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Old 6th December 2011, 08:44 PM   #1
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Default Need Testers/Developers for open-source Excel based Crossover Design Tools

Over the past 6 months I have been developing and testing an Excel-based active loudspeaker crossover design tool. I am at the point that I would like to open up testing and development to other DIYers and create an open source development group. When the tools look like they are ready to go, I will open it up to everyone.

I am looking for a few people with the following:
  • experience measuring driver frequency responses (and current capability for doing measurements)
  • general knowledge of active crossovers
  • DIY loudspeaker design experience
  • access to a MiniDSP, Behringer DCX2496, or other configurable crossover/delay unit
  • general knowledge of transfer functions (in s and z^-1) for various types of audio filters is helpful but not absolutely necessary

If you are interested in participating in the development effort, or just want to know more, please read on:

I have attempted to create a set of flexible tools for describing and designing multi-way loudspeaker crossovers given user-supplied frequency response measurements in the FRD format. The tools use linked Excel spreadsheets. I have avoided the use of macros or VBA code in the hopes that the tools will also run without modification in OpenOffice Calc (this is one of the things that needs to be checked out). I'd like to keep the tools completely open source, so there will not be any hidden worksheets or cells. The tools can be expanded to include any number of drivers, e.g. if you want to design a line array, no problem.

Designing the crossover
The tools permit the user to apply various filters to the measured driver data, and then to combine (sum) the responses from all the drivers in the system to obtain the "system response". The filters that can currently be described include:
  • gain block
  • first order: high pass, low pass, all-pass, and shelving filters
  • second order: high pass, low pass, all-pass, notch, and biquadratic filters
  • EQ: parametric EQ bands
Each driver response can have up to 8 filters and four EQ bands applied to it. The system input can also have 4 filters and 4 EQ bands applied to it. Plots in the system response design spreadsheet show the response for each driver, the summed system response, and a "reference" response that the user can supply. Plots in the driver response spreadsheet show the raw and filtered driver responses, and the magnitude and phase response of the filters. All input files should use the FRD format. Driver and filter responses are calculated using Excel's complex number operators in order to properly keep track of phase and amplitude. Phase is unwrapped to avoid glitches during interpolation and calculation, and when adding in driver acoustic delay.

The tools comprise "system response" and "driver response" spreadsheets. For each loudspeaker system there is one system response spreadsheet, and for each driver there is one driver response spreadsheet. All measurements are taken at the same point in space (e.g. on the listening axis) and the system response is calculated for that point in space only. The tools are flexible in the sense that they can be expanded to accommodate any number of drivers, and advanced users with knowledge of Excel can customize any aspect of the spreadsheets. This could be adding functionality, adding or removing series from plots, etc. I would like to start the open-source development group to explore various uses of the tools and check functionality, and I can host a forum on my web site for this purpose.

Implementing the crossover
Once the crossover has been designed and the user is satisfied with the result, it's time to implement the crossover. For this purpose, I have provided info for designing:
  • Analog active crossovers
  • Digital active crossovers
For designing analog active crossovers, the filters are described both in terms of corner frequency and Q, and as transfer function coefficients in s and in z^-1. I have a full set of circuit designs for analog circuits that I would like to make available for people who want to build up their own op-amp based crossovers. Digital crossovers can be implemented similarly to analog crossovers - using a digital crossover unit like a Behringer DCX2496, or with the more flexible MiniDSP crossovers. I have been testing out the tools using a pair of MiniDSP-in-a-box 2x4 units and the advanced crossover module. In order to take full advantage of the advanced biquad programming capabilities of the MiniDSP units, the tools calculate the biquad coefficients that are required to be programmed in to the MiniDSP units. I have compared all the first and second order filters against the analog functions to make sure that they are equivalent.

I'd like for developers to have the ability to run through the entire process from start to finish. This would include measuring driver responses in-box, designing the crossover, implementing the crossover, and then re-measuring the speaker's response. For this reason I would prefer if people have access to some kind of advanced crossover unit such as the MiniDSP, but the Behringer DCX or dbx Driverack units could work too.

With the popularity of Jeff Bagby's Excel based passive crossover design tool (PCD), it seemed that a free design tool for designing DIY active crossovers was needed. Jeff has struggled with problems getting his tool (which uses macros and VBA code) to work for various versions of Excel, and it is limited by what is available in the interface because it is not open source. I'm hoping that an open source active crossover design tool will not create too many obstacles for users, and will allow for complete customization or extension when needed.



If you are someone who is interested in helping with the testing and development of these tools, please send me a PM.

-Charlie

.
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Old 7th December 2011, 03:36 PM   #2
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Just as an example of what I have done with these tools to date, while I have been developing them, please check out this thread on the PE TechTalk forum. I show plots of the crossovers for a couple of 2-way speakers:

MiniDSP crossover development - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com

I'm still looking for testers/developers!

-Charlie

Last edited by CharlieLaub; 7th December 2011 at 04:01 PM.
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Old 7th December 2011, 05:00 PM   #3
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Default Porgramming/Debug Excel/VBA

Quote:
Originally Posted by CharlieLaub View Post
Just as an example of what I have done with these tools to date, while I have been developing them, please check out this thread on the PE TechTalk forum. I show plots of the crossovers for a couple of 2-way speakers:

MiniDSP crossover development - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com

I'm still looking for testers/developers!

