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Damping Factor! What does this mean?


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When scrolling through the "Specs" for my Onkyo integra A-8170, I come across "Damping Factor: 50 at 8 ohms". I always wonder what "Damping Factor" is, what it means with regards to audio/speaker performance.

I've seen other amplifiers with damping factors such as, 100, 150 & so on.......

I will admit, i haven't yet searched the web for any info. I just wanted some info from SNA forum first. Any information, or web links with regards to "damping factor" explained, would be very welcome.

Cheers

Jase

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It's the load impedence divided by the amplifiers output impedance= Damping factor.

The total load impedence is governed by the speaker and the speaker cable together.

Basically a speaker still has some movement/vibrations after the signal it has recieved has stopped, a higher damping factor stops this extra movement.

That's why you get people saying that certain speakers don't sound good with tube amps [loss of control in the bass speaker, so bass sounds wooly or muffled depending on your turn of phrase], as usually tube amps have a low damping factor, where transitor amps tend to have high or at least higher as a rule damping factors.

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Damping is an awkward way to specify the amplifiers output impedance. Awkward as it assumes a fixed load (8 ohms in this case) and there are VERY few speakers that have a flat impedance. Usually specced without the speaker cable, once you factor in the impedance of the wire there is a practical realworld limit to how high damping factor can actually be (10-20?)

Matter of fact if you had a speaker with a flat impedance curve (like Joe Rasmusun's B200 TL) you could take advantage of an amplifier with the same output impedance as the speaker for maximum power transfer or an amp with a high output -- something that brings a whole lot of benefits sonically. With a speaker like Joe's you don't actually want a low impedance amp as you will likely overdamp the bass and end up with a thin sounding system.

Unfortunately we have a Catch-22 in that most speakers (especially commercial ones) are designed assumming that the amp is a pure voltage source (ie high damping)

As always speakers, amps and the connection between them need to be considered as a system.

dave

Edited by planet10
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Damping is an awkward way to specify the amplifiers output impedance. Awkward as it assumes a fixed load (8 ohms in this case) and there are VERY few speakers that have a flat impedance. Usually specced without the speaker cable, once you factor in the impedance of the wire there is a practical realworld limit to how high damping factor can actually be (10-20?)

Correct. A damping factor of around 20 is usually sufficient. As you say, though, the impedance of the speaker must be known. Some speakers can fall to 2 Ohms or less. At 2 Ohms, a damping factor of 50 (@ 8 Ohms) becomes a damping factor of 12.5. An inadequate figure. Additionally and possibly more crucially, few manufacturers cite the damping factor of their amplifiers at a frequency much higher than 1kHz. This disguises the fact that the vast majority of high global NFB SS amplifiers exhibit very low damping factors at high frequencies. This can cause big problems with certain loudspeakers (notably ESLs).

Matter of fact if you had a speaker with a flat impedance curve (like Joe Rasmusun's B200 TL) you could take advantage of an amplifier with the same output impedance as the speaker for maximum power transfer or an amp with a high output -- something that brings a whole lot of benefits sonically.

Not so. Maximum power transfer is not an appropriate way of dealing with audio. It is appropriate with RF transmission systems, where load matching is essential for antennea and transmission cables. Audio wavelengths are extremely long (electrically speaking) and thus cable impedances are essentially irrelevant. A speaker that has been fitted with extensive conjugate networks will benefit from the use of an amplifier with a low output impedance (high damping factor), UNLESS the designer has specificifally tailored that speaker to perform better with an amplifier that exhibits a high damping factor. Such an approach is fraught with dangers. For the record, the KEF104.2 was the first moving coil speaker to be extensively fitted with conjugate networks to provide a very flat impedance curve. AFAIK, not evn KEF go to the same lengths anymore. The cost is excessive and the benefits are dubious, at best. Some feel (and I am one of them) that extensive use of conjugate networks 'sucks the life' out of a speaker system. Additionally, speakers like Magnaplannars exhibit extremely flat impedance curves, due to the nature of the drivers used (ribbon and plannar). They have been shown to benefit from using a low output impedance amplifier too.

With a speaker like Joe's you don't actually want a low impedance amp as you will likely overdamp the bass and end up with a thin sounding system.

Only because Joe has probably designed his speaker to be operated with a high output impedance amplifier.

Unfortunately we have a Catch-22 in that most speakers (especially commercial ones) are designed assumming that the amp is a pure voltage source (ie high damping)

Precisely. Designing a speaker for use with one, specific amplifier is fine, but it can lead to problems later. It would be smarter for the manufacturer to supply the amp and speaker as an active unit.

As always speakers, amps and the connection between them need to be considered as a system.

dave

Well, yes, but it is usually reasonable to assume that the speaker manufacturer has designed his/her product for use with a low output impedance amplifier, as this is, far and away, the norm.

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