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Impedance Matching

Oldynewby

Oldynewby

New Member
Hi,

I'm returning to hifi separates after a 20 year break. To say that things have moved on would be an understatement!

In 'the good old days' you bought your amplifier and the speakers you chose would just be 4,8 or 16 Ohms, usually 8's, but nowadays speakers are advertised with a nominal impedance of, say 6, and a minimum impedance of, say 4. How does this translate into a speakers' suitability for a given amplifier?

I've decided on a new pair of speakers to go with my Sansui AU-317, which has a speaker impedance rating of 8ohms minimum. Most of the speakers in my budget range are 6ohm with 4ohm minimum, in particular the Q Acoustics 2010i or 2020i.

I've recently read somewhere that driving 4ohm speakers with an 8ohm amp isn't recommended, I can't remember the full reason but it's not good for the amp. Is there any way that I can increase the impedance of the speakers?

Thanks in advance,

Paul.
 
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I am not familiar with that particular Sansui, but in many cases the "minimum impedance" rating listed on units that have the ability to run more than one pair of speakers at the same time is taking that chance into account. Looks like this Sansui can run the A and B speakers at the same time, which would be a 4 ohm load even with two pairs of 8 ohm speakers. As long as you're just running one pair, a single 6 or 4 ohm pair should be fine. Just don't forget and end up running a 2nd pair also.
 
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Works the same now as it did then. If the amp literature says 4 ohms minimum impedance then it's OK to use speakers 4 ohms or higher.

The back of the amp may show something like -

A or B = 4 ohms or higher per speaker
A + B = 8 ohms or higher per speaker

Bear in mind lower ohms makes the amp work harder.
 
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Chris Brown said:
I am not familiar with that particular Sansui, but in many cases the "minimum impedance" rating listed on units that have the ability to run more than one pair of speakers at the same time is taking that chance into account. Looks like this Sansui can run the A and B speakers at the same time, which would be a 4 ohm load even with two pairs of 8 ohm speakers. As long as you're just running one pair, a single 6 or 4 ohm pair should be fine. Just don't forget and end up running a 2nd pair also.
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The note on the back of the amp says that BOTH pairs of speakers should be 8ohm.

whoaru99 said:
Works the same now as it did then. If the amp literature says 4 ohms minimum impedance then it's OK to use speakers 4 ohms or higher.

The back of the amp may show something like -

A or B = 4 ohms or higher per speaker
A + B = 8 ohms or higher per speaker

Bear in mind lower ohms makes the amp work harder.
Click to expand...

No, it's the speaker specs that say 4ohms minimum, the amp only mentions 8ohm. I'm concerned that the amp design dastes from 1978 and doesn't have auto impedance matching like a modern one does.

Would bi-wiring make any difference?
 
On the 317 it says "when you connect two pairs of speakers systems each of them must have an impedance of 8 ohms or more".

The Q Acoustics at 6 ohms/ 4 min will be fine.
I would go with the 2020i since it has a 25mm larger woofer and is ~ 2 dBs more sensitive.

"Would bi-wiring make any difference?"
No
 
Thanks opnly bafld. I've sort of half-decided on the 2020i's but would I be right in thinking that the amp would still be working slightly harder with the 6ohm load? Also would the extra 2dBs be of any benefit? If that reduces the load slightly further would that be a benefit?
 
Oldynewby said:
No, it's the speaker specs that say 4ohms minimum, the amp only mentions 8ohm. I'm concerned that the amp design dastes from 1978 and doesn't have auto impedance matching like a modern one does.
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There were 4 Ohm speakers being made when your Sansui was new. There is no such thing as an auto impedance matching amp/receiver. The question is, "does the amp/receiver have the capability of driving 4 Ohm loads?". You're far more likely to find low impedance restrictions on newer gear, much of which has a 4/8 OHM switch that limits the power supply with 4 Ohm loads. IMO/E you're making a mountain out of a molehill.
 
JoeESP9 said:
IMO/E you're making a mountain out of a molehill.
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Perhaps I am, but it was my mountain and thanks to some of the more helpful members here it's now my molehill! My last question, if it needs any justification, was just out of curiosity. Shall I get your coat?
 
