It's a play off of PMC, with more musically related titling.
Basically, a small format TMM consisting of Seas Al/Mg 27TAC/GB and a pair of Peerless 830991 glass-fiber midbasses in a ~30" tall tower. It's meant to have really low HD for minimal cost, and be a designed update/improvement to the PMC 'Twenty5' design- or at least initially that was the goal. The '25' appears to use the 830991's larger 6.5" sibling singly with the 27TDFC as the tweeter, formerly the 25TAF. We'll see where it comes out in results.
The Titan 27TAC/GB I'm using is a serious upgrade over the previous tweeters, and Joachim Gerhard measured it to have the lowest HD of any similar tweeter with level being at -65dB from 2kHz up. I found this out as an added bonus after I made my previously noted purchase.
The tentative F3 is ~45Hz, and a target sensitivity is ~86dB. The midbasses are of the series that RobSan (Digi) tone-burst tested (830992) to have the lowest HD for the cost, and rivaling that of much more expensive drive units. Using 2 of the drivers will up my sensitivity, further reduce HD at output by halving Xmax requirements, and allow more room pressurization before rolloff. The '25' sounded really good and had extension, but seemed the level at that extension was a bit reduced in output. Using 2 will improve this.
Design being a short tower means optimizing for above the tweeter axis, 10" at the listening position. I designed for this to have an increasing lobe direction instead of being straight forward. I did this with the Nephila project, and it did quite well. The summation in the EMP still aligns well even below axis, so I feel this is a good compromise. The comb-filtering of the woofers in addition to being mainly (above) off-axis contributes to a large hump at about 200Hz I had to filter out. This lends to a more complicated xover in the bass range, but leaves the unpeaky rolloff of the glass fiber cones rather straight forward. It appears that 3rd order works better for the woofers above the tweeter. 3rd on the tweeter electrically was my result, plus a couple other things. Since the tweeter has no FF, I comped the Fs with a full LCR. The 27TAC FR exhibits an ultrasonic breakup at 25-27kHz, which I also have a notch to compensate. I have a switch on this circuit and have measured both with and without the notch engaged to both see and hear the performance differences in measurements and listening. Unfortunately, my measurements showed virtually no change between engaged and open.
Also of note- I obtained 4 of these initially, because the first 2 did not match closely to me. One from the first and one from the second pairs matched without changes. The other 2 were modded and (according to the HD sweeps) improved by better positioning of the internal cotton ball, and adding Ultratouch to the chamber. They also matched well after the adjustments. The 1" ball was inserted into the pole, and the added fill atop that in the chamber and reglued with E6000. Stock, the ball is wedged between the cup's divot and the backplate.
I will agree that from 2-4k, these are very low HD tweeters, and I like their sound a lot. Above there, the HD2 rises with a spike at 4k for the unmodded stock units, while the modded units had a flat HD2 line.
I'll add the graphics later....
Wolf
Basically, a small format TMM consisting of Seas Al/Mg 27TAC/GB and a pair of Peerless 830991 glass-fiber midbasses in a ~30" tall tower. It's meant to have really low HD for minimal cost, and be a designed update/improvement to the PMC 'Twenty5' design- or at least initially that was the goal. The '25' appears to use the 830991's larger 6.5" sibling singly with the 27TDFC as the tweeter, formerly the 25TAF. We'll see where it comes out in results.
The Titan 27TAC/GB I'm using is a serious upgrade over the previous tweeters, and Joachim Gerhard measured it to have the lowest HD of any similar tweeter with level being at -65dB from 2kHz up. I found this out as an added bonus after I made my previously noted purchase.
The tentative F3 is ~45Hz, and a target sensitivity is ~86dB. The midbasses are of the series that RobSan (Digi) tone-burst tested (830992) to have the lowest HD for the cost, and rivaling that of much more expensive drive units. Using 2 of the drivers will up my sensitivity, further reduce HD at output by halving Xmax requirements, and allow more room pressurization before rolloff. The '25' sounded really good and had extension, but seemed the level at that extension was a bit reduced in output. Using 2 will improve this.
Design being a short tower means optimizing for above the tweeter axis, 10" at the listening position. I designed for this to have an increasing lobe direction instead of being straight forward. I did this with the Nephila project, and it did quite well. The summation in the EMP still aligns well even below axis, so I feel this is a good compromise. The comb-filtering of the woofers in addition to being mainly (above) off-axis contributes to a large hump at about 200Hz I had to filter out. This lends to a more complicated xover in the bass range, but leaves the unpeaky rolloff of the glass fiber cones rather straight forward. It appears that 3rd order works better for the woofers above the tweeter. 3rd on the tweeter electrically was my result, plus a couple other things. Since the tweeter has no FF, I comped the Fs with a full LCR. The 27TAC FR exhibits an ultrasonic breakup at 25-27kHz, which I also have a notch to compensate. I have a switch on this circuit and have measured both with and without the notch engaged to both see and hear the performance differences in measurements and listening. Unfortunately, my measurements showed virtually no change between engaged and open.
