Wednesday, June 29, 2011

Small Subwoofers Project

I picked up a couple of cheap 8 inch subs to help fill out the bottom end in my RX-8. Not sure yet what the install will be, hoping they will fit between the back seats in an IB configuration.



I remembered seeing an image of a driver installed in this location on the RX8Club.com forums, but couldn't remember whether that install had used one or two drivers. With a little googling, I was able to locate the thread about the installation, which included this image provided by the guys who did the install (MotorMusic, Inc, who appear to be based in Oakland, CA).

The stock configuration looks like this.

And with the pass-through cover removed.

When I picked up the speakers I had intended to install both in this location, because I thought I remembered seeing an install like that. While the space is physically large enough to fit both drivers there (particularly if mounted basket-out), the layout of the plastic would make it a pretty tight fit. It would be possible to strip it out that stuff for a fully custom install, but I'm not going to get that deep into it.

From this it appears that if I want the driver facing into the cabin here without a lot of work, it'll need to be a single driver. There are a couple of other installation options to consider though.

A 4th order bandpass with the speakers in the trunk with a shared vented chamber ported through the passthrough would allow me to use both speakers, but would require a lot more space. This isn't necessarily a problem, since I'll probably have to remove the spare in any case and will likely have more trunk space even with a bandpass box.

Stacking the drivers in an isobaric configuration would reduce the sealed box size from 0.5 cubic feet down to about 0.25 cu.ft. I'm not all that interested in this configuration for one and only one reason: power. Isobaric configuration trades a driver for box size, and I hate to trade half of the possible output power for a quarter of a cubic foot.

A more typical configuration for this car would be to place the drivers at the sides of the trunk in sealed boxes.
I'm a little hesitant to hide relatively low powered drivers in the trunk though. Might have to stuff the spare 12" box in there and see how it sounds.

To test fit the driver at the side of the rear of the trunk, to verify that i would have enough volume to meet the recommended 0.5 cubic feet spec, I cut a cardboard panel to fit where the front baffle would be.
This defines the space and lets me see what the speakers will do to my available trunk spack. To estimate the volume I filled the cavity behind the cardboard with packing peanuts.
I then transfered the peanuts to a rectangular container to calculate the volume.
In this case it worked out to 0.8 cubic feet. That is a good start. The front baffle will be 3/4 inch MDF, and so ends up taking up about 183 cubic inches. Combined with the 10 cubic inch displacement of the driver, this reduces the space to 0.69 cubic feet. This will be reduced somewhat by the fiberglass shell and bracing, but it looks like it will work out quite well. I will still need to mount the amps somewhere. I think the best place for these is going to be on the backs of the seats. Thay will be way back out of the way that way. This configuration will let me keep my spare tire.
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