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Jim Coash

Next! Bob's Amazing "Nuclear" Loudspeaker!

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Greetings:  My forums about speaker technology have generated a lot of discussion.  Some have asked about my "next" or "ultimate" design.  If you have paid attention you know that Bob has followed the great speaker gurus of the past and built on their contributions.  I have too.  My early speakers were just as flawed, or much more so, than others.  Bob and I have never collaborated but I think we have arrived at many of the same conclusions.  Their will never be a perfect box.  Others have decided that planar, line source, single point and far more bizarre things need exploration.  I saw some at CES years ago. One guy made his box from poured concrete.  The resonance point was very low but imagine them in your living room or trying to move them anywhere.  Another design required large tanks of LP gas to make "plasma" into a full range driver.  The first thing you noticed in that room was not the sound, it was the temperature and the smell.  When the Fire Marshall arrived, the demo was over.  One factor that has remained the same for speaker design is the limitations of the raw materials available.  Despite constant improvements in what was available to make them out of and the computer power to refine the design, some things remain largely the same.  Let us take a look at some of those changes.20140302050717424.jpg
The speakers above are the raw drivers from two of my guitar amps, a Fender Twin Reverb and a Fender Princeton Reverb. They were considered among the best when they were made in the 1970s and are still respected today.  BB King and Eric Clapton still use twin reverb amps today.  They have done the same thing to them that I have; replaced the speakers with E/V musical instrument speakers.  Joe Banamassa, Stevie Ray Vaughn and many others do(did) the same thing.  Leo Fender was in the business to make money and these speakers, the 12" by Oxford and the 8" by Jensen were a big bang for the buck. They used Alnico magnets which were "state of the art" in the 50s for any speaker.  Notice the paper cones, cloth surrounds and small diameter voice coils.  Those things were extinct in the higher end home audio world by the 60s.20140302052205747.jpg
This is an Ampeg B-15S cabinet for bass guitar.  It was called a "Portaflex Flip-Top" because the 60 wrms tube amp fit upside down inside the cabinet for transport and then "flipped" for use.  There are gaskets and clamp-locks for this purpose. This amp came with a 15" Cleveland speaker and amps just like this were favorites of many bass players.  James Jamerson (Motown) used them exclusively and most recording studios had at least one.  This one is mine and like the Fenders, it now has an E/V 15G speaker in it.  Upgrading to an E/V is routinely done by professional musicians because it they sound so much better and are at least 3 db more efficient.  Late in the 1950s E/V made the best technology for sound re-enforcement  along with the JBL "D" series and the Altec "Voice of the Theater" models.  They all shared larger, higher temperature voice coils, much better wire in the voice coil, heavier baskets, many using a casting instead of a stamping and much closer tolerances.20140302053437381.jpg
Look closely at this McIntosh ML-10C and notice the dust cover over the woofers center.  Clearly a much larger voice coil than before.  It also has a tweeter that is not a horn and not quite a dome.  Very similar to the "Phenolic ring" tweeters that were the best available at the time.  It is much like those in the A/R, Advent, Dahlquist and other audiophile speakers of the mid seventies.  The wire mesh over the mid and tweet is for protection.  They were fragile.  This is one of the earlier models to have a large diameter true dome midrange which makes it much better than most other speakers.  The cabinet was furniture quality, veneer over MDF and the crossover well designed.  The jack plate was HD with five way binding posts that fit banana plugs.  McIntosh made a full line, up to the ML-4 which had four 12" woofers.  All were used with a matching "EQ".20140302054354357.jpg
Radio Shack Minimus 7 speakers were actually built by ADS and they were very good considering the source.  I had the "woofers" re-coned and the original dome tweeters are excellent by any standard.  With a good sub, these are amazing.20140302054726319.jpg
 I believe that this pair of speakers are the best ADS ever made.  They are ADS 710s and I sold this pair 30 years ago.  Notice that both tweeter and mid are very high quality dome designs.  Domes outperformed all others because of their superior dispersion which was close to 180 degrees.  The two small diameter woofers were actually perfect for the sealed box
and the steel mesh grills, needed to protect the very fragile domes, also attractive, especially with the oiled walnut veneer cabinet.  This pair looks fine but during a move, they were dropped.  No cabinet damage, but now one woofer has a voice coil rub.  I have tried to find a replacement but no luck yet.  The more expensive models were no better.  In fact, I found the "better" bass of the 810, 910 and 1210 to be flabby.  If I can't find a driver, they might wind up being very large speakers that can only be used with a sub.  Or I could cannibalize those beautiful high and mid drivers for another project. 20140302065606612.jpg