Also of note- I obtained 4 of these initially, because the first 2 did not match closely to me. One from the first and one from the second pairs matched without changes. The other 2 were modded and (according to the HD sweeps) improved by better positioning of the internal cotton ball, and adding Ultratouch to the chamber. They also matched well after the adjustments. The 1" ball was inserted into the pole, and the added fill atop that in the chamber and reglued with E6000. Stock, the ball is wedged between the cup's divot and the backplate.
I will agree that from 2-4k, these are very low HD tweeters, and I like their sound a lot. Above there, the HD2 rises with a spike at 4k for the unmodded stock units, while the modded units had a flat HD2 line.
I'll add the graphics later....
Wolf
Turns out I have more time that I thought at the moment, so on with the details...
One of many things that are different about this build for me, is that there is no major bracing in the middle of the panels. All of the corners in the box accept for the side-to-top junctions have added corner bracing. This is due to the slot-port, the inner rails to mount the baffles, and the pieced rails to either side of the xover docks in the rear panel to make the width I needed. The sides/top have 4" square 1/4" thick marble(?) tiles with the mass-loaded Sonic Barrier chunked between them. The inside top wall of the slot has a thick rubber slab and 1" SB foam. Then I laid 4 layers of 100% wool batting over the back-mounted xovers.
But I digress... AND- I used plywood.
The box is very strong and does not resonate. I managed to get rid of the plywood box hollowness that I despise using the techniques above. I don't normally use ply much, but it is easier stapled to than MDF. This meant that I could do the finish I want. More on that part later, but I'll have some spiked feet outriggers on the bottom.
Since I had to use Xsim to model the bass sector, I've just included the schematic from there. It really does work well as seen in the last plot.
The 0.1uF bypass caps are only there to see/hear what they did if anything. Honestly, the measured additions really did not change the FR enough to warrant posting them. They are Russian K40Y9 PIO caps, and Russian Silver-Mica metal canister types.
The ultrasonic notch really did not measure differently either in terms of FR, and the impedance was less than a half-ohm change in the audible band.
As to the overall sound, they do not sound bright or hot as the last Omnimic plot suggests they should. Remember that these are measured at +10" above the tweeter, and at about a meter distance. A few others have heard them and agree that they are not bright. If anyone were to find them bright, a simple parallel LR of 2.0 ohms and 0.1mH placed in series at the tweeter will mitigate the occurence.
I am happy at the HD levels in a small tower for less than $200/cabinet in drivers. These really do sound quite good, and detail/openness is rather nice. The difference between the stock and modded tweeter HD is also attached, and clearly seen.
I'll add more internal photos in the next post...
Wolf
One of many things that are different about this build for me, is that there is no major bracing in the middle of the panels. All of the corners in the box accept for the side-to-top junctions have added corner bracing. This is due to the slot-port, the inner rails to mount the baffles, and the pieced rails to either side of the xover docks in the rear panel to make the width I needed. The sides/top have 4" square 1/4" thick marble(?) tiles with the mass-loaded Sonic Barrier chunked between them. The inside top wall of the slot has a thick rubber slab and 1" SB foam. Then I laid 4 layers of 100% wool batting over the back-mounted xovers.
But I digress... AND- I used plywood.
The box is very strong and does not resonate. I managed to get rid of the plywood box hollowness that I despise using the techniques above. I don't normally use ply much, but it is easier stapled to than MDF. This meant that I could do the finish I want. More on that part later, but I'll have some spiked feet outriggers on the bottom.
Since I had to use Xsim to model the bass sector, I've just included the schematic from there. It really does work well as seen in the last plot.
The 0.1uF bypass caps are only there to see/hear what they did if anything. Honestly, the measured additions really did not change the FR enough to warrant posting them. They are Russian K40Y9 PIO caps, and Russian Silver-Mica metal canister types.
The ultrasonic notch really did not measure differently either in terms of FR, and the impedance was less than a half-ohm change in the audible band.
As to the overall sound, they do not sound bright or hot as the last Omnimic plot suggests they should. Remember that these are measured at +10" above the tweeter, and at about a meter distance. A few others have heard them and agree that they are not bright. If anyone were to find them bright, a simple parallel LR of 2.0 ohms and 0.1mH placed in series at the tweeter will mitigate the occurence.
