AudioBanter.com - View Single Post

In article ,
says...

"Mark" wrote in message
th.net...
In article ,
says...
I have had no luck in measuring speaker response at low frequency's,

Then you may not be using the right tools.

What tools do you use?

What is needed is a measurement mic that is calibrated to
the device being used for the test measurements.

I've personally used a number of different set-ups, from a
number of different manufacturers. My favorite for best
bang for the buck is the Audio Control Industrial SA 3052.
There are plenty of other devices that will do a respectable
job as well.

First off, you should Never use a stereo mic (or any stereo
set up) for measurement purposes. You are guaranteed to get
inaccurate results. Secondly, the mic is only part of the
equipment. What else are you using?

Never?
Yes, never. If what you're interested in is the frequency
response from a single driver or cabinet, you want to make
that measurement from one point in space.

By using a stereo setup I can collect two data streams rather than
one, I can compare the streams and quickly analyse microphone placement and
any other abnormalities.

Standard measurement is done at 1 meter, on axis. Period.
(Unless, of course, you're creating a polar chart.) Any
abnormalities that exist are a result of either poor
driver/box design, or space-induced aberrations.

And speaking of which, I note in a different response of
this thread that you put nominal weight on the influence of
the space in which you're testing. I would suggest that
Ethan is dead-on in his comment, _particularly_ when the
concern is low-frequency response. By testing in a confined
space that is Not truly anechoic, you're guaranteed to
introduce abnormalities in the response curve.

I have access to / a collection of equipment, some built by HP other stuff
designed and manufactured for the BBC or others. All the HP gear uses HPIB
which is not what is the most convenient, The A2D - D2A card in the PC is a
much quicker and generates the same results (But much quicker) I have a
number of amplifers, but typically use a Class A 2n3055 based 60 watt mono
amp, It has acceptable characteristics for the type of measurement that I
usually do, 20Hz to 20Khz on / off axis at 1w / 1m / 1khz. Microphones is
the biggest issue as I have not yet found anything that I am really happy
with. I can use the Shures, I have some clone shure that are very flat from
60hz to 20Khz and cost like $60 each! (vs 3 grand for the shures) (I can
compensate in software for the low end droop or use a opamp based corrector
that was build before I started with the PC based A2D card. I have a nice
transducer (Probably from a bridge or Crane) that works from a few Hz.

None of which matters if the measurement tool and the
microphone are not calibrated _To Each Other_. Otherwise
you're fooling yourself into thinking you're getting
accurate measurements.

and a flat panel
with a transducer is the only repeatable method of measuring the output,

Balderdash.

Now thats a technical response!,

Alright, here's the longer response. _Any_ calibrated
mic/tool combination designed for the job will accurately
measure to 20 Hz (and lower) within its own tolerance.

Ok, Can some one tell me what mics / transducers I need to be using to get
accurate low frequency measurements. Not just 'use your ears' as this is far
too subjective!

As I indicated, it isn't just a matter of choosing a mic.
If the mic and measurement tool aren't calibrated to each
other, than accuracy is, at best, a crap shoot.

--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.