Amplifier Output Impedance (Damping Factor) and Speakers

[Geert]

You can't be serious. This is the umpteenth time different engineers spend a lot of time explaining you everything about DF, and you start all over again as nothing happend. And all you have is a marketing brochure? A brochure that, as I also explained already doesn't depict how they implemented their DF switching, and doesn't take into consideration the impedance of different speakers, which we also just discussed.

This is starting to look like trolling.

 

[solderdude]

A high damping factor tends to produce a more clearly defined, very precise and analytical sound image, whereas a reduced damping factor produces a more warm and softer sound image.

Nonsensical and not universally applicable.

 

[SIY]

A high damping factor tends to produce a more clearly defined, very precise and analytical sound image, whereas a reduced damping factor produces a more warm and softer sound image.

There is just nothing on Earth that's going to stop you from spewing this nonsense. I originally thought it was you trolling, but I'm now finally convinced that you truly can't do basic math or electrical calculations and have no intention of ever learning. So my apologies for thinking it's deliberate, it's a matter of being utterly incapable of basic understanding.

 

[solderdude]

Pogo merely quoted from page 30 of this manual.

Fortunately for T+A they also included the disclaimer:
Since this setting depends very much on the connected speakers, no universal recommendation can be given here. Choose the setting after a listening test and your personal
listening preferences.
Invalidating their own thesis.

 

[Geert]

Pogo merely quoted from page 30 of this manual.

"Merely", well.. , for the umpteenth time in more than 10 different topics in the last year. According to his standard mode of operation he will go undercover now and hit again in the next topic about amplifiers.

 

[xnor]

Well, amps do try to 'grip' the drivers, but they are usually quite stubborn.
I guess you'd want a driver with low voice coil resistance and high Bl, very little mechanical resistance of the suspension and high compliance, and low mass wouldn't hurt either. Some of these contradict each other and you have to make lots of compromises because of damn physics.

Electrically, this would be reflected as a very high peak in the impedance plot at the resonance frequency. That's where the energy stored in the moving mass and suspension compliance is max.

Another way to think about it is this: a high impedance peak means the driver needs much less current/power at that frequency.
A current source (or very high output impedance amplifier) would still try to push loads of current through it by outputting a very high voltage. That's the SPL "boost" you get in that area.


Thinking back... iirc, the HD555/595 headphones had a 50 ohm driver with like a 250 ohm resonance peak at like over 90 Hz (high f0 is one of those compromises...).
And that was a real "problem" for people without basic EE knowledge. I remember quite a lot of people complaining that it had no bass and others saying that it had very bloated bass. Taste aside, everyone that had complained about bloated bass and responded to my question turned out to be using a high impedance output like the headphone jacks on stereo receivers that were simply connected to the speaker amps through a voltage divider. (Back in the day we also found out that many on-board and front-panel audio jacks had like 80+ ohms output impedance.)
A 120 ohm output impedance gave you like a +7 dB peaking EQ at 90 Hz.

 

[Tim Link]

This is great thread. I'm here because of a surprising difference in sound that I'm perceiving when switching between an older Cambridge Azur 540R 6 channel receiver and a new Denon PME900HNE 2 channel receiver that I was asked to evaluate. I'm using them on Sony SSCS5 speakers and didn't expect to hear any meaningful difference. However, the overall balance seems to be more rolled off in the treble and stronger in the bass with the Denon, and this works nicely with the little Sonys. I'm going to take measurements with REW tonight. I'm saying this in advance to put myself on the spot because I've been lazy about doing this for several days now. I'll be very surprised and confused if I can't see a meaningful difference in the measured response between these two amps powering this speaker.

 

[SIY]

I'll be very surprised and confused if I can't see a meaningful difference in the measured response between these two amps powering this speaker.

Surprised is fine. But don't be confused. And I'm not familiar with these two particular products, but don't neglect power delivery as a potential difference if their ratings are significantly different..

Getting data: excellent idea. Many thumbs up to you.

 

[Tim Link]

Surprised is fine. But don't be confused. And I'm not familiar with these two particular products, but don't neglect power delivery as a potential difference if their ratings are significantly different..

Getting data: excellent idea. Many thumbs up to you.

Thanks for the encouragement to measure. I should have some graphs posted tonight. I'll try it with a few other speakers I have too.

