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Old 1st July 2009, 07:47 PM   #381
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Join Date: Feb 2006
Location: Chicago, IL
Yes, it really is that simple. Two amps might be enough, but sometimes with bigger capacitors on the power supply especially, you might get a rush of current that might blow the fuse, but you can always go to a higher-rated fuse if that's the case.

Go ahead and hook everything up and see how you like the sound. These kind of projects are real simple from an electronics point of view--it's not like designing some new kind of amplifier. Let the amp burn-in for a few days and see if the speakers are OK. You can get a pair of the cheap piezo tweeters and add them to see if you like the sound better.

Just messing around until you get things sounding better to your ears, that's the fun of these projects.

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Old 2nd July 2009, 12:38 PM   #382
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Join Date: Jun 2009
Originally posted by Gaichuke
Yet another question...

This time regarding the bipolar design in boominator. It's true that you get almost 360 degree of music blasting, but you can only be on one side of the thing itself.

So doesn't this design "waste" half of the power because you can only music mostly from two speakers at a time?

Or does the increased sensitivity of bipolar design cancel this?

I'm now contemplating on bipolar design, but I'm afraid that I'm loosing half of the power to the people behind the boombox.

What do you think?
Can someone answer this please?

Construction will start tomorrow and I'm still undecided of what I'll do.
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Old 2nd July 2009, 12:54 PM   #383
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I'm not a big expert on bipolar speakers but I do have a pair of dipoles in my living room.

A lot of that sound coming from from the back speakers is not wasted. It rolls around the box t5o the front and also bounces off any flat surfaces behind it and that bounced sound tends to create a much wider field of sound than you otherwise get from a pair of speakers close together. If you are worried about it, it should be easy enough to put in a switch that will let you turn off the back pair(s) of speakers when you want to. You could actually use a three-position switch and change the polarity as suits the situation.

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Old 2nd July 2009, 01:06 PM   #384
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This would be in outdoors, so I doubt there is that many flat surfaces for sound to bounce off.

Second one is automatic bass compensation; try placing a normal speaker outside on a grass field and play something, now as you walk around it you will find that on the opposite side of where the speakers are facing treble and midrange will be lower than directly in front of it, this is because the air works as a gentle acuostic filter of higher frequencies but letting lower frequncies pass. Now in a bipolar design you add the response of the front facing driver with acoustically filter back facing drivers and thereby get a completely free bass boost.
Based on that I guess it's not a total loss at least.
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Old 2nd July 2009, 01:12 PM   #385
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I think once you have a fine portable stereo in your hands, you will find yourself taking it everywhere, using it in many, many places, not just in a wide open field.

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Old 3rd July 2009, 10:47 AM   #386
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Join Date: Jul 2009
Default Marine speaker suitability?


Given that my system will be used primarily on a boat, I was checking out Marine speakers as being an option.

I found the following specifications for some 6" and 6x9", high-sensitivty Dual marine speakers which sound like they would be OK, though clearly not in the same size range as the P Audio HP-10W woofers.
Looking at the DMS655SM, the DMS692 and DMS 652.

Can anyone comment on their likely suitability for such a project?
Benefits would be:
-durability to elements
-smaller size/weight/enclosure required
Costs would be:
-Decrease in bass/sound/volume

Oh, and thanks buckapound for the previous reply.

Any info appreciated
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Old 3rd July 2009, 05:54 PM   #387
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Originally posted by whelibob
ZOTA, nice looking ghettoblaster. Which speakers have you chosen?

Anyone here done a ghettoblaster with 24V? im planning on going for it with sure-electronics 2x100W amplifier, but i noticed a problem. While using two 12V batteries in series, the voltage of the other battery always drops faster then the other ones. Any way gettin around it?
If i use the batteries in parallel and buy a 12V to 24V DC/DC converter, will it work properly or do the converters have a very bad efficiency?
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Old 4th July 2009, 07:25 AM   #388
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In boominator design, are the speaker magnets really touching?

Or is that the case only for boominator? Does the bipolar design require this?
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Old 6th July 2009, 07:31 PM   #389
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Let see ...

I chose 150 Ohm resistors from listening tests. I originally used 133 Ohm resistors but the piezos overlapped the woofers too much. Please note, that I have explained earlier in this thread how piezos work and how to calculate the resistor value if you use other piezo than those I use.

Yes, the magnets really touch eachother, they're actually glued together. As I already explained this design is entirely based on that because the structural strength with a centerbrace and the speakers themselves is so much rigid than a traditional design that you can use much thinner, and thereby light materials.

I chose 82 Hz because calculations showed 80 Hz was optimal, so a tiny overtuning is ok plus it makes up for cabinet might be a bit less closed than expected from for example from a slightly bad glueing or the cable holes not being completely siliconed.

Maybe I should try to start a new thread with all the questions (many of which a the same) answered.
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Old 7th July 2009, 07:47 AM   #390
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Welcome back Saturnus,
I hope you enjoyed Roskilde this year as well.

About my questions... damn, I guess I'm still too ignorant with this stuff.

I mean, I've read this thread through several times already and I recapped the ones where you talk about the piezos, and I still don't get it. I've now reach the conclusion that the resistor choice for the piezos depend on the capacitive property of the piezo element itself, but I have no idea how to calculate it.

I think I got the 0.22 mH coil choice now though, if I use this formula,

4ohm = 2*pi * F * 0.00022H

F = 2900Hz

So the crossover point for the drivers is roughly 3000 Hz, right?

Most piezo horns have a sharp peak in the 2KHz range and then a deep dip in the 3-4KHz range before becoming more linear above about 5KHz. Generally it's that initial range peak that account for most of the bad qualities in a piezo horn, so generally they should just be used over 5KHz. Luckily that's an easy fix. Just add a series resistor. That will work a highpass filter in itself and at the same time make the piezo a reasonable load for the amp since a piezo is a capacative load the equation is exactly the same as for a normal 1st order highpass but instead of calculating the capacitor, you calculate the resistor value you need. R = 0.159 /(C*f) R = resistor value in Ohms C = piezo's capacitance in Farads f = desired x-over frequency in Hertz(a good starting point is 3.5KHz).
edit: found this from an another thread. Too bad that the manufacturer doesn't tell me the capacitance of my piezos.
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