Question IMPEDENCE.

[ianrjones]

Hello everybody.
It's something I know next to nothing about. I have the opportunity to purchase; NEAT ACOUSTIC ULTIMATUM XLS used speakers.
My problem is this; they are 6 ohms average, minimum 4 ohms. The amp I am currently suffering with is the YAMAHA as701.
Which is 8 ohms. the amp I will replace it with will also be 8 ohms. So here is my question (at last), are they compatible ?
or is it a no-no?
P.S. apologies to NOPIANO, whom I insulted some time ago, no excuses.
Thanks in advance,
IAN.

 

[Al ears]

Shouldn't be any problem. Just about any amp you can buy is nominally 8 ohm, some valve amps have 4 ohm speaker taps but it merely depends on how well an amp can drive low impedance speakers.
What are you considering to replace the Yamaha?

 

[ianrjones]

Thanks AL, The amps I am considering for next year, (JAN-SALES) are the LUXMAN Z series. 505Z, 507Z or the 509Z. To be realistic, waiting for one used or ex display will be highly competitive, with hundreds of bidders. So I believe I will have to buy new.
THANKS,
IAN.

 

[good_enough]

This is about the power reserves of the amp. At 4 ohms the speakers will take more current as there is lower impedance to the voltage the amp creates. Similar relationship to the familiar formula V=IR between resistance voltage and current for DC.

Amps SHOULD have indicated power into 8 ohms and 4 ohms. Hence my amp the Roksan K3 is rated at 140 watts per channel into 8, and 220 into 4 - the higher figure into 4 reflecting the fact that the current is going to be higher.

And behold - looking at the Luxman specs, the 505Z says "100W+100W (8Ω) and 150W+150W (4Ω)" which implies that they have anticipated different loads and given it a power supply adequate to the task.

 

[davidf]

I'm surprised the Luxman only outputs an extra 50% into 4ohms - most well designed amps with a stable power supply will double their output when the impedance halves.

 

[ianrjones]

Thank you gentlemen. How about A+B speakers when one pair is 8ohms, and the other is 4 ohms? I'm not trying to wind you up, I really need to know, before I make a purchase.
Thanking you.
IAN.

 

[manicm]

I'm surprised the Luxman only outputs an extra 50% into 4ohms - most well designed amps with a stable power supply will double their output when the impedance halves.

Only discovered recently that Luxman is part of the IAG group. Back to topic I don't think the Luxman would have trouble driving the speaker anyway.

 

[good_enough]

I'm surprised the Luxman only outputs an extra 50% into 4ohms - most well designed amps with a stable power supply will double their output when the impedance halves.

Not necessarily so. Most I've seen (see my Roksan) don't quite make it. I guess it's just value for money calculations - 220W should be enough, this side of an Oasis gig PA. I've never had my amp much beyond nine o'clock on my (nominally 8 ohm) speakers. On the grounds I'd like to keep my windows from blowing out.

In reality these max power stats are about having the headroom to handle transients. And if your amp is rated higher than your speakers, then you'd be fine on that score. Provided you don't turn it up to 11.

 

[good_enough]

Thank you gentlemen. How about A+B speakers when one pair is 8ohms, and the other is 4 ohms? I'm not trying to wind you up, I really need to know, before I make a purchase.
Thanking you.
IAN.

Should still be fine unless you turn the dial to max before switching to the 4 ohms - in which case you would have other problems like speakers jumping through the ceiling.

If the amp drives A or B, then you'd just need to adjust volume when switching.

If A and B (not sure why you'd do that as you'd have different volumes on the two) the amp would see a blended impedance of 2 and a bit ohms* (careful with that dial, Eugene) but send twice the amps to the 4 ohms as the 8 ohms hence the volume disparity.

*1/R = 1/R1 + 1/R2

 

[Gray]

How about A+B speakers when one pair is 8ohms, and the other is 4 ohms?

The impedance the amp sees will always be lower than the lowest parallel impedance.

And don't forget that, in use, the actual impedances will, at times dip below your 8 and 4 ohm figures.

Manufacturers provide connections for a second pair of speakers as a convenience feature - but I'd never be running more than one pair at a time.