Celestion 7000 Modification Project

[hspend]

I have a pair of Celestion 7000's driven by a valve amp (for mid-range and treble) and a beefy 100 w. per channel transistor amp for the bass units (below 120 hz.)

The ribbon treble and imaging is such that I do not want to change these speakers. However, they are far from perfect and have two major weaknesses: mid-range and bass. I tried a mid range unit (8") from a spare Spendor speaker and whilst it did improve things in terms of mid-range quality, the unit was not matched in terms of sensitivity etc. producing too much output.

Feeding the 8 " bass speaker separately via an active X-over and transistor amp helped the bass, but it still sounds boxy and flabby--I am not a fan of infinite baffle bass! I find it woolly. Don't get me wrong, I don't like bass that is too solid and shaking either, but I do like it to be tuneful, fast and musical.

So can anyone suggest any mods? The mid-range I guess is just a question of replacing the cheap Celestion units with something of better quality. But how do I ensure a good match in terms of sound output? Will it mean redesigning the X-over?

The bass seems to be the greater problem. I don't mind making mods to the cabinet but what mods and what drivers? I think there is some sort of double column construction inside the bass part of the cabinet. Would it simply be better to forget the bass (just run it at a low level) and get a REL sub woofer instead? I don't think it's just the low quality Celestion drivers that are the problem--the cabinet has a lot to do with it as well.

Any suggestions will be gratefully received. I am away most of September, so please don't be offended if I don't reply straight away to a post.

Many thanks in advance,

Frank

[petercom]

First of all have a look at this series of articles, recently published in Hi-Fi World...http://www.world-designs.co.uk/Impspkrs.html

If you find you must change the units then it will be difficult to do this without adjusting the crossover. Crossovers are designed to match specific drive units, so you can't just substitute any old driver.

To give an example we recently worked on a Jamo Concert 8. This had a SEAS treble unit from the Excel range but sounded dim and distant in the upper midrange. We put in (at the customer's request) a SEAS Millenium treble unit, also from the Excel range, and changed the value of the crossover capacitors and substituted Soniqs PXX caps where suitable. We also adjusted the bass/midrange filter to match the new upper midrange performance. We used Soniqs PDC on some of the cabinet walls to reduce midrange resonances and changed the thin internal foam for a layer of Soniqs CDF. Labour cost was £90 excluding components. The result was hugely improved transparency and the customer was delighted.

But had we just substituted the treble unit the output of the latter would have been 2dB too low and there would have been a big suckout in the midband. If two drive units from the same manufacturer's range can be so different in characteristics then you can imagine what might happen by just substituting drive units in your speakers!