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PostPosted: Sat Jan 28, 2012 10:11 pm 
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Hi Stuart,

Quote:
Panel traps have to be sealed, yes, but I don't understand how yours will work, since they seem to be angled across the corner, and therefore the cavity depth is not constant: So how is that going to work? What frequency did you tune them to? I'm not aware of any theoretical basis for how such a trap would work, or how you would go about tuning it, so I'm intrigued about how you did that! Maybe you could explain?


Well to be honest, I did not create them to be tuned to a specific frequency. The way that I understood Ethan's panel traps to work were more across a range of frequencies. Perhaps I misunderstood his design altogether?! :shock: He had several designs that he labeled "low frequency" ,"low mid", and "High Frequency" absorbers. He never specifically stated which frequencies they were "tuned" for. It was my understanding that they were effective over a range of frequencies not tuned to a specific frequency. Perhaps I am wrong?! Regardless, I can attest that they are quite effective at smoothing out the low frequency response in my room. I have measured my room's response and am quite pleased with the results.

Quote:
Hangers are great, but yours seem to be touching each other, so they won't be working too well either. You might want to try strapping thin insulation closer to the board, so that they don't touch each other. Maybe wrap them with wire, or some such. Unless the hangers are able to swing freely, with air gaps between them, then they'll just act like expensive absorbers, not like hangers. You also should put some absorption on the rear wall, behind the hangers. That's part of the system.


Once again this is why it is important to post while you are building. I hope people will learn from my mistakes. Even so, as I mentioned above the low frequency response in my room is really great.

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Are those N7 QRD's? Looks like they might be.


I don't know what N7 means?! Please explain. My diffusors are custom QRD's. They have a low frequency effective range of 800 cycles and a high frequency effective range of 6700 cycles.

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Also, you never did answer my question from back in November, about how you isolated the light cans after you cut the big holes in the ceiling drywall.


Yes, sorry about that Stuart. I overlooked you question. Those light cans are in the live room ceiling not my control room. I thought about using "putty pads" as are commonly mentioned around here on the forum but in the end I chose not to. They are not sealed other than some caulk around the rims where the can meets the drywall. Mistake? Perhaps?! But I have not had any isolation issues in the live room. Perhaps the distance from the live room to my control room makes a difference?!


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PostPosted: Sat Jan 28, 2012 10:42 pm 
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The next set of photos are of my front wall in my control room.
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Once again here are some custom panel traps that I made in the corners of the front wall.
Next are photos of the stands I made to hold my Air 25's. These are concrete blocks that I mortared together and filled with concrete. They are very heavy.
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The speakers are in custom boxes that I built out of 3/4" MDF. These MDF boxes sit on top of the concrete stands. I put a piece of 1/4" Neoprene on top of the concrete blocks before I fit the speaker boxes on top of the concrete stands.


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PostPosted: Sat Jan 28, 2012 10:49 pm 
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Next I began to frame out the front wall. I made sure to build a frame work around the speaker stands and boxes without actually touching them.
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I also put some more hanger bass traps around the speaker stands.


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PostPosted: Sat Jan 28, 2012 11:02 pm 
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I added 3 layers of drywall to the frame work around the speaker boxes. You can also see the vent holes at the top of each wall for my speakers. My speakers are active speakers.
Next I made the frame work to mount my Monitor screen to.
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This is a photo of measuring out the cloth that will be attached around the face of the TV frame
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PostPosted: Sat Jan 28, 2012 11:07 pm 
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These next photos are of the wood paneling I cut and stained to finish off the front wall.
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PostPosted: Sat Jan 28, 2012 11:15 pm 
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I also cut and stained wood slats for the side walls next to the speakers.
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PostPosted: Sat Jan 28, 2012 11:33 pm 
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Next I began work on my ceiling. This photo is of the light soffit I made directly above the ceiling against the back wall.
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Next I made three clouds. Each cloud has some more custom QRD diffusers mounted inside the clouds. The diffusors have an effective frequency range of 900 cycles to 4520 cycles
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PostPosted: Sat Jan 28, 2012 11:46 pm 
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I also custom built my desk.
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Finally here are some better photos of my finished Control Room.
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Fish eye lens just for fun
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PostPosted: Sun Jan 29, 2012 5:56 am 
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Quote:
Well to be honest, I did not create them to be tuned to a specific frequency.
Panel traps (a.k.a "membrane traps") are always tuned to a specific frequency. They are resonant devices consisting of a known mass mounted resiliently over a known fixed-depth, sealed air cavity, which usually has insulation in it. The surface density of the panel and the depth of the cavity are what determine the frequency. It's a simple mass-spring system: the spring is the air trapped in the cavity, and the mass is the panel itself. The system resonates at a specific frequency, and therefore removes energy from the room whenever that frequency is present. The insulation inside the cavity serves to damp the resonance, and absorb some of that energy. Without insulation, or with very little insulation, it has a very narrow Q, meaning it is tuned sharply to one frequency. The more insulation you put in, the broader the Q gets, meaning that it affects a small range of frequencies around the one it is tuned to, but less effectively. But in your case, the depth is not fixed: since the cavity is a triangular shape, there's no simple way of figuring what is going to happen in there, plus it seems like you didn't mount the wood panel resiliently, so it isn't very effective anyway.

