Newbie Question(s)

[Aetius]

I recently took a speaker design class and ended up with the following pair of bookshelf loudspeakers. They're built with one Dayton RS-150-8 and one Dayton RS-28A-4 per box and have the response curve attached.

The next logical step would seem to be to build a subwoofer. Ultimately the system will mostly be used as L-R-Sub for TV and movie watching, with music occasionally thrown through the system. I'd also like to build it with room to add a center channel and two back surrounds if I so desire, but have no immediate plans to do so.

I'm pretty much looking to build a moderately priced subwoofer that'll get decent bang for the buck that'll complement these bookshelves. I almost never blast sound, so as long as they can provide decent volume power isn't a big issue. That being said, I'm at a bit of a loss as to where to begin. How to select the right driver, plate amplifier and so on; any special things to be aware of in box design and construction.

sidenote: I don't have an amplifier yet, so in that regard the system can be designed for any amplifier within a reasonable price range.

[revboden]

what SPL range do you want? how much room do you have for a box? how large is the room?

[Aetius]

The bookshelves are rated at 86-87 dB, and when I tested them the other day they were providing plenty of volume without pushing the receiver very high, I'd probably be looking for a subwoofer in the same range.

The room is as yet unknown. I'll be building these when I have some free time this summer while job hunting, and the job I get determines where I live and so on.

Subwoofer size is flexible, something under 2 feet cubed would be ideal, probably closer to 1.5 feet cubed.

[chris661]

Some more questions.

How low do you want this sub to go (a decent pair of headphones can give you an idea)?
And would 2 subs be out of the question? Having stereo (or dual mono) subwoofers flattens the in-room response considerably, due to a more even excitation of the room.

Can you measure the SPLs you listen to at listening position? Alternatively, any ideas how many volts the speakers see? 2.83v at 8ohm = 1 watt (per channel).

So for a pair of speakers each receiving 1w, one speaker at 1 watt = 87dB. 2 speakers at 1 watt between them = 90dB. 2 speakers with a watt each = 93dB.

All those figures are much louder than one might think - I've seen recommendations of >100dB @1w speakers for a low power valve amplifier (this would be 106dB with each channel seeing 1w). Though 90dB continuous will permanently damage your hearing.

Personally, I'd get a couple of decent 10" drivers, give each a sealed box and eq to ~30Hz. Frequencies lower than this require lots of air movement. 40Hz is an easier goal, and would be easy enough with a pair of 8" drivers.

Chris