Jenzen Diamond mkII
Copyright 2012-15 © Troels Gravesen

DISCONTINUED DUE TO DIAMOND TWEETER OUT OF PRODUCTION
Go to Accuton version.

DRIVERS     CABINET     CROSSOVER     CROSSOVER LAYOUT     WIRING     CROSSOVER KIT     SOUND     MEASUREMENTS    

Diamonds may not only be a "girl's best friend"; could be men's too. If we google "diamond tweeter domes" we find quite a few discussions amongst B&W owners up-grading their alu domes to diamonds. There seems to be consensus diamonds are better; maybe not surprising considering the extreme cost, but going from aluminum to diamond is quite a jump so maybe there's something to it. What I am certain about is that their alu domes and new diamonds will not perform exactly the same with regard to amplitude and phase and this alone will compromise comparison. But how about going from ceramics to diamonds? How does the Jantzen Audio JDT-1024 compare to the Accuton C30-6-024? Read below.

Some basic info on diamonds for tweeter domes can be read here.

Based on mail response, there may be some confusion on what treble really is. Obviously our definition of frequency ranges are arbitrary, but treble starts - per definition - at 1280 Hz, that is "lower treble". Mid-treble is 2560-5120 Hz and upper-treble 5120-10240 Hz. What's above is "top octave". So, in most 2-ways the midbass is often handling the lower treble area and sometime going into mid-treble too. Getting the upper-mid/lower-treble range right is to my experience of pivotal importance for making good sound. Lower treble is the area where many 6-8 inch drivers start beaming and where tweeter units have extreme dispersion, thus the variation in dispersion is often an issue in making a happy marriage of midbass and tweeter. 2 inch mid-domes or small 3-4" conventional drivers can sometimes be a good idea in bridging the gap in radiating diameters of 6-7" midbass drivers and 1" domes. Problem is complexity of crossover and added cost. SP44, SP38 and Ekta are examples of this approach.

The domes presented here are roughly four times the price of the Accuton C30 and the obvious question is if they are worth the dough? It's a tough question because yes, they are better and even so by a comfortable margin. Whether they are worth the price is a futile question; like asking if a Ferrari or Rolex is worth the money. At a certain level of quality and sophistication price becomes irrelevant as the subjective appreciation of these qualities cannot be argued. Depositing carbon onto a silica substrate takes sophisticated machinery, skilled personnel - and it takes time. And I guess that when a batch of domes are made a certain number must be discarded due to variation in weight, etc., thus, diamond domes become expensive. Hopefully some day diamond domes can be made at affordable prices reaching current high-end domes because there are qualities to be had - and enjoyed.

My first Jenzen cabs ended up with the ScanSpeak Illuminator drivers, so I had to make new cabs for my final Jenzen D. It uses a slightly modified crossover compared to my first launch due to an optimised front panel layout for the middriver and tweeter dome. My intention with the modified front panels is optimisation of working conditions for the tweeter stuck in between mid and bass with a mid panel protruding some 20 mm in front of tweeter to time-align the two drivers. The tweeter and bass panels have the same thickness to reduce diffraction/reflection. Next I made the MT cabinet vented and with a tilted rear panel making the overall appearance less bulky.
Thus, a more stealth layout for mid and tweeter. Faceting the front panels was done on a table saw and by hand with chisel, planar and sandpaper. MDF is excellent for this due to homogeneity and in particular the black MDF used here for the front panels. This black MDF is really HDF, high-density fiberboard, weighing some 0.84 g/cm^3 compared to 0.64 g/cm^3 for the common brown MDF, although it depends on MDF thickness. Thick MDF sheets often have a rather soft center as producers may cut production cost by reducing glue content. This black MDF has an almost ceramic feel to it and comes at approx. twice the cost of standard MDF.
As can be seen, the tweeter has it own separated front panel and is suspended between Sorbothane pads on vertical braces mounted on the rear of the panel. Check images for details. This to reduce any impact from the middriver. I'm not sure it pays off, but it feels good - and it gives the possibility of tweeter swapping should I feel like trying out other tweeters, which I probably will.
The mid cab is vented and tuned for 40 Hz, and I used a vent because it gives three options for the mid: vented, closed and aperiodic; the latter from stuffing the port lightly, and this is what I actually use. These options do not exactly sound the same, so try it out.

