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Lowther no shout

S

Sussex Hornman

Member
It's been a while since logging into the forum and upon doing so have found some messages unanswered for a few years. Apologies.

One such message asked me for advice and referred to the Lowther Shout. Thus this post.

I've been looking at interesting speakers in the past years including Manger Zerobox 103, Lowther TP1 London, Lowther TP1A, Lowther Audiovector, Acousta, Voigt horn and the large full size Worden Panasona together with some front horns from John Richardson of Prophecy Audio, adopted and enhanced in designs by Mike Wallis with a bass horn to die for.

Many people have asked me to repair Lowther drive units and in doing so I've discovered a lot about the myths and the facts of the Lowther units sometimes having the opportunity to carry out experiments with Lowther cones in AER magnets and AER cones in Lowther magnets.

For many Lowther applications the phase plug is crucial and I'm not a fan of the modern pepper pot as it's directional. The bullets are normally excellent but for front horns, the light-bulb shape is crucial, both in dispersion of sound and in applying proper balance to the high frequencies, acting as an impedance transformer lower down the treble range than the bullets.

When one applies the lightbulb shaped phase plug, there's no need for the roll-back surround design of the whizzer cone. That roll-back muddies the high frequency, creating bouncing and interference, and makes the Lowther sound ordinary. It's best flipped forward so as to give open clean treble balanced by the proper phase plug.

Ferrite vs AlNiCo vs Neodynium. There's a big secret in all of this - the difference in sound wasn't the magnet!

In the PM6C there wasn't a shout that I ever noticed but with the PM2C in a front horn, the aggressive treble of the stronger magnet exaggerated a particular frequency of cymbals, which once heard caused madness ever after. I guess that's why the PM2C isn't on the production list nowadays.

The A series and neodymium series do not suffer from that at all and can be used with the straight cone with impunity. No shout. With them the shout's a myth.

Those speakers of mine take up rather a lot of space. Which will I keep? Um.

But interviewing all of them has given an insight into their strengths and weaknesses and which drivers are best in which units.

TP1 Londons - DX2
TP1A and TP1B - PM5 or DX4
Audiovector - DX4 or PM4
Acousta - PM6C PM6A or PM7A or Audio Nirvana Neodymium
Corner or Dual Position Acousta - PM6 or DX2 facing forward or PM2C or DX4 bouncing off the wall. In particular these can give an extraordinary stereo image.

In addition to the Lowther units I rate highly Audio Nirvana Neodymium and also the David Louis Audio neodymium 8 inch units from Hong Kong together with the renowned Philips 9710 although the treble from that can be beamed centrally and possibly it needs a phase plug.

What I really appreciate about these other units is their reliability - no foam to rot and no fragility of the voice coil . . .

Very many apologies to all those who have sent messages to me unanswered.

Best wishes

Hornman
 
I've had the unfortunate experience of refoaming a pair of AER BD2 units. Unlike a pair of MD units which I refoamed which had a wide magnet gap, the BD2 units have the Lowther style 1mm voice coil gap and which therefore requires very precise circularity of the voice coil.

This caused unexpected complications. When preparing a voice coil after refoaming for reinsertion into such a gap, it has to be precisely circular to within less than 1/4mm. The way of doing this is with a Lowther jig, a tapered mandrel upon which you force the voice coil down as far as it will go to stretch all give arising from non-circularity so as to ensure that it's as precisely circular as it can be. For good measure, I reverse the cone on the mandrel ensuring the whole voice coil tube is precise.

Using an aluminium mandrel the problem is that this can leave grey or black marks on the paper.

When the bloke saw this, even though it's hidden by a phase plug in normal use, he accused me of devaluing his units. There was a history to his dissatisfaction as the units had presented other problems, worse.

Another problem of refoaming units is that when the foam is really old and brittle, it snaps away from the paper crisply and gives little problem in cleaning. But when the foam is just on the point, it goes like a toffee goo and is a right beast to clean. And you have to clean it perfectly as you can't stick new foam on top of goo. So I use meths to dissolve it. The problem is that once dissolved, it can be carried by the meths on one's fingers and I accidentally left a dark finger-smudge on the cone from the meths in handling the cone whilst cleaning.

Oh dear. As far as I'm concerned speakers are to be heard, to sound, to sound perfect, and visual matters especially of old refurbished units are of secondary importance.

Of course the bloke could have sent them to AER to have them done at four or five times the cost . . . . but I really wonder if when you send a unit to AER for refoaming whether they really do send you back the original cone rather than simply inserting a freshly made one. The problems of removing goo, to say nothing of glue, and get perfect results make me wonder.

