Need Testers/Developers for open-source Excel based Crossover Design Tools

[charlielaub]

(Note, this is also posted in the Multi-way forum at DIYaudio.com)

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

[Pete Schumacher ®]

I'd dive in Charlie, but I'm not an active XO guy. Sounds like a cool project for sure.

[Modmark]

On this issue of open source....

Would the DIY audio community be better served by using the GNU license for design tools AND the speaker designs?

A GNU type license means you are free to use it for any means you want which includes commercial sales.

For example, if you designed a amazing home theater system, JPL would be free to sell this system but any tweaks or modification to the design must be made available to others ie: I can sell JPL's modified version of the cross over or their internal supports for the cabinet.

This model worked quite well for LINUX which is still growing in popularity.

[johnnyrichards]

This model worked quite well for LINUX which is still growing in popularity.

It's gotta be close to 2% of the home desktop users by now, huh? Not bad for almost 20 years

I kid, though. For something like a media player, the GPL isn't a bad idea. For niche software like this, I would not blame the developer for wanting to hold on to his rights.

[donradick]

On this issue of open source....

Would the DIY audio community be better served by using the GNU license for design tools AND the speaker designs?

A GNU type license means you are free to use it for any means you want which includes commercial sales.

For example, if you designed a amazing home theater system, JPL would be free to sell this system but any tweaks or modification to the design must be made available to others ie: I can sell JPL's modified version of the cross over or their internal supports for the cabinet.

This model worked quite well for LINUX which is still growing in popularity.

<IANAL "I am not a lawyer" >
The GNU Public License (GPL), which has differences in versions 1,2, and 3 basically says that source code must be available, and you may not use the source in a commercial closed source application.

The BSD license on the hand allows any and all use of the source code, even in commercial products. That's how BSD unix source got to be used in Sun Solaris unix and Apple IOS.

[Modmark]

It's gotta be close to 2% of the home desktop users by now, huh? Not bad for almost 20 years

I kid, though. For something like a media player, the GPL isn't a bad idea. For niche software like this, I would not blame the developer for wanting to hold on to his rights.

LINUX really was not designed for the home market, it is better suited for servers and embedded application such as DVR players. And many government (China and India) are moving towards LINUX.

[Modmark]

<IANAL "I am not a lawyer" >
The GNU Public License (GPL), which has differences in versions 1,2, and 3 basically says that source code must be available, and you may not use the source in a commercial closed source application.

I am not sure what "commercial closed source application" means. My understanding, if you modify the LINUX source code then your modification must be open source.

So IBM can modify LINUX and sell it with a web-based server application. The server is not open source, that is owned by IBM. But the modification to the LINUX kernel for example must be open.

[Modmark]

For niche software like this, I would not blame the developer for wanting to hold on to his rights.

If you wish to commercially sell a product then you should not look to the general public for development help.

I fully support what Charlie trying to do, use labor from the general public to build a set of design tools. But it is unrealistic or unfair for Charlie to hold the exclusive rights to these tools.

[charlielaub]

If you wish to commercially sell a product then you should not look to the general public for development help.

I fully support what Charlie trying to do, use labor from the general public to build a set of design tools. But it is unrealistic or unfair for Charlie to hold the exclusive rights to these tools.

Maybe someone should ask Charlie what he actually intends before speaking for him???

I am not using "labor from the general public to build a set of design tools". I already built the tools myself. I am just looking for some knowledgeable people to check out the tools before I release them, and in the future to make suggestions on how they can be approved and perhaps help with that effort.

Where did you get the idea to say I want to hold rights of any kind? What gave you the idea that I am trying to sell something??? This thread is about developing free and open tools for the DIY community!

I hope I made myself very clear.

-Charlie

[Modmark]

Maybe someone should ask Charlie what he actually intends before speaking for him???

Where did you get the idea to say I want to hold rights of any kind? What gave you the idea that I am trying to sell something??? This thread is about developing free and open tools for the DIY community!

I hope I made myself very clear.

-Charlie

Yep and my apologies, I am quite clear on your intent (open source) and this "sell something" issue was just trying to elicit a debate.

OTOH

I am just looking for some knowledgeable people to check out the tools before I release them, and in the future to make suggestions on how they can be approved and perhaps help with that effort.

You are looking for people in the DIY community to help out which is a good thing! I am a strong supporter of the open source model and it would be nice if a JPL engineer drop by and offered his help. Are you going to use the GNU license model for your tools?

LINUX is a far superior operating system than Windows and the majority of the work done by "DIY" computer folks. A dear friend of mine was instrumental during the early days of porting UNIX libraries to LINUX.

[Pete Schumacher ®]

Yep and my apologies, I am quite clear on your intent (open source) and this "sell something" issue was just trying to elicit a debate.

OTOH



You are looking for people in the DIY community to help out which is a good thing! I am a strong supporter of the open source model and it would be nice if a JPL engineer drop by and offered his help. Are you going to use the GNU license model for your tools?

LINUX is a far superior operating system than Windows and the majority of the work done by "DIY" computer folks. A dear friend of mine was instrumental during the early days of porting UNIX libraries to LINUX.

But why use Linux, when the vast majority of potential users are Windows?

[charlielaub]

But why use Linux, when the vast majority of potential users are Windows?

If I can get the tools to work on OpenOffice Calc, then Linux users can play, too. That's one area that needs to be checked out.

Does anyone out there use OpenOffice on a Linux machine?

-Charlie

[GIS_PHAN]

Any chance that this application could be a hosted app from a web site? Everyone with a browser could run it then.

