So, the board's been a little slow this week :Z and I’m about to wrap up my original Mentor omni project.
I have started the think about the next generation, so I thought I’d start a thread on it. I’m going to need even more help on this one, since it will be my first 3-way design. I’m still a newbie, so don’t hesitate to jump in and offer advice or correct my erroneous assumptions, etc. I’m enthralled with the omni sound and hope to improve my implementation of that concept with the second project.
Here are some of the goals I have for it:
• An omnidirectional, direct firing hybrid like the original, but perhaps with an extended omni midrange, maybe with a switchable dipole tweeter implementation.
• A more attractive design aesthetically, with higher SAF, a smaller front footprint, and a shorter height.
• Something simpler and easier for most anyone to build.
• No subwoofer included this time, probably with sealed woofers rolling off around 50hz.
• Perhaps a crossover with significantly lower order slopes and crossover points where this will be allowed or drivers that are more accommodating. Entirely passive crossover.
• Extending the omni coverage up higher in frequency by higher mid to tweeter crossover and possibly lower order slopes, but not extending as low in frequency as the previous project.
• Equivalent or increased efficiency, but possibly higher output without strain on drivers.
• No use of any diffusers, deflectors, etc.
• Front firing woofers for good bass punch.
• Attempt to align the acoustic centers of the drivers (at least physically aligning the vc’s.
• Improved imaging, while maintaining the omni soundstage benefits.
Ok, that’s what comes to mind at this point. Next are some of the challenges I will need to overcome. For the omni effect, the midrange(s) will need to be upfiring, perhaps on a sloped baffle. Because the mid(s) will be performing in full space and because you are listening at more than 60º off axis, they will lose a good 6db of output on the listening axis. This means that there must either be two mids or one high efficiency mid (probably a Pro driver). If there are two mids, then you run into issues of needing to use some kind of delay circuit and/or lobing issues along the driver’s axis. Fortunately, I think the off axis db loss in the mids might match up quite well with the baffle step losses of the woofers.
Attached is an early plan with two options. The differences between the two plans are simply the orientation of the mids and the tweeter baffle. The dual front firing woofers are set back as needed to align their VC’s with the mids. How much they are set back is therefore dependent on the mid chosen. There is about 54L available for the woofers and 7L for the mids.
I’m using a 15º sloped baffle for the upfiring mids. Mirage suggests that this is the optimum slope for a combination of imaging and omni sound, so I’m going to coop that idea. This will also mean you are not listening 90º to the driver axis, as is the case with the original Mentor, but at about 75º off axis.
The tweeter baffle is direct firing, but I want to test the possibility of going dipole with the tweeter, either with a front and rear firing tweeter, or something like the Neo3 PDR that can be implemented dipole, as I understand it.
To keep the box size down, I plan to use ¾” BB or mdf on the sides, with 1.5” baffles for the drivers, but lots of bracing and dampening to deaden the cabinets. I may change the design of the base to incorporate a place to put the crossover in, with an access to the outside.
I’m far from thinking about finishing, but my first thoughts are either to use hardwood baffles over BB or mdf, with a anti-vibration material in between and a second type of hardwood veneer on the boxes (all natural, no stain for this guy), or to do a lighter hardwood veneer on the main box, but do a piano black finish on the woofer and mid baffles.
Ok what drivers. Well, I want to use the RS225 for the bass drivers.
RS225 In 50L or so, they get down to and F3 of 50hz, F6 of 39hz and F10 or 30hz, without room gain and can reach an output of about 107db at 30w without exceeding xmax. They could be crossed over to subs as 40-50hz for HT.
The mids depend on whether I go with two smaller 4”-5” drivers and deal with the potential problem that brings, or go with a high efficiency pro mid, at least 94db. Also, off axis performance is an important consideration. In the research I’ve done so far, some of the better respected small mids, like the Seas L12, look like they drop off quite severely at 60º off axis, while some others don’t and still others I’d like to consider have no published data. Choice of the right mid is probably critical for success of this design. Some contenders I have at this point and I’m interested in feedback on them or others I should consider.
Tang Band W5-704S: W5-704S
And reviewed by Zaph here:
It is inexpensive, can be crossed pretty high, thus extending the omni section, allows more tweeter flexibility and probably makes lower sloped crossovers possible, though I don’t have any off axis performance data at this point. It has decent distortion performance and no cone break up issues. It looks like it will reach about 109db at 30 watts. It is too big to fit side by side on the baffle size I have, however, so would have to be implemented in a front to back arrangement.
Tang Band W4-1337:
W4-1337 Jon is considering it for a mid in one of his 3way projects and has a FR shown here:
It appears to have good extended range, good distortion numbers and will do all the things I mentioned for the W5-704s. It is quite a bit more expensive at $55ea. It could fit side by side or front to back on the baffle size I have in the plans. It would get up to about 108db at 30w.
