm

Okay.
I know neurosis when I see it.

Why do your monitors have LEDs on them?

Why can't you size that image so I don't have to side scroll to read your post?

Why do you have four monitors?

You read like the most neurotic audiophile ever yet you have a cordless mouse and keyboard, from two manufactures. Do you have any idea what kind of noise they generate?

I understand you want to compose, mix, master and order the world from your battle station... I just noticed the cordless phone...

From your words and photo I can surmise you strive for the very best.

Can you post examples of your mixes?

Posted: Sun Jul 06, 2008 1:03 pm

Ouch! Nah, I'm not that bad really, just at the end if my tether acoustics wise. After 5 years of thinking "I'm obviously not 'getting it" I realized how messed up my acoustic enviroment was, so I'm doing all I can to get it to a workable solution.
It sounds bad, real bad.
Keyboard and mouse are silent FWIW otherwise I wouldn't use them
My monitors have leds on them because that's how they're made
I have four montiors because it's useful to have a second frame of reference
I tried ordering the world but it won't listen! Very Happy

YOU sound like a very grumpy induvidual indeed, hope someone comes along who can offer some useful advice.

Btw here's a 'beach' house remix I've just completed
http://www.yousendit.com/download/TTdIZXR5Z2dlcExIRGc9PQ
I dont' only do dance btw it's just the last thing I've finished

Thanks for trying to tear my post apart

Posted: Sun Jul 06, 2008 9:24 pm

scoobz,

Don't mind greener, his wife musta put too much starch in his shorts or sumpin'.... Lighten up a bit there Greener... maybe try decaf?

As for your issue with mix translation... What I suspect is that you're running into a couple of issues due to your mix position.

Your almost flat up against that wall. Maybe try putting your ears at the 38% point from that front wall and pulling the rest of the gear (esp speakers) out from the wall.

I don't recall who it was, probably Eric Desart, who had actually calculated a minimum distance at which to place your speakers from the wall. Unfortunately, I don't recall that measurement, but seems like it was x inches for each inch in diameter of the largest driver in the speaker.

Maybe someone else still has that reference and will post it before I can dig and find it...

In the meantime, you might want to snag a waterfall/eq curve of your room. That will most likely tell you what problem frequencies you have to contend with.

Posted: Sun Jul 06, 2008 11:46 pm

Thanks MM

I think it must be a decpetive photo, it's a 15 ft room and I'm 6 feet from the back wall, that about 38% isn't it? Well roughly.

I'm still reading up, I think I'm getting it now. I need to use thin plastic sheeting, spray bonded to the insulation, this ties the vibration in the front panel to insulation behind it, thus killing the vibration. This also has the by product of stopping the rockwool acting in the traditional way of converting the air passing through it's fibres into heat, so mid/high frequencies are reflected.

Am I anywhere close?

Also, is it worth hanging barrier mat behind my existing traps? I was thinking about getting some L brackets and suspending them parallel to the back of the trap

And did some tests tonight...

Any (well nearly any, greener) thoughts welcome Wink

Posted: Sun Jul 06, 2008 11:52 pm

Well that shut me up.

Sexy track you posted.

I still think you're neurotic, but now I can see it's working for you.

Just to clarify, I was grumpy because of the girlfriend not wife (I rent) and drunk side-scrolling seems to make me go all hulk. My apologies.

Posted: Mon Jul 07, 2008 4:57 am

All things being relative, to me, I'd be looking to kill that hole at 80-100 and trap out some more of that bump at 30-40.

Granted we're picking some nits, but while you're at it, what does the rest of the curve look like? Are you showing any significant peaks or valleys at upper frequencies? You mention using an EQ, (a major phase shift inducing no-no) in your process, but you don't say what frequencies you are boosting/cutting while you are mixing. (Glad to see you take it out of the chain on actual mixdown.)

I'm not saying that the membrane won't help, or isn't the proper solution, but I can't help but think that there is a much more obvious solution that is less involved.

I may be drawing the wrong initial conclusion, but my guestimation is still centered around your speaker placement and the fact that you may not yet have enough bass trapping in a small(ish) room... You still have corner traps you could put in the wall/ceiling corners, plus the rest of the ceiling... e.g. If your low frequency curve is significantly higher than your high frequency curve, you probably still need more bass trapping.

As has been said here and many other forums, by some of the better minds in acoustics... You cannot have enough bass trapping in a small room.

Max

Posted: Mon Jul 07, 2008 11:07 am

Hi Max,

I don't know how to go about sorting out the problems (30-40 and the 100hz hole) there's a square inch on the back wall I haven't done! Wink

I'll have to look into the top ceiling wall corners like you said, for now I'll just try to optimize what I have.

