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Author Topic: severe rolloff at 70hz  (Read 1995 times)

itsapleasure

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severe rolloff at 70hz
« on: September 12, 2008, 11:49:50 am »

Hey guys,

I'm curious if you guys have any opinions on where my super-obvious problem areas are in this room.

I just built the closet/rack on the right a couple of weeks ago, so that corner obviously needs trapping.  Unfortunately w/ all of the soffets in this room, I'm going to need bass traps a-plenty.  Just wondering where to begin (again).   The trap on the left is Ethan's design from his site using (if I remember correctly) 1" roxul inside a 1x3 frame w/ something like a 1/4" ply on the outside.   index.php/fa/9926/0/

I ran Ethan's test CD and it seemed that moving the monitors back closer to the wall yeilded a better freq response overall.  I'm open to suggestions on that as well.  
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itsapleasure

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Re: severe rolloff at 70hz
« Reply #1 on: September 12, 2008, 11:51:47 am »

here's a side angle.  this could be the worst part....the rooms a bit wider than it is long.  

index.php/fa/9931/0/
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itsapleasure

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Re: severe rolloff at 70hz
« Reply #2 on: September 12, 2008, 12:05:01 pm »

and the rear...

The plan as of now is to move the red panels above the window and build a diffuser for the rear wall.

index.php/fa/9932/0/
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Steve Hudson

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Re: severe rolloff at 70hz
« Reply #3 on: September 12, 2008, 01:09:07 pm »

Your room appears to be about the same volume as mine, and we have 22 4" panels (2" of 705 plus 2" of 703 each, offset from the walls by 4") plus two large traps (6'x4' each with 6" of 703 plus 5" of air space) in the back of the room. It took all that to deal with all the peaks and nulls below 120 Hz.
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itsapleasure

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Re: severe rolloff at 70hz
« Reply #4 on: September 12, 2008, 07:04:39 pm »

Yeah...i feel like that's what it's gonna take.  

do you have any pics Steve?  

Interestingly enough, when I moved my my monitors closer to the front wall, the weird hump at 140 went away and everything is sorta smooth down to about 70-80.  Do you think going 4-6" of insulation in the corners is going to deal w/ the lower frequencies better?  

any thoughts on Bill's bass trap/diffusers?

Bill Mueller wrote on Tue, 27 September 2005 18:51

Rich,

Very simple, very effective and very cheap diffusors are also some of the oldest designs, dating back fifty years or more. I have seen these for years in top recording studios and film houses. They do not look like what you would consider a diffusor however, but when used properly, they work very well at both diffusion and low frequency absorption. A good book to read is F. Alton Everest's book on Building a Recording Studio. Good stuff in there.

Ok, the structures I am talking about are called polycylinders. I have made these things for thirty years. The simplest way to make them is to mount verticle strips of 1"X3"X8' oak, 44" apart, to the wall with heavy duty wall anchors. I like to make a length wise cut in the strips creating a V between the strip and the wall to capture the panel. Then take a 1/8" X4'X8' Oak Luan panel (I like to finish them with Polyurethene) and wedge it between the verticle strips. It will bow out a few inches from the wall and create a nice poly surface. If you make the distance between the strips shorter, the bow will be deeper and it will be a bit harder to get them in, but I find it is better to slightly vary each one so they don't all resonate at the same frequency.

Because they resonate, they also act as a bass trap. You can calculate the exact F0 if you buy the book but I find them to be very effective bass traps no matter what spacing is between the strips. I further recommend that you staple raw fiberglass to the wall in between the strips. It will add absorption and effectiveness to the unit and of course will be invisible after the panels are up.

I usually mount them about 24" up the wall from the floor. This uses up less floor space, does not cover the AC outlets and gives you a convenient place to store your guitar amps. If you ceiling is not 10' then cut them down to 6' height.

