Peluso P-K47 capsule vs cheap 32 mm K-67 style capsule - Freq. Plot

[Michael_Joly]

In his seminal series of articles for Mix Magazine in 1989, the late microphone modification guru Stephen Paul called attention to the fact the Neumann K67 capsule has a built-in HF emphasis intended to be followed by a compensating de-emphasis circuit. This design created an acoustical pre-emphasis / electronic de-emphasis noise reduction circuit pioneered in the U 67 microphone that increased its electronic system headroom and provided the spectral shaping this mic made famous.

By now, many of you know that almost all low-cost microphones available today (Oktava mics being one of a very few notable exceptions) use a copy of the Neumann-designed K67 capsule. However, in these mics the capsule is not followed by a de-emphasis circuit, but rather a flat-response circuit. This leads to a brighter sound than Neumann intended to be heard from the K67 capsule.

For some time I've wanted to share just how significant the difference is between the flatter-response K47-style capsule and the brighter K67-style capsule. Tonight I ran a test for your listening and dancing pleasure...please see the graph below. For my test platforms I used a couple of Nady SCM-800 mics fully modified with all the good acoustic and electronic stuff I do to them. Both mics were identical. Then I outfitted one mic with a Peluso P-K47 capsule while the other mic was fitted with a standard issue Alctron 32 mm K67-style capsule found in many low cost mics.

I ran white noise through a 4" inch speaker and placed the mics, in turn, directly in front of the speaker at a 3" distance. PLEASE NOTE: The graph below is not an "absolute, anechoic frequency response measurement". It is a relative measurement of two different capsules - all other variables held constant. We are not looking for a flat line response but rather the difference between the two capsules as indicated by their plots. As such, the graph below is a valid measurement of relative (not absolute) frequency response. Now that this is clear, I'll point out what I see in the graph below. Oh, btw - this is an actual digital camera picture taken of my spectral response monitor - its just quicker than grabbing a screen plot file and transferring to my 'Net computer.

The graph starts at the left at 1kHz and extends to 20 kHz at the right. Vertical divisions are 10 dB. There are two areas of interest to me - the range between 6 kHz and 7.5 kHz, and the range between 8 kHz and 16 kHz.

In the first range, notice how the Alctron K67 capsule (light blue line) has an 8 dB rise from just below 6 kHz to 7.5 kHz (less than 1/3 of an octave for you graphic EQ types) while the P-K47 (red line) is essentially flat in this range. Second, notice how the Alctron K67-style capsule has a consistent 3-5db boost above the P-K47 from 8 kHz to 16 kHz. In other words - the K67 copy has a significant and sharp, narrow-band boost from 6 - 7.5 kHz and a moderate, broadband boost from 8 - 16 kHz. Both of these amplitude boosts are clearly audible when program material is recorded with mics equipped with K67-style capsules followed by flat-response audio circuits - especially the 7.5 kHz spike.

While this graph doesn't explain time domain problems (transient response ringing) that exist in inexpensive mics using 32 mm K67-style capsules (smeared "S"), it does agree with the commonly heard frequency-domain complaint of "edgy, too bright sound" in cheap mics that do use K67-style capsules followed by a flat response circuit.

[feral frequency]

Thanks for this Micheal. Been really interested in what you do. Love a man that does his homework.

-Jay

[kidvybes]

...you're time and efforts are well appreciated...very clear differential, as you describe...

[Groberts]

clearly the eq graph for the Peluso capsule has less high end. So the question is, how well does the mic with the Peluso capsule follow something like an authentic Neumann? Would we see a similar result where the Peluso capsule has more high end emphasis than the Neumann? Or would differences be attributed to other factors such as de-emphasis circuits etc? Hope that made sense.

[Chris Lago]

I can't wait to someday hear a custom mic sounding exactly like a neumann, now that would be impressive.

[Brad McGowan]

IMHO there are plenty of boutique mics that sound better than Neumann's. It all depends on what your tastes are.

Michael - so in the K67 sytle mics that you encounter, are you implementing the de-emphasis filter that the Chinese manufacturers are leaving out?

This is great work. It's nice to see some technical research like this.

Brad

[Chris Lago]

Originally Posted by Brad McGowan

IMHO there are plenty of boutique mics that sound better than Neumann's. It all depends on what your tastes are.

Michael - so in the K67 sytle mics that you encounter, are you implementing the de-emphasis filter that the Chinese manufacturers are leaving out?

This is great work. It's nice to see some technical research like this.

Brad

No no, I'm not talking about boutique mics, I'm talking about affordable 300-400 dollars custom mics that would sound as good as a Neumann. I'm not talking about mics almost sounding as good as what they're trying to emulate either.

