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Old 6th February 2007, 09:52 AM   #11
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Thanks for all the replies!

0) Actually this is not for Burning Man, though I might lend it to someone who is going. This is for membership to a bicycle dance gang. (Don't ask...)

1) While I like the idea of adding another amp to the system, I think for simplicity I'd like to try to keep it a one amp setup -- maybe later I'll try another amp. Plus there's something aesthetically attractive about powering this whole thing with 8 AA batteries. I think I'll take your advice and skip on the really low frequencies, if it takes too much power. Dance music is the important thing here.

2) AFAICT, passive radiators are an alternative to porting? The advantage for me being size of box reasons?

3) I can't find inexpensive planar speakers with decent bass. Am I not looking in the right places?

4) I got one "yes" for the Dayton SD215-88 8". They seem to have incredible Xmax (6mm) for the price ($21), and it's a dual voice coil which is great for me (size reasons.) Any other opinions? Or other driver recommendations?

5) A 4th order bandpass will have a pass band top end of around 80-120Hz. Is that going to fill up enough of the low mids or should I go for a standard bass reflex with a port or passive radiator (possibly loosing some low end volume?)

6) You can fit about 3.5-4 inches between your pedal crank arms. I made a box that was about 288 cu in (that takes into account the speaker volume of the fe166e's.) Right now I'm really liking the idea of using the soundpads and cardboard in the triangle (since I already own the soundpads!) and using sonotube for a sub / woofer on the rear rack.

7) I've NEVER designed a crossover. Given the simplicity / cost issues, I'm thinking of what I find on the internet as called "1st order crossover." Given that the 4th order enclosure will roll off around 80-120 Hz already, should I pick that same level as my crossover point? I can't seem to find caps / inductors big enough...what about using the partsexpress "bass stoppers" and letting the sub play full range?

Thanks again! I'll send pics when I make the thing.....

Ben
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Old 8th February 2007, 01:19 AM   #12
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Freak them out with an ice cream bike. paint the ice cream box black and put a huge efficient woofer in there

plenty of space for solar panels or batteries or whatever.

OR you could build an inverted U shaped box that would go on a rear carrier where panniers would be . it could be quite large indeed.
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Old 8th February 2007, 02:30 AM   #13
infinia is offline infinia  United States
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Hi
Some really good and creative idea's on this thread. Using D amps you are way ahead of the game already. Not sure of the sound pads eff. but what ever they end up being, your bass driver should have at least 4-6 dB more sensitivity (open space eats bass)! If not they will sound weak whatever the frequency response, but you could always pad down the sound pads which IMO would be counter productive to the goal.
The 8 in DVC driver looks pretty good and should give good bass in a larger ported enclosure. The sensitivity is not all that good tho at 89 db into 4 ohms is comparable to 86dB at 8 ohms pretty poor IMO. What I would do is look for a smaller PA driver (2x8"?) and build a practice amp type of box (partially open back box) use 3/8 ply frnt baffle with 1/4 ply sides with a few extra braces/cleats.
Driver should >93 db sens wth fs around 50-60Hz Qts around 0.7 or so should be good. Maybe a pioneer or eminence with wizzer cone for almost full range.
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Old 8th February 2007, 02:37 AM   #14
Ang is offline Ang  United States
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as far as planars w/ bass, nope you won't find them. I was saying planars as dipole mids - you can radiate to both sides of the bike. You can use the fps planars found in pretty darn cheap computer speakers or some bohlenders.
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Old 8th February 2007, 04:10 AM   #15
Variac is offline Variac  United States
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Her are some observations. If the prices don't scare you off, you could probably get sone serious noise and decent sound quality from the little amp..

You are making some sense so far. The bass should be in a sonotube and should be mounted on the back rack as you propose.

Places like Whitecap - a contractors supply store will cut pieces of cardboard sonotube I believe. I'm thinking 16" diameter by about 3' long!!!

The main point I think to make this work reasonably is you HAVE to use efficient speakers. If you find some that are say 96 dB efficient at one watt at one meter, they might be eight times as efficient as a standard speaker, ie 1/8 the power required..compared to the 8" you mentioned.. With that little amp it is crucial.

About the only bass speakers that will do this are pro (PA) drivers. Pro drivers in a reasonable size don't really go that low but that's OK 'case most music doesn'trealy go so low. A 10" or 12" pro driver could easily weigh 20 pounds, BUT get drivers with neodymium magnets and that same driver would weigh about 6-8 pounds.

BUt it will cost a couple of hundred dollars. Maybe $150 on sale...

Maybe 98 db efficient!

If that price is too high you could go with regular magnets and get a cheapo at about $40-60 Since it's a cheapo, the magnet will be small and not that heavy..


Then for your mids/ highs- how about a cheaper Fostex fullrange. at about $60? Also very efficient, and you could make an open baffle by just having a 1/2" piece of foamcore or wood inside the triangle, and mounting the driver reasonably on center - a little off is better...
You don't need a box, just a panel.. then sound goes out both sides ,,and the panel is big enough fo you to cover most of the midrange

I'd stick with just one of these drivers too, and run the whole thing mono by combining the channels. You could use one channel for the bass driver and the other for the mid/high driver...Then you use an active crossover to make it abiout twice MORE efficient. The active vcrossover splits the frequencies Before the amp, so is small light and no power is wasted being cut off....

