102 db/wM battery powered bicycle trailer subwoofer

[pulexirritans]

I'm working on a battery powered sound system to tow behind my bicycle for bike parties. The idea is to have pseudo club type sound output for 4-5 hours while minimizing the weight of the whole setup.

My current thinking for the sub is 8 of these 10 inch woofers:

10" Ribbed Paper Cone Woofer Speaker 299-284

Specifications: *Power handling: 30 watts RMS/60 watts peak *VCdia: 1" *Le: 1.60 mH *Impedance: 8 ohms *Re: 6.47 ohms *Frequency range: 34-3,000 Hz *Fs: 33 Hz *SPL: 93.15 dB 1W/1m *Vas: 6.46 cu. ft. *Qms: 5.07 *Qes: 0.52 *Qts: 0.47 Xmax: 4 mm *Dimensions: Outside diameter: 10", Cutout diameter: 9-1/4", Depth: 4".

I like these woofers because they're dirt cheap and light, yet still have nice specs. A 2x2x4ft vented box (2 cubic feet per woofer) tuned to 40-45 hz, gives an f3 of ~50 hz, a 3-4 db bump at ~80hz and an output of 102db/w. My past experience tells me this will be a good trade off between perceived bass extension and efficiency (although I could be wrong =).

For power I'm thinking I'll use one of these things:

4x100W @ 4 Ohm TK2050 Class-D Audio Amplifier Board 320-302

The setup would be a pair of woofers in parallel for each channel, lowpass filtered at 200-300 hz. Someone mentioned in the reviews that the amp is good for about 40wpc at 24v with a 4 ohm load, which seems reasonable to me.

Anyway, anyone have any thoughts on the setup? The alignment? Any better ideas?

I thought about using a giant bass horn, but I'm guessing I'd need a way larger box to get decent extension outdoors as well as some expensive woofers with strong motors. I also have no horn design skills....

[mdocod]

Assuming 2x2x4 outside dimensions with 3/4" ply, that's ~11-13 ft^3 for the 8 drivers after driver and bracing and port consumes some space (port might not with some tuning as it can just be a hole cut in the baffle). I modeled it up, looks fine to me. Xmax limited to ~180-200W depending on tuning in the specified range. I might personally be tempted to tune a little lower (25hz) purely for the safety of having the woofers loaded down lower to prevent over-excursion in the sub-30hz arena. (not that I would expect much program material there, but accidental stuff like dropping the pickup or whatever), also, the lower tuning will keep the group delay a tad lower but this is probably a non issue. 25hz tuning will drop Xmax limited Pe to ~140W but that's still going to be a pretty loud sub.

I would be afraid the sub might not have that live music slap you get from more traditional PA drivers, and I am concerned about the weight of pulling around something the size of a small refrigerator behind a bike. Other than that, for the money, it's hard to beat that much oomf for so little dough.

[m R g S r]

Hmmm I might have something you would be interested in. Where in the US are you located??

[pulexirritans]

Originally Posted by m R g S r

Hmmm I might have something you would be interested in. Where in the US are you located??

I'm in the SF bay area.

[m R g S r]

Ohh okay the other coast never mind. I have my beach radio...this would deff rock whatever block you ride your bicycle down lol

[m R g S r]

[pulexirritans]

Originally Posted by m R g S r

Haha! nice. Are those taped horns? And what are you using for an amp?

[m R g S r]

Yupp they're jbell's ss15's!
Alpine PDX class D amps underneath the white portion of the "cooler". Fan cooled amp housing, strictly solar powered fans. The rest runs on 12V batteries...choose whatever size you want (I use two deka 908d's....heavy mo fo's...and not cheap)

[pulexirritans]

Originally Posted by mdocod

Assuming 2x2x4 outside dimensions with 3/4" ply, that's ~11-13 ft^3 for the 8 drivers after driver and bracing and port consumes some space (port might not with some tuning as it can just be a hole cut in the baffle). I modeled it up, looks fine to me. Xmax limited to ~180-200W depending on tuning in the specified range. I might personally be tempted to tune a little lower (25hz) purely for the safety of having the woofers loaded down lower to prevent over-excursion in the sub-30hz arena. (not that I would expect much program material there, but accidental stuff like dropping the pickup or whatever), also, the lower tuning will keep the group delay a tad lower but this is probably a non issue. 25hz tuning will drop Xmax limited Pe to ~140W but that's still going to be a pretty loud sub.

I would be afraid the sub might not have that live music slap you get from more traditional PA drivers, and I am concerned about the weight of pulling around something the size of a small refrigerator behind a bike. Other than that, for the money, it's hard to beat that much oomf for so little dough.

Yeah, I'm also worried about the "punch" or "music slap" as you call it. I think if the port frequency is lowered it will have less boom and possibly less punch. Maybe I can turn the input buffer of the active crossover into a subsonic filter...

I was playing around with some non-optimal vented alignments last year that were similar to this and I was very impressed with the bass. I really feel like some misalignment can enhance the bass without sounding boomy or "one note". One setup was a grosswood gw-6024 (fs = 56, qts = 0.84, vas = 12L ) in a .5 cu/f enclosure (if I recall correctly) and the response was nearly identical to the alignment above except for some odd behavior around -6db. It gave the impression of deep, powerful bass, significantly more so than my old sub which was flat to ~25hz. The only thing is I was listening indoors, not in free space and the speakers were only 87db/w or so...

[pulexirritans]

Originally Posted by m R g S r

Yupp they're jbell's ss15's!
Alpine PDX class D amps underneath the white portion of the "cooler". Fan cooled amp housing, strictly solar powered fans. The rest runs on 12V batteries...choose whatever size you want (I use two deka 908d's....heavy mo fo's...and not cheap)

That's pretty awesome. How does it sound? Ever take any measurements?