| Sealed, to damp or not to damp??? - Click HERE for Original Thread |
| mace |
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. |
|
|
| Bill Fitzpatrick |
| If the lowpass filter is 4th order, no additional damping is necessary. If 2nd order, I'd use the foam you have on hand. |
|
|
| mace |
| Sorry to sound like a Noob(I am) but how would I determine if it is 4th or 2nd order? |
|
|
| keyser |
| 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. |
|
|
| keyser |
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) |
|
|
| 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. |
|
|
| Dave Jones |
| 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. |
|
|
| BillFitzmaurice |
| 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. |
|
|
| kfr01 |
| 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. |
|
|
| 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. |
|
|
| BillFitzmaurice |
| quote: | | Please explain how no damping works better |
Simply put, damping absorbs energy. That's a necessity with frequencies short enough to reflect off interior surfaces back to the cone and arrive there in degrees of phase sufficient to alter response, as in the midrange. In the bass where the internal distances are too short for this to occur that energy tends to be more useful not being absorbed but rather acting as an additional bit of 'spring' to the air in the chamber and the driver suspension, often resulting in stronger output. |
|
|
| kfr01 |
| Very succinct yet complete answer. Thank you! |
|
|
| mace |
| Thanks alot guys, and especially Billf and Billmf. |
|
|
|
|
