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Not quite FR, but a FR driver does most ~ A tower of power with balls (spheres)
Not quite FR, but a FR driver does most ~ A tower of power with balls (spheres)
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Old 27th October 2011, 08:29 PM   #1
TimboinOz is offline TimboinOz  Australia
diyAudio Member
Join Date: Aug 2006
Red face Not quite FR, but a FR driver does most ~ A tower of power with balls (spheres)

Timbo's planned new 3-ways - instead of QUAD 63s?!? Yes!

Dave Dlugos has encouraged me to share this outline design with you. Those of you who have heard Coral Flat 5s will know ahy this choise is a happy one for me.
Not quite HE @ only 91db/w, but being multi-amped it should play loud enough, with headroom to burn.

A single main driver 5" WR Coral Flat 5 (running >200hz to 6Khz OR above 10Khz). IE a point-source per front channels, with bass and EHF support.

And another pair of the WR modules sans ELF and EHF support but reflex tuned for the rears! Using the pair of Model 2 'spheres I already have on LTLoan. Will buy more and more spare drivers.

The front L & R arrays will be either tri-amped or bi-amped [which the big 2-way spheres are now.] Done with passive-line-level 1st order filters on power-amp input sockets, and added to a Nakamichi 2nd-order active crossover for a 3rd-order low-pass to the bass section. The latter will allow a 3rd order knee-shaped low-pass curve, to put a dip over the room's strong 200 hz mode, when added to the WR/MR module's own high-pass. Gives me gain control in the bass - many recordings seem to be either bass light or heavy. Odd-order slopes, 1st and 3rd, adding in-phase!

Rear speakers? Two more of the little spheres on their own, fed a differentially delayed, derived signal (L-R and others through two Old HT processor amps) through 2chs of PP 6BM8s. OEM Rb's 80hz- 15khz.

Absolute polarity switching?! either with sufficient DPDT spkr level relays off a wired remote, that I use now. But only on the front channels.
OR an at the seat powered two valved module to do Volume Control and Abpol. Containing probably two of John Swenson's beam-deflection tube circuits balanced out L and R circuits, for Ab.Pol switching AND line drive. 6db extra gain. Lots of Mini-XLR three-pin sockets and plugs. But SE inputs and outputs.

Sources, phono stage, tape and line-out-pre still well away over in the 'dining room' end of our L-shaped room.

The bass amp will be an AKAI SS integrated (zero-loop-feedback amp - to be blueprinted / pooged soon!!), for ELF extension control and getting gain-structure right.

Later? Two mono-block versions of the LEAK St20 (TL12 Plus?) and the mains and treble powered by my two LEAK St20s. I know where they are but would have to be paid for AND persuaded away, and then brought into line with my 'Once_were_LEAKs'. PSU, gain and NFB circuit changes ($1K?!)

Both the bass drivers (Foster) and the Coral Flat 5 WR mid have matching 91db/w sensitivities and a reasonably good match in their accelerations. And, nice clean / calm top end stop-bands. They thus don't need to be KILLED with steep low-pass filters.

The Coral 5s may not get an electrical low-pass at all (see below), and I may only need a PLLevel 1st order high-pass filter*. To match the 3rd order knee'd low-pass!

*? Because the WR M2 sphere's OEM Vb - when sealed - gives a 150hz second-order slope. With a bit of dense foam layered on the walls and a roll between magnet and rear wall, plus some long-fibre wool I should be able to push that up above 200hz. Less filters / components is A GOOD THING, or so I am told ;-)!

A Q'n, what are the polarity/phase shift and 'adding' effects of a 2nd order sealed high-pass slope, with an electrical first order PLLevel high-pass possibly a bit higher in freq?! When adding to the low-pass 3rd-order electrical&acoustic slope of a bass bin? Both will have to have a 'bent-leg' shape, to 'gently' notch-out a strong room-mode centred on 200Hz. I THINK that mode is due to the 2.4m/8foot ceilings? Yes?!

EHF? I bought four run-out OEM Fostex RPT tweeters @ 8ohm & 92db/w. They were being sold off by an electric organ maker. Their 4 bolts do protrude around them, but I can probably add 2-3mm MDF front and back to relieve that. I'll use an old Tandy stereo spkr pot to see how much attenuation they and their valve amps need, so as not to be too bright, and then build that 1 to 3db attenuation (a voltage-divider) into the PLL input filter calculations, with nice caps and R's as with the other PLLs.

I will also be experimenting with letting the Coral's high-end roll-off without a L-pass, and bringing the ribbons in quite high up, above 10K. OR using a matching high and low-pass around 6-8k. With PLL filters.

For the WR middle amp that would require a band-pass PLLevel filter, is such a thing achievable!?

