Sennheiser MKH8020 pressure rings

studer58 · 27th February 2010

Occasionally I experience situations when I'd like a little more diffuse field HF lift from my 8020 pair (this isn't built into their design, unlike some Schoeps, Neuman KM183, Rode NT55 etc). I remember that a pair of pressure build-up washers were supplied with the older MKH20 omni mics, to achieve this end without electronic or software-based eq...at source if you will.

I found a couple of plumbing store washers and slid them over the end of the mics, in an attempt to emulate the MKH20 procedure...they are approximately the same dimensions as the washers for that particular mic. The grille cover of the 8020 is a bit 'wavy' (doesn't mate with the body quite flat, you may see this in the photos) so mine is a best attempt to line the washer up with the lower edge of the grille. I'm sure this (if it works) would provide a much more subtle 'lift' than APE spheres, for example, but may address the concerns of those who find the mic's flat response to be a little dull ? Don't forget that the MKH20 really hedges it's bets, because in addition to the pressure rings it also includes a Diffuse Field Eq switch which introduces a gentle (?) lift beginning above 2k of 6dB from 8k to 20k. Can anyone here see any reason why they wouldn't function in a similar way to the MKH20 rings ?

NoKi · 27th February 2010

Hi,
I'm afraid it will not work as you expect as a pressure ring will only lower the frequency where the pressure bump and the increasing directivity starts at. So, for a diffuse field equal. mic the bump gets wider to lower freq., for a free field equalized mic like the MKH8020 you will only get a small bump at mid frequencies and very few HF lift (this is already compensated by the mic itself). The best way to achieve a variable diffuse field compensation is to use a software eq afterwards. A rule of thumb is +3 dB when half the wavelength is equal to the mic diameter increasing linearly up to a boost of about 6-10 dB (depending on the polar pattern of the mic).

Nils

JEGG · 28th February 2010

studer58-
In addition to what Noki has said, remember that with the pressure rings, in addition to the boost of a limited range of frequency on axis (about 2 or 3 to 8k), there is also there is also a depression of those same frequencies from obtuse angles. It makes the mic more directional-a bit toward hypercardioid.

So, as Noki has said, this isn't related much to the issue of free/diffuse field omni's.

The effect of the rings (limited shelf) with the HF shelf produces a frequency response that is a little counter intuitive, it is much more of a peak, something like the chart of a Neumann 183/130.

No reason not to try DIY rings-the Sennheiser supplied ones leave a sticky deposit on the on the mic-not something you want near the diaphragm.

Used without the lift, the rings can contribute texture and detail.

27th February 2010	#1
studer58 Lives for gear Joined: Feb 2008 Posts: 512 Thread Starter	Sennheiser MKH8020 pressure rings Occasionally I experience situations when I'd like a little more diffuse field HF lift from my 8020 pair (this isn't built into their design, unlike some Schoeps, Neuman KM183, Rode NT55 etc). I remember that a pair of pressure build-up washers were supplied with the older MKH20 omni mics, to achieve this end without electronic or software-based eq...at source if you will. I found a couple of plumbing store washers and slid them over the end of the mics, in an attempt to emulate the MKH20 procedure...they are approximately the same dimensions as the washers for that particular mic. The grille cover of the 8020 is a bit 'wavy' (doesn't mate with the body quite flat, you may see this in the photos) so mine is a best attempt to line the washer up with the lower edge of the grille. I'm sure this (if it works) would provide a much more subtle 'lift' than APE spheres, for example, but may address the concerns of those who find the mic's flat response to be a little dull ? Don't forget that the MKH20 really hedges it's bets, because in addition to the pressure rings it also includes a Diffuse Field Eq switch which introduces a gentle (?) lift beginning above 2k of 6dB from 8k to 20k. Can anyone here see any reason why they wouldn't function in a similar way to the MKH20 rings ? Attached Thumbnails

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27th February 2010	#2
NoKi Gear Head Joined: Jan 2010 Location: Stuttgart Posts: 45	Hi, I'm afraid it will not work as you expect as a pressure ring will only lower the frequency where the pressure bump and the increasing directivity starts at. So, for a diffuse field equal. mic the bump gets wider to lower freq., for a free field equalized mic like the MKH8020 you will only get a small bump at mid frequencies and very few HF lift (this is already compensated by the mic itself). The best way to achieve a variable diffuse field compensation is to use a software eq afterwards. A rule of thumb is +3 dB when half the wavelength is equal to the mic diameter increasing linearly up to a boost of about 6-10 dB (depending on the polar pattern of the mic). Nils

28th February 2010	#3
JEGG Lives for gear Joined: Feb 2008 Posts: 941	studer58- In addition to what Noki has said, remember that with the pressure rings, in addition to the boost of a limited range of frequency on axis (about 2 or 3 to 8k), there is also there is also a depression of those same frequencies from obtuse angles. It makes the mic more directional-a bit toward hypercardioid. So, as Noki has said, this isn't related much to the issue of free/diffuse field omni's. The effect of the rings (limited shelf) with the HF shelf produces a frequency response that is a little counter intuitive, it is much more of a peak, something like the chart of a Neumann 183/130. No reason not to try DIY rings-the Sennheiser supplied ones leave a sticky deposit on the on the mic-not something you want near the diaphragm. Used without the lift, the rings can contribute texture and detail.