Magnetic Personalities

This is a personal article about an esoteric speaker device, namely the permanent magnet full range driver and the difference in sound their magnets can bring to the overall sound quality. It’s a purely subjective exercise but, given a rare opportunity to try no less than 5 different pairs of fuIl rangers, we felt worth reporting for you.

I know for some this is, and always will be, a “no go area”, but for the converted no other type of speaker unit will do. For me personally the plus points are a lack of cross over and the “point source” sound. Add to that their natural home is in a horn loaded loudspeaker and I will rest my case. As with many things HiFi they originated from the genius of Paul Voigt who initially developed the full range field coil driver, which was followed by the permanent magnet version after WW2. This was when much more powerful magnets became available to manufacturers.

Now I love a good magnet. As a child I spent hours exploring them. Iron filings on paper, horseshoe magnets, and little ones that jumped apart when pushed together. When I finally realised they were responsible for making lovely music, in so many 1950’s devices, my young mind was truly blown!!

For the last 14 years or so I have relied on full range drivers to satisfy my musical loves and desires, as I own a pair of quarter wave horns designed by John Howes, on the very principles aspired by Paul Voigt so long ago.

Way back when I first acquired my loudspeakers they were fitted with a pair of Lowther DX2 drivers. The magnets were Neodymium, a rare earth element famed for its very high magnetic properties.

Alnico magnets by contrast are made of an alloy of Aluminium, Nickel and Cobalt, and its magnetic properties are not quite as strong as Neodymium. Alnico being an awkward alloy means manufacturing costs are higher, and the weight of the magnets is increased. Therefore, as Neodymium magnets became more readily available they have become the popular choice for most speaker manufacturers.

Over the subsequent years I have been fortunate to try Lowther full range Alnico designs, and even the legendary Field Coil courtesy of my good friend John Howes (owner and curator of the Lowther Voigt Museum). All sounded fabulous and each design had its plus points (although I will say if you can afford them Field Coils are undoubtedly the ultimate listening experience).

My DX2’s were sometime ago replaced by the German Voxativ AC-3X design another high magnetic neodymium driver. For many years they have served me very well and I was content not to see if other designs and permanent magnet materials would make a musical difference.

Who got me thinking about different magnetic sound qualities was that great loudspeaker reviewer the late Paul Messenger. Paul loved the sound of Alnico drive units, of any kind, in any loudspeaker.

Like a fine wine connoisseur he once told me he could always distinguish when an Alnico speaker was being played. He knew its signature sound. I did not doubt him, but the question was, could I also? I thought I might.

The opportunity to find out conclusively happened when Lowther offered me a tryout of two pairs of their new Sinfonia drivers, the PM6A and the PM7A, both Alnico designs. I’ve been wanting to try Alnico v Neodymium since I heard a pair of the older Classic permanent magnet PM7A sometime ago.

This would be an opportunity to arrange a meaningful comparison using the very latest redesigned Sinfonia collection drivers. Would the different magnets allow me to hear a clear difference between both types of drive units?

John Howes was keen to participate in any comparison listening session and as he knows more about full range drivers, than anyone I know, I felt his help and advice would be invaluable.

John suggested he bring along a pair of reasonably priced Neodymium, Chinese made, wooden cone drivers, plus a pair of the Neodymium AER BD4 drivers, which although not the latest version, are still very highly regarded.

Along with my Voxativ AC-3X drivers we had three Neodymium drivers to listen to, and two Lowther Alnico designs to try. It occurred to me that what we were doing, and our listening experience, would be of special interest to other lovers of the full range fraternity. It’s not every day a chance like this happens!

We decided that all the drivers would be used in my quarter wave horns and that the same three pieces of music be played with each driver. Music program included jazz guitar, female vocal, and deep double bass via Tidal streaming high resolution (see music choice below).

To make sure impedance was correct we used a John Howes modified Leak Stereo 20 power amp, which allowed us to set precisely the correct impedance for each speaker. (Impedance varied between 11 and 4 ohms). With this all in place we began listening to each set of drivers in turn. Three sets of drivers before lunch and two sets after. I kept detailed listening notes, and John was happy to add his own knowledgeable opinion.

A word of caution. Those of you who use and own full range drivers know the potential pitfalls of installation. They are very heavy, delicate, and easy to damage. Therefore our handling at all times was careful and consistent with these expensive devices. I was really glad John was to hand to help with fitting and handling. If you intend to do something similar at home get a knowledgeable friend to help, or better still get Lowther or a dealer to do it for you! A dropped driver is not going to sound good! A bang or jolt to the magnet depletes its magnetic properties.

As I have been using these for many years I was familiar with their sound. My drivers are well run in and sounding at their best these days. An 11 ohms device, the Leak was set appropriately. On all the tracks used the sound was very good. Words used in my listening notes included fast, clean and detailed. Vocals were handled very well and bass came over as clean and deep, with good stop/start to the music playing. Was this Neodymium sound I asked myself? If it was I could understand most listeners being very pleased and impressed.

These were brand new and so had no run in. Nevertheless they sported substantial Neodymium magnets and very nice wooden cones similar to those available to Voxativ customers.

As an 8 ohm load the Leak was adjusted downward. The tweeters were made of nice looking parchment paper. I was concerned that the high quality finish would not necessarily be reflected in their sound. I was wrong.

