TQWT-mkIII and DTQWT-mkIII
Copyright 2014-15 © Troels Gravesen

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It's been six years since I had the first production samples of the JA8008 driver and quite a range of speakers have been made around this high-efficiency driver: TQWT, DTQWT, DTQWT-212, QUATTRO, 8008-CENTER, OBL-11 plus quite a few never published.

There are two main features of the new TQWT-mkIII and DTQWT-mkIII constructions: New JA8008 HMQ driver and stepped baffle allowing a true LR2 filter to be implemented. The JA8008-HMQ driver features a high mechanical Q (low damping) and a better match to the magnificent Eminence bass driver(s), thus enhanced transient response and low-level detail. The stepped baffle allows true LR2 filter, which has become my favorite from the constructions made over the last few years. To properly implement LR2 filters we need to acoustically align the drivers, thus the stepped baffles.

This is - like the mkI and mkII - a speaker I can listen to for hours and hours. Not having a high-pass filter to the midrange pays off and the waveguide and crossover makes a seamless integration of mids and highs. How the bass will respond to your room is out of my control. Based on response from the numerous builders of mkI and -II, I guess 90% are happy, 5% have too much bass and 5% too little. Too much is always due to near-corner placement and the 5% too little had expected more or their room simply suck up bass energy. For those requiring more bass, add a 12-15" bass driver driven by a plate amp. Put it against the wall to get the necessary room gain and you should be able to tune things into place.

Questions are already coming in a few days after launch: Should I upgrade to mkIII. The answer is: If you're happy with mkI/mkII, don't. I try to implement new things when it makes a difference, but whether this will make you a happier person, I can't tell. So please do not ask!

Next question is on the choice of tweeter and it's my experience they perform equally well. This doesn't mean they sound exactly the same as they will have minor differences in frequency response, hence different sound and only your ears can tell which one you prefer.
I added the T35 as an option as some people think that old is bad and new is good - and there's nothing I can do about it. So, take your pick.

To my ears the LR2 filter delivers enhanced transparency and micro detail and at the same time protects the tweeter properly compared to 1st order filters. The large domes available for these constructions have no trouble in terms of power handling with the target 2 kHz point of crossover.
The DTQWT-mkIII now features as standard a single 12" Eminence DeltaLite mkII driver as most people, based on feedback, do not use flea-powered tube amps, rather solid state - or higher powered push-pull valve amps not having any trouble running a minimum 4 Ohms impedance. Those wanting a higher impedance (6 Ohms) can obviously still use two 10" bass drivers coupled in series as was standard the DTQWT mkII. Go to DTQWT mkII page for cabinet details and bass section crossover.
The 12" Eminence DeltaLite 2512 delivers deeper bass compared to DTQWT mkII - a bit surprising as the horn is basically the same length. Together with the high-Qm JA8008 HMQ the bass performance is significantly more dynamic compared to mkII. It now has the speed and punch quality I have become addicted to from my ATS4 speakers.

Last, but not least, my ambition here is to launch a better speaker at the same price as the classic DTQWT-mkII. This due to the money saved from using only a single bass driver. The TQWT will be a little more expensive when using the SEAS T35C001 tweeter, but you can keep the price of the TQWT-mkII by using the Audax TW034 tweeter without changes to the crossover.

Read about the new JA8008-HMQ driver here

Read the story behind the JA8008 driver and TQWT construction

Read the story behind the DTQWT and the special cabinet design

 


Click images to view large

Like the TQWT and DTQWT mkII versions, these new speakers will play any kind of music. The mkIII version is in no way a discriminative speaker leaving out certain recordings as is often the case when speakers excel in particular aspects of music reproduction. The "thing" about these speakers is having a single driver handling all of the midrange with no crossover between the bass and midrange. In this respect the TQWT and DTQWT can play a few tricks any other of the larger 3-4-ways systems on these pages cannot. Regardless of how smooth a transition we can manage between bass and mid and regardless of how good crossover components we use, the absence of a crossover between bass and mid can be appreciated. The JA8008-HMQ driver is in fact the same size as the 23I52 driver used in the ATS4 for upper bass and does deliver the same punch and dynamic qualities as the 23I52.
We cannot tell other people what a speaker sounds like and regardless of how much we could write about the sound, it would never tell you what it's like, as little as I can tell you the taste of a vintage wine or French goat cheese. If you haven't tasted French goat cheese - and they come in many varieties - it doesn't matter how much reviewers write. You have to taste it yourself to know.
What you can do is read the many reports from TQWT and DTQWT builders here. Regardless of preference for rock, jazz or classical music, these speakers have found an audience and maybe you will like it too. One thing is for sure: These mkIII are better than the mkI and mkII versions. More detail, better dynamics.


Drivers
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The new driver is JA8008-HMQ and the new main speaker constructions are TQWT-mkIII and DTQWT-mkIII as the modified crossover versions of both were called mkII.
Standard tweeter is the new SEAS T35C002 but AUDAX TW034 is still available and can be used with no changes to the crossovers.

