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Old 11th April 2012, 01:45 AM   #1
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Default Passive to active conversion software

I am trying to convert this design from passive to active crossover (miniDSP).

My plan was to trace the transfer function shown on the website, convert to biquad and insert in DSP. However im not sure which software allows me to import the filter function as an FRD file and use it as a target to finally export the filter as biquad.

Ive tried x-over pro which seems to have potential but is buggy. Any other suggestions?

Last edited by samadhi; 11th April 2012 at 03:54 AM.
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Old 28th April 2012, 10:54 AM   #2
AndrewT is offline AndrewT  Scotland
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The passive crossover relies on the impedances of the drivers to determine it's EQ and filtering effects.

If you reverse engineer the passive filter, you will be excluding all the driver/crossover interactions.

I tried to use the dcx2496 to mimic the passive crossover, with the intention of calling up all the dcx settings and implementing them in a discrete active filter/eq setup.

But I could not get the dcx to sound like the original passive filter. I lost patience after a couple of months, but I will try again.
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Last edited by AndrewT; 28th April 2012 at 10:57 AM.
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Old 30th April 2012, 02:09 AM   #3
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Andrew, as far as I understand a typical filter transfer function graph plots the final filter effect on the drivers AFTER taking impedence into account.

For example, this graph here from a zaph design: http://www.zaphaudio.com/ZD5-modeled...erfunction.gif

Is this not the actual electrical function applied to the driver including impedence, one that can be transposed directly to an active crossover?
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Old 30th April 2012, 03:57 AM   #4
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by samadhi View Post
..... a typical filter transfer function graph plots the final filter effect on the drivers AFTER taking impedence into account.

Well, a typical electrical filter transfer function plot shows the transfer function of the filter working into its intended load.

Quote:
Originally Posted by samadhi View Post
For example, this graph here from a zaph design: http://www.zaphaudio.com/ZD5-modeled...erfunction.gif

Is this not the actual electrical function applied to the driver including impedence, one that can be transposed directly to an active crossover?
No

The zaphaudio transfer function you link to appears to be a plot of SPL, for given input, against frequency, of two drivers.

In order to calculate the electrical transfer function of the crossover in the speaker you're interested in, you need to know the electrical impedances of the drive units used, plotted against frequency, in those enclosures.

If you want to duplicate the response of the speakers with passive crossovers, using dsp, it might be a better starting point to plot the transfer function of the crossovers working into the drive units, in the enclosures, then work out how to obtain that.
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Old 30th April 2012, 04:26 AM   #5
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Simon, thanks for clarifying. Converting to DSP is trickier than I first thought.

Quote:
If you want to duplicate the response of the speakers with passive crossovers, using dsp, it might be a better starting point to plot the transfer function of the crossovers working into the drive units, in the enclosures, then work out how to obtain that.
Is this easy enough to extract from a model in LspCAD, soundeasy etc?

Im not sure I undertand the process completely. Would you be kind enough to break it down into a few steps?
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Old 30th April 2012, 12:58 PM   #6
Simon B is offline Simon B  United Kingdom
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If you can get an electrical model of those drivers, in those boxes, then possibly. I've no experience of the programs you mention so I can't say.

If you have these speakers, or are building them, you could test the transfer function from the speaker terminals, through the passive crossover to the drive unit terminals, with the drive units in the enclosure, using something like spectra lab or spectra plus. Then implement that transfer function in dsp.

But it seems a lot of effort to go to, implementing this in dsp and bi-amping, just to duplicate the passive crossover - surely you want some benefit or improvement from it?
You could use the given passive crossover for a while to see if there's something about it that you'd like to alter, eg make adjustments for listening room conditions.

As I said, I've no experience of the software you mention, you'd have to immerse yourself in their manuals to find out what they will and will not do.


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Old 16th May 2012, 04:02 PM   #7
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by samadhi View Post
Is this easy enough to extract from a model in LspCAD, soundeasy etc?
Have you tried modelling or even measuring the acoustic response with and without the crossover?
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Old 19th May 2012, 12:33 AM   #8
Davey is offline Davey  United States
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samadhi,

LspCAD will allow you to optimize to a "target" response. The target response can be an electrical transfer function of a passive network, or other "generic" responses you might pick. (.FRD files (ascii text) are certainly usable for this optimization.)

I believe the transfer function links to Zaph's ZD5 project are indeed electrical transfer function equivalents (that include driver parameters.) If you performed a transfer function measurement right at the speaker terminals relative to the input jacks, that's exactly what you'd measure. In that case, those would be the curves you would want to match with a line-level crossover and you'd create an exact duplicate of the (now removed) passive crossover.

The easiest way to do a passive-to-active conversion is to measure an actual speaker right at the driver terminals and save the measurement so it can become the target. If you don't have access to an actual speaker you can simulate the transfer function but you need to do some estimation on driver impedances, inductor DCR, etc, etc.

Cheers,

Dave.
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Old 21st May 2012, 08:49 PM   #9
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by Davey View Post
.......I believe the transfer function links to Zaph's ZD5 project are indeed electrical transfer function equivalents (that include driver parameters.) If you performed a transfer function measurement right at the speaker terminals relative to the input jacks, that's exactly what you'd measure.......

Which "transfer function links" are you referring to here Davey?


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Old 21st May 2012, 09:38 PM   #10
Davey is offline Davey  United States
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The link in Post #3.

Dave.
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