Thanks, guys. I was actually thinking about turning them upside down and putting them on top of a flared 10" high stand. Stability would be a problem, so I would have to bolt the speaker to the stand to keep it from tipping over. That would probably look really cool with the big 12" woofer on the top, kind of an "ET" type shape. Not sure how it would sound. I would certainly lose energy in the 80 to 500Hz region and need to apply much more BSC.
The Audio Concepts JC-12's have vented pole pieces, so I could build my own coax using a small Dayton tweeter. The MDT-33's double magnet system is way too big for a coax. I haven't cut the driver holes yet, so maybe I should give this a go!!
@PWRRYD said:
Do you have any concerns regarding wood movement with the baffles and backs being glued on?
Yes, very much so. I was initially planning to screw the baffle and backs in place with a gasket, but decided to risk it and glue them in place permanently. The expansion/contraction pressure on the lower baffle area will be relieved substantially by the larger 11.2" woofer cut out. The mid, tweeter, port and input cup cutouts will also help to reduce the pressure somewhat, although nowhere near as much as the woofer cutout. The fact that I have glued up multiples of 6, 5.5, and 1.5" boards may also help a little bit. My hope is that the expansion/contraction will take place in a uniform manner and not cause a problem. But if I do get a few cracks here and there, I will simply pull the woofer out and seal it from the inside with silicone sealer. The external crack will be left exposed and used as a conversation piece.
https://diy.midwestaudio.club/discussion/569/matrix-revolution-build
I built Scott's Matrix Revolution speakers 3-1/2 years ago out of solid knotty pine stair tread material and they are currently showing no signs of cracks or splintering. These boards were glued up at the factory from multiple strips of pine. Sealed up with multiple coats of lacquer and stored in an air conditioned space.
Some species of wood moves more than others. Also the finish itself will help control the rate of expansion and contraction.
I have a untested theory that if wood is assembled dry it will expand and contract well. Moist wood shrinks and breaks.
I agree. All the woods I am using were kiln dried by the manufacturer to a certain low percentage before being milled down to the final thickness. I kept the wood firmly clamped in "open air" type drying racks prior to final trimming and glue up. It is important that the wood be allowed to accept moisture evenly on all edges and sides to avoid warpage. Now that I have the wood firmly glued into the cabinet, I think it is important to keep both the inside and outside of the box evenly exposed to the open air. So, I need to get the driver holes cut out as soon as possible so that the inside of the cabinet can "breathe". Later on, when it is time to put the finish on, I need to seal coat both the inside and the outside of the cabinet to stabilize the wood.
Another thing to consider is situations where the wood grain makes an extreme, perpendicular shift along a glue line. On this speaker, the grain runs parallel from top to bottom along all the glue lines for the full length of the sides, backs, and baffles. The only perpendicular grain glue up situations occur at the extreme top and bottom edges of the cabinets, along the glue lines where the baffles and backs meet the bottom and top panels. Therefore, the most likely spot for a break or crack would be somewhere along these edges or corners.
Thanks, Tom. Next up will be removal, cleaning, and replacement of the ferrofluid and domes on my two old Morel MDT-33 tweeters. I'll post details with "before" and "after" FR graphs & DATS V2 curves. This will be my first time doing this, so, hopefully, I will not destroy them in the process.
I finished cleaning & swapping out the ferrofluid and voice coils on both of my MDT-33 tweeters. The project was highly successful. Detail pics & before/after graphs below.
:
Faceplate and VC removal: I used a butter knife to slowly pry up the VC and remove it. It was not glued in, simply pressfit into place, so it was a very easy task to pry it up and out without damage. Morel engineers designed this well, as perfect VC alignment is automatically created by the large, plastic pressfit ring. No alignment pins or glue are used or needed.
Cleaning: I cleaned out the old ferrofluid with the kit supplied filter paper. There was not much ferrofluid in the gap, most of it had dryed out over the years. When I installed the new ferrofluid, it visually filled the gap completely and significantly reduced the Fs measurement.
Finished tweeter with new ferrofluid and VC installed:
Before/After DATS V2 measurements: I measured both tweeters with DATS V2 before and after the swapout. It seems to have worked out pretty well. The new ferrofluid dropped the Fs and Qts data significantly and they are now much closer to the original spec sheet data and curves. If you look closely, the small impedance hump around the 1.5-2kHz area is also shown on the original spec sheet.