If you have a large recording room, stagger them on either side of the parallel walls. You probably don't need them on both walls and they are very effective at breaking up standing waves. In a control room I put one dead center on the back wall with one or two on either side, depending of course on the width of the room. I also like to place them on the rear side walls to create a "live" end of the room. They are great for adding a live component to a Reflection Free Zone design.

They are very easy to take down when you move, and don't permanently damage the wall. They also look stunning and can give a very professional flavor to a room.

For the rest of the room, (front wall and side walls back a foot or two past the listening position) I recommend absorptive panels like Ethans RealTraps.

Hope this is helpful.

Best Regards,

Bill


thinking about that for my back wall...
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rankus

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Re: severe rolloff at 70hz
« Reply #5 on: September 13, 2008, 01:16:16 pm »



Found this thread with some great pics of a fellows experience with poly's:

http://www.canuckaudiomart.com/forum/viewtopic.php?t=8520

Cheers


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itsapleasure

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Re: severe rolloff at 70hz
« Reply #6 on: September 13, 2008, 02:37:29 pm »

cool,

thanks!
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Steve Hudson

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Re: severe rolloff at 70hz
« Reply #7 on: September 13, 2008, 03:56:38 pm »

I'll try to get some photos done and post them next week.

Generally, a DIY bass trap using 703 (or 705 if you want a stiffer material for a "bagged" versus framed trap) should be at least 4" thick to be effective at the kind of low frequencies you're worried about. 6" or more would be even more effective. Check out this link:

http://basstraps.net/index.php?topic=29.0

We sandwiched 705 on top of 703 to give the "bagged" traps stiffness; from what I've read, denser material doesn't have any better bass trapping efficiency than the same volume of less dense material. We also have four of Ethan Winer's Real Traps in the front of the room (which the studio owner had bought before I got involved) and a 4'x4'x4" cloud above the mix position.
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"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs.  There's also a negative side."

- Hunter S. Thompson should have said this, but didn't

http://www.myspace.com/steventoddhudson

itsapleasure

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Re: severe rolloff at 70hz
« Reply #8 on: September 13, 2008, 11:13:53 pm »

interesting.  thanks for the help.  

Not sure why I used the thin stuff...it sorta seemed counter-intuitive at the time but for some reason that's what Ethan's recipe called for.  

Easiest thing might be to start off by replacing the corner traps w/ 4-6" ones and do some polys on the back wall.  

I noticed a major change as well when I ditched my couch in the back of the room.  
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Ethan Winer

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Re: severe rolloff at 70hz
« Reply #9 on: September 15, 2008, 12:30:15 pm »

itsapleasure wrote on Sat, 13 September 2008 23:13

Easiest thing might be to start off by replacing the corner traps w/ 4-6" ones and do some polys on the back wall.


Polys are okay from a distance, but I'm not a fan of them in small rooms. You may find my recent video All About Diffusion useful. It's partway down the list on the RealTraps Videos page.

--Ethan

itsapleasure

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Re: severe rolloff at 70hz
« Reply #10 on: September 15, 2008, 07:15:55 pm »

Good stuff Dr. W!

I definitely think something like the QRD design would do wonders in my room.  I'm already feeling the effects of a lot of absorbtion and I don't want to deaden the space too much.  

That said, I don't want to compromise the bass response in the room.  

The appealing thing about the poly design is the ability to simultaneously diffuse and deal w/ bass problems.

Should I beef up the corner traps first than assess the situation?
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Ethan Winer

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Re: severe rolloff at 70hz
« Reply #11 on: September 16, 2008, 02:22:27 pm »

itsapleasure wrote on Mon, 15 September 2008 19:15

The appealing thing about the poly design is the ability to simultaneously diffuse and deal w/ bass problems.


I'm not aware of polys doing anything useful at bass frequencies unless they're specially designed to absorb below the range they reflect.

Quote:

Should I beef up the corner traps first than assess the situation?


Yes, I think so.

--Ethan
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