Damping Factor: Tube Amps and Full Range Drivers, Need Advice...

Greetings to all music lovers out there.

I'm trying to understand how to interpret the tube amp's damping factor spec, in conjunction with the full range driver's spec, in order to know if will be a nice match, or a bad match (overdamp or underdamp the driver, in case of a bad match).

Example:

Luxman LX-380, Damping Factor is described at 4 Ω. 1

see the link: https://beterbeeldengeluid.nl/wp-co...man-lx-380-d-380-stereo-magazine-issue-12.pdf

Fostex FE280EZ

see the link: https://www.fostexinternational.com/docs/speaker_components/pdf/fe208ez.pdf

Where on the Fostex driver's spec sheet I have to look at, and how to interpret, in order to know if will be a nice or bad match with the Luxman amp?

Many thanks, best regards!

 

I'm guessing you didn't like the answers you received over at diyaudio.com?

jeff

 

Not understood the explanations on DIY.

Tried to be more concise with the doubt anyway, via the example above, I think I will be able to understand now.

Is possible for you to explain me?

Thanks.

 

There is no reliable method to determine if a speaker will be an excellent match for a given tube-amp other than by trial and error. Matching the damping factor to the driver's impedance isn't going to tell you much which is useful.

 

It's the same with headphones. Headphones are full range drivers. I've listened to some lowish impedance headphones that have an impedance bump that you'd think wouldn't pair well with a high output impedance tube amp. And yet the pairing worked very well. On specs they shouldn't work together that well. Yet on listening they were great.

 

but checking the driver's specs and amp's damping factor, not even at least, tell you something useful?

 

The impedance curve will start to affect the response curve as the amplifier output impedance increases (damping factor decreases). So in general, when looking for speakers compatible with low damping factor amps, it's useful to choose ones without wild looking impedance plots.

 

Okay, the Fostex driver that I mentioned appears to have a very flat impedance plot, so it's good to match with a amp with low damping factor, right?

How to know if an has a low damping factor?

Luxman LX-380, Damping Factor is described as 4 Ω. 1

This is a low damping factor? medium? (high I think it's not, because it's a tube amp)

Thanks.

 

The measured output impedance is 4 ohms, so referenced to a 4 ohm speaker load, the damping factor is 1, which is pretty low. But as you say, the Fostex response is fairly flat, just the normal inductive rise as frequency increases. The response is just one consideration, the amplifier output impedance does provide some speaker voice coil electrical damping that may result in tighter cone motion control, and hence the term.

 

I think I'm becoming to understand...

Appears that this one way of how the damping factor measurements are presented, (aka output impedance)

In the case of this Luxman amp, damping factor is 1, using as a reference, a speaker with 4 ohms nominal impedance.

My interpretation is correct?

 

I think if u just Google "amplifier damping factor and speakers" you'll find tons of articles on the world wide web. These explain what a low and high damping factor number mean and how it might affect a speaker, from there you need to then really demo the combo you are interested in and listen for any problems.
I'm an SS guy so damping factor for me is a useless spec because the numbers are so high, like more than 500, I understand for tube amps the number can be very low like less than 50. But to see and hear what happens I don't think can be expressed on paper, you need to demo different gear.

 

Not sure I'd agree it is a very flat impedance plot. I see that it's about 8 ohms just under 300Hz, and about 50 ohms at 42Hz. This means the signal applied to the terminals of the speaker will have almost a 3dB (2.85dB) boost at the resonant frequency with respect to the higher frequencies. This is actually a good thing, and will help boost the falling frequency response in the low end.

But, unless you mount this driver in free air, your resonant frequency will be at a different frequency with a different impedance peak magnitude. Still, will probably help more than hinder.

 

What dampjng factor value would be too high for this driver? What would be too low?

I know that the listen experience is the most important factor, but what values would tell, that not even worth a listeninig?

By the way, the interpretation that I‘vê done on the previous post, about Luxman’s damping factor was wrong then?

Thank for the advices.

 

Many far more knowledgeable members than myself tried, so no.

jeff

 

I don't feel that the damping factor of any amp can be too high. With high damping amps, the limiting factor becomes the cables themselves. But, if you don't mind, I feel you may be over-thinking this whole thing - in my opinion. Typically, knowing the damping factor is a means for understanding the performance of a system, and not the basis in building a system. If that makes sense.

Personally, this is the lowest I've ever seen for a claimed damping factor. I would likely avoid this amp, but that's just me. But, like I said previously, this low damping factor may actually be a plus for the speaker's you plan to you, so this is a good thing.

You've already said it, but listening is the way to go.

I haven't looked at the amp's datasheet yet, but it sure appears from what you've written that it is 1 @ 4ohms. That would imply a damping factor of 2 @ 8ohms.

Another good thing about this situation is that you will probably never hear any differences with whatever speaker cable you try, so you can use the cheapest available to you.

