TQWT/DTQWT-10/DTQWT-12 mkII T35 option
Copyright 2013 © Troels Gravesen


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Download driver data files: SEAS T35C002

When the SEAS T35C002 dome was released in Europe I ordered a pair to see if they would fit the TW034 waveguide because due to the rear chamber it might do the same thing as the modified Audax TW034 dome can do: Go lower and allowing the point of crossover between 8008 and dome tweeter to be taken down to around 2 kHz providing a bit more presence and better dispersion in upper mid and lower treble.
The T35 does not sound anything different from the TW034 dome; in that respect they're too alike. The SEAS has a voice coil diameter of 35 mm, the Audax 34 mm, fabric weave slightly different, coatings very much alike, dome shape very much the same, etc. Only major difference to the standard TW034 is the rear chamber.
Any difference in sound is based on minor differences in frequency response and this can be corrected in the crossover. I've used my modded TW034 the same way as I now use the T35 but never released an alternative version of TQWT and DTQWT as very few people have the tools to do the TW034 modifications. No point in making a speaker only a very few people can copy. It has to be said the TW034 can be used un-modified with the same T35 crossover with a minor dip around 2 kHz but it's no big deal - if audible at all.
I suggest taking a look at performance of the T35C002 and modified TW034 here. Study the waterfall plots and you'll find very little difference.


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Making a seamless integration of an 8" driver and a dome tweeter is the trick, regardless of being a 1" or 1½". The T35 - as is - can easily handle the treble range down to even 1.5 kHz from a LR2 filter - and it was tried and it didn't sound right. No matter what, the treble stood out and the T35 just kept calling: Here I am! And it wasn't due to point of crossover, slopes or levels, but due to the transition in dispersion from a large 8" driver to a small dome. It didn't produce the coherent sound of the TQWT and DTQWT speakers fitted with the TW034/waveguide.
So, a pair of waveguides were brought in and threads were made to allow mounting of the T35 by the four screws holding the face plate. Here we remove the T35 face plate and mount the tweeter directly to the waveguide.
Back to measurements, simulation and crossover fine-tuning. With a point of crossover at 2.1 kHz an even simpler crossover could be achieved compared to the standard DTQWT crossover and now it started sounding right.
Finding the right tweeter attenuation is important and in fact takes quite some time as we are easily seduced by detail from an over-emphasised treble level. I ended up with 1011 = 2.2 ohms.
Should you want to change your current TW034 for the T35 you can also fasten the T35 dome by making a flange like I did for the ScanSpeak 7100 tweeter. Click here to see how. I used the flange for my initial testing. But you then have to be able to make threads for the screws and need a 4 mm thread forming tap, hand taps.

What the new crossover does is two things: More presence in upper mid/lower treble due to better dispersion of sound, hence more detail. It kind of brings the music a little better into the room, where the mkII more provides a window to the music to somewhat exaggerate the difference. I have chosen not to call this a DTQWT mkIII as the basic crossover topology is the same, only the point of crossover has been lowered to 2.1 kHz.
Now, should you rush to change your DTQWT mkII crossover and buy the T35 tweeter also? Maybe, maybe not. The change is sound is significant, but only your ears can tell which one you like the best.

From left: T35 rear/T35 front/TW034-rear-front

The T35 dome including surround is actually slightly smaller than the TW034 dome, probably about 0.8 mm difference in diameter despite having a 1 mm larger voice coil, but nevertheless fits perfectly into the TW034 waveguide. Only problem is making four threads that will take the four screws holding the standard T35 front plate. I never succeeded doing this properly by hand and eventually mounted the T35 dome with a flange, the same used for the ScanSpeak 7100 dome.
When the next batch of waveguides were ordered I went to the factory and had them make a batch of waveguides suitable for the T35 dome. Thus, only thing to do is loosen the four screws, remove the face plate and fasten the T35 to the waveguide. Tighten the screws with caution! Firm - but no more. If you have a box of 4 mm thread taps, the diameter is 60.4 mm and the threads need to be effective down to 4 mm. Drill to 5 mm depth and you won't penetrate the waveguide.

From left to right the procedure in removing SEAS front plate and attach dome to Jantzen Audio waveguide. Click images to view large.

The Crossover
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Simulation is one thing, practical experience quite another. This turned out even more simple than I had hoped for. 2nd order on the electrical side and a perfect LR4 topology on the acoustical side with positive polarity on all drivers. Point of crossover is 2.1 kHz.
An LCR filter on tweeter impedance peak turned out unnecessary. If you're wearing belt and suspenders use (4R7 + 68 uF + 1.0 mH) in parallel to the tweeter (before R1041). 
The bass driver crossover is really 1st order but residual midrange response is filtered acoustically by adding felt discs in front of drivers like the DTQWT-mkII.
For the TQWT you leave out the bass section.
If you want to try out the crossover topology before investing in T35 - or stay with the TW034, you can add 5.6 uF in parallel to the 6.8 uF capacitor in the 8008 section. This makes 12.4 uF and is fully acceptable. Obviously you need new coils for L2011 and L1031 and 6 pcs 1.0 ohm, 2 pcs 1.5 ohm and 2 pcs 2.2 ohm resistors.

Crossover layout
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The finished crossovers. Above for the mid-tweeter, below for the bass drivers. Click images to view large.
Please note R1041 is missing on the board here (tweeter series resistor, was added later)
The 8008 series WAX coil is quite a chunky beast with its 1.8 mH inductance.
A smaller (500 watt) C-coil has been chosen for the bass drivers as previous C-coil was wildly oversized due to availability of suitable cores.
With 95 dB sensitivity the current C-coil is still overkill with a 500 watts capacity.


Crossovers mounted in cabinet. Bass crossover on rear inner panel and mid-tweeter crossover on front inner panel.
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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 anything 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 way 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.

Left: The two T35 domes mounted on waveguides. Rigth: Individual and summed response from drivers driven from crossover.
Point of crossover = 2100 Hz.

Left: Tweeter response from R1011 = 0.47, 1.0 and 1.5 respectively, I use 2R2. Right: Response from inverting tweeter polarity.

Left: Horizontal dispersion at 0, 10, 20, 30 and 40 deg. Right: CSD at 25 dB scaling.

Speaker Kit
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For full quotation incl. shipping, please contact Jantzen Audio at contact@jantzen-audio.com
Remember to state where you live to calculate shipping.

Download kit sales presentation for DTQWT mkII (10" & 12") T35 option:

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

All technical question at: troels.gravesen@hotmail.com


TQWT mkII T35 version

For full quotation incl. shipping, please contact Jantzen Audio at contact@jantzen-audio.com
Remember to state where you live to calculate shipping.

Download kit sales presentation for TQWT-mkII T35 option:
All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark

All technical question at: troels.gravesen@hotmail.com