custom enclosure
Evolving Member
Joined: Feb 2004
Posts: 342
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From: Saskatoon, SK, Canada
SPL? Those are sealed boxes....
If youre going for SPL, theres no point doing 2 side enclosures...go rear-firing, ported. that's the way to do it for SPL...
I'm doing a side-well this weekend...going to try and keep it under a cube (i have a JL 10W3 now, but im buying a 10W6v2 in the next month so I need to be able to swap...
If youre going for SPL, theres no point doing 2 side enclosures...go rear-firing, ported. that's the way to do it for SPL...
I'm doing a side-well this weekend...going to try and keep it under a cube (i have a JL 10W3 now, but im buying a 10W6v2 in the next month so I need to be able to swap...
Evolving Member
Joined: Sep 2002
Posts: 295
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From: Millersville, PA
Originally Posted by SK Lancer
SPL? Those are sealed boxes....
If youre going for SPL, theres no point doing 2 side enclosures...go rear-firing, ported. that's the way to do it for SPL...
If youre going for SPL, theres no point doing 2 side enclosures...go rear-firing, ported. that's the way to do it for SPL...
Evolving Member
Joined: Feb 2004
Posts: 342
Likes: 0
From: Saskatoon, SK, Canada
and SQL means sound quality level...
(I had a HUUUGE schpeel made up but i hit the back button and it got erased...now im pissed off)
Ported enclosures go louder because the rear wave can interact with the front wave...(sub moves in, creates rear wave. sub moves out, *you guessed it* creates front wave). When the port is designed properly, the rear wave hits the windshield at the same time as the front wave. You get the effect of 2 subs, which in theory makes you go 3 db louder. 3db is a fair amount....Ported boxes require more airspace, so are not always possible.
Sealed boxes can be fairly small depending on the sub. You can have the sub in tiny spots that rock (heh, look for threads by me in the future
) They sound better (for the most part)...
OK hope that helps..this post was twice as long before the stupid back button incident ...
(I had a HUUUGE schpeel made up but i hit the back button and it got erased...now im pissed off)
Ported enclosures go louder because the rear wave can interact with the front wave...(sub moves in, creates rear wave. sub moves out, *you guessed it* creates front wave). When the port is designed properly, the rear wave hits the windshield at the same time as the front wave. You get the effect of 2 subs, which in theory makes you go 3 db louder. 3db is a fair amount....Ported boxes require more airspace, so are not always possible.
Sealed boxes can be fairly small depending on the sub. You can have the sub in tiny spots that rock (heh, look for threads by me in the future
) They sound better (for the most part)...OK hope that helps..this post was twice as long before the stupid back button incident ...
Newbie
Joined: May 2004
Posts: 13
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Oddly, I happened on this thread looking for rough size of trunk to see if fitting a JBL W12GTi in a bandpass would be feasible and leave some trunk space.
In a properly tuned ported enclosure, below the resonant frequency of the enclosure, the subwoofer is 180 degrees out of phase with the port. The port makes all of the pressure waves. At the resonanat frequency, the sub will hardly be moving. Below that, the excursion of the sub is squared with the frequency which is why most poorly designed vented enclosures trash subs regarless of power...too high a tuning frequency. Of course big post area = big port length so there's a tradeoff. When I had my stereo shop, I saw a lot of subs that were never seeing their potential example - 12" sub with a 2" diameter port 4" long in a 3 cubic foot box. Sounded like absolute dung - crank it and the sound level didn't increase with sub movement at the standard 1:4 ratio. Once of the best sounding was a single 8" bandpass with a 4" port. Less important the name / power handling / magnet size of the sub than properly matching it with the right enclosure.
At subwoofer frequencies (below the resonant frequency of the air space in the vehicle), there's no bouncing around and interacting of pressure waves with anything in the vehicle. More like filling a balloon and letting it f@rt around the room 20 - 100 times a second. This is why a sub will sound 6 - 9db louder in a vehicle than it does in open space. The sub has far better loading in a closed vehicle.
Also, the split sub thing where there is a sub in each rear fender well is killing sound quality and sound pressure level. I've been down that road. Frequency response on an RTA looks like a cheap ace comb from 20Hz to an octave above the crossover frequency. Yes, it looks really cool and symmetrical, but better to do an isobaric mount with 2 12" subs on one side. Multiple speakers that are fed the same signal shouldn't be more than 1/4 wavelength of the highest frequency they will produce away from one another. The closer the better.
Sorry if this sounds cocky, but I'm trying to save some aggravation and help you get more bang for your buck.
In a properly tuned ported enclosure, below the resonant frequency of the enclosure, the subwoofer is 180 degrees out of phase with the port. The port makes all of the pressure waves. At the resonanat frequency, the sub will hardly be moving. Below that, the excursion of the sub is squared with the frequency which is why most poorly designed vented enclosures trash subs regarless of power...too high a tuning frequency. Of course big post area = big port length so there's a tradeoff. When I had my stereo shop, I saw a lot of subs that were never seeing their potential example - 12" sub with a 2" diameter port 4" long in a 3 cubic foot box. Sounded like absolute dung - crank it and the sound level didn't increase with sub movement at the standard 1:4 ratio. Once of the best sounding was a single 8" bandpass with a 4" port. Less important the name / power handling / magnet size of the sub than properly matching it with the right enclosure.
