Ekta mkII
Copyright 2017 © Troels Gravesen

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DRIVERS   CROSSOVER    CABINET    MEASUREMENTS    SPEAKER-KIT     CROSSOVER LAYOUT     SOUND

The first Ekta dates back to around 2005 and many times I wanted to update this construction based on a client job and not taking into account an optimal front panel design. The result was a 4th order filter to the tweeter and even a notch filter to tame a 7 kHz peak creating quite some sibilance if not attended. I believe I can do better today by combining design and acoustics at the very beginning. And not only that, I think I can make a more sensitive speaker, better bass, better power handling, better midrange, a better sounding treble - and not least, at lower price! The latter due to the use the the D2608/913000 tweeter, which is kind of an overlooked tweeter, originally derived from the Peerless HDS series. There's a lot of money to be saved from not using the 7000 ring-radiator. The money saved can be used on better crossover components. The 9130 tweeter simply delivers top-notch treble performance with its double magnet, die-cast face plate, low-mass diaphragm, low Fs, etc., although I'm sure someone will think not. Not much I can do about it. Some people believe expensive always means better. Or it's a matter of show-off. You cannot use any other tweeter here than the 9130, or you need a new crossover - and I can't help. And you cannot use 2 x 18WU/8741T00 either and make an Ekta Grande mkII from the same crossover. This will require a complete re-tuning of the system. Have to say the single 18WU delivers a surprisingly potent, deep and articulate bass.
The cabinet front panel is going to be easy, only with the tweeter off-set some 19-20 mm to bring it into acoustic alignment with the midrange driver.
Better sensitivity is the easy objective using the 4 Ohms version of the 18WU Illuminator mid-bass. Not an issue for solid state amps, neither for my 32 wpc EAR 861 tube amp, but maybe not for an anemic 6 watt SET amp, but the speaker wasn't designed for such amps.
The sandwich cone beats the Revelator in dynamic headroom - can be pushed harder before compression sets in. I've used the 12MU before in the Illuminator-5 construction and well, we simply do not find a better 4" driver. It pays off in the reproduction of female vocals, saxophones, oboe, clarinet, etc. Due to excellent dispersion in the critical range of 1-3 kHz, listening position is less critical - even compared to my reference ATS4-HE. What they also do is maintain focus and image stability at very low levels. 6-7+4+1"s can simply be played louder than similar 6-7+1"s.
The 12MU has found its way into seriously expensive high-end speakers over the last few years, from Wilson Audio, B&O to Gryphon and others. See Munich report. Interestingly we don't see any OEM versions of this driver! I guess they could only be worse than the standard product.


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Basics:
Three-way floor-stander from 7+4+1 inch drivers.
You cannot use an overall flat front panel without modifying the crossover and I can't help you here. And you cannot use any other than the specified drivers - or you need a new crossover.
Sensitivity: 87 dB/2.8V/1 meter.
Impedance: 4 Ohms.
Points of crossover: 800 and 3200 Hz.
Cabinet dimensions: 22 x 34 x 100 cm (WxDxH) (without base support)
Power requirement: 20+ wpc.
Power handling: 150 watts, please also read this: http://www.troelsgravesen.dk/power-handling.htm. Any burned driver is a misused driver!

All technical questions to troels.gravesen@hotmail.com


DRIVERS
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Download spec here:  18WU/4741T00    12MU/8731T00    D2608/913000


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CROSSOVER
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Above the much simpler crossover compared to Ekta mkI. It features an overall 2nd order LR topology with points of crossover around 800 and 3200 Hz. With a 19-20 mm off-set of the tweeter we can manage a good phase integration of mid and tweeter. At 800 Hz wavelength is of a size that doesn't call for any off-set of mid-driver with reference to bass driver. We could pull out the bass by adding another 10-15 mm to the front panel, but it doesn't pay off in terms of overall performance.

All technical questions to troels.gravesen@hotmail.com


CABINET
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The cabinet is designed to make it as easy as possible. The chamfering of the side panels to the rear and front panel is optional. I only did it because I think it looks nice and slims the overall look of the speaker. The net volume of the bass cab is ~30 litres, making an F3 of 37 Hz. Quite good for a 7" driver. You can place the port to the front or to the rear to your liking. And obviously you can make a straight rectangular box as show above in the right lower corner.
The drawing above is based on 20 mm Baltic birch. You can use 19 or 22 mm MDF. Keep front panel dimensions and drivers' placement! And please read this before cutting wood: http://www.troelsgravesen.dk/crossovers.htm
Chamfering of the side panels to the rear is optional. Chamfering of front panel optional too. I used 20 deg to a depth of 16 mm. Also cut the top of the bass-mid panel 20 deg. towards the tweeter.
The finished cabinets are rock solid and seriously heavy from the added internal panels, bitumen pads and double front panels. What you get is the sound coming from the drivers with no added cabinet colouration.

Please check this "tips" page before writing: http://www.troelsgravesen.dk/tips.htm

Workshop images


First thing I did was gluing top panel and ensure 90 deg angle.
Next gluing rear panel. Bit tricky as we can't use the front edge for the clamps. I know I don't make life easier with the choices I make.
Next I glued all braces in place held in position by the remaining side panel.
Final side panel and front is glues last - and at once. This is necessary when panels are cut 45 deg. Not easy!


