13BRX

When installing 2 12inch subs would there actually be any difference in putting them in seperate enclosures as opposed to a common enclosure? In sound quality or SPL.

LoveBone

Do you mean sound-wise? If so, no, not at all. Just the way you wire the subs would be different.

13BRX

How do you mean wired differently?

DamonB

It is preferable for each sub driver to have its own airspace and not share it. This prevents any slight distortion in one from effecting the other. It also makes for a sturdier cabinet in that there is now a "wall" inside. I feel that is reason enough to seperate them.

SPL is completely unaffected either way.

rynberg

I completely disagree that sound quality and SPL will be unaffected.

Assuming the same size enclosure, placing a divider in the box will half the volume each driver sees. This will make the driver roll off faster -- less low frequency output and less overall output. You can achieve the same enclosure rigidity by using a divider panel that has large slots or perforations to allow free air movement.

I do agree with DamonB that the distortions of each driver will effect the other. That's why the "push-pull" method used by M&K works so well. Not practical for a car enclosure though....

DamonB

This is incorrect. Each driver is ALREADY seeing half the airspace because it must share it with another driver. The enclosure volume is basically determined by comparison to Vas. Vas is an equivalency of air volume as compared to the driver. Two drivers in the same enclosure merely means that the Vas is doubled, so the enclosure is twice as large as it would be for a single driver. No difference in rolloff or SPL.

Now if you put two drivers inside an enclosure sized for only one, your statements would be correct.

Multiple drive enclosures are very easy to make. You compute the volume for one driver and then just multiply it by how many drivers you intend to use. A two driver enclosure is twice as big as a single. A three driver is three times as big etc. This is again because the enclosure volume is in direct proportion to Vas of the driver(s). Fs is an inherent quality of the driver and cannot be changed without mechanically altering the driver. Fb is the rolloff of the driver/enclosure combination and as such Fb can be tuned with different enclosure alignments. Again though volume is still directly proportional regardless of how many drivers you are using.

This can all be modeled and easily proven.

DamonB

Those two drivers do not share the same enclosure; that is an isobaric configuration. What this allows you to do is basically couple two drivers together mechanically and electrically and so drive the enclosure as if the two drivers were in fact one. This leaves the enclosure size half as it would be for a single driver because Vas for the driver combination is now halved since the cones and suspension are basically united, so again enclosure volume is halved in direct proportion. As for efficiency it is only half as efficient because only one driver is contributing to sound output. The advantage of an isobaric is higher power handling and slightly less distortion, but for no net gain in sound output. Therefore it takes twice the power to achieve the same output as a single driver.

This is easily modeled and proven too

Vance Dickason's Loudspeaker Cookbook. Buy it. Read it. Experiment with it. Build it. Love it.

rynberg

Damon:

Actually the "push-pull" mounting method I referred to is not a compound (iso-barik) design. The two drivers share the same volume but one of the drivers is mounted "backwards" -- so that the magnet end faces the exterior. That driver is wired in reverse polarity. So both drivers operate in phase but in opposite directions. Therefore, much of the distortion (2nd order) generated by each driver cancels each other out. This configuration has some of the advantages of the iso-barik mounting without the efficiency penalty.

Going back to the original issue, I understand what you are saying. I think I just looked at the original question in a different way than you did....