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In Reply to: RE: +1 on stronger amp posted by Satie on April 01, 2015 at 13:59:51
Satie...
You have a lot of theory going here without any facts.First off. EMF is an electric phenomena.
In Your theory all other planar magnetic speakers would have lower efficiency then a Magneplanar because when You have lower efficiency it's because You have lesser magnet field strength and with lesser magnet field strength you will have a weak EMF and thus no slap.This is a wrong theory and not based on any facts.
You can see that now, right!?Then You go and speak of amps of Yours clipping and going into over heating.
Didn't You just write that You had BRIDGED those?You can't just say that You play 3db louder.
It has to be in controlled forms with a known sound source.
There are references for for this kind of measurements.I will still tell You this, if You can keep an amp from clipping You are well off.
Thousands of watt (into what Ohm??) will not automatically render You high dampening. Those are NOT linked.The art of slapping is not hard to do with hi wattage output as you will have a low magnet to membrane distance ratio on a Magneplanar.
If the membrane is shot then it will slapp even earlier because of lesser tension.
That is a fact.
Take care!
The one who succeeded was the one who didn't know it was impossible.
Edits: 04/01/15 04/01/15 04/01/15Follow Ups:
Whatever the theoretical cause the observations are still there. The signals used were 1/3 octave warbles at 20 25 and ~32 hz and the amps used are rated for 4ohms in bridged mode.
The Crown has a damping factor of > 1000 on spec and the Bryston and Classe were > 100. The Bryston is not really a high current design and is not stable into 2ohms at significant power drain and definitely not so when bidged. The Classe DR9 is stable into 2ohms and less, and the Crown is stable into 1ohm and is rated to 2 ohms. The Crown can draw 25 amps and got its own dedicated circuit and breaker.
IIRC the SPL readings at onset of slap at 25 hz were about 96-97 db with the Bryston and a bit better with the DR9 and north of 100 db on the Crown. In more recent tests it was 103 db without bracing and too loud for me to be in the room with bracing. I think the difference was that the old tests were done with the stock crossover bass filters while the recent ones were done with the line level XO and Crown amp directly connected to the bass panels.
Thanks for the good info Satie!
I am not sure Your old amps were up to the challenge as I am sure you do know that bridging makes the amp see the load as half of what it initially was.
Also a speaker X-over is a inhibitor for the amp to damp. Riming! :)
So you have changed 1 too many parts in the chain to make a sure conclusion of power being the solution.
Your Crown amp may have a damping factor of > 1000 but again, this has nothing to do with power.
We have factors of amps not being up to the load, not having enough damping factor, maybe lack of current and different way of connecting the x-over.
I hope You can see how this makes it impossible to say that the use of 1000 watts (into what Ohm again!?) is not the finite answer to slapping.
You are however 100% right in that damping factor have an input in controlling the membrane.
This I have myself been experiencing with tube amps.
The bass membrane will easier go into self oscillation where it should not have.
And this is where the important part is.
The slapping will occur at (at leas on segmented Magnepans) mostly the lowest tuned part of the bass membrane.
It was much easier to slap the 43Hz tuned bass of the MG3,6 then the 44Hz tunes Tympani panel at a lower db.
This because that the Tympani 1 tuned membrane is MUCH bigger and can push MUCH more air then the smaller tuned part of a MG3.6.
It's a trade off from Magnepan, I know.
And this happened both with a rated 65 watt (8 Ohm) Technics amp and my Carver 300 watts (8 Ohm - 2400 watts @1 Ohm).
No difference!
The only difference was that the Technics amp was not able to slap the Tympani bass panel at all. It only went into distortion and this is easy to hear. At least on those "Class AA" amps. hehe
I am NOT arguing Your experience at all.
I am however questioning the use of high wattage (into what Ohm?) as a solution to this.
Read this info on damping factor. Interesting reading!
Re: Amps and damping factor.
Postby Groove-T on Fri Jul 29, 2011 10:16 am
IMHO, there is something with the damping factor, which is not understood well.
Basically, we have usually a passive x-over, creating a resistance around 0,3 Ohms or more due coils, caps, wires, connectors and so on.
Next we have the transducers, cones usually having impdance around 4 Ohms, at F res it rises easy up to 40 and more ohms, our apo foils are also around 3-4 ohms, at Fres also much higher.
