Specifications when choosing right speaker / amp combo?

[admin_exported]

I’m going to replace my Rotel integrated amp (RA971mkII) and have begun collecting brochures, reviews etc. to narrow down the number of candidates I will eventually be trying to audition at a dealer - or even better at home. Looking at my speakers specifications: Recommended amplifier power 25-200 W
Impedance 4 Ohm
Frequency range 30 Hz - 33 kHz
Sensitivity 91 dB Now this might as well be in Chinese but from what I understand 4 Ohm speakers are hard to drive - what specs should I look for in a new amp? And could my current Rotel amp damage the speakers if pushed too hard? I was playing Instant Karma by John Lennon the other day (an over the top “Wall of Sound” Phil Spector production) and for the first time noticed how distorted the vocals are. I got a little worried that the speakers might be at risk.This is one of the amps I have been looking at: Power in to 8 Ohm (both channel driven) > 100W
Power in to 4 Ohm (one channel driven) > 250W
Separation > 60dB
Signal to Noise > 78dB
How should I use the technical data to find the right amp + speaker combination?

 

[John Duncan]

Little bit of theory first - 4ohm are 'easier' to drive than 8ohm, since they offer less resistance. But they look pretty average in terms of sensitivity - 91db (being the volume level attained by 1 watt at 1 metre) is pretty normal.

But in practice specs mean nothing - an 8w valve amp might be louder than a 40w transistor blah blah. What speakers are they, and what amps have you been considering?

 

[Anonymous]

My original post looks like rubbish - sorry!

I'm looking at Creek Destiny, the speakers are Audio Physic Scorpio. Are you suggesting that there's no right or wrong combination in purely technical terms?

 

[Anonymous]

[quote user="JohnDuncan"]Little bit of theory first - 4ohm are 'easier' to drive than 8ohm, since they offer less resistance. But they look pretty average in terms of sensitivity - 91db (being the volume level attained by 1 watt at 1 metre) is pretty normal.

But in practice specs mean nothing - an 8w valve amp might be louder than a 40w transistor blah blah. What speakers are they, and what amps have you been considering?[/quote]

Doesn't higher impedance mean they are easier to drive because less current is needed?

 

[fatboyslimfast]

That's the way I understood it worked...

 

[John Duncan]

I just wrote something there which might have been nonsense, so am editing it. I see what you're getting at now.......

 

[John Duncan]

ooookkkkaaayyyy. I've just read two statements on the internet - 1) "lower impedance speakers are easier to drive" and 2) "lower impedance speakers are harder to drive".

I think the first is correct. Shall we have a poll?

 

[Anonymous]

4ohm speakers are going to load your amp by a lot more than 8ohm speakers and generally require far more grip and control to get a good sound. May I refer you to this article that uses a good analogy:

http://www.hometoys.com/htinews/feb04/articles/polk/impedence.htm

By having an amp that is not powerful enough to drive a speaker you are far more likely to damage the speakers than if you have an amp that is too powerful!

 

[Anonymous]

That's a very good article, thanks!

Since it's very hard to know and understand the implications of the impedance characteristics of a speaker, and because you never know what the future may bring, your best bet is to get a receiver or amplifier that is capable of driving a 4-Ohm load. It will cost you more but it will be the better long-term investment. When shopping for an amp or receiver, do your homework. No impulse purchases please.

The Creek I'm looking at should be okay then - I'm not sure I understand the one channel bit?

Power in to 8 Ohm (both channel driven) > 100W
Power in to 4 Ohm (one channel driven) > 250W

 

[drummerman]

There are a lot of factors that make amplifier/speaker matching rather more complicated. - An amplifiers output impedance characteristic is arguably as important as speaker load variations.

These days, most speaker designers use 4ohm bass driver units so the often rather optimistic quoted 8ohm speaker is usually around a 5-6ohm average (an example though of course this varies with design). This however can easy drop to 3ohm (lower with some electrostatics) and as high as 60ohm through the frequency spectrum. Modern Solid State and well designed Valve amplifiers have no problems to drive these loads but there are differences elsewhere.

Amplifiers damping rates/factors vary. For example, Naim have lowish damping factors, usually around 15-30 depending on the model. Valve amplifiers have intrinsically low rates, perhaps between 5-10 (a generalization) though there are exceptions to the rule too. They ideally should be partnered with speakers that have well damped bass units.

Then you have low output impedance, high damping factor amplification such as the creek which can drive most speakers without any obvious compromises (other than outright sound quality but thats another issue).

Does all this matter? In theory yes but in the end you just have to listen to your chosen combo and if it sounds good to you dont worry about the technical aspects.

 

[Anonymous]

[quote user="drummerman"]
Does all this matter? In theory yes but in the end you just have to listen to your chosen combo and if it sounds good to you dont worry about the technical aspects.
[/quote]
Yes, but always keep the tech specs in the back of your mind. I understand that there's a lot more to it than Watts and nominal impedance, but you should be sensible about what sort of speakers you expect to drive with any given amp. You could end up with a pair of speakers delivering well away from their best. As an example, I wouldn't dream of driving a pair of Monitor Audio RS6s with less than 70W. Come to think of it, I just wouldn't drive them at all...

 

[drummerman]

[quote user="MusicLover"]The Creek I'm looking at should be okay then - I'm not sure I understand the one channel bit?
[/quote]

Its a way of making the figures look better MusicLover. Different manufacturers use different ways to present power measurement. Its confusing.

In theory an 'ideal/perfect' powersupply is unconditionally stable in to any load for example 100W 8ohm/200W4ohm and so on. In practice this is very rare and expensive to implement. A cheaper way and the more usual one is for compromised power supplies to have dynamic power or headroom. This just means they are able to supply more current at short bursts when peak signals demand it rather than continuously. It's usually measured at 10/20ms bursts.

Again, all theory and it does'nt correlate directly to sound quality.

 

[drummerman]

[quote user="igglebert"] As an example, I wouldn't dream of driving a pair of Monitor Audio RS6s with less than 70W. Come to think of it, I just wouldn't drive them at all...[/quote]

You are so right

 

[Thaiman]

[quote user="JohnDuncan"]I just wrote something there which might have been nonsense, so am editing it. I see what you're getting at now.......[/quote]

LOL.....Did you get the Job, John?