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Old 10th November 2009, 08:07 PM   #1
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Default DoItYourself sub without amp

Well to start with, im not that rich so cant afford a real hi-fi systems. At the moment i got decent front speakers, and now i would like to get a decent subsound.

1) What is a cheap way to make a subwoofer? Or is it just worth having nothing untill i can afford ready amplifier + subwoofer?
2) I dont have an amplifier, and i would like to skip it because cant really afford one, so can i skip amplifier and still get a subwoofer done?
2.b)Should i try to make something out of PCB that only sends through low sounds? (would need help with the schematic)

Friend linked me the schematic in the picture, saying it should do the trick, but does it work in cars?
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Old 10th November 2009, 09:13 PM   #2
Xoc1 is offline Xoc1  United Kingdom
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Do you have a power amplifier running your front speakers or are they just running off your stereo unit?
Most car amplifiers have a phased output so they can run in stereo or be used in bridge mode.
I have in my junk box a simple set of crossover components for running a single sub and a pair of mid tops off a single stereo car amplifier.
The sub runs in mono bridge mode, with an inductor coil connected in series and the mid tops run in stereo with capacitors in series. This gives a gentle 6dB per octave crossover.
Most Car subwoofers seem to be fairly inefficient, and need lots of power.
If you have the space for a big enough enclosure most pro drivers are far more efficient ie LOUD!
My first car sub project used a 15" bass guitar speaker. This was mounted in the boot on a sheet of timber behind the seat and fired into the car by removing the centre arm rest.
I only had a 15w amp and a simple transistor low pass fiter. But the rear view mirrors would blur with the bass beat, Great fun!
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Old 11th November 2009, 02:41 AM   #3
jol50 is offline jol50  United States
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An inductor will do it, but they can take power to run. Depends on where you are at, in the US you can find power boosters for near nothing if you have no budget. Even amps can be found for <20 if you hunt for a while. If you run a more efficient sub in a larger ported box you can get fair output from very low cost. I used to run $15 pyramids like that, on small amps.
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Old 11th November 2009, 03:24 AM   #4
mattmcl is offline mattmcl  United States
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My head unit has a way to switch rear output to sub, it doesn't power it but it does offer crossover options. I ran it that way until I could afford a power amp for the sub. It definitely added some low end, but I didn't "feel" the bass until I added a 100w sub amp. You don't really need that much.
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Old 11th November 2009, 11:04 AM   #5
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My stereo unit gives 50x4 watts, and my front speakers are only connected to a box that separates the high and mid sounds. (not really sure if it boosts also the power or not, but its like + and - input, then mid output + - and high sound + -)
But i was mostly thinking of putting the rearspeaker cables together (directly from the headunit), into a low-sound-separator, and then to the element. Would that work, or does it need an amp? With the 2 cables together, shouldnt it then be a 100w i get from it?

Xoc1: yes, i have a lot of space in the trunk for whatever is needed to build :P
mattmcl: sadly, my head unit cant do that. But is it hard to build a thing that separates the sound into sub sound?
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Old 11th November 2009, 11:49 AM   #6
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No matter the power rating of the head unit, it isn't likely to deliver more than 20w/channel of real power.

If you directly connect any 2 speaker wires, the internal amp is likely to fail.

If you want to get more power to a single speaker, you'll need a dual voice coil speaker.
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Old 11th November 2009, 12:18 PM   #7
Glowbug is offline Glowbug  United States
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Save up until you can afford a used sub and amp.
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Old 11th November 2009, 01:55 PM   #8
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I'll second the dual voice coil suggestion, as well as the need for an efficient woofer. It won't be loud and car-shaking powered from a head unit. But for the price of an inexpensive woofer and a couple of coils, it could be fun.

Another suggestion, depending on how the car is built, would be a pair of 8" or 10" woofers in a rear deck or package tray. You can even add tweeters and run them full-range as coaxials.

The filter you posted is a little overkill for a simple add-on, the component values will depend on the specific woofer you choose and may cost as much as a decent used amp with built-in crossover.
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Old 11th November 2009, 02:39 PM   #9
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I got a pair of these - ported box (30L) gives f3 of 40Hz, ish.

8'' Dual Voice Coil Woofer | MCM Audio Select | 55-1455 (551455)

I use them sealed, with Linkwitz. They'll also model well in a horn (f3 of 28Hz)

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Old 12th November 2009, 08:48 PM   #10
dangus is offline dangus  Canada
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Amps can be cheaper than a fill-up of gas... Check out yard sales, pawn shops, thrift stores.

As for the (sub)woofer, try 10" to 15" drivers out of old speaker cabinets. Some can work very well, although they won't have extreme power handling.
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