DA Atkins:

Believe it or not, I have been paying attention to your post for the past couple of days. Unfortunately, I have not been able to post anything.

I am unfamiliar with the driver in your link. I have been going through the database of WinISD to find a suitable substitute. I found a couple, but there are problems. The Fujitsu Eclipse 86080.4 and the 8708 4 ohm have promise, but the sensitivity is listed as 84 dB, which is sufficient. However, BoxModel, which calculates sensitivity based on Thiele-Small parameters-it is usually accurate-says the sensitivity is really 80 dB @ 1W/1M. That is too low.

Then there is the Polk db 8.8, but lo and behold, that is last year's model and may not be available. And Polk's new models are a ten and a 12 only.

Gimme time, I'll keep looking.

The reason I am doing this is that I think you have an interesting challenge. The question I feel that you are really asking is: How low can you actually go in a .6 cu ft enclosure? And I think it is a question actually worth answering.

A few observations. The speaker is in a sealed box of .6 cu ft, and the amp driving it is between 50 and 80 watts. In a sealed enclosure, the speaker has to move all the air necessary to produce bass-the enclosure has no output. Forget about an 8" in a .6 cu ft. sealed enclosure having usable bass output down to 15 Hz. Whatever such a speaker can put out at 15 Hz, it will be too low to be worth anything. Try 30 Hz.

Even 30 Hz is daunting. According to a chart provided by Small, (of Thiele-Small fame), it takes 6 cubic inches of air moved to produce 112 dB @100 Hz. For every half octave you go lower, you need twice as much air moved. For every 6 dB you raise the SPL, you double the volume. For every 6 dB the SPL goes down, you cut the volume of air moved in half. Using these formulas, we arrive at the fact that at 30 Hz, a speaker has to move 33 cubic inches of air to produce a 30 Hz note @ 106 dB.

The volume of the air moved is the area of the speaker, (Sd) times the excursion from the midpoint to the position all the way in front, (Xmax). If Xmax is given as peak-to peak movement, divide that figure in half to find the real excursion.

An 8" speaker has about 32 sq inhes of area, so it has to move about an inch to produce that 30 Hz note @ 106 dB. Incidentally, your link says that the speaker in the MJ subwoofer has an excursion of about an inch, midpoint to back. Whether it ever gets to use that excursion is another question.

To me, a 30 Hz that is played at 102 dB is barely hearable. Any SPL below that, and the note will not be noticeable. I think it is realistic to concentrate on 30 Hz as a cutoff for a small box.

For a speaker powered by 100 watts to get up to 102 db, then at one watt it must be at 82 dB SPL. An SPL any lower, and a 1100 watt amp cannot drive it up to 102 dB.

Am I making sense so far?

All I am saying is that for you to get hearable bass out of your .6 cubic foot box, your UNEQUALIZED curve at one watt better show that your speaker is playing at least at 82 dB @ 30 Hz. Otherwise, it is a waste of time.

A ported or bandpass speaker, because the enclosure adds output, is much more likely to fulfill these requirements. If I find a subwoofer that puts out 82 dB @ 1W/1M in a .6 cubic foot box, I will certainly let you know. Right now, so far the only ones I have come across can fulfill that requirement can do so only in a ported or bandpass enclosure.

I should also point out that a speaker in a ported or bandpass box can produce 102 dB @ 30 Hz while using MUCH less excursion than the sealed box. An 8" sealed box woofer must travel 1" forward and 1" back to produce that note at that volume. An 8" in a ported box can travel only .25" to produce it. A bandpass box can travel about .5" to produce it.

So your choice of drivers is enhanced if you go bandpass, ported, or passive radiator, (ported's first cousin).