[Modmark]

But why use Linux, when the vast majority of potential users are Windows?

For embedded application such as DVR or machine controls, Linux can be strip down to a lean&mean OS and does not require 1 Gig of memory and quad core processor to be effective. Same goes for server application, just accessing hard drives is a very simple operation and the overhead found in Windows just slows down the system. I believe Facebook has stop using Windows in its server farms which are massive.

Linux was created from UNIX which had to be a secure operating system from day 1 back in the 1960's. Back in the old days, 20 user would all be logged on to the same computer, talk about an insecure environment. Just type in cd /usr/obz and there is your co-worker files.

And finally, Linux is free. If the government of China owns 50 million computers, that is a big bill to pay MicroSoft if they want to upgrade.

For myself, Windows is free but I would switch to Linux if force to pay the $600 licenses for Windows. Except for a laptop, I build all my computers.

[charlielaub]

Any chance that this application could be a hosted app from a web site? Everyone with a browser could run it then.

Not likely when we are talking about Excel. If some other people want to take the time to complete re-write everything in something like Java, all the power to them. There would be a lot of server side calculations, too. I don't think it is a trivial thing.

I actually explored this with some other Excel spreadsheets that I developed for circuit design. There are some commercial (and free) products out there that allow you to port/post a spreadsheet to a web page, however I haven't found one that supports Excel's COMPLEX number functions, which are used everywhere in these tools. Anyway, you need up upload/import the driver data to the web page port, and I don't think that is possible either.

-Charlie

[charlielaub]

For embedded application such as DVR or machine controls, Linux can be strip down to a lean&mean OS and does not require 1 Gig of memory and quad core processor to be effective.

The crossover design tools are actually pretty intensive, computationally. This is largely due to the fact that Excel's native computation speed is pretty low, and there are lots and lots of cells to compute. If you plan on using a stripped down or re-purposed old computer running Linux for doing the calculations, be prepared to wait a bit.

For reference, my computer's CPU is an Intel E8400, a Core2 Duo processor, part of a midrange Dell machine that was purchased about 3 years ago. The spreadsheets are set for manual recalculation, and when I hit F9, it takes about 5-6 seconds (for a 2-way) or about 9-10 seconds (for a 4-way) system to recalculate all the cells.

Here are some comparisons of the performance of the E8400 against some recent CPUs:
http://www.cpubenchmark.net/cpu.php?...00+%40+3.00GHz

-Charlie

[Modmark]

If I can get the tools to work on OpenOffice Calc, then Linux users can play, too. That's one area that needs to be checked out.

Does anyone out there use OpenOffice on a Linux machine?

-Charlie

In your original post, you state "open source development group". The open source implies that the source code will be released.

With the open source model, there is no need to find someone OpenOffice on Linux, hopefully they will find you with any require modification needed for Linux. They take the source, modify and submit it back to you.

And your role become more of a keeper of the source code and you can accept or reject any modification.

Sorry, I know I am being the bad guy here but any debate needs a bad guy :-)

[Modmark]

If you plan on using a stripped down or re-purposed old computer running Linux for doing the calculations, be prepared to wait a bit.

-Charlie

I agree, old computers are quite slow concern math.

However, a strip down version of Linux running on a PS3 cell processor is one blazing fast calculator!

[Pete Schumacher ®]

Not likely when we are talking about Excel. If some other people want to take the time to complete re-write everything in something like Java, all the power to them. There would be a lot of server side calculations, too. I don't think it is a trivial thing.

I actually explored this with some other Excel spreadsheets that I developed for circuit design. There are some commercial (and free) products out there that allow you to port/post a spreadsheet to a web page, however I haven't found one that supports Excel's COMPLEX number functions, which are used everywhere in these tools. Anyway, you need up upload/import the driver data to the web page port, and I don't think that is possible either.

-Charlie

You could have a web page for porting the values into a hosted spreadsheet that spits back the values to the screen when run. No one is actually touching the Excel sheet. Only the host server runs the spreadsheet for creating the data that is linked back to the web page.

Don't know how easy that would be to do.

[charlielaub]

In your original post, you state "open source development group". The open source implies that the source code will be released.

With the open source model, there is no need to find someone OpenOffice on Linux, hopefully they will find you with any require modification needed for Linux. They take the source, modify and submit it back to you.

And your role become more of a keeper of the source code and you can accept or reject any modification.

Sorry, I know I am being the bad guy here but any debate needs a bad guy :-)

OK, let me clarify. The standard here, and the inspiration for my efforts, is Jeff Bagby's Passive Crossover Designer. A fabulous piece of work, and Jeff has poured countless hours in to this great and free tool. Jeff's tool has a busy GUI type interface, but all the calculations and formulas are hidden, either in macros, VBA code, or in hidden worksheets. You can not change anything (more or less). This is not the model I am using.

Instead, I will be leaving all the cells in the worksheets open for inspection. You can see all the formulas. You can change any element that you would like, plots, calculations, etc. You can also screw up the whole thing, too, if you go around changing stuff without knowing what you are doing, but that is part of the deal. I want to give people the opportunity to learn how all of this is done (e.g. by checking out the formulas) and give them the power to make changes if they so desire. In fact, I am hoping to have a forum where people suggest changes, or show what they have done, and anything that would improve the "product" will be wrapped in to a "release", all with public input and overseen by the "development group". This is the basis for my "open source" claim. Maybe I am using the wrong terminology. Remember, this is just a couple of big spreadsheets, there is no "source code", only formulas, and it is all visible.

-Charlie