 Yamaha built some very good speakers in the late 70s.  They were what was called a "Vertically Oriented Company" meaning that they did not outsource many parts from other manufacturers.  When you buy anything with the Yamaha name on it, a piano, motorcycle, generator, guitar or audio component, it is likely that they made all the parts from ground up.  Yamaha owns the forest in Canada that their wood comes from and it is milled in their factory.  They mine, smelt and cast their own metal parts & make glass and plastics from the raw materials.  That gives them unique abilities.  These NS-500 speakers, like the larger NS-1000s utilized Beryllium metal for the dome high and mid drivers.  Very good and very expensive.  A replacement for the blown one (courtesy of my nephew) was hard to find and way to expensive.  I had a nice pair of Vifa tweeters and they sound very good.  I also had to replace the crossovers with Dayton's and re-cone the woofers.  You can see the quality in these.  The woofers have cast alloy baskets and large voice coils with a huge alloy magnet structure.  The cabinets are rock solid.  The larger NS-1000 is on many "best" lists.  I bought a pair of each and I liked the NS-500 better. It was much more efficient and sounded excellent.  The NS-1000 went to at least two dozen gigs and really did the job.20140302070629779.jpg
They are huge and heavy but besides working well for any stage application they also sound better than many home speakers. These EV-S-1503 cabinets are a true three-way with a 15" woofer almost identical to the ones used in EVs home speakers. 2" Teflon voice coils, cast alloy basket, hybrid paper cone and rubber impregnated surround made them as close to bullet proof as they could be.  The E/V VMR (vented midrange) was a breakthrough design.  The ports are on the front and the rear sealed from the cabinet by a solid metal basket.  Great clarity for vocals and lead instruments.  The "Baby Cheeks" tweeters were the weak link and newer ones have the famous E/V DH Series horn driver instead.  This pair have many hours on them, mostly at close to their limits driven by several very large amps.  The only reason the tweeters have survived is the "special" protection circuit E/V installed soon after introduction.  It saved them a lot of money by saving a lot of tweeters.  I used these for many gigs (in the 80s) to great effect but I cannot carry them anymore.  Thank goodness for the E/V SX-200 System!20140302071746874.jpg
This is the JBL answer to E/V.  I have a pair of these that my son had given to him because the owner got tired of buying new horn diaphrams.  He insisted on over driving a Peavy PA amp.  JBL parts are expensive.  Repair on these two would be $200
easy but we will buy generic parts which I can install and it will be about $75.  Driven by a Carver they will be fine. Here are the horns.  Once repaired they will sound pretty good but no match for the E/Vs in my estimation.20140302072433431.jpg
 You can clearly see what has happened.  Pro audio is more about the size of the hammer than ultimate sound quality but there are a number of technologies that that are "shared" to the mutual advantage of both worlds.  It is also clear that box technology has run its logical course and is no longer viable for the very best home audio applications.  This is exactly the same place Bob and many other speaker designers have come and I agree entirely.  You do not see any speaker boxes on the Enterprise!20140302072917917.jpg
 These KEF 102 speakers were designed by Raymond Cooke and Laurie Fincham.  They were part of the last Reference Series speakers to use the "old" KEF drivers.  Nice fabric, treated dome tweeter and a cast woofer with Bextrene cone, rubber surround and "isolated" mounting in the box.  The larger models used the same tweeter and the whole line needed a KEF "Kube" EQ to sound right.  It worked only on deep bass.  The next step was on the design tables in the late 80s and the 103.2 & 104.2 were the first KEFs to used "Coupled Cavity bass".  The woofer(s) were totally inside the box and the port became the woofer.  No "EQ" needed and very good bass.  Then came the amazing "Uni-Q" driver.20140302073731420.jpg
 This picture is the front of my KEF Reference One speaker.  Below it is the port from the "Coupled Cavity" and you see the dome tweeter mounted in the center of the mid-range driver.  Finally, all frequencies above 100 hz are coming from the same place.  They are co-axial AND co-planar.  KEF called them "Co-Incident"  It took a while to work out the bugs.  The design was complicated and along with the new tech, all of the previous ideas are employed.  All drivers are "floating", i.e.they are not tightly screwed to the box.  They sit in cushioned rubber mounts.  KEFs well designed phase coherent crossovers are made with the very best caps and coils.  They are bi-wire/bi-amp ready and the box so inert that Laurie Fincham did an experiment I still remember.  We had a pair of Reference Threes on the floor connected to a a pair of 1.5 Carvers in a bi-amp arrangement.  Even in our largest room they were extremely loud and there was no audible distortion.  Mr. Fincham asked me for two nickels which I brought him from the cash register.  He placed one on it's edge, on top of each speaker.  It took a moment to find the balance but there it was.  He asked for some records with plenty of deep bass and we listened to several selections with the 1.5s just touching the warning lights.  The nickels never moved.  We tried it with nearly every speaker in the store and the nickle either rolled off or fell over.  Truly superb cabinet design and they were compact.  Only perhaps 50" tall, 12" wide and 14" deep.  In your choice of five gorgeous woods.  The KEF Reference Series have long been my favorites. This technology is also available for in wall use and for the car.  KEF UK is gone now but still around from China.
 
