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Posts: 1037
Location: Uppsala
Joined: April 26, 2010
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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.
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