Cerwin Vega AT-100 Boombox on wheels - diyAudio
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Old 12th July 2012, 10:57 AM   #1
Skoven is offline Skoven  Denmark
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Cool Cerwin Vega AT-100 Boombox on wheels

Hello Do It Yourself experts

I have just returned from Roskilde festival and now plans to make my own boombox on wheels for next Roskilde festival and other outdoor events.
I am quite new to this DIY audio area, so forgive me for any stupid questions that might come up

I have a couple of old Cerwin Vega AT-100's that i would like to use for this project.

Cerwin Vega AT-100 Specs:
400 watts rms
102 dB SPL (1W/1M) (possible only 96 dB)
(20)28-(20)28,000 Hz
127 dB Maximum SPL pair, 3 M @ full power
roll off point +\-3db 30Hz
1 x 15" bass
2 x 5 1/4" midrange speakers
1 x 1" tweeter

Here is a picture of the units:
Click the image to open in full size.

Requirements for the boombox:
12 or 24 volts (one or two car batteries: preferible only one due to the weight)
As compact as possible
As light as possible
As loud as possible
Long battery life (i am thinking Class D(F) amplifier)

I plan on using some light/stiff wood for the cabinet with a thickness around 12 mm.

Because i would like the boombox to be as small and light as possible, i am thinking of creating something like this:
Click the image to open in full size.
The two 15" basses will be mounted back to back like the in the Boominator made by Saturnus. I am thinking that it will be okay to have the basses directed to the sides and the midrange and tweeters to the front?

Questions:
Should the volume of the cabinet be a specific size?
When mounting the basses back to back, do they have to be very close to each other?
Is this construction actual any good?
What kind of amplifier should i get? I am considering a Amp6 (41Hz Audio:AMP6-BASIC kit) or a Lepai LP-2020A+ (Amazon.com: LP-2020A+ Lepai Tripath Class-T Hi-Fi Audio Mini Amplifier with Power Supply: Electronics). Are these amplifiers going to cut it?
If it is possible to cram the big basses into this small cabinet, should i make bass reflex ports in the box and how big should it/they be?

I have also read somewhere that a too small amplifier will "cut" the signal if it is not powerful enough - and by doing so, it can damage the speakers? Will a more powerful D amplifier be able to run on 12v and will the power-consumption be proportional with the output? If it is, then i see no reason not to get a more powerful D amplifier (the ones i have linked to is about 2 * 25W).

If it is possible to construct this beast, and if the sound is good, i will properly install solar-panels on the top of the box to recharge the batteries so they will last longer and also buy or make some bass-protection grills.

Suggestion and ideas are very welcome

Last edited by Skoven; 12th July 2012 at 11:50 AM. Reason: more info in main tread instead of extra post.
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Old 12th July 2012, 12:44 PM   #2
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The cabinet should have the same rough inside dimensions as the original AT-100 or you will both not get any bass and destroy the rather fragile bass speakers. Having owned a set of AT-100s a very long time ago I remember them being the same size as a small fridge each. Good luck lugging that around.

In other words: It will not work.
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Old 12th July 2012, 12:58 PM   #3
Skoven is offline Skoven  Denmark
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Thank you for your quick reply Saturnus
I am guessing that the big org. "fridge " cabinet has the purpose of keeping the pressure down/up right? Would a big hole in the cabinet not accommodate this so the speaker is able to suck in air and push it out again? I could make a big hole in the bottom that would make the speaker very open.
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Old 12th July 2012, 01:54 PM   #4
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Quote:
Originally Posted by Skoven View Post
Thank you for your quick reply Saturnus
I am guessing that the big org. "fridge " cabinet has the purpose of keeping the pressure down/up right? Would a big hole in the cabinet not accommodate this so the speaker is able to suck in air and push it out again? I could make a big hole in the bottom that would make the speaker very open.
hehehe no.

Think you should probably read up on dynamic loudspeaker basics on how they actually work. Wikipedia is a good place to start.
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Old 12th July 2012, 02:49 PM   #5
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Old 13th July 2012, 01:32 PM   #6
Skoven is offline Skoven  Denmark
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Ohh what a shame I was looking forward to building this...

I looked around the internet trying to undertand the cabinet size in relation to the speaker units - i think i might need an engineering degree in acoustics before i will be able to undertand any if it :S

Anyways - thanks for your help guys
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Old 13th July 2012, 01:50 PM   #7
Skoven is offline Skoven  Denmark
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Also... i have just checked the old AT-100 cabinets: the cavity behind the mounting hole of the bass is not that big (the bass cavity is separated from the midrange/tweeters by som foam-like thing). If i can make the same size cavity for the basses in the boombox it should work right? I am guessing that the midrange/tweeter does not need that much space?
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Old 13th July 2012, 02:23 PM   #8
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Quote:
Originally Posted by Skoven View Post
Also... i have just checked the old AT-100 cabinets: the cavity behind the mounting hole of the bass is not that big (the bass cavity is separated from the midrange/tweeters by som foam-like thing). If i can make the same size cavity for the basses in the boombox it should work right? I am guessing that the midrange/tweeter does not need that much space?
Again no. The foam does not separate the upper from the lower part of the cabinet in the AT-100, so it's the full volume inside the cabinets.

But you don't need an engineering degree. Just an understanding on how the driver and it's parameter interact with the cabinet in broad terms.

And since it'd probably be difficult for you to measure the speaker parameters of the driver, you only have one thing you know works, and that's the original cabinet.

You cannot just take a random driver and stuff it in a random sized cabinet and expect it to work. If you get it to work that way, I'd suggest buying a lottery ticket as well because the chances of winning the lottery should be infinitely higher.

Last edited by Saturnus; 13th July 2012 at 02:27 PM.
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Old 13th July 2012, 02:43 PM   #9
Skoven is offline Skoven  Denmark
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Ok, i will leave this project alone then Tugging around a "portable" boombox with the size of two small fridges combined, might be a little to much...

Thanks again for your help - much appreciated
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