Sealed, to damp or not to damp??? - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

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 26th November 2004, 08:35 PM   #1
mace is offline mace  United States
diyAudio Member
 
mace's Avatar
 
Join Date: Nov 2004
Location: Oklahoma
Default Sealed, to damp or not to damp???

Hello all, I am new here so please bare with,

I am building a cab for a Titanic3 12"
I will be using 1" MDF with internal bracing(shelf type)
My net volume will be 2cf^3 after driver/amp displacment, for a Q of .6
The amp I will be using is a 500watt PE amp.
The amp and driver will be mounted using machine screws and t-nuts, not wood screws.
Here are the basic specs on the driver:
Power handling: 500 watts RMS/700 watts max
Impedance: 4 ohms
Fs: 22.2 Hz
Xmax: 18.7 mm
Sensitivity: 88.6 dB 2.83V/1m
Qts: .44
Vas: 2.61 cu. ft.

My question concerns stuffing or lining the cab walls.
Being as this will be a fairly rigid cab, using a sealed design, will it be necessary to add any additional damping material?
I have some acoustic foam lying around, I believe it is 2" thick, but in my original design, I didn't factor in any displacment for the foam. Once again is it necessary????
Oh, by the way, this is for music only.
Thanks in advance for your responses.
  Reply With Quote
Old 27th November 2004, 12:31 AM   #2
diyAudio Member
 
Bill Fitzpatrick's Avatar
 
Join Date: Jun 2001
Location: Eugene, OR
If the lowpass filter is 4th order, no additional damping is necessary. If 2nd order, I'd use the foam you have on hand.
  Reply With Quote
Old 27th November 2004, 12:47 AM   #3
mace is offline mace  United States
diyAudio Member
 
mace's Avatar
 
Join Date: Nov 2004
Location: Oklahoma
Sorry to sound like a Noob(I am) but how would I determine if it is 4th or 2nd order?
  Reply With Quote
Old 27th November 2004, 12:59 AM   #4
keyser is online now keyser  Netherlands
diyAudio Member
 
keyser's Avatar
 
Join Date: Oct 2004
Location: The Netherlands
if i'm not mistaking, a 1st order cross-over that crosses (or filter...) at 6 db/octave. A 2nd order cross-over does that at 12, a 3rd at 18 and a 4th at 24 db/octave.
  Reply With Quote
Old 27th November 2004, 01:06 AM   #5
keyser is online now keyser  Netherlands
diyAudio Member
 
keyser's Avatar
 
Join Date: Oct 2004
Location: The Netherlands
damping...
i guess your sub will be mainly used as sub for music (low Q).
don't be afraid to put in too much damping. i don't know what acoustic foam is. stuffing just never seems to be a bad idea if you want to lower the Q of the system. Stuffing with(whichever you want to use) good damping material can usually increase the volume "that the woofer sees" with 10-15 percent. This means that when you stuff the cabinet of the sub, the Q will be 10-15 percent lower. You could use the stuffing to make the box smaller, or lower the Q.
Lower Q usually is better with music (bass becomes faster. Not deeper though)
  Reply With Quote
Old 27th November 2004, 01:26 AM   #6
diyAudio Member
 
Bill Fitzpatrick's Avatar
 
Join Date: Jun 2001
Location: Eugene, OR
The manual you got with the plate amp should state the low pass roll-off. 4th order = 24db/o. If it doesn't say, mail PE.
  Reply With Quote
Old 28th November 2004, 01:24 AM   #7
diyAudio Member
 
Join Date: Jul 2003
Location: Silicon Valley
Quote:
Originally posted by Bill Fitzpatrick
The manual you got with the plate amp should state the low pass roll-off. 4th order = 24db/o. If it doesn't say, mail PE.
The only one at PE that has 24db/octave is the 804. All the others are only 12.
__________________
Davy Jones
  Reply With Quote
Old 28th November 2004, 10:42 PM   #8
Banned
 
Join Date: May 2004
Location: New Hampshire
The source has to be considered as well for the slope; if the source is a receiver with a built in crossover at 12dB and the amp is also at 12dB the total will be at 24dB. With 24dB of LP filtering and a crossover at 80 Hz or less no damping usually works better.
  Reply With Quote
Old 29th November 2004, 01:48 AM   #9
kfr01 is offline kfr01  United States
diyAudio Member
 
kfr01's Avatar
 
Join Date: Oct 2004
Please explain how no damping works better. Not trying to be flip, I'm a bit of a newb and am actually interested in why.
  Reply With Quote
Old 29th November 2004, 02:32 AM   #10
diyAudio Member
 
BassAwdyO's Avatar
 
Join Date: Jun 2004
Location: Illinois
Send a message via AIM to BassAwdyO
Keyser, Low Q provides the best LF extension. Look at a response curve of a sealed enclosure with a Q of .5 and compare to a Q of .7 you will see the .5 will have a lower F3 giving it higher efficiency at those extremely low frequencys. I dont know that stuffing will help much either way, (with or without a steep crossover slope). It will give a slight advantage without a steep slope, but the major problem arrises in that the driver is going to play and radiate the unwanted frequency band with or without stuffing. Stuffing the enclosure will only absorb the backwave better, but the frontwave is going right into your room. I've also heard that a increase in apparent box size can be achieved, but I doubt it is anywhere near what some claim. To stuff or not to stuff, decide for yourself. Try it without, then try it with, if you like the sound better one way, then thats your preference.
__________________
The golden rule of DIY:
Build nice, or build twice!
  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
Sealed midbass vs BR, why not sealed ? mbon Multi-Way 4 2nd February 2014 11:23 PM
Sealed box and ESL Bazukaz Planars & Exotics 29 27th November 2005 06:41 PM
Using rope caulk (mortite) to seal drivers and damp vibrations percy Car Audio 0 31st July 2005 04:16 AM
TL or sealed... Chris8sirhC Multi-Way 17 22nd February 2004 01:02 AM
Notch Filter to damp resonance. Dave Multi-Way 1 8th December 2001 02:59 AM


New To Site? Need Help?

All times are GMT. The time now is 09:44 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