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Discussion Starter · #1 ·
I have just bought an Onkyo 7.1 receiver, and I'm thinking of building my own DIY surrounds using car speakers.

Surrounds are not so demanding in frequency extremes and levels, so smaller boxes can be used as well as full range speakers. Car speakers have similar limitations, and can be found in different shapes as single, coaxials or triaxials.

Has anyone built such stuff and is willing to comment about them?

Are there any similar projects in the web to go have a look?

A variation of this would be to investigate dipoles used for the surrounds, also using car speakers.
 

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The only big issue is that Car audio is almost always 4ohms and this will put quite the strain on a receivers amplifire section. If all your sorrounds are 4ohm thats way to much for the receiver to handel.
 

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depends on the quality of the receiver and also the signal being applied, if you are *pushing* the speakers, trying to get things quite loud for a long time say for example a house party, I would in the least make sure the receiver has good ventilation and check how warm it is periodically... You can also check the specs of the receiver to see if it can take it :)

running @4 ohms will not necessarily wreck the amp, it will just produce more heat because at 4 ohms, giving everything else being constant; you will have twice the power being output, so if a 'scene' averaged 20 watts at 8 ohms, it will average 40 watts at 4 ohms.

The other thing is I *BELIEVE* that a 4 ohm speaker relative to an 8 ohm speaker (everything else being equal) will be 3 db louder (+3db= 2x the watts) so you could just turn down the volume proportionally and 'convert' your receiver being at -3db to "mean" that you are really at 0 db :)
 

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Discussion Starter · #4 · (Edited)
The only big issue is that Car audio is almost always 4ohms and this will put quite the strain on a receivers amplifire section. If all your sorrounds are 4ohm thats way to much for the receiver to handel.
Maybe that's one more reason to try the dipole version, which I think is recommended by THX. Then I can simply wire both speakers in series.

depends on the quality of the receiver and also the signal being applied, if you are *pushing* the speakers, trying to get things quite loud for a long time say for example a house party, I would in the least make sure the receiver has good ventilation and check how warm it is periodically... You can also check the specs of the receiver to see if it can take it :)
The receiver is an Onkyo RC180, 807's smaller brother. There's ample reserve power to handle 8 or 4 ohms, and loud stuff will only be incidental on some movie.

running @4 ohms will not necessarily wreck the amp, it will just produce more heat because at 4 ohms, giving everything else being constant; you will have twice the power being output, so if a 'scene' averaged 20 watts at 8 ohms, it will average 40 watts at 4 ohms.
So in fact you will simply lower your volume down, and stress will be over.

The other thing is I *BELIEVE* that a 4 ohm speaker relative to an 8 ohm speaker (everything else being equal) will be 3 db louder (+3db= 2x the watts) so you could just turn down the volume proportionally and 'convert' your receiver being at -3db to "mean" that you are really at 0 db :)
In fact I think Audissey will take care of that when its measurements are carried on. A 4 ohm speaker will sound louder, so it will lower it down, and viceversa for 8 ohms.

What I have to watch is that the speakers are not too much less than 4 ohm. Such a load is dangerous for the amp when you listen at high level and the frequencies are low. As surrounds do not carry too much LF information, and you also can assign where to cut it in the receiver, I think I am covered.
 

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Unfortunatly most receivers can not drive al 7 channels with 4ohm spaekers atached, only the mains. You will damage the receiver if you do.
 

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When I talked about 4 ohm speakers being 3 db louder than 8 ohm speakers, I was pointing out that (as far as I know) you can treat a 4 ohm system as an 8 ohm system, you just need to maintain 3 db less on the receiver's gain ("Volume control") knob... I could be wrong here...
 

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Discussion Starter · #7 ·
Unfortunatly most receivers can not drive al 7 channels with 4ohm spaekers atached, only the mains. You will damage the receiver if you do.
Oh, no. My main speakers are and always will be 8 ohms, so there'sno danger of damaging anything.

And if the surrounds get to be 4 ohms, there won't be much energy coming from them, as it's usually the low frequencies that usually drain the most current from the amp and may cause problems.
 

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I used a pair of Sony 6" car speaker for a long time with a cheap Yamaha RXV with no issues about heat etc. They sounded terrible in drywall (no surprise). as the back of the wall was the garage I ripped a hole in it and reinforced the drywall around the speaker with plywood and filled it with insulation. This helped but when I used a similar pair for downstairs I used boxes (about 1^3 ft).
 
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