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Originally Posted by frankmehta JBL sub documentation says that the enclosure must be 1 cu ft. in size. They haven't given the exact dimensions |
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Originally Posted by abhinav.gupta88 non cubic enclosure of around 1.08-1.1 cu ft. |
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Originally Posted by frankmehta How does one tune a port??? I am confused. |
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Originally Posted by frankmehta even my Luccents outperformed it in terms of sheer quantity of bass.
And when the volume is pumped up, it sounds like a ONE NOTE sub.Can someone help me design a 'ported' enclosure (PURELY FOR SQ) please? |
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Originally Posted by frankmehta ported enclosures can sometimes give better results than sealed ones. |
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Originally Posted by low_bass_makker Size I can help you design the enclosure but what thing you are missing. How is the sub performing now ? |
Sorry for jumping in late. From the comments Frank has made I assume his expereince is as follows:
On some music the sub does not play loud enough (atleast when compared to his Illusions), on other music it sounds boomy and very tubby (one note).
Frank am I right in assuming this?
1. Remember a subwoofer system is 1/3 sub and amp, 1/3 subwoofer enclosure (design and execution), and 1/3 room.
You can determine real world tuning frequency by measuring the current with an A.C. ammeter hooked in series between the power amplifier and the loudspeaker; the maximum current reading will coincide with tuning frequency. Once you have the tuning frequency you can use the calulations on the websites (mentioned by above) to get the port length. see links below
PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES The Subwoofer DIY Page - Port Calculations
2. I have not seen your FG enlclosure but many who make FG enclosures forget that an enclosure must not only be stiff (which most FG enclusures are) but also
non-resonant and well damped (which most FG enclosures are not). For many years I have been propogating the idea of using layers of MDF or marine grade ply along with FG to make the enclosures not only stiff but also damped as well as easy to build (using other more difficult to work with materials like marble/stone, carbon fiber, etc...).
3. From the symptoms Frank has described he is PROBABLY facing 3 seperate issues. A resonant FG enclosure, a subwoofer whose frequency response is not in accordance with the transfer fucntion of the car, and a box that might be a triffle too small.
4. Also in the old days we used to usually add a Infra-bass filter (a filter that rolled off bass below bass tuning frequency) to ensure that the woofer does not decouple below port resonant frequency. Below the Port frequency there is little control over the cone and the the subwoofer acts like it's gone nuts and flaps around like a loose sail on a sail boat. This can permanantly damage the suspension of the subwoofer. In the old days when we could not make big voice coils the added issue we used to face was that above resonant frequency since there was less cone movement required for any particular SPL there was also less air being pushed through the voice coil keeping it cool and subwoofers would burnout. Today with aluminum formers and vented pole pieces this is not much of an issue but something to keep in mind with a subwoofer as massive as the Gti.
Frank please remember that the published specs for most drivers deviate by as much as +/-10%. Now if the Fs is -10% and the Qts is +10% (a rare but possible condition) you might end up with a box that is not nessacarily correct for your given woofer. You need to measure your woofer's T/S specs.
Sealed boxes are more tolerant of deviation from published specs. However you might be able to control your subwoofer using resisant damping see link below
Strassacker: Speaker, Do-it-yourself
Some amps have this built in
http://icondealerservice.com/catalog...&productId=169
In principle this works similar to aperoidic loading of sealed boxes. The diffference being that one is electrical and one is mechanical. Both are resistive and that means there will be some loss of overall efficiency - there is NO free lunch.
Another option might be to tune the subwoofer to where your car transfer function is falling. This way the subwoofer's resonance peaks do not add with the car's transfer function peaks. The emperical way to do this is to make athe port a bit longer than required (abtou 30% longer) and cut and test many many times. In my 800 and Zen for example we found that tuning a 8" sub to about 45Hz worked best. Yes I lost out the last octave or so but atleast there was no boom that distracted me from the music. For me audio is about music, not about Fs, Qts, Vas, Watts, Amps, FFT curves, or any specifications.
Hope this helps.