Having heard wooden cone drivers before I hoped they would impress me and they did. The sound was very very good and my notes mention the very impressive bass quality (something I had noticed before listening to wooden cone drivers).

The other quality I noted was their imaging ability, which was prestigious. I can see anyone on a tight budget finding these speakers highly appealing. They had a sound up there with both the other Neodymium drive units we tried.

So far Neodymium was sounding good..

Our first Alnico driver and a new one on me having never heard it before. Straight out the box so again not run in. This good looking driver was from Lowther’s new Sinfonia range, as was the PM7A we would listen to later. Again another 8 ohm load.

The magnets look entirely different from the Neodymium’s being bigger, heavier, and with a bulbous look. How do these Sinfonia drivers differ from the older much loved Classic design? Well the Sinfonia designs all have silver voice coils. The back suspension has been altered and improved (this being a spin off from the work carried out on the flagship Lowther Field Coil), and the cones are paper treated, whilst the tweeter cone supports some strategically placed holes!

I had previously heard these changes, (the first in over 50 years), and had been mightily impressed. What would all this do to the sound of the PM6A? Well the changes certainly don’t hurt!

Immediately apparent was a very different sound from Neodymium magnet designs. My notes indicate a sweeter organic sound, very smooth but at the same time detailed and well defined. For me the sound felt more natural than the Neodymium drivers. The bass was full with the treble precise and clean. Vocals sounded natural.

This really was a different sound from the previous drivers which both John and I both found appealing. Not as expensive as the PM7A, I can see the PM6A being the “go to” speaker for those wanting a “sweet” Alnico sound. Once run in I can see this being a Goldilocks driver. It had a lovely all round sound.

Following the lunch break it was time to try these highly regarded top end drive units. Nowhere on the AER website could I find what magnets were used on these drivers, but they looked and sounded like Neodymium!

Supposedly they have extra powerful magnets, and a measured impedance of 4 ohms, so another change to the taps on the Leak was required. As the BD4’s were now several years old they were at least run in.

The sound was extremely detailed, with an impressive bass and very crisp presentation. John decided trying them initially on an 8 ohm setting, but 4 ohms gave a more natural sound.

In some respects the sound was just a little too clean and detailed for my taste, but having said that I can see anyone who likes to hear the very last gram of detail in a recording will absolutely love these drivers.

Clear, clean, detailed, and packing a punch these sounded like Neodymium drivers on steroids. The next and final drivers to be auditioned, would highlight concisely the difference between Neodymium and Alnico magnet drivers.

The Lowther PM7A Sinfonia is a step up in the Alnico range. With a bigger and heavier magnet it’s more the “alloy fist in a velvet glove” job. Again straight out the box, it will undoubtedly sound better once run in. Requiring 8 ohms so another tap change.

The last time I heard a PM7A it was in the original Classic form a good few years ago, so I was keen to hear what the full set of Sinfonia improvements would do to the sound. To be honest my previous experience of the Classic had left me a little ambivalent to its obvious charms. I had found the sound warm and relaxing and by contrast the Voxativ AC-3X was fast and detailed.

The new Sinfonia PM7A provided a much different experience than that older Classic model. This was by far the most natural, non flashy and controlled sound of the day. Vocals proved breathtaking, bass sounded natural and not as “showy” as with Neodymium drivers. The higher magnetic power in this particular Alnico was providing more control.

Different but, to my ears, better than the smaller magnet PM6A, not sweet, but with a musical quality that was very infectious. Our three set tracks played, John and I had some refreshing tea and cake, and sat listening to a lot more music.

I love the big PM2A driver, and the PM4A in the Lowther TP2 cabinets are a personal favourite. The PM7A gives you a taste of that big sound in frankly a more manageable packet. My previous experience of the Sinfonia PM7A was provided by new Lowther Edilia loudspeakers which are now available for audition. I was lucky enough to hear these on home demonstration for a few weeks.

Do have a listen to PM7A in the new Lowther Edilia, it’s a stunning combination.

The reason for this exercise was twofold. Firstly, and mainly, to see if we could find a sound difference between Neodymium and Alnico drivers? Secondly, and importantly, to see if the new Lowther Sinfonia drivers made a difference to the Lowther Alnico sound? It’s a firm yes to both.

As to the first question both John and I were somewhat shocked at how all these drivers sounded different, and then specifically how different the Alnico drivers sounded from the Neodymium. We both preferred the Alnico sound finding it more natural and musical. All of the drivers we listened to were exceptionally good, and all bought something different to the table. It’s clear everyone in the market for full range drivers needs to listen to as many different drivers as they can before making a choice.

Ceramic or Ferrite drivers are also a further option, so with this in mind listening at the Lowther demonstration room, or at a Lowther dealer, is essential. Let them do the hard work of changing the drivers, while you imbibe a cup of tea or coffee.

The second part of the questions above is about the changes to the sound the new Lowther Sinfonia drivers make. Both John and I can’t impress upon you what great improvements in sound quality are to be had by investing in these new Sinfonia drivers. Lowther do a part exchange offer on the older Lowther drivers you may own. They also retain the Classic drivers (The Concert Collection) for those who are so inclined.

Please though have a listen to the new Sinfonia range. Believe me Lowther’s hard work has not been in vain. It’s definitely again a case of “Towards Perfection” for Lowther.

Mike Blackmore
Lowther lover and connoisseur.

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