Another brand to look at is Tangband (the TB someone mentioned.- they have small drivers for the mids, that have neodymium drivers also so they are light, and the magnets are small , which will allow sound to easily come out od bothe sides of the bike.. BUT aren't crazy efficient I don't think

If any of these ideas appeal we can fill inthe details....
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Old 8th February 2007, 04:55 PM   #16
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This reminds me when I was at uni and had a bike with a 55w headlight! I had a lead acid battery the weighed ~4kg and could power the light for about 50 minutes.

It's an interesting challenge. Getting bass outdoors is the hard part. The room adds a lot to the bass

For the bass - definately bandpass - 6th order. You want a dual VC driver so you can use each channel of one amp to power each VC. You can't really get much real bass, so instead you probably want to put a bit of a peak in at around 60 Hz. For the box, think cardboard cylinder, with hemisphere ends and for the driver baffle (internal) plywood. You could make the hemisphere ends out of paper mache with a layer of fibreglass for rigidity. The above will give you the maximum output and the lightest box. You might look at a driver with a neo magnet. Consider total driver weight.

For the satelite, I'd go with a driver rather than a soundpad. If you want no box, then you can use a driver without a box - open baffle. Give it a cardboard baffle and reinforce it with ribs and cardboard if you like. Fold wings, perhaps balsa wood reinforced with fibreglass.

I'd put the sub on the rack behind and put the sat above it, the closer it is to you, the better. Moving it from 1m to 0.5m means 1/4 the power.

For the sat, why not keep it simple? Look for an efficient fullranger, it will make xo easy. Add a tweeter where it rolls off, if the fullranger can get to 10k then just do a simple highpass first order on the tweeter at that point.

Use one channel of the 2nd amp for the tweeter, one for the fullranger. To save power, how about passive line level filters?

Look for a fullranger with a fairly high fs. What you want is efficiency above 120 Hz, say an 8" driver. Then you put it in a vented box where the vent is needed to get it down to the xo point, say 120 Hz. Ideally you want a driver that will actually need to be vented as it will be more efficient above that point. For the box I'd use materials like a cardboard cylinder, balsa wood, paper mache, ply and fibreglass reinforcement.

An alternative is ditch the tweeter and use two fullrangers that can get up high. They would probably be smaller, and having two brings the efficiency back up.

Now that I look at some sims, I see that with that 8" driver a bandpass doesn't easily gain an advantage over vented. You could just use it in a 12L vented box tuned to 50 Hz. You can get 100 db @ 40 Hz! Not bad, that's with 25 watts from one channel. Use the other channel for a fullranger like a tangband, or a few to get the right efficiency. Ideally you would use a passive line level to save power.
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Old 9th February 2007, 04:27 AM   #17
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Forget the box, the weight isn't necessary. Mount one of these http://www.musicsupplycenter.com/Pro...Code=100%2D186 on the end of a 20" sonotube open at the other end. Stuff the pipe with polyfill. Sure it will be directional, but so are your mids and tweet. If no more of the $15 units are availabe, you'll have to pay $35 for regular ones. Cheap, efficient, easy, lightweight and plenty of great sounding OB bass with an Fequal less than 60hz and an F3 of about 45hz.
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Old 9th February 2007, 05:17 AM   #18
Ang is offline Ang  United States
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want to second johninCR's woofer suggestion - looks great for the price
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Old 9th February 2007, 06:57 AM   #19
Variac is offline Variac  United States
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That's what we needed - some practical advice. And the efficiency is probably more than the full range you should be getting for the mid/highs, which will prob work out about right!

If you mount the tube across the bike then it will be pointing the direction that the mid/high driver is also pointing. On the other hand the rocket look with the cone facing backwards would be totally tempting.

HOw about the rocket look, but the baffle in the frame is mounted so you could swing it out perpindicular to the bike ,ie the mid/hi driver faces same direction as the woofer faces, when you are stopped.


Looks like you'll need a small frame with a tall seatpost so you can step over the frame to get on!
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Old 9th February 2007, 02:30 PM   #20
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Too bad this didn't come up last week. I would have recommended 2 of those woofers. They run up high enough to cross to a tweet, but in the U config it may get too resonant up in that range. Really stuffing it may handle the pipe resonances, but you'll end up with at least one strong null in the 300-400hz range with a straight ended pipe. Cut the pipe end at an angle making one side about 2-3" longer. ie Driver end square so the driver fits squarely in the end, and the driver baffle to other end ranging from 20" to 23" due to the angled cut at the other end.

Then at the shortest part, cut a K-slot shaped curved triangle that starts at about 5" wide and is 5" deep, so instead of 20" that short side tapers down to a point at 15-16" from the baffle. This shape with some stuffing will really smooth out the resonances enough that all you need to add is a tweeter, not audiphile sound but pretty darn good. A 1st order XO may cover you.

If you use one of those bullet tweeters like this http://www.partsexpress.com/pe/pshow...number=272-115
and stuff 6 pencil eraser sized pieces of foam rubber down in the throat around the bullet plug to tame the harshness. Add an L-pad to balance the output of the tweeter, and since it already comes with a cap, the only thing else you might need is a choke on the woofer.

Last week, when there were plenty of woofs for $15 you could have done stereo, hanging 2 tubes off the sides of the bike rack like a pair of rocket engines. One or 2 doesn't matter, and you'll end up with a cheap, lightweight, high output system that will blow the socks off of something using the little panel speaker.
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