| Jason Watts |
What type of alignment do you use for an SPL Box? Do I use just a standard fourth order boom box alignment, extended bass shelf or what?
Next question.
Do I tune the box to 57 Hz? |
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| danielkelley10 |
A standard vented box is your best bet for spl, as bandpasses require much more knowledge and effort to build, and you have more room for error with a vented box.
tuning frequency depends on your car, most cars peak between
50 and 60Hz though estate cars can be in the 40s. build a box with removable port tuned 5Hz or so below your cars resonant frequency, test the SPL, cut 1/2 inch off the port if spl increases cut a further 1/2 inch off the port test and repeat untill the spl drops off. then rebuild port to peak size. round all edges to port and edge of box etc to enable smoother airflow (this gained me 1dB) aim for a port of similer surface area as the driver you use, space allowing.
Bigger boxes tune lower so if your car peaks at a low frequency generally a bigger box is best. my car peaks at 54Hz and im using a 6^ft box tuned to 51Hz.
tuning frequency is always slightly lower than peak frequency btw.
What driver will you be using and with what amp? |
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| Jason Watts |
| I suspected as much concerning the band pass. I measured the frequency response in cab by taking a sweep function and playing it through my amp. I got two peaks in the spectrum one about 110 Hz and one around 50Hz. I suspect one is the cab resonate frequency and the other is the box fb. How do you measure your cab resonate frequency? |
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| SupraGuy |
As long as you're very careful with measurements, a bandpass box is going to be more efficient, and as such will supply better SPL for a given woofer cone. A horn is also very efficient. Either a bandpass or a horn should yield results that are signifigantly better than a sealed or ported enclosure.
Actually, ported enclosures aren't much more efficient than sealed in typical SPL ranges. At 50Hz, (as an example) both will be very close to the same. At 35Hz, the ported box is likely to be more efficient than the sealed box. At 20Hz, the sealed box is (usually) better than the ported box, because the ported box falls off very rapidly below tuning frequency. In addition, the sealed box will exhibit much greater power handling at low frequencies. Many SPL competitions use 63Hz tones, though some will use 30-35 as well.
If you aren't up to the task of building a bandpass or a horn enclosure, I'd personally just stick with sealed. |
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| Jason Watts |
| The first box I helped design brought second place in the db5 class. They clocked in at 152.5db last week at the usaci world finals. I was just goofen off that time but I'm fixen to pull the gloves off this go around. Do allot of people use bass horns in SPL? If I could do something unusual like a horn and get good results it would bring in allot of visibility from ours sponsor. Could you share any good tips? I have allot of experience designing many types of enclosures but I have never actually done a bass horn. I think I could do it. I have several papers written on horn theory and the necessary instrumentation to do the testing. |
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| djkib |
Check out Bill Fitzmaurice's AutoTuba design. Could be killer with the right amp and speaker!
Peace,
Keith |
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| danielkelley10 |
in SPL comps ported is virtually te only kind of box used, tuned to the resonant frequency of the car you gain substantially over sealed boxes.
for example i used to run 2 15" subs with 3KW rms and hit 142dB
im now running just one of the same sub and 3KW and hitting 148.6dB(on the termlab sensors) thats about 153-154 on the AC mics
Horns are good for extended low bass output, but the easyest and generally best option is a large ported box with the same sort of area of port as the subs cone area, with a maximum port length of 6-8 inches (the shorter the better, though with lower resonant frequency you may have to sacrifice port area so the length isn't silly long. |
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| Jason Watts |
| At this point I am simply looking at the magnitude of the transfer function for a single fourth order enclosure. I assume the leakage is constant hold the resonant frequency constant to the cab tuning frequency then change the volume until the maximum value of the spectrum peaks out. There appears to be no strict mathematical way of determining the box volume other than what I have been doing. |
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