Almost everyone familiar with the high end mics will recognize the name DPA, or Danish Pro Audio. What they probably don't know is the history behind them other than the standard g**gle or wik* searches. If the kids are DPA, then we ask the parents, B&K, for some more history.

Bruel and Kjaer started with their first mic in 1945. Though their handbook does not say what the model number is. The B&K mics go through an extraordinary amount of painstaking detail for production. For one thing, all of their assembly takes place in a clean room, more than likely a class 100 room, the same type used in hard drive production.

Diaphragms are made of very fine grained nickel foil or special stainless steel alloy. B&K will use different thicknesses of the material, anywhere from 1.8 microns to 8 microns, depending on the desired result and application of the microphone. Note that this is a foil and not a vapor deposited polymer for reasons of stability and longevity. The normal distance from the diaphragm to the backplate is 20 microns with a tolerance of 0.5 microns.

The backplate is also made to a very tight tolerance. During production, the backplate is smoothed, polished and cleaned to a very level surface with a tolerance of 0.5 microns.

For the mics that are pre-polarized to 200 volts, there is an electret polymer layer that is deposited on top of the backplane. The "frozen charge", as B&K puts it, remains and stays stable for thousands of years.

We are all familiar with the cheaper electret microphones that are in the inexpensive recorders but the implementation is quite different. Inexpensive mics will have a polymer diaphragm that includes the electret material. B&K went many steps up to keep the nickel/stainless foil in the diaphragm without the added mass of the electret material. This also helps with the aging process as electret material on a flexible diaphragm will not have the longevity that B&K was designing for. Diaphragms on the market using polymers will not have the longevity of the 0.1 dB over 50 years (for 1/2 inch mic). I would dare any other microphone manufacturer to list their stability and longevity with the numbers to back them up.

During the diaphragm installation, the foil is pressed into place. The foil tension and distance to backplate are computer monitored.

B&K microphone cartridges are put through a forced aging process. The completed cartridge is literally cooked to 150 degrees C, at a certain humidity, for a specified amount of time. B&K specs their microphone cartridges, for most types, to have a predicted change of less than 1 dB for 500 years at room temperature. The microphone cartridges with a shorter life spec is usually employed at higher temperatures approaching 150C and beyond.

Housings of the microphone cartridges are made from a material with high nickel content, that of Monel.

The insulator material used to keep the backplate and the diaphragm separate is usually made out of either sapphire, ruby or monocrystalline quartz. A thin layer of silicone is applied to the insulator during manufacture and is fused by a high temperature process.

Fast forward, B&K Master Catalog, 1989. There is a section called "STUDIO MICROPHONES" listed on page 273. Types of 4003, 4004, 4006, 4007, 3529 and 3530 with the power supply 2812 are listed. The 4003/4006 are listed as "general purpose". 4003 is the Line Level model which requires the 2812 transformerless supply. The 4006 is the P48 model.

4004 and 4007 are the higher SPL/dB mics. 4004 being the line level model which requires the additional power supply and the 4007 being the P48.

Flip a few pages and you'll find the 4011 mic, which are still being used today. 1st order cardioid pickup with the pre polarized cartridge. P48.

1992. Founding of DPA.

1999. Introduction of the 4041 1 inch class mic, probably one of the worlds most accurate, bar none.

B&K still manufactures the 1/2 and 1 inch cartridges for DPA with the full technologies listed (aging, diaphragm material, etc). DPA will reject a number of them during testing. Since B&K has to ship overseas to Colorado, I wouldn't be surprised if they have a bit of rough handling along the way.

Hope you have enjoyed my FIRST post.

Good first post - thanks.

What you probably didn't know is that the back-electret (electret material on the backplate rather than the diaphragm) was a Sennheiser invention and used on most quality electrets today.

DPA tend to call these "pre-polarised" to distinguish them from the diaphragm electrets.

Also - Microtech Gefell are also leaders in measurement mics and nickel diaphragms that are used in both measurement and recording microphones. Also, Gefell also use ceramic capsules that don't change with temperature changes and have also developed an optical coupling for phantom power which keeps any DC nasties out of the audio chain.

The top microphone companies:- DPA, Microtech Gefell, Neumann, Schoeps and Sennhriser are all innovators in their own way.