Woofers have higher impedance at higher frequeny, simply rising up.
Now divide those apx. 4 ohms with the x-overs 0, 3 ohms , and you will find, the damping factor is limited around 1 : 15. This is the static damping factor.
At Fres its much higher, BUT the current flow is much lower, THUS we have LESSER control from the amp.!!!!!
Now lets have a view with MR TWs (Ribbons),
For Example, the FR Midrange Foil is around 0,1 Ohm, wires and connectors at least the same value, so the damping factor is cut down and will be maybe 2 or lesser.
The Scintilla uses a preresistor ( apx. 0,8 Ohms) for the MR (lesser then 0,1 Ohms), this keeps the DF at a value of lesser than 0,2 !!!!!!!!
Using the Duetta or similar TWs, we have maybe 3 Ohms ribbon resistance, the returns and x-over parts will be aroudn 1 Ohm, so we end with damping factor apx. 4.
Thats means, the static damping factor is limited for 15 or lesser, no matter what the amp does.
The we have amp without negative Feedback, creating a DF around 10.
Negative feedbacked amps have much lower inner resistance, giving a DP around 100 or more, BUT he cannot work since the x-over limit for 15 or so. :shock:
Now a speaker is not only a transducer, it is also a generator producing voltage and current, because it does not stop after an impulse and creates some pre and after impulse ringing.
Thats the reaon why an amp can affect the damping factor somewhat, but it is limited.
What happens with speakers? The Total Q will change the value of the DF, thus the sound changes somewhat.
Get a small box speaker which has not much bass. Get a resistor ( apx 2 -4 Ohms) in series and it will do more bass. Or add a heavy wight to the cone and it has more bass due lesser damping. Or use small magnet with less field strenght and get more bass.
BUT we loose the control!
Is this cool or not?
Anyway, what i found with apos, especially with MR TWS, that the have a tendency to dance (bouncing) at high levels, since they are kicked from the woofers.
But if I have correct ribbon tension ( defined Q) and proper cleaned contacts everywhere in the x-over, the bouncing effect is much lesser.
Why?
Simply because i can lift the DF from very low value to a high value.
IF we go active, the situation changes dramatically, since the passive x-over is away and only the wires and connector resistance remains and allow us to control the transducer by a much better margin.
( if we also remove tank circuits and preresistors).
This counts mainly for the woofers, since they have lots of mass, compared to MR and TWs.
Now you can think a little bit about the reality.
BTW: Tube amps have output transformers, limiting the DF around apx. 10 or 20, BUT those are made to have more or less the same inner resistance for the whole audioband. :idea:
Take care!
The one who succeeded was the one who didn't know it was impossible.
The Crown has a power rating of 2kw@4 ohms, It measures 2.5kw at clipping.
The Bryston was rated 800 W/ch bridged into 8 or > 4 ohms, below 4 ohms power output is limited to below 600W there is no official power rating bridged into 4 ohms.
The Classe DR-9 was rated at 8/4/2 ohms 400/800/1150 watts
The bass panes are 4 ohms of course.
i am aware of the speaker level XO effect on damping.and after trying the DR 9 in bridged mode on one panel and realizing I was going to clip it fairly routinely and the slap convinced me to go for the higher power Crown amp. So my plan for biamping with 2 bridged DR-9 and one stereo were gutted and I bought the Crown.
On my Tri-amp MGIIIa's I run the bass panels using a Acurus A200. The speakers were in need of the usual banana peal repair 6 years ago which I did. since then I have moved them into Maple Frames with braced stands. They are actively tri-amped with the bass panels playing to 32hz 18db butterworth slope. The Acurus has never slapped the bass panels ever. I have had a group of audio heads over and they put them through their paces, and were amazed that the Acurus was barely warm after an afternoon of extremely high volume levels. Is it the amp, the hardwood frames, the braced stands? I don't know nor care, but even running them using the Magnapan passive crossover using 1 A200 then Bi-amping them using 2 they never slapped, and this was in the stock frames. :^)
Regards,
Jim
The slap was with low freq test tones and bracing really stopped it at anything like bearable volumes. I rarely got slap with music even with the lower power amps. And definitely none with the big Crown.
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