bridging a cd deck to a subwoofer - diyAudio
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Old 30th December 2005, 07:56 PM   #1
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Default bridging a cd deck to a subwoofer

I've been playing around with speakers and amps since i was 10 but im not so sure if i want to mess around with my current setup before getting some advice from people who know what there talking about as i've blown amps and speakers several times.

I just bought a car, (92 volvo 240 if it makes any difference). The previous owner put a nice cd deck in there (model Pioneer DEH-P7500MP) and replaced the front speakers with some new speakers but the ones in the back weren't abd sound like crap. So i wanted to upgrade them. The cd deck is 50 watts x 4. I had a subwoofer (JSW-110 450 watts max, 225 RMS, 4 ohms) that never really worked in any vehicle i had and was kicking around so for ***** and grins i connected it to see what it would sound like. It sounds really good, better than when i had it hooked up to a very good amplifier. I connected it with out an external amp using only the power from the deck itself. I also bridged it ( i think that is what i did anyway, connecting the + from the sub to the + from one channel, and the - from the sub to the - from the other rear channel) So anyway my question is, will this damage my system at all? I looked on-line trying to figure it out if it was alright but there was a lot of stuff i wasn't sure about. I heard plugging in a speaker that is higher wattage than the amp could cause damage, which is why i bridged it, so in theory it would be amplified to 100 watts and the speaker would be 225 RMS or does this change because it is bridged. Not sure if the ohms change or how any of that works. If anyone knows about this stuff and could lend me a hand with some knowledge that would be greatly appreciated. I would hate to not use a nice sounding setup because im parinoid of damaging the system, but it would suck even worse if i blew the deck or sub because i don't know what im doing. Thanks, Justin
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Old 30th December 2005, 08:42 PM   #2
Stocker is offline Stocker  United States
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It's not the healthiest thing to do. Most 'high-power' head units are internally bridged already. Use one channel... does it get just as loud? it should.
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Old 30th December 2005, 10:06 PM   #3
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wow im surprised the deck lived! regardless of the crazy power ratings on the deck,ive never seen one reviewed with more than 22 watts per channel with an very high thd, i would not think the deck amp will live very long hooked up in that config,like said before the internal amps are bridged already to give max pwr into 4 ohms,i would go get a small inexp. amp and hook it up,it might save you from buying a new head unit!!
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Old 1st January 2006, 11:05 PM   #4
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Ok well my next question is this, if i have two of these subs and hook them up individually to the rear channels is that ok? Can i damage the speaker or deck if the deck only pushes out 50 watts (22 RMS i think) per channel and the subs are 225 RMS? I changed it to that set up and it still works.
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Old 2nd January 2006, 01:19 AM   #5
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I would worry less about the watts and more about the Ohm load. If both subs are single VC 4 ohm you should be okay, but you will be sending a signal to the subs that consist of the whole audible spectrum (20hz to 20khz) unless your head unit has built in low pass crossovers or you add some coil inductors as a passive low freq. crossover, it may harm your subs trying to reproduce 20khz. I would'nt think it would sound that good, but if what you want is loud bass and don't care about SQ go for it. happy new year Jed
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Old 2nd January 2006, 02:07 AM   #6
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High frequencies won't damage subs. There are only two ways to blow a speaker, mechanically and thermally. For a given power level, higher frequencies yield much lower levels of excursion, so mechanical damage isn't an issue. With music there is much less power being delivered at higher frequencies than at lower frequencies, so compared to what the sub normally sees there's really no difference, so thermal damage isn't any more of an issue, especially since the headunit can't deliver more than 35-40rms per channel even in full clip. It will sound stupid though if you don't lowpass the sub at a reasonable frequency, no headunits that I'm aware of will let you lowpass the rear outputs at a frequency suitable for subwoofer use, which means you'll either need to build a custom passive lowpass or deal with your singer sitting in your trunk.
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Old 2nd January 2006, 03:31 AM   #7
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Looking in the manual there is a sound focus equilizer (SFEQ) that has an option of boosting treble in the front and bass in the rear, it sounds pretty good but im going to check out one of these crossovers so i can get the best sound quality. The subs are 4 ohms but im not sure what the vc means. My only concern is that the subs were a much higher wattage than the amp pushes out. The one good thing i do like about it though is no matter how loud i turn it up it doesn't clip even on max volume.
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Old 2nd January 2006, 03:31 AM   #8
Eva is offline Eva  Spain
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It is impossible to bridge high power headunits (the ones with anything above 25W advertised and 15W real) as they are already internally bridged. Connect the sub to both wires of one channel instead, the result will be the same.

On the other hand, driving a 4 ohm subwoofer with a full-range signal won't damage either the headunit or the speaker, as the average impedance over frequency of any subwoofer is actually higher than the average impedance of a full range speaker (the sub shows low impedance only for low frequencies, while a full range speaker shows low impedance at all frequencies), in other words, it will put little stress on the headunit and the sub.

However, it won't sound loud at all as the low-frequency power available will be very small, and any attemt to make it loud will result in lots of distortion. Otherwise it's fine.
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Old 2nd January 2006, 03:51 AM   #9
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Quote:
Originally posted by volvobuyer4life
The one good thing i do like about it though is no matter how loud i turn it up it doesn't clip even on max volume.
I HIGHLY doubt that, the internal amp on nearly all aftermarket decks will begin clipping around 2/3 volume. If you start adding in boosts (especially in the bass), like that SFEQ thing, it will clip even sooner.
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Old 2nd January 2006, 05:03 AM   #10
Eva is offline Eva  Spain
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This is quite normal. Sometimes I get puzzled by how insensitive are untrained people to clipping, particularly with low power gear (even with headphones) thus yielding lots of broken sound equipment "for no apparent reason". I can confirm that most of the Pioneer headunits that I've serviced strart clipping above two thirds of maximum volume, and this is with all controls flat.

Note that a headunit is capable of blowing small or medium sized voice coils, or even blowing itself, if it is left clipping hard enough for a long enough time...
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