Bode Plot of Frequency Response

[mcp6453[_2_]]

How can I create a Bode plot of the frequency response of a crossover network without using a sweep function generator?
I have a scope and a function generator, but the generator is not sweepable. A file generated in Adobe Audition could be
used for a source, but there is no sync pulse.

[[email protected]]

The old fashioned way, you do it by hand one point at a time.
Set a frequency, take a reading, wash rinse and repeat.
Plot the results.
Mark

[Scott Dorsey]

mcp6453 > wrote:
>How can I create a Bode plot of the frequency response of a crossover network without using a sweep function generator?
>I have a scope and a function generator, but the generator is not sweepable. A file generated in Adobe Audition could be
>used for a source, but there is no sync pulse.

You will have to do it by hand, one point at a time. If you pick third
octave points, you'll do pretty close. Just get a sheet of semilog paper
and a pencil and plot amplitude with frequency.

You may need to know the exact frequency at which a peak occurs... in that
case, sweep the knob back and forth by hand while watching an analogue
meter and looking for the peak.

And... as always.... be aware that the frequency response of the network
when it's terminated with real loudspeakers may be totally different than
that when it's terminated with resistive loads...
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[mcp6453[_2_]]

On 2/27/2015 8:52 PM, Scott Dorsey wrote:
> mcp6453 > wrote:
>> How can I create a Bode plot of the frequency response of a crossover network without using a sweep function generator?
>> I have a scope and a function generator, but the generator is not sweepable. A file generated in Adobe Audition could be
>> used for a source, but there is no sync pulse.
>
> You will have to do it by hand, one point at a time. If you pick third
> octave points, you'll do pretty close. Just get a sheet of semilog paper
> and a pencil and plot amplitude with frequency.
>
> You may need to know the exact frequency at which a peak occurs... in that
> case, sweep the knob back and forth by hand while watching an analogue
> meter and looking for the peak.
>
> And... as always.... be aware that the frequency response of the network
> when it's terminated with real loudspeakers may be totally different than
> that when it's terminated with resistive loads...
> --scott
>

Here's what I'd like to do. It's not a highly accurate system, but it's useful.
http://www.youtube.com/watch?v=uMH2hGvqhlE

[Mike Rivers[_2_]]

On 2/28/2015 12:18 AM, mcp6453 wrote:
> How can I create a Bode plot of the frequency response of a crossover network without using a sweep function generator?
> I have a scope and a function generator, but the generator is not sweepable. A file generated in Adobe Audition could be
> used for a source, but there is no sync pulse.

If you have a computer you can use Room EQ Wizard. It's designed to have
a room between a speaker and a microphone, but you substitute your
crossover network and calibrate the program as if you were using a
microphone with flat response. You can even have the speaker connected
to the crossover so you'll know how it actually performs. It generates a
sweep and plots both frequency and phase response.

The program's free and is available for Windows, Mac, and Linux. You
need to register on the host web site, but as far as I can tell, they
don't bug you for anything.

http://www.roomeqwizard.com/


--
For a good time, visit http://mikeriversaudio.wordpress.com

[Don Pearce[_3_]]

On Fri, 27 Feb 2015 21:16:46 -0500, mcp6453 > wrote:

>On 2/27/2015 8:52 PM, Scott Dorsey wrote:
>> mcp6453 > wrote:
>>> How can I create a Bode plot of the frequency response of a crossover network without using a sweep function generator?
>>> I have a scope and a function generator, but the generator is not sweepable. A file generated in Adobe Audition could be
>>> used for a source, but there is no sync pulse.
>>
>> You will have to do it by hand, one point at a time. If you pick third
>> octave points, you'll do pretty close. Just get a sheet of semilog paper
>> and a pencil and plot amplitude with frequency.
>>
>> You may need to know the exact frequency at which a peak occurs... in that
>> case, sweep the knob back and forth by hand while watching an analogue
>> meter and looking for the peak.
>>
>> And... as always.... be aware that the frequency response of the network
>> when it's terminated with real loudspeakers may be totally different than
>> that when it's terminated with resistive loads...
>> --scott
>>
>
>Here's what I'd like to do. It's not a highly accurate system, but it's useful.
>http://www.youtube.com/watch?v=uMH2hGvqhlE
>

You can do the whole thing with just Audition very accurately.
Generate the sweep then transfer it to multitrack.

Now play back that track while recording another track. Connect the
crossover between the output from Audition and the input you are
recording. You should have a power amplifier and speaker load in
circuit to get the impedances right.

The recorded track now has your crossover response. Double click it,
select the whole trace and do a frequency response plot.

Job done.

d

[Frank Stearns]

Mike Rivers > writes:

>On 2/28/2015 12:18 AM, mcp6453 wrote:
>> How can I create a Bode plot of the frequency response of a crossover network without using a sweep function generator?
>> I have a scope and a function generator, but the generator is not sweepable. A file generated in Adobe Audition could be
>> used for a source, but there is no sync pulse.

>If you have a computer you can use Room EQ Wizard. It's designed to have
>a room between a speaker and a microphone, but you substitute your
>crossover network and calibrate the program as if you were using a
>microphone with flat response. You can even have the speaker connected
>to the crossover so you'll know how it actually performs. It generates a
>sweep and plots both frequency and phase response.

>The program's free and is available for Windows, Mac, and Linux. You
>need to register on the host web site, but as far as I can tell, they
>don't bug you for anything.

>http://www.roomeqwizard.com/

I'll second this; REW is a remarkably complete and fairly well-documented program
given its free status. The host site will bug you occasionally, but it's all quite
reasonable. And, even though oriented toward home theater, there are some things of
interest on the site which makes all that easier to take.

Frank
Mobile Audio
--

[Scott Dorsey]

mcp6453 > wrote:
>
>Here's what I'd like to do. It's not a highly accurate system, but it's useful.
>http://www.youtube.com/watch?v=uMH2hGvqhlE

This is the method people use for aligning receiver IF strips and the like.

The thing is, you need a swept oscillator to do that, and for a useful-looking
plot you need one with a log sweep. You don't have that, so you'll have to
do it by hand.

Just do it by hand, it'll take longer to watch that video than to do the
thing by hand on paper.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."