Damping factor can equate to less bass ?

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Nico Ras

Nico Ras

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Joined 2005
There is much more to a loudspeaker than its electrical impedance, it is a complex system that transform electrical energy to mechanical movement to acoustic energy.

Amplifier and power supply impedance makes a huge difference to what the system finally sounds like.

Ask yourself why more capacitors in the power supply or paralleling output devices provides for tighter control of the sound. Why does an amp with 1000 uF rail capacitor booms instead of thumps?
 
J

JdAo

Member
Joined 2011
Ok, but then (so I've read some more stuff about this and it seems that opinions vary but over a certain limit it's not that important) how do you explain that certain amplifiers with higher spec power supply and regulation seem to have less bass than lower df counterparts, is it the psu regulation ?
 
J

JdAo

Member
Joined 2011
Ok, but then how do you explain that an amp with a beefier PSU and better capacitance reserves can sometimes seem to have less bass than one with a PSU with lower specs but less damping factor ? Is it the power supply regulation ? I allways read that having higher capacitance in the PSU gives better bass (then again, what is better...right ?)...
 
system7

system7

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Joined 2008
djk said:
system7 said:
A valve amp behaves like a 4 or 8 ohm resistor in terms of damping.
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Not likely.
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I just checked this, and I think I am right. You see I used to have a SWEET and MUSICAL Radford STA25 valve amp, but it never gave the tight bass control that my transistor Pioneer SA-9100 did on big bass reflex speakers. Fiddling with the 4-8-16 ohm selectors didn't help much either, though I expect 4 ohm would have been tightest even if not the most efficient. But then, you tend to use sealed box or IB speakers with valves, and they are less affected by electrical damping.

An externally hosted image should be here but it was not working when we last tested it.


IIRC, valves have an output impedance around 1K, and the transformer merely converts the 8 ohm loudspeaker load to be in this range. Voltage negative feedback plays a part, but is not really a game changer if you want good valve efficiency. Discussed in this diyAudio thread where they arrive at 3 ohms:
http://www.diyaudio.com/forums/tubes-valves/165634-typical-output-impedance-tube-amps.html

A consequence of the different output impedance of a current amplifier like a valve amplifier, is that it dislikes driving open circuit. A transistor voltage amplifier dislikes short circuit.
 
D

DF96

R.I.P.
Joined 2007
myweb.tiscali.co.uk/g8hqp/
system7 said:
A consequence of the different output impedance of a current amplifier like a valve amplifier, is that it dislikes driving open circuit.
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No, nothing to do with output impedance. The issue is transformer parasitic inductance which can produce damagingly high voltages when unloaded.

The output impedance of a valve amp depends on the circuit. Pentode SE with no feedback has a high output impedance, higher than the loudspeaker load so DF can be less than 1. Triode or UL with feedback can have an impedance well below 1 ohm. An average figure is thus not very meaningful.
 
system7

system7

Member
Joined 2008
DF96 said:
No, nothing to do with output impedance. The issue is transformer parasitic inductance which can produce damagingly high voltages when unloaded.

The output impedance of a valve amp depends on the circuit. Pentode SE with no feedback has a high output impedance, higher than the loudspeaker load so DF can be less than 1. Triode or UL with feedback can have an impedance well below 1 ohm. An average figure is thus not very meaningful.
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I'm just a simple man, and I understood this explanation of why running valves with no speaker is VERY BAD! :D

OK now for running valve amps without a speaker. With no speaker plugged in there is, in the typically-wired amp, no load at all, which is an infinite impedance. Put an infinite value for R into V=IR, remembering that the bias and the potential in the amp will try to hold I constant, and have a think about it. What happens is that the valves make attempts to chuck out enough voltage to drive an infinite impedance. They can’t, of course, but they are high-voltage devices and they have a damn good try. The flash voltages they generate can be high enough to cause arcing inside your output transformer- and outside it too, spectacularly. Arcs can occur inside the valves too, and on the valve bases. Internal feedback from these events probably makes things even worse. Typically one or more valves go out, and there are fused turns in the output transformer, causing either no output or reduced, distorted output.
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Pulling out valves, running without a speaker, and other output impedance matching issues Steve’s Amps

