Celestion Ditton 15 - Article
Celestion Ditton 15
Celestion's affordable Ditton 15 was a popular loudspeaker that sold in thousands through the 1960s. Haden Boardman takes it apart...

These days Celestion are the pure 'Pro' side of Gold Peak industries loudspeakers division, the domestic side being represented by another classic hi-fi company, KEF.

Celestion's fame in supplying guitar 'speakers is more legendary that even the company's domestic output. Celestion first appeared in 1924, making them one of the oldest names

in the industry.Wartime problems forced a merger with British Rola and the name expanded to Rola Celestion for a period.The company was located at Thames Ditton, Surrey for a while and the name Ditton is used on some products. However, come the nineteen seventies the factory ended up miles away in Ipswich.

I must confess to having no great

love of most Celestion speakers: my early exposure was a late set of Ditton 33XRs, and to be honest I thought them pretty boring speakers to listen to. The 'domes' fitted just did not sound right and even on a good set up you could hear this an almost 1970s "prog rock" sound - and I am not into prog rock so much.

My next experience was of their

Die cast chassis on Celestion unit, well engineered and constructed.
more and more this thing seemed to move, and the less the bass unit seemed to be doing anything whatsoever. What was a surprise to me was there was still some movement down at 16Hz, which is pretty darn impressive for a 'small', less than two cubic foot box.

The electrical crossover is about as simple as it can get. A first order, 6dB/octave single coil feeding the bass unit, with a second order l2dB/ octave capacitor and coil on the HF

"a seriously well engineered loudspeaker, A bargain for the money"
I 300 tweeter. Crossover frequency is 3kHz. The units matched in sensitivity, so thankfully no resistors were needed.

Connections on the 15 are via a couple of'finger' terminals on the back panel. For easy access the simple hard wired crossover is mounted directly to the back of the terminal panel.

The Celestion is a pure 4 ohm load, designed to get the most out of those new fangled transistor amplifier things of the period. However, it measures a very easy load (average 4.2 Ohm) and no valve amp would struggle driving these. Sensitivity measures just under 90dB per watt, pretty sensitive, but not amazingly so. Power handling quoted is thirty watts on the cabinet back. Celestion specs are 30-15,000Hz on frequency response.

After carefully checking the speakers out, they where wired up to my little EL84 push-pull pentode valve amp, Marantz DI DAC, trusty old Garrard 401 with my active valve phono stage.All cable was Chord Co: Indigo interconnects. Rumour speaker cable.The Ditton 15s were

placed close to the wall on twenty inch stands.

From the off, what a delight! Initial surprise was a much lower level of'coloration' than I was expecting. Playing very well known Jazz (to me!) Ella Fitzgerald and Dinah Washington tracks, the power of these two ladies really communicated through these little boxes.

Moving forward a few years to the audiophile recording of Sara K, again I encountered a quite magical sound. Stereo imagery on the latter disc was quite powerful and distinct; the little Celestions played this track amazingly well, doing a great disappearing act.

Treble on the HFI300 comes in for criticism. If anything I found it a tad bright at times; but very clear, lacking in sibilance and beautifully balanced into the midrange.

The bass could be a tad odd. Playing my usual Jimmy Smith favourites. The Cat and Walk On The Wild Side, there was mildly

constricted bass, but then a bit of Sly & Robbie was quite awesome, if limited in just how loud it would get.

And that is the Ditton I5's biggest down fall. lOOdB is about the limit in the bass before it starts to sound a little congested. Digging out some fairly heavy cathedral organ recordings showed lower bass was no disgrace. But what impressed was the cohesive nature of the design. Everything blends beautifully. Electrically this may not be a three way design, but acoustically it is.The ABR works in perfect harmony with the main mid/bass driver.The design's simple first order crossover allowed it to melt into the tweeter at three thousand Hertz. Compared to more modern designs it was near impossible to spot the seams...

As mentioned, this speaker was sold in thousands. A lot were sold to 'non' enthusiasts who are now clearing the garage out discovering these old wooden boxes, and either taking them to land fill or popping them on that

well known internet auction site. I bought two sets. The first set cost £20 and was collected from Blackburn. Nice old chap, cabinets in a state - and every unit busted! The second set was less than one mile from my front door, the ones you see here - cost £50 and all drive units work.