Put it this way, go ahead and connect your speakers, just don't connect any OTHER speakers art the same time. Or use them at the same time.

Actually the amp would probably handle it, at worst you might need a fan because transistor dissipation goes up rapidly. Same voltage, double current equals double wattage.

What is really said there is do not use TWO PAIRS of four ohm speakers and do not use four ohm with eight ohm either. (that is like 2.3 ohms)

Some amps put A & B speakers in series, and I think that is criminal. It is cheating. But they did not want to use beefier transistors and enlarge the heatsinks. It is a matter of cheapness.

If the amp does not have current limiting you can parallel up some speakers, but you better put a fan on it. I got this Pioneer SA-1270 which most people will say is BFC and junk, but I had it working into 2.3 ohms for years, with a box fan on it. Really, it was stood up on its side under the computer desk with an eight inch box fan blowing through it all the time. If you forgot to turn on the fan and cranked it for a while, remember the smell you get when you turn a clothes iron too hot and just leave it alone ? It is like oil oozing out of the steel. Well if you forgot to turn on the fan this amp started smelling like that after jamming a bit. And it survived, it is still working.

Be careful with four ohm speakers, watch the heat. Not every amp can handle it. They get hotter, or sometimes they put out some bad distortion. Or the relay cuts out. If none of that happens you are OK usually. (except on really really old stuff, older than this)
 
Oldynewby said:
Perhaps I am, but it was my mountain and thanks to some of the more helpful members here it's now my molehill! My last question, if it needs any justification, was just out of curiosity. Shall I get your coat?
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This is an open forum. No need to be rude. My response wasn't in any way rude or denigrating. I was simply honest.

BTW: I checked the specs on your amplifier (HiFi Engine has the manuals). Although they don't mention 4 Ohm operation it's a virtual certainty your AU-317 will have no problem driving a single pair of 4 Ohm speakers. Vintage gear usually has no problem driving a single pair of all but the most difficult speaker loads. My ESL's and any Apogee Ribbon speaker are examples of difficult loads. This is very different from the new Sony receiver I was interested in buying for my bedroom system. Sony service told me via email that they recommended not using 4 Ohm speakers. I bought a Yamaha which has no such restrictions.
 
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JoeESP9 said:
This is an open forum. No need to be rude. My response wasn't in any way rude or denigrating. I was simply honest.
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Sorry Joe, I thought you were being dismissive with the mountain/molehill thing when you were probably just being reassuring. The thing I find with forums is that you sometimes need to help the narrative along;).

I can see by your signature that you're well into this and probably have been for a number of years so I do respect your answer and thanks. I've checked the manuals on HFE but I don't know enough theory at this point to make a judgement call, and I won't ask at the shop because I'll just get some pimpley-arsed numpty who's only interested in his commission telling me what he thinks I want to hear.

Are we good?

JURB, Thanks for the very informative reply although if I fitted a fan I'd be listening out for the fan and not the music!

whoaru99, Don't be so impatient, I've got to buy the f@#$ing things first!
 
Or, do what I do when in doubt - add a 2 ohm wire wound power resistor in series with the speakers on one leg. It won't hurt the amp and will help by adding some safe load. It might effect the tone a bit. but most times it does not. A 10 watt power resistor should suffice. It will be absorbing 25~33% of the power output in this case so you can crank it to pretty high levels w/o worry :)
 
I ran my AU-317 into 4 Ohm, Smaller Advents and it worked fine. I would suggest that if you run the 317 at higher volume for an extended period, go ahead and check the top of the amp for excessive heat from time to time. It would benefit to have your gear set up so that the amp has plenty of room around it for ventilation.
 
Well you don't have to use a fanzilla. Actually, we did not give a **** there. I had a roomie also pushing about 400 watts and we ties the systems together and for the first time (I used to go shooting in the backyard there, damn I miss that house) in a long time the cops came. Actually they would not set foot on my property, used their lights to make their presence known and one of us had to come out, or else. Or else what ? Never found out.

But there are fans that are like 4 inches that are quiet as all hell. I used to have a bunch of them out of old IBM mainframes. You can probably buy much better much cheaper now.