Thanks for a very interesting, informative and entertaining first post!

Interesting indeed. Though it kind of sounds a little like self promotion.

It's a very unusual 1st post and I thought the same thing. I wonder what's about to be sold to us.

DPA 4040.

j/k

I'll take a matched trio please!

Saw a pic of 6 of them - all matched. Just amazing!

Surely I am not the only one wondering if I actually NEED a microphone that will last 500 years..... I figure if it makes it another 30, I'm waaay good to go.

well with the advances in medicine and retinal tracking technology I will be a head floating in a syrup mixing tunes in 500 years from now, and would love a DPA circa turn of the century. That is if the world doesn't blow itself up first trying to ward of an ancient prediction.

I don't know man, you've got a point. But I think I may hold out for a mic that will last 700 years just in case medical technology gets better than expected....

Very interesting post PM01! I'm sure it would be helpful to everyone here if you could share a little info about yourself and how you came by this knowledge.

Very enjoyable read, O/P. Nice tight writing. You should consider audio recording journalism. I believe a few of the mags accept freelance reviews and such. I love this kind of historical retrospective. There is a thread on here somewhere about Trident A ranges that is truly fun to read, if you enjoy such things. Cheers, and welcome.

Will this be a full range syrup so as to maintain an uncolored listening environment?

The knowledge comes from various sources, mostly being the older B&K master catalogs. Back in the 1960s, they were thin little books, literally half the size of a magazine cut in half widthwise. Also, B&K published lots of technical books that were dated from the 1950s on up. B&K only published the master catalogs once every few years. In 1974, they were about the size of a moderate population phone book, approaching 700 pages and hardcover. The other master catalog I have is dated 1989, and is probably one of the last ones made before they switched over to advertising "slicks". The 1989 edition is about 910 pages and has the section dedicated to the first studio microphones, the classic 40xx series.

Pretty obvious that someone at B&K had a love for music and the recording of, otherwise the big wigs at B&K would have never allowed such a venture to go into studio / live recording. Traditionally, the mic responses at B&K were meant to be as flat as possible for scientific measurements. The repeatability aspect comes from their durability and their use of materials as well as adhering to the ANSI S1.12-1967 standards as well as the IEC-651 standards. Sort of like the ISO9001 certification several decades before the ISO9001, Six Sigma, etc came about.

Engineers and techs in the field wanted to make sure that the microphone and measurements that they were taking could be easily referenced, and that they had a standard of measurement. B&K keeps several "reference standard" mics available on site as well as off locations. They measure the unknown mics to the reference mic at a specific temp, specific humidity and specific barometric pressure. 23 degrees C, 50% relative humidity, 1013 mbar of mercury. Very serious stuff. Plus the engineers and techs wanted to make sure that the mic that they were using didn't drift significantly over a period of time.

For those mics that are subject to high temperatures, they list a certain amount of hours that they are good for. 150 degrees C is fairly toasty for any mic, but certain B&K mics will do the job nicely. I do believe that at the high temp rating, the mics are only good for a few hours.

And if that wasn't enough, some of the mics allowed for a dehumidifier attachment, basically a chamber of desicant gel that can be rebaked that is installed behind the microphone cartridge.

The modern day versions of the DPA 40xx series studio mics are identical to the ones that B&K produced back in the late 1980s. Same materials, same response, same build quality. The only thing they might have changed are the internal preamp board components for the mics. Usually they switch over to different parts, same value. This is done since manufacturers of discrete components won't produce the same part forever.

Durability of the mic cartridge is also part of the build. I've seen B&K mics submerged into faucet water and then dried off. Perfectly functional. Mind you, this is just the capsule portion of the mic. B&K did this to simulate the moisture encountered with a active singer - that of sweat and saliva. Fairly nasty combo to any mic, but the stainless steel/nickel diaphragm handles it with no problem. If I have anyone behind the mic, I'd rather use the DPA/B&K in case they are like Sylvester the cat with all of his spitting. Granted, the pop filter stops most of it but I don't want to see the damage it does over time with a mic diaphragm made from mylar.

The mic cartridge is also robust enough to survive a 1 meter drop onto hardwood with less than a 0.1dB change across the entire operating range. Fairly impressive since the diaphragm is a thin foil.