So now that we have completed a journey of sorts, what would I do if I had the money and the physical capability to build my "Ultimate" speakers.  Like Bob Carver, no box, except for the sub and I would use a Sunfire.  For the high end I want a very good, 1" soft dome tweeter, in fact, I want a whole row of them in a vertical array.  I would build them in modules of four tweeters each, wiring them so that the net impedance of it would be 8 ohms (roughly).  No crossover but an active one set at about 2500 to 3500 hz and driven by a large dedicated power amp.  For the mids, the same exact design, using 1 1/2" or 2" dome mids in the same kind of vertical array, net impedance, 8 Ohms too and covering everything below the tweeters to the subwoofer.  Probably about 100 hz., another active crossover and large amp.  Each array and all of the assembled arrays bolted directly to metal, probably aluminum, rails.  One on each side of each driver, perhaps using the center one for one side of the tweeters and one side of the mids.  All wire, heavy gauge, oxygen free copper either soldered directly to the terminals or possible soldered to spade clips that would securely fit the terminals.  One set of 5-way binding posts at the bottom of each row of drivers for input.  No other parts.  There could be a number of choices for the drivers from different companies.
 
In my room I would want them placed symmetrically  on either side of my bay window where my KEFs are now.  Mounted on the wall about a foot or two out and on pivots that would allow them to be turned on their vertical axis slightly to fine tune the image.  The whole array would be between 6' and 7' tall leaving equal space at the floor and ceiling.  My Sunfire sub would remain right where it is under the CD rack near the right corner.  Optional stands would not be hard to devise for anyone needing them.  I have found several good active crossovers that would work and the signal from the pre-out would go to the Sunfire first, then to the active crossover, then the highs and mids to the pair of dedicated amps.  Gain controls would allow fine tuning and there would be no tone controls or EQ of any kind.  I believe I could adequately compensate for room acoustics with the crossover points and level controls.  I think this is actually very similar to Bob's design.
 
I would shop carefully for drivers from companies like Vifa, Hiquphon, B&O, Yamaha, Onlyo, Peerless, KEF, E/V, JBL and others.  I would prefer that they ultimate choice for both highs and mids be from the same company for complimentary reasons.  I would try to find drivers that radiated to the front only to eliminate any back waves or interference.  I think they could be very attractive and I would keep them as simple as possible but as rugged as they can be made.  The faces of the two vertical arrays would be flush with each other and there would be NO protrusions for sound to diffract off of.  It might be important to protect the drivers by providing "U" shaped hoops over the gaps between them.  If this were done a long tube "sock" could be made and then carefully slipped over the whole unit hiding the individual parts in whatever color double knit you might prefer.  I think Martha would like brown.  Anybody ready for a project?  Time and a couple grand needed!
 
