Efficiency low on Magnepan

Davey · « **Reply #20 on:** 28 Nov 2015, 04:34 pm »

The meter in the Pass amplifiers is an indirect indication....at best.

As I've mentioned previously, the best gauge for speaker power consumption is to attach an oscilloscope and monitor peak-to-peak voltages for a period of time.
Since power amplifiers are voltage sources, a little arithmetic then yields a very good estimation of how much power is being used in your environment with your material and your preferred SPL's.
With Magnepan's this method works even better because the impedance curve is largely flat for most of the frequency range.

Cheers,

Dave.

josh358 · « **Reply #21 on:** 28 Nov 2015, 04:59 pm »

Agree, scopes are ideal. Unfortunately, I don't think most audiophiles have access to one. IMO, amps should have peak clipping indicators, peak power indicators, and maybe a light to tell you you've left Class A (and another one for push-pull if you have a Pass!). In their absence, I don't know why somebody doesn't make a simple, inexpensive peak voltmeter you could put across your amp terminals. Maybe they do, and just don't tell you about it. The circuits are trivial and you can make one yourself, but who has the time?

Davey · « **Reply #22 on:** 28 Nov 2015, 05:27 pm »

Josh,

LED peak indicators are relatively easy to construct, but it needs to be a circuit that will threshold on/off at a defined level and then "hold" the LED on for a period of time so your eye catches it. LED's have a brightness "range" which would need to be "disabled." They would also need a calibration routine with any particular amplifier to set said threshold.
A nice (somewhat complicated) example: http://sound.westhost.com/project23.htm

Many DVM's nowadays have a peak-hold feature on the AC ranges. That could used as well.....although a bit more primitive.

Dave.

josh358 · « **Reply #23 on:** 28 Nov 2015, 05:56 pm »

Yes, that's fairly baroque, isn't it? I designed one years ago (more than 35, ouch) for work and while I don't remember specifics it was a good deal simpler!

I.Greyhound Fan · « **Reply #24 on:** 29 Nov 2015, 02:17 am »

Quote from: josh358 on 28 Nov 2015, 02:45 pm

Interesting, thanks. I took a look at that thread and it suggests that the meter doesn't read peaks:

"If one does it the way Nelson Pass suggested then there is no need for rectification at all. You just have to care you don't mess up the circuit's properties.

"I once did it on an ordinary class AB amp (abouit 20 years ago). I simply connected the series connection of a POT and a cheap meter across the emitter resistors of the output stage. No rectification, no filtering (the latter might be beneficial, specially in in my case). What the meter then showed whas the current load on the amp. On a highly biased amp like the X-series amps it is an indicator showing the actual "working area" of the amp. And as already remarked it looks quite cool."

A schematic would tell us for sure.

This might help

https://passlabs.com/articles/leaving-class-a

josh358 · « **Reply #25 on:** 29 Nov 2015, 02:21 am »

Saw that earlier, thanks.

harri009 · « **Reply #26 on:** 29 Nov 2015, 02:59 am »

Quote from: a.wayne on 24 Nov 2015, 01:05 pm

127 db !

I would bet the distortion was peaking with the meters too .....

Yeah that's crazy loud

Davey · « **Reply #27 on:** 29 Nov 2015, 04:40 am »

Quote from: harri009 on 29 Nov 2015, 02:59 am

Yeah that's crazy loud

It's dangerously loud. Hearing loss would result.....and a headache.

When I see quoted numbers like that I have to assume they're incorrect.
Either the person was using the SPL meter incorrectly and/or the meter was not functioning properly and/or there was some other variable at work which yielded "measured" SPL's above what was actually being produced.

Dave.

*Scotty* · « **Reply #28 on:** 29 Nov 2015, 05:35 am »

The math did not add up either, the sensitivity spec was 91dB 2.83volts at 1 meter, a 4 ohm load. 200 watts yields 111dB, 2000 watts = 121db. 600w watts doesn't seem to equal 127dB.
Scotty

josh358 · « **Reply #29 on:** 29 Nov 2015, 02:07 pm »

I'm having trouble believing that an electrostatic with a 10" woofer could produce 127 dB anyway. Few consumer speakers can play into that territory. Permanent hearing damage will occur rapidly if the levels are sustained, as with pop -- this is way above the 120 dB OSHA exposure limit -- but brief peaks at that level do occur in acoustical music, and it seems that not all rock concerts respect the OSHA limits:

SteveFord · « **Reply #30 on:** 29 Nov 2015, 02:43 pm »

It's my understanding that my guitar amp will hit 125 decibels. You can hear this sucker quite some distance away.
I've never heard a set of planar speakers that can drown out a Marshall.

I did hear a pair of prototype Carver Amazing 4 speakers (which never went into production) driven by Lightstar amps which came pretty close to Marshall amp levels but after a 15 second blast of noise one of them popped a ribbon. That was a relief, actually!

josh358 · « **Reply #31 on:** 29 Nov 2015, 03:38 pm »

A friend of mine has a pair of Voice of the Theaters. Best party speakers ever! Though for regular listening, he uses Acoustats or an old pair of Janszens.

Studio monitors can produce that kind of level, and do it cleanly to boot. It's one of the few areas in which the sound I heard from commercial recordings in the studio beat most audiophile gear. Some consumer horns and the big Wilson's might do it, or close . . . but then, if you played music at that level, you'd lose your hearing and it wouldn't matter! It's already happened to friends who spent to much time in recording studio control rooms.

