using 4 ohm speakers with my 6-16 ohm receiver.

[morphemes]

my receiver doesn't officially "support" 4 ohm speakers... but I'm considering some anyway. I figure the manufacturers main concern is heat. I'm using an Onkyo TX-SR608. The manual states these specs:

• 100 Watts/Channel @ 8 ohms (FTC)
• 160 Watts/Channel @ 6 ohms (IEC)
• 175 Watts/Channel @ 6 ohms (JEITA)



I've read elsewhere that in a perfect world, an amp that supplies 100 watts to 8 ohms will supply 200 watts to 4 ohms. The Onkyo's specs seem to support those claims.

Anyway, I'm looking at some speakers that are 4 ohms with a continuous power handling of 150 watts (89 dB @ 1W, 1 m). On paper, it appears that the amps are capable of 200 watts to 4 ohms, though they are not adequately equipped to handle the thermal load. I know the resistance actually jumps all over the place depending on the speakers characteristics (enclosure, frequency, etc.).

However, since the speakers are rated for 150 watts continuous, I figure I probably wont run into any major issues... may actually end up with a bit of head room..

If heat is the main issue, couldn't I just improve the cooling in my amplifier?

I really just don't want to waste my money & am wondering what input you may have on the matter.

are there any measurements I can do on the amplifier to help me figure this out, like with a multimeter?

 

[morphemes]

what I meant about headroom was that the amp may "attempt" to supply around 200 watts to a 4 ohm speaker, but since the speakers are rated for 150 watts, perhaps this would equate to the speakers needing to draw less power & therefore lessening the load on the amps? I don't know if that's logical or not...

 

[morphemes]

my current speakers are some bi amped two way bookshelfs I made.. each driver is rated for around a hundred watts @ 8 ohms, so I've just wired them up in parallel to see if this causes any problems... if it doesn't I suppose I can go ahead & get the 150 watt 4 ohm speakers & not loose any sleep over it?

 

[morphemes]

with the 4 ohm load, if I max the volume with a 10Hz frequency, the receiver starts clicking & turning the volume down. if I run 1Hz, the amp shuts itself down at around 95% gain. If I add a fan blowing some extra air into the top of the unit, it clicks less often at 10Hz max volume... @ the thx reference volume (82%) no ill effects seem to occur, except a bit of extra heat..

I can't help but wonder if modifying the heatsinks & fans would solve the extra current/heat problem... though I'll never listen above 82% anyway... I'd still prefer to boost the cooling just to reduce the thermal strain.

 

[morphemes]

it appears that I'm answering my own questions...

 

[TLS Guy]

Are you going to post every thought that comes into your head?

If you look Onkyo quoted those specs misleadingly by using three different yardsticks. You have found your answer. No, your receiver will not put 200 watts into four ohms, because it can't supply the current, and the voltage drops. You have found that engages the protection and if you keep it up you will quickly have a blown receiver. Onkyo blow quicker than the rest by the way. Onkyo state 6 to 16 ohms, that is code for "just about gets away with 6 ohms if you are lucky." The only way you would get away with this is to play it at a very low level.

And no, fans will not allow the output devices to supply more current.

Bear in mind that speaker impedance is all over the map with frequency. However most speakers these days that are any good have baffle step compensation which drops the impedance below 500 ohms where the power is. Now a lot, and probably most, speaker manufacturers are deceptive about the impedance of their speakers. If you can find it you want to find the minimum impedance of a speaker. It is a fairly good rule that the impedance of the speaker is the lowest impedance + 10%. We haven't even got to phase angles yet, as in speakers current and voltage are out of phase to a significant degree. Adverse phase angles can create an effective impedance power than what is measured. The truth of the matter can very seldom be cleaned from a spec sheet. So amp and speaker matching becomes basically a game of chance.

One other tip. If a speaker has more than one woofer, it is almost certainly four ohm no matter what the spec sheet says.

 

[j_garcia]

GR has their midbass with 8 Ohm version and 16 Ohm version. For their sealed speakers they use the 16 Ohm and achieve a 8 Ohm nominal speaker. For the vented ones, they use the 8 Ohm and have a 4 Ohm nominal speaker. So not *every* dual midbass design is 4 Ohm

with the 4 ohm load, if I max the volume with a 10Hz frequency, the receiver starts clicking & turning the volume down. if I run 1Hz, the amp shuts itself down at around 95% gain. If I add a fan blowing some extra air into the top of the unit, it clicks less often at 10Hz max volume... @ the thx reference volume (82%) no ill effects seem to occur, except a bit of extra heat..

I can't help but wonder if modifying the heatsinks & fans would solve the extra current/heat problem... though I'll never listen above 82% anyway... I'd still prefer to boost the cooling just to reduce the thermal strain.

What you're doing basically is called "playing with fire", and effectively abusing your speakers. Keep going down this path and you will be replacing tweeters in no time. To me, biamping is a bit of a waste of time. Just get an amp with enough power for the SPL you desire and be done with it. Heat in the amp is not really the issue.

 

[TLS Guy]

GR has their midbass with 8 Ohm version and 16 Ohm version. For their sealed speakers they use the 16 Ohm and achieve a 8 Ohm nominal speaker. For the vented ones, they use the 8 Ohm and have a 4 Ohm nominal speaker. So not *every* dual midbass design is 4 Ohm



What you're doing basically is called "playing with fire", and effectively abusing your speakers. Keep going down this path and you will be replacing tweeters in no time. To me, biamping is a bit of a waste of time. Just get an amp with enough power for the SPL you desire and be done with it. Heat in the amp is not really the issue.

That is why I said almost. The fact is there are precious few 16 voice coils wound these days. If manufacturers use them to keep impedance at 8 ohms with BSC, then they loose 3db of sensitivity in the spec. Can't have that, can we?

 

[j_garcia]

That is why I said almost. The fact is there are precious few 16 voice coils wound these days. If manufacturers use them to keep impedance at 8 ohms with BSC, then they loose 3db of sensitivity in the spec. Can't have that, can we?

Nope and that's a downside of his sealed versions too, which is why I have vented ones.