Bitumen pads in place. I used 0.8 sqm. 4 mm bitumen in total.
Bitumen pads are optional due to weight. Order special if you want bitumen pads.
Add felt as seen on image. No felt on front panel. I used 0.9 sqm. in total. 1 sqm. supplied.
 


BTW: I use a scalpel for cutting felt. 2-3 blades are needed for a small speaker like this. They go blunt very quickly.

Add acoustilux as seen on photo:
Roll one piece 25 x 50 cm for the bottom.
One piece 16 x 50 cm behind 18WU driver.
One piece 15 x 25 behind midrange driver.
2 pcs. 16 x 50 cm in upper compartment.
In total I used 0.8 sqm. 1 sqm. supplied.


Routing and chamfering inner front panel. Make holes as wide as bracing allows and chamfer as much as possible. Holes are Ø 170 and 130 mm.
This time I added lacquer twice to the front panels before routing for drivers. This to avoid edge ripping. Quite a problem with laminated panels.

 

 
Left: This time no edge ripping from routing for the drivers due to the lacquer.
Right: Chamfering driver holes for 18WU and 12MU.


Make sure sealing the wire hole for mid and tweeter! There must be no leakage here.
Middle: Measuring drivers' response for crossover simulation. Right: Crossover fine-tuning in living room.


MEASUREMENTS
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Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted". Albert Einstein.

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 speaker, because speaker cones made from polypropylene, aluminum, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of adding spices to the stew. Nor do measurements tell what impact the quality of the crossover components add to the sound, from state of the art components to the cheapest of coils and caps, they all measure the same if values are correct. .



Response of midrange and tweeter with no crossover. Nice frequency response making crossover work easy.


Final system impedance. This is a 4 Ohm speaker with a minimum impedance of 3 Ohms.


Response of drivers driven from crossover and summed response measured at tweeter height, 1 meter, 2.8 volts.
Points of crossover = 800 and 3200 Hz. Overall system sensitivity 87-88 dB/2.8V.




SPEAKER-KIT
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The kit includes screws for drivers as the 12MU requires screws with smaller heads than those needed for tweeter and bass.

You can buy the kit with or without the drivers - or some of the drivers if you already have some.
Please ask Jantzen Audio for options.

Bitumen pads are optional due to weight.

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

Download Complete Kit Sale Presentations (pdf file):

All technical questions to troels.gravesen@hotmail.com

All questions regarding purchase of kits, please mail Jantzen Audio at contact@jantzen-audio.com


CROSSOVER-LAYOUT
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Bass section.

 

You may object to my choice of C4 and C5. Believe me, extensive test with Sup-Z for C4 and CrossCap for C5 DID NOT produce any difference. My aim here is to use the money where it counts, e.g. series capacitor for the tweeter. Building this speaker with all standard PP caps would be like a Porsche with a VW engine.


MT section.
L3 was later replaced by air-core coil and board extended to 13 x 25 cm, allowing C4 to be Superior-Z if you cannot live with the STANDARD-Z here. It's inaudible, but some believe not. Use a piece of wire connecting C4 to the output of L4. See image below.

WIRING


Mid-tweeter section


Bass section


Mounting the crossover. Fortunately we have lots of space for this.



SOUND
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What you get here is something rarely seen in commercial speakers, a 7+4+1. The vital 4" midrange driver bridging the gap between bass and tweeter. That's not to say the 6+1 or 7+1 cannot be made very well, it surely can, but it doesn't compare to the real thing of paying attention to the troublesome upper-mid/lower-treble. The transition from a 6-7" midbass to the 25-28 mm tweeter is a compromise.
The rationale for few commercial speakers using this design is cost. And fair enough, adding a 4" midrange driver adds considerably to overall production cost. For the DIY guy, not so much, although I admit the 12MUs are not exactly cheap. A speaker like this from a commercial company would probably reach some 5-10 kEUR depending on overall fit'n finish. Production cost must be around 10-20% of final retail price to make a commercially viable business. This rarely leaves room for the quality crossover components used in this construction.

The midrange is clean, neutral and effortless in character and the 4" midrange driver allows us running the speaker louder than a similar sized 6-7+1. It obviously doesn't match a bigger speaker with 10-12" bass drivers, but the 18WU can be driven quite hard here, thanks to the 4" middriver handling the delicate upper mid. The 9130 tweeter delivers a crystal clear treble very well integrated with the midrange. Fortunately we have soft-domes these days that rival the best hard-domes and choice is down to a matter of taste - and belief. Vocals have delicate presence and clarity with no edginess - unless poorly recorded or poorly mixed, the latter not an unusual thing.

The Ekta mkII throws a wide and deep soundstage and my 32 wpc EAR-861 has no trouble driving the speaker to significant levels, this from the 8 Ohm taps! Solid state amps may produce a slightly more solid and firm bass, but maybe not the delicate midrange of the modded EAR-861. Same goes for my GlowMaster KT88 power amp. In fact, the EAR 868(P)L + EAR 861 + the Ektas mkII make one hell of a system.
Playing my OPUS3 Test Record #4 presents a soundstage with performers precisely located similar to my reference ATS4-HE speakers, only lacking the impact of the lowest octave although I'm pretty impressed by the bass performance of this single 18WU. Phenomenal driver!
Adding my 26W subwoofers, makes these speakers almost similar to my reference, although it cannot cope with the 10" upper bass of the ATS4-HE. Size matters as always.