 

[Jim Shaw]

This is great thread. I'm here because of a surprising difference in sound that I'm perceiving when switching between an older Cambridge Azur 540R 6 channel receiver and a new Denon PME900HNE 2 channel receiver that I was asked to evaluate. I'm using them on Sony SSCS5 speakers and didn't expect to hear any meaningful difference. However, the overall balance seems to be more rolled off in the treble and stronger in the bass with the Denon, and this works nicely with the little Sonys. I'm going to take measurements with REW tonight. I'm saying this in advance to put myself on the spot because I've been lazy about doing this for several days now. I'll be very surprised and confused if I can't see a meaningful difference in the measured response between these two amps powering this speaker.

Non-technical audio tinkerers cannot get their heads around the 'transfer function' between amplifier output terminals and speaker terminals. Instead, they write volumes of mostly nonsense about tight bass, shouty treble, glorious midrange, etc.

The amplifier output transfer function is a complex one, especially if it includes feedback. The speaker input is just as complex, due to the crossover circuits and the non-linear nature of the driver motors and the box.

Take a look at Amir's speaker impedance vs. frequency, especially phase angles. Now, estimate that the amp has much different impedances and phase angles of its own. Imagine how erratically they transfer current, voltage, and power.

Now, stir in a myriad of transients from music, remembering that the Klippel-esque data is just valid for steady-state sine waves in simple sweeps. To exaggerate the illusion, think of one fat 'slinky' attached to another different size one... and how they interact... as Mozart or The Rolling Stones figuratively push them across a rocky, downward incline...

Does this make your head hurt? Well, then change amplifiers and start all over...

Are you still wondering why amplifier/speaker combinations sound different?

Sorry for hurting your poor head. It's why people can't fathom engineers or issues they may face versus those of 'cut and try' tinkerers.

-Just one man's view

 

[pablolie]

These discussions drive me to think the only possible upgrade to my system is active speakers (w/ Dirac or similar), where hopefully amp and speaker characteristics are optimized. Shame the LS60 don't come in red.

 

[fpitas]

These discussions drive me to think the only possible upgrade to my system is active speakers (w/ Dirac or similar), where hopefully amp and speaker characteristics are optimized. Shame the LS60 don't come in red.

Well, it's not that bad. Judicious EQ can fix any problems.

 

[Jim Shaw]

Well, it's not that bad. Judicious EQ can fix any problems.

Replace 'any' with 'many' and I'm almost on board.

 

[Tim Link]

Alright, the measurements have been taken comparing the Denon PME900HNE and the Camgridge Azur 540R. The measured difference is minimal, and in the opposite direction of what I expected. The Denon actually has a little more output above about 7k. This was measured with just 1 speaker (Sony SSCS5) hooked up to 1 channel and both receivers used their optical inputs and built-in dacs. The llight blue is the Denon, hot pink is the Cambridge. Taken at 1 meter on axis with tweeter. One thing that seems to be true looking at the impulse response is that the polarities are inverted from each other.

So why the heck do I think the Denon sound softer in the highs? One possibility is that I was using the line level subwoofer outputs while listening to both amps, and maybe the output is higher on the Denon than the Cambridge. The thing is I didn't always listen with the sub. I guess I'm just going to have to listen for a while more to both of them without the sub. Now that I've seen this result I wonder if I'll still perceive a difference.

There's another potential complication. I've been listening with my 3 speaker matrix mixed setup, which has the center channel playing left plus right channels mixed, and the sides play left minus right mixed. The side channels were wired in parallel and out of phase from each other so one amp channel was seeing a lower impedance load than the other. Maybe the Denon could handle that a bit better than the Cambridge?
I guess I'd better measure the response with 2 speakers wired in parallel and out of phase with each other.

So here's the results of both amps pushing 2 SSCS5s wired in parellel off of one channel, with one speaker out of phase of the other and spaced about 3 feet apart - microphone in the middle. Orange is the Cambridge. Again seeing a little more roll off up top compared ot the Denon. Some slight differences here and there but I wouldn't expect to hear much looking at that graph. Maybe those differences are more significant than they look.

 

[Tim Link]

Non-technical audio tinkerers cannot get their heads around the 'transfer function' between amplifier output terminals and speaker terminals. Instead, they write volumes of mostly nonsense about tight bass, shouty treble, glorious midrange, etc.

The amplifier output transfer function is a complex one, especially if includes feedback. The speaker input is just as complex, due to the crossover circuits and the non-linear nature of the driver motors and the box.

