How does condenser mic capsule load affect THD?

[MicUlli]

Two tone measurement was introduced because the high frequency limit of measurement equipment. Its basically "folding back" THD into the audible range. Using two speakers has the big advantage of avoiding speaker THD disturbing measurement accuracy.
For testing microphones it is completely sufficient to use a good tweeter (I personally prefer SB Acoustics SB26CDC-C000-4) and loading it with two sines that produce an SPL of approx. 85 dB. This is small enough to avoid distortion of the speaker itself. Then you can adjust the microphone distance (1 cm away you may get 125 dB). All these things are supported by REW

 

[kingkorg]

Two tone measurement was introduced because the high frequency limit of measurement equipment. Its basically "folding back" THD into the audible range. Using two speakers has the big advantage of avoiding speaker THD disturbing measurement accuracy.
For testing microphones it is completely sufficient to use a good tweeter (I personally prefer SB Acoustics SB26CDC-C000-4) and loading it with two sines that produce an SPL of approx. 85 dB. This is small enough to avoid distortion of the speaker itself. Then you can adjust the microphone distance (1 cm away you may get 125 dB). All these things are supported by REW

I'll be thankful for the rest of my life for the tip on that tweeter!!!

 

[MicUlli]

I'll be thankful for the rest of my life for the tip on that tweeter!!!

You're welcome
Yes indeed, this tweeter performs outstandingly well. I also use it for cardioid frequency response measurements: Put the DUT (mic) 10 cm away, compensate for near field effect (proximity) with a 1st order highpass at 270 Hz. Hypercardioids need a corner frequency around 340 Hz. Because of the small measurement distance room effects are very small..

 

[kingkorg]

You're welcome
Yes indeed, this tweeter performs outstandingly well. I also use it for cardioid frequency response measurements: Put the DUT (mic) 10 cm away, compensate for near field effect (proximity) with a 1st order highpass at 270 Hz. Hypercardioids need a corner frequency around 340 Hz. Because of the small measurement distance room effects are very small..

Do you know if the specified sensitivity
2.83 V / 1 m is RMS? At 1K i guess?

 

[kingkorg]

Found the answer on another forum, so i guess this applies.

At 8 ohms 2.83V will translate to 1W while at 4 ohms it will translate to 2 watts. So at 8 ohms they are equal, while sometimes a 4 ohm speaker will be quoted the sensitivity at 2.83V/1m to sound more efficient or just because it's easier to match driver sensitivity knowing the 2.83V sensitivity when you have drivers of different impedences.

 

[kingkorg]

Scored this one basically for peanuts. No idea if it works, but if it doesn't at least we'll get a chance to take a peek inside. I hope it's of the right capacity, so i could try it out with @rogs RF mic.

 

[rogs]

Scored this one basically for peanuts. No idea if it works, but if it doesn't at least we'll get a chance to take a peek inside. I hope it's of the right capacity, so i could try it out with @rogs RF mic.

Wow! -- some folk get all the luck!
Unless the membrane is irreparably damaged, there's not a lot else that could fail, hopefully?..... fingers crossed.

As it's a smallish diameter, instinct suggests it might have a lowish capacitive value? -- which would be shame for using with the inductors I've suggested in my project notes.. ( Still looking for alternatives there..)

Although, as it's likely to have a lot lower tension - and possibly wider 'gaps' - than your standard condenser capsule, maybe the value is in the useful range?..

 

[Tim Campbell]

 

[Tim Campbell]

Scored this one basically for peanuts. No idea if it works, but if it doesn't at least we'll get a chance to take a peek inside. I hope it's of the right capacity, so i could try it out with @rogs RF mic.

I was going to buy this also but you won't learn much. The Sennheiser capsules are not flat. There is heavy eq applied in the amplifier.

 

[kingkorg]

I was going to buy this also but you won't learn much. The Sennheiser capsules are not flat. There is heavy eq applied in the amplifier.

Sure, i get that, it's the part of the design. Shouldn't be a problem to make a deemphasis filter, or just apply eq curve in post. I'm mostly interested in THD performance and off axis properties of the design.

 

[Tim Campbell]

Sure, i get that, it's the part of the design. Shouldn't be a problem to make a deemphasis filter, or just apply eq curve in post. I'm mostly interested in THD performance and off axis properties of the design.

The whole point of the push/pull design is to lower distortion which it does and the off axis response of the mkh series is phenomenal
I have built some of these type capsules. It is easier to acheive some of their better qualities without resorting to compensating for their drawbacks.

 

[emrr]

However they do it, the push-pull MKH resolve incredibly clean background harmonic and transient details in complex musical arrangements. I don't have any other mics that act so much like an audio CAT scan.

 

[rock soderstrom]

View attachment 103999

Manger Schallwandler! Pretty impressive, I heard them once in a studio. Do you use these to measure your capsules?

 

[Tim Campbell]

Manger Schallwandler! Pretty impressive, I heard them once in a studio. Do you use these to measure your capsules?

Yes

 

[kingkorg]

Two tone measurement was introduced because the high frequency limit of measurement equipment. Its basically "folding back" THD into the audible range. Using two speakers has the big advantage of avoiding speaker THD disturbing measurement accuracy.
For testing microphones it is completely sufficient to use a good tweeter (I personally prefer SB Acoustics SB26CDC-C000-4) and loading it with two sines that produce an SPL of approx. 85 dB. This is small enough to avoid distortion of the speaker itself. Then you can adjust the microphone distance (1 cm away you may get 125 dB). All these things are supported by REW

The drivers arrived. However, some preliminar measurements show much different response, nowhere as flat as published specs. How are yours behaving in that regard? Against a calibrated reference mic, if you use one.

 

[MicUlli]

The drivers arrived. However, some preliminar measurements show much different response, nowhere as flat as published specs. How are yours behaving in that regard? Against a calibrated reference mic, if you use one.

They behave very well for my opinion. You should be aware of the driver mounting (infinite baffle). Pls find attached my measurement...

 

[kingkorg]

They behave very well for my opinion. You should be aware of the driver mounting (infinite baffle). Pls find attached my measurement...

Could be due to mounting, thanks

 

[abbey road d enfer]

What are your thoughts?

I fully agree with all your conclusions. However, distortion due to capacitive loading is:

• rather small compared to the other sources of distortion
• 2nd harmonic, which is considered benign by many, although it produces non-negligible intermodulation distortion

 

[abbey road d enfer]

Which brings me back to thinking if designing (modding) a capsule by increasing the distance between the backplate and diaphragm in order to reduce parasitic capacitance of the capsule itself, and increasing the pol. voltage might be something worth trying.

When you increase "the distance between the backplate and diaphragm", you reduce the capsule's nominal capacitance, which in turn increases the ratio of parasitic capacitances due the diaphragm surround and wires, which in turn increases distortion.

 

[kingkorg]

When you increase "the distance between the backplate and diaphragm", you reduce the capsule's nominal capacitance, which in turn increases the ratio of parasitic capacitances due the diaphragm surround and wires, which in turn increases distortion.

Is there any at least theoretical way to get rid of the "passive" or parasitic capacitance of the capsule. By using bootstrap, or negative capacitance?