What does more power do for Magnepans?

Mr. T,

Just how close do you sit to your 1.6's to get 72 - 82db with 4 watts?

Jim S.

Mr. T,

Wasn't picking on you, just wondered. About where I sit from my 1.6's.

I know you like solo and small ensemble acoustic music and evidently the smaller tube amps work well for you. It is just so opposite from my (I will admit, limited) experience.

I went from single 170w integrated, to two 170w amps in a passive biamp, and finally two 170w amps in an active biamp configuration and enjoyed an improvement with each addition of power.

Different strokes for different folks!

Jim S.

I tried to go back and study some of the math about maggies and power. These were pointed out by others; I am just trying to pass on their work and analysis correctly.

First thing I ran across was the way Magnepan spec's the efficiency. 86db/1m/2.83V. Evidently 2.83V into 4ohms is 2 watts and not the traditional ~db/1m/1w scale. At 1m/2w efficiency works out to 83db.

If you listen to music at a level that produces 83db peaks (fairly restrained, but still dynamic) and sit 3 meters away it flows like this.

2w/1m = 83db with one speaker
Second speaker adds 3db for 2w/1m = 86db
Subtract 3db for each additional meter away from the speakers 2w/3m = 80db
Each additional 3db doubles power required - to add 3db – 4w/3m = 83db
Figure the peaks @ 83db are 6db above the average spl = 1w/3m/76db

This ignores room loading, absorption, and the fact that the 2w/1m/83db is with a test tone, but on the surface, the amount of power needed doesn’t seem that great for modest listening levels.

If you listen at a level that produces 95db peaks it would go something like this…

2w/1m = 83db with one speaker
Second speaker adds 3db for 2w/1m = 86db
Subtract 3db for each additional meter away from the speakers 2w/3m = 80db
Double power for each additional 3db;
4w/3m = 83db,
8w/3m = 86db,
16w/3m = 89db,
32w/3m = 92db,
64w/3m = 95db

64w. Still not a lot of power for what, to me, is a fairly loud 95db peak.

It doesn’t match my (admittedly limited) experience, so I am fairly assured that I have stated something incorrectly or there is another important factor that is missing.

You won’t hurt my feelings by pointing out the flaws in the above but I do find the result interesting if it holds true

Jim S.

Thanks Bob,

A fundemental misunderstanding on my part. Does change the result, doesn't it!

Jim S.

I think I have corrected a couple of mistakes. Still ignores room loading, absorption, and full spectrum of frequencies.

86db/1m/2.83V = 86bd/1m/2w. Not 83db/1m/2w.

If you listen at a level that produces 96db peaks it would go something like this…

2w/1m = 86db with one speaker
Second speaker adds 3db for 2w/1m = 89db
Subtract 3db for each doubling of distance away from speakers. 3m = – 5db, or 2w/3m = 84db
Double the power requirements for each additional 3db;
4w/3m = 87db,
8w/3m = 90db,
16w/3m = 93db,
32w/3m = 96db.

32w. Not a lot of power for what, to me, is a fairly loud 96db peak.

I sat down yesterday and checked the SPL’s at the levels I listen. Loud to me is measured peaks at 85db on a RS meter. There may be unmeasured spikes in there from transients, but certainly no higher than 90db.

The reason this intrigues me is; I recently went to an active biamp setup from a passive biamp on 1.6’s with rather startling improvements. Much greater clarity and coherence all around, and at higher volumes. Having started on the more power helps bandwagon, I have being looking to pull the trigger on more powerful amps than the current 170w Arcams’ that I own (probably better quality too).

I want to be “smart” about it, but the analysis on paper doesn’t match my limited experience. No substitute for auditioning to learn is there?

Jim S.

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.

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.

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.

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.

El,

No, it is a digital multi-meter. Just slow to react. Less than $10 at RS.

To do total amp output I would have to undo the active biamp setup and reinstall the passive crossovers in the 1.6's. And get better measuring equipment! Your early results and postings gave me enough motivation to check the seperate panels driven by seperate amps. It was mostly just general curiosity.

But, I got a lot out of the little experiment. Learned a small fraction of electronics theory, its pratical application, and why there is so much potential in a vertical biamp setup with the Arcam/1.6 combo. Clearly, dividing the 2x+ current draw of the low frequency panels between the power supplies of a pair of 2 channel amps instead of using a single 2 channel amp and its power supply for the low frequencies has a great benefit potential. I think there is the potential for added IM distortion when running HF and LF through the same transformer in a vertical setup. We will see if I can hear it.

Here in Cincinnati, we are rained in today. Guess what I am going to do today. Go Vertical!

Then I got to quit fussing around with electronics and make some room treatments!

Jim S.

El,

Thanks. More coherent than I could of posted to Dan's question.

Dan... I went to active biamping for a couple of reasons. The 1.6's are reputed to benefit greatly from better crossover parts. My little Arcam Alpha 10's are 100w/8ohms 170w/4ohms and theoretically a little short of wattage at SPL levels I occasionally listen at. A Bryston 10B came up used at a good price, so let’s kill 2 birds with 1 stone. Improve the crossover with the Bryston (bypassing the stock) and get the best I can out of the little Arcams with active biamping.

After the change, it became obvious that I had been straining the amps through the stock crossovers. Clarity and control were immediately present and at much higher SPL’s. There is some reading available on the theory. I don’t really have a good enough grasp on the basics to completely understand all of the principals. In case you want to read it.

http://sound.westhost.com/biamp-vs-passive.htm
http://www.passlabs.com/products.htm (XVR1 manual)

Now the bad news... all those new and old pop/rock CD’s that I used to love so loud... well some of them aren’t so great when you can actually hear what is going on in the recording.

BTW – I made the change to a vertical biamp yesterday. It made a tremendous difference in presentation. Don’t know what to make of it yet.

Jim S.

Dfhaleycko,

I will post impressions, but I think it would be better if I let Pal have his thread back and post to my system.

I haven't had a chance to sit down and listen for long periods. Too much work!!! I didn't expect a huge difference between horizontal and vertical with "identical" 2 channel amps (maybe not so "identical" after all). Just a little bit of extra headroom. But the presentation is different. Some talk of letting a system settle after changes. I am beginning to wonder if that isn't part of the difference.

I am going to run RTA when I get a chance and see if it measures slightly different. Will post the results.

Jim S.