Though I fully accept that a high frequency oscillation might fry it too. I'd also agree output impedance will vary with tube design and feedback. You'd design speakers for valve setups to have quite a flat impedance for best result, I reckon.
 
system7

system7

Member
Joined 2008
DF96 said:
That explanation is wrong, so 'understanding' it will lead you astray.
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I expect you are right, but it's a bit easier than "transformer parasitic inductance", so it'll do for me. :D

Another way to ruin your damping was to use long runs of cheap speaker cable, of course. 30 yards of 5 amp lighting cable would kill most loudspeakers performance in the bass. A few ohms there, for sure.
 
tvrgeek

tvrgeek

Member
Joined 2009
SoNic_real_one said:
For bass usually are used inductors with a magnetic core. Those are in the 0.05-0.1 ohm range.

But yes, the series resistance is a reason why 8 ohm enclosures sound better than 4 ohm ones... Even if not as loud for a given amplifier.
And why #12-14AWG wire connecting sounds better than the usual #16-18AWG.
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Well, we will just need to agree to disagree on both statements.
 
J

jez

Member
Joined 2004
planet10 said:
There is an "ideal" damping factor for each loudspeaker. It is very enlightening to hook up a range of speakers to a variable transconductance amplifier and then dial in the output impedance for each speaker.

Most loudspeakers today are designed with the assumption that the amplifier approximates a voltage source (ie damping factor >>1). THis allows the design of the loudspeaker to have wild impedance swings. It also means that that impedance is the R in the voltage to current converter (speakers are current devices)

There are good arguments for using a current amplifier (ie damping <<1) to directly provide current to operate the speaker, eliminate the nasty effects of back EMF, voice coil heating, etc.

Since most available woofers do not have adequately low Qms, one can sidestep much of the skew in the market place by using a voltage amp on the bottom (to deal with the impedance peak at resonance) and current amps elsewhere on your multiamped speakers.

dave
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I totally disagree with the above. Competently designed speakers are intended to be driven by a good voltage source. End of story.
 
system7

system7

Member
Joined 2008
It's pretty easy to build a current amplifier with transistors with a 2 ohm wirewound ballast resistor on the emitter, and I've done it in the past. You set up the output transistors as voltage controlled current sources. You do need to lower the output impedance to avoid it applying huge volts to tweeters where their impedance goes high though. Either passively or with voltage feedback. Never fancied current feedback, because that is difficult to implement.

FWIW, mauropenasa has a nice transconductance design here:
http://www.diyaudio.com/forums/chip-amps/54571-my-audiophile-lm3886-approach-3.html

The difficulty I had was getting a current amplifier to work acceptably in Class B to keep power consumption reasonable. Class A is a doddle. It is very musical, tonally different, and has the soggy bass control you'd expect from a highish output impedance. I'd quite fancy building a headphone amplifier with a current amp though. :)
 
C

chrisb

Member
Joined 2002
jez said:
I totally disagree with the above. Competently designed speakers are intended to be driven by a good voltage source. End of story.
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y'all might wanna talk to this guy about that

np_digital.jpg
 
planet10

planet10

frugal-phile™
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planet10-hifi.com
Paid Member
jez said:
I totally disagree with the above. Competently designed speakers are intended to be driven by a good voltage source. End of story.
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It is certainly possible to build a competently designed loudspeaker that is intended to be driven with a highish output impedance amplifier.

I've built/designed more than a few. Joe Rasmussen's 2 multi-ways (Elsinore requires latest XOs) are another example. Nelson has an article on optimizing some sealed boxes for current drive.

One always needs to consider the amp & speaker as an interdependent system.

dave
 
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