Car Speakers in Theatre Speakers NEED HELP FAST!!! - diyAudio
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Old 2nd March 2003, 03:31 AM   #1
Psionic is offline Psionic  Canada
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Default Car Speakers in Theatre Speakers NEED HELP FAST!!!

Sorry for this newb question, but I have an auction ending soon and I need an answer

Im building home theatre speakers, and I found an amazing deal on amazing speakers. The only problem is that they are for a car and are 4 ohm s. My reciever is 8 ohms. I hear that if the ohms on the speaker are too much lower than the ohms on the reciever, the reciever will blow

So how would i go about converting the speakers to 8 ohm? I hear you can reconfigure them somehow, like hook them up in parallel instead of series???

Is there any problems with this?
I don't really know what i'm talking about
Somebody explain

Thanks
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Old 2nd March 2003, 05:06 AM   #2
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In a perfect world with a perfect amplifier, power output would double every time the impedance was halved. For example, a two channel amplifier rated at 50 watts RMS per channel into a 4 ohm speaker load would produce 100 watts per channel when loaded by a 2 ohm speaker load. Unfortunately, no piece of electronics is 100% efficient, and most amplifiers can't do that.

If you parallel wire two 4 ohm speakers, the load from the amplifier's point of view is only 2 ohms. This lower resistance load (fewer ohms) draws more power from the amplifier, and causes it to run hotter.

If you series-wire two 4 ohm speakers, the amplifier will see an 8 ohm load. This higher resistance load (more ohms) impedes the flow of current out of the amplifier. You get less power, but the amplifier runs cooler and is more stable.
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Old 2nd March 2003, 05:06 AM   #3
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i assume you are talking about subs --- how many are u using?? if you wire two 4ohm subs in series it will be 8ohms nominal, which your amp can do fine... the house amp you are using, did u make it yourself or it is store bough?? alot of house amps can do 4ohm as well, just check to make sure..

just for reference

1 / R = 1/R1 + 1/R2 + ... 1/Rn for parallel
R1 + R2 + ... Rn = Rtotal for series

therefore, in series 4+4=8

-chris
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Old 2nd March 2003, 11:48 AM   #4
Psionic is offline Psionic  Canada
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the amp is store bought
no these aren't subs they are 6 1/2" 2 way speakers (JL's)
how much less power would i have?
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Old 2nd March 2003, 05:33 PM   #5
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Hy there!I'm not an expert like most of this guys here but I can tell you about my experience.I have an ordinary bought amp that is rated by a so called firm as bing able to suport from 4 to 16 Ohms.I have a pair of 4 Ohm loudspeakers so i went to a party and after a while ,let's say about an hour my am was so hot that you could have fryed eggs on it.
When I got home I decided to see what is in ti.So I found a Stk441 that supports only 8 ohms loads.
The solution was to get another pair of loudspeakers at 4 Ohms and put them in a series so 4+4=8.I works prety good for partys because the amp run's indeed cooler but I lose some power and it affects my bass.Thats why I prefer a low power listening.
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Old 2nd March 2003, 05:41 PM   #6
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If you're only using 6 1/2" speakers on the amp I'm thinking you won't be pushing so much power so as to fry it. How much power are the speakers rated for anyway? Also, what make and year are your amp? I have a Harman/Kardon A 402 and its rated at 8ohms, however, I can run it at 2 ohms without very much heat at all. I wouldn't recommend this with yours unless it's really a high current monster like mine but if you're careful I wouldn't expect any problems running 4 ohms on yours unless it's a total weakling amp.
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Old 2nd March 2003, 05:44 PM   #7
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Quote:
Originally posted by Psionic
how much less power would i have?
If you run your speakers in series you have the same amount of power. So, if you had an amp which gave 20 watts into 8 ohms, two 4 ohm speakers would still give give you your 20 watts, each speaker handling 10 watts. Obviously, no two speakers are exactly identical (impedance varies somewhat with frequency anyway) but it will be as near enough as dammit.
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Old 3rd March 2003, 12:15 AM   #8
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The speakers im getting are 6 1/2" 2 way JL's

50w rms
150w pmpo (not that it matters)
59-22k freq resp.
91 db
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Old 3rd March 2003, 01:34 AM   #9
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at 91db I think it should go loud enough before you overrun your amp. Still, how powerful is the amp supposed to be and what make is it?
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Old 3rd March 2003, 11:11 AM   #10
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Yup,

If you were going to use use four speakers, two per channel on a two channel system, you would have a sustained power handling capability of 200w total - I would have thought quite adequate for a home theatre. If you need more you could go to eight speakers per channel, in two series of four paralleled together to keep the 8ohm impedence, which would give you sustained power handling of 400w per channel, 800w total.....

These car speakers only give a useful response down to 59hz anyway - more expensive woofers would go down to at least 30hz. It's the bass that requires the power to drive at volume.
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