Damping Factor and Bass

[plasnu]

In F7 manual, Nelson says, “Most of your “better” amplifiers have higher damping factors like 20 or 100”. Augspurger and JL Murphy also concluded damping factor of around 20 is just adequate.

Butler Audio
Butler Audio

But Nelson also says “You could argue that single-ended tube amplifiers sound good and don't have much damping factor, and you would be right”, and he is talking about SIT amp with damping factor of 1 or 2.

In my experience, I can agree with the statement saying DP=20 or 100 is high enough, but since I don’t have any experience with low DF amp like SIT, I would like to know how the lowish damping factor would "really" affect the bass response (or if it doesn’t matter at all, or does matter significantly depends on music genre, playback level, speaker unit, room, taste, etc.).

The reason why I’m asking this is I’m planning to build L’SIT SE tri-amp (high, mid, low, active crossover). It’s theoretically safer to have higher DF amp for the woofer, but I would like to challenge all SIT SE system if there is no significant drawback.

 

[rayma]

I would like to know how the lowish damping factor would "really" affect the bass response
(or if it doesn’t matter at all, or does matter significantly depends on music genre, playback level,
speaker unit, room, taste, etc.).

It certainly matters, but depends much on the speaker. Listen for yourself by connecting a series
resistor in the line to each speaker. One ohm would be DF=8, and eight ohms would be DF=1,
assuming 8 ohm speakers. Also consider the resistors' power rating.

 

[Circlomanen]

Most loudspeakers are designed with the assumption that the amp will have a high damping factor.

If you build your own loudspeakers you can design them for whatever damping factor you wish.

A low Qms, high Bl - pro-driver in a large open baffle is suitable for amps with a low damping factor.

Cheers,
Johannes

 

[plasnu]

A low Qms, high Bl - pro-driver in a large open baffle is suitable for amps with a low damping factor.

The woofer will be 15" JBL 2215H with QMS 5.5 Bl 22 in huge ported box. Is this suitable for low DF amp?

 

[plasnu]

It certainly matters, but depends much on the speaker. Listen for yourself by connecting a series
resistor in the line to each speaker. One ohm would be DF=8, and eight ohms would be DF=1,
assuming 8 ohm speakers. Also consider the resistors' power rating.

Thank you, I'll try to test in this way in the future, but it's too hard to do in my current situation...

EDIT: Actually, I have found the way doing it, so I'll try this.

 

[plasnu]

It certainly matters, but depends much on the speaker. Listen for yourself by connecting a series
resistor in the line to each speaker. One ohm would be DF=8, and eight ohms would be DF=1,
assuming 8 ohm speakers. Also consider the resistors' power rating.

OK, I just finished testing Aleph 5 with a serial 8 ohm film resistor attached to the small heatsink.

Since there was a level difference that wasn't matched precisely, but I still can clearly hear the difference with not only the kick / bass, but also overall dynamics.

I'm not sure if the difference I just heard can be simply translated to DF difference. I have a feeling that it would be somewhat dangerous if I draw a conclusion from this simple test that low DF amp is less dynamic and has poor bass with my speaker.

 

[awheeler]

Increased amplifier output impedance increases the Qes of the speaker changing Qts. Ported designs are a little more finnicky with box volume. Try blocking the port of the speaker to simulate a closed box and repeat the test with the simulated low DF.

 

[planet10]

We have done experiments using a variable output impedance amplifier to drive a number of speakers. We found that for each loudspeaker there was an ideal sounding output impedance.

The figure 20 arrises because given that the amp is typically driving speaker wire and a voice coil, 20 is about the practical limit to damping… anything rated higher is dragged down by those connections.

A speaker (in an enclosure) will have a bass response that may or may not be damped perfectly, overdamped (boomy?) or underdamped (thin?) response by an amplifier. You really cannot judge the amps output impedance (~1/damping) without evaluating its behaviour with the speaker it will be used with.

dave

 

[papasteack]

anything rated higher is dragged down by those connections.

Except the very rare amps with remote sensing wires wich can really give higher damping

 

[Cal Weldon]

P10 do you mean
overdamped (above 100) = thin
underdamped (below 10) = boomy

 

[Nelson Pass]

Except the very rare amps with remote sensing wires wich can really give higher damping

Or those with a negative damping factor.

 

[plasnu]

Try blocking the port of the speaker to simulate a closed box and repeat the test with the simulated low DF.

Thank you, I did it. I found there wa not enough bass (=less boom) with ports blocked.

The test with 8 ohm resistor is very interesting. Although my 8 ohm thick film resistor changes the overall sound a lot, including level, dynamics and frequency response (from low to high), but it seems like it certainly simulates under damped woofer sound. For some music, the bass actually sounds (subjectively) better than without resistor.

 

[plasnu]

We have done experiments using a variable output impedance amplifier to drive a number of speakers. We found that for each loudspeaker there was an ideal sounding output impedance.

I love to try a variable output impedance amplifier like Dave has. Is it possible to make something like single ended SIT with variable negative feedback?

Since negative feedback seems to be illegal for SIT SE design, I can't find any information about it.

 

[aspringv]

Rob Elliott has an article on esp audio detailing a variable damping factor amp... as well as a few articles on damping factor in general.

http://sound.westhost.com/project56.htm

 

[planet10]

P10 do you mean
overdamped (above 100) = thin
underdamped (below 10) = boomy

Huh?

Ideally (speaker (in box) + amp + room + placement in room) would be optimally damped, but there is always room for differences in taste.

dave