           
Above the JA8008-HMQ
Click image to view large.
A special coating ring between the cone and foamed rubber surround smooth the 800-1000 Hz frequency range.

 

     
Audax TW034 and SEAS T35C002 tweeters and Jantzen Audio waveguide.
The waveguides are machined from solid non-resonant POM plastic, not some cheap cast PBS plastic.
Click images to view large.

 


Mounting the TW034 waveguide.
Click images to view large.
This is diy, so you have to do a little more yourself: Center the tweeter on the waveguide as seen on photo.
Mark for holes on waveguide and add a 10 mm mark on the drill. Drill 3 x 10 mm holes in waveguide,
check if dome is properly centered and fasten with the screws supplied with the kit, 2 x 4 pcs M4 x 10 mm. That's it!

 

   
Mounting the T35 waveguide. Use the SEAS screws from the standard face plate.

You can use the T35 waveguide with both tweeters as you have to drill the screw holes for the TW034 yourself.
The TW034 waveguide cannot be used with the T35 tweeter unless you can make extremely precise threads at 60.4 mm diameter.

 


Eminence Deltalite 2512 bass drivers
Click image to view large.

PA drivers are often pretty rigid out of the box and I always do some "break-in" by pushing and pulling the membranes to their limit before mounting. On a fresh unit you can hear the lacquer on the spider cracking when doing so. This will do the same as at least 50 hours off burn-in. Take care and do no puncture the membrane with your fingers when doing so. In addition to this - and if you have a test CD with some 40-50 Hz sine waves - give the bass drivers a couple of hours at +/- 6-8 mm membrane excursion. All this helps loosen the suspensions and reach optimum performance quickly.

Get Deltalites here:

Europe:
12" bass drivers: http://www.thomann.de/gb/eminence_deltalite_ii_2512.htm
10" bass drivers: http://www.thomann.de/gb/eminence_deltalite_ii_2510.htm

Go
od Old England:
12": http://www.lean-business.co.uk/eshop/eminence-deltalite-ii-2512-neo-8ohm-12-250watt-speaker-p-850.html
10": http://www.lean-business.co.uk/eshop/4-x-bundle-eminence-deltalite-ii-2510-neo-8ohm-10-250watt-p-1136.html

USA:
http://www.music123.com/accessories/eminence-deltalite-ii-2510-replacement-pa-speaker, or
http://www.usspeaker.com/homepage.htm
 


Crossover TQWT mkIII
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Please read below at DTQWT, same crossover except for no bass section. 


Crossover DTQWT mkIII
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The bass section runs 1st order and due to the single 8 Ohms driver we here have a 10 mH coil rather than the 18 mH needed for two 8 Ohms drivers in series from the mkII version. The "thing" about this speaker - and the mkI and mkII versions - is that the middriver does not have a high-pass filter. Thus an 8" driver that can handle the bass range as well as midrange. This has indisputable benefits and is to be heard, even compared to my ATS-4. But every speaker is a compromise.
The mid tweeter section features LR2 topology and due to the time alignment we here have to invert tweeter polarity. 8008 section is as simple as can be and the tweeter section takes use of a rather unusual RL circuit with a 10 ohms series resistor. The LCR circuit flattens the impedance peak and helps shaping the tweeter roll-off, which is as close the target LR2 as can be. C1041 is a 100 uF electrolytic cap and believe me, it doesn't sound better with a 100 uF PP in this place. It was tried. If you cannot stand the sight of electrolytic caps, order a 100 uF PP. C1021 needs to be as good as can be, thus JA Superior-Z or Silver-Z. They differ by their termination, copper for one, silver for the other.

Should you want to maintain higher impedance (SET amps) and a slimmer design, you simply replace the bass crossover with the same as for the DTQWT mkII and buy four Eminence DeltaLite II 2510 bass drivers and adjust the rear panel like the mkII. Please ask Jantzen Audio for a quotation on this set-up: 2 x 18 mH C-Coil, 0.17 Ohm, 2 x 15 Ohm 10W resistors and 2 x 10 uF CrossCaps.



Bass section crossover.  Click images to view large.
The RC circuit flattens the impedance rise towards higher frequences and allows the coil to form a 1st order roll of.


Mid-tweeter section crossover. Click images to view large.
Images here before the equalising circuit was added. See layout below.


Wax coils are rather heavy and I use a dowel to secure the coil.
The coil is added a ring of Superfix, view here for more details.


CROSSOVER LAYOUT
Click images to view large


For the TQWT you only use the above.


Crossover for bass in DTQWT

 

Speaker Wiring
Click image to view large


Cabinet TQWT mkIII
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Click image to view large.

Cabinet damping is the same as for the DTQWT front chamber and top. No damping in rear chamber.
Go to cabinet damping


Cabinet DTQWT mkIII
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Click image to view large.

Go to cabinet damping

If you choose to do the 2 x 10" version for the sake of higher impedance, you can obviously leave out the rear fillets and do the rear panel like the mkII version:
http://www.troelsgravesen.dk/JA8008_DTQWT_cabs_files/DTQWT_cab_draw_v3.png

 

 


You can also make the bottom like this if cutting angles is tricky.