Celestion may claim 30 Watts, but 15 Watts would be a safer margin. In hindsight making the speakers 8 Ohm may have saved some of them. When purchasing, be warned! The tweeter will blow easily; amplifier clipping will instantly kill it. I have, in the past, managed to pull an HFI300 apart and nine times out of ten it is the lead out wire that has fried. Those with finger skills could easily tease a tiny amount of copper wire from the speakers voice coil and repair it.

Throw the grills in the bin and rewire internally to tweak them. Biwiring isn't worthwhile with a simple design like this. Better terminals? I soldered Chord Co Rumour directly to the terminals on the back.

The original Ditton 15 is a seriously well engineered loudspeaker, a bargain for the money, something you can play with, and play real music on. Buy carefully and get a bargain.

Front of the ABR unit, damped polystyrene cylinder. Note acoustic treatment.
Back of ABR mirrors the front of the unit, note depth and same acoustic treatment.
From the top; HF1300/II tweeter, 8" paper pulp heavily doped bass/mid, and ABR at the bottom.
budget models, the little 3 and 5 with bright ringy tweeters that were horrid! And don't get me started on the DL8 and SL6...

I know there is a big fan of the SL600/700 not a million miles away from me here, but for me the only salvation at the time was the ribbon equipped 3000 / 5000 / 7000, all slightly marred by using the rather poor bass unit fitted to the DL8.The ribbon was the work of the late Dr Karl Pinfold at Liverpool University / Merseyside Acoustic Developments; I will let you put the latter's acronym together.

The 'big daddy' Celestion Ditton 66 failed to impress me, and neither did the 44, and the tiny 10 came and went.

Only in fairly recent times did I audition the nineteen sixties designed Ditton 15... of which Celestion sold thousands throughout the late 'sixties and nineteen seventies. It was eventually replaced by the I5XR...

which, in my opinion, is best avoided.

Stick with the original!

By the day's standards, the Ditton 15 is quite a slim, elegant design. Enclosure size is twenty one inches tall, by nine and a half inches both back to front and side to side; available in both teak and walnut real wood veneers. The box, for its time, is very modern in its construction, with drive units loaded from the front behind the grill.The deeply recessed baffle gives the age away a little, and the grill is pretty dreadful acoustically, and they do seem to break very easily. However, all the drive units are mounted via secure bolts, the tweeter routed in to the baffle, the die cast bass unit and ABR device mounted proud.The cabinet is well lagged inside.

Launched in '67, the speaker boasts some quite unique features. At the top of the cabinet is the classic HF1300/11 tweeter, seen in BBC monitors, Rogers and Spendor speakers, including the famous BC and SP models.

A ring radiator, it was developed in the 1950s by the famous General Electric Company as an accompanying 'presence unit' to
range speaker G.E.C. where making at the time.The tweeter design passed on to Celestion. Opinions remain divided, but I think it is an absolutely superb thing.Voigt was the first to use a central spider to hold the loudspeaker diaphragm, and this unit mimicks it.The actual radiating material is phenolic resin, as used in printed circuit board manufacture. In Mkll form the tweeter has a plastic housing, and a ceramic magnet mounted onto special shaped pole plates.

The bass unit has quite an impressive cast chassis. Again modest on (ceramic) magnet size, the heavily doped, paper pulp cone has, by modern standards, a very low resonance of 25 Hz.This is ultimately complemented by an ABR or Auxiliary Bass Radiator mounted at the bottom of the cabinet. ABR units were certainly not a new invention; dating back at least to Olson's classic texts, but Celestion's was quite unique for the time.ABRs behave in a different manner from the 'organ pipe' design of a standard tuned reflex port. I spent a merry ten minutes making this thing move about with various low frequency sign waves from my old oscillator.

The ABR itself is constructed from a six inch diameter polystyrene block, three inches deep. At both ends it has deep rubber surrounds, and the polystyrene is damped by little 'discs' glued on both sides of the cylinder, the whole thing mounted in a plastic basket. I am not sure what its resonant frequency is, but by shaking the unit out of the box it was possible to detect quite a low frequency low level 'rumble' coming from the modulated air.

Back in the cabinet, above 100Hz, it may as well not exist, all output coming from the main eight inch bass/mid unit. Once down at 1 kHz. the ABR begins to join in the lower the bass note.

Simple first order crossover on bass and second order on treble.
Classic HF1300/II distinguished tweeter of high performance, used in many quality designs.