In article , Ian Molton
wrote:
On Wed, 22 Oct 2003 19:09:28 +0100 Chris Morriss
wrote:


Now I've had to buy my own mic, I use a MUCH cheaper Behringer
ECM8000.

The price is right...

The response is good, but being an electret it is rather noisy.
Easily good enough for LS measurements though.

Ok, so given that, the next question is:

How do I fudge a 'phantom powered' XLR mic into the mic in on my PC ?

The currents required are quite small. Hence you might find a suitable box
of batteries will be cheaper and simpler than a mains-based design. Should
make it easier to avoid noise and hum problems.

Your *next* question will then be: How do I deal with the room acoustics?
;-

FWIW I have some B&K mics which I borrow from our research lab, and use
these for in-room measurements of speakers at home. These can be useful as
guides to the sound balance at a chosen listening position. But they
probably tell me more about the room than the speakers when I do this. To
measure the speakers I'd have to take them to the chamber at work. Even
then, the chamber is small, so not much use below 100 Hz or so.

People do not usually use measurement mics for recording purposes as they
tend to be too expensive and fragile. Also, as other have said, recording
engineers often choose a mic with particular 'characteristics' that they
like for various tasks. The 'imperfections' of the mic is then felt to give
a 'good' result. (Matter of judgement.)

If you just want to get an idea of the speaker performance in a room, a
reasonably calibrated mic and 1/3rd octave signals should be fine. However
if you want to understand the actual speakers, you'd need to use a chamber,
or do pulsed measurements, or an alternative that allows you to unscramble
the effects of the surroundings.

Also, if you want to understand why speakers that give similar in-room
responses still can sound different, you'd have to explore things like
speaker directionality patterns and their interactions with the room
acoustic. :-) For various reasons, a response that does not seem 'flat'
in a simple 1/3rd octave measurement may turn out to be preferred in
practice. Hence this info can be useful for reference purposes, but should
not be taken as meaning you have to get a 'flat response' from such
measurements for the system to be at its best.

The harder you look, the more details appear. ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On Thu, 23 Oct 2003 09:11:41 +0100
Jim Lesurf wrote:


The currents required are quite small. Hence you might find a suitable
box of batteries will be cheaper and simpler than a mains-based
design. Should make it easier to avoid noise and hum problems.

Indeed. When it says '15-48V' does it really mean anything in that
range? if so, the pair of 12V cells someone suggested is probably the
way to go.

Your *next* question will then be: How do I deal with the room
acoustics?
;-

I suppose really I want to profile the room. pulsed measurements of my
speakers would be fun though.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.

In article ,
Ian Molton wrote:
The currents required are quite small. Hence you might find a suitable
box of batteries will be cheaper and simpler than a mains-based
design. Should make it easier to avoid noise and hum problems.

Indeed. When it says '15-48V' does it really mean anything in that
range? if so, the pair of 12V cells someone suggested is probably the
way to go.

Unless you intend long periods of use 4 PP3s should give about 50 hours at
least, although it's very much dependant on the mic. Some older AKG types
like the early 451s are happy on 9 volts - others may need 40+.

--
*Remember not to forget that which you do not need to know.*

Dave Plowman London SW 12
RIP Acorn

In message , Dave Plowman
writes
In article ,
Ian Molton wrote:
The currents required are quite small. Hence you might find a suitable
box of batteries will be cheaper and simpler than a mains-based
design. Should make it easier to avoid noise and hum problems.

Indeed. When it says '15-48V' does it really mean anything in that
range? if so, the pair of 12V cells someone suggested is probably the
way to go.

Unless you intend long periods of use 4 PP3s should give about 50 hours at
least, although it's very much dependant on the mic. Some older AKG types
like the early 451s are happy on 9 volts - others may need 40+.


On my SSM2017 pre-amp I use two gel-type lead-acid batteries to give me
+/- 12V for the chip, and I then use an isolated dc-dc convertor running
off the total 24V to provide a 0V referenced +30V for the phantom feed.

On the CM8000 the phantom feed is only to power the pre-amp as the mic
cartridge is an electret and doesn't need an external polarising supply.

(On the professional capacitor mics like the B&K 4133 the battery supply
is stepped up to a couple of hundred volts to polarise the capacitor
cartridge).
--
Chris Morriss

In message , Dave Plowman
writes
In article ,
Ian Molton wrote:
The currents required are quite small. Hence you might find a suitable
box of batteries will be cheaper and simpler than a mains-based
design. Should make it easier to avoid noise and hum problems.

Indeed. When it says '15-48V' does it really mean anything in that
range? if so, the pair of 12V cells someone suggested is probably the
way to go.

Unless you intend long periods of use 4 PP3s should give about 50 hours at
least, although it's very much dependant on the mic. Some older AKG types
like the early 451s are happy on 9 volts - others may need 40+.


On my SSM2017 pre-amp I use two gel-type lead-acid batteries to give me
+/- 12V for the chip, and I then use an isolated dc-dc convertor running
off the total 24V to provide a 0V referenced +30V for the phantom feed.

On the CM8000 the phantom feed is only to power the pre-amp as the mic
cartridge is an electret and doesn't need an external polarising supply.

(On the professional capacitor mics like the B&K 4133 the battery supply
is stepped up to a couple of hundred volts to polarise the capacitor
cartridge).
--
Chris Morriss

In article ,
Ian Molton wrote:
The currents required are quite small. Hence you might find a suitable
box of batteries will be cheaper and simpler than a mains-based
design. Should make it easier to avoid noise and hum problems.

Indeed. When it says '15-48V' does it really mean anything in that
range? if so, the pair of 12V cells someone suggested is probably the
way to go.

Unless you intend long periods of use 4 PP3s should give about 50 hours at
least, although it's very much dependant on the mic. Some older AKG types
like the early 451s are happy on 9 volts - others may need 40+.

--
*Remember not to forget that which you do not need to know.*

Dave Plowman London SW 12
RIP Acorn

On Thu, 23 Oct 2003 09:11:41 +0100
Jim Lesurf wrote:


The currents required are quite small. Hence you might find a suitable
box of batteries will be cheaper and simpler than a mains-based
design. Should make it easier to avoid noise and hum problems.

Indeed. When it says '15-48V' does it really mean anything in that
range? if so, the pair of 12V cells someone suggested is probably the
way to go.

Your *next* question will then be: How do I deal with the room
acoustics?
;-

I suppose really I want to profile the room. pulsed measurements of my
speakers would be fun though.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.