@hifijim I see you have a passive and DSP notch on the M74A, which I think is a good idea.
Your choice of MF - HF crossover is also well done IMO. I'd run the M74A that high even with the T34B. I'm curious though, why you chose to cross the woofer that high with the mid being able to easily deal with a much lower crossover?
Your choice of MF - HF crossover is also well done IMO. I'd run the M74A that high even with the T34B. I'm curious though, why you chose to cross the woofer that high with the mid being able to easily deal with a much lower crossover?
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Edit - I just noticed you had a HP at 500 hz in there which makes sense. It just didn't look like it was crossed that low on the individual driver response curves.
@profiguy thank you for the comments.
Yes, the midrange high pass is 500 Hz 2nd order with Q=0.5 (i.e. LR2). When combined with the natural rolloff of the driver, and the other EQ I have, this results in an acoustic LR4 at 500 Hz.
The woofer (with filter) has an acoustic response which is close to a 500 Hz 2nd order Q=0.7 (i.e. BW2). I found this combination to minimize the directivity bump at 500 Hz.
I have some wiggle room to try different woofer-mid crossovers. For example, I could make the woofer have an acoustic LR4 at 500 Hz. This causes a noticeable hump in the directivity index at 500 Hz, but I would need to listen to it to make a decision. How important are small changes in directivity in the 400 - 700 Hz range?
Here is a filter which has a slightly higher DI bump at 500 Hz, but it retains the asymmetric 4th order mid + 2nd order woofer crossover. I made the midrange high pass to be 500 Hz Q=0.707, and then adjusted to woofer low pass for flat response.
Would this sound better? or worse? The only way to know is to try it. The Hypex amps are being shipped to me now.
j.
Yes, the midrange high pass is 500 Hz 2nd order with Q=0.5 (i.e. LR2). When combined with the natural rolloff of the driver, and the other EQ I have, this results in an acoustic LR4 at 500 Hz.
The woofer (with filter) has an acoustic response which is close to a 500 Hz 2nd order Q=0.7 (i.e. BW2). I found this combination to minimize the directivity bump at 500 Hz.
I have some wiggle room to try different woofer-mid crossovers. For example, I could make the woofer have an acoustic LR4 at 500 Hz. This causes a noticeable hump in the directivity index at 500 Hz, but I would need to listen to it to make a decision. How important are small changes in directivity in the 400 - 700 Hz range?
Here is a filter which has a slightly higher DI bump at 500 Hz, but it retains the asymmetric 4th order mid + 2nd order woofer crossover. I made the midrange high pass to be 500 Hz Q=0.707, and then adjusted to woofer low pass for flat response.
Would this sound better? or worse? The only way to know is to try it. The Hypex amps are being shipped to me now.
j.
@hifijim Looking at the FR curves, it appears the woofer LP frequency is too high, but it may be a result of the baffle step being too aggressive. It can be difficult to dial in BSC and set a LP point when blending with a considerably smaller driver above this. I'd however leave the mid HP set to begin with.
I'd personally retain the 500 hz LR2 HP, as it improves transient response and phase relationship better between woofer and mid. The 4th order filter will worsen this and introduce a noticeable hard shift in phase, making the directivity swing further and linearity suffer. It will also affect FR balance in the nearfield, as higher order filters typically don't sum very smoothly in this area. This is a common trait with higher order filters used at lower frequencies, as timing will noticeably suffer.
The ear is quite sensitive in the range of 300 - 1k to relative phase and timing errors. Getting this area right is likely the most important part in blending the woofer with the mid. It will also have the most influence on how vocals sound, including many other acoustic instruments which are difficult to accurately reproduce.
I'd set the mid HP first and then dial the woofer LP in to blend. This usually ends up being easier to implement as a method of getting the LF - MF transition as best as it can be, both from a DI and phase POV. If after all this you can't achieve the desired DI uniformity, move the mid HP and then try again adjusting the woofer HP slope and frequency.
I'd personally retain the 500 hz LR2 HP, as it improves transient response and phase relationship better between woofer and mid. The 4th order filter will worsen this and introduce a noticeable hard shift in phase, making the directivity swing further and linearity suffer. It will also affect FR balance in the nearfield, as higher order filters typically don't sum very smoothly in this area. This is a common trait with higher order filters used at lower frequencies, as timing will noticeably suffer.
The ear is quite sensitive in the range of 300 - 1k to relative phase and timing errors. Getting this area right is likely the most important part in blending the woofer with the mid. It will also have the most influence on how vocals sound, including many other acoustic instruments which are difficult to accurately reproduce.
I'd set the mid HP first and then dial the woofer LP in to blend. This usually ends up being easier to implement as a method of getting the LF - MF transition as best as it can be, both from a DI and phase POV. If after all this you can't achieve the desired DI uniformity, move the mid HP and then try again adjusting the woofer HP slope and frequency.
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@hifijim The more I look at your measurements, the more convinced I am about the BSC needing attention first. The LP point is already lower than I thought and may need to be initially dialed up closer to that of the mid to start with. This will make things easier to begin with as a starting point.
Drivers with as wide directivity as these are easily influenced by every lump and bump in their path. The midrange dip at about 1.5K looks to be diffraction related and is consistent with the baffle step shift shown in the polar. It could also be influenced by the transition thing (I don't have a good description as they would all sound unkind and not how I want to frame it). If you wanted to know which, you could test by placing some felt foam or other fairly aborbent material around the transition or on the final sharp edge.
Not sure if you saw it but @stoneeh printed and measured the waveguide and baffle shape I simulated for you earlier on.
https://www.diyaudio.com/community/threads/t25a-simple-waveguide-profile.423131/post-8008337