6 posts / 0 new
Last post
Gerrardasnails's picture
Offline
Last seen: 9 months 2 weeks ago
Joined: 06/09/2007 - 15:33
Posts: 6396
Nominal impedance - Andrew, someone can you explain please?

My speakers of choice offer 120w per speaker at nominal impedance 6 ohms. My amp of choice offers 45 watts at 8 ohms and 60 watts at 4 ohms. Would I be able to set the amp at 4 ohms with my speakers at choice. What sounds best 4 or 8 ohms. Just when I thought I was starting to understand...... Any explanations would be appreciated...

Andrew Everard's picture
Offline
Last seen: 9 months 4 weeks ago
Joined: 30/05/2007 - 12:34
Posts: 28837
Re: Nominal impedance - Andrew, someone can you explain please?

What's the amp?

Nominal impedance is what it says - a nominal figure for the purposes of comparison. All speakers have impedance that varies with frequency, to a greater or lesser degree depending on the design. The ideal is a ruler-flat impedance across the frequency range, just as a ruler-flat frequency response with no spikes or dips is also the ideal, but in reality this is all but impossible to achieve, and it's not unknown for a speaker with an 8ohm nominal impedance to dip as low as 2-3ohms at certain frequencies.

So if you have a speaker with a nominal impedance of 4ohms, say, I'd select the 4-6ohm setting available on some AV receivers to protect the amp, or the 4ohm taps on a valve amp offering 4ohm and 8ohm connections. With speakers of a nominal 6ohms I wouldn't worry too much. 

And BTW your speakers don't offer or deliver 120W - the figure just means they can handle an amp delivering 120W, but again check whether this figure in the specification is a peak value or a continuous one.

In other words, a speaker able to handle 120W continuous would be fine with a 120W amplifier running flat-out, whereas one able to handle 120W peak would be better used with a less powerful amp.

However, it's much easier to damage speakers by running them on the end of an amp working so hard that it's clipping, rather than one with a power output greater than the speakers' nominal power handling that's only operating at a modest part of its output.

Gerrardasnails's picture
Offline
Last seen: 9 months 2 weeks ago
Joined: 06/09/2007 - 15:33
Posts: 6396
Re: Nominal impedance - Andrew, someone can you explain please?

I'm looking at BR5s or RS6s with the Pioneer A-A6-J

Andrew Everard's picture
Offline
Last seen: 9 months 4 weeks ago
Joined: 30/05/2007 - 12:34
Posts: 28837
Re: Nominal impedance - Andrew, someone can you explain please?

No problem at all. And no, you can't set 8ohm or 4ohm on that amp - the two figures just mean the power output rises as impedance dips, just as Ohm's Law would suggest... 

huddo's picture
Offline
Last seen: 8 months 2 weeks ago
Joined: 13/11/2007 - 11:11
Posts: 84
Re: Nominal impedance - Andrew, someone can you explain please?

If I can hijack this thread for a minute is it going to be OK for me to use my Musical Fidelity A1 amp with Monitor Audio RS6's ???

Anonymous
Anonymous's picture
Re: Nominal impedance - Andrew, someone can you explain please?

I'd be keen to hear the resposes to this as I'm under the impression both MA and MF are both slightly on the bright side of neutral, but MA uses MF products in its testing/developing etc etc of its speakers.........

Log in or register to post comments