Celestion SL6s restoration: Part I
Celestion SL6s restoration: Part II
Celestion SL6s restoration: Part III
TS parameters of the Celestion SL6s woofers
I measured the woofer driver TS parameters with the Clio Pocket. Before I did that I run the drivers for about 36hrs on a 15Hz signal at close to maximum excursion. Just out of curiosity I measured the impedance and TS parameters before and after burn in.
There is some difference between the two woofers, but what do you expect. They are about 40 years old.
Impedance woofers A&B
Spkr B (only) woofer impedance response red=1volt white=3,46volt.
The cabinets
Outside measurements (HxWxD) 376mm x 201mm x 250
Inside measurements (HxWxD) 351mm x 174mm x 195mm
- Baffle thickness 19mm (HDF/MDF)
- Backpanel thickness 12mm (HDF/MDF)
- Sidepanels thickness 13mm multiplex
- Internal brace 19mm (HDF/MDF)
Internal volume of cabinet 1,95 x 1,74 x 3,51 -1 = 10,9 ltr (0,5 ltr for the drivers).
The cabinet is simple, made form a combination of MDF (HDF?) and multiplex. The construction is very rigid, and heavy for such a small cabinet. Note the back panel, which is mounted 22mm inside the cabinet. This is done in order to better supress cabinet resonances.
Cabinet sketch and crossover schematic
The crossover mounted on the inside backpanel, and some of the pulverized damping material.
The crossover
The crossover is simple, with a 12dB/oct lowpass for the woofer and a 18dB/oct highpass for the tweeter. Tweeter and woofer are connected in phase. The crossover is asymmetrical, which will influence the (vertical) polar diagram.
All capacitors are originally (as shown here) Alcaps. I checked the capacitor values.
| Capacitor value | Measured | Δ % |
| 10µF | 11,28 µF | +13% |
| 10µF | 11,44 µF | +14% |
| 6µF | 6,56 µF | +9% |
| 6µF | 6,56 µF | +9% |
| 4µF | 4,28 µF | +7% |
| 4µF | 4,25 µF | +6% |
Not bad for 40 year old capacitors. I still repaced them with Visaton 10µF MKM, and MCaps.
Cabinet damping
The cabinet is almost completely filled with damping material. There are three layers of two types of foam stacked from the backpanel up to the back of the woofer magnet. On top of that there are pieces of foam along the sides up to the baffle. The three top layers of foam, like the green type in the picture below, are in good condition, the bottom layer (of a different type, see the grey foam in the picture below) was essentially reduced to dust, and fell apart when I touched it. This foam layer had to be replaced. It is a sort of reticulated foam, widely used as packaging material, and for water filters.
Part III to follow.
Attachments
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Celestion SL6s Spkr A impedance no xover red=woofer white=tweeter.png -
Celestion SL6s Spkr B impedance no xover red=woofer white=tweeter.png -
Celestion SL6s Spkr A impedance+xover red=woofer white=tweeter green=speaker.png -
Celestion SL6s Spkr B impedance+xover red=woofer white=tweeter green=speaker.png
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The Hi-Fi Choice description states that the SL6S sealed cabinet is made from MDF, and has thinner panels than its predecessor the SL6 in order to reduce energy storage.
Apparently, the higher order high pass filter compared to that of the SL6 altered the polar distribution and made stand height less critical.
P.S. Typical price per pair in 1986/87 inc VAT was £350. According to the Bank of England inflation calculator, that's equivalent to around £1,000 today.
See Part I regarding the dual rubber surround: https://www.diyaudio.com/community/threads/celestion-sl6s-restoration-part-i.425452/#post-7964176
The 6.5" Kobex-coned mid/bass driver has a unique two-part surround that is effectively a mechanical crossover. The inner half sufficiently reduces traveling waves in the cone while the softer outer half gives a freer suspension at low frequencies for "improved bass articulation and 'speed'".
The lugged die-cast chassis of your woofer is similar to that in the SL6S. The woofer in the SL6 was clamped onto the baffle rather than bolted as in the SL6S.
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Hi Galu,
Re the cabinet, I read the samen statement about the cabinet beimng made of MDF. However, if you look on the iside you ca see the difference between the smooth (MDF) surface of the baffle and backpanel, and the grain of the side panels. So for my pair they are clearly differen, but maybe the materials changed over time?
About the crossover and the stand height, you are right. I measured this long time ago, but can't find the files. there is a upwards pointing lobe around thge xover frequency. I will repeat the measurement when the wheather here improves.
And finally about the prices, I sold a few pairs in my time, in the Netherlands, and the price you quote seems to be about right.
Re the cabinet, I read the samen statement about the cabinet beimng made of MDF. However, if you look on the iside you ca see the difference between the smooth (MDF) surface of the baffle and backpanel, and the grain of the side panels. So for my pair they are clearly differen, but maybe the materials changed over time?
About the crossover and the stand height, you are right. I measured this long time ago, but can't find the files. there is a upwards pointing lobe around thge xover frequency. I will repeat the measurement when the wheather here improves.
And finally about the prices, I sold a few pairs in my time, in the Netherlands, and the price you quote seems to be about right.