Click images above to view large.

Left: Terminals and tweeter attenuation loop. Right. Connection between bass and mid-tweeter cab.

THE DRIVERS
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Click images to download driver specs - or from links below:

JDT-1024 diamond tweeter     Accuton 173-6-191E midrange driver   AudioTechnology 10C77-2510-KAP

The Sound
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How does this diamond dome compare to the ceramic tweeter? Diamonds have the quality of not really having a "character" - if you get my meaning. Those selling diamond domes will tell us the are "silky" and "smooth" because we like to read "silky" and "smooth" and we want the things we buy to have some kind of "quality".
With really good tweeters we forget about "tweeter" and we start listening to treble and not only that, we forget listening to something at all - except for the music. Ribbons have always been praised of neutrality although I've always felt they had "something" that wasn't quite right. Maybe my crossovers weren't good enough but I did try quite a lot and they always ended back up on the shelf.
The diamond story is trivial because it's about micro detail, resolution and forgetting about tweeters and listening to treble. The delicate overtones of acoustic instruments, listening to the flute as it never sounded before, the oboe, the violins and not least the piano. Acoustic instruments having a rich overtone structure seems to benefit the most. I'm not sure electrostatics are a proper benchmark for diamond domes although it's tempting calling treble quality here for electrostatic, but even electrostatics have their sound, not least due to dipole operation and usually poor dispersion characteristics.

I first tried the diamond domes with the ScanSpeak 18WU drivers (same front plate diameter..) and got so exited I couldn't wait implementing the diamonds in the Jenzen Accu speaker. In replacing the Accuton C30 dome I tried to render a frequency response as close as possible to the Accuton for the sake of comparison and they're close enough to dare comparing. Properly implemented, diamonds may urge you to go through countless LPs and CDs to hear what was hidden before. Based on history we're programmed to be suspicious on hard-domes for sounding - well, hard. The diamonds are neither hard nor silky, they are a significant step towards more fidelity. Cymbals, bells, triangles, btw, are a delight, and frankly, I never thought a dome tweeter could make this much impact because I've tried a lot over the years. It not only delivers effortless treble, it improves the response from the midrange driver - or so it is felt as the midrange is obviously doing the same as before, but the ear cannot for sure determine where the transition is. If mid-tweeter integration ever meant something, this is it. Another thing that was surprising was listening a low levels. I thought the diamonds would fade turning down the volume. Not so, clarity and transparency goes all the way down and tells the story of generally low-loss drivers.
I have second-hand two-dollar LPs I bought out of curiosity and never heard more than once, either because the recording wasn't that good or the music not really inspiring. The Jenzen diamonds require a second listen and pearls are found from time to time.
Based on efficiency related to moving mass, radiating area and BL factor, the diamonds are nothing special, yet delivers an unprecedented transient response, which took me by surprise. These diamonds are not particularly "fast" based on measuring data, yet supercedes anything I've heard so far.

The quality of the bass from the Audio Technology 10" sandwich bass driver in this transmission line cabinet is the best I've ever heard from a medium-sensitivity bass driver. Articulate, precise and responsive - and even so at low levels!

I could go on, but before even finishing listening to more music, the inevitable question arise: What's next? You may object that this isn't the time to think "what's next" when what I have described sounds like aural nirvana! It is the best I've ever had in my room and it is going to be a reference speaker, but the Jenzen cabs are a bit too big for our living room. So, can all this be preserved in a smaller enclosure making less impact on room decor. Time will tell. I had a Jenzen Accu four-way on the drawing board with the Accuton 2" dome bridging the C173 and C30, but now I'm not so sure. The added cabinet and crossover complexity may not pay off - and I would get less of the diamonds having a point of crossover in the 4-5 kHz region. Right now I can't get enough of the diamonds and 2" Accuton diamonds are way out of reach.

There's nothing like a new tool that allows you to learn new things and create new standards. All things written about the Jenzen Accus go for this speaker as well and I shall not repeat myself here. Please read the Accu file and find out what I mean.

Final front panels under construction. These will have more stealth appearance compared to first launch.

