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....
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....
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.
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.
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Ohh okay the other coast never mind. I have my beach radio...this would deff rock whatever block you ride your bicycle down lol
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)
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)
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...
Out of curiosity, what sort of power source did you have in mind to deal with 4-5 hours of "party" in an off-grid scenario? By my calculations, that would require something like 1-2KWH of stored energy. Or, roughly 150 x 18650 size lithium cobalt cells. Or, about $1000 worth of battery pack if you are lucky.
I am thinking to myself, that perhaps the way to achieve this "battery powered" party on a budget, is to go with even more box size, really maximize efficiency, and lower powered amplification. As much as I hate to ask, How much "speaker box" do you think you can safely pile on a bike trailer?
I am thinking to myself, that perhaps the way to achieve this "battery powered" party on a budget, is to go with even more box size, really maximize efficiency, and lower powered amplification. As much as I hate to ask, How much "speaker box" do you think you can safely pile on a bike trailer?
Time to get real...
How much weight do you plan or want to tow? You would need active braking on the tow trailer or that weight will push you into a nice accident. A couple big tapped horns properly built for low response are going to be very heavy, plus the amp power source and mid and high drivers & cabs. I believe you should rethink your plans. I'd consider a couple ordinary ported cabs. Use a low Qts driver to keep the size reasonable and don't tune real low.
How much weight do you plan or want to tow? You would need active braking on the tow trailer or that weight will push you into a nice accident. A couple big tapped horns properly built for low response are going to be very heavy, plus the amp power source and mid and high drivers & cabs. I believe you should rethink your plans. I'd consider a couple ordinary ported cabs. Use a low Qts driver to keep the size reasonable and don't tune real low.
If the power was split evenly at 350hz or so (see: BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1) and I was using 40wpc x 8 channels at 90% efficiency I get 355w/hr. Over 5 hours thats 1775 watt hours, or 74 amp hours using 2 12v batteries. The smallest johnson controls lead acid trolling battery just happens to be 75 AH and is sold for ~$60 at costco and walmart. I think they weigh about 60lbs each....
So you're right, if I double the box volume and the weight gain is less than one lead acid battery it could be a worthwhile. The only bad part it 35ah batteries cost almost as much as 75ah ones. Maybe I could just use one 12v with a DC-DC converter =)
The box could be made out of polystyrene and luan sandwich to save weight:
http://www.boatdesign.net/forums/at...olystyrene-xps-xps-foam-doorskin-sandwich.jpg
I've carried about 150lbs on a cargobike without a trailer, and that wasn't bad. I'm thinking 200lbs would be ok, but if I can keep it down to 150lbs that would be nice (although unlikely with trolling batteries)
see here:
How Much Weight Can A Bike and Trailer or Cargo Trike Carry?
Most audio has around a 10 dB (or better) dynamic range, so you only draw on average 1/10th the power of peaks.
Assuming a 90% efficient amp, and 1000 watt peaks, average power draw is only around 110.1 watts.
1000 watts in to 100 dB 1w 1m speakers is 130 dB, enough to make dancers happy, and pee off everyone else.
To avoid power compression, which can rob half that power, multiple drivers rather than a single or two TH is probably a slightly better approach, though the difference will be slight. Driver weight vs construction material weight is of course the decisive factor, if cost is not a consideration.
A BR cabinet can directly be crossed to a horn tweeter, $15 gets a Foster horn of 105 dB or so, the TH will require mid drivers and HF drivers.
I have an Electric Paddle boat motor that happens to draw 100 watts.
Power consumption was less than expected, the 100 watt motor on full power for 2 hours, pushed my boat four miles, and voltage only dropped to 12.48 and 12.49 on the two 22 AH AGM batteries (35.28 pounds for the pair), leaving them around 90% charged after a recovery period.
Spend the extra on AGM, they have better discharge capability than standard LA batteries, and also take the bumps much better, and require no maintenance.
From what I figure, you should have no problem running 5 hours with less than 50% discharge, which prolongs battery life.
Art Welter
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