Now this may all sound like good advertising for DPA, and it is. But the fact is that DPA doesn't have most of the information that I mentioned on their site. Reason being - it's way over too many heads for their customers. DPA would much rather concentrate on providing info that the studio manager/recording guy can understand. That's why they publish papers pertaining to the placement of mics, AB, XY, recording techniques and tips, etc. This is a wise move on their part as many recording engineers that I know of won't have a high level science degree. Quite frankly, it's not needed in the recording studio. Keep it simple and have the recording engineer understand what some of the effects of sound will be, whether it come from the room, acoustic attenuation through materials (foam egg crates anyone?), how the mics react to sound and other sources, etc. They really don't need to know that the diaphragm of the 4041SP/T 1 inch mic is 2 microns thick and made of nickel / stainless steel foil. Or the longevity of the mic in dB shift per hundreds of years. That's more for the physics/science guy.

As for me, definitely applied science guy. Good mix of book and street smarts with the practical knowledge in the industry to back it up. And I find a huge interest in what manufacturers aren't telling you. Fortunately, the parents (B&K) are more than willing to talk while the kids (DPA) get to play. Other companies aren't so nice and they just look at you funny. heh

Thanks much! Now you got me curious about Trident A ranges...

Actually my inner ear drum will be connected to the outer glass container much like the anvil, stirrup and stapes. So it will sound a little different but I will have hundreds of years to adapt. Just need reference mixes. Lol

Very interesting info in this post - thanks!

I always liked DPA's "Mic University" applications guide page

Used the 4011 once - great mic! Very realistic sounding

Yes, Bruel & Kjaer still does produce the larger diaphragm mic capsules for DPA. Same quality as when the recording mics were introduced in the early 80's.

I attended a DPA seminar last fall where I learned that they produce only 2 capsules now. Both are miniature capsules. One round one is used in the 4060 series and the other is used in the new "Reference" series. Round one for omni and football shaped one for directional (cardioid) mics. So even the full sized "Reference" series with the detachable capsules are using miniature DPA made capsules.

Only full size (non detachable head) 4006, 4007, 4011, 4015, 4040 et al family uses the genuine Bruel & Kjaer manufactured capsules.

Recently I converted all my B&K mics to 60 volt active powering. This involved replacing all the electronics in the microphone. The resulting sound was free of all the strident and ringing treble characteristics that one always heard in the B&K and DPA mics. The designer of the new electronics told me that the DPA surface mount electronics sold in the current mics are low quality and they sounded not as good as the old B&K electronics.

The differences I heard in my converted mics were astounding. It was so much diffferent and so much better.

Modern DPA has Bruel & Kjaer quality at the top end and DPA quality throughout the rest of the range.

Can you provide more info about this modification, or a link to a site? I'm interested if the price is right.

No I cannot provide it. The design is not public.

Plush,

If you're in the chicago area, I'd like to compare the modded ones to the 4041SP that I have. Would be most interesting.

For the rest - I'll try to take some pics of the preamp that's in the mic itself. Perhaps that will give us a better idea of what's going on in there. Usually, B&K implements discrete components but that may have changed over the years.

The DPA mics I have used (modern SD versions) were too noisy for my uses. I prefer Gefell mics, M29x Series and UMT 800 in particular.

Any sound samples before and after the conversion? Also, since you're running a +/- 60 rail vs the +/- 48 rail, do you think this contributed to the difference?

Too noisy as in self noise for the mic or was it another audio characteristic? Ringing / oscillation?

Isnt that a nice headroom, 500 years

Spoke to the guys at DPA and they mention that the preamp for the smaller 1/2 inch mics have changed over the years, mainly to reduce any RF noise in the system. The big 4041 has seen very little change with their preamps for the 130 volt and P48 versions.

PM01, are you affiliated with DPA or B&K ?

Nope. Just like them for their history and I use their B&K equipment for some of the mics. Used to be into car audio about 15 years ago when it was at it's peak. Back then, everyone was using 1/3rd octave spectrum analyzers from audiocontrol. I've always used B&K and when I mentioned this to some of the car guys, they gave me a puzzled "what's a B&K" look.

60 volt supplies.

Rens Heijnis custom-built audio equipment

wonder how much of a difference these make.