Peerless PBB 830860:
830860
This driver has better off axis performance than the Nomex and due to its flat sides, can be placed quite close together for a driver of its size and works in either side to side or front to back orientation. I have not seen any testing of this driver however. It gets up to about 108 db at 30w. It is a little less than the W4-1337 at $50ea.
Dayton RS150 (4 or 8):
RS150-4
The 8ohm version has been heavily used and is know to be low distortion and inexpensive (I have 4 of the 4ohm version already waiting to be used). However, it probably can’t be crossed too high and/or will take a steep slope to use and will limit the tweeter choice considerably, I would think.
For Pro mids these are possibles I’ve found so far:
B&C 6MD38:
6MD38
It is not too expensive at $78, given I would only need one per speaker rather than two. I have no off axis or distortion information, but it looks like it could crossed pretty high with low slopes. It has the benefit of not causing lobing or crossover timing problems like two mids might and is small enough to be offset in the baffle. It looks like it will also get up to about 108db with 30w.
Eminence Beta 8A:
Beta 8A
Again, I have no off axis or distortion info on it, but it appears it could offer the benefits of the B&C above and is pretty inexpensive at $60ea. There appear to be a lot of bobbles in the impedance plot, however, as does the B&C, for that matter. It also does about 108db at 30w.
Tweeters are pretty dependent upon which mid is selected, but I’m interested in a reasonably priced dome, since I’m considering front and rear firing tweets, and also in the B&G Neo3 PDR, since it can go dipole. Neo3 PDR
I’d sure like to get feedback from folks on driver choices and the vexing potential problems that dual mids might cause. As I understand it, MTM’s are known to have lobing issues vertically and subsequently can be a benefit due to reduced floor and ceiling bounce. The front to rear mid driver arrangement therefore may point the lobing issues on the listening axis and it definitely presents driver timing issues. Maybe the side by side mid arrangement presents the lobing at 90º to the listening axis and would seem to have less of a driver timing issue, at least until you get further off axis, maybe it has better potential. Those flat sided 830860’s can be within about 5.2” center to center of each other, while the 4” W4-1337 can be just under 5”.
Crossover points might depend on the mid, but I’m thinking of around 400-500hz for the RS225 and as high as the mid will allow to the chosen tweeter.
Does anyone have any thoughts or other considerations? I’m open to ideas!
Whew, that came out much longer than I expected it to be! Have I exceeded the maximum message length yet? (write a book why don't you) :E
I have started the think about the next generation, so I thought I’d start a thread on it. I’m going to need even more help on this one, since it will be my first 3-way design. I’m still a newbie, so don’t hesitate to jump in and offer advice or correct my erroneous assumptions, etc. I’m enthralled with the omni sound and hope to improve my implementation of that concept with the second project.
Here are some of the goals I have for it:
• An omnidirectional, direct firing hybrid like the original, but perhaps with an extended omni midrange, maybe with a switchable dipole tweeter implementation.
• A more attractive design aesthetically, with higher SAF, a smaller front footprint, and a shorter height.
• Something simpler and easier for most anyone to build.
• No subwoofer included this time, probably with sealed woofers rolling off around 50hz.
• Perhaps a crossover with significantly lower order slopes and crossover points where this will be allowed or drivers that are more accommodating. Entirely passive crossover.
• Extending the omni coverage up higher in frequency by higher mid to tweeter crossover and possibly lower order slopes, but not extending as low in frequency as the previous project.
• Equivalent or increased efficiency, but possibly higher output without strain on drivers.
• No use of any diffusers, deflectors, etc.
• Front firing woofers for good bass punch.
• Attempt to align the acoustic centers of the drivers (at least physically aligning the vc’s.
• Improved imaging, while maintaining the omni soundstage benefits.
Ok, that’s what comes to mind at this point. Next are some of the challenges I will need to overcome. For the omni effect, the midrange(s) will need to be upfiring, perhaps on a sloped baffle. Because the mid(s) will be performing in full space and because you are listening at more than 60º off axis, they will lose a good 6db of output on the listening axis. This means that there must either be two mids or one high efficiency mid (probably a Pro driver). If there are two mids, then you run into issues of needing to use some kind of delay circuit and/or lobing issues along the driver’s axis. Fortunately, I think the off axis db loss in the mids might match up quite well with the baffle step losses of the woofers.
Attached is an early plan with two options. The differences between the two plans are simply the orientation of the mids and the tweeter baffle. The dual front firing woofers are set back as needed to align their VC’s with the mids. How much they are set back is therefore dependent on the mid chosen. There is about 54L available for the woofers and 7L for the mids.
I’m using a 15º sloped baffle for the upfiring mids. Mirage suggests that this is the optimum slope for a combination of imaging and omni sound, so I’m going to coop that idea. This will also mean you are not listening 90º to the driver axis, as is the case with the original Mentor, but at about 75º off axis.
