Room resonances - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd December 2003, 08:02 PM   #1
diyAudio Member
 
Join Date: May 2003
Location: Morton, Illinois
Default Room resonances

I had to move my testing, for the time being, into a small room, 12wx18wx7H and am having trouble getting the response flat from 1khz down to 31.5hz.

The trouble spot is around 50 and 40 hz areas, down 10db from 1khz spl. 31.5hz spl is the same as 1khz. Other than those two frequencies, the response is within +2.5db -3.5db from 1khz to 31.5hz.

Any ideas?
  Reply With Quote
Old 3rd December 2003, 08:19 PM   #2
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Aside from electronically applying some correction, you could try what amounts to a speaker box with no speakers in it? Just a resonant chamber to increase things.

Or adjust your speaker boxes themselves so they tune to 40-50Hz. Idunno, I ain't no acoustics expurt..

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 3rd December 2003, 10:19 PM   #3
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: USA
Throwing a dead cat in a room usually improves acoustics, almost never hurts.

There are people making a living that way (except they sell ultra-foam and super-fiber absorbers; no profit in dead cats).

No precision needed: Most rooms will be "better", at least different, with any reasonable number of dead cats added.

For 40Hz troubles you need BIG dead cats.

You want absorption more than 4" 100mm thick, and preferably more like 12" 300mm thick.

Bring in as many over-stuffed chairs and sofas as you can.

When you need to suck-up bass: dead cats in corners are better than laying in the middle of the floor.

Two layers of fiberglass attic insulation 6" thick to make a 15"*12" 380mm*300mm batt, jammed into each corner from floor to ceiling, will damp most rooms' bass. In your low long room, you may need to damp one or both of the 12' and 18' long-corners, probably at the wall-ceiling corner.

There are actually ways to calculate all this. You probably have bass waves the same length or width as the room, so it works like a pipe organ for 2 or 3 notes. It would be nice to damp JUST those notes without affecting others. But tuned absorbers are very tricky. And broadband absorbers don't work at bass unless they are thick, but do have a very broadband effect. Emphasize the bass absorption by using a small area (less than 20% of total room surface area) of thick (10" or more) fuzz jammed in corners. You may need very little of it to kill the resonance at 40 and 50, and maybe not enough to significantly change the 100-1,000 response.
  Reply With Quote
Old 3rd December 2003, 11:03 PM   #4
diyAudio Member
 
Da5id4Vz's Avatar
 
Join Date: Feb 2003
Location: lost in america...
Send a message via AIM to Da5id4Vz
Default "polycylindrical diffusers"...

Try doing a Google search on "polycylindrical diffusers"... Did I just hear someone grown?

These can be quite effective in reducing LF resonance while not killing the all of the HF.

Filling them with dead cats for dampening material works well too.

A word of caution about fiberglass insulation, in addition to making you scratch like a monkey for a few days after installing it, it has been known to cause respiratory distress. It seems those little jagged edges can really mess with your lungs too. Rigid duct liner is a black fiberglass material that has less *****ly edges. Its still a beast to handle but it wont make your lings hurt.

Iíve hung rigid duct liner behind a throw rug using heavy duty curtain hangers. Leaving a dead space (about 4") between the 2" duct liner and the wall seemed to do well at reducing low frequency resonance.

Of course being that this subject is posted in the tube column, you could think about using some sonotube for homebrew tube-traps too.

Lots of acoustics threads floating around lately. Perhaps we have the basis of a new forum topic brewing?
Attached Images
File Type: jpg ttrap.jpg (9.2 KB, 470 views)
  Reply With Quote
Old 10th December 2003, 02:29 PM   #5
diyAudio Member
 
Join Date: Apr 2003
Location: NY
About this "dead-cat" issue. Mine are alive and are therefore "mobile" sound absorbers. Keeps things interesting...
Now, as far as bass traps are concerned. We have been building quite a few of them ourselves. Look for cardboard "concrete" tubes from Home Despot (sic!), they come in diameters up to 12", I think, all are four feet long. Stuff these with the new "Miraflex" fiberglass insulation from Owens-Corning (usually a special order item). This stuff is SO much easier to work with than the regular stuff - no itch (in fact, part of its advertising) - and it is comparable to cotton in a perforated plastic wrap. Step 3: cover the tube with nice fabric or paint. The tube itself as a Helmholtz is most effective at its resonance frequency (diameter!!), and the "stuffing" will broaden its effective trapping range. Use different size tubes for different bass "center" frequencies - similar to organ pipes.
Price for DIY: about $ 10 per tube - or you can buy a similar item from Tubetraps for about $ 200/ each - your choice.
PS: If you need high frequency absorption, wrap the tubes with some foam before you cover them with fabric.

