What does more power do for Magnepans?

Eldartford,

Thanks and I do remember your thread now that you brought it up. I've read so many maggie threads it becomes a blurr. I am slowly learning how to figure this stuff out myself. (Mostly by putting my foot in my mouth).

Quick question if you have time. How do you measure voltage across speaker terminals? Voltmeter in series with either pos. or neg. side? Can you do this with a cheap RS multi-meter and get an "accurate" measurement?

Jim S.

Stilljd...Even a "cheap" multimeter is plenty accurate enough. (An oscilloscope. if you had one would be the best because you could see the peak voltage directly). My RS meter is digital, and displays a new measurement about once per second. As the music volume varies you monitor the reading and take the highest one as the short term (1 second) rms value.From the rms value you can estimate what the peak would be. The meter is connected directly across the speaker terminals, at the amp or at the speakers. Not in series. That would be for a current measurement, but don't try that with a voltmeter.

You will be happy to see how little power is applied most of the time at moderate volume, but the increase during loud passages played loudly is surprising.

Thanks Eldartford.

Jim S.

Just to follow up. I got to sit down with a RS multi-meter, SPL meter, and check voltages at the speakers for different levels and kinds of music. Because the 1.6's are setup "active" (acoustic crossover is around 700 hz) I was able to easily measure the input into the high frequency and low frequency sections.

Playing tracks of Allison Krauss (acoustic ensemble) and Dandy Warhols (bass heavy psychedelic) with fairly narrow dynamic ranges at levels I occasionally listen at… 93-95db peaks measured @ 11 feet (observed) produced these peak voltage readings (observed);

A. Krauss track
HF ~ 1.8 – 1.9 V
LF ~ 3.9 – 4.1 V

D. Warhols track
HF ~ 1.8 – 1.9 V
LF ~ 4.2 – 4.3 V

In my limited understanding, these readings should be higher by a factor of 10, but I probably have a setting wrong on the multi-meter.

What struck me was the power consumed by the low frequency section of the 1.6’s. Twice the power was needed in the mid/bass panel over the QR section in both cases. This leads me to two observations.

I need to change from the current horizontal biamp to a vertical biamp. Both amps are the same Arcam Alpha 10’s and their transformers would probably benefit from sharing low frequency duties.

I might be able to use more, or cleaner, power to the speakers. 43V observed peak / .707 = 60V theoretical peak. 60V/4ohms = 15 amps. 15A x 60V = 900watts!!!!!! In one channel! The Arcams are 170W@4Ohms. Active is supposedly 4X, so it works out to about 680 watts. Not to mention we are on a 15 amp circuit.

Not the end of the discussion by any means. But interesting.

Jim S.

Stilljd...93-95dB at 11 ft is indeed loud. I believe you are right about the voltages being ten times higher than you recorded due to meter scale error. 2.84 volts into these 4 ohm speakers would be only 2 watts.

I never tried to measure the woofer and tweeter sections separately, but your observation that the woofer takes a lot more is to be expected. While the voltage is about 2.2 times higher, the power is almost five times higher. Look at the areas of the woofer and tweeter sections, and the reason is obvious.

The RMS power rating of the appropriate amp would be based on the 43 volt rms reading, not the 60 volt estimated peak.
(43 * 43)/4 = 462 watts.
A 462 watt rms amp would need to swing up to 60 volts to avoid clipping a sine wave.

You might make some more measurements at a lower SPL. The
power requirements will be more reasonable. But I think you probably understand why some people (like me) have used 600 watt amps on these speakers.