I did have a lot of fun the other day rocking out at 110 dB+ to see what the Tympanis could do, but now that I'm at the age where you lose your hearing I want to preserve what I have left . . .

SteveFord · « **Reply #32 on:** 29 Nov 2015, 04:16 pm »

josh358 · « **Reply #33 on:** 29 Nov 2015, 04:30 pm »

I was playing some warble tones and it seems that my hearing only goes into the 11 kHz range now -- scary.

SteveFord · « **Reply #34 on:** 29 Nov 2015, 04:51 pm »

My hearing seems to have a dead zone at my wife's vocal frequencies.
Worse things could happen, I suppose.

josh358 · « **Reply #35 on:** 29 Nov 2015, 05:11 pm »

miatadan · « **Reply #36 on:** 1 Dec 2015, 01:52 am »

Quote from: *Scotty* on 29 Nov 2015, 05:35 am

The math did not add up either, the sensitivity spec was 91dB 2.83volts at 1 meter, a 4 ohm load. 200 watts yields 111dB, 2000 watts = 121db. 600w watts doesn't seem to equal 127dB.
Scotty

Did see I did a typo , it was actually 117 dB, I stand corrected
measured with Radio Shack spl meter and Audiotools software SPL meter by studio six digital on iphone 6

Tonight playing music loudly , 111dB average with 117-118 dB peaks for few seconds , room size 10ft width by 19 ft length with meter 5 feet away from speakers

Dan

raindance · « **Reply #37 on:** 17 Dec 2015, 12:17 pm »

117dB. I assume it is momentary peaks, otherwise you need to give up on high end audio as you would need hearing aids. As an average measurement this is louder than a typical rock concert. I designed sound systems for clubs at one time and was called on to measure one of them as folks were complaining about ringing ears, etc. It averaged 106 dB C-weighted with dance music. This is mighty loud, people. We had to get it down to about 96-98 dB to stop the complaints.

In my 24' x 14' x 8' room I can get to 93-94 dB average with my Maggie 1.6's without clipping with a Jolida 100 x 100 watt tube amp (long wall speaker placement). This is too loud for my ears and will actually cause hearing damage after an hour. At your measured level your ears are toast after 30 seconds, which is the max permitted exposure time for that level according to industrial noise standards. You will experience permanent hearing shift. And no, it will never come back.

I see all these posts on AC about Maggies causing amps to clip and I just scratch my head.

By the way, in my book, clipping is the most obviously audible form of distortion. This is why I can't listen to most Mapleshade recordings, as they intentionally allow the mic preamps to saturate.

I certainly would not want to live next door to you

josh358 · « **Reply #38 on:** 17 Dec 2015, 01:33 pm »

Amen to your warning about hearing damage.

It's important to note that rock and unamplified acoustical music are different in this respect. Acoustical music has a peak-average ratio of 10-20 dB and those brief peaks and hearing loss is dosage-related. It may seem paradoxical, but loud acoustical music requires more power than heavy metal, because both perceive loudness and haring damage have more to do with average than peak levels.

The ear is relatively insensitive to peak clipping. I read recently about some experiments in which people couldn't hear up to 11 dB of clipping. (On trumpets, however, they heard only 1 dB of clipping, so it isn't really realistic.) Tube amplifiers, with soft clipping, sound better when overloaded than transistor amplifiers, and good amplifiers recover more rapidly from overload than cheap ones making clipping less audible.

An SPL meter DOES NOT read peaks! A peak isn't a crescendo, it lasts milliseconds and is responsible for the attack or "bite" of a sound. SPL meters are dosage-measuring instruments that were intentionally designed with averaging dynamics. They're good at protecting against hearing damage (use "A" weighting for that) but they won't tell you whether your amp is clipping. You can add 10 dB to the highest meter reading for a ballpark estimate.

Finally, from what I've read, the OSHA dosage maximums aren't tight enough to fully protect hearing.

miatadan · « **Reply #39 on:** 22 Dec 2015, 03:15 am »

Quote from: raindance on 17 Dec 2015, 12:17 pm

117dB. I assume it is momentary peaks, otherwise you need to give up on high end audio as you would need hearing aids. As an average measurement this is louder than a typical rock concert. I designed sound systems for clubs at one time and was called on to measure one of them as folks were complaining about ringing ears, etc. It averaged 106 dB C-weighted with dance music. This is mighty loud, people. We had to get it down to about 96-98 dB to stop the complaints.

In my 24' x 14' x 8' room I can get to 93-94 dB average with my Maggie 1.6's without clipping with a Jolida 100 x 100 watt tube amp (long wall speaker placement). This is too loud for my ears and will actually cause hearing damage after an hour. At your measured level your ears are toast after 30 seconds, which is the max permitted exposure time for that level according to industrial noise standards. You will experience permanent hearing shift. And no, it will never come back.

I see all these posts on AC about Maggies causing amps to clip and I just scratch my head.

By the way, in my book, clipping is the most obviously audible form of distortion. This is why I can't listen to most Mapleshade recordings, as they intentionally allow the mic preamps to saturate.

I certainly would not want to live next door to you

Yes , it is momentary peaks for fraction of a second