what is dynamic headroom?

Zaikesman,

Good info in your post borne out of experience I note & point well taken. Thanks for sharing the same.

BTW, I wrote some basics on D.F. without meaning to write how much is high enough (as Fishcall posed a basic question); rather, pointed out that d.f. is freq. dependent & that if the B&K can hold df=100 across the band, it would be doing very nicely. Why 100? 'cuz Fishcall read that off his amp's spec sheet so I stuck with that #. Is it enough for his room, his music, his volume level? Don't know!

How much df is enough is very debatable & many view points exist. The Gamut website has a paper saying that df=25 is more than enough. This # falls in your 10-100 range but it is rather subjective whether df=25 will suffice. What I find when the df is on the lower side that such amps cannot be used in any system that one pleases i.e. the amp & speaker have to be carefully matched. I consider this to be a negative aspect as the user's favourite speaker might be precluded from the list. Others might not feel this way at all. However, I agree with your view point that too much of df can be detrimental. It seems easier to pick out the lower limit (where bass is wooly) & the upper limit (where the bass is dry) but I'm not sure that 10-100 is that range as I've not done any tests myself to quantify this range. I agree that each one of us needs to choose the level of DF & its impact on sound in their resp. system.

Aleph 5 50 nominal is the damping factor
Aleph 3 100 nominal is the damping factor
SF Power 2 100 damping factor
ML 33 greater than 800 @ 20 hz, this is a very good figure to look at as this is typically where you want the greatest control of the drivers, in the low bass region. The Aleph products because they don't over control drivers are considered more tube like. Tubes also don't control drivers as well as SS.
This didn't answer your question about DH but should give a reference on Damping Factor.

wow! thanks for all the great responses. i love this site! the B&K's dampening factor is 100 at 50Hz. that's all the info that the specs give, but it looks like i do not need to worry with the specs and see how she sounds.....
thanks,
fISHCALL

Gs: "As far as damping factor is concerned, a ratio of speaker impedance to total output impedance greater than 10 will adequately control most cone drivers."

Does this mean that an amp with an output impedance of .1 ohm will be able to control a speaker with an impedance of 1 ohm ? That is a 10:1 ratio. : )

Other than that, the higher the output impedance of the amp and / or the lower the impedance of the speaker, the more the damping factor is reduced. The lower the ratio of damping factor, the higher the potential for the speaker to load down the output of the amp. This can result in higher distortion levels, frequency response abberations, poorer transient response, etc... Given typical SS amplifier designs, an 8 ohm load would be more desirable than a 4 ohm load in terms of "control" even though power transfer is reduced. As you go lower in impedance on the speaker, the amp is not only working harder to pass more current and dissipate more heat, it could become less linear depending on the design. When you start combining low impedance with low sensitivity AND high levels of reactance in a speaker, you really hurt yourself in terms of limiting the amount of amplifiers that you have available to choose from. Unfortunately, some very good speakers combine all of those attributes, making the need for "tank-like" amps a necessity for use with those speakers. Sean
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Hi
Here are three decent online articles on damping.
Probably in the order they should be read if you are not familiar with the topic.

Murphy: http://www.trueaudio.com/post_013.htm
Pierce: http://www.diyspeakers.net/Articles/Richard%20Pierce%20DAMPING%20FACTOR.pdf
Tomcik: http://www.otlamp.com/articles/tomcik/index.html