I was able to suck the dust caps back out quite easily by careful application of a vacuum cleaner nozzle. However having connected the speakers up and tried them out, I felt that something was missing from the top end. When I put my ear close to each of the drivers, the two bass/mid-range units in each speaker seem to be working fine, but there is virtually no output from the right-hand tweeter compared with the left-hand one. It's bi-wired, so I disconnected the LF cable from both speakers so I could just listen to the tweeters on their own. This confirmed my original impression. At normal volumes, there is hardly anything coming from the RH tweeter, although there is a bit more from the LH one. However the output from both is considerably diminished compared with that from the tweeters on my RTL3 operating at the same overall volume level (ie when all drivers are connected).

 

It seems fairly clear to me, therefore, that the Prologue's tweeters are either blown or have suffered physical damage by being poked, and I have accordingly started to investigate sourcing replacements.

 

The tweeter used in the Prologues is the Morel MDT22, which is now discontinued. Their availability on the internet seems to be confined to the US or Far East, where they are quite expensively priced.

 

This bring me to my question regarding the subject of this thread (sorry about the rather long-winded preamble). There is a pair of Morel MDT39 tweeters currently up for sale on eBay at a very reasonable price. Looking at the Morel website catalogue, they appear to have an identical spec to the MDT22 in all respects save two:

 

1) the Resonant frequency of the MDT22 is 650Hz, whereas the MDT39 is 750Hz;

2) the Sensitivity of the MDT22 is 89 dB (2.83V/1M) compared with 88dB for the MDT39.

 

Now I don't suppose that a 1 dB difference in sensitivity is going to be a problem, but is the higher resonant frequency of the MDT39 likely to cause any issues? Bear in mind I am not a techie, I am really just seeking reassurance that these units would be OK to use as replacements with no significant adverse effects on audio quality.

 

 

 

But I'd still be interested to know the answer in case a similar pair come up.

 

I shall also try Ruark in the morning. Although they no longer manufacture loudspeakers, they may apparently still be able to supply spare drive units. If all else fails, I could get a new pair from parts-express.com for $68.96 + shipping + customs duty + VAT etc, etc . Why is it are they so difficult to come by in the UK?

 

Well, an update:

 

The US seller in that eBay listing was very obliging and is prepared to ship to the UK if I should decide to bid on and win that auction.

 

I did contact Ruark, who could supply me with a pair of MDT-22s. Unfortunately the price I was quoted was more than it would be buying new from the USA, even allowing for the extra shipping costs & customs charges, etc.

 

And now, events have come round full circle - I have just received a SCO on the MDT-39s I was outsniped on at the weekend. It seems that the winning bidder is in Italy, and the seller will only ship within the UK. 

 

I have agreed to purchase based on a price of what would have been my winning bid under the proxy bidding rules, had the winning bidder's last-second intervention not come into the equation. I would have preferred MDT-22s as the safe option, but the MDT-39s will be less than half the price that the "correct" replacements would cost, so I decided to go for them.

 

So - back to the original point of this thread. The only differences in spec between the MDT-22 and the MDT-39 are:

 

                  Frequency response           Resonant Frequency            Sensitivity 1W/1M

 

MDT-22          1800 - 25000 Hz                         650 Hz                                89 dB

MDT-39          2200 - 20000 Hz                         750 Hz                                88 dB

 

In practical terms, will there be any perceivable difference in what I will hear through my Prologues with the MDT-39s fitted, compared what they would have sounded like with the MDT-22s they had as standard?