Technical Subwoofer Question - Chevy Impala SS Forum
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post #1 of 6 (permalink) Old 04-29-2002, 10:27 AM
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I am in the process of building a box for my JL 10W6's and could not remember the specs, so I went to JL's website and downloaded the PDF's. To my suprise they now have specs for 3 different size boxes. Each box is designed for different type desired bass. Here is where my reading went opposite of my thinking. For "Monster Bass" they recommended a box of 0.5cf. For "Normal" bass the recommended a box of 0.65cf. For "Audiofile Bass" they recommended a box of 1cf. I have always thought speaker boxes with more internal volume will allow the speaker's cone to move more than a box with less volume using the same driver. These specs given by JL go against what I thought would happen. My thinking would say that the box with the most internal volume would produce the most sound because the cone is able to move more because the "spring" characteristic of the box is weaker. On the flip side, the box with the least internal volume would control the speaker's cone more, thus limiting exursion and making the speaker "cleaner"

Thanks for enlightening me,
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post #2 of 6 (permalink) Old 04-29-2002, 11:50 AM
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could it possibly have something to do with air pressure? The smaller the box the more air pressure it can build up, resulting is more pounding sound?

I dunno its just a thought!
post #3 of 6 (permalink) Old 04-29-2002, 12:37 PM
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the smaller the box the tighter response the speaker will give and the bass will be alot tighter sounding and louder if you use a smaller box. JL is nuts if they say that you should use 1qf. of space only if you have 12 inch subs should you ever use 1qf. of space. In a bigger box the sound waves bounce around inside more and therefore you loose quality of sound.

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post #4 of 6 (permalink) Old 04-29-2002, 02:52 PM
Aaron D
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BASICALLY, it works like this. Assuming everything is the same ecxcept for varying the volume of the box a SMALLER box will play LOUDER but not as LOW ("monster bass") and a BIGGER box will play LOWER but not as LOUD ("audiophile bass"). "Normal" bass is a compromise of the two and somwhere in the middle.

Cone movement will be less w/ a smaller box but this is immaterial if the driver is operating w/in it's designed limits. The smaller box will be able to handle more power (excursion or movement wise) than a larger box due to it's "tighter spring" as SSQATCH put it. Contrary to what a lot of people assume, monster bass really isn't that low. The bass you feel that punches you in the chest is around approx. 60 Hz which isn't all that low, especially in a car. If you center output in that region w/ the smaller box you will get louder bass, if you add the extra power that this type of box affords you will add to that gain.

To put it in gearhead terms, the enclosure is like a camshaft that determines where the output of the system happens. Like a camshaft you have to decide how you want the curve to look, if you want a lot of high RPM power (loudness) you will have to sacrifice some low RPM torque (low bass).

Finally, JL builds excellent speakers and their reccomendations for their use are accurate for the reasons I mentioned above. Soundwaves do not bounce around in subwoofer enclosures. The wavelengths of sub frequencies are much longer than the enclosures used to contain them, longer than our big ass cars for the most part as well. The subs cone will only work to perssurize and depressurize the enclosure. Higher frequency drivers/enclosures are another matter and will bounce around, to use simple terms.

post #5 of 6 (permalink) Old 05-01-2002, 11:14 PM
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Also... you must consider your amplifier when decididing on enclosure volume. If you are usindg amplification that approaches the limits of the sub, then you should use the smallest enclosure volume recommended. Alternately, you should use the larger recommended volume for amps on the smaller side. It is simply a matter of efficiency. A smaller box resists the cone excursion with its air spring better than a larger one.

Just my 2 cents.
post #6 of 6 (permalink) Old 05-03-2002, 06:30 PM
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My $.02- (Most comments relate to high power and long duration use).
Limiting cone excursion using a small box(smaller than recommended) can cause the voice coil to reach thermal limit faster than a longer stroke due to the air pumping between the pole piece and the former tube that occurs with a larger enclousure(long stroke). A small enclousure also limits the volume of air for thermal transfer of heat generated by the driver. This will cause the internal box temperature to rise quicker, increasing power compression and may lead to faster VC burn-out. Another problem is under powering a driver. The amplifier may clip, causing a rapid VC heat-up with little excursion to disipate the heat.
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