Needed a big electrostatic center speaker - So I built one

[JonFo]

Ever have that sense that something is not quite right with your setup, and you know there just has to be something that will do the job a bit better out there?

Well, that's how I felt back in 2006 about the MartinLogan Logos center channel I had paired with my all ML setup with Monolith III fronts and Sequel II rears.

I looked around, thought a lot about the problem, especially given the fact that the center carries 80% of dialog and sound in most modern movies, and decided that I needed a high-performance center that could match my Monoliths.

So I set out to design and build such a beast. The entire journey is detailed in the associated build thread on the MartinLogan Owners forum.

Now that I've had it in use for six years, I can say it has been an incredible success, there has not been a mutlichannel disc or movie soundtrack that has phased this thing. It just rocks out and is crystal clear.

IMHO none of the factory designs come even close to delivering a great MCH experience, this is what it takes to truly achieve a seamless soundstage.

And, here is a picture of it with the acoustically transparent screen removed (and no acoustic treatments applied yet):

 

[JonFo]

The specifications are:

System Frequency Response
77 - 24,000 Hz +/-3dB

Electrostatic Frequency Response
125-24,000 Hz +/- 2dB

Line Array Frequency Response
77-2,000Hz +/- 3dB

Crossover Frequency - Using DBX DriveRack 4800
ESL to Line array: 420 Hz at 24 dB per octave
Line Array to Sub: 80 Hz at 24 dB per octave

Dispersion
Horizontal: 30 degrees
Vertical: 4' Line Source

Sensitivity
88dB/1 watt/meter

Power handling
High
Supplied Amplifier Power
ESL - 800 watts
Line Array - 200 watts

Impedance
ESL - nominal 4 ohms; minimum 2 ohms - Direct drive
Line Array - 11 ohms

Weight
154 lbs

 

[ack]

I've always enjoyed your engineering, Jonathan!

Peter

 

[cjfrbw]

Amazing. I am struggling to rebuild a Sony VFET TA 8650, and rewired a Wavac 15 watt amp with great trepidation. When I see stuff like this, I feel like a total wuss.

 

[Bill Hart]

So, both the line array and the electrostatic panel serve midrange- explain how they are coherent together (I've used electrostats since the early 70's, and could never integrate them effectively with woofers so I'm curious, not critical). and kudos to you for making something rather than buying something and bitching about it! do you have engineering as a background? (sorry for the quiz, just a reflection of my interest).

 

[JonFo]

While both the line array and panel overlap, it is not in the critical mid-range, more in the upper mid-bass (450Hz crossover point with steep slopes). The panel can't deliver my target output (105dB at low distortion) at anything below that point. Also, dipole cancellation becomes increasingly significant below that point as well.

The real secret to making the integration between panel and mid-bass array work is the speaker processor and the total elimination of passive crossover elements from the system.

This is the furthest thing from plug-and-play, but it if you know what you are doing, a speaker processor like the DBX DriveRack 4800 (a $5K pro-gear unit that is extensively used in the field) lets one adjust phase, delay, crossover slopes, multiple variants of parametric EQ (inputs and per output), gains (per input, per output) and many many other features. Along with a good calibrated mic and an audio measurement rig, one can dynamically adjust any and all parameters until the panel and mid-bass array have their impulse responses aligned, and critical crossover phase angles adjusted to provide time-coherent wave-launch across the systems target frequency band.

The final layer of 'integration' comes courtesy of Audyssey Pro room correction applied via the Reference Denon AVP-A1HDci preamp. Using a careful measurement process (I documented in detail here for large panel speakers), one can achieve a seamless integration between all speakers in the surround array. The FIR-based correction lends that final layer of articulation and image 'snap' to what is already a very accurate foundation.

Tonal balance is so smooth, I often can not tell from the listening position whether the center is even being used. It could be a great 2ch mix, or a multichannel mix sending most of the energy to the center and using the L/R for soundstage width.

As for my background, as a kid, I wanted to be a EE and built Heathkits, modded audio gear and all that, but wound up in the Software field for the past 35 years, so my audio hobby is my outlet for playing with electronics. I also study acoustics and psychoacoustics to better design and treat my room and engineer solutions like this one. My day job is as CEO of an enterprise oriented mobile app technology company. So I haven't played with this stuff in over three years, just get to enjoy the system when I can.

 

[Bill Hart]

Impressive. Well you do have geek credentials, so it's not like you were a history major, or pyschologist The idea of being able to play Stats at those levels is incredible. Do I understand that the L + R are old Monoliths? I heard the Statements back in the day, driven by a floor full of Jadis tube amps, and their sound was almost equaled by the incredible amount of heat generated by that many tubes!
Well done.

 

[DonH50]

Nice to see an incredible DIY system, and using time-domain analysis to optimize speaker integration! Very impressive. Id love to hear it, but then I'd want one...

BTW, the dbx DR 4800 is on sale for only $4k at Sweetwater Sound...

 

[JonFo]

Impressive. Well you do have geek credentials, so it's not like you were a history major, or pyschologist The idea of being able to play Stats at those levels is incredible. Do I understand that the L + R are old Monoliths? I heard the Statements back in the day, driven by a floor full of Jadis tube amps, and their sound was almost equaled by the incredible amount of heat generated by that many tubes!
Well done.

Thanks Whart!

As for 'old Monoliths' these are anything but. Yes, the boxes and the ESL drive board are still OEM from 1993, but everything else about them was refreshed and customized in 2006 as well and detailed in this thread at the MLO forum.

I'm seriously into DIY and customization, none of my speakers are remotely stock.

BTW- Statements were awesome, much better than the current CLX in some ways, and my system (in this room) beat a CLX demo I recently heard.

 

[JonFo]

Nice to see an incredible DIY system, and using time-domain analysis to optimize speaker integration! Very impressive. Id love to hear it, but then I'd want one...

BTW, the dbx DR 4800 is on sale for only $4k at Sweetwater Sound...

Thanks Don, and yes, the reaction of all who've heard this system is to develop an instant case of upgraditis WRT their own setups, and that includes more than one $100K+ system owner.

But systems like this have a pretty high barrier to entry due to the expertize required to appropriately configure your own active speaker system. Luckily products like DEQX automate that for people who might not quite want to go into the minutia like I did.