I would like to get some opinions on the specification for damping factor.What I know is that damping factor is explained as The ability of the amplifier to control the speaker.In other words:The amplifier's ability to put the speaker precisely where it needs to be,precisely when it needs to be there.If the amplifier can't do this,distortion between speaker and amplifier is the result.I was wondering if someone with more expertise than me could elaborate on this,or even debunk it.My first question would be how important is this spec in the real world?Is it a useful tool in selecting an amp/speaker combo?And my next question would be why is my Beomaster 2400 showing a much better number than my 3000-2 when,clearly the 3000-2 is a superior amp?

Some examples of given damping factors for a few peices of vintage B&O amplifiers are:

Beomaster3000-2   >15

Beocenter7000        >25

Beomaster4400       >65

Beomaster2400       >70

Wikipedia has a pretty good explanation here so I'm not going to rewrite it (at least not completely ).

I'll try to keep this not too technical, but to really understand what's going on you need to look at the diagram on the WP page. The amplifier is a voltage source, which is followed by the amplifier's output impedance (modeled as a resistor Zs). The speaker cone has mechanical mass and therefore it tends to overshoot the required position and the suspension wants to keep it oscillating around the final steady state position, if the ampifier output voltage first moves and then stays level.

These oscillations make the speaker work as a generator, which creates an oscillating voltage, which the amplifier then "sees" and tries to compensate (as it is a voltage source, it tries to keep the voltage at the left side of Zs related to the control signal = audio as closely as possible). But, the speaker sees the voltage at the right side of Zs. Looking from the viewpoint of the speaker, this creates an unbalanced state, which reaches equilibrium the faster the smaller Zs is = better speaker control.

Coming to your examples, I believe the 3000-2 is the only one to have AC coupled outputs (routed through large series decoupling capacitors). Therefore, its source impedance is higher and damping factor thus lower. But as you say, many consider it better than the 2400 - which just goes to show that damping factor isn't a very important criterion with modern amplifiers.

Interesting,thanks.

Makes sense.

Yes my 3000-2 is the only one of the four I listed there with capacitor coupling to the speaker due to the fact that it is the only one with a single rail power supply.

Paul

The damping factor and restored products.

The damping factor change significant over time. The reason is components degrading.

I am measuring the damping factor on all restored products and I find result like this:

Beolab 5000 (1967)

Damping factor before restoration: 4 (4 ohm)

Damping factor after a full restoration: 25 (4 ohm)

Beomaster 4400

Damping factor before restoration: 8 (4 ohm)

Damping factor after a full restoration: 75 (4 ohm)

The figures are typical results.

But please remember the cables between the amplifier and the speaker have a heavy influence of the system damping factor. Specially the original cable dimensions for B&O speakers are critical.

Edit(23-4-2010)

The original cables of e.g. Beovox 5000 was actually 0.5mm2 - my point is to show how much you can improve just by using e.g. the cable dimension B&O used later on for loudspeakers. I am not in favor of using expensive cables (I agree with Peters points of course)

/Frede

I have attached a pdf file with the link between damping factor, amplifier and cable dimension.

/Frede

Wow.Nice work Frede

Amazing how poor the damping factor is on an unrestored amplifier! I was always sceptical about the importance of so called audiophile grade speaker wire but it sounds like it is indeed pretty important to have speaker cables of very low resistance.When you are talking about a fraction of an ohm of speaker wire resistance throwing off the damping factor.In the capacitive coupled amp like my 3000-2(and the beolab 5000)these already have a modest damping factor,it seems that a few components in the output circuit must be pretty critical.It wouldn't take much oxidation to get an ohm of resistance out of the speaker switches,or speaker connectors,which would hurt the damping significantly.

Thanks

Paul

Not sure that is quite what Frede is saying - B&O provide perfectly good wire with their speakers and there is no point messing round with ridiculously expensive wire instead. B&O have performed many listening tests on wire and the supplied items are a very good example of what suits the speaker. Obviously with passive speakers, avoid long runs and use decent connectors. Look at the Wikipaedia entry and you will see some audiophiles swear by low damping factor!!

Peter,I didn't know that the B&O engineers had done so much research on this,of course I am not surprised as they seem to have left no stone unturned in any area.I wasn't implying that the B&O cables were sub par,I was simply stating that a quality cable is,indeed very important,and that a low grade cable(or long runs as you mentioned) do compromise the damping factor.As you say,the engineers have already done their homework on this.None of my vintage gear came with B&O cables so I just use a short run of a modestly priced 12 or 14 guage speaker cable.I assume these to be of suitable quality?

Paul

I am sure they will be just fine!

With speaker cables I can see the benefit of having a decent quaity OFC cable with sufficient gauge to ensure minimal resistance, and of making sure you have a very good connection, but that does not mean overly expensive. A few pounds a meter should be the absolute maximum expenditure that could possibly have any benefit. Over that and the marketing hype takes over and all the super-expensive speaker cables on the market are simply audio-quackery.

Simon

I tend to agree Simon.I have seen speaker cables costing thousands of dollars US for just a few meters!Of course the claims of Utopian sound matched the price.Clearly though,as seen by Frede's research,a good low resistance wire of suitable gauge is pretty important.Capacitance,I suppose can also be a factor as runs get longer.

I was actually thinking of starting a thread on this forum to get some rational opinions on some of the audio-quackery I have heard.

Paul