Quote:
The way that I understood Ethan's panel traps to work were more across a range of frequencies.
As far as I know, Ethan doesn't sell panel traps (membrane traps). He sells bass trap
Quote:
panels
, yes, but they are not panel traps for bass frequencies. Those are rather different things! I may be wrong, but most of the products that Ethan makes are absorption based, not resonance based. That makes sense, since broadband absorption is what home studios need most! Like I said, I may be wrong but I don't think Ethan makes any tuned resonant devices.

Quote:
Perhaps I misunderstood his design altogether?!
It looks like you might have!

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He had several designs that he labeled "low frequency" ,"low mid", and "High Frequency" absorbers.
That's right! They are ABSORBERS, not tuned resonant devices. Not panel traps / membrane traps.

Quote:
He never specifically stated which frequencies they were "tuned" for. It was my understanding that they were effective over a range of frequencies not tuned to a specific frequency.
Yup! Because they are broadband absorbers, not tuned resonant devices! Most resonant devices are tuned to very sharply to specific frequencies, and are not broadband. You can't tune absorption to specific frequencies like that. You can make it to cover a range of frequencies, yes, which is what Ethan does. But he sells panels of absorption, some of which are bass trap, but they are not panel traps. Two different things.

Quote:
Regardless, I can attest that they are quite effective at smoothing out the low frequency response in my room. I have measured my room's response and am quite pleased with the results.
I'd say that's mostly due to the absorption you have on the rear wall: those "almost hangers" are pretty deep, so they should be doing a reasonable job. They probably act like full width superchunks, or something like that. Your panels are probably helping to keep the highs in the room, since they are reflective, but they might or might not be absorbing energy in the bass range.

I'd really, really suggest that you should download REW and do a full analysis of your room, to see how it is really doing: it might sound good subjectively, but you'll never know what it is actually doing, objectively, unless you test it! :) I'd live to see the response and waterfall plots for your room: They should be pretty good, but it would be nice to see them.

Quote:
I don't know what N7 means?! Please explain.
That's the modulus you choose when you did the calculations for the well depths. Seven is a pretty common choice, and gives good results.

Quote:
They have a low frequency effective range of 800 cycles and a high frequency effective range of 6700 cycles.
So the low frequency cut off is 800 Hz, they'll still be scattering down to an octave lower, about 400 Hz, meaning that the minimum distance between the diffusers and your head should be about 9 feet, recommended 12 feet or more. From your diagrams, it looks like you should be OK there for the ones on the rear wall, but not the ones on the ceiling. Your head seems to be only about 5 feet from those, whereas the minimum distance for that low cut-off should be 7' 6" (preferably 9' or more), so you are probably in the region where phasing, lobing and timing distortions are an issue. You might want to consider taking those down.

By the way, I love the way you did your speaker soffits! Very solid, very neat, good design, and I'm betting those are very effective. You should be getting a really accurate, tight sound stage with those. And they look great, too! Nice work there! And the lighting also looks pretty cool, all around.

