Celestion first began on the Thames River in Hampton Wick, England in 1924, producing loudspeakers designed by founder Cyril French and Eric Mackintosh for ‘wireless’radio sets. In 1927 the Celestion Radio Company and Celestion Limited were formed, and by the 1950’s, loudspeaker production had reached 30,000 per week with a staff of 400 employees. The development of the famous G12 Celestion speaker in the ‘60s launched what would become an extensive and evolving line of Celestion speakers for guitar amplification, with many becoming classics that are still treasured (and hoarded) by guitarists today. Among these are the original ‘Greenback’ G12M, and the G12H (heavy) low resonance speaker. In January 2005, Celestion announced the introduction of its new ‘Heritage’G12M and G12H speakers made in England to the original specifications of the very first ‘Greenbacks.’ We queried Senior Project Engineer Paul Cork about the R&D undertaken for production of the new Heritage speakers, and our review follows this interview. 

TQR: The Heritage Series G12H is described as “the perfect recreation of the low resonance model, right down to the voice coil former material, glue formulations and vintage, solder-only tag panel,” while the G12M “adheres precisely to the design notes and specifications for the original speaker, using exactly the same materials and construction tech niques of the classic 1960s G12M.” To fully appreciate the magnitude of this endeavor, it would be helpful to understand how the specifications, designs, and materials may have changed in the years since the original, vintage models were first developed.

As methods of speaker development and manufacture have evolved and changed over the years, this has impacted on the more modern releases. All of these variations although individually small, each represent a deviation from the “original recipe” that would have been used in the production of the original G12M and G12H. When combined, there is a noticeable difference, which gives the more modern versions of these classic speakers a unique tone all their own. The following is not an exhaustive list, but will give an idea of some of the changes made since the creation of the original G12M and G12H speakers:

  • The shape of the coil former was simplified to reduce waste material. The adhesive used on the dustcap was changed to a faster curing (and less smelly!) type.
  • Dustcap material had to be changed when the original supplier went out of business. An easier-to-apply and more “robust” edge treat ment was sourced.
  • The voice coil former was increased in height to accommodate a twin cone version that was produced during the 1970s. Economies of scale meant that a number of different models of speaker, both with and without twin cones, used the same coil former.

When developing the Heritage Series, the exercise was to see if we could re-visit as closely as possible the earliest versions of these speakers by “regressing” speaker development back to its fundamental origins. By doing this, we stripped away changes like those listed above, to recapture the tonal qualities of the speakers of that era. To provide the faithful recreation that we were aiming for, it was important for us to consider, not only tonal elements, but also more cosmetic aspects. For example, at the time the original G12M and G12Hs first came out, all Celestion speakers would have had a solder-only tag rather than the “quick disconnect” type we use now. We wanted the owner of a Heritage Series speaker to feel like they had acquired a little slice of history, so details like this, or the incorporation of the “Pre-Rola” label were important finesses to complete that overall impression.

TQR: What were the most significant challenges in recreating the G12H and G12M in regard to duplicating the materials used in the construction of the cone, voice coil, glue formulation and magnet, and the original assembly process?

Quite by chance we unearthed, while moving premises in July 2003, a lot of archive information: drawings and blueprints, parts lists and specifications. This made the job of recreation considerably easier as all of a sudden we had access to a greatly expanded pool of knowledge. We were also fortunate to be able to call upon the expertise of a former Celestion engineer – he was an employee during the mid to late sixties and so was able to qualify much of this archive information and describe how many of the processes were carried out in practice. In terms of challenges, the original adhesives were no longer available; they had been superceded by modern equivalents. With some record of what adhesives had been used around that time, we were able to replicate with a reasonable degree of accuracy the formula that would have been used at that time. Of course, the method of application, drying time and so on were kept as close as possible to how it would originally have been. Similarly, the original edge treatment was no longer available. Thankfully, Celestion has a great deal of experience in tailoring edge treatment to specific applications and so we were able to mix a very similar “sound-alike” formula here in Ipswich.

A significant part of the speaker’s character is determine d by the magnet and any variation in magnetic flux (how much magnetism the magnet assembly produces) has an effect on overall tone. Accordingly, we had to spend a great deal of time finding exactly the right kind of magnet and perfecting the G12M and G12H magnet assemblies, better to replicate the magnetic effect and hence, that original tone.

Now, you can specify the characteristics of your cone in a number of different ways, in terms of thickness, density, or, even more scientifically, “fluffiness” (yes, that really was part of the brief!) We’ve had long relationship with our cone supplier, so we all had a pretty good idea of how we wanted the cone itself to turn out (“kind of like the modern ones only fluffier”) but you can dictate the specification only so much; in the end it’s the ear that carries the day. Only listening will enable you to judge whether you’ve found the winning formula and that’s how the final decision was made. Manufacture and assembly processes are still largely the same as they were in the ‘60s, hand assembled on the production line here in Ipswich, England. Some of the production staff have been working at Celestion for over 30 years.

TQR: During the development of the Heritage Series, how many different vintage speakers did you have access to for comparison, and was it necessary to choose a “baseline” sound as your final target due to various vintage speakers sounding slightly different from one another?

The brief was to replicate the tone of these speakers as they would have sounded “out of the box” circa 1967. Of course there’s no way we could benchmark this with 100% accuracy. As you well know, as soon as you play a new speaker, its tonality alters (what’s generally referred to as “breaking in”). Even a speaker from that era that has never been played at all would shift in tonal characteristics for reasons such as changes in humidity during storage and also due to creep – where the cone sinks under its own weight (which can happen during extended periods of storage).

That’s not to say we didn’t listen to speakers from that era to get an indication of the ‘60s tonal “flavour.”An awful lot of listening went on – we have a room in the factory dedicated purely to that! We also spoke to a wide range of interested and knowledgeable parties; former and long-standing Celestion engineers, customers who would have used the original G12M and G12H speakers, and a number of other “interested individuals” who, through listening and playing experience, had strong ideas about what the tonal qualities of these speakers should be. Eric Johnson, for example, was very keen to give us his input on the G12H and that was one of the elements that helped to shape the final product.

So really, the story of the Heritage Series is a combination of a lot of listening, some extremely good “educated guesswork,” a firm understanding of the manufacturing processes that have been used down the years, and the knowledge, experience and support of a lot of people who know and love the Celestion tone.

TQR: Are there plans to expand the Heritage Series to include other models from the past? 

Over the first nine months of their lifespan, we’ve already well exceeded our first year’s sales forecast for both G12M and G12H. When we started development, we knew that it was a good idea, but we were a little unprepared for just how popular the Heritage Series would prove to be! I guess it really does underline the fact that there’s a tremendous enthusiasm for true vintage tone. It’s also meant that the case for expanding the Heritage Series is that much more compelling. So, right now we have another two very exciting products under development, which we’re intending to debut at Winter NAMM 2006.

Paul Cork Senior Project Engineer, Celestion International

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