View Full Version : You might find this a little strange.....But
11-19-2002, 11:00 PM
Ok ok I might be a bit of a hack for doing this.
My sub started rattling badly after I overstressed it watching AOTC the other night. Seeing as I have been dropping a pile of cash lately I didn't have enought to replace it. Trying to find an OEM replacement driver for an old and discontinued JBL PSW1000 was a little tough here in Canada. So I dropped in an MTX Thunder 6000 10" car cub I had kicking around and WOW what a difference!
The replacement is a 4ohm driver so it does stress the onboard amp a little but it REALLY rumbles. Now the only problem I have with it is it pushes a pile more air through the front port. I mean a lot of air. What would be the best way to prevent the whoosing noise? Another port? I know it might sound scabby, but it is a cheap temporary, get me through till after christmas, fix.
Has anyone else ever done this? I am actually quite impressed with the LFE this little box is creating now.
Go ahead Flame away, not exactaly a PC+ but it was cheap and it kinda looks cool too.
11-19-2002, 11:08 PM
Here is a pic...
11-19-2002, 11:47 PM
Got any wadding inside that box? If not, rip open a $5 Wal-Mart pillow and stuff that mofo.
Any stats on the MTX driver? Q, Fs, Xmax, optimal box types/sizes?
11-19-2002, 11:51 PM
What the heck - it's already been modified once - what's another port going to hurt? Get out the scroll saw and make another one! Just avoid cutting internal wires/components, etc.
You could even radius the inside and outside for less flow turbulence than the stocker port and really feel like you did a custom job!
The Polk PSW350 has two ports, and is similar sized. So I can't see the problem if you really don't care too much about this sub.
Adding the second port will probably alter (increase) the natural tuning point a few Hz, but it should also give you more SPL if you feel the driver is being choked right now with just one port.
11-20-2002, 01:03 AM
QTS = .56 QES = .62 QMS = 5.83
FS = 30.5hz
Xmax = .37"
Volume Acoustic Suspension? = 1.36 Ft^3
Freq Response = 31-150hz
RMS power handling = 250 watts
Sensitivity 1w/1m = 85.2 dB
Those are some of the multitude of stats. The sheet has all kinds of technical Data that I just don't get.
It does have some fiberglass insulation (not much), should I cut a couple of smaller ports in the rear of the cabinet, ie. 1.5" holesaw. Or one larger 2.5" front or rear. Then stuff it full of some kind of batting or not?
Thanks for not flaming me here guys.....
11-20-2002, 12:45 PM
There are several subwoofer DIY sites on the internet that can explain fully each of those terms.
In fact, since you have the driver specs, you can determine the exact enclosure size and venting requirements that will get the most out of that particular driver.
I'd stick the second port right next to the first one if there is room. The port size will be dictated by your research. Typically, ports are at least 3" in diameter and radiused to prevent noise. I would avoid small diameter ports - they are probably noiser than larger ones.
I have 21 square inches of port area on my sub. You will probably need less, but it's almost a given you'll need more than you have now if the port is noisy.
Typically, most subs have some set quantity of batting inside - the DIY sites can help you with that too.
11-20-2002, 01:04 PM
You're going to have to choose a frequency at which you want to tune the port. This isn't simply a matter of cutting another hole or enlarging the one already there. You'll have to work with internal box volume, port diameter as well as the length of the tube.
If you can't find information on the internet, I have Vance Dickenson's "Loudspeaker Design Cookbook" (latest edition, I believe). Can't do it today, but I could fax you some pages if you're interested.
There are also computer programs that will calculate the dimensions for you.. don't know if any of it is free or shareware.
11-20-2002, 01:28 PM
From mtx, the vent should be 2" x 7" in a 1 cu ft enclosure, tuned to 32 Hz.
11-21-2002, 06:47 AM
Is that a slot type vent with no depth (other than the thickness of the enclosure?
Also, Burdette makes a salient point - the port length also changes the tune of the enclosure. Notice how I avoided the term "hole" and stuck to the term "port". It goes without saying that your second port should be around the same depth as the stocker. Looks like about 6" deep from your photo. These ports are also available from DIY sites. They come in standard diameter sizes and are radiused at least on one end.
11-21-2002, 07:28 AM
2" diam, 7" long, cylinder
I also notice we only have 4 screws holding it in? Was a mounting kit (gasket) used?
11-21-2002, 11:09 PM
There are actually 8 screws holding it in 4 had silver heads and 4 had black.
Thanks for the help guys, what do you think of a slot type vent?
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