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'[PICLIST] Has this been done before? Speaker testi'
2001\09\24@224039 by Consulting And Electronic Repairs

picon face
Hello All,

I have a project that I want to do in a pic but
want to make sure it hasn't been done before.
I really hate re-inventing the wheel.

Anyway,

What the circuit will do is have a speaker connected
in a test setup and pass a range of frequencies to the
speaker testing the impedance at each frequency. I would
like to have the pic connected to a computer running
a basic program for graphing the results. The results will
later be used to calculate the enclosure size for the speaker.

Questions

I know I can use a pic with an A/D for measuring a voltage
but how would you have a pic generate a frequency?

The frequencies needed are in the audio range from 1hz to about
20khz.

If it hasn't been done already I have a schematic of the manual
test setup using a freq generator and dvm to do the test manually.
I could scan and send the schematic if anyone is interested.



Any help would be great,
Steve
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'[PIC]: Has this been done before? Speaker testing'
2001\09\24@231849 by Jinx

face picon face
> I know I can use a pic with an A/D for measuring a voltage
> but how would you have a pic generate a frequency?

Use a timer interrupt. There is code at http://www.piclist.com for
setting the interrupt period. If you can generate a triangle wave
with a D/A, this circuit

http://home.clear.net.nz/pages/joecolquitt/tri2sine.html

will convert it to a pretty good sine wave. You can send this to
the audio amp to drive the speaker

I hoped to follow up on using a PIC pin a voltage source, which
would have been handy for the +/-12 and -5 needed (in this and
other analogue circuits), but perhaps you can derive them from
your amp PSU unless you already have a suitable one

> The frequencies needed are in the audio range from 1hz to about
> 20khz.

20kHz is OK, that's 250 instructions/hertz (at 20MHz) to approximate
a triangle wave

> If it hasn't been done already I have a schematic of the manual
> test setup using a freq generator and dvm to do the test manually.
> I could scan and send the schematic if anyone is interested

You could host it on your own page at PIClist, one of the admin
can help you do that

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2001\09\25@080624 by Allen Mahurin

picon face
I'm no PIC expert (yet), but wanted to point out that
the "audio" range is typically specified as 20 Hz to
20 kHz.  No need to generate quite as low a frequency
as you mentioned (I know, not much difference, but it
could save you some time/programming).

I've done my share of speaker testing on Audio
Precision and LMS.  It could be interesting to see how
a PIC-based measurement system turns-out.   :)

Good luck,

ATM

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'[EE]: RE: Has this been done before? Speaker testi'
2001\09\25@082123 by Fok, Ben

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face
Your best bet would be the MAX038 sine wave generator chip.
It has a bandwidth of 0.1Hz to 20MHz.  Its frequency can be
changed by changing a voltage.  You can easily interface
a DAC to digitally control the frequency.

Go to http://www.maxim.com and check out the spec sheet.

Ben

{Original Message removed}

'[PICLIST] Has this been done before? Speaker testi'
2001\09\25@111937 by SkinTech

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face
Steve,
No comment on the pic part of your project, but are you sure you want to
calculate box size from the freq/impedance data? Are you aware that what you
need to measure are things like Qc, Qt, Fs etc which is done at specific
frequency points. No offense meant!

Jan Didden

{Original Message removed}

2001\09\25@125200 by Mike Hardwick

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face
>I know I can use a pic with an A/D for measuring a voltage
>but how would you have a pic generate a frequency?

Steve,


http://www.fairchildsemi.com/pf/ML/ML2036.html

More than once, I've thought about using this chip for another type of
audio measuring instrument (non-acoustic). I would be pleased to know how
you get along with it, if you decide to give it a shot...

Mike Hardwick
Decade Engineering

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'[EE]: RE: Has this been done before? Speaker testi'
2001\09\25@184347 by Tom Handley

picon face
  Steve, take a look at Fairchild's (formerly Micro Linear's) ML2036
Programmable Sinewave Generator. I've been looking into this as part of my
PIC-based DAQ system. I'm currently testing the ML2036, MAX038, and looking
at Analog Devices' DDS family.

  For your application, the ML2036 seems ideal. All you need is a crystal
(literally, no capacitors). It requires +/- 5V and has a 3-wire SPI-style
interface. You clock-in 16 Bits, LSB first, and set a Latch Enable line to
set the frequency from 1 to 50KHz (I tested it to 65,535KHz). By using a
8.388608MHz crystal (Digi-Key PN: SE3415 / Epson CA-301 family), you get a
direct one-to-one program data to frequency setting with a 1Hz resolution.
The chip provides Osc/2 and Osc/8 outputs which may be of use if you want
to clock a PIC at 4.194304MHz.

  There is a voltage reference input. Tying this to +5V gives a maximum
output swing of +/- 2.5Vp-p. You can reduce this via an external reference.
Harmonic distortion is -45db max. The device comes in a 14-pin DIP or 16-pin
SOIC package. For more info:

     http://www.fairchildsemi.com/pf/ML/ML2036.html

  - Tom

At 07:18 25-09-01 -0500, Steve wrote:
{Quote hidden}

------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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2001\09\26@213020 by Kasm Consulting

picon face
Jan,

No offense taken at all.
I'am aware of the Qc,Qt,Fs figures.
The optimum way to get these figures for a given
speaker pair (For Matching) would be to take an
actual impedance reading over a range of freqs and then
calculate from the graph produced. There is quite a bit
of variance amoung speakers, even if the same model.

Steve.

{Original Message removed}

2001\09\27@012231 by Kevin J. Maciunas

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picon face
On 26 Sep 2001 21:28:33 -0400, Kasm Consulting wrote:
> Jan,
>
> No offense taken at all.
> I'am aware of the Qc,Qt,Fs figures.
> The optimum way to get these figures for a given
> speaker pair (For Matching) would be to take an
> actual impedance reading over a range of freqs and then
> calculate from the graph produced. There is quite a bit
> of variance amoung speakers, even if the same model.
>

Not that this particularly my field (he hides behind his CS academia!)
but the way a colleague and I have done this in the past is to use an
impulse noise spike (a maximum length sequence) and then capture this
(with a calibrated mic) and do the FFT...

We have an old bit of kit called the "IMP" which plugs into a PC
parallel port which does all the noise/capture and then you can do your
own thing and get all the Q's and impedance curves and response curves
too...

Just my $0.02
/Kevin
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Dept. of Computer Science   Ph : +61 8 8303 5845
University of Adelaide      Fax: +61 8 8303 4366
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'[PICLIST] Has this been done before? Speaker testi'
2001\09\28@083105 by Edson Brusque

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flavicon
face
Hello,

> There are several software packages around that makes up an audio testing
> center around a sound card.

   I've been using it for some time. The programs I use are "Sonic
Foundry's Sound Forge" and "Sound Technology's SpectraLAB".

   I've heard ElectroVoice have a good audio testing software. Have you
tried it? Any other suggestion?

   Thanks,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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