90 dB/2.8V, 40 litre vented design from JA8008-HMQ and SEAS T35C002 drivers
Copyright 2019-21 Troels Gravesen

Cabinet     Crossover     The Kit   Measurements

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QUATTRO mkII is the up-dated version of the original QUATTRO based on the JA8008 driver, here with the new JA8008-HMQ driver. There were only a few changes to the crossover and only to the low-pass section of the bass driver. The SEAS T35C002 tweeter is noiw standard.
With the new JA8008-HMQ driver the performance is further increased by a more tight bass and enhanced midrange transparency. QUATTRO is a true 8 Ohms speaker with a minimum impedance of 7 Ohms and suitable for medium power valve amps.

was the forth construction based on the JA-8008-HMQ/SEAS T35C002 high-efficiency drivers, thus "QUATTRO". The other constructions are
TQWT mkII, DTQWT-mkII and OBL-11 with the up-dated mkIII versions here.
Quite a number of people have asked for the JA8008/T35C002 sound in a smaller cabinet and there are a few issues to address when doing so. The JA8008 driver is a low-Qt, high-efficiency driver and not directly suitable for small vented cabs unless we sacrifice some bass extension or system sensitivity. If we target F3 around 40-45 Hz from 40 liter vented enclosure, we have to sacrifice system sensitivity and settle for some 90-91 dB sensitivity.
To equalise the response of the 8008 driver, a baffle step compensation circuit may be used, simply consisting of a coil bypassed by series resistor. From thereon we can start modelling the response of the two drivers to make a point of crossover similar to what is used for the TQWT/DTQWT/OB9.

I have added measurement files
on another page as measurements in reality tell close to nothing about how a loudspeaker actually sounds. What we can get from measurements is a good idea of what amps may be needed, roughly an idea of the tonal balance of the speaker and we may get an idea of bass extension too. The QUATTRO is tuned more flat compared to TQWT and DTQWT and I won't hesitate to recommend the speaker also for recording studios, although I know these guys sometimes listen to the weirdest things. They may listen for specific qualities in a recording requiring a lot on linear distortion, but what I can assure from this speaker is a linear response with tons of detail. It does
Siri's vocal very well and it does all the acoustic instruments as well, like the flute, oboe, violin, piano, which I use for voicing a speaker.

Drivers and components

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Cabinet made from 22 mm MDF, except for front panel (30 mm), should make 2.56*2.98*5.56 = 42.4 liter net volume. Adding bitumen pads, port, braces, drivers, etc., will further reduce volume a liter or two. Do not be too keen on this, anything from 38-42 liters will work perfectly as long as front panel dimensions and driver placement is maintained. For my cabs I used 21 mm Baltic birch and 30 mm for the front panel laminated from 21 + 9 mm sheets. Front panel fillets are made from 30 x 50 mm solid maple wood.

I often have the question whether Baltic birch is better than MDF and I honestly can't tell. I never made two pairs of speakers from both materials to compare sonic impact. From a well-braced cabinet added bitumen pads, I don't think there will be much difference.
I use Baltic birch as it gives me the final finish without having the trouble of applying veneer - and I just happen to like the appearance of lacquered Baltic birch although it's not an easy material to use. Read below.

The QUATTRO need stands. To my ears - and sofa - 45 cm height. I listen to the QUATTROs slightly toed in and as usual in my living room, 1 meter from the front wall and ~1.8 meters from side walls. My speakers are placed on the long side of the room, thus very little roomgain.


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To reduce system sensitivity some 4-5 dB compared to TQWT and DTQWT, a 3.9 mH coil bypassed by ~3.3 ohm is used. Eventually during fine-tuning, R1011 was set to 5 ohms consisting of two 10 ohms (10 watt) resistors in parallel. We do burn some energy here and we want R1011 (R2011 in schematics below) to stay cool.

The port:
Fb = 36 Hz, port dimensions: 68 mm x 112 mm length (don't change the supplied port of 120 mm length)
Fb = 38 Hz, port dimensions: 68 mm x 110 mm length.
Fb = 40 Hz, port dimensions: 68 mm x 84 mm length.
Don't expect any significant changes to the sound from the suggested port tunings. Going from Fb = 36 Hz to as high as 45 Hz only makes + 1 dB @ 63 Hz.

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The tweeter's simplistic crossover is basically an LR2 filter at 2.5 kHz. Making a true LR4 filter was tried by adding a second capacitor in series with the tweeter. This looks really nice in paper but didn't sound as good as the simple LR2 filter.
Fine-tuning tweeter crossover was done extensively with the help of a sampled and multiplied sequence of
"Siri's Killer Note". This proved extremely useful and eventually gave a crossover that would never have emerged from modelling alone.
Tweeter attenuation may be fine-tuned to personal taste, your front gear and room acoustics. I think 4R7 is suitable for most. If you want more treble, reduce R1011 to 3R9. Also try 5R6 if you find the treble too forward. My default is 5R6 to make a natural blend of basic notes and overtones. 5R6 actually means treble range above 5 kHz 1-1 dB below average midrange level. I've almost always found this voicing to produce the most natural timbre.

Midwoofer crossover could be simplified with the new JA8008-HMQ driver as the RC circuit across L2021 could be omitted.
To lower system sensitivity L2011 is bypassed by R2011. Next we have the usual series coil, here 1.0 mH. R2031 and C2031 shapes the roll-off close to an LR4 profile, thus an overall asymmetrical crossover.
A lot of things were tried to omit the midrange notch filter (R2041+C2041+L2141) but this minor 1.5 dB bump at 600 Hz just proved too much in the long run. Not having the notch filter on certain recordings just made the 8008 driver say: Hey - look at me! Some midrange, huh... Drivers should draw as little attention as possible. Check measurement page to see what it means. Link below.