 

Thanks, for your feedback..

Maybe my overthinking about this, is due the fact that lots of people, especially guys that build loudspeakers with full range drivers, told me that a low damping factor tube amp is vital for full range drivers perform the bass well..

 

by the way, the magazine that published the damping factor of this Luxman amp, presented in this way that i described earlier, and you converted to 2 at 8ohms.

Damping factor always are presented with a number and ohms, right?

When manufacturers publish the damping factor as Impedance Output, how is the presentation?

Many thanks.

 

I looked up a review which showed the damping factor at 1 referenced to 4 ohm. Because the amp does not have different output taps for different speaker nominal impedance, this suggests that the amp has a quite high output impedance of 4 ohms for any speaker connected to it. This is something you see with some tube amps, although 1-2 ohms is a little more common. This might make the amp not suitable for many speakers with a nominal 4 ohm impedance because of the effect on frequency response (this is NOT a safety or damage to equipment issue; it is a sonic issue). This amp is more suited to some old school speakers with 16 ohm nominal impedance. In any case, a home audition with one's own speakers is even more important with an amp like this than most other amps.

I have not heard this particular amp, so I don't know how it sounds. But, I like most of the Luxman gear I've heard, and I generally like the 6L6 output tube, so I would bet this amp is promising.

 

The Fostex driver has a fairly flat impedance curve and stays above 8 ohms across the frequency range. You should be able to drive it with any amp you like and damping factor will not be an issue.

 

Depends on how many layers of this onion you want to peel back. When it is stated in this case that the damping factor at 4ohms is one, this implies an internal 4ohms in the path to the speaker terminals (4/4=1). The assumption then is that at 8ohms it is 2 (8/4=2). Likewise 4 at 16 ohms (16/4=4).

The knee-jerk assumption is that this is a resistance, but in reality, damping factor intends to describe output impedance, not output resistance. As such, this value likely changes with frequency. In the early and middle age of solid state design, an inductor was usually wound around a small value resistor after the output devices. This would cause a falling damping factor with rising frequency. This would help ensure stability with capacitive loads, like whacky crossovers or electrostatic speakers. In times past, damping factor was often specified as:

Damping Factor (at 8ohms): 65 (at 50Hz)

Damping factor at high frequencies was not considered as big an issue as it was at lower frequencies because the huge impedance swings usually happen at the lower frequencies from box tuning (and port tuning if a ported speaker).

With the advent of high damping amplifier's and quality speaker cables (meaning enough copper to not get in the way), aberrations in a speaker's frequency response due to its impedance curve have pretty much gone away. Still, when using speakers with anemic bass response, any extra boost can be deemed beneficial - even if it does then favor a "one-note bass" sort of effect. This is what has lead a number of people to conclude that old tube amps have superior bass response as compared to competent modern designs.

You can always dick around with your setup and lower the effective damping factor of a system, but it is hard to increase it. For example, you could get a transistor amp with a specified damping factor of 1000 and put a 4ohm resistor in line with the speaker to make it have a nice whoompy sound of the amp you're looking at. Or, even easier, skip the resistor and use 20 ft of 30ga speaker cable. The advantage there is that the cable is almost invisible.

 

Thanks for detailed explanation.

Let me ask you guys something about how to read the speaker's impedance curve, taking the Fostex that I mentioned earlier as a example:

My interpretation in general when I look at the graphic, is that this driver doesn't have a lots of fluctuations impedance, stays pretty flat in general, and never goes down bellow 8ohms, in fact, most of the time stays above 8ohms and close to 16ohms. Correct?

Trying to understand, what about the big peak at the graphic's beginning, how interpret this?

Many thanks.

 

That big peak is at the resonant frequency of the driver. A speaker is like a motor in that the current flowing in the voice coil creates a magnetic field that interacts with the magnetic field of the permanent magnets in the speaker to move the voice coil/diaphragm. But, this movement of the voice coil in the magnetic field also acts like a generator and so the voice coil is generating a current and force moving in the opposite direction (referred to as back electromotive force-back EMF). This opposing current creates a resistance to the current that is driving the speaker. At the resonant frequency of the driver, it is moving back and forth at the highest rate of movement, hence it delivers the most back EMF (this is why there is a peak in the electrical resistance at this frequency.

 

I'm not sure I fully understand OP's damping factor question and responses, I'll have to study up on it. I do have a question on the Luxman LX-380. I looked at the Luxman website and it lists the rated output of the LX-380 as: 20W + 20W (6Ω), 18W + 18W (8Ω), 14W + 14W (4Ω). That seems odd to me when the speaker taps on back of the amp are noted as 4, 8, & 16 Ω. Is the rated output a misprint, and is it actually 20W + 20W (16Ω)? I could not find a user manual online or any conclusive information. Any owners out there of the LX-380?