Speaker's efficiency, sensitivity and impedance

06-26-08: Jeffjarvis
So, what would be easier to drive?
A speaker with 90DB and 4 ohms or a speaker with 88DB and 8 ohms?

The two speakers in your example don't differ a great deal assuming their impedance curves are similar. If one has a flatter impedance curve, then that one would be more successfully driven by a larger selection of amplifiers.

The 90dB speaker would require slightly less power to produce the same output level as the 88dB speaker in the same room.

If the 4 ohm speaker had a flat impedance curve, it could be driven successfully by a good PP tube amp (balance meaning an even frequency output from bass through treble without one are being more prominent than the other). If the 8 ohm speaker had a flat impedance curve, it'd be a better candidate for a tube amp. If the impedance curves have large dips and peaks, the speakers will be more successfully driven by a solid state amp that doubles power output as impedance is halved.

Frequency imbalance as a result of large, varying impedance curves combined with the wrong amplifier is a primary cause of speakers sounding "tipped up" with high frequencies sounding more prominent than bass frequencies.

So, the answer to which of the two speakers is easier to drive depends on several factors: impedance curve, room size, type of amplifier being used.

IMO.

Jeff- View the last site(URL) in my last post. There's a brief treatise on how impedance, amp output and sensitivity affect a system's SPL(just past the halfway point of the article).

I'll admit, I only completed freshman college calculus and I'm no math wizard, but I can't follow the author's math. I wish he'd explain how he arrives at the following:

Let’s say the loudspeaker has an efficiency of 90 dB for one watt at one meter and the desired maximum sound pressure level during peaks is 110 dB (that’s really loud). This will require 100 watts. If the signal source is 1 volt maximum, how much amp gain is required?

100 watts into 8 ohms requires 28 volts. So the amp needs to provide a voltage gain of 28 times which is 29 dB.

Tvad- Read Robert Harley's "Complete Guide to High End Audio" available from Amazon=8>) The sections on "How Much Power Do I Need?" and "The dBW Power Rating" may lend some clarity. The only aspect Mr Harley leaves out is converting volts to dBW.(pages 159 through 162 in the Third Edition) I had skipped over the part you sited, and concentrated on the section right after when reading the Transcendent article. The writer forgot to say, "Trust me!"

Audiokinesis Duke, Thank you for the first complete explanation of this commonly misleading conundrum, I’ve heard..

Happy Listening!