The tweeter baffle is direct firing, but I want to test the possibility of going dipole with the tweeter, either with a front and rear firing tweeter, or something like the Neo3 PDR that can be implemented dipole, as I understand it.
To keep the box size down, I plan to use ¾” BB or mdf on the sides, with 1.5” baffles for the drivers, but lots of bracing and dampening to deaden the cabinets. I may change the design of the base to incorporate a place to put the crossover in, with an access to the outside.
I’m far from thinking about finishing, but my first thoughts are either to use hardwood baffles over BB or mdf, with a anti-vibration material in between and a second type of hardwood veneer on the boxes (all natural, no stain for this guy), or to do a lighter hardwood veneer on the main box, but do a piano black finish on the woofer and mid baffles.
Ok what drivers. Well, I want to use the RS225 for the bass drivers.
RS225 In 50L or so, they get down to and F3 of 50hz, F6 of 39hz and F10 or 30hz, without room gain and can reach an output of about 107db at 30w without exceeding xmax. They could be crossed over to subs as 40-50hz for HT.
The mids depend on whether I go with two smaller 4”-5” drivers and deal with the potential problem that brings, or go with a high efficiency pro mid, at least 94db. Also, off axis performance is an important consideration. In the research I’ve done so far, some of the better respected small mids, like the Seas L12, look like they drop off quite severely at 60º off axis, while some others don’t and still others I’d like to consider have no published data. Choice of the right mid is probably critical for success of this design. Some contenders I have at this point and I’m interested in feedback on them or others I should consider.
Tang Band W5-704S: W5-704S
And reviewed by Zaph here:
It is inexpensive, can be crossed pretty high, thus extending the omni section, allows more tweeter flexibility and probably makes lower sloped crossovers possible, though I don’t have any off axis performance data at this point. It has decent distortion performance and no cone break up issues. It looks like it will reach about 109db at 30 watts. It is too big to fit side by side on the baffle size I have, however, so would have to be implemented in a front to back arrangement.
Tang Band W4-1337:
W4-1337 Jon is considering it for a mid in one of his 3way projects and has a FR shown here:
It appears to have good extended range, good distortion numbers and will do all the things I mentioned for the W5-704s. It is quite a bit more expensive at $55ea. It could fit side by side or front to back on the baffle size I have in the plans. It would get up to about 108db at 30w.
Peerless PBB 830860:
830860
This driver has better off axis performance than the Nomex and due to its flat sides, can be placed quite close together for a driver of its size and works in either side to side or front to back orientation. I have not seen any testing of this driver however. It gets up to about 108 db at 30w. It is a little less than the W4-1337 at $50ea.
Dayton RS150 (4 or 8):
RS150-4
The 8ohm version has been heavily used and is know to be low distortion and inexpensive (I have 4 of the 4ohm version already waiting to be used). However, it probably can’t be crossed too high and/or will take a steep slope to use and will limit the tweeter choice considerably, I would think.
For Pro mids these are possibles I’ve found so far:
B&C 6MD38:
6MD38
It is not too expensive at $78, given I would only need one per speaker rather than two. I have no off axis or distortion information, but it looks like it could crossed pretty high with low slopes. It has the benefit of not causing lobing or crossover timing problems like two mids might and is small enough to be offset in the baffle. It looks like it will also get up to about 108db with 30w.
Eminence Beta 8A:
Beta 8A
Again, I have no off axis or distortion info on it, but it appears it could offer the benefits of the B&C above and is pretty inexpensive at $60ea. There appear to be a lot of bobbles in the impedance plot, however, as does the B&C, for that matter. It also does about 108db at 30w.
Tweeters are pretty dependent upon which mid is selected, but I’m interested in a reasonably priced dome, since I’m considering front and rear firing tweets, and also in the B&G Neo3 PDR, since it can go dipole. Neo3 PDR
I’d sure like to get feedback from folks on driver choices and the vexing potential problems that dual mids might cause. As I understand it, MTM’s are known to have lobing issues vertically and subsequently can be a benefit due to reduced floor and ceiling bounce. The front to rear mid driver arrangement therefore may point the lobing issues on the listening axis and it definitely presents driver timing issues. Maybe the side by side mid arrangement presents the lobing at 90º to the listening axis and would seem to have less of a driver timing issue, at least until you get further off axis, maybe it has better potential. Those flat sided 830860’s can be within about 5.2” center to center of each other, while the 4” W4-1337 can be just under 5”.
Crossover points might depend on the mid, but I’m thinking of around 400-500hz for the RS225 and as high as the mid will allow to the chosen tweeter.
Does anyone have any thoughts or other considerations? I’m open to ideas!
Whew, that came out much longer than I expected it to be! Have I exceeded the maximum message length yet? (write a book why don't you) :E
Comment