Crossover Layout

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Pay notice the new 15 uF Sup-Z caps are larger than seen on drawing and needs to be stacked.

Wiring. Click image to view large.

Crossover Layout Standard-Z/Superior-Z Version

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Left: Soldering wires to terminal tags. Middle: C-Coil at bottom of cabinet, fastened with screws through felt layer. Right: Both sections in place.

Left: Damping material covering C-coil at bottom. Middle: Main board on rear panel fastened with screws. Right: Damping material covering main board and side panels next to 8008 driver.

Measurements on finished speaker
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A few comments on MEASUREMENTS before you start interpreting all the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. 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.


Left: SPL at 1 meter, 2 8 volt. Overall system sensitivity = 90-91 dB/2.8V/1 m.
Right: Final system impedance. Minimum where is matters is 9.5 ohms at 40 Hz and ~7 ohms around 200 Hz.
My 20 watts Audio Mirror SET amps just love these speakers!

Left: Impedance displaying 6.9 Ohm @ 180 Hz (dotted line).
Right: SPL from drivers driven from crossover and summed response (red). Point of crossover is around 2.3 kHz.

For those addicted to measurements, click here to view it all.
These are the old measurements but as the new 8008-HMQ is tuned to the same frequency response I shall not repeat all the measurement.

Cabinet construction pics

Generally: Never route for ports and drivers before at hand! Nor drill holes for terminals before at hand.
Do your own measurements and make test routings before doing the actual cabinets. With Baltic birch there's no room for errors.

Last but not least: Below is an attempt to make a nice Baltic birch solution. Baltic birch is not a particularly easy material for cabinet construction and the front panels take solid maple and mahogany fillets, not something that can be made without access to a decent table saw. Obviously the same cabs can be made from 8 sheets/cabinet of MDF - and the sonic results will most likely be the same. Choice is yours. Happy building!

Left: All parts for one speaker. Right: Test assembly with painter's tape. Mahogany fillets for front panel.

Left: Checking rear panel fit before gluing.

Routing the brace panels. Quite some holes, but with a 6 mm router bit Baltic birch is easy. I rounded the edges because it looks nice.

Left: Gluing the first cabinet. Only painter's tape and two straps are used. Measure front diagonal to make sure it's truly rectangular!
Right: Placement of port and terminals.

Routing for the port. Diameter = 96.5 mm. Make a hole having a diameter approx. 0.2 mm less than measured diameter of port base so that
you have to squeeze in the port and it stays firm - and can be removed again for preferred port tuning.

Left: Drilling holes for terminals (7 mm). Right: Gluing front panel vertical fillets. Only tape is used.

Left: Checking top and bottom front panel fillets before gluing. Right: Gluing the same.

Left: Gluing front panel side fillets. Right: Routing for the waveguide. When routing for the 8008 driver, the waveguide must be in place.

Routing finished. Final thing I do is cutting length of front panel on a table saw.
Front panel side fillets have been trimmed by routing, keeping the front in place by two clamps.
This I do before routing for drivers to have a place surface for the router. Sliding over holes is not a good idea.

Trimmer router bit.

Do not forget to chamfer JA8008 driver hole on rear side. 45 deg. at ~15 mm depth.

Router bit used for chamfering.

Before gluing the front panel:

Gluing a front panel to the cabinet will never be 100% perfect, thus before gluing the front panel to the cabinet I always make a small groove, 1.5 x 1.5 mm, on cabinet front edges.
This is also a way of handling the real drawback of Baltic birch: Ripped edges. The outer veneer of Baltic birch is rather soft and either sawing or routing will often lead to a ripped edge.

Left: Router with guide. Right: Smooth the groove with some grade ~400 sandpaper and start sanding the opposite way of routing not to rip edges.

Bitumen damping pads

First of all: Bitumen pads damp panel resonances. It does not absorb sound at all. (I have this question regularly).

Adding the first 4 mm bitumen layers. Although the bitumen pads I use are self-adhesive,
I use an adhesive meant for floor vinyl, having flexible properties - and presumably adds to damping properties.
Self-adhesive pads like these heavy 4 mm sheets tend to fall off over time if not glued.

Bitumen pads used for damping panel vibration.
In total 1 m^2 bitumen pads is needed.

Cabinet damping

Two materials are used for cabinet damping: 8 mm felt and 30 mm acoustilus (supplied with the kit).

8 mm FELT

Felt on all internal panels except front panel, that is:
On front panel in front of the vent I added felt too plus a layer of acoustilux.
For keeping the felt in place I used Pattex "no-more-nails" glue. Three strips of glue/felt sheet.



Finally! Sanded, lacquered, ready for mounting of drivers, ports, terminals, etc.

Left: Cheap trick: If your routings are tight, you may have trouble removing drivers for changing damping materials, crossover tweaking, etc.
Chassis holes are 5 mm, make 6 mm threads in two opposite holes! Makes life a lot easier when removing the driver :-)

Secure leads from drivers like seen on photos. Ripped terminals are a real pain! Wires used are silver plated copper in teflon.
here how you fasten the waveguide to the tweeter.

Parts list
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Above the parts list for the all-Superior-Z cap version.


Above the parts list for the Superior-Z/Standard-Z cap version.

Complete kit only available from Jantzen Audio:
Contact Jantzen Audio for shipping details - please state where you live to calculate shipping cost.

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

All technical questions at

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