Posted by Wayne Parham [ 65.69.120.70 ] on April 19, 2004 at 16:01:32:

In Reply to: 8 Pi with Alpha 10 posted by Skip Pack on April 19, 2004 at 15:09:22:

The eight π loudspeaker will use an Alpha 10 for bass and midrange, and a PSD2002 for treble. The cabinet is shaped so that it sits nicely in the corner, but does not require corner placement. The Alpha 10 will act as a direct radiator below horn cutoff.

There were two implementations I had considered. One was to use a relatively small back chamber for the Alpha 10, so that the system was underdamped. An example is to use a 1ft³ back chamber port-tuned to 75Hz, which would give about 5dB peaking to increase bass output. This could be used to extend output of the midhorn down to 75Hz.

Another solution was to use a reflex alignment that gave flat response, but this would then provide stepped response sort of like EBS. Output would be reduced below the cutoff frequency of the midhorn, forming a bass shelf that was flat down to reflex cutoff. Personally, I prefer this latter solution. I've decided on 5.5ft³ volume, port tuned to 35Hz. This will provide flat response down to 33Hz from the reflex system.

The π crossover that has been developed works very well in this configuration. The tweeter circuit is the same 3rd order with compensation that is used elsewhere, and the midwoofer circuit uses a small series coil to shave just a bit of the top end. The midwoofer is also padded with a couple of resistors, and a large value bypass coil is also used to remove attenuation at the lowest frequencies.

Overall, I think it makes a very pleasant system, both in sound quality and aesthetics. I've already made a sort of prototype, in that I've connected the midhorn to two π tower loudspeaker. I then disconnected the piezo tweeter and connected a compression horn, placing it physically so that the mouth edges were flush. In short, it was pretty much the same thing as the proposed eight π speaker, but shaped differently. Back chamber volume and port tuning were as specified. And man, it really sounds great.

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