I am happy at the HD levels in a small tower for less than $200/cabinet in drivers. These really do sound quite good, and detail/openness is rather nice. The difference between the stock and modded tweeter HD is also attached, and clearly seen.
I'll add more internal photos in the next post...
Wolf
Attachments
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I searched until I found the most cost-effective Film/Foil capacitors for the tweeters because I felt the supposed performance deserved them. These are NOS Plastic Capacitors, Inc branded model LQ 2kV series. They were inexpensive compared to the audio-branded items we all know, just that they were huge and that I needed 3x at roughly 2.2uF each. For the buzz-word familiar, these are bifilar-wound, oil-impregnated, Dupont Mylar (R) film and foil caps- and they do the job well.
The woofer circuit large 650uF cap-bundle consists of a pair of 1000uF polarized 250VDC caps back to back (measured to 450uF), and a pair of 100uF poly caps. I found a great deal on the C-Coils so I used them.
The xovers pictured alone in the rear panel are shown without some of the connections made, without the 24uF bypassing caps, and with a different Solen cap on the one end. The large Silvers were 33uF, and the design was better with the 25uF smaller value.
Did I go overboard? That depends on your opinion, but I likely did at least a little. Lower costing parts substitutions could easily be made.
Thanks for looking!
Wolf
The woofer circuit large 650uF cap-bundle consists of a pair of 1000uF polarized 250VDC caps back to back (measured to 450uF), and a pair of 100uF poly caps. I found a great deal on the C-Coils so I used them.
The xovers pictured alone in the rear panel are shown without some of the connections made, without the 24uF bypassing caps, and with a different Solen cap on the one end. The large Silvers were 33uF, and the design was better with the 25uF smaller value.
Did I go overboard? That depends on your opinion, but I likely did at least a little. Lower costing parts substitutions could easily be made.
Thanks for looking!
Wolf
Attachments
Bravo 🙂
I also use cotton loosy ball just behind these hard dome type and it works well subjectivly; never tried the tunnel damping nore the chamber yet though.
that's very interresting to experiment about C3 & C10 and looking forward if you find difference between measure and listening.
Some questions please:
The Fs of the Peereless are around 65 hz. I don't understand how are reproduced the notes below the Fs ? Also why the serie resistor in the bass notch and finally the // of the 25 uF ?
I also use cotton loosy ball just behind these hard dome type and it works well subjectivly; never tried the tunnel damping nore the chamber yet though.
that's very interresting to experiment about C3 & C10 and looking forward if you find difference between measure and listening.
Some questions please:
The Fs of the Peereless are around 65 hz. I don't understand how are reproduced the notes below the Fs ? Also why the serie resistor in the bass notch and finally the // of the 25 uF ?
The Fs of the quad were all very close, but closer to 75Hz. The tuning of the vented alignment allows the tuning of 42Hz in this box and has a gradual rolloff and then would unload lower than the Fb of the box. Thing is- these midbass drivers are very well controlled and I have not been able to get them to move much.
If the resistor were not there, the damping for the notch to work appropriately would not be present. It makes the transition portion smoother between the Fc's of the 3.0mH and 650uF cap and allows them to work better. The magnitude at 100Hz was in the 100s of ohms without it there, and there was still a peak present of 3-4dB, as well as a substantial dip at the components' resonance point. I tried it without, but found it was required. 1 ohm was not enough and it drooped, and nothing and larger than 1.5 had a peak.
The 24uF cap across the bass-EQ was necessary. Without it, the midrange was about -2dB from the proper junction with the tweeter at around 2k. This has to do with the required 1.5 ohm resistor you asked about, as it will attenuate above the Fc of the 650uF cap. In conjunction with the ESR/Le of the large NPE, this can create the reduction in output I was seeing. The smaller cap decreases both the ESR and Le, as well as bypasses the resistance, and returns the midband to the higher nominal output.
I know it's a funky circuit, but it does the correction that was required as evident in the FR plot.
Thanks for asking!
Wolf
If the resistor were not there, the damping for the notch to work appropriately would not be present. It makes the transition portion smoother between the Fc's of the 3.0mH and 650uF cap and allows them to work better. The magnitude at 100Hz was in the 100s of ohms without it there, and there was still a peak present of 3-4dB, as well as a substantial dip at the components' resonance point. I tried it without, but found it was required. 1 ohm was not enough and it drooped, and nothing and larger than 1.5 had a peak.