 I honestly wonder if at some point we will see "Bob Carver and his Amazing Nuclear Speakers".  I can see the radiation hazard warning on the door to his lab and Pacific Edison having to dedicate a reactors electrical output for Bob's latest "Experiments".  That plasma design may only need a power source of sufficient size to make it work.  If anyone can do, it will be Bob Carver!  Any questions?  Jim
 
 
 
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For the high end I want a very good, 1" soft dome tweeter, in fact, I want a whole row of them in a vertical array.
Dome, not a ribbon-ish planar?  I am surprised.  For reasons I do not understand, I have a soft spot in my head for ribbons and quasi-ribbons.
 


Each array and all of the assembled arrays bolted directly to metal, probably aluminum, rails.  One on each side of each driver, perhaps using the center one for one side of the tweeters and one side of the mids.
For prototype or short-run purposes, a formed (bent from sheet) and perhaps welded assembly would work very well.  The weldor will have to be careful of warpage.  If this were to become a production effort, a dedicated extrusion will be preferred.  With some effort, it may be possible to find an existing form that can be adapted--but I'd expect a custom extrusion.  "I" would build the thing with some full-height hollow sections, to fill with sand or BBs or concrete or .45 ACP rounds, or whatever the preferred "audiophile" damping compound becomes.


 I would try to find drivers that radiated to the front only to eliminate any back waves or interference.
The inexpensive "ribbon" tweeter that I'm using is built this way.  Is there a midrange unit like that?  I figured a midrange driver would move too much air, capturing the back-wave appropriately would result in the need for a relatively huge "box" housing the voice-coil and driver dome.  At that point, you've got a whole series of relatively small (air suspension???) boxes rather than one large one.  Am I wrong?
 
It might be worth your time to investigate this kit from Parts Express.  Done in wood, not aluminum, but of similar concept.
 
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I see no problem at all with those of you who prefer ribbon/planar drivers over domes.  I fell in love with them too when I first heard Arnie Nudell explain the Infinity IRS.  He developed the Electro Magnetic Induction Tweeter (EMIT) and Midrange (EMIM) in an effort to solve a number of problems and he did solve some.  He also created a few.  All similar designs since have shown improvements and they are superb but the reason the IRS are tall and use a vertical row of drivers for both highs and mids is to overcome the inherent problem with that kind of driver, limited dispersion, particularly in the vertical plane. They are not as good as a dome in terms of horizontal dispersion either but other than improve that through improvements in the driver itself which has happened but has been limited, the only way to address vertical problem was the vertical array.  The KEF Uni-Q is as close to a point source as I have ever seen but it also has some problems. First, the tweeter dome is recessed into the midrange cone in order to make the unit co-planar.  Unfortunately, the cone of the mid then becomes a sort of  "horn" and it limits the domes dispersion in both planes as well as adding a tiny bit of the "honkiness" I have heard in every horn design since Paul Klipsch built the first Klipschorn.  Second,  both the high and mid drivers are dumping any waste heat energy into the same space.  If there is even a slight amount of distortion (clipping) in the signal, temperature can quickly rise and there is no place for the heat to go.  I have never had a problem with that but I had many customers who did.  After replacing several Uni-Q tweeters in KEFs owned by customers I had to tell them to bring the KEFs back and take home a different speaker.  Some said "But I love my KEFs"! I said, you are loving them to death.  If they already owned a Carver 1.5 I could not solve the problem any other way.  I made them happy with something more efficient so they got more volume albeit with less sound quality.  My brother was one of these people.
 
I sold Dick a pair of Carver 1.0t amps and a pair of KEF Reference 105.3 speakers.  Truly a fantastic system.  It took him a almost 5 years but he did finally call and tell me he had a blown tweeter.  The KEF 105.3 was one of the earliest Uni-Q designs and the high/mid driver used a relatively small tweeter.  The later models had a larger voice coil mid and hence, more room for a larger diameter tweeter.  That did not solve the problem completely, but it helped.  I sent Dick a new tweeter that came from KEF, under warranty and it was a perfect match for his other.  KEF always kept careful records of each speaker. When I gave them the serial number of his matched pair, they looked up his "build order" and found the data they needed. Before KEF built a speaker they first assembled all the drivers and the crossover by matching them for frequency response and efficiency.  The sheet would show the precise parameters of each individual unit and a near perfect match was found.  I explained to Dick how to fix it and he did.  I also sold him another power amp and a KEF sub with a built in high pass filter. He loved the improvement.  Deeper bass and even more volume potential.  No problems, for 10 years.
 
