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Old 3rd January 2007, 02:50 PM   #11
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Quote:
Originally posted by Magicdj
That Podzuma in the "stock" form should be ~ 107 SPL. Bump it up to 30 watts per channel, now your in the area of 112 SPL.
Whoa! Slow down. You can't just look at the nominal efficiency and power and determine spl. The Dayton driver used in the Podzuma is a 5" driver with 1.5mm xmax. In a PA application this driver would probably be crossed at 800Hz or so, and could then play pretty loud. As a full-range driver it simply doesn't have the xmax to do much - it'll do 100dB at 200Hz, and about 80dB at 60Hz. (per driver - add 3dB for a pair)

So, adding more power to the Podzuma is a pointless effort. If you want something louder you have to completely re-design the entire project, and to be honest expecting 110+dB from a 'boom box' is wildly optimistic.

For reference, I own these speakers. http://www.yorkville.com/products.as...&cat=38&id=254. These will in fact play at 110dB+ from 30W from about 60Hz on up, and I certainly will not be volunteering to carry them anywhere.
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Old 3rd January 2007, 05:20 PM   #12
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One strategy would be to use multiple smaller (2 x 4-5" per channel?) with lots of extension for the bass, and use one amp channel for each bass driver and each tweeter, perhaps even a midrange. That would get your total wattage up.

--Buckapound
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Old 3rd January 2007, 07:21 PM   #13
Magicdj is offline Magicdj  United States
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Sorry, yes at 3ft... The speakers are P.A. type speakers (with muiltple drivers). I may even to go to a compression horn. It's for projecting sound in a large area.

My wife is a cheerleading coach, when they are on the road her girls have trouble hearing those "off the shelf" boom boxes. I bought the biggest and baddest one made (JVC Kaboom) and still dosent cut it (around 101-102 SPL @ 3 ft).

Any ideas would greatly help.
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Old 3rd January 2007, 08:18 PM   #14
Pano is offline Pano  United States
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Well it's a cool idea, just hard to make it battery powered and small. Think how much power is needed to get 112dB at the mix position for a concert. And the size of the rig...

There was a guy last year who wanted to build a backpack boombox for his inline skating groups. Seem like a lot of them do, and they use car amps and speakers.

What you really need is a JBL Eon 10". Not battery powered, but it would be loud enough and is easy to carry. And it's easy to add more. Plus it has a mic input so your wife can get on the horn and tell the girls what they're doing wrong.

You should be able to find then used at a decent price. Really a good option if you can get AC power.
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Old 3rd January 2007, 08:48 PM   #15
Magicdj is offline Magicdj  United States
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I'm just using 112 SPL (peak @ 3ft) as a target goal. I realize I won't get thumping bass from a small box. It will be more like mid-bass mid-range for throw.

I do have some powered speakers I use on ocasion (FBT http://217.58.3.195/intranet/Inglese...-100/index.asp
) along with Mackie SRM 450's... But using AC is a pain some times

I'm thinking about using http://www.partsexpress.com/pe/showd...number=290-020
Speakers instead of those Daytons. They are much lighter and higher SPL (95 1 watt 1 meter). They don't go very low (150Hz) but for what I will be using them for it's not a problem. Compression horns around 101-105 SPL. Hitting 112 SPL, should be a problem. The only grey area is the 12 volt AMP
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Old 4th January 2007, 12:40 AM   #16
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I'm working on a similar project. It's in the planning stages still. Battery powered + high volume levels. My project will be quite a bit larger than a boom box, but it might give you some ideas.

Speakers:
Cyburgs Viech
Beyma 8AG/N horn or "the Viech"

These are 8 ohm, 96dB @ 1W/1m and go down to 50Hz. The Beyma driver in these goes from 60-18KHz according to spec. At least they seem to go lower than the 5" Dayton driver. Cheap driver, too.

Tripath amps give a bit more power with the same voltage with 4 ohm speakers compared to 8 ohms. There's a 4 ohm version of the Beyma driver available. Might be something you'd want to look into. According to the designer of the Viech, it peaks out at 120dB.

Also, what about paralleling two 8 ohm Beyma drivers per channel? Wouldn't that make the amplifier see them as a 4 ohm load? Should get you to 99dB at the first watt.

Dunno if that's any better than the Podzuma though. Just thinking out loud here.

Here's a wild idea:
41hz Amp9 ("Outputs can be paralelled for even higher outputs into very low impedance loads, Mostly hole mounted components. Relatively low component count.", says the page.
4 paralleled 8 ohm Beyma drivers Unless I'm getting this all wrong. Wouldn't the amplifier then see that as a 2 ohm load? Should get you some useful volume out of a low-voltage supply.

Unless I'm completely wrong, which I could very well be!
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Old 4th January 2007, 12:48 AM   #17
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One more car amp.
Look for a Blaupunkt PA2150 - discontinued but it is a tripath. Here's one:
http://techronics.com/index.cfm?fuse...1110&aff=72182
I've seen them cheaper.