The 24uF cap across the bass-EQ was necessary. Without it, the midrange was about -2dB from the proper junction with the tweeter at around 2k. This has to do with the required 1.5 ohm resistor you asked about, as it will attenuate above the Fc of the 650uF cap. In conjunction with the ESR/Le of the large NPE, this can create the reduction in output I was seeing. The smaller cap decreases both the ESR and Le, as well as bypasses the resistance, and returns the midband to the higher nominal output.
I know it's a funky circuit, but it does the correction that was required as evident in the FR plot.
Thanks for asking!
Wolf
Attachments
The plot below has no damping resistor, and no 24uF cap. Same modded tweeter.
The range between 100-200 Hz is the effect of the Bass-EQ with no resistor.
The dip at 250 is the Floor-Bounce.
The range at 500Hz is not attenuated due to no resistor.
The range at 1-2k is not high enough with no 24uF cap.
In the finished FR plot in post #2 above, I placed them on a chair to mitigate the Floor-Bounce in the measurement. So it is not shown in that plot.
Later,
Wolf
The range between 100-200 Hz is the effect of the Bass-EQ with no resistor.
The dip at 250 is the Floor-Bounce.
The range at 500Hz is not attenuated due to no resistor.
The range at 1-2k is not high enough with no 24uF cap.
In the finished FR plot in post #2 above, I placed them on a chair to mitigate the Floor-Bounce in the measurement. So it is not shown in that plot.
Later,
Wolf
Attachments
I have done a bunch of listening over the last few weeks, and there is no need to add the LR filter suggested for the top-end, IMO. It sounds really well balanced on anything from classical to bluegrass to jazz to rock to metal. I even listened to what I consider 'bright' recordings and nothing really came out harsh, hot, or sssibilant.
The bass is really something. They sound a lot bigger than they have a right to. Tympani, bass guitar, and stand-up bass are all tuneful and distinct in tone. Dynamics can make me jump, so that's very good.
Preferences-
I have found I like having the ultra-notch engaged. I'm not sure how to describe it, but it just sounds cleaner up on top to me, like a blacker background. Neither is bad on/off.
Same with the bypass caps in that they are also hard to describe, but I feel the addition of either messes with the spectral balance a smidge. Were I to pick one, the Silver Mica would be my choice since it just sounds cleaner on top, if not a little louder in level. The PIO do influence lower in the treble, but more of a vintage or analog combination. Again- I don't prefer the tweeters with either of these engaged over that of without both.
Later,
Wolf
The bass is really something. They sound a lot bigger than they have a right to. Tympani, bass guitar, and stand-up bass are all tuneful and distinct in tone. Dynamics can make me jump, so that's very good.
Preferences-
I have found I like having the ultra-notch engaged. I'm not sure how to describe it, but it just sounds cleaner up on top to me, like a blacker background. Neither is bad on/off.
Same with the bypass caps in that they are also hard to describe, but I feel the addition of either messes with the spectral balance a smidge. Were I to pick one, the Silver Mica would be my choice since it just sounds cleaner on top, if not a little louder in level. The PIO do influence lower in the treble, but more of a vintage or analog combination. Again- I don't prefer the tweeters with either of these engaged over that of without both.
Later,
Wolf
I don't know what happened, but I've not been able to log in for awhile now. They have sent me reminders about paying the premium that never used to exist, and when I try to log in, it redirects me to an 'app' website and never loads.
I've no loaded anything into it for over a year now since they updated their terms of use and paying hierarchy.
Is their anything in particular you want to know about? I saved all but the event photos before I was locked out of it.
Later,
Wolf
I've no loaded anything into it for over a year now since they updated their terms of use and paying hierarchy.
Is their anything in particular you want to know about? I saved all but the event photos before I was locked out of it.
Later,
Wolf
I took these to a friend's house recently, and they sounded a little bright there.
The LR is up to the end-builder or not.
Wolf
The LR is up to the end-builder or not.
Wolf
Back in May, I added a 1 ohm resistor before the tweeter to lower its level a smidge.
I prefer it this way, as it does not have any sharpness at all. Before, it seemed fine. It however seems that the balance is just that much better over all.
So- final voiced and preferential circuit is attached.
I will also say that 2x 1.6" diameter ports equal that of the slot end-area, so dual 2" ports will work. You just have to have the tuning between 40-42Hz.
Really liking these...
Wolf
I prefer it this way, as it does not have any sharpness at all. Before, it seemed fine. It however seems that the balance is just that much better over all.
So- final voiced and preferential circuit is attached.
I will also say that 2x 1.6" diameter ports equal that of the slot end-area, so dual 2" ports will work. You just have to have the tuning between 40-42Hz.
Really liking these...
Wolf
