So glad you pointed me to line 8 on the VIFA D.S, spent forever trying to spot it, still haven't found it on the scan speak!
I would expect the 'recommended' 500Hz aligns to the recommended 2nd order electrical filter and could be pushed a lower with the steeper 4th order. Definitely makes me want to get the DLCP up and running so I can measure the actual difference in SQ with different Fc's and slopes.
At any rate, we still need to establish if the OP wants to tweak the transfer function or just levels, and if the measurements are accurate.
I would expect the 'recommended' 500Hz aligns to the recommended 2nd order electrical filter and could be pushed a lower with the steeper 4th order. Definitely makes me want to get the DLCP up and running so I can measure the actual difference in SQ with different Fc's and slopes.
At any rate, we still need to establish if the OP wants to tweak the transfer function or just levels, and if the measurements are accurate.
This I didn't see in the posted doc, though finally did find one in an image search with a good view, so thanks for this, but his woofers are in individual sealed cabs, so shouldn't be an issue.
GM
No, I haven’t sealed the mid from the woofer. After listening, I found no any distortion on mid or vocal. Everything seemed to be fine. But, touching to the dome when played at high level, I can feel bass pressure from the woofer to the dome despite having no distorted sound heard. Still, do I need to seal the midrange?
Yes you should have a small cup or similar behind the mid dome assuming it is actually open as indicated by others, even if you don’t hear any distortion it will be there and also it is not good for its power rating and impedance curve as it will either try to work against the woofers (causing higher impedance and possible audible compression, and less electrical power handling from coil overheat) or play along 180 degrees inverted phase pulling it mechanically out of its intended electrical input position causing a very different result all together (possible lower impedance and lack of sensitivity at the crossover point, less mechanically power handling from running outside x-max).
Further I don’t really see a good reason for having separate enclosures for each bass driver when they share the same crossover circuit and as such common frequency range. I would drill some holes between the two sections and let them share the entire volume I believe this will let you have a deeper and more sensitive bass and possibly also correct the 100hz issue (if that issue isn’t a mic position problem as indicated by others). It’s nice to have separate sections for cabinet stiffness and reduces resonance so don’t take away the whole divider just drill some holes in it bass reflex size.
I promised not to give bad advice so you may want to let others comment on this before you go on.
Also FYI when I have some more time I will try to simulate your crossover so see the electrical response only to compare with your acoustical results maybe it will highlight something for you to look more into.
Hope some of this makes sense (to you and also others, given the feedback on non valid and ill advice).
Further I don’t really see a good reason for having separate enclosures for each bass driver when they share the same crossover circuit and as such common frequency range. I would drill some holes between the two sections and let them share the entire volume I believe this will let you have a deeper and more sensitive bass and possibly also correct the 100hz issue (if that issue isn’t a mic position problem as indicated by others). It’s nice to have separate sections for cabinet stiffness and reduces resonance so don’t take away the whole divider just drill some holes in it bass reflex size.
I promised not to give bad advice so you may want to let others comment on this before you go on.
Also FYI when I have some more time I will try to simulate your crossover so see the electrical response only to compare with your acoustical results maybe it will highlight something for you to look more into.
Hope some of this makes sense (to you and also others, given the feedback on non valid and ill advice).
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Assuming your woofer cabs are truly sealed, then the D75 with its super high Qts is 'sealed' in the relatively large [~infinite baffle'] box chamber it resides in, so only need a smaller chamber if wanting more power handling down low and as this latest info states, at 0.5 L the usable BW is the ~600-6 kHz decade.
The pressure waves you feel on the dome are obviously from the front of the woofers and any interaction is just part of the total sound experience, so can be ignored as your distortion measurements have proven.
GM
The one potentially useful advantage of running 2 woofers in separate chambers with 2 separate ports is that it gives you LF tuning flexibility for different size rooms and/or speaker placements. So if the combinations of room size and/or speaker placement result in a perceived bass boominess, plug 1 of the ports to reduce the LF output. Running 1 woofer ported and 1 sealed may just give you the right in-room LF rolloff that is going to sound right in a specific situation.
Move the speakers to a bigger room or perhaps place them further away from the walls in a future scenario and 2 ports unplugged may be the better way to go.
One could argue about the stiffness of braces with vs without cutouts and perhaps about the potential for lower frequency standing waves to form because of the brace cutouts but I don't think those are very serious problems.
Move the speakers to a bigger room or perhaps place them further away from the walls in a future scenario and 2 ports unplugged may be the better way to go.
One could argue about the stiffness of braces with vs without cutouts and perhaps about the potential for lower frequency standing waves to form because of the brace cutouts but I don't think those are very serious problems.
Before you do anything else you HAVE to get that mid sealed from the woofers.
I had two motives driving the discussion behind crossing the mid lower, firstly that someone had suggested it wouldn't go lower than ~800Hz, and secondly that running car audio subs you may get a better SQ from crossing the mid lower (assuming the lowmids from the subs aren't all that good). Plus as already said, mind are crossed much lower and I know of other commercially successful designs with very similar schematics.
Let's get the mid sealed off, you'll likely be delighted by the difference.