[bace]

Originally Posted by Michael_Joly

By now, many of you know that almost all low-cost microphones available today (Oktava mics being one of a very few notable exceptions) use a copy of the Neumann-designed K67 capsule.

I thought they ware copys of K47. And too me they look the same. What feature is it that distinguish a K67 from a K47 in their constructions?

[Michael_Joly]

Originally Posted by bace

I thought they ware copys of K47. And too me they look the same. What feature is it that distinguish a K67 from a K47 in their constructions?

The K67-style backplate (bottom right) has a simpler hole pattern than the K47-style (bottom left) backplate. I guess when all this Chinese mic stuff got going ten years ago the U87 was the mic to copy and that's why so many mics contain the K67-style capsule. That, and the fact the K67 is easier to copy with its simpler holes sizing and patterning. Now that the marketplace has started to shift away from super-bright mics and re-discover the joys of flatter-response mics we're starting to see a few K47-style capsule mics appear.

Its easy to distinquish a K47-style or K67-style backplate in a cardioid-only capsule with a clear back-side diaphragm as shown in the capsules below. In dual-sided capsules you'll have to shine a light through the capsule to detect the hole pattern through the gold diaphragms. Though some K67-style capsule have the characteristic "4 hole / 6 hole" edge pattern partially visible just outside the gold area of the diaphragm.

Originally Posted by Groberts

clearly the eq graph for the Peluso capsule has less high end. So the question is, how well does the mic with the Peluso capsule follow something like an authentic Neumann?

I have not measured the frequency response of an authentic Neumann K47 against a Peluso P-K47 or the best-available Chinese K47-style capsule so I can't speak from experience. And let me state upfront - there's more to getting the U 47 sound than just the capsule. But John Peluso has said, and Dave Thomas agrees, the Peluso P-K47 follows the Neumann K47 curve within 2db across the entire audio range. I have not seen documentation of this, and let's avoid getting sidetracked into whether or not we can believe John or Dave.

But it is safe to say a K47-style capsule is going to be less bright than a K67-style capsule. And one can make a microphone with clearly "U 47-ish" qualities by starting with a K47-style capsule. As to quality of capsule execution by vendors - some of the capsule vendors are perfectly capable of making accurate Neumann backplate reproductions and holding "thru" and "blind" holes to close diameter and (in the case of "blind" holes") depth tolerances as well as hole distribution patterning. The problem, in most cases, is vendors have been pushed to achieve lowest price - not highest quality. After all, backplate production is CNC machining, with care it can be done anywhere in the world with excellent results - as folks in the US, Europe, Eastern Europe, Australia and China are proving.

Originally Posted by Brad McGowan

Michael - so in the K67 sytle mics that you encounter, are you implementing the de-emphasis filter that the Chinese manufacturers are leaving out?

Yes and no. You can see from my site that I've got a pretty small stable of Chinese mics that I work on. This is because these mics have generally proven themselves to be solid workhorses or are excellent values. In most cases combination of the particular K67-style capsule used and its following circuit provide a pleasing spectral balance - such as found in the V67g. A mic like this doesn't need spectral balance re-shaping but does benefit from other mods.

Some other K67-style equipped mics do require HF taming so that becomes part of my modification suite. If you go back and look the response chart above you'll see the challenge in the particular K67-style capsule I documented - an 8dB rise in less than 1/3 octave. A 24 dB / octave peak in other words. This requires a 4 pole active filter to deemphasize. That much de-emphasis instroduces substantial phase shift - so while the frequency domain gets flattened out the time domain suffers. I've made the decision to only deemphasize with less phase shift inducing passive EQ. But in general, I've looked for mics that have better than average capsules to start with, whatever brightness remains after distortion components are lowered by modification is much sweeter than in the stock mic.

Though after swapping in a few K47-style capsules I believe this is a very effective and universal problem solver for K67-style mics that are too bright and is a better solution than trying to de-emphasize a narrow band response peak.

[bace]

Thanks for the answer. I seems that Peluso P-K47 is not available on their shop.
And if you compare the K87 and K67 capsule?

[JoeyM]

Completely cool Michael, thanks for the enlightenment. I look forward to doing business with you in the near future.

I wonder if anyone remembers Mr JJ Blairs comments about the siblence range in microphones, but the topic was (I think) certain clone mics that lacked deemphasis. If anyone knows the link, it would seem to compliment this thread very well.

[Michael_Joly]

Thanks. JJ Blair's comments about the high frequency rise of the K67 capsule have appeared in Klaus Heyne's forum and at Lynn Fuston's forum. A Google search with variations on the terms "K67 bright", "K47 K67 swap" or "K67 high frequency" etc will turn them up.

I do remember the Neumann K67 spec mentioned by JJ Blair was something like "up to an 8dB boost at 10kHz". This is consistent with my own measurements of Chinese K67-type capsules.