At subwoofer frequencies (below the resonant frequency of the air space in the vehicle), there's no bouncing around and interacting of pressure waves with anything in the vehicle. More like filling a balloon and letting it f@rt around the room 20 - 100 times a second. This is why a sub will sound 6 - 9db louder in a vehicle than it does in open space. The sub has far better loading in a closed vehicle.
Also, the split sub thing where there is a sub in each rear fender well is killing sound quality and sound pressure level. I've been down that road. Frequency response on an RTA looks like a cheap ace comb from 20Hz to an octave above the crossover frequency. Yes, it looks really cool and symmetrical, but better to do an isobaric mount with 2 12" subs on one side. Multiple speakers that are fed the same signal shouldn't be more than 1/4 wavelength of the highest frequency they will produce away from one another. The closer the better.
Sorry if this sounds cocky, but I'm trying to save some aggravation and help you get more bang for your buck.
Evolving Member
Joined: Feb 2004
Posts: 342
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From: Saskatoon, SK, Canada
Any particular reason why you would do a band pass? All of the experiments I've done with BP haven't sounded as good as sealed, and dont have the low frequency extension of the ported....
BP's do go really rank loud when done right *a hell of a lot of testing*, though...
Just looking for clarification
BP's do go really rank loud when done right *a hell of a lot of testing*, though...
Just looking for clarification
Newbie
Joined: May 2004
Posts: 13
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My first choice for sound quality is a sealed box - especially for jazz and classic rock. For low frequency extension and overall efficiency is a ported box - super great for newer rock and heavilly electronic music. I prefer the 4th order bandpass for the efficiency gain (3 - 6db over sealed and usually 3db when tuned properly ported) and can be almost as linear in the pass band as a sealed box. 6th order (port on front and rear chamber) are horrific to build and get the results you've planned on without some very intense modeling and speaker parameter measurments. It's the best tradeoff IMHO.
Check these specs... http://manuals.harman.com/JBL/CAR/Bo...2GTi_rev_f.pdf
Using the JBL W12GTi, in a 1 cubic foot sealed box, it's efficiency is 95dB @ 2.83V in the vehicle. Very linear pass band resonse. The same woofer in their recommended bandpass design (internal volume of 1.5 sealed and 2 cubic feet ported to 50Hz) has a peak at 30Hz where efficiency is 105dB @ 2.83V in the vehicle. Above that, it rolls off sharply, but the phase of the wave is more like the sealed box. (Plus 130dB of 30Hz makes a really nice back massage!) The difference in efficency between the two boxes is like having an amp that's 10 times more powerful. {Net SPL = SPL @ 1W/1m + 10 *(log(amp wattage))} BUT the bandpass is larger than any of the other models - about 5 cubic feet on the outside.
If you're good with tools and you like to roll your own box, you can usually pick up some reasonably good box modeling software for $100 - far cheaper than my first method of "yeah, that'll fit in there, but it really sounds like cr@p". I still use Bass Box 5.1 that I bought back in 1996. The sub database is a little out of date, but it still gets me pretty much what I'm looking for. I had some pretty rad sub systems designed on that, but those went with the shop 
.
Another good source for the theory is The Loudspeaker Design Cookbook with more math in there than I have buttons on my trusty Casio calculator, and doesn't allow for variables like power compression or other dynamic factors. Still it's an awesome resource that has paid for itself many times over.
Check these specs... http://manuals.harman.com/JBL/CAR/Bo...2GTi_rev_f.pdf
Using the JBL W12GTi, in a 1 cubic foot sealed box, it's efficiency is 95dB @ 2.83V in the vehicle. Very linear pass band resonse. The same woofer in their recommended bandpass design (internal volume of 1.5 sealed and 2 cubic feet ported to 50Hz) has a peak at 30Hz where efficiency is 105dB @ 2.83V in the vehicle. Above that, it rolls off sharply, but the phase of the wave is more like the sealed box. (Plus 130dB of 30Hz makes a really nice back massage!) The difference in efficency between the two boxes is like having an amp that's 10 times more powerful. {Net SPL = SPL @ 1W/1m + 10 *(log(amp wattage))} BUT the bandpass is larger than any of the other models - about 5 cubic feet on the outside.
If you're good with tools and you like to roll your own box, you can usually pick up some reasonably good box modeling software for $100 - far cheaper than my first method of "yeah, that'll fit in there, but it really sounds like cr@p". I still use Bass Box 5.1 that I bought back in 1996. The sub database is a little out of date
, but it still gets me pretty much what I'm looking for. I had some pretty rad sub systems designed on that, but those went with the shop . Another good source for the theory is The Loudspeaker Design Cookbook with more math in there than I have buttons on my trusty Casio calculator, and doesn't allow for variables like power compression or other dynamic factors. Still it's an awesome resource that has paid for itself many times over.