Dick had moved into a new home with a large "utility room" over the two car garage which became his A/V man cave.  He also moved in his drum kit, a beautiful Pearl set in black gloss with 6 Zildian cymbals, his guitars, amps, PA and 50" Panasonic Plasma set.  One night, after several glasses of red, he was playing with Neil Peart on his kit, and when he checked the next morning, both tweeters were gone.  He had only recently called to tell me his friends B&Ws had "better bass" than his KEFs and I told him, "Impossible"!  He invited me down to see his new place on my birthday in 2005 (March 5th) so that I could hear the proof.  As soon as he turned on his system I told him.  The foam on your woofers has rotted out.  How do you know he said.  Get a flashlight, look through the port at the surrounds of the woofers and tell me what you see.  He saw that there were no surrounds left, just a pile of foam chunks.  I had him disconnect the speakers and we took them apart.  When we had all four woofers in our hands, none of them had a scrap of surround foam left.  I did visit his neighbor who had B&W 801s with an Adcom GFA-500.  It sounded OK, but I told Dick, when yours are fixed, his system won't stand a chance.  It didn't.
 
When he called me about his tweeters a few months later we had very limited options.  KEF (Kent Engineering Foundry), Tovil Rod, Maidstone, England was gone forever.  The name and patents were now owned by a Chinese firm.  The only parts available were NOS, if you could find them.  Dick did find a couple of single tweeters (not matched) that would fit but the price was outrageous.  I came up with a fix.  I had him remove the high/mid assembly, remove the blown tweeters, rout the wires around to a small hole on each side of the front, seal up the opening where the tweeter was, fabricate a metal plate that fit over the outside without in any way interfering with the mid and mount a new, top of the line, Vifa tweeter on each plate. The speakers are still co-axial but no longer co-planar.  The tweeter magnet just clears the midrange cone and the dome is flush with the front of the assembly.  After connecting the wires, sealing up those holes and putting it back together he re-connected them for evaluation.  He was so stunned that he called me at 4:00 AM.  I couldn't shut him up.  "Incredible, unbelievable, amazing, way better than before"!  He had cut away all the metal he could from his custom mounting plate. smoothed all the edges and glued on a layer of felt to cut down diffraction.  When Mr. B&W came over he was just as impressed.  It's been another 10 years.  He loves them dearly and never had a problem with any of his Carver equipment.
 
So my "problem" with planar drivers isn't anything to do with their open sound quality, accuracy, detail or imaging as long as they are in an array.  Looking at Bob's designs from the first amazing to his newest design, he seems to agree.  I could be perfectly happy using ribbons instead of domes but I frequently have a dozen or more people in my main room so most are well off axis.  Domes  are a better choice for me.  I have given more thought to my "ultimate design" and from a financial point of view (no way could I afford 64 quality drivers) I think I need to downsize.  That can be done with dome drivers.  It has been done to great effect with D'Appolitto designs.  One excellent dome tweeter with two excellent dome mids vertically aligned in a "boxless" configuration would be an awfully good way to go and a lot less money and effort.  I could not be happy using planar or ribbon drivers that way.  I saw it tried by several companies.  I'm sure you remember Arnie's smaller speakers that used the same EMIT/EMIM drivers but just one each or a few.  Pretty good if you are listening in one relatively narrow spot.  Just don't get up or move off axis.  I will never give up my Sunfire sub no matter what I decide to do.
 
Given my love for E/V (in case you hadn't noticed), I would really like to try a pair of their new EV-ZXA1 speakers.  I'm sure they would be very good for a pro product but the dispersion isn't what I like.  I think it would be comparable to planar designs (90 X 50).  The built in amp, bi-amp capability, included high pass filter and high efficiency would be useful for me and they are even smaller and lighter than my SX-200 System.  I could build something very nice with better dispersion using 2 excellent dome tweeters and four matching mids in a small cabinet the D'Appolito way.  Anyone care to try that?  Jim
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