Damping Factor question

There was a recent letter in The Absolute Sound about damping factor(s) that piqued my interest.

The letter said that high-damping factor amps might not produce bass with certain speakers.

This pretty much described a situation a friend went through in the early 80s. He updated his amp from a mid-power Sansui, to what I remember as a Phase Linear 400, and he lost all the bass from his speakers. I can remember switching phase on his speaker wires repeatedly and not hearing any difference in the bass. Thinking the amp was at fault he took it back to Tech HiFi and it had plenty of bass in the store with the speakers that they connected it to. I believe he returned the Phase Linear and stayed with the Sansui amp.

Is this common knowledge and something I have never run across before?

BTW, the letter referenced the Burnmiester 159 amp which has a user-adjustable damping factor.

Have you seen AG's adjustable Damping devices? Very interesting and @Ernie was able to attend a demo and was quite impressed. Having ability to match the damping factory to the best sound out of your speaker seems like a great idea. If you have a mismatch for sure.

Always interesting. DF relates the source impedance to the load impedance. Disregarding the load impedance for any one situation because it's a given, DF is just a matter of output impedance, Z. You can, in effect, raise the source (output) Z by imposing resistance ahead of the load.

As that Z increases, the control by, electrical braking, that the amp holds over the moving system of the woofer diminishes. So the woofer rises less quickly then overshoots, sometimes a lot. Definitely a distortion and definitely not a good one. But the perception can be one of "warmer" bass that, for some listeners, and in mild cases, can be more pleasing. Resolution has fallen off, yes, but the net can be seen as positive. You just don't realize what you're missing in detail resolution.

One of the old industry war stories among speaker designers is about an upstart speaker maker who, having demonstrated his new product to a retailer hears, "No bass. Sorry." So the speaker guy returns to his lab, scratches his head, and inserts a series resistor into the low pass circuit. Upon return to the retailer he hears, "Splendid! I'll take two pair."

Most tube amps, having output transformers, have naturally higher output impedances than a typical SS amp. That "warmth' is part of the charm. Smart designers check their work for tube amp compatibility, lest they've wandered too far off the mark with the speaker's damping. The cumulative effect can cross the line from "warm" to "bloated".

Ideally, you want an output Z = 0 for maximum DF, hence maximum control of the moment-by-moment position of the woofer's moving system. Ideally, to maximize that control, you want to deliver enough force at the voice coil to overcome the inertia of the moving mass and the elasticity of the suspension and of the cabinet's captured air spring. That's why today's racing woofers push the limits on motor force factor and also have soft suspensions. You can get superb signal tracking but the penalty is, yep, rolled off low frequency. Happily, now, you don't have to resort to tossing out the damping.

Punker X said:

Have you seen AG's adjustable Damping devices?

Click to expand...

Nope, AG who?

Angela-Gilbert Yeung, of Blue Circle fame.

We were listening to Heresies, one of my least favourite speakers, and, from a design perspective, probably the polar opposite of today's high-performance drivers.

I was explaining this exact thing to @nickrobotron the other week.

I've experienced this many times. When I got my Odyssey monoblocks years ago they had better control of the woofers and it caused a perceived lack of bass on my Tekton's. But the same amps on my Philharmonic 3's with their MLTL design and Revelator woofs they kept from sounding bloated in my small room.

I think it's an important spec that is oft overlooked.

- Woody

Ernie said:

Angela-Gilbert Yeung, of Blue Circle fame.

We were listening to Heresies, one of my least favourite speakers, and, from a design perspective, probably the polar opposite of today's high-performance drivers.

Click to expand...

Found this, will have to read it later.

There is nothing new under the sun...
😎

mhardy6647 said:

There is nothing new under the sun...
😎

1958 Allied Radio Catalog

Flip-through every page of this 1958 Allied Radio Catalog containing vintage radios, phonographs, amplifiers, amateur / short wave radios, knight kits & electronic parts.

www.alliedcatalogs.com

View attachment 62471

Click to expand...

My Fairchilds had that feature too. Dave Gillespie opted to remove it for simplicity sake when he did their restoration. They're from 1957.

- Woody

Joseph Marshall, an American designer of many amplifiers and a prolific writer for the hobbyist magazines of the 1950's designed quite a few amps with variable damping. The amp I am building now has that "feature " as an option you can build in. BUT !!! that goes against my grain.
I designed and built the output transformers on huge high quality iron with low flux density to get the lowest DC resistance possible. Im not going to ruin that with adding series resistance. I wound them to be flat at 30 Hz at full power of 50 watts RMS, and it uses 4 off 807's per channel. Actually I used 5B/254 which are a modern version with a loctal base. Here is the bit of circuitry for the boffins about the amp and the variable damping circuit.