In handling a number of Lowther units and seeing how AER have copied them, clearly doing enough to avoid Lowther being hot under the collar, I really wonder what's necessary sonically and what's necessary simply not to be like Lowther, and when I see that claim that AER reproduce up to 80,000Hz when frequency graphs put it at around 20kHz top, I really wonder about everything.

Lowther units don't all have the "Lowther Shout". I think the reputation has been unfairly attributed. The C units which have Ferrite magnets can produce resonant frequencies in the region of the sound of cymbals - but this isn't because of the magnets. It's because there's a short paper cylinder connecting the voice coil to the cone, and resonances between one end of the paper and the other are not damped. This is cured by the A series and DX and EX with Alnico or Neodimium magnets. It's not the magnet that cures the shout but the longer length of paper cylinder connecting the two units and this provides enough disconnexion to interrupt any travelling waves. The paper is a treated paper like the rest of the cone. The foam spider used to be glued on with a brown glue, possibly shellac, which is brittle and often snaps away from the paper. I use Copydex, a latex glue for gluing the spider, which in future will always simply peel away from the paper.

It was coming to the gluing of the spider on the AER that I ran into real trouble. AER use some sort of glue possibly like silicone which can't be peeled off the paper without danger of tearing the paper. Unlike Lowther treated paper, the AER voice coil is on an untreated paper of the consistency of photocopy paper. Not only could I not remove the original glue, and can't imagine how AER can either, upon gluing on the new spider the water content of the Copydex glue simply disintegrated the paper. Inserting it onto the mandrel as a former to keep shape, it simply tore off. This was a surprise and a nightmare beyond contemplation.

Upon consulting an old friend who used to work for Lowther he said that they had this sort of problem from time to time and it was possible simply (not actually) to glue a new slither of paper inside to reconnect the voice coil to the cone and resolder the wires, and which even to my surprise I did successfully. So the unit was in working order again and working well, with no audible difference between the sound of the two newly refoamed units, the other one on which I'd used a thin silicone as glue.

As soon as I had the problem I confessed to the owner and this put him into the blackest of moods.

I'd loaned him a pair of the 97dB Lowther Challenge units available on ebay, which are rather good. (Perhaps I might talk about those on another thread) When he arrived to collect his AER units I asked him if he had brought my Chinese units back. He hadn't and from which I deduced that the bloke had come merely to haul me over the coals and give me grief.

He complained that I'd devalued his units, but the reality was that I handed back to him two perfectly serviceable newly refoamed working units.

AER charge 560eu each for refoaming (if in the light of what I've seen whether that's really possible) or 1500eu each for reconing and upgrading. So for anyone really wanting the latest most improved AER experience an upgrade should be the way to go and to ensure top value is kept in the units.

As he was extremely dissatisfied with the quality of my work, with a mark on one and the other with a repaired voice coil assembly, I didn't charge and I'll be surprised to see my Chinese units back again.

I wouldn't be surprised were he to have intended keeping and using my Chinese units, as they're good, and expecting to sell the refoamed AER units for top whack.

He told me that he'd seen on YouTube how simple it was to replace Lowther foams. Ha ha! I responded that if he'd done his AERs himself he'd have got into a worse mess than I had found myself in, and then not have been able to repair them at all.

Having looked at the AER and the Lowther units, for a number of reasons I know which I'd choose for myself. The roll back surround to the whizzer on the Lowthers needs to be flipped forward to restored to the original vintage format and then the A, DX and EX series are superb.

And for anyone wanting a cosmetic as well as a functional restoration of AER units, please do go to AER. I don't want to be in a situation of dissatisfaction ever again.

Best wishes

David P
 
I would agree with you about the unfairly attributed 'shout'. The TP1 corner horns are one of my all time favourite speakers.
 
I've had the misfortune to work on a few Lowthers. I'd rather not see another one of them.

The voice coils are very fragile, and, as you say the voice coil gap is so tight that alignment as per normal practice just doesn't work on lowthers. Total PITA.

Pushing the coil over a mandrel is quite likely to result in an open circuit!
 
Using the Lowther jig to ensure circularity is the only way of ensuring adequate tolerances to get the coil to be free in the voice coil gap.

The wire is thin and soft, but the mandrel does no damage to the voice coil - unless it's weakened already by a fracture of the varnish insulation and oxidisation has set in. In practice I have never had one voice coil go open circuit by the use of the mandrel. The common places for continuity breaks are just at the junction with the lead-in wires, 5mm or so from them, 5mm or so from the junction with the voice coil tube and at the point of going through the spider. Sometimes one finds a break on the first turn of the outside part of the voice coil. (Lowthers have two voice coils wound inside and outside the former, AER only one)

Best wishes

David P
 
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