Alternative:

get a few old futons and use them rolled up with a cover in corners

Cheers
__________________
RB
  Reply With Quote
Old 10th December 2003, 03:28 PM   #6
diyAudio Member
 
Da5id4Vz's Avatar
 
Join Date: Feb 2003
Location: lost in america...
Send a message via AIM to Da5id4Vz
Tube traps for the Mason Hall studios? But Jeesh that rooms so big I cant imagine it needing much LF treatment (just move the bass drum around abit)

My cats are fat and happy too.

I think its the length of the tube that effects the resonant frequency with the diameter effecting the amplitude that they resonate at.

-Dave
  Reply With Quote
Old 10th December 2003, 04:00 PM   #7
diyAudio Member
 
Da5id4Vz's Avatar
 
Join Date: Feb 2003
Location: lost in america...
Send a message via AIM to Da5id4Vz
This company has been very popular with acoustic device manufactures. Its not uncommon to see them listed as the reference for standard color options. Ypholstery fabrics work well also.

http://www.guilfordofmaine.com/

I think if I were playing around with tube traps these days that I would think about trying to extend there response by cutting slots in the side of the sono-tube with a router and by sing some kind of a limp mass (heavy rubber or vinyl) inside of the tube.

The commercial tube traps always struck me as having a wire coating over the tube, under the fabric. I always wanted to take one apart to see what magic they pack inside, but was always afraid of what would happen if all the trapped tubes got loose from the inside.

The Owens Miramax insulation sounds great. Ill need to check it out.
  Reply With Quote
Old 10th December 2003, 04:23 PM   #8
tiroth is offline tiroth  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Will one of these cylindrical tube traps really be effective at 25Hz, assuming it is sized appropriately? I have a +6dB resonance at 25Hz, perhaps 1/10 octave ewide. Very problematic to EQ.

Maybe I just need a couch along the back wall of my room. ^_^

Hmm, are we talking some 35" wide tube at these f? I think the SAF is definitely down to zero.
  Reply With Quote
Old 10th December 2003, 04:37 PM   #9
diyAudio Member
 
Da5id4Vz's Avatar
 
Join Date: Feb 2003
Location: lost in america...
Send a message via AIM to Da5id4Vz
25Hz, well thats about 22 feet long?

1/2 wave would be round 11 feet, and a 1/4 wave would be about 6.5 feet.

Do any of these dimensions seem familiar in your room?

A 6.5 foot chunk of stuffed sono-tube would be a cheap experiment. The biggest trick I can see would be positioning it to optimize its resonance with the room mode.
  Reply With Quote
Old 10th December 2003, 04:43 PM   #10
tiroth is offline tiroth  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Indeed, my room is narrow (10-15', varies) but long (~22'). It is conceivable that there is reinforcement of the major axis. I have a minor problem at 42Hz but EQ alone fixes that.

I am pretty sure that there is a local maxima at the rear wall, low bass is nearly 10dB higher there than at the listening position. I don't even need to look at the meter, I can feel the difference! Seems like a great place for the traps?

Doesn't the tube need to be wider as well, for lower frequencies? Thanks for the info.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Nasty Room Resonances in New Listening Room TubeHead Johnny Multi-Way 4 23rd May 2009 11:13 PM
Pipe resonances. perpetual Subwoofers 22 12th June 2005 05:44 PM
Speakers in corners - room resonances rick57 Everything Else 1 22nd November 2004 08:35 AM


New To Site? Need Help?

All times are GMT. The time now is 03:10 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2