You'll be sorry if you cut the bass - it won't be a boom box.

Speakers can make a big difference. A few DB of efficiency can make up for a whole lot of wattage. Look into horn loaded designs. check out http://www.billfitzmaurice.com/

Or look into line arrays. Using the Galaxy in a line array may be the ticket.
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Old 4th January 2007, 02:21 AM   #18
v-bro is offline v-bro  Netherlands
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Quote:
Originally posted by kristleifur
Here's a wild idea:
41hz Amp9 ("Outputs can be paralelled for even higher outputs into very low impedance loads, Mostly hole mounted components. Relatively low component count.", says the page.
4 paralleled 8 ohm Beyma drivers Unless I'm getting this all wrong. Wouldn't the amplifier then see that as a 2 ohm load? Should get you some useful volume out of a low-voltage supply.

Unless I'm completely wrong, which I could very well be!
I think you're right, I have an AMP9 low profile (12V) version that produces about 30W/ch. from 12V... I also have an Audiodigit class T MC4x100 which is about the same amp (same chip).. Amp9 costs only 49EUR. and sound fantastic from 12V supply....

And the four outputs can be parallelled for more power...

Amp9 in test:
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Old 4th January 2007, 09:46 AM   #19
Pano is offline Pano  United States
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Quote:
Originally posted by kristleifur
The Beyma driver in these goes from 60-18KHz according to spec.
I can't find that driver on any English language site, not even Beyma. Is it still current?

FYI, yes, 4 ohms is a good idea. The T-AMP can supply more power at 4 ohms than 8. But be careful of the SPL rating. Often it is given at 2.8 volts for 4 ohm drivers. That's 2 watts, not 1.

Putting two 8 ohm drivers together will give you a lot more SPL for the same voltage. That's what I do with T-Amps. Do you have room for that.

I'd stay away from the Galaxy driver unless you can find someone who has used it and likes it. On paper it looks awfull. Don't know what it sounds like.
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Old 4th January 2007, 06:14 PM   #20
Xspunge is offline Xspunge  United States
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What type of batteries are you using to power that boom box? I would suggest 12v Sealed Lead acid. They are cheap, can supply enough power for just about all amps (especially the Tripaths) but they are heavy. I would also suggest Li-Ion or Li-Polymer since they are much smaller and lighter, but of course are much much more costly.

I can assure you that if you are using Alkaline batteries with that JVC then it will start to clip and distort at high volumes. And to make matters worse when the batteries run down the max volume decreases and the clipping starts at lower volumes until the batteries run out. You also have to figure in the high cost of constantly replacing those things.

I use Li-Ion batteries for my DIY pack. You can expect real world voltages 12.4-12.6v from a 3 cell pack, or 16.8v from a 4 cell pack. The big advantages of these are the much smaller size and weight. The drawbacks are their costs and the requirement of special chargers. The fire danger is there, but only if you over charge them, and most chargers nowadays have voltage cutoff. You can make them with as much capacity as your budget allows. You will need a 3s 2p pack if you want something in the 4AH range, which is what mine is. 3 Li-Ion cells wired in series to yield 12.8v, and then paralleled with a similar 3 cell pack to double the run time. Currently it is 4800mah or 4.8AH and 12.6volts and it weighs in the neighborhood of 200+gm and is only a

You can make higher or lower voltages with a voltage regulator like an LM317 (available at your local Radio Shack or other component store) but the drawback here is that it will limit the current and not give you full volume. At least my unit did.

Anyway I have made a homemade boom box which is portable, and it gets loud. I used a Tripath based chip amp from www.41Hz.com, which has been suggested already. They are much better than just about any standard amp in any factory made boom box since they are audiophile quality. If you start with a better amp and a better powersupply than alkalines you will get a better sounding DIY boombox.

You can take a look at the one I made here.

http://s101.photobucket.com/albums/m59/Xspunge/

The thing you probably already noticed with your JVC boom box is that once you take it out into free air, the volume drops considerably. So in the store or home, that boom box is more than loud enough, but once outside on the practice fields, they lose a whole bunch of volume since there is nothing for the sound waves to reflect off. Add background and ambient noise and you hear even less. Still with all these factors mine is actually pretty good, even at relatively longer distances. I use 4 ohm drivers, mids and tweeters hooked up to a 3 way crossover.

Some have asked why my mids are side mounted, but that is because if you front mount everything, then you will only be able to hear it when you are standing in front of it, move laterally in relation to it and perceived volume drops significantly. So thus I moved my mids to the side so that you can still hear it reasonably well if you aren't prefectly aligned with them. Yes, I did test several designs before I made this, all outdoors. Front firing is the best, but only indoors or if your listening position doesn't change. Outdoors not so great if you move or your listeners aren't lined up.

If you have any questions regarding battery type feel free to ask. I too basically needed a small portable boom box that got as loud as possible that could be heard by people whose listening positions were not fixed. The design is a compromise (just like everything else in audio) that works well for its intended application.

So maybe this can help you in figuring out what to do and how to build yours.
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