- Stuart -

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PostPosted: Mon Jan 30, 2012 6:45 am 
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Well Stuart,

I made a mistake calling my corner bass traps, "Panel Traps." You are of course correct and I called them the wrong thing. Below is a picture of Ethans original design in which he calls his traps "Deep Bass Traps", he never calls them "panel traps." I screwed up and used the wrong term to describe my traps. I suppose I did so because his design uses a piece of 1/4" plywood glued air tight to the front of his trap. I loosely threw the term panel out because I think of that piece of plywood as a "panel". Mine is a modified design in that I straddled it across a corner of 2 walls instead of against the flat part of 1 wall. But it is constructed in the same method. Ethan states that the deep bass trap is effective at frequencies between about 80 Hz. and 160 Hz. I chose to straddle mine across the corner because I know that low frequencies build up in the corners of rooms. It seemed logical to place the bass trap there.
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Quote:
I'd really, really suggest that you should download REW and do a full analysis of your room, to see how it is really doing: it might sound good subjectively, but you'll never know what it is actually doing, objectively, unless you test it! I'd live to see the response and waterfall plots for your room: They should be pretty good, but it would be nice to see them.


I am a big fan of Room EQ Wizard. I used it to help me set up my room when I initially completed construction. For the sake of objectivity I took these measurements last night.

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I've been very pleased with the low end response in my room. What do you think?

Quote:
That's the modulus you choose when you did the calculations for the well depths. Seven is a pretty common choice, and gives good results.


The calculator I used allowed only for 5 different depths. it can be found here:http://web.archive.org/web/20070429235805/http://www.mhsoft.nl/DiffusorCalculator.html

Quote:
So the low frequency cut off is 800 Hz, they'll still be scattering down to an octave lower, about 400 Hz, meaning that the minimum distance between the diffusers and your head should be about 9 feet, recommended 12 feet or more.


Darn, I thought I had a pretty good grasp on how these diffusors worked? Can you please refer me to some further documentation which explains your comment regarding scattering down to an octave lower than the lower frequency limit which I have listed? My understanding was that the length of each block determines the lower frequency limit while the width of each block determines the upper frequency limit. Any further reading you can point me to would be much appreciated.

Quote:
By the way, I love the way you did your speaker soffits! Very solid, very neat, good design, and I'm betting those are very effective. You should be getting a really accurate, tight sound stage with those. And they look great, too! Nice work there! And the lighting also looks pretty cool, all around.


Thank you very much. Yes the imaging and sound stage in my room is incredible.


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PostPosted: Tue Jan 31, 2012 2:48 am 
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Actually, just to confuse things, the first and third diagrams you show there actually ARE panel traps! The middle one isn't. But I thought you were referring to the products that Ethan sells, not something that he posted as a suggestion. In any case, the drawing says that it was done by Phil Cramer, not Ethan, and they are based on the design given by Everest in MHoA, so things get even more confusing...

Anyway, the first and third option in that diagram are panel traps. The top one is tuned to about 110 Hz, roughly, and the bottom one is tuned to about 240 Hz. The middle one is just a plain old absorber.

The issue with yours is that the cavity is not a constant depth, which is what those diagrams show. It will still act somewhat like panel trap, yes, since it is a mass suspended over a sealed cavity, so it will resonate, but the effect will be over a broader range of frequencies, centered around the average depth of the air gap, and the effect on each frequency will be lower (in other words, the trap will have low Q). So if you tell me what thickness of plywood you used there, and the average depth of the cavity between the plywood and the wall, then I can tell you what the center frequency is that your traps are tuned to.

Quote:
I chose to straddle mine across the corner because I know that low frequencies build up in the corners of rooms. It seemed logical to place the bass trap there.
Well, in a small room it's not really that bass "builds up" along the walls or in the corners (although that's what it sounds like!). Rather, it is simply that all room modes terminate in corners, which makes corners the best place to deal with them. When you put your head close to a wall or corner, what you are hearing as "bass build up" is really just mostly the modal response of the room (plus sound "bouncing back" form the walls).
Quote:
I've been very pleased with the low end response in my room. What do you think?
Looks pretty darn good to me! That's nice flat response, and pretty even for the low end. +/- 5 dB is very good, and the waterfall shows that you have the deep bass under control too. Nice!


