Originally Posted by Toscano
Hi, I am new to this venerable thread, my name is Marc. I am planning a 3-way speaker with one SEOS 18 (Beyma CP380M, 107 dB)), 2 Seas H1262-08 MCA15RCY ( 89 dB, VAS 12, Fs 51, Qt 0.25, Xmax 3.4) and 2 AE TD15H (94 dB, VAS 467, Fs 21, Qt 0.26, Xmax 14). The crossover-calculator gave this result : 1st order normal polarity, 6400 Hz, 800 Hz for the 8 Ohm Tweeter / 4 Ohm Mid / 4 Ohm Woofer, 0 db Bandpass Gain, Spread = 8 : 3 octaves. Can anyone tell me if the XO points, the bandbass gain etc are in an acceptable range, should the horn start lower ? Thank You !
Tbh, there's quite a bit here that is questionable.
The purpose of using a waveguide of that size and a compression driver is that they can work down to 1 kHz or even lower. 6.4k+ could be covered by a .5" dome tweeter on a small waveguide. To put this in perspective, the SEOS-18 can be used from about 800-20k Hz. 800-6.4k is 3 octaves. 6.4k-20k is a little over 1.5 octaves, and there is less power per octave at those frequencies in most music.
The midranges don't really match up with the rest of the system in terms of directivity, sensitivity, or power handling. You could do them next to each other horizontally; that would sort of match the horizontal directivity of the horn but you'd have to cross a little higher than desired and the vertical would be too wide. Also, when you turn the stereo up, the 1" coils on the mids will heat up much faster than the other drivers, causing a dip in the middle of the overall response. If you don't listen very loud this might not be a huge problem but it's something to consider.
First order crossovers are generally a bad idea. Even if they sum perfectly on-axis, when you go off-axis vertically the path length differences to the drivers causes a relative phase shift which makes them sum differently. That effect is present with every crossover, but the shallow roll-off of 1st orders makes it a problem over a large range of frequencies. So even if the response is flat on axis, if you move up or down you get huge holes in the response. Even if you only listen in front of the speaker, what you hear is also shaped by later arriving reflected sound that may have originally emanated from off-axis.
My suggestion would be to simplify. Do the SEOS-18 + CP380M and a single TD15H. Cross them around 1 kHz, maybe slightly lower, with 4th or 8th order slopes. If you don't have a lot of experience with passive crossovers, you're probably better off going active. This is a setup that, properly tuned, can give you first rate sound quality and serious output. Adding a midrange in-between these doesn't really provide a lot of benefit and it makes the system harder to tune and more costly.