bruel and kjaer (b&k) mics

ubertar · Post by **ubertar** » Thu Feb 09, 2006 9:23 pm

I scored a couple b&k mics off ebay-- I can't find any model # on the mics, but the preamps are 2613 and 2615 and the power supply is 2801. From looking at the pics on the b&k site, it looks like the capsules are 4145 and 4191 but there are others that look similar, and these may be discontinued models that aren't on the site. I'ts not obvious how to remove the capsules, and I don't want to damage them-- does anyone know how to take these off safely to see if there's a model # inside?

They just arrived today and they work and sound good. The whole thing-- 2 mics, 2 preamps w/cables, power supply, extension cable and output cables including shipping was $275. The only lame thing is the power supply is just for one mic, so I can use either one, but not both at the same time.

joel hamilton · Post by **joel hamilton** » Thu Feb 09, 2006 9:55 pm

I love B&K's, but I cant picture the ones you are talking about, nor do I know how to take them apart.

Hows that for helpful./..

Nice score though. B&K's are really nice...

Professor · Post by **Professor** » Thu Feb 09, 2006 10:56 pm

They are test and measurement microphones which is why there might be multiple mics but only one PSU - you only measure with one at a time.
I'm pretty sure the capsules unscrew, but I've not used those models in particular. It's possible they are more like a bayonet style push & turn connection.
As to the specifics of how one differs from the other - no idea.

-J

klangtone · Post by **klangtone** » Fri Feb 10, 2006 1:23 am

i work in the telecom field and we use B&K stuff for all of our electroacoustic measurements.

the 4191 is actually a mic i use. if that's what you have, it should say 4191 on the side of the mic, all the way at the top. the problem is, the writing is silver on silver. so it's kinda hard to see.
so the way to switch capsules is to just unscrew the top. but you have to be careful because there are two ways to unscrew it. one way exposes the diaphragm (bad!). the other way just exposes a metal pin that makes the connection between the preamp body and the capsule.

that's an insane deal, considering these mics are pretty darn expensive when we buy them new at work.

we have their Head and Torso Simulator (HATs) and I'm going to bring that darn thing home one day to make some binaural recordings. the ears really feel fleshy. it's scary.

Roy

ubertar · Post by **ubertar** » Fri Feb 10, 2006 8:27 am

Thanks. I opened them up, and the 1" capsule is 4131 and the 1/2" capsule is 4134. There's no info on the b&k site, and google hasn't been helpful either. I'll try emailing b&k.

ubertar · Post by **ubertar** » Fri Feb 10, 2006 10:10 am

I called them on the phone, and they emailed me the specs for the 4134-- it's a pressure field/random incidence type (whatever that means) and the freq. response is 3-20k +/- 2db and from the chart, it goes up to 40k within 5db.
4131 data just came in as I was typing this, by fax: free-field, 20-18k +/- 2db. The same sheet gives 20-20k for the 4134, but I'm happy either way-- I'm not planning on recording elephant calls.

ubertar · Post by **ubertar** » Sat Feb 11, 2006 1:10 pm

Does anyone know what the pickup pattern categories for b&k mean? There are three:

1. free-field
2. pressure-field
3. random incidence

I read the stuff on the b&k site about those, but I'm still confused. Are they sub-categories of omni?

Professor · Post by **Professor** » Sat Feb 11, 2006 2:58 pm

They are subcategories of omni and have to do with the frequency response, but I don't remember the specifics. It's something along the lines of one type for reverberant fields (indoors) and another for free-fields (outdoors or anechoic rooms) and something like that. Somewhere around here I have a couple of old B&K handbooks that I got with a big pile of recording books I bought off eBay about four years ago. I'm pretty sure that stuff was covered so I'll see if I can look it up.
It might be handy for you to link us to the place you read about it on their site, maybe someone can translate.

-Jeremy

ubertar · Post by **ubertar** » Sun Feb 12, 2006 10:57 am

Here's one thing I found:

Sound Field Type
Your choices are...

Pressure Field
A pressure field is characterized by sound pressure with the same magnitude and phase throughout the field. This is the condition when the microphone sensor is small in relation to the wavelength of the sound.

Free-Field
Plane wave propagating freely in one defined direction. This is a somewhat theoretical condition representing a point source of sound producing an essentially plane wave at a distance with no reflection off surfaces. A practical free field can be realized at 2 meters or more from a sound source with no other interfering sources.

Diffuse Field
Sound waves arriving approximately simultaneously from all directions ("Random Incidence"). Sensitivity is frequently calculated using free-field measurements. True diffuse fields are closely approximated by hard-walled chambers with many noise sources such as factories.

This seems to be a good explanation... sounds like it's really not important unless you're using them for measurement.

ubertar · Post by **ubertar** » Sun Feb 12, 2006 11:00 am

Did a search for b&k mics on TOMB and someone was saying how they're great on oud, so I dusted off the oud and recorded this with the 4131 capsule. My oud playing is really rusty, but I think the sound is good.

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bruel and kjaer (b&k) mics

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