OmniMic FR data: I also measured both tweeters with OmniMic before and after the swapout. I flush mounted the tweeters on my DIY 52.5 x 64" IEC test baffle for all measurements. Even with the new voice coils and ferrofluid installed, the channel to channel match appears very good. The spec calls for a match to within +- 0.6dB for the pair, and it looks like I am still meeting this spec. I offset the before and after curves by 10dB for clarity and used 1/96th octave smoothing to show as much detail as possible.
I don't know, I think I would have preferred the "before" tweeter to be honest. You've got a lump at 2kHz now, both in impedance and frequency response. Maybe that will work to your advantage, maybe not. Given a crossover frequency of 2500-3500Hz, maybe not that important at all.
Would be nice to see a direct overlay of before and after that isn't shifted by 10dB
Ya, I agree. I added the curves back into OmniMic and did a direct overlay of before and after. You can now clearly see the problem around 2kHz. Looks like I may have inadvertently messed up my tweeters. It's very easy to swap the voice coils in and out, so I will put the original voice coil back into one of the tweeters and re-measure. If the 2kHz peak persists, I will try removing a small amount of ferrofluid and re-measure. I poured the entire contents of the 100uL package into the gap and maybe this tweeter is designed to use a little less fluid.
I wouldn't say that they're messed up, I'm sure they're still perfectly usable, but given the "before" measurements I don't see anything that needed fixing. In any case, I'm sure you'll get them in good enough working order for this design.
I have faith in your skills, Bill! I'm betting you'll get them to hit your target slope without much effort. A little contour on the top end and Bob's your uncle!
I reduced the amount of ferrofluid in both tweeters by wicking it out, in stages, using q-tips. This flattened out the impedance peak at 2k quite a bit. Before and after FR measurements are now much closer as well. I'd guesstimate that I took about half of the ferrofluid out, so I now probably have about 50uL in each one. Based on how much I originally took out, I'd say that I am now probably back to the original level.
Fs now measures 756Hz and 785Hz compared to the original 926Hz and 997Hz measurements. This reduction appears to be solely due to the changeover to the new domes. The old domes measure with a very high 920Hz+ Fs regardless of how much ferrofluid is in the gap. Also, the two new domes measure in the 750Hz or so area regardless of ferrofluid level. So, the high Fs reading was probably due to the aging of the dome suspensions, stiffening up over the years.
I initially thought that the amount of ferrofluid was the cause of the Fs change, but I was wrong.
It seems to have no influence on Fs at all.
My other two MDT-33 tweeters are a few years older and they both have an Fs measurement of about 1400Hz. I haven't done it yet, but when I replace the domes in these tweeters, I am going to leave the ferrofluid alone and see what happens to Fs by simply swapping out the domes.
@Nicholas_23 said:
How much change would you see in FS after running them? Thermal comes to mind. Probably moot at this point
I have not tried that. I'll hook a small cap in series with one, play music for a half hour to warm the VC, then re-measure. See if it makes a difference. I have noticed slight variations when running the test a day or two later. Same tweeter, but Fs measures 790Hz on day 1 and then after booting the computer on day two it then measures 808Hz (or something like that). And sometimes I get variations of 5Hz or so when re-running the sweep several times in succession. Makes me wonder what is going on sometimes.
I just played music through an 8uF cap into one of the two tweeters, and Fs dropped from 785Hz to 770Hz after about 1/2 hour of moderately loud music. Qts dropped from 0.55 to 0.49 as well.
Thanks for the vid, John! Lots of good info packed into a very short presentation. I'm still testing samples and debating what to do. I've noticed that quite of bit of the color tone and darkening depends on the sample that I happen to use. To get a valid test, I need to pull my comparison samples off the same board and sometimes off the same section of a board.
Comments
Thanks, Kornbread! The plan is starting to come together.
Damn you do good work!
Man, if you turned them upside down, you might have actual monkey coffins😛
I love> @4thtry said:
I love It when a plan comes together!
Looking good, Bill
Thanks, guys. I was actually thinking about turning them upside down and putting them on top of a flared 10" high stand. Stability would be a problem, so I would have to bolt the speaker to the stand to keep it from tipping over. That would probably look really cool with the big 12" woofer on the top, kind of an "ET" type shape. Not sure how it would sound. I would certainly lose energy in the 80 to 500Hz region and need to apply much more BSC.