Quote:
Darn, I thought I had a pretty good grasp on how these diffusors worked? Can you please refer me to some further documentation which explains your comment regarding scattering down to an octave lower than the lower frequency limit which I have listed? My understanding was that the length of each block determines the lower frequency limit while the width of each block determines the upper frequency limit. Any further reading you can point me to would be much appreciated.
There's a lot of theoretical papers out there on QRDs, and the web site you link to actually mentions one of the classics, from the BBC:

http://web.archive.org/web/200505142329 ... 990-15.pdf

They mention the effect briefly (scattering below cutoff), but only say that they'd like to know more about it, but didn't actually study. They also mention why it is important to have thin dividers between each well and its neighbors (yours don't), and talk about the what happens when you don't do that, but once again only to say that it needs more research.

Since then there has been more research, and the effects are better understood.

Here's some things that you might find interesting.

I quote from the last one on that list:

http://web.archive.org/web/200505142329 ... 990-15.pdf
http://www.scribd.com/doc/17846889/RPGs ... -Diffusers
http://usir.salford.ac.uk/14652/1/From_ ... sorber.pdf
http://www.subwoofer-builder.com/qrdude ... -lobes.htm

"It is generally accepted that scattering can take place down to one octave below the lowest diffusion frequency. In this range, the panel is still working, but does not have the same potential for equal energy lobes."

But here's probably the best one, by the two leading "gurus" on Shroeder diffusers: Cox and D'Antonio.

http://books.google.cl/books?id=f19_6NF ... rs&f=false


Anyway, even though there's some things that you didn't do exactly right, fortunately they weren't biggies, and there's plenty that you DID do right. So it turns out that you built a great room, that not only sounds good, but looks real nice too!



- Stuart -

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PostPosted: Wed Feb 01, 2012 3:05 pm 
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Quote:
Actually, just to confuse things, the first and third diagrams you show there actually ARE panel traps! The middle one isn't. But I thought you were referring to the products that Ethan sells, not something that he posted as a suggestion.


Those designs were posted by Ethan as part of an article he wrote many years ago titled "Build a Better Bass Trap." The article also appeared in the June 1995 issue of Electronic Musician magazine. When you google "build bass trap", it is in the top three results that comes up. In that article Ethan talks about how he has built several studios using those designs and also shows some photos of him and a friend building them in his current home. Yes, they are very different from his products that he sells.

Quote:
In any case, the drawing says that it was done by Phil Cramer, not Ethan, and they are based on the design given by Everest in MHoA, so things get even more confusing...


Sorry, I did not mean to say they were Ethan's designs necessarily. I simple meant he has the designs posted as part of an article he wrote. And that it was from that article that I first learned about them.

Quote:
So if you tell me what thickness of plywood you used there, and the average depth of the cavity between the plywood and the wall, then I can tell you what the center frequency is that your traps are tuned to.


The plywood is 1/4" thick. I used 2" thick insulation. The design above calls for 1" thick insulation. The average depth of the cavity between the plywood and the wall is roughly 12".

Quote:
Looks pretty darn good to me! That's nice flat response, and pretty even for the low end. +/- 5 dB is very good, and the waterfall shows that you have the deep bass under control too. Nice!


Thanks. And thank you for the links regarding diffusion!


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PostPosted: Wed Feb 01, 2012 11:24 pm 
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Quote:
The plywood is 1/4" thick. I used 2" thick insulation. The design above calls for 1" thick insulation. The average depth of the cavity between the plywood and the wall is roughly 12".
Theoretically, that's tuned to around 60 Hertz, but with spread over a range of a few Hz. Guessing that the effective depth varies from about 6" to 18", that would give you a range of maybe 85 Hz down to 50 Hz. So that might have something to do with the dip on your EQ graph around 65 Hz, that turns out to have have a "tail" on the waterfall plot, and also the peak around 75 Hz. Just a guess.

The 2" thickness instead of 1" is actually probably helping: It will be providing more damping than the original design, and therefore lowering the Q slightly and increasing the spread slightly.

Just curious: Did you take any readings with REW in the empty room, before you put in any treatment? It would be cool to compare two. I'm betting there's a pretty substantial difference between "before" and "after".


- Stuart -

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