Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
In Reply to: RE: 4 ohms vs. 8 ohms posted by JefferyK on March 14, 2012 at 21:28:34
Ah yes, the big "IMPEDANCE" switch. Now, don't QUOTE me on this...
But these impedances "switches" on amps do not TYPICALLY envoke some magical reconfiguration / bridging modes of amplifier output transistors to optimize for load impedance. I have heard it SAID that on some amps (especially HT receivers) that the switch simply engages a sort of current limiting circuit to allow the amp to drive the load, with some sonic penalty aka dynamic range compression, while preventing the amp from bursting into flames or melting into a puddle.
In fact, the existence of these switches does not instill confidence in me that the amp is very stable at lower impedances at all. Conversely, even some (admittedly top shelf) home theatre receivers can drive loads as low as four ohms with NO switch. Some PA amps are stable at 8, 4 and even 2 ohms - but many are fan cooled, so it's not a fair comparison to an amp that relies only on convection cooling with heat sinks.
So here is what you do. Give us the make and model of the speakers, and make and model of the amp. We can look at what size "cahonas" this amp has, and what the impedance plot of this speaker looks like if a camp like, say, Stereophile magazine has reviewed them.
Sorry for the long winded "non answer" but "buy them and turn it up slowly and see what happens" is something I do all the time and don't recommend to others! ;)
The speakers are PSB Image B6.
The amp is a Yamaha A-S500.
Guess my question is which setting will do the best job of driving the speakers?
Looking at the Stereophile review these speakers dip to 4 ohms in a couple of spots despite their 6 ohm rating. This can be expected in some cases with "nominal" loads. Impedance is not a "number" - it's a frequency dependent phenomenon, aka a graph.
Your speakers are 6ohm so according to the manual you can set the switch to the "HIGH" impedance position.
If you get amp overheating or distortion, you should try the "LOW" setting.
This amp is rated down to TWO OHMS which is amazing for an amp in this price range. Due to it being only a 2 channel amp (weighing in at 26 pounds) they had room for wonderfully large heatsinks in there.
Survey Says: Set it to HIGH and give her a go! Risk to the amp is almost non-existant.
Hmm. I'm doing some searches and it looks like the consensus is to use the 8 ohms setting.
What about for a Harbeth C7 which is at 6 ohm? Which setting is best, 4 or 8?
Any 6 ohm or higher rated speaker, run on the HIGH imedance switch.
Any 4 ohm speaker run on the LOW impedance switch.
If a 6 ohm speaker gives you problems (overheating, etc.) then just switch to the LOW setting.
Your amp will be fine. If you want to experiment, run your 6 ohm speakers on each switch setting and pick the one that sounds the best.
In this case, Elizabeth was right! ;)
Hey Presto I post on several forums and it is always great to see someone who is willing to go above and beyond to research specs and help people out.
The world of forums needs more guys like you
I notice you jump in a lot with help and advice too. The nice thing about so many people seeing the same question is that we can formulate what amounts to the best "collective response". Plus we all learn in a collective way too... it's a win win. When we're all playing well with others, that is! ;)
Great - thanks a lot.
Learned some things from all of the responses.
If your amp is a ss one then, as Presto said, in all likelihood the switch merely introduces a current limiter.
As long as you don't push the amp hard it should not make a blind bit of difference and 8ohm will be fine.
If the amp is a tube job impedance settings are important but I could not answer your question as I don't use them.
I have 4-and 8-ohm speakers, run pretty stout 70's receivers and have no problems whatsoever when swapping speakers in and out (just that I never mix pairs, common sense, and never mix impedances on any one amp, again common sense). Just my experience here, YMMV.
Freedom is the right to discipline yourself.
If the amp is shutting off because it is overheating...
you can't use your ears anymore! ;)
Although this can affect sound, it's really more about the amps ability to handle the heat of the higher current due to the lower impedance.
Edit: Except this time you're correct! ;) He can probably use either setting safely.
Post a Followup:
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: