Impedance

[PiotrekN]

Hi Everyone,

I have a receiver (vintage Sansui G-301) being shipped to me that is rated "8 ohm minimum" but the highest rated speakers I have are rated 6 ohm.
I need to test the thing when it arrives and here is the question: will it be safe to hook up those speakers to the receiver, keeping the volume at 4/10 at most?

If it checks out I plan to buy proper 8 ohm rated speakers for it, but don't want to invest until I actually know the receiver is working.
Thanks in advance!
P.

 

[F1nut]

You'll be fine as long as you keep the volume level down.

 

[Yamaki]

Yes, it will work fine. Just don't crank it to 11.

 

[PiotrekN]

Great, thanks!
So am I correct to think that if the current drawn by, for instance 4 ohm speakers will be 2 times the current drawn from the amp by 8 ohm speakers and that means volume up to 5/10 with 4 ohm speakers should also be safe?
(For 6 ohm rescaled to 1.5 times the current and volume up to 6/10).
I don't know if the dependance of all these quantities (current/volume/impedance) is linear.

Not that I want to test the limits, but I just want to know what to expect.
Thanks! P.

 

[PiotrekN]

Volume control position does not indicate how hard the receiver is working to drive the speakers.

Wait, so I can overload the receiver in the above situation even at low volumes? Can you indicate how does this work? I'd really like to understand...

 

[opnly bafld]

Not likely, just be cautious as already mentioned.

The Sansui has an input sensitivity of 150mV. I don't know what your source is, but say you have a CD player or DAC that has a standard output of 2V, the receiver will reach maximum output way before 10/10 on the volume control. Applying numbers like 3/10 or 7/10 doesn't mean anything.

 

[onplane]

Wait, so I can overload the receiver in the above situation even at low volumes? Can you indicate how does this work? I'd really like to understand...

Just about ALL amplifiers can put out more power than their official rating. There are many factors that enter into that "official rating". Of primary concern is heat. Heat as we all know will destroy electronic components. Amps rated at 4 ohms are designed to handle the higher currents and the heat that goes along with it.

The other important issue is distortion. In short, as I mentioned earlier most amps are capable of putting out more power than their official rating. Problem is distortion will begin to significantly creep up as you exceed those ratings.

So while your amp may handle the higher current draws at modest volumes WITHOUT SELF DESTRUCTING, you may experience an increase in distortion.

Like others have said, keep your volumes modest with the 6 ohm speakers and you'll probably be just fine. Pushing to 4 ohms, however, is a significantly higher risk. Just remember that many of those old vintage acoustic suspension speakers can drop to 3 ohms at low frequencies.

Hope this helps,
Jerry

 

[PiotrekN]

Thanks! I'll be using 6 ohm speakers, I was just using 4 ohm as an example. I already chose a nice set of vintage speakers, rated at flat 8ohm, to buy for this receiver, the Beovox X25, as soon as I test it.
As a side note, I like B&O speakers but it turns out that there is very few of them rated 8 Ohm. Almost all Beovox are either 4 ohm or 4-8 ohm (which probably means more like 4 Ohm, I couldn't find the impedance graphs for these anywhere online).

 

[Spiceman50]

I run a pair of roughly 30 year old ADS L1230's 6ohm at -14 which produces around 85db at 10.5 ft away with a Yamaha 2017 model amp set at 8ohm. I have no issues with heat to the amp, or the speakers. I have cranked it up to 0db but there just wasn't enough gain to justify that much volume. I have no idea what speakers your driving or the quality of the amp though. I'm just providing a reference for you is all.

 

[PiotrekN]

I think modern amps and vintage amps differ quite a bit in construction, so I am not sure if this is an example that can be applied here as supporting evidence. The Sansui G-301 is -- as far as I know -- a decent little receiver, but it is an entry level receiver from the G-series. It has 26 WPC into 8 ohms and is not rated for lower impedance loads.It was produced 1978-1980, so can be very different in what it can handle from modern amps.

 

[toxcrusadr]

It may be perfectly capable of driving 6 ohm speakers at moderate levels, but was just never officially rated for anything less than 8.

Speakers also don't have the same impedance across the entire spectrum. It's a curve. Some 6 ohm speakers may not drop below 6, but others might, at some frequency range. All depends on how the manufacturer called it. Just to add a further variable to the equation.