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Speaker ratings, how to interpret?

Can someone clue me in on how to interpret the impedence side of speaker ratings? The sensitivity in dB is pretty straightforward but the impedence ratings are less intuitive (for me anyway). So when a speaker is said to be nominally 6 ohms, minumum 4 ohms, what is this conveying? Especially in relation to choosing suitable amplification.

My confusion centers around the link (or lack of) between the dB and ohms ratings. Example, speakers having the same 91dB rating but one being nominally 4 ohms, the other 8 ohms. What will be the practical difference when choosing an amp?

Is there a layman's reference (book, internet, etc) for these sorts of questions?

TIA,

Thomas
tmitchell
bomarc
501 posts
 
Marakanetz: Actually, Boyk said it about ALL spec sheets. The only way to know if a particular amp has enough oomph to drive a particular speaker is to put both in your listening room, and crank up the volume (slowly!).
clueless
763 posts
 
Bomarc, With all due respect, the only dimensions that matter are not if it will fit on your shelf and whether the shelf will hold it. Specs can't tell the whole story but they have a lot of important things to say and some basic mistakes can be avoided by paying attention to them. Listening is not the whole story. I agree that ultimately the ear has final say but the ear cannot tell if the speaker is bad or if the amp is underpowered or if the room is acoustically poor or if there is some other design problem involved. You need to use and respect both. You cannot rely on specs in the marketing material.

Sincerely, I remain
bomarc
501 posts
 
Clueless, First, we need to distinguish between measurements and specs. Specs ARE marketing material, and I've yet to see a spec sheet that really told me anything I would trust.

Now, the right kinds of measurements can tell you plenty about the performance of a speaker, but those measurements are represented by 2- and even 3-dimensional graphs, not numbers. And very few manufacturers publish such graphs.

As for underpowered amps, leaving aside the extreme cases (5-watt SETs driving huge sealed boxes), the best test is to listen for clipping distortion.
clueless
763 posts
 
Bomarc: Well, as usual, it's hard to say clearly all you mean in these short posts and, when you make the distinction between "specs" and "measurements", I tend to agree with you. Sometimes I think some folks around here are measurement adverse and so I periodically go off the deep end.

Sincerely, I remain
clueless
763 posts
 
T, If you still need a few internet sources let me know.

I remain,
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