BASS? A squat cylinder with one of the larger 2-way spheres - emptied of drivers but not the BAF - facing down into the cylinder. ~ 60 litres Vb. 8" Foster driver from the sphere, facing the big 24" round paver by a suitable tested gap. Ported to around Fs or 2/3 of Fs. A big Rb box is the way with these short throw Foster/x drivers.

The mid's sphere will be held in place by an adjustable-height stand, and either a friction lock spkr to wall-mount device, or a cut-down and enamelled basket-ball-hoop. Plus gravity and some blu-tak!

The ribbon tweeter may go on the MR sphere - surrounded by 3/4 to 1" wool felt (black) OR get their own teeny solid spheres turned from a nice timber and with routed out (_) holes.

The squat cylinders will be made from already cut 24" rings of 3/4" and 1" of MDF table tops, block-board doors, old chipboard, and kitchen bench tops, many veneered or with hard laminex sides. All pressure-glued to form a squat cylinder with a cut-out on top to take the sphere. Given the mixture of material stiffness's, and the big heavy sphere facing down on top, I expect that it will be very quiet. An easily re-tuned accessible port (adjustable length) to boot. All the used boards and tops were scrounged ($0), so not quite as wasteful or high-carbon as it might appear. ;-)!

Anyone want me to drop the idea and re-sell the QUAD 63s idea to Patricia? I've gone with this plan partly because the full cost of 63s would be higher, eg. dipole subs Eq and perhaps more power than the 100W H&K I have waiting, and when I showed her how 63s looked she baulked.

These spheres do have a narrow sweet spot, like most point sources, but not as narrow as 63s. So, two people can get 90% of that 3D wow factor.

Being spherical the WR enclosures (and their ribbon tweeters) can be very finely aimed/aligned - swivelling up/down, side to side, and even rotated - at the listener's ears. Or to a mike on a tripod! I'll definitely be starting with the hoops, and learning the angles that way.


Any answers? Suggestions?


Timothy Bailey
The Skyptical Mensurer and Audio Scrounger

And gladly would he learn and gladly teach - Chaucer. ;-)!

'Still not saluting.'

Tim Bailey
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Old 27th October 2011, 10:46 PM   #2
talaerts is offline talaerts  Belgium
diyAudio Member
Join Date: Oct 2005
An interesting project, but don't sell your Quad ESL 63's just yet - one of the most natural sounding speakers I ever heard.
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Old 27th October 2011, 11:13 PM   #3
TimboinOz is offline TimboinOz  Australia
diyAudio Member
Join Date: Aug 2006

IME I don't think the 63s pull off the magic quite as well as 57s. And, without steep high pass filtering and steep low-pass subs both models just will not play LOUD. And while real stereo acoustic music is where my heart and mind is. My heart loves to rock out, too.

The 63s were not mine, and might not have been for sale anyway. They do come up for sale down here in Aussie - with Otto Major's rebuilds - and usually cost about $Au2.5k to 4k a pair. Patricia was offering me a budget and 'we decided together' that she didn't want them in her lounge-room ;-).

I have set up 5 systems with 63s and a few more than that with single or stacked 57's. One of those was a clone of the Mark Levinson HQD system stacked 57s with a Kelly , but with dipole subs using big long-throw double 15's a side and two Aussie movie theatre amps, and Leak TL50s for each 57, and a pr of TL12.1s for the Kelly. Passive line level filters except for the low and high pass around the subs.

It took forever to get right, and his wife didn't help!

For my size of room, single 57s and double 10" dipole subs would I think be better.

This other project was a mental exercise of some years. I wanted to retain the time and phase coherent nature of the 8" 2-way spheres, but get down to about 20Hz and up to 20kHz. I bought the sphere 3's instead of newish QUAD 57s, and some other used classics.

The idea of using a Coral Flat 5 is central, as it would give me a clean-diffraction near point-source, IE with cleaner wave launch than 63s, and yet retain most of what I now have.

Panels are in fact quite noisy devices compared to a stiff sphere!

So we compromised, and I can go ahead.

What I am hoping for is that the process of getting the transitions right is relatively easy. I am anticipating that I may need spread electrical f3 points in the mid to bass transition. I may also need to do that with the ribbons and the Coral WR driver too!

What I am looking for is advice and suggestions on how to go about it all.

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Old 28th October 2011, 09:22 AM   #4
talaerts is offline talaerts  Belgium
diyAudio Member
Join Date: Oct 2005
Yes the 57 is very nice as well. I just wanted to say that, despite the 63 being quite subdued and polite in nature, they are also very neutral, without the warts in the frequency response that most FR drivers have, even the best ones. But often they do offer indeed dynamics which the esl63 cannot match.

Back to the main topic: I don't have opinions about coral driver implementation, sorry.
I can only say that these spheres will be very visible in your living room, more so than most classic speakers, and you should be sure that any significant other likes that.
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