Crossover
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There are only a few changes to the crossover compared to first launch. Middriver's notch-filter has been fine-tuned at little by the 0.33 mH coil. Tweeter circuit is basically the same, only C1011 is reduced to 8.2 uF and the notch filter has been further improved to provide a smooth reponse roll-off towards lower frequences. Point of crossover has moved up some 200-300 Hz, now around 2.5 kHz. For tweeter attenuation R1031 can take any value from 3R9 to 5R6. My default is 4R7. It depends on associated gear, listening distance, overall room acoustics and not least taste. 3R9 gives tremendous detail but may turn harsh on certain recordings. Don't forget the bass notch-filter. R3031 can be changed from 15 ohms to 33 ohms - or the circuit can be left out.
And don't think there is one final truth to the crossover as can be seen below, but we have to be able to follow what is happening by simulation, measurements - and the ear.

Jensen D, as-is with R1031 = 4R7.

Impact of R2031 being 22, 33 or 47 ohms.

Impact of R1031 being 3R3, 4R7 or 6R8. My default is 4R7. 

I hope this will also demonstrate that there is no such thing as a final crossover. When the basic crossover is in place, we can make numerous minor variations that do not impair overall performance but may alter tonal balance a little and fine-tune performance to improve synergy with our gear and create a better balance with given room acoustics.

CABINET
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Click here to go to cabinet construction page for bass transmission line.

Click image to view large.

Bass cabinet is identical to all other Jenzen construction except for panels made from 9 mm Baltic birch +16 mm standard MDF like the MT cabs. Rear panels were made from 10 mm black MDF + 16 mm standard MDF. Go to Jenzen construction page here for further details and damping instruction.

Click image to view large.

Add 13 mm felt to all internal panels and fill lower compartment with acoustilux. I have two sheets, 10 x 25 cm, of 30 mm acoustilux behind middriver on each side of the vertical brace. Mid cabinet volume is around 22 litre and with the chosen port, Ø50 x 100 mm, we have Fb = 40 Hz. Just for those interested.

Click image to view large. Click here to go to images below.

Two vertical braces are glued to the tweeter front panel on each side of the tweeter. Shock absorbing pads, Sorbothane, are added to suspend the front panel. Adjust size of braces and pads to your actual tweeter cavity. No dimensions will be given here. I bought some 1/8" (3.2 mm) Sorbotane sheets, Duro 30 and 50, and made pads from these.

 Entire cabinet seen from front and side.
Optional tilt of bass front panel by inserting wedge; add 25 mm at bottom.
Click image to view large.

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CONSTRUCTION PICS
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For all outer panels except rear panels a laminate of 9 mm Balic birch and 16 mm MDF was used. For rear I used 10 mm black MDF + 16 mm MDF.

Left: Cut-out for the huge 10C77 magnet.

Right: For ports I use two 68 mm ports cut to 3 cm length (not shown on image above). Just to make the holes look nice.

FRONT PANEL CLOSE-UPS
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Front panels will have a black finish by a professional painter.

Right: Top of bass panel made from 2 x 16 mm black MDF.

Left: 68 mm ports cut to 3 cm length used to terminate TL vents.
Right: Base made from 10 mm Baltic birch + 20 mm black MDF. Make sure you can have the 240 mm wide crossover board in between.

Brackets for keeping tweeter panel suspended. Sorbothane pads will replace these felt pads.

Left: Tweeter panel in place. Right. Mid vent stuffed with acoustilux.

CROSSOVER KIT INCL JDT 1024 DIAMOND TWEETER
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Please contact Jantzen Audio for full quotation incl. shipping. Please state your address.

contact@jantzen-audio.com

Download sales presentation here:

PLEASE ALL TECHNICAL QUESTIONS AT: troels.gravesen@hotmail.com

The Crossover Layout
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Crossover layout, click image to view large.

CROSSOVER WIRING
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Crossover images

 
Superior Z-Caps for tweeter were later replaced by Silver Gold Z-caps, 3 x 2.7 uF in parallel.

Measurements
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SPL of MT section @ 0.5 meter normalised for 2.8V/1 meter.

Left: Frequency response of C173-6-191E on new front panel. Smooth as ever.
Right: Tweeter at 0 and 10 deg horizotal, red and green. Blue is response on old baffle.
Basically significantly improved response making crossovers even more simple.

Left: Step response of MT section. Right: SPL of MT driven from crossover incl. summed response. Point of crossover ~2.4 kHz.

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