Anyway, the outputs in that amp can handle like seven amperes or so. But they can only dissipate 70 watts. I highly recommend a fan, but like I said you don't have to do what I did. I mean, that thing was under the computer desk and it made our feet cold. You do not need that much. I don't like that 70 watt dissipation, I might be tempted to change them out with some good Onsemis or something. But then, if it ain't broke don't fix it.

If you can rig up something keeps the amp off the shelf, and then somehow get a fan under there blowing up, you will greatly increase the longevity of your amp. It might not fail due to heating and blowing the outputs, but there are alot of electrolytic caps in there which do not like heat.

They make this thing with fans, runs off USB and sit beneath your laptop to cool it off. One of those might be great for this. They are quite quiet, I had one. They only take five volts obviously. They just enhance the airflow. Just get one of those, and four things you can use as spacers to elevate the amp to where this thing can fit under it. I can almost guarantee you won't hear it. Almost.

And after looking at the print, that 317 uses relay cutout for current protection, so you'll know if it is bitching about the impedance. I would go along with increasing the max current output, but not eliminating the current protection. And if the current output capacity is increased, use a fan, period.

If the thing goes into protection, you can change R69 to like 150 or maybe 120 ohms. No lower unless you want to risk blowing it. And if that is necessary you KNOW you are pulling alot of current so you KNOW to use a fan. You keep it cool enough and that meager fifty watt dissipation means nothing. Can you keep it at 25C ?
 
As far as fans go; my bridged Crown XLS's came with internal fans that I found to be obnoxiously loud. I replace both with a couple of exact replacement whisper fans that are for all practical purposes inaudible at 3'. As I sit ~10' away from them I hear nothing.

Vintage gear is much more likely to have no problem driving 4 Ohm loads than a lot of new gear.
 
BrocLuno said:
Or, do what I do when in doubt - add a 2 ohm wire wound power resistor in series with the speakers on one leg. It won't hurt the amp and will help by adding some safe load. It might effect the tone a bit. but most times it does not. A 10 watt power resistor should suffice. It will be absorbing 25~33% of the power output in this case so you can crank it to pretty high levels w/o worry :)
Click to expand...

Not sure why add a resistor to lower the load (raise impedance) yet then turn it up 30% more.
 
JURB said:
Well you don't have to use a fanzilla. Actually, we did not give a **** there. I had a roomie also pushing about 400 watts and we ties the systems together and for the first time (I used to go shooting in the backyard there, damn I miss that house) in a long time the cops came. Actually they would not set foot on my property, used their lights to make their presence known and one of us had to come out, or else. Or else what ? Never found out.

But there are fans that are like 4 inches that are quiet as all hell. I used to have a bunch of them out of old IBM mainframes. You can probably buy much better much cheaper now.

Anyway, the outputs in that amp can handle like seven amperes or so. But they can only dissipate 70 watts. I highly recommend a fan, but like I said you don't have to do what I did. I mean, that thing was under the computer desk and it made our feet cold. You do not need that much. I don't like that 70 watt dissipation, I might be tempted to change them out with some good Onsemis or something. But then, if it ain't broke don't fix it.

If you can rig up something keeps the amp off the shelf, and then somehow get a fan under there blowing up, you will greatly increase the longevity of your amp. It might not fail due to heating and blowing the outputs, but there are alot of electrolytic caps in there which do not like heat.

They make this thing with fans, runs off USB and sit beneath your laptop to cool it off. One of those might be great for this. They are quite quiet, I had one. They only take five volts obviously. They just enhance the airflow. Just get one of those, and four things you can use as spacers to elevate the amp to where this thing can fit under it. I can almost guarantee you won't hear it. Almost.

And after looking at the print, that 317 uses relay cutout for current protection, so you'll know if it is bitching about the impedance. I would go along with increasing the max current output, but not eliminating the current protection. And if the current output capacity is increased, use a fan, period.

If the thing goes into protection, you can change R69 to like 150 or maybe 120 ohms. No lower unless you want to risk blowing it. And if that is necessary you KNOW you are pulling alot of current so you KNOW to use a fan. You keep it cool enough and that meager fifty watt dissipation means nothing. Can you keep it at 25C ?
Click to expand...

Ya know, if one has to go to this extent maybe it would just be better to get a more robust/capable amp.
 
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