Request: Study of Damping Factor and Planar Magnetic Headphones

It's a well known fact that low damping factor leads to EQ in the shape of the headphone's 'impedance vs frequency' plot.
(ie. the amplifier is not flat for headphones with variable impedance). This is a pretty simple phenomena that can be measured, it's audible and pretty easy to put on numbers.

I'm interested in the measurability of the effects of Low Damping Factor in headphones with a flat impedance.
Not sure if someone has done this kind of study in the past. If you know one, please share the link.

I've used a K702 in the past, plugged into a Yamaha A-S500 (470 Ohm output impedance)
Extreme case: damping factor = 0.13
And the sound was still ok, not ultimately transparent, but not ruined either.

So it would be really interesting to have a few measurements that put these effects in perspective.

It would be ideal to measure a planar with really flat impedance like the LCD-2 plugged into an amplifier with really low output impedance (say, less than 2 Ohm) and the same headphone plugged into a similar amplifier with 50 Ohm or higher output impedance. Maybe a resistor can be used in series with the 2 Ohm amplifier to simulate the 50 Ohm, similar performing amplifier.

The objective is:
Frequency response, harmonic distortion and CSD in both cases:
1- High Damping Factor (Less than 2 Ohm output impedance)
2- Low Damping Factor (More than 50 Ohm output impedance)

Thanks,
Klasse

Relevant Findings: #48

 

I have a Dayton measurement mic coming today and will be putting together a measurement rig based on that asap. I also happen to have HD650, Alpha Dog, and Geek Out 1k v1 (with the 0.47 and 47 ohm output impedances).

So... thought I'm a total measurement n00b, I'll give this a shot and report back.

 

Damping factor doesn't really affect planars because they are purely resistive loads and that is precisely why they have flat impedance curves.

 

If we're gonna argue that, then the flip side is that planars still technically have mass and a natural resonance due to tension. Just because nothing shows up on an impedance curve doesn't mean there isn't unwanted movement/energy to damp out.

 

I mean if you wanted to go really extreme with the output impedance for testing/measurements you could try them straight out of a DAC, right? Obviously not useful for real world stuff but the extremity of it would provide a clearer idea of what is happening. Would just need some more sensitive 'portable' headphones like the PM-3 or HE-400S.

 

Although it is pretty efficient for an ortho, my Oppo PM-2 sounds way better on the Cavalli Liquid Carbon than on my high output impedance Marantz amp (which is otherwise quite good with my high-impedence Senn HD 600). Maybe this is one of the reasons why.

 

The furthest I've tested was on my HE-6 with and without a 15ohm resistor in series with the output (correcting for volume difference of course). I thought there was a difference, but it was small enough that I could have dismissed it as placebo. My only takeaway from that is 15ohms was not enough for me to confidently detect a difference.

 

Most decent cabling should get you at least 100' without appreciable loss (and if you're running a mic cable for power then you oughtta be slapped upside the head), perhaps half that length if you're bridging your amps and running some stupid amount of subs to crank enough oomph to help you pass a kidney stone. If you're going greater distances than that, then serious consideration should be given to placing amps closer to the speakers and keeping your long runs for signal lines only. If you're going even further, then fidelity is probably not a main concern and you should be switching to a constant-voltage distribution system where wire gauge is less of a concern.

 

It applies in the same context, but it is being looked at from the wrong end.

Max power transfer theory says that given a source with a given output impedance, the largest amount of power it can transfer to a load is achieved when the load impedance matches the output impedance.

It does not say that given a load, the max power transferred to the load is when the output impedance matches the load. From the perspective of the load, the greatest power transfer to the load is when the source impedance is 0.

Thus, if the ZD has an output impedance of 20 ohms, the largest power transfer out of the ZD is possible when the load is 20 ohms. Above or below that number, you will see lower power transferred to the load.

 

impedance matching is only needed for HF signals such as video, digital signals and RF.

 

This is not for power transfer reasons, though. It is for signal integrity reasons.

 

It is only important to consider for high frequencies because these are the frequencies where nearly any length of cable run becomes a "transmission line". A transmission line is defined as having a length greater than λ/8. For this reason in the audio bandwidth (up to 20 khz) anything less than 1875 meters!!! is NOT considered a transmission line at these frequencies. Obviously when dealing with RF signals this is a hole different story and I'm also not suggesting that there are no signals above 20 khz being output by audio equipment.