Just to add to Pats post, the lower the output impedance, the better the damping factor will be. Thats why really good output transformers for valve amps are so expensive and hard to find. A really good output transformer is a piece of very excellent art. Read what Pat has said as he has it written down perfectly.

If anybody is interested in the whole article I can post it, just ask.

Joe

I had a rebuilt Accuphase E202 and I could never really tell any difference between the damping settings with various speakers.

I think, bafld, that you would need to go back to either open baffle, or BIG horns to make this work.
Its another reason I didnt build it into my amp. I have modern speakers. ( well 1970 anyway ).

Joe

joebog1 said:

I think, bafld, that you would need to go back to either open baffle, or BIG horns to make this work.

Click to expand...

Do you also think I have had the speakers listed in my signature forever?
Although I didn't purposely list them in order, 3 years, 2 years, and 1 year.
E202 was quite some time ago.

FWIW based on my experience (and the numbers) I'm firmly in the camp of over a certain low number, higher is meaningless.

opnly bafld said:

FWIW based on my experience (and the numbers) I'm firmly in the camp of over a certain low number, higher is meaningless.

Click to expand...

me, too... FWIW

mhardy6647 said:

me, too... FWIW

Click to expand...

Sort of like the THD numbers that all my friends and I hyper-focused on during the late 70s. “My amp has THD of 0.000000020!”

Remember the Audio Magazine annual equipment issue that listed page after page of gear with a set of specs? You could just pick the piece with the best specs!

The dirty little secret is that the specs that are published, are so simply because they're the easiest to measure. The consumer then takes the dumb mental leap into using them as a basis for comparison.

Just me, my published specs were always as short on detail as possible. The guy who wants to buy by comparing, say, F3 ain't my guy. Although sensitivity is pretty much a liar's game, that's one of the few specs that can legitimately be used by a buyer for, at least, eliminating non-starters.

Even so, that number can be wildly misread. I recall one S(major magazine)e review with bench tests by JA who "discovered' that one of Jim Theil's new babies measured 6dB above the published sensitivity spec. Really? REEEALY? The guy apparently concluded that Jim, no slouch at the bench, didn't know his speaker was producing FOUR TIMES the output per Volt as he thought it was. Yeah, don't believe any of that stuff.

JoeThePop said:

Sort of like the THD numbers that all my friends and I hyper-focused on during the late 70s. “My amp has THD of 0.000000020!”

Click to expand...

Guilty as charged here, too.



"You can hear the specifications"
That's not necessarily a good thing. 😎

Early on I had a customer who bought a Nakamichi power amp entirely based upon the specs as touted in the glossies. I went over to put it in her system in place of a Hafler I'd loaned her. Well - the thing just laid there like a limp dishrag. No energy, just lifeless and dull. She, no audiophile, recognized the shortfall immediately. After I recovered from the surprise I realized that the single most salient spec is not customarily stated: dynamic linearity. I still can't imagine how they did it; a room full of engineers and managers approved this thing for production without noticing? They were building to the standard specs to the exclusion of everything else? I dunno.

When I mentioned it to my dad, who had spent the late 1960s and the 1970s as a VP of EE inside Sony USA, and had spent a lot of time in Japan, he just shook his head. He'd a pretty good idea what was going on there. He said: that's why Sony always sent it's prototypes to us (in New York).

The lady returned the Nak the shop and bought the Hafler. Saved some dough.

Pat McGinty said:

Early on I had a customer who bought a Nakamichi power amp entirely based upon the specs as touted in the glossies. I went over to put it in her system in place of a Hafler I'd loaned her. Well - the thing just laid there like a limp dishrag. No energy, just lifeless and dull. She, no audiophile, recognized the shortfall immediately. After I recovered from the surprise I realized that the single most salient spec is not customarily stated: dynamic linearity. I still can't imagine how they did it; a room full of engineers and managers approved this thing for production without noticing? They were building to the standard specs to the exclusion of everything else? I dunno.

When I mentioned it to my dad, who had spent the late 1960s and the 1970s as a VP of EE inside Sony USA, and had spent a lot of time in Japan, he just shook his head. He'd a pretty good idea what was going on there. He said: that's why Sony always sent it's prototypes to us (in New York).

The lady returned the Nak the shop and bought the Hafler. Saved some dough.

Click to expand...

Marketing. As in the ad above posted by @mhardy6647. Sometimes engineers are forced to do stupid things to better market something.

Damping factor? As I understand it, the high amplifier output impedance of some amplifiers can be factored into a speaker cabinet design to provide decently damped bass performance. It might be helpful to see input from the folks doing this - they tend to hang out on DIYaudio. Nelson Pass wrote a little about this a few decades ago, I believe, and I know of a few speaker designers who do this. My Bisons were designed this way and my drummer friend likes the bass performance of that speaker driven by SET amps: with a decent recording, he can get a sense of the tension on the skins, so I guess it must work at least decently.