12" coax
The Audio Concepts JC-12's have vented pole pieces, so I could build my own coax using a small Dayton tweeter. The MDT-33's double magnet system is way too big for a coax. I haven't cut the driver holes yet, so maybe I should give this a go!!
Do you have any concerns regarding wood movement with the baffles and backs being glued on?
Yes, very much so. I was initially planning to screw the baffle and backs in place with a gasket, but decided to risk it and glue them in place permanently. The expansion/contraction pressure on the lower baffle area will be relieved substantially by the larger 11.2" woofer cut out. The mid, tweeter, port and input cup cutouts will also help to reduce the pressure somewhat, although nowhere near as much as the woofer cutout. The fact that I have glued up multiples of 6, 5.5, and 1.5" boards may also help a little bit. My hope is that the expansion/contraction will take place in a uniform manner and not cause a problem. But if I do get a few cracks here and there, I will simply pull the woofer out and seal it from the inside with silicone sealer. The external crack will be left exposed and used as a conversation piece.
They will probably be fine if you don't take them from Wisconsin to Guam!
When I have constructed cabinets of solid wood with all sides glued, they ended up breaking at a glue joint, so not terribly conspicuous.
https://diy.midwestaudio.club/discussion/569/matrix-revolution-build
I built Scott's Matrix Revolution speakers 3-1/2 years ago out of solid knotty pine stair tread material and they are currently showing no signs of cracks or splintering. These boards were glued up at the factory from multiple strips of pine. Sealed up with multiple coats of lacquer and stored in an air conditioned space.
Some species of wood moves more than others. Also the finish itself will help control the rate of expansion and contraction.
I have a untested theory that if wood is assembled dry it will expand and contract well. Moist wood shrinks and breaks.
I agree. All the woods I am using were kiln dried by the manufacturer to a certain low percentage before being milled down to the final thickness. I kept the wood firmly clamped in "open air" type drying racks prior to final trimming and glue up. It is important that the wood be allowed to accept moisture evenly on all edges and sides to avoid warpage. Now that I have the wood firmly glued into the cabinet, I think it is important to keep both the inside and outside of the box evenly exposed to the open air. So, I need to get the driver holes cut out as soon as possible so that the inside of the cabinet can "breathe". Later on, when it is time to put the finish on, I need to seal coat both the inside and the outside of the cabinet to stabilize the wood.
Another thing to consider is situations where the wood grain makes an extreme, perpendicular shift along a glue line. On this speaker, the grain runs parallel from top to bottom along all the glue lines for the full length of the sides, backs, and baffles. The only perpendicular grain glue up situations occur at the extreme top and bottom edges of the cabinets, along the glue lines where the baffles and backs meet the bottom and top panels. Therefore, the most likely spot for a break or crack would be somewhere along these edges or corners.
And that is exactly where mine have broke.
They are beginning to look alot like loudspeakers!!
Routing the midrange recess:
Completed baffles:
Those look great, Bill! The baffle and stripe really work well together.
Thanks, Tom. Next up will be removal, cleaning, and replacement of the ferrofluid and domes on my two old Morel MDT-33 tweeters. I'll post details with "before" and "after" FR graphs & DATS V2 curves. This will be my first time doing this, so, hopefully, I will not destroy them in the process.
I finished cleaning & swapping out the ferrofluid and voice coils on both of my MDT-33 tweeters. The project was highly successful. Detail pics & before/after graphs below.
:
Faceplate and VC removal: I used a butter knife to slowly pry up the VC and remove it. It was not glued in, simply pressfit into place, so it was a very easy task to pry it up and out without damage. Morel engineers designed this well, as perfect VC alignment is automatically created by the large, plastic pressfit ring. No alignment pins or glue are used or needed.
Cleaning: I cleaned out the old ferrofluid with the kit supplied filter paper. There was not much ferrofluid in the gap, most of it had dryed out over the years. When I installed the new ferrofluid, it visually filled the gap completely and significantly reduced the Fs measurement.
Finished tweeter with new ferrofluid and VC installed:
Before/After DATS V2 measurements: I measured both tweeters with DATS V2 before and after the swapout. It seems to have worked out pretty well. The new ferrofluid dropped the Fs and Qts data significantly and they are now much closer to the original spec sheet data and curves. If you look closely, the small impedance hump around the 1.5-2kHz area is also shown on the original spec sheet.
