The more logical descriptions of designing a crossover generally start with measuring the performance of the individual drivers. Rather than my approach of adjusting the combined system. Only rarely the Acoustats by themselves, and without the crossover.
I have an excuse. For the last 6 years and up to last month, I had been using Behringer DEQ 2496 to perform the crossover functions for each way of the system, the subs, panels, and tweeters. I use two high cut filters or low cut filters to make an LR4 lowpass or highpass crossover function. Most EQ functions can be turned on or off without issue, but the high cut and low cut filters often "stick" so that if you turn them off, they stay on, and may stay on after more than one power cycle of the unit, though ultimately power cycling usually fixes it, sometimes I've tried certain button pressing like bypassing and unbypassing the EQ to achieve that same effect.
Now I have one setting on the OpenDRC-DI unit I use to perform crossover functions for the panels set to bypass the crossover functions. Such a setting isn't safe on the bass or the tweeters.
However, for these measurements, I did not bypass the small number of EQ adjustments I make to the panels.
Also, I am interested in the acoustic crossover responses on the Acoustats, so I made measurements with the crossovers on also.
Briefly, the (lightly equalized) Acoustat response is reasonably flat within it's bandwidth, but limited on the low and high ends to some degree (mostly on the low end). That's why I use subs and supertweeters.
Even without the crossover, my back-of-the-envelope calculation suggests this is close to 48dB/octave performance starting at 16kHz or 17kHz as the 6dB down point. It actually looks even steeper than that, but you must account for the approximate 10dB error in the 20kHz band of the iPhone RTA. In the 1/3 octave from 16kHz to 20kHz there should be 48/3 = 16dB rolloff, combined with 6dB at the crossover frequency, so it should be 22dB down, and here it appears to be 35dB down, but adding in the 10dB error it's only actually 25dB down, just a bit more than 48dB/octave if your reference is the default here, or less if your reference is a higher frequency that 1 kHz.
When the crossover is dialed in, the bottom end takes a hugh hit, with that bass peak being almost entirely suppressed, but the top end doesn't signficantly change (high ambient noise level makes the bass look worse than it probably is):
There is some difference at 20kHz shown, a mere 1.6dB difference, despite the crossover subtracting 6dB at that point (the electronic lowpass frequency is 20kHz). This is because we are hitting the noise level in the room the output is already so small. So take all these measurements with a grain of salt. Other differences in the highs are barely noticeable, the crossover might actually make it smoother at 14kHz, as we see in the combined response. Basically I'm getting the benefits of the crossover (less wasted power, potential interference between speakers) at no visible cost--even actually some (though limited) benefits, as I've show in earlier measurements (the response at 14kHz is smoother with the crossover dialed in).
The above measurements used an uncorrelated pink noise, which I find more stable and accurate. I also did the measurements with correlated pink noise. Here's the speaker by itself (but with minor EQ):
Just looks a bit rougher than the one with uncorrelated noise.
The response with the crossover looks even more rougher than the one with uncorrelated noise, but otherwise basically the same.
Now take a look at the combined system response, with uncorrelated then correlated pink noise:
The true response at 20kHz would be just slightly above the apparent peak at 18kHz.
Correlated noise looks rougher again. Of course, everything is "interfering" with everything else. Real stereo music is not like this. Note that the dip around 100Hz is worse. Bass changes as I move the iPhone mere millimeters with the correlated noise, features like that shift around.
I think I've done pretty well in making what appears to be nearly flat response, 20-20kHz, with deviations from that being harmless or even beneficial, in the uncorrelated pink noise response.
I have an excuse. For the last 6 years and up to last month, I had been using Behringer DEQ 2496 to perform the crossover functions for each way of the system, the subs, panels, and tweeters. I use two high cut filters or low cut filters to make an LR4 lowpass or highpass crossover function. Most EQ functions can be turned on or off without issue, but the high cut and low cut filters often "stick" so that if you turn them off, they stay on, and may stay on after more than one power cycle of the unit, though ultimately power cycling usually fixes it, sometimes I've tried certain button pressing like bypassing and unbypassing the EQ to achieve that same effect.
Now I have one setting on the OpenDRC-DI unit I use to perform crossover functions for the panels set to bypass the crossover functions. Such a setting isn't safe on the bass or the tweeters.
However, for these measurements, I did not bypass the small number of EQ adjustments I make to the panels.
Also, I am interested in the acoustic crossover responses on the Acoustats, so I made measurements with the crossovers on also.
 |
| Acoustats, Both Channels, No Crossover |
Even without the crossover, my back-of-the-envelope calculation suggests this is close to 48dB/octave performance starting at 16kHz or 17kHz as the 6dB down point. It actually looks even steeper than that, but you must account for the approximate 10dB error in the 20kHz band of the iPhone RTA. In the 1/3 octave from 16kHz to 20kHz there should be 48/3 = 16dB rolloff, combined with 6dB at the crossover frequency, so it should be 22dB down, and here it appears to be 35dB down, but adding in the 10dB error it's only actually 25dB down, just a bit more than 48dB/octave if your reference is the default here, or less if your reference is a higher frequency that 1 kHz.
 |
| Acoustats, Both Channels, with Crossovers |
There is some difference at 20kHz shown, a mere 1.6dB difference, despite the crossover subtracting 6dB at that point (the electronic lowpass frequency is 20kHz). This is because we are hitting the noise level in the room the output is already so small. So take all these measurements with a grain of salt. Other differences in the highs are barely noticeable, the crossover might actually make it smoother at 14kHz, as we see in the combined response. Basically I'm getting the benefits of the crossover (less wasted power, potential interference between speakers) at no visible cost--even actually some (though limited) benefits, as I've show in earlier measurements (the response at 14kHz is smoother with the crossover dialed in).
The above measurements used an uncorrelated pink noise, which I find more stable and accurate. I also did the measurements with correlated pink noise. Here's the speaker by itself (but with minor EQ):
 |
| Acoustats, Both Channels, Correlated Noise |
Just looks a bit rougher than the one with uncorrelated noise.
 |
| Acoustats, Crossovers, Correlated Noise |
The response with the crossover looks even more rougher than the one with uncorrelated noise, but otherwise basically the same.
Now take a look at the combined system response, with uncorrelated then correlated pink noise:
 |
| System Response, Uncorrelated Noise |
 |
| System Response, Correlated Noise |
I think I've done pretty well in making what appears to be nearly flat response, 20-20kHz, with deviations from that being harmless or even beneficial, in the uncorrelated pink noise response.
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