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[tom eaton]

Does anyone have any good ideas?

Fran... I'd actually love to chat with you on the phone to get into specifics, but don't know if you have a consult fee that would cover your time for something like that.  MORE than happy to pay for the expertise.

Situation:

Control room in commercial faciltiy.  20' L, 15' W, 10' tall. Ceiling slopes slightly up as it goes back, roughly 9'6" at front and 10'6" at rear.  Double walls/ceiling all the way around, window to live room 6' wide and 3' high at center of front wall.  3'x3' window to iso room is on left wall roughly at the end of the console.

Room is well treated for first reflections and has quite a bit of bass trapping.



Here are the issues:

1. BIG dip at 61Hz at mix position, which is also strong at 122.  Rolling my chair backwards 18" resolves the dip.  Moving the console back into the room would be very, very difficult as there is a center table/equipment rack between the mix position and the client sofa.

2. Window to iso room is flush, and gives me a perfect relection of the right monitor speaker.  I have left the wall opposite the window free of treatment for symmetry.  


Solutions that occur to me:

Tuned trap for the dip. I have no idea how, where, how big...etc.  I have all the acoustics books, but no direct experience building any of the various tuned traps (perf, slat, membrane, etc.).

Putting an additional angled piece of glass in front of the iso room window to angle the reflection back into the room, and then doing a similar panel on the opposite wall.  

Like I said, I'm happy to pay Fran for a conversation, just thought I'd lay out the issue to see what folks have to say.

Thanks-

tom
(978) 465-5102

[Wes Lachot]

Tom,

While you're waiting for Fran's reply, I'll offer you this assessment: I think that the problem must be due to side wall reflections from the opposite side speakers. A 61 Hz wave is about 18 1/2 ft. long, so half a wave would be 9 1/4 ft--meaning that a signal delayed by taking a route to your ears which is 9 1/4 ft. longer than the direct signal will be exactly out of phase, causing the null. Judging from your diagram, that looks to be about the difference between the direct signals and the bounces off the opposite side walls.

It would benefit you greatly to do as you suggested, and put some angled glass in those spots.

Also, I don't know how you've treated the ceiling...

But it looks as though moving back 18 inches or so would just barely allow those side wall absorbers to kick in.

[tom eaton]

Thanks, Wes.  I'd not been to your site before... nice portfolio!

The side reflection thing had never occurred to me, honestly.  All I had in my head were modal issues!

Thanks much-

Tom

[jetbase]

Tom, in the two studios I work in we draw thick curtains over CR glass when mixing. Perhaps you could try something similar?

[tom eaton]

I actually get sounds while tracking... covering the windows wouldn't be a great option for mic choice and placement aasessment with other folks in the other rooms...

I can see where it would help for mixing, but I'd rather have a permanent fix, rather than gettig to the mix and having to undo what I did at tracking!

-tom

[franman]

Tom,

I think Wes in on track, but I also think you might have modal issues... Both 10 and 20ft dimensions will tend to cause issues at around 56 and 112 Hz.. close to your listed frequencies... Acoustic dimensions (for lf) may be slightly different than the physical dimensions as well...

This low down, I would suspect modal issues (and / or) speaker boundary interference (Wes' suggestion).. This depends on where your woofers are physically located in relation to the reflective side walls and the listening position..Try treating (temporarily) the side reflection points and see what effect it has... this will tell you whether you are headed in the right direction... Remember, you will need something thick (deep) to affect 60Hz area... pretty thick!! Pile of blankets thick!! Medium sized acoustic consultant thick!!! You get the idea.

It is getting a little specific.. you can feel free to email me as well..

[tom eaton]

Update...

Wes and I had a great chat the other day and after running the numbers he came up with a couple of very good, affordable ways to help the issues I'm dealing with.  

Thanks for the input everyone!

The main issue was the front to back mode of the room relative to my listening position, which was clarified once the sidewall reflections were dealt with.

I love this forum...

-tom

[tom eaton]

Further update:

Wes chose some very specific solutions to my room and did a redesign of the rear wall.

I drove down to RPG a week ago and wandered the factory before picking up my new treatments.  I thought I would finally be able to stand in a anechoic chamber, but apparently the one featured on their website is not on site.  In hindsight I should have just paid for shipping and not spent the two days driving.  Nice folks, just not a great way to get the scope of what they do and all the products they make.  The website is actually better than the factory if you're trying to learn about the products.

I've installed an RPG Modex plate to each back corner of the room, done a bunch of  bass trapping and added eight RPG Omniffusors to the rear control room wall.

So far so good, sounds much better than it ever has and I'm still working on completing the rest of the design as Wes intended.

I'm very happy so far... will update as things become more complete.

tom

[compasspnt]

Good.  Now you can properly use all your PAIA gear.

[tom eaton]

Are you accusing me of being a do-it-yourself-ist?

Well, I know how to build stuff... I just don't always know what to build.  I like building things, actually.  

Never did the PAIA thing, though.

Reminds me too much of Anderton.

There is a guy here on the forum who builds his own gear... Lucas someone?

t

[franman]

My first synth was a PAIA.. what an awesome learning experience.... Anyway.. tough crowd!!

[tom eaton]

Control room is sounding good.  If only I had some new monitors to try out.

I wonder if anyone here has heard these:

http://www.griffinaudiousa.com/

Some guy had them at AES and I thought they sounded pretty darn good.

Anyone?

t

[franman]

yeah, I know those... I like em too!! You might get a surprise in from the UPS man next week....

[tom eaton]

Another sand bag charged to my UPS account?

The UPS guy is onto you.

I have Morph the Cat on order so Wes can hear the bass response from home.

t

[Bill Mueller]

tom eaton wrote on Tue, 18 September 2007 07:49

Further update: I drove down to RPG a week ago and wandered the factory before picking up my new treatments...  The website is actually better than the factory if you're trying to learn about the products. tom

Tom,

If you want to learn, Pete's office is the place to hang out!

Best Regards,

Bill