Impedance DATS V2: Before/After:
Tweeter A:
Fs 926Hz/ 790Hz
Qts: .52 / .34
Zmax: 14.2 ohms / 11.3 ohms
Tweeter B:
Fs 997 Hz/ 766 Hz
Qts: .53 / .33
Zmax: 12.7 ohms / 11.8 ohms
OmniMic FR data: I also measured both tweeters with OmniMic before and after the swapout. I flush mounted the tweeters on my DIY 52.5 x 64" IEC test baffle for all measurements. Even with the new voice coils and ferrofluid installed, the channel to channel match appears very good. The spec calls for a match to within +- 0.6dB for the pair, and it looks like I am still meeting this spec. I offset the before and after curves by 10dB for clarity and used 1/96th octave smoothing to show as much detail as possible.
I don't know, I think I would have preferred the "before" tweeter to be honest. You've got a lump at 2kHz now, both in impedance and frequency response. Maybe that will work to your advantage, maybe not. Given a crossover frequency of 2500-3500Hz, maybe not that important at all.
Would be nice to see a direct overlay of before and after that isn't shifted by 10dB
Ya, I agree. I added the curves back into OmniMic and did a direct overlay of before and after. You can now clearly see the problem around 2kHz. Looks like I may have inadvertently messed up my tweeters. It's very easy to swap the voice coils in and out, so I will put the original voice coil back into one of the tweeters and re-measure. If the 2kHz peak persists, I will try removing a small amount of ferrofluid and re-measure. I poured the entire contents of the 100uL package into the gap and maybe this tweeter is designed to use a little less fluid.
I wouldn't say that they're messed up, I'm sure they're still perfectly usable, but given the "before" measurements I don't see anything that needed fixing. In any case, I'm sure you'll get them in good enough working order for this design.
I have faith in your skills, Bill! I'm betting you'll get them to hit your target slope without much effort. A little contour on the top end and Bob's your uncle!
I reduced the amount of ferrofluid in both tweeters by wicking it out, in stages, using q-tips. This flattened out the impedance peak at 2k quite a bit. Before and after FR measurements are now much closer as well. I'd guesstimate that I took about half of the ferrofluid out, so I now probably have about 50uL in each one. Based on how much I originally took out, I'd say that I am now probably back to the original level.
Fs now measures 756Hz and 785Hz compared to the original 926Hz and 997Hz measurements. This reduction appears to be solely due to the changeover to the new domes. The old domes measure with a very high 920Hz+ Fs regardless of how much ferrofluid is in the gap. Also, the two new domes measure in the 750Hz or so area regardless of ferrofluid level. So, the high Fs reading was probably due to the aging of the dome suspensions, stiffening up over the years.
I initially thought that the amount of ferrofluid was the cause of the Fs change, but I was wrong.
It seems to have no influence on Fs at all.
My other two MDT-33 tweeters are a few years older and they both have an Fs measurement of about 1400Hz. I haven't done it yet, but when I replace the domes in these tweeters, I am going to leave the ferrofluid alone and see what happens to Fs by simply swapping out the domes.
How much change would you see in FS after running them? Thermal comes to mind. Probably moot at this point
I have not tried that. I'll hook a small cap in series with one, play music for a half hour to warm the VC, then re-measure. See if it makes a difference. I have noticed slight variations when running the test a day or two later. Same tweeter, but Fs measures 790Hz on day 1 and then after booting the computer on day two it then measures 808Hz (or something like that). And sometimes I get variations of 5Hz or so when re-running the sweep several times in succession. Makes me wonder what is going on sometimes.
I just played music through an 8uF cap into one of the two tweeters, and Fs dropped from 785Hz to 770Hz after about 1/2 hour of moderately loud music. Qts dropped from 0.55 to 0.49 as well.
Here's a video that hits quite a few of the finishes talked about in Bill's project.
Thanks for the vid, John! Lots of good info packed into a very short presentation. I'm still testing samples and debating what to do. I've noticed that quite of bit of the color tone and darkening depends on the sample that I happen to use. To get a valid test, I need to pull my comparison samples off the same board and sometimes off the same section of a board.