So - Damping factor...how much does it really matter?

Taketheflame

Super Member
Hey all,

I've been curious about this tech spec on amps/receivers - I seem to be finding a lot of conflicting info on DF numbers - some say it's a useless spec, others say the more the merrier...some say 20 is too low, 30 too low...etc, etc...

The only thing I've really been able to determine is that it's a measurement of an amp's ability to control the driver movement of a speaker, particularly the woofers/in the low end..

I'm running an Akai AA-R30 into Advent 5012s, and I believe the original DF rating of the receiver is about 40 (but who knows if it still holds spec) - bass response seems tight and clear to my ears...out of curiosity, I've seen DF ratings ranging from 30 to 50-ish on some other receivers from the same era (mid 70's - early 80's).

I guess what I'm wondering is - would I hear a pretty audible difference hooking up a reciever w/a DF of 25 or 30 up to the Advents (10" woofer) over my current receiver?
 
DF is one of many spec's that shed light on an amp's performance and cannot be taken alone. In general, DF will increase with wattage rating. Higher DF amps tend to be faster and more objectively accurate. You will hear this as sharper, more resolved sound. Looking at the gear you have and your specific question, the difference between 25 and 40 is minimal so you will not hear a dramatic difference, all else being equal. And that is a big question considering old components such as caps and out of spec resistors. You will hear a difference going to a 200 wpc separates amp which typically sport DF in the 200 plus range.
 
Just my opinion, but I do use damping factor when considering amps for power hungry speakers. The larger the number, the better the bass seems to be on them. I don’t really consider it with more efficient speakers.
 
Just my opinion, but I do use damping factor when considering amps for power hungry speakers. The larger the number, the better the bass seems to be on them. I don’t really consider it with more efficient speakers.
Got any specific loudspeaker and amplifier examples you can share? It would be interesting to consider what other variables might be operating between the amplifiers.
 
Celestion Ditton 66, Celestion Ditton 44, Celestion Ditton 15, Kef Concerto, Kef 105, Kef 104/2,Kef 103.2, Camber 2.0, Wharfedale Dovedale 3, Tangent RS8, infinity RS7, and actually, any infinity I’ve tried, etc. These are all speakers I have personal experience with. The amplifiers would be a Kenwood Supreme 500, Kenwood Supreme 600, Yamaha M40, Bose 1801, and NAD C370. I might have missed a few amps. Remember these are are gear I have had in my house and used.

These speakers don’t work well with Pioneer SA-9100, Pioneer SA-9500, Sansui B2101, Sansui AU-9900, NAD C370, etc.

I look for a df of 50 or higher for power hungry speakers. Doesn’t always work, but for me, it is an indicating factor they should work well together. I’ve also noticed that df is more important with sealed enclosures and 10 inch or larger woofers.
 
It was an important consideration when I was trying to find affordable power for my Quantums. Everything I'd tried before seemed to have flabby or slow bass response. The Yamaha P2200's solved that problem. Wish I could find some more for what I paid for them.
 
Just my opinion, but I do use damping factor when considering amps for power hungry speakers. The larger the number, the better the bass seems to be on them. I don’t really consider it with more efficient speakers.
How power-hungry are my Advent 5012's considered in the grand scheme of things?

I think they have a sensitivity rating of 87db/1 watt IIRC.

Does the damping factor matter as much at modest volumes? I don't have to push my receiver too hard to get the Advents going, IME.
 
I have found the OLAs to be quite easy to drive overall. They would work well with the Pioneer SA-9100 and the SA-9500 and the Sansui AU-9900. I have a pair of NLA in the house right now! I just brought the woofers for refoaming today. There is a thread here on AK that goes into the characteristics of each of the advent line. I’ll post it if I can find it.
 
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Just my opinion, but I do use damping factor when considering amps for power hungry speakers. The larger the number, the better the bass seems to be on them. I don’t really consider it with more efficient speakers.

True. Very efficient speakers have lighter cones which do not change direction as well as less efficient speakers. So, a low powered, low DF amp is a good choice for very efficient speakers. Horns are better with low DF amps as well. High powered amps will make horns ring which can cause ear fatigue. IME and IMO.
 
As DF is "regarded as a resistor" damping the loudspeaker, a DF of 40 would make the amp act as having 0.2 ohms internal resistance in series with its output if the loudspeakers are 8 ohms. ( 8 / 0.2) .
DF of 25 would result in something like 0.3 ohms. So just add a 0.1 or 0.12 ohm resistor to the DF 40 amp in series with the loudspeaker and hear the difference. (Myself I have always failed to hear such small difference)
 
My SE-9200 Technics power amplifier has a rotary selector switch to choose between various DF. Ain't that funny? If higher is better, why would they put a switch to make it worse?
Using it to drive 8Ohm speakers, the effect is smaller compared to 4Ohm speakers,even if they are designed to be a resistive load (KEF 107).
Using a lower DF setting, the result is a more boomy bass response, which for the first few seconds sounds nice but quickly becomes apparent that it's un-natural.
The settings give you an output impedance ranging from 0.08Ohms (normal), 0.9Ohm, 2.7Ohm and 8Ohm. The highest output resistance setting is becoming similar to the speaker impedance (twice as much with 4 Ohm speakers) so the DF becomes ridiculously low (around 1 or lower). In practice, a difference between DF 50 and 100 may give you a signal difference of about 0.35dB
DF is one of the specs I don't even look at for amplifiers. Makes more sense to me to check distortion at lower power output as some amp circuits suffer from increased distortion at 5-10% output, which is the rating mostly used.
 