DTQWT mkIII CABINET CONSTRUCTION IMAGES
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Left: Gluing inner baffles in place. For no particular reason I used 18 mm black MDF for inner panels. 18-20 mm panels of any kind will do.
Right: Gluing rear fillets.


Left: Routing for the bass driver finished, 280 mm diameter. Right: Testing bass driver.
Bass driver is not flush mounted. If you want to do so, increase rear panel thickness by 15-18 mm and keep internal dimensions.

 
Rounting the front inner panel towards floor. I had this question quite a few times: How do you chamfer the inner front panel towards floor?
Hope the images are self explanatory.


Cabinet damping of front horn.
Top and reflectors are added 8 mm felt material.
Front horn internal baffle is added felt in entire length and 50 cm length on sides as seen on photo.
At bottom a piece of 50 x 24 mm 30 mm acoustilux is folded and attached like seen on photo. I used staples.
View drawing at bottom for complete damping instruction.


Gluing front panels.


For the terminals I decided to place these on a mahogany bar on the bottom to the rear. Makes wiring very easy and wires very short.


Crossovers sections placed on front and rear inner panels. Note easy access to tweeter attenuation resistors.


Midrange equaliser circuit on separate board as this was added later in development.
Obviously this can be mounted on a single board together with the other components.

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TQWT mkIII Kit
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Complete kit only available from Jantzen Audio, contact@jantzen-audio.com

Please state where you live for full quotation incl. shipping.

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

 

Download sales presentations for four versions of TQWT here.

The Stand-Z versions still holds Superior-Z cap for the tweeter.

Sup-Z: All Superior-Z caps
Wax: Wax series coil for 8008 driver
TW034: Audax TW034 tweeter
T35: SEAS T35C002 tweeter

All technical questions to me at troels.gravesen@hotmail.com


DTQWT mkIII Kit
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Complete kit only available from Jantzen Audio, contact@jantzen-audio.com

Please state where you live for full quotation incl. shipping.

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

Download sales presentations for DTQWT mkIII with 1 x 12" or 2 x 10" bass drivers:

Download sales presentations here (pdf file)

All technical questions to me at troels.gravesen@hotmail.com


Measurements
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A few comments on MEASUREMENTS before you start interpreting all the readings below.
First of all, if you think measurements will tell you how a speaker sounds, you're wrong, very much wrong indeed. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of us diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz.  

What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range. 
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the drivers, because cones made from polyprop, alu, kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of colouring the sound.

Here are some DTQWT mkIII screen shots from the CLIO measuring system:

Above the basic response from the new 8008-HMQ driver in DTQWT cabinet. Red is without any filter, green with 1.0 mH in series with the driver.

Above the T35 tweeter incl. waveguide mounted in DTQWT cabinet. The waveguide will boost the response in the 2-7 kHz range. Overall a response that makes crossover work easy.

 

Above the two most important measurements. Left: SPL from drivers driven from crossover and summed response. System sensitivity around 94 dB/2.8V. Here the midrange counts. How we tune the treble level is a matter of taste and overall system set-up. With R1011 = 0 ohm we have a fairly flat response. I prefer 1 ohm in series with the tweeter making a better balance of basic notes and overtones. Point of crossover is around 2.1 kHz.

Above the impact of mid LCR equalising circuit. Initially I left out the circuit and enjoyed a slightly vintage presentation from the elevated 500-800 Hz range and it's easy to be seduced from a response that emphasize a particular frequency band a little. We tend to think it delivers more detail. However, after some months of listening I started fine-tuning the midband and removed the ~1.5 dB bump and this is what it should be. Slightly less presence but more depth and perspective. Try it out and decide for yourself. The crossover provides you two opportunities to modify the sound to your taste: Mid equalisation and treble level.

System impedance displaying 5 ohms in most of the range and a minimum of 3.8 ohm at 38 Hz. My KT88 PP amp has no trouble running this speaker. The minor ripples around 100-300 Hz are normal for a horn-loaded system, in fact this looks very good compared to the few who dare publish such data. The 12" Eminence here goes deeper than the mkII version and I was a bit surprised to hear that as the horn basically is the same length, but apparently the 2512 bass driver does a bit more in the low end. And by the way, this 12" takes some beating to loosen up before delivering. Stretch the suspensions by pulling and pushing the membrane to its extremes and don't stick your fingers through the membrane! This simple exercise is equivalent to hours of burn-in. For the 8008-HMQ and T35 I don't find any change in sound over time.


Treble level tuning. Red is R1011 = 0.47 Ohm, green = 1.0 Ohm and orange = 1.5 Ohm.
Do not be seduced by tizz and treble detail from the highest level.


CABINET DAMPING

Cabinet damping follows the same rules as for the original version of the DTQWT. Above what comes with the kit.
Only the top of the internal side panels are added 8 mm felt material. Otherwise no damping materials in the center horn.


 

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