Corner trap design question...

Snyderman · Post by **Snyderman** » Fri May 05, 2006 1:21 am

I’m building four corner bass traps based on John’s design. My front layer of insulation comes right up to the front edge of the panel. Once I add the fabric cover and the front slats there will be little to no air space between them and the front layer of insulation.

1. Does this compromise the acoustic benefits & should I try to cut off thin layer of the 705 insulation to narrow the width? Or can I let it be and finish them?

2. Should I definitely have two insulation layers? Any tips on cutting them without creating a lot of insulation dust?
Thanks,
derek

Snyderman · Post by **Snyderman** » Fri May 05, 2006 2:15 am

Never mind the cutting question. Just found out a sharp knife slices right thru the insulation, senza dust.

How about the air space in front question though?

Post by **John Sayers** » Fri May 05, 2006 10:34 am

I've had success in cutting insulation and foam with an electric carving knife.

cheers
john

knightfly · Post by **knightfly** » Sat May 06, 2006 7:35 am

See if this helps -

http://www.johnlsayers.com/phpBB2/viewtopic.php?p=43358

Steve

Snyderman · Post by **Snyderman** » Sat May 06, 2006 12:57 pm

Thanks John & Knightfly,
I did see that post Steve & it was helpful. I also like the idea of the electric carving knife.

Currently I’m trying to wrap my mind over the choosing of slat width/spacing. Can either of you point me in the direction of better understanding how to use the Helmholz calculator ands apply the results? I am but a simple cellist and am quite confused as to determining optimal slat placement. I have built the shells of four corner traps and a few side absorbers but am not sure how to utilize the Helmholz calculator to best treat my space.

This site is an incredible resource. Thanks!
Snyderman

knightfly · Post by **knightfly** » Thu May 11, 2006 5:29 am

Derek, every stringed instrument I know (even solid body electric guitars) has resonances (body as well as strings) - these can color the tone as I'm sure you're aware. If you know what those are for your particular instrument, you may want to center your helmholtz calculations around them to smooth out the room's response as it applies to your specific instrument.

If you don't know what your instrument's (not your room's) resonances are, you can find out by using acoustic test software and a laptop - but to keep the room itself out of the equation temporarily, this needs to be done either in an anechoic chamber (expensive even to just rent) or somewhere outside on a quiet day (difficult unless you're close to the countryside) - any other location and you have little hope of keeping outside influences from changing the response. Analyzing the recording(s) from this will help locate resonances that result from the instrument's characteristics.

Also, room dimensions and shape are very important; that's why they are included in the "Don't even THINK about posting..." topic at the top of every forum. If you can (re) read that topic and include ALL of the bold points that could possibly apply to your situation, we can help you more.

Keep in mind that EVERYTHING about a room affects what things SOUND like in that room; ratio of all dimensions, cubic volume, juxtaposition of walls/instrument/mic/your body/furniture in all THREE dimensions...

Don't panic, we're here to help you sort this out - you just need to help us help you... Steve

Snyderman · Post by **Snyderman** » Wed May 17, 2006 2:45 am

Thanks Steve,
I’ve been away on a gig but am back and want to give more info on my room. Sorry, I did read the ‘Don’t even think post’ but somehow forgot to give all the pertinent info anyhow. Shameful. Sorry. Thanks for the help.

My recording needs:
I am recording mostly acoustic cello projects. I live in a quiet environment and am alone in the house during recording times so isolation and sound bleeding isn’t a large concern right now. I am interested in treating the room to work better around the frequencies of a cello.

The Room:
The room is about 21’L x 14’W. The ceiling has two covered air ducts (about 3’ wide) running the length of the room. The ceiling height below the ducts is 6’5”. The ceiling height for the rest of the room is 7’3”. Do you need more info?

The floor is covered in a tight weave carpet, but I’m investigating hardwood.

The walls at this point are just thin painted wood paneling.

I have built the frames for 4 corner bass traps based on John’s design. I have made them as a bottom and top unit so as to be easier to move. I’ve also put them on 2” casters. As you can see from below, I’ve put the front slats on one of the ‘bottom’ units. But I didn’t uses the Helmholz calculator for placement of slates and don’t want to finish the units until I understand how to plane for the best slat placement. I’ve also made the frames for two floor-ceiling side wall units and am thinking of putting up a cloud based on Davis French’s design.

