What does more power do for Magnepans?

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.

El,

I did make some measurements at lower SPL's and although I didn't make note the specifics, you are correct. Voltages go proportionately lower, by a bunch.

Also understand your point about rms vs. peak, and yes, that was a misstatement on my part.

The voltage differences between the 2 panels caught me off guard. I hadn’t reasoned through it properly… i.e – panel size, higher magnitude of excursion at the lower frequencies, etc.

93-95db… that is reading the bar graph on the RS meter. Lord knows what the real peaks are. Only ½ dozen or so songs that I can actually listen to that loud. It is overloading the large, sparsely treated room on 99.9% of music, and probably straining the amps on all music. But someone with an extensively treated, large room… I can see them pushing amplifiers to those kinds of voltages to get 90-91db peaks at the listening position and being quite comfortable at those volumes.

I know most here will yawn, but going through the reasoning and measurements the first time (like me) is fascinating and educational.

Best Regards,
Jim S.

Hi Jim, you said : 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

I was wondering if you adjusted/changed the volume levels for the two different songs when you obtained these measurements?

Bob

Bob,

I set the volume pot at a level that I occasionally listen to and left it there. I was more interested in measuring at a known volume level to see how much juice the speakers were pulling.

They are both "modern" recordings (CD) and fairly close in "average" level. The D Warhols just has a ton more bass energy. So the peak SPL for that recording were probably higher.

If there is something specific your wondering about, I can rerun the little experiment and equalize volumes as best I can. Watching the little bar graph jump on a RS meter is not the most precise thing in the world. Nor is watching a fluctuating multi-meter. I also have some analysis software, but I don't know if it will measure a lengthy enough sample to find the peaks.

I have to learn to be careful in my statements here, too many sticklers for precision. This was just meant as an interesting observation, not accurate science.

Jim S.