XSim free crossover designer

I'll be publishing a simple "spec" for making "Standard FRD" files at some time in future addressing this. Basically, this will stipulate that the curves are to be measured at 2.83Vrms at 1m distance (or equivalent combination of drive voltage and distance to get the same levels). On an infinite baffle. And with a delay reference plane specified in the header (nominally and ideally, at 58usec behind the driver's mounting plane). All that to be stated in a header of the file like:

"| Standardized FRD file, measured by OmniMic "xxxxxx.omm" on 11/19/2013 by userID:
"| Equivalent to driven with 2.83V and measured at 1m
"| Acoustic origin is 58.23useconds behind the mounting plane.
I'm puzzled by the spec of a delay plane. Are you going to build in some kind of function to adjust the delay? This seems like it's going to lock in to using the Omnimic which might confuse those who won't be using it. I've been using the three-measurement method since 1996 when it first occurred to me to do that. It works nearly flawlessly.

I've also made measurements available at my site that are made as you suggest (using LAUD), on a large (2mx2m), 2.83v but at 0.5m which only requires subtracting 6db (as I've added to my program). However, over time I've found that there seems to be little interest in providing these, so I've quit that. Having actual measurements on the intended baffle when possible is the best way to go anyway. I've never liked trying to move to the crossover design phase without actual on-baffle measurements.

Thank you so much for providing this - it looks to be less frustrating to use than SoundEasy or Speaker Workshop :)

I've never liked trying to move to the crossover design phase without actual on-baffle measurements.


I agree - and having measurements of each driver such that they are at, relative to each other, the same distance (offset) from the listener (as they will be "on baffle" from a standard listening position) makes the simulation completely accurate and reliable.

When I read "simulator" I became excited thinking you meant the same kind of crossover simulation feature as LspCAD has, which uses your PC to simulate the crossover so you can play music through the program and send one output from the PC sound card to each driver - but that's not what you meant by "simulator", is it?

It is very cool to listen to what your finished speaker will sound like without actually building the crossover yet - then you can go through the "fine tuning" phase bumping values up/down on the PC screen instead of swapping parts / winding/un-winding inductors as you listen :)

The idea of Standard FRD files doesn't lock anyone into OmniMic, the files could be made with any system that measures response. In the tuning window for drivers (in XSim) there is an adjustment for delay you can use to adjust the "z-offsets" for a design, either compared to another measured driver, or from another driver that is on the "Standard FRD" system.

The three-measurement method on a real baffle works great and will be the most accurate way. But it requires that you select your drivers first and make a baffle to mount them onto as the first steps.

The idea of Standard FRD files is to allow people to select drivers and devise a first-shot crossover design before any time and money have been invested. Making Standard files delay plane measurement with Omnimic uses the 3-measurement collections with a known driver that has a Standard file (like the one Dayton is using), but allowing all drivers to refer to a common plane (rather than just relative to one other unknown driver's plane). You could instead measure delay plane (relative to baffle mounting plane) using an absolute-delay measuring setup like Praxis, or Holmimpulse or REW (if used with a soundcard that maintains synchronization and time lock between Record and Play... which are not universal by any means, BTW! The TI-based USB sound chips, for instance, will cause the delay plane to dance around too much to be used that way).

The reason for the odd "nominal" reference plane (58usec behind the physical mounting plane) is because of a particular driver (I don't recall the model at the moment) that is being used as a delay plane reference when collecting data on Dayton drivers. If no reference delay is stated, that value will be assumed for Standard FRDs.

For an accurate sim, some baffle effects will have to be included in the simulation, though - that's being worked on. Ideally with that arrangement, a person could design a baffle, box, and passive crossover before buying any hardware and without measurement gear, and still get pretty good results. That's the goal, at least.
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I have used the BDS for most of my previous designs, prior to using John K's dipole spreadsheet as I am going that route now. But I always considered that as coming after selecting drivers. I know some like to try to design before buying. I always select a driver first considering desired crossover Fc/slope and off-axis response. I guess to me the baffle is a consideration after the fact, except for a dipole that is. Even considering baffle step loss, it will always be there, so that can be considered before buying.

A reference driver would be a good way to go, but of course there needs to be some sort of uniformity in measuring and the delay somehow. I considered doing that on my test baffle measurements, but I never saw enough concern or attention to detail in the DIY community to take the time. I did provide measurements that all had the same excess phase so that the measurements could be easily used one against the other for design prior to buying, but no other measurements would match that. Even so, there seemed to be zero interest in that aspect.

Part of the issue may be that I measured at 0.5m and didn't subtract 6db right from the start. That's partly why I added the level control to make it easy to adjust for measurements that differed in reference level. That and my list of drivers is not extensive.

Most of my drivers, many of which I still have on the shelf, are not recent vintage, though many are still available. Maybe when this is established I'll go back to them and re-measure them.

Back to the delay plane. What concerns me is that if some driver is used as reference with a specific delay, it still requires that any measurement be post-processed for calculated minimum-phase response to make use of that delay. Given issues with windowing, I don't see how you could use it with excess-phase (direct) measurements. This in turn requires that the measurement be "tailed" appropriately. But the problem then begs the question "What are the appropriate tails"? For the highpass it's easy. The lowpass is not. In all of my testing I've never found a way to ensure consistency in estimating the lowpass such that others could use one person's minimum-phase measurement with another paired driver that uses another person's minimum-phase measurement. That's why I have mostly stayed out of the threads concerned with designing without measurements.

Most respectable driver co's provide SPL plots. It seems to me a no-brainer for them to be able add zma and frd file download capability at their websites for their drivers in light of the growing interest in DIY speaker building and the simming software that's available.
It could only help their sales.
Bill, have you had any success in nudging those co's in that direction - other than Dayton you have already mentioned?
dlr -- the delay is used with the supplied phase response that is given in the FRD file. Which is the phase response measured as if the mic were that delay/distance behind the baffle.

You don't need min phase calculation unless you want to use it to avoid out-of-band noise. In which case XSim's driver tuning window has a checkbox for that and allows you to choose cutoffs and slopes to match the measured phase in the in-band regions.

speakerdoctor -

I haven't really started to promote it directly to suppliers, not even much to Dayton yet, really. I'm in the process of selling a house and moving across the continent, so time is in short supply for now. The plan is for vendor to host these files (along with T/S parameters, if applicable) in a directory format that XSim can automatically access from an internal catalog.. that currently-empty Driver/Parts browser. Same plan for crossover parts.