Crossover modification on the fly...

[Rickysa]

So I built a speaker (first one) from plans, but had to substitute one manufacturer's AMT tweeter for the AMT tweeter specified. I have the .frd(s) and .zma(s) for all the drivers, and I used XSim to modify the crossover for the different tweeter. When I then measured the frequency response of the speaker (REW), it was quite different from the nice flat prediction. What software can I use to suss out the problem?

--As much as anything, I'm hoping to get a better understanding of the whole process (this being my first speaker project). For example, if I have an idea for a speaker I want to build, I buy the drivers and cut the lumber based on plans and driver specs...I put the drivers in the cabinets to measure (using DATS) and get the .frd(s) to plan the crossover...then I test the speaker (using REW) and, if it doesn't meet the expected results, where do I look?

[I asked over at DiyAudio as well, but hoping more folks might be familiar with measuring/software here?]

 

[a4eaudio]

....and get the .frd(s) to plan the crossover...

Where do you "get" the frd's from?
THIS is the hard part - taking accurate measurements to put into a simulation program. The simulation programs themselves are quite good IF you input accurate data.

 

[Rickysa]

Where do you "get" the frd's from?

data file from Dayton Audio for the tweeter, and both data files and graph traces for the woofers.

 

[a4eaudio]

You need to take actual measurements (with a measurement microphone) of the drivers in the cabinet to get reliable results.
One of the better resources currently available on HOW to do this is the measurement guide for REW HERE.

 

[levimax]

As @a4eaudio noted above one of the best free resources for speaker design is VituixCad. There is a steep learning curve but the through documentation takes you through the process from start to finish. Full Documentation with download links here. https://kimmosaunisto.net/Software/VituixCAD/VituixCAD_help_20.html

 

[alex-z]

Proper way to design a crossover is using in-cabinet driver measurements, especially off-axis. Otherwise you might fail to account for baffle step loss, edge diffraction, and differences in driver radiation pattern.

Room EQ Wizard and VituixCAD are where you want to start. Buy a calibrated mic and build a turntable that rotates the speaker around a reference point.

https://kimmosaunisto.net/Software/VituixCAD/VituixCAD_Measurement_REW.pdf

The VituixCAD guide does not mention it but acoustic timing reference is useful if you already own a USB mic and don't want to invest in XLR.

Making Measurements

 

[levimax]

The VituixCAD guide does not mention it but acoustic timing reference is useful if you already own a USB mic and don't want to invest in XLR.

Making Measurements

The author specifically says to use loopback timing measurements and not to use USB Mics. A UMIK2 and acoustic timing can work but if you haven't invested yet a 2 channel interface and standard MIC allowing for loopback measurements makes things easier, faster and more accurate.

 

[alex-z]

The author specifically says to use loopback timing measurements and not to use USB Mics. A UMIK2 and acoustic timing can work but if you haven't invested yet a 2 channel interface and standard MIC allowing for loopback measurements makes things easier, faster and more accurate.

The author was being overly cautious IMO.

Loopback timing is certainly easier but the accuracy is not meaningfully better. As long as the reference output device can play a 5-20kHz signal cleanly acoustic time reference works well for speaker design.

 

[levimax]

The author was being overly cautious IMO.

Loopback timing is certainly easier but the accuracy is not meaningfully better. As long as the reference output device can play a 5-20kHz signal cleanly acoustic time reference works well for speaker design.

I have done it both ways and for tweeters and most mid-ranges it is fine but woofers can be hard as you have to wire up the tweeter to fire simultaneously with the woofer and then try to figure out how far the actual acoustic centers are apart and allow for it, it is especially hard for off axis measurements and makes a hard process harder. If you are starting fresh a 2 channel interface and regular Mic are wise to consider. It is always nice to have an interface around and they are not that expensive and regular Mics are not more expensive than a USB MIC, especially a UMIK2, a UMIK 1 is not really suitable for timing measurements as it relies on the USB bus for timing a UMIK2 has it's own clock https://www.avnirvana.com/threads/acoustic-phase-measurements.13300/#post-99941 . If cost is number one concern then USB can work if you are willing to learn the work arounds.

 

[Keith_W]

If you are measuring a port, a loopback timing reference is essential. Well, you COULD use an acoustic timing reference, but you would have to be careful not to move the mic or the timing reference when you are repositioning your speaker to measure the port.