Funnily enough the 'corrective eq' consists of a 6db wide Q bump @ 100hz with a similar topend (3-4db HS at 6k with a bump 8k) So my ears were hearing the right missing freqs. I got some thin plastic for the membrane, gonna do that tonight and remeasure.

And thanks for the compliment greener

Will keep you posted

S

Posted: Mon Jul 07, 2008 11:08 am

BTW the test i did was using a digital spl meter and swept sine @1 hz intervals. I've just ordered a measurement mic and etf analysis software.

Posted: Mon Jul 07, 2008 11:15 am

What mic and software are you getting?

I am still saving for a real time spectrum analyser and I'm keen on other options.

Posted: Mon Jul 07, 2008 1:36 pm

scoobz wrote:

BTW the test i did was using a digital spl meter and swept sine @1 hz intervals. I've just ordered a measurement mic and etf analysis software.

Scoob,

that's good - because the swept sine is not really representative of sound in a room.

It would be very strange for any music to be represented by a single frequency (with it's corresponding wave) - rather its the sum total of the sound coming out of the speaker (which is a combination of all of the various signals being simultaneously transmitted) that you're actually treating for in the long run.

That is what you want to test for and the ETF software (actually RPlusD is what it's called now) is an excellent way to test your room.

Rod

Posted: Tue Jul 08, 2008 6:41 am

The real world can't be described by numbers, but I did a little math, maybe it will help.

The dip at about 95Hz is 71" for half a period. If you are sitting 71" from your speakers, and from the speaker to the ceiling to you is twice that (142") then there will be a phase cancellation. What is that cloud made of? Maybe backing it with something denser to catch the low frequency would help.

The bump at 37Hz is 361" (30 feet, 1") for a full period. Sounds like it could be a front to back standing wave reflection given the size of your room.

I notice that your surfaces all seem to be pointing toward you. Is there a reason for that? I'm just learning about room treatment, so I would not be surprised if there is a very good reason for that. I would think that would reflect all the sound at you creating echoes that you don't want. Maybe some sound diffusion would help?

Posted: Tue Jul 08, 2008 7:54 am

Hi,
Thanks Rod, I agree, I'm at the stage now where I need to stop trying and hoping for the best and now need to get some solid info, I'm getting a cheap behringer test mic (first thing I've bought from them in about 10 years! lol) I checked the repsonse curve of the mic and it looks fine, that's arriving tomorrow.
Gecko, thanks for getting the calculator out! Wink

I'll try to get some accurate room dimensions when I go back in there in a bit. I think I've missed a trick when it comes to the rear wall, there's a door right in the middle of it and it's got trapping in the corners but not alot else, I've got a deep bookshelf for diffusion and some 500mm2 diffusers, if I took the bookshelf out I'd have room for another 2 square metres of absorption, I'm thinking 6" deep 4" from the wall, floor to ceiling.
Anyway, a little update. I've taken down all treatment off the left hand side (so far). I've taken the front corner trap and spray mounted a very thin sheet of plastic to the face and replaced fabric. I'm also experimenting hanging barrier mat 30mm behind the back of the trap (between the two pieces of rockwool, it can vibrate freely).
There was a similar trap running along the floor wall corner, faced that, even though it doesn't really see many reflections being on the floor.
Back corner, same as front, but no barrier mat.
Previously I had 3 big bin(trash) bags full of off cuts stacked in the corners (making the traps stick out a bit), I've now made much smaller bags (200mm x200mmx800mm) and lined them along the floor wall corner (all the way down the left side) This leaves one full upright panel behind each corner trap.
So I've taken stuffed corners and redistributed it along the back wall and long wall, does this (and the other ideas) sound ok?
Even though I've only done one side, I had a quick listen last night and it sound radically different, LOADS more top end. I'm going to do the other half of the room now and take some measurements tomorrow.
Thanks for all the help so far

S

Posted: Tue Jul 08, 2008 10:46 am

Interested in how this turns out...

EDIT: Forgot to say that the studio looks great!

Posted: Wed Jul 09, 2008 8:03 am

Thanks scurrier. Right little update for you all, completed the right side too yesterday, although it was late when I was done I had another quick listen. It's changed alot, last night I couldn't decide if it was for the better! Wink

All I know for sure is that commercial tracks sounded very different to each other, I could tell those which had been engineered in a top studio. The low LOW end seemed alot fuller, walking around the room the bass was alot more even, there was still a collection of bass in the top left and right front (speaker end) corners, felt like I was walking into a big ball of pressure! Everywhere else tho was, my instincts tell me, loads better.
Right, I've got this behringer measurement mic today, I'm looking into which software to use ETF (RplusD) or EAW or maybe there's another option I'm unaware of.
I'd like some feedback please if you get time

S

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