Thoughts ?

THANKS!

Mario Petrinovich · Post by **Mario Petrinovich** » Thu May 18, 2006 9:33 am

Hi people.
I am new here, and I am not in the recording business. The reason I am interested in this is becuase I had simply awfull room acoustics, but I love music. What was wrong? The highs were SCREAMING. But, it was not an ordinary scream. Imagine those capital signs that I used in "screaming" word, if they are three times larger. It was a scream you wouldn't believe. When I listened to acoustic guitar recording, I would hear only the high notes, and only the highest parts of those notes. I wouldn't hear anything else.
Well, I decided to improve the acoustics of the room. I knew that something is terribly wrong, but what? Finaly I've found it, and the solution was very simple. I have a few closets in my room. Those closets don't go all the way to ceiling, but are 44 cm lower. Between top sides of closets and my ceiling the flutter echo formed. I've put some insulation, and now everything is as should be.
So, I suggest you, don't leave the top of that thing unthreated, under any cost. -- Mario

Snyderman · Post by **Snyderman** » Fri May 19, 2006 3:09 am

Hi Mario,
Glad you came up with a solution! Don't worry the tops aren't done. I have another insulation layer in front of the one in the picture and have covered them with fabric. Just waiting to determine the best placement of the slats.

Hope all is well in Zagreb!
Derek

Mario Petrinovich · Post by **Mario Petrinovich** » Fri May 19, 2006 3:17 am

Snyderman wrote:Hi Mario,
Glad you came up with a solution! Don't worry the tops aren't done. I have another insulation layer in front of the one in the picture and have covered them with fabric. Just waiting to determine the best placement of the slats.

Hope all is well in Zagreb!
Derek

Of course, I thought about the wood below ceiling.
Regarding Zagreb, I hope too that all is well. I haven't been out yet,

. Same for Cleveland,

. -- Mario

knightfly · Post by **knightfly** » Fri May 19, 2006 6:31 am

The lower unit's slats look like they're wide enough apart to act more as a broadband trap, so that's fine - the rest of the trap dim's would partially depend on any resonances of your cello. In order to find those, you'd need to record a chromatic run from lowest note to highest, OUTDOORS, with a good mic and at a constant playing pressure, in order to avoid room colorations. Any instrument resonances should show up as louder notes when viewing the waveform in a DAW, or if using spectral analysis software.

That info can then be used to design a trap to even out the response, along with compensation for possible room mode interferences.

If you try to do this test in the room, you'll not know for sure whether loudness variations are due to the instrument or to various room interactions such as modes or boundary interferences... Steve

Oh, if possible use an omni mic for the test; less possibility of proximity boost...

len-morgan · Post by **len-morgan** » Wed May 24, 2006 6:48 am

Just out of curiosity Steve, if he does the test in the room and finds peaks in the response, does it matter whether they are from the room or the cello? If that's all he's recording in there, it would seem to me that if a mic in the room hears a flat response, it's the same either way. Or am I missing something?

len

Snyderman · Post by **Snyderman** » Wed May 24, 2006 8:20 am

I was kind of wondering the same thing as I won’t always be using my instrument. I plan to borrow various colleagues’ cellos as I do my multi-tracted recording to create more of a sense of multiple cellists playing. It helps to make it seem like it not just me playing.

Anyhow, I plan to do the outdoor test on my instrument at some point just to know the results.

BTW, can I use WaveLab to do any room analysis? It seems that ETF is the program to use but I’m dealing with budget issues and already have WaveLab. (The wood cost really start to add up when you’re building four corner units and two wall unit covered with stats!)

Derek

Snyderman · Post by **Snyderman** » Wed May 24, 2006 8:22 am

Mario,
I will do something to treat the gap between the top of the units and the ceiling. Thanks for pointing that out.
Hope all is well,
Derek

andrebrito · Post by **andrebrito** » Wed May 24, 2006 9:31 pm

Hello all !

To check the vibrations of a stringed instrument you need to use an accelerometer.

Also the fact that at a certain frequency there's a ressonance it does not mean the instrument will sound louder on that frequency ! So it's useful to compare the data from the accelerometer to the information recorded in a anechoic chamber

John Sayers' Recording Studio Design Forum Archive

Corner trap design question...

Corner trap design question...

placing the slats