Take a look at Amir's speaker impedance vs. frequency, especially phase angles. Now, estimate that the amp has much different impedances and phase angles of its own. Imagine how erratically they transfer current, voltage, and power.

Now, stir in a myriad of transients from music, remembering that the Klippel-esque data is just valid for steady-state sine waves in simple sweeps. To exaggerate the illusion, think of one fat 'slinky' attached to another different size one... and how they interact... as Mozart or The Rolling Stones figuratively push them across a rocky, downward incline...

Does this make your head hurt? Well, then change amplifiers and start all over...

Are you still wondering why amplifier/speaker combinations sound different?

Sorry for hurting your poor head. It's why people can't fathom engineers or issues they may face versus those of 'cut and try' tinkerers.

-Just one man's view

What I'm wondering is how to measure the difference in a way that can show us more about what's going on, why we're hearing something, assuming we actually are hearing something.

 

[Tim Link]

I'm listening to music with the Denon right now, the microphone and mic. boom still right in front of me. It doesn't seem to do anything terrible to the sound. No subwoofer. It sounds very nice. I wonder if maybe it's the extra output in the highs that I like. It adds air instead of sounding bright to me. Maybe my old hearing needs a little of that. I'm going to try to EQ the Cambridge up above 7K to match the Denon. I hope it works. My experience in the past has been that proper use of EQ is far more potent than I would intuit but it's tricky, and often what needs to be done is not what I think needs to be done.

 

[Jim Shaw]

What I'm wondering is how to measure the difference in a way that can show us more about what's going on, why we're hearing something, assuming we actually are hearing something.

Engineers might use ICE to simulate the entire circuit. But in-circuit emulation only helps predict how a circuit performs, not how it might 'sound' to a human of indeterminate taste. [For that we need a witch doctor, like a subjective reviewer with sticks, bones, hokus-pokus, incense, and faithful followers.]

 

[SIY]

What I'm wondering is how to measure the difference in a way that can show us more about what's going on, why we're hearing something, assuming we actually are hearing something.

Excellent work! If you have the means to record the outputs, it might be fun to use @pkane's software to look at nulls and do a quick level-matched ABX.

 

[Tim Link]

Excellent work! If you have the means to record the outputs, it might be fun to use @pkane's software to look at nulls and do a quick level-matched ABX.

I don't have the means to record the electrical outputs, only the acoustical outputs of the speakers. DeltaWave looks really cool but I get the impression I couldn't use it to meaningfully compare recordings of the speakers playing the same file with the different amps. Am I wrong on that? I didn't see any examples of people doing that and the cat is very likely to meow or the refigerator turn on or a loud car go by, etc.
I'm evnsioning some kind of blind A/B test that I could simply set up. I've found amp selector boxes but they're not random so I'd need to come up with a way of hiding from myself which amp is selected.

 

[egellings]

Well, amps do try to 'grip' the drivers, but they are usually quite stubborn.
I guess you'd want a driver with low voice coil resistance and high Bl, very little mechanical resistance of the suspension and high compliance, and low mass wouldn't hurt either. Some of these contradict each other and you have to make lots of compromises because of damn physics.

Electrically, this would be reflected as a very high peak in the impedance plot at the resonance frequency. That's where the energy stored in the moving mass and suspension compliance is max.

Another way to think about it is this: a high impedance peak means the driver needs much less current/power at that frequency.
A current source (or very high output impedance amplifier) would still try to push loads of current through it by outputting a very high voltage. That's the SPL "boost" you get in that area.


Thinking back... iirc, the HD555/595 headphones had a 50 ohm driver with like a 250 ohm resonance peak at like over 90 Hz (high f0 is one of those compromises...).
And that was a real "problem" for people without basic EE knowledge. I remember quite a lot of people complaining that it had no bass and others saying that it had very bloated bass. Taste aside, everyone that had complained about bloated bass and responded to my question turned out to be using a high impedance output like the headphone jacks on stereo receivers that were simply connected to the speaker amps through a voltage divider. (Back in the day we also found out that many on-board and front-panel audio jacks had like 80+ ohms output impedance.)
A 120 ohm output impedance gave you like a +7 dB peaking EQ at 90 Hz.

A lot of times, in wasn't even a voltage divider driving the 'phone jack; it was just a series resistor.