Next get the measurement mic tested so we need know what we're working with.
I wouldn't be at all surprised if sealing the mid gets you over the line, the difference is night and day.
I had two motives driving the discussion behind crossing the mid lower, firstly that someone had suggested it wouldn't go lower than ~800Hz, and secondly that running car audio subs you may get a better SQ from crossing the mid lower (assuming the lowmids from the subs aren't all that good). Plus as already said, mind are crossed much lower and I know of other commercially successful designs with very similar schematics.
Let's get the mid sealed off, you'll likely be delighted by the difference.
Next get the measurement mic tested so we need know what we're working with.
I wouldn't be at all surprised if sealing the mid gets you over the line, the difference is night and day.
Just get a midrange enclosure “pot”, available from PE and the like, or Amazon if you’re desperate, and mount it behind the mid. Fill the enclosure with some damping like mineral wool or other acoustic material. Vifa used to produce a dedicated enclosure, but that's discontinued. I wouldn’t bother connecting the woofer sections acoustically. The microphone probably isn’t that bad, nonlinearities mostly appear under 100Hz and above 5kHz with these ones, they perform all right for crossover developing.
I had changed again the resistors on mid and tweeter. I tried to maintain the ratio of the mid and tweeter to be 2 Ohms difference. From 8.2 and 6.2 to 12 and 10 Ohms for mid and tweeter, respectively. There was smoother tone overall, but had likely low SPL. These two sets of resistors both gave me resonable tonal balance. I think to stop the tweak at this point and further think for fun whether it'd be great to have a switch to swap the set of resistors. Lol
However, there's an issue still remain. I couldn't find the convenient way to enclose the midrange. It is difficult to bring my floor-standing cabinets to the carpenter and let him edit the construction. PE pots for the midranges were not found on any websites, at least, I myself couldn't find them. Could anybody help to suggest?
However, there's an issue still remain. I couldn't find the convenient way to enclose the midrange. It is difficult to bring my floor-standing cabinets to the carpenter and let him edit the construction. PE pots for the midranges were not found on any websites, at least, I myself couldn't find them. Could anybody help to suggest?
Finally got around to calculating Vas and the only way I can get a somewhat approximate response to measured is in a 100x Vas IB/2pi with my previously recommended 600 Hz/2nd order XO.
Same in a 0.5 L sealed, it's max flat with a ~372 Hz F3, so seems the way to go, though with no Xmax, no way to know how it will perform above a few watts.
GM
Same in a 0.5 L sealed, it's max flat with a ~372 Hz F3, so seems the way to go, though with no Xmax, no way to know how it will perform above a few watts.
GM
Search for Seas K2851, that would be a perfect solution as they should fit in the mounting hole so you'll be able to mount the full enclosed mid frontside. Otherwise Adorama and Parts Express do offer solutions as well. Or Reichelt, Europe has those in stock. They say...
+1 Did quite a few this way and with today's software, know we can easily fine tune it till Fs shifts up to ~400 Hz.
GM
Well, one last tip on this, while I understand that changing the cabinet isn't that simple. Get the D75's out and go find a large mug or round plastic food storage box of about 0.5l that will fit on the magnet assembly. Over here a decent household store would give multiple options. Fill the mug/box with acoustic absorbing material and don't use too little of it. If using fibrous materials like rockwool, consider covering the magnet hole with fabric if that's not already the case (nylon panties actually do fine). Tape/glue the mug/box to the magnet assembly (check though whether it all fits in the existing space in the enclosure). Consider aluminium tape (don't short the leads) but gaffer tape or acrylic kit will do too. And be sure not to damage the leads doing this all. Remount the units when done and remeasure the result.
I think we scared off the OP here!
This thread did make me dig out my design notes for the D75 mid range though, so I thought it would be worth sharing them for anyone else who google-stumbles on this thread and is trying to build an application for the scan speak D7608/920010 mid dome.
Key points are:
1. Ensure there is a small sealed volume behind the dome.
2. Ensure this volume is well stuffed
To achieve 4th order Linkwitz slopes at approx 500Hz and 3000Hz:
3rd order electrical high pass, 2nd order electrical low pass
In addition:
Woofer had an impedance correcting resistor and capacitor in parallel across terminals and was then driven by a 3rd order electrical filter, this generated excellent phase alignment between the two drivers at 4th order acoustic.
Tweeter is driven by a 4th order electrical xo.
This thread did make me dig out my design notes for the D75 mid range though, so I thought it would be worth sharing them for anyone else who google-stumbles on this thread and is trying to build an application for the scan speak D7608/920010 mid dome.
Key points are:
1. Ensure there is a small sealed volume behind the dome.
2. Ensure this volume is well stuffed
To achieve 4th order Linkwitz slopes at approx 500Hz and 3000Hz:
3rd order electrical high pass, 2nd order electrical low pass
In addition:
Woofer had an impedance correcting resistor and capacitor in parallel across terminals and was then driven by a 3rd order electrical filter, this generated excellent phase alignment between the two drivers at 4th order acoustic.
Tweeter is driven by a 4th order electrical xo.
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