CR Rear Wall Question

knightfly · Post by **knightfly** » Tue Nov 11, 2003 4:05 pm

Michael, I'm thinking of two different possibilities for that corner - it would kind of depend on exactly where your piano is going to "live" for most of your recordings, as there may be some modal considerations for micing to get the most even frequency response.

One possibility (and probably the safest, considering the effective room shape variations, is simply that corners are where ALL modes build up, so the safest thing should be just making that entire corner into a broadband absorber by enclosing it with 3-4" 703 or mineral wool.

The other might be more interesting, but easier to screw up on - how well this would work would depend mainly on the actual positioning of the piano within the room, and could be really sweet or really crappy with very little movement.

It would involve tuning a panel trap (not deep enough for either a slat resonator or absorption type bass trap) for one of the length modes in order to lessen the depth of its node, so that the piano could sit in a relatively even sound field. With your vaulted ceiling, mic height will likely be at optimum at different heights depending on the distance the piano is away from the wall, due to ceiling modes. This could be next to impossible to predict though, and I'm not enough of an acoustician OR recording engineer to even try to BS my way through it. Still, it could be a fun experiment if you were more into that than finishing the studio...

I've marked up an approximate modal chart for your room, showing some possible positions for piano and mics relative to room boundaries - the LAST place you want a mic would be at the lowest points on the mode curves, the GREEN lines are possibilities. Note that I've used 12/6" for ceiling height, which should be about right for where (I think) you're putting the piano. On the Height chart, the green lines I've drawn are possible heights for lower and upper mics if you mic the piano that way. An XY or Blumlein pair might not like the horizontal position I drew on the length chart, I've only used XY pairs a bit and it was before I even KNEW there were wrong places in rooms for mics.

Mainly just ramblings, if push came to shove I'd probably just put 4" of absorbent in front of that corner and see what happened. Same with the OTHER corner, between the other column and the Mech room... Steve

Michael Jones · Post by **Michael Jones** » Wed Nov 12, 2003 7:14 am

You know, it never ceases to amaze me how that when the level of detail, and the factoring of conditional variables increases, my understanding of acoustics in general decreases.

Its a very interesting study.
I wish I knew more, but I really just wanna make and record music.
No art without science though.

I think I understand, albiet it on a limited basis, the graphs you posted.
The ideal sweet spot for that room would be at a point where all modes intersect?
Of course, the graphs are 2 dimensional, and the room is 3 dimensional, I'm having a little problem visualizing the intersection of the modes in 3 dimensions, particularly for the height, but in general, I think I get it... and I'm an engineer.

Thanks again, Steve. You never fail to educate.

Michael Jones · Post by **Michael Jones** » Wed Nov 12, 2003 7:22 pm

Interesting design on the rear wall treatments, John. Something like that wont change any of the framing I've already done.
I'm curious on the facing of the area that houses the hangers though.
Are those just cloth covered wall studs?
No plywood on the backside?
No 703?
No "port to bass"?

How do you "client proof" something like that?
Suppose someone casually leans up against it?
They'll push right through that cloth. These things are about 4' long and at least 9' high.

Michael Jones · Post by **Michael Jones** » Wed Nov 12, 2003 7:35 pm

Here's a pic of the beginings of it, all jigged up.

knightfly · Post by **knightfly** » Wed Nov 12, 2003 11:16 pm

Michael, join the club, it's not an easy concept to visualize. In the end, your ears are the authority. All this may do (besides confuse the issue) is suggest a place to START with instrument AND mic placement. I'm close to being late for the "DDJ", but I'll get back to you on this more tonight, and maybe some comments on the back wall construction if John doesn't get back to you first... Steve

Michael Jones · Post by **Michael Jones** » Thu Nov 13, 2003 1:06 am

knightfly wrote:"... In the end, your ears are the authority. All this may do (besides confuse the issue) is suggest a place to START with instrument AND mic placement. ... Steve

Yes.
Based on the modal response of the TREATED room.
How cool is that!

Michael Jones · Post by **Michael Jones** » Thu Nov 13, 2003 10:42 pm

Any thoughts on how to client proof a cloth covered wall?

At the very minimum, I'm going to put a 12" "kick panel" at the bottom.

Post by **John Sayers** » Fri Nov 14, 2003 6:34 am

Michael - you make a 2" x 1' frame with cross pieces at 2' intervals - no one will go through it - believe me

:) Back wall of Left Bank is exactly that kind of contruction.

cheers
john

Michael Jones · Post by **Michael Jones** » Fri Nov 14, 2003 7:15 am

2"X1 foot?

OR 2"X1"?

frederic · Post by **frederic** » Fri Nov 14, 2003 9:55 am

Michael Jones wrote:Any thoughts on how to client proof a cloth covered wall?

At the very minimum, I'm going to put a 12" "kick panel" at the bottom.

John's suggestion is good, but I would staple large-hole chicken wire of the front of it just below the cloth, because then an elbow or a mic stand won't puncture the cloth either. Well, staples is probably a bad idea but the concept is conveyed. I would think that 1" hole chicken wire of a thin gauge steel would do the trick and not hamper sound at all.

What do you think John and Steve? I'm all for client-proofing. Its usually worse than baby or cat proofing!

knightfly · Post by **knightfly** » Fri Nov 14, 2003 11:21 am

Actually, the BBC uses even "herkier" stuff than that with no apparent ill effect. As long as you don't make the hole pattern small enough for it to start acting like a perforated Helmholz, you're good. I might even consider expanded steel diamond mesh screwed to studs with the cloth over it for looks... Steve

Post by **John Sayers** » Fri Nov 14, 2003 9:43 pm

I don't hang around with people who fall against walls

seriously - I've never witnessed anyone going through a cloth framed wall.

cheers
john

Michael Jones · Post by **Michael Jones** » Sat Nov 15, 2003 12:41 am

My concern was just if someone were to casually lean up against it, not realizing what it is. You know??
The framing, which I have cut to pin-point accuracy and screwed and glued, is really stout, but ultimately there's no hard surface on the face of it At any rate, I'm really pleased with the way thats comming along.

BTW, so.... there's no 703 in the wall, just behind the cloth?

frederic · Post by **frederic** » Sun Nov 16, 2003 1:48 am

Don't forget to apply 440V to the chicken wire, so when the darwin folks lean on it, they are eliminated from the gene pool.

For a while I was considering reworking my flip-floor vocal booth so that it can flip up, and down, on a pushbutton to eliminate irritating sopranos.

LOL

knightfly · Post by **knightfly** » Tue Nov 18, 2003 9:11 am

"BTW, so.... there's no 703 in the wall, just behind the cloth?" -

I was gonna wait for John to catch this but it looks like it fell through the cracks -

I would think that if you want broadband absorption there (more bass trapping) you'd need to put 703 between your frames up front (behind the cloth) - otherwise, you would be wasting quite a bit of space for just a midband absorber... Steve