The only thing I've really been able to determine is that it's a measurement of an amp's ability to control the driver movement of a speake
It's the ratio of the amplifier's output impedance to the total load impedance. It includes all additive resistance from the speaker cable as well as any and all crusty mechanical connections.

To properly calculate actual damping factor you MUST know the actual load impedance as presented at the amplifier terminals over the bandwidth where damping matters, usually from 200hz on down. As impedance of the speaker system changes with frequency, so does the effective damping factor. Just like actual measured impedance, damping factor is frequency dependent and will swing as the impedance swings.

As a rule of thumb, high impedance speakers will most often play best with high output impedance amplifiers, read transformer coupled amplifiers, and low impedance speakers will most often pair best with amplifiers having a low relative output impedance. It's not a hard and fast rule, but it applies more often than not.

Sometimes, it's possible to get lower impedance speaker systems to play better with high output impedance amplifiers by adding some series resistance to the speaker cable/circuit.

The damping factor of most amplifiers is usually spec'd at an 8 ohm load. How many speakers have an actual impedance of exactly 8 ohms down in the frequency range where damping matters?

If you have math skills, and can measure impedance at frequency, then an amplifier's output impedance is a more relevant and useful specification than simply stating DF/8ohms.

Just my .02...................
 
This is another case where "simple" specs don't help you much. As above, you need a proper impedance curve for the speaker and a proper damping factor curve for the amp. If you have a long run of speaker wire it all becomes moot, as that high damping factor disappears due to the resistance of the wire. An argument for heavy low resistance wire, though I've no idea what differences are audible and what the root cause is, damping factor or something else.
 
I've played around with Damping Factor over the years. Here's some (hopefully) interesting things I've observed:

- DF is a figure of merit. That is, it has not measrure in and of itself. You're calculating Output Impedance of an amp and the Input impedance of a speakers. Both are measured in ohms (assuming you take out the complex AC calculations). So, x Ohms / x Ohms, as a formula, yields a number but the measures cancel out. So, it is a figure of merit. That's really helpful, no? Sounds like something we could sit around a pub and discuss over many beers!

- Since it is hard to get a idea of what effects it has, you can run a simple test with a raw woofer and a piece of jumper wire. What you'll be doing is testing the extremes of the DF formula. Here's how it works:

1) Take the woofer, completely disconnected from anything and hold it up to your ear.

2) Tap on the cone and listen for the resonance as the cone comes back to rest. Multiple taps will help you get a sense of that free air resonance.

This is the effect of no Damping Factor at all.

3) Now, jumper the 2 terminals with a piece of wire so they're a dead short.

4) Repeat Steps one and 2 again and note how the woofer cone has changed in its ability to respond to the tapping of your finger.

You've now tested the 2 extreme ends of the effect of Damping Factor in a simplistic way that your ear can understand.

5) Extra Credit: You can also use a variable resistor connected across the terminals and get an idea of what happens in between those extremes we just tested.

****** My DF observations ***********

For most sealed cabinet speaker designs, DF isn't really a big deal. You've already got a spring build into the woofer's resonance control with the air-tight chamber. For ported and open baffle designs, some DF might be nice but I doubt you'll hear the effects if you could isolate all the other variables mentioned above.

So, I really don't pay attention to DF as a criteria for purchase or operating. Its like discussing how many angles can dance on the head of a pin.

Cheers,

David
 
- Since it is hard to get a idea of what effects it has, you can run a simple test with a raw woofer and a piece of jumper wire. What you'll be doing is testing the extremes of the DF formula. Here's how it works:

1) Take the woofer, completely disconnected from anything and hold it up to your ear.

2) Tap on the cone and listen for the resonance as the cone comes back to rest. Multiple taps will help you get a sense of that free air resonance.

This is the effect of no Damping Factor at all.

3) Now, jumper the 2 terminals with a piece of wire so they're a dead short.

4) Repeat Steps one and 2 again and note how the woofer cone has changed in its ability to respond to the tapping of your finger.

You've now tested the 2 extreme ends of the effect of Damping Factor in a simplistic way that your ear can understand.

5) Extra Credit: You can also use a variable resistor connected across the terminals and get an idea of what happens in between those extremes we just tested.

To take this a step further into the rabbit hole, this is also how you can use a woofer as a passive radiator with electrically tunable damping. One would tune the damping by varying the resistance across the passive's voice coil.
 
Since I generally like older Infinity speakers I have learned, by listening to speaker performance, to seek amplifiers that have high current and higher damping factors. Been through too many amplifiers that didn't have that and it definitely was a waste for me. Didn't know it though until I finally purchased one and it grabbed ahold of the bass output like none other.
 
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