The Tale of Three Horns... Variations of the Western Electric 32A Horn

Many questions come in about the Western Electric and Altec 32 horns which we reproduce.

This post will illustrate some of the differences in this horn as it evolved in production.

Here are the three main profiles. On the left is the WECO 32A, centre Altec 32A, on the right Altec 32B (which is the same as the 32C but without the strengthening fins for the throat). There were some other minor differences - mountings, external braces, etc... however these three types are the most significant in representing the horn profiles themselves which are all different. Most obvious difference in this picture is the shorter throat on the right horn - Altec 32C. More on that later.

We should begin at the beginning which was the Western Electric 32A Horn. This horn was featured in one of the legendary speakers of Western Electric - the 753c where it was coupled with the 713 driver.

This horn has a recess for a sealing washer of 1" and its throat then begins with a 0.76" aperture which corresponds to the 713. The throat expands smoothly from this aperture in a complex, exponential expansion which could be a post all its own. Suffice to say that it is asymmetrical and appears to have a high frequency dispersion feature on the rear of the expansion. 

Next is the 32A which came to Altec as part of the 1938 consent decree that established Altec. This horn is externally very similar to the WECO 32A however there is a considerable difference inside.

First of all there is no recess for a sealing washer and the aperture begins at 1". As can be seen from the first picture in this blog the throats appear to be the same length (and it is). 

A question poses itself: 

"If the horns are the same length, have the same mouth area, and there is an increase in initial aperture size of almost 35% what are the differences in horn expansion?"

To see this more clearly a silicon relief was taken of the Altec 32A throat.

It is quite apparent these were cast in the same mould and then reamed to 1". 

Here you can see the tool mark where the drill penetrated the rear expansion.

Since Altec produced 1" drivers such as the 802 perhaps this was the quickest way to adapt the horns for them. Every Altec 32A I have seen is the same including original paint inside the throat.

Lastly the Altec 32C. It is quite clear this horn was produced differently from the other two. It is made of plastic instead of aluminium. Its two halves are joined together along the sides instead of top and bottom and the throat is shorter. 

Instead of drilling out the throat it is truncated at the point where it is 1" and so the expansion does not suffer parallel sides as in the Altec 32A. It is no wonder that the 32A and 32B or C sound different as this is a greater difference than the horn material. (The only difference between the 32B and 32C are external braces to avoid the plastic throat from breaking during shipping and handling as this horn was used extensively in stage monitors.)

It is for this reason that if a 1"driver is used here is cause for the metal Altec 32A to be avoided and the plastic version preferable IMHO. There is also a lot of mislabelling these horns which adds to the confusion.

The Western Electric 32A with an appropriate sized driver like the 713 or (gasp!) the Klipsch K55 is the finest sounding of these horns - to these ears - especially in the vocal range. 

For smaller venues such as the home the smaller diaphragms work very well - for the vocal region. 

For this reason we reproduce just the WECO 32A and Altec 32C versions in bronze material. 

Here are some picture detailing differences in finishing.

Western Electric 32A

Altec 32A

Altec 32C

Western Electric 32A

Altec 32A

Altec 32C

No question where the quality was. The WE is built like a tank, better post processed and the one you see here has seen military action and is still with us.

I hope this sheds a little light on this most interesting and fine sounding horn. Put the appropriate sized driver on the WECO 32A or Altec 32B/C and enjoy...

Horns in small detail and how we put them in our speakers.

After being out and about recently in the wide world of audio many conversations were encountered about horns. Since I like horns and to talk about them, certain terms are used which should be conventional. The first of which what kind of horn has what name and how they compare to each other. Here is a well recognised comparison.

A common term which is missing from this chart is the "Spherical" horn profile.

Some say it is the Kugellwellen, others the Tractrix. It is actually closer to the Exponential lying closer to it than the Le Cleac'h. This, I have seen, is commonly misunderstood.

Here is a horn created with JMLC's expansion for a particular driver optimising for its exit angle and frequency range including the coefficient T expansion.

The roll back has been argued by armchair theorists as superfluous since the crossover point is ususally higher than the mouth cut-off frequency however in practice this has not been my experience. The roll back reduces mouth reflection and I believe is in part responsible for it being one of the most natural and best sounding of horns.

Not only that but it looks nice as well.

Some other things we do a little different are rear wave treatments.

Instead of attempting to eliminate rear wave energy with dampening our goal is to distribute it. This means not only diffracting gross reflections into small ones but also using shape to proportion them harmonically.

Pressurised construction allows the structure to be rigid and resonant resistant.

The cabinet is impregnated with resin as well as reinforced.

Front panel preparation.

Final Inspection and bottom plate assembly.

Here is the horn installed complete with its rollback.

Binding posts.

Completed Speakers.

This is the Mojo.

 Model One and Model Three.

We are now taking orders.
Please email for pricing and lead times.

Speaker Design in 3D

Here is a little bit on loudspeaker design using modern tools.

Many will recognise Autocad drawings from the days of old...

It is an excellent tool.

3D however adds another dimension - literally.

It has quickly become a native part of design as it allows visualisation and detail which 2D simply cannot compete with.

Not only can the objects be viewed from all sides but X-Ray views...

and scaled investigations allow an intimate understanding which is as unique... 

as it is powerful.

A new design for instance can be seen from all sides...

and angles not only to examine its expansion...

but also how it will be mounted, its clearances, 

and its overall appearance.

All before the first prototype is built.

This however does not come free. Learning these tools takes time as does the creation of the objects.

Sometimes it looks a little like architecture...

Here from concept to model.

Here is a preview of a new speaker.

A speaker cabinet is more than box, it part of an acoustic system.

It is as critical and complicated as any other component however this is often overlooked. The hierarchy of 1) design, 2) layout and 3) component quality is just as valid here as it is in electronics - in my humble opinion.

The box or "monkey coffin" has been over used due to its simplicity in design and construction.

Computer aided design and manufacture allow more elegant and effective solutions to the heavily braced and overly damped box. 

There is no substitute for wood and other natural materials and no magic bullets. It takes work to chord the modern with the ancient in pursuit of harmony to find solutions that excel.

We accept commissions for 3D design work - for both 3D modelling and 3D printing. If you have a project that you would like us to help you with please contact us.