I have some old drivers that I am considering using. One is a very old cup midrange. I measured it using HOLM, and compared it with a more current driver at approximately 100 dB at 6 or 7 feet. The old mid is very flat, and has no breakup that I can see. The 3rd order distortion is roughly -50 dB. The newer driver is roughly -60 dB. Most of my listening is below 90 dB, so 100 dB would be the max for music for very short periods. (Maybe one song.) What are the odds that I could even hear a difference? I would think that 50 dB down would be inaudible.
In my experience THD is generally a reasonable proxy for IMD and -50dB IMD is about the limit of audibility; I would suggest including other harmonics besides the third and seeing where the drivers end up. I've found I hear distinct differences between drivers measuring at -40dB THD and ones at -50dB THD in similar conditions, though that's sighted A/B between drivers with different Thiele-Small parameters and hence includes factors besides the IMD floor. FWIW, my subjective impression is the change in IMD levels is noticeable amongst the other differences.
Really the best way to settle it would be to set up both drivers and blind A/B them. You might find you notice the distortion. You might find you notice other things. I would be surprised if you found they sound the same.
Really the best way to settle it would be to set up both drivers and blind A/B them. You might find you notice the distortion. You might find you notice other things. I would be surprised if you found they sound the same.
Second order harmonics were higher than the third order harmonics on both drivers. Maybe 10 dB higher in a few spots. Everything else was down about -70 dB. I mostly just want to make use of the mid, but knowing the newer driver is a little better just kind of naws at me. I'm lazy and impatient when it comes to building boxes. The baffle of this speaker has already been altered several times, but this time I need to replace the baffle. I could build a mid enclosure, and use the newer driver, but I'm just having trouble deciding. The Q of the woofer box will be less affected if I use this cup mid, instead of adding a .4 cu-ft box for the newer driver.
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