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Safe to use 6ohm speakers?

A

agentsim

New Member
Hi,

I read the "Why 4 Ohm Loads Stress Your Amplifier" post and I understand that the use of 4ohm speakers greatly increase the transistor's power dissipation. However, I am not sufficiently mathematically versed to do the same calculations for my setup - so now I'm paranoid!

I have a vintage 1974 Technics SA-5400X amplifier, 20wpc output for 8-16ohm speakers. I have a pair of 6ohm Wharfedale Diamond 9.1s. Can I use my speakers with this amp without damaging it? I'm using it in 2ch output, if I switch to 4ch, will that help, hinder or do nothing?

Thanks!
 
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you should have no problem doing that. Most speakers even though rated at 8 ohms will shift around in impedance depending on what signal it is getting at certain points in time.
 
bryblob said:
you should have no problem doing that. Most speakers even though rated at 8 ohms will shift around in impedance depending on what signal it is getting at certain points in time.
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I second the motion. Just don't try to bring the house down.
 
Thing that gets most people in trouble is when they try to play 2 pair of speakers at once. You should have no problems, just keep an eye(hand) on how hot your receiver is getting.
One thing I would recommend if u have not done it yet is to check the bias - no matter the speaker
 
While its true that the impedance does move around alot depending on the freq , should this ever drop below 4 ohms? Thanks.
 
I think I'm going to be the dissenter here. There is a drop to 3.9 ohms at about 200 but I think my greater concern is the fact that these speakers are very inefficient, 85.5 db. With the small receiver you have it is going to have it's hands full just making noise. Unless you are pretty consistently listening to chamber music as a 40db background I might be looking for some more power.

And, of course, with more power usually come a little greater stability.
 
The amp will probably deliver more power to the lower impedance, but you have to be careful not to overdrive it-too much current out=something going kapooey.
 
ryuuoh said:
See if you can find an impedance plot for your speakers. Some speakers have huge low impedance dips.
http://www.stereophile.com/content/wharfedale-diamond-91-loudspeaker-measurements
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saeya said:
There is a drop to 3.9 ohms at about 200
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According to the graph, the speakers seem to spend to spend much of their time below 8ohm, at least that is my impression. Is this a worry, or should I be more concerned about the 3.9ohm nadir?

As for power, I get decent volume out of them, but I have to go to 75% of max. If I use better speaker cables then I need 100% power. Given the impedance characteristics of the speakers, is this going to be a problem for the amp?

I don't know if this is relevant, but what is an autotransformer, and would it help in this situation?

Thanks for your help!
 
saea501 said:
I think I'm going to be the dissenter here. There is a drop to 3.9 ohms at about 200 but I think my greater concern is the fact that these speakers are very inefficient, 85.5 db.
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I will join you. I think the Technics will probably clip and sound terrible long before it burns up, but this does not seem like a sufficient amp for these speakers at all.
 
saea501 said:
I think I'm going to be the dissenter here. There is a drop to 3.9 ohms at about 200 but I think my greater concern is the fact that these speakers are very inefficient, 85.5 db. With the small receiver you have it is going to have it's hands full just making noise. Unless you are pretty consistently listening to chamber music as a 40db background I might be looking for some more power.

And, of course, with more power usually come a little greater stability.
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Well said.
 
agentsim said:
According to the graph, the speakers seem to spend to spend much of their time below 8ohm, at least that is my impression. Is this a worry, or should I be more concerned about the 3.9ohm nadir?

As for power, I get decent volume out of them, but I have to go to 75% of max. If I use better speaker cables then I need 100% power. Given the impedance characteristics of the speakers, is this going to be a problem for the amp?

I don't know if this is relevant, but what is an autotransformer, and would it help in this situation?

Thanks for your help!
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This is very telling. You are running the receiver beyond its design capabilities. If you are going to use these speakers and, most importantly, you want them do perform as designed, then are going to need more power.

"If I use better speaker cables then I need 100% power."

I don't know what you mean by this. 'Better speaker cables' will make no difference in this situation. Truthfully, there is no such thing as 'better speaker cables'. If you are using wire of a decent gauge, say 14 or so, and the wire is of good quality, that is about as good as speaker wire gets. We do not need to get into the speaker wire discussion here.

Your particular situation is fairly simple and age old. The speakers are placing demands on the receiver that are not being met. As a result the speakers and the receiver are, at least, marginally in jeopardy and cannot perform as they were designed.

There is only one solution.
 
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Always better to have too much power than too little power. Clipping amplifiers tend to damage tweeters when pushed beyond their limits. Your Wharfedales are inefficient. I'd recommend at least triple the power you have to run them.
 
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