Inspired by Linkwitz: presentation of a dipole speaker system

[StigErik]

This will be the story of how this sketch.....



.....inspired by this great piece of work (the Linkwitz Orion).....



.....also inspired by some of my own experiments.....





... turned into this !

[StigErik]

Let me say a few words about the finished product first. We will dig into the development process later, which was quite long and had a lot of design changes up to the last minute.... My customer was also largely involved in the design process - this is a custom design (almost) entirely to his own specifications. I hope he will comment in this thread.


The speakers are 3-way dipole, with closed box ELF subwoofers. All XO and EQ is PC-based.

Drivers are:
Tweeter: Mundorf AMT2340 without faceplate
Midranges: Two Seas Excel W15CH001
Woofers and subwoofers: Two Beyma 12P1000nd each

Crossover frequencies:
40 - 300 - 1800 Hz

Tweeter and midranges are baffle-less and supended, hung in wire.
Woofers are mounted in an H-baffle. The outer shell is made from 12 mm MDF and internal structure is 18 mm birch ply. Subwoofers are closed box with two 12" drivers mounted on each side, and they are playing in opposite directions. Cabinet made from 12 mm MDF and 18 mm birch ply.

All amplifier modules are mounted inside the speakers. The amps are:
Subwoofer: bridged ICEpower 125ASX2
Woofers: ICEpower 250ASX2 (one channel for each woofer)
Tweeter and midrange: ICEpower 125ASX2

Note: ICEpower amps are not availble for DIY. This is however not a DIY project, but a finished speaker system sold by my own company.

XO and EQ:
Software solution based on Console and Waves EQ-plugins.
Atom CPU based mini-laptop (Packard Bell)
RME Fireface UC external computer soundcard
Logitech Transporter as playback source

We also use the DAC in the transporter together with the DAC's in the RME Fireface. More on this later.

[skorpion]

Very pleasing to see innovative thinking turned into beautiful, good sounding speakers. Respect !

/Erling

[sqlkev]

looks like an excellent project!

I have one question though, won't the dipole woofer units create vibration through the threaded poles?

[Valentino]

Before this system I always had box speakers, the last one also a StigErik design, the Gjallarhorn 25:



But I had been reading a bit of Linkwitz, so when I first heard the pine board dipoles StigErik and a friend had put together last spring I got really interested. Then after a halleluja-report on a MBL 101 listening session a Norwegian hifi forum, and the thead that spun off it I got the inspiration to make the rather uneducated but half-jokey sketch at the beginning of this thread.

[Valentino]

Originally Posted by sqlkev

looks like an excellent project!

I have one question though, won't the dipole woofer units create vibration through the threaded poles?

Thank you, I'm very happy with the result. It is also good to know that the amplifiers, drivers and baffle are good enough for upstream upgrades. It never ends, this audiophilia.

There is vibrations transmitted through the poles, yes, but the mids and tweeter are well decoupled with that single point suspension they are hanging from.

[Rudolf]

Would you please explain the reasons why the AMT is on top of the SEAS drivers now and no longer between them? Is it about acoustics or just mounting convenience?

[StigErik]

Mostly the latter... and the tweeter would be mounted a little too low if it was an MTM. Its a good thing to have the tweeter at ear-height I think.

I've looked into if there were any advantages or disadvantages with MTM or not with these drivers and XO at 1800. I really couldn't find anything to gain with an MT config, rather the opposite. The two drivers couple somewhat acoustically when mounted like this, causing slightly less roll-off below the dipole peak.

[Valentino]

I made that first sketch end May 2009. It took two months later before StigErik and I started to play ball on a dipole design. This drawing is the first we came up with:



The looks were heavily inspired by my existing loudspeakers (I'm very much into how things look...). The idea was a 12mm MDF wraparound and cloth on the front and back hiding the drivers. Those 5 degrees were taken straigt from my existing speakers. Therefore the tweeter was mounted below the mid in this early design.

The drivers were a Beyma TPL-150, a Seas Excel 6.5", and two Beyma 12". U-frames in both sections.

At this stage the plan was still to keep my existing subs, controlled by my Behringer DCX2496 as before, but the initial idea of an active/passive dipole had been abandoned. A PC and six DAC channels would be necessary.

Dimensions were crucial: I have a wife, my listening room is our living roomand the right speaker partly obstructs a beautiful view of farmland, a large lake and hills and mountains. So W33xD20xH102cm.

The climb up the Dipole Learning Curve had just begun.

[StigErik]

The design process was rather long, as was running in parallell with my various dipole experiments:
My open baffle dipole with Beyma TPL-150

Most of what I learned there was incorporated into this design, so we changed it quite a few times - almost everytime I tried something new in my own project...

We actually did build a prototype baffle that was a variation of the schetch shown above. It was the only prototype we made. It was a failure.... I dont know if that failure was the reason we stopped prototyping? Maybe we just felt very brave and confident, and went straight for the finished version?