-Charlie
Hi CL,

I will be glad to help with the math and programming only. The time I have free to do this is limited; so, I cannot do the labor intensive lab work you require. My wife's accounting business will be consuming most of my time during the first half of 2012 due to the increased client workload we have during that period.

Regards,

WHG
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Old 7th December 2011, 05:10 PM   #4
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Quote:
Originally Posted by whgeiger View Post
Hi CL,

I will be glad to help with the math and programming only. The time I have free to do this is limited; so, I cannot do the labor intensive lab work you require. My wife's accounting business will be consuming most of my time during the first half of 2012 due to the increased client workload we have during that period.

Regards,

WHG
The tools are fully developed and working. At this point, I am looking for people who can test them. If problems are discovered then maybe there will be some small bug fixes. Additional development would be later, only when warranted or to address some aspect that is not covered.

-Charlie
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Old 7th December 2011, 05:44 PM   #5
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Quote:
Originally Posted by CharlieLaub View Post
The tools are fully developed and working. At this point, I am looking for people who can test them. If problems are discovered then maybe there will be some small bug fixes. Additional development would be later, only when warranted or to address some aspect that is not covered.

-Charlie
Charlie,

Don't know how much this will affect what you are trying to implement, but DSP is not created equal:

DSP Tower of Babel

Well, THAT's Not Gonna ******* Work!!

In the latter thread, it is found that polarity is reversed on the high band in the DriverackPA+, and on all three bands (from input to output) on the Driverack PA.

The lack of concurrency in filter Q and even polarity across different DSP platforms might result in "bugs" that have nothing to do with your programming.

Art Welter
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Old 7th December 2011, 05:53 PM   #6
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Quote:
Originally Posted by weltersys View Post
Charlie,

Don't know how much this will affect what you are trying to implement, but DSP is not created equal:

DSP Tower of Babel

Well, THAT's Not Gonna ******* Work!!

In the latter thread, it is found that polarity is reversed on the high band in the DriverackPA+, and on all three bands (from input to output) on the Driverack PA.

The lack of concurrency in filter Q and even polarity across different DSP platforms might result in "bugs" that have nothing to do with your programming.

Art Welter
I don't see how the reversed phase in the Driverack is a problem per se... you can just set the phase for "reversed" when you know you will be using that unit, or reverse the phase on the DriveRack. If the Driverack has such poor implementation of filters, then maybe people should avoid using it. Thanks for bringing that up.

I really intend for people to use the MiniDSP, but thought if they could live with less flexibility they could also use a DCX2496 or similar.

-Charlie
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Old 7th December 2011, 06:23 PM   #7
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Originally Posted by weltersys
Charlie,

Don't know how much this will affect what you are trying to implement, but DSP is not created equal:

DSP Tower of Babel

Well, THAT's Not Gonna ******* Work!!

In the latter thread, it is found that polarity is reversed on the high band in the DriverackPA+, and on all three bands (from input to output) on the Driverack PA.

The lack of concurrency in filter Q and even polarity across different DSP platforms might result in "bugs" that have nothing to do with your programming.


Art Welter
Quote:
Originally Posted by CharlieLaub View Post
I don't see how the reversed phase in the Driverack is a problem per se... you can just set the phase for "reversed" when you know you will be using that unit, or reverse the phase on the DriveRack. If the Driverack has such poor implementation of filters, then maybe people should avoid using it. Thanks for bringing that up.

I really intend for people to use the MiniDSP, but thought if they could live with less flexibility they could also use a DCX2496 or similar.

-Charlie
DRPA and DRPA+ have no polarity reverse settings, you have to pay more for that feature.

In the case of the DRPA, where all outputs are polarity reversed from the input, not a problem, unless combining another system that does not have that "feature".

In the case of the DRPA+, having the HF polarity inverted from the LF and MF is simply hosed.

As far as the other filter Q differences between different DSP, some even from the same company, the problem is a crossover designed for one platform will unfortunately not be correct for another.

As the midway hawker says "close, but no cigar" .

Art Welter
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Old 10th December 2011, 02:24 AM   #8
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Default Its a go in OO Calc

I finally had the time to download the latest version of OpenOffice and tried out the tools in Calc. Apart from a couple of minor glitches, everything seems to be working exactly like in Excel. I'd even go as far as to say that the OO Calc recalculation speed is faster than in Excel!

This is really great news. These tools can be used under Linux, which really widens the potential user base.

Now to write some documentation...

-Charlie
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Old 10th December 2011, 09:54 AM   #9
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Q1 : Do you intend producing an all-in-one Crossover Wizard, spreadsheet-based, encompassing the gain and phase measurement of all drivers, in-axis and off-axis ?

Q2 : Is the FRD standard taking the phase curve into account ?
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Old 10th December 2011, 10:52 AM   #10
Boden is offline Boden  Netherlands
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Dear Charlie,

Your thread attracts my interest. I have very extensice experience with Calsod 3.1 and LSP cad Pro 5.6. Both have the most powerful tool, being the so called Optimizer.

Highly simplified: Load a measured driver file, assemble a textbook filter for starters, load the desired filtered acoustic output. Simply click Optimize Filter. The software wil calculate the exact, optimized filter component values.

The same can of course be done for DSP programming. As a matter of fact SE and the UE work this way.

In my humble opinion, any filter design program without an optimizing function is like a car with a flat tire; it moves, but will only get you there in a slow time-consuming and tiresome fashion.

So pleazzzee include an Optimizer.....

Kind Regards,

Eelco de Bode
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