I've come to consider Couesnon Monopole clarinets to be something of a "best kept secret". Since I have two of them in superb condition I'll let the secret out so others can discover what a treasure Couesnon clarinets can be.
I have David Speigelthal to thank for his rave comments on the Woodwind.org clarinet forum about vintage Couesnon clarinets. This inspired me to look for a Couesnon. The alinements of the Universe must have gotten behind my search for a Couesnon. Within only three days I found one that had just been restored. Not only that, its price was a fraction of the cost of a new R13. My first impressions of this Couesnon were extremely positive. I especially fell in love with the Couesnon's dark, vibrant sound and its consistancy of tonal quality throughout its range. When I took the Couesnon to my repair tech for a check over he raved about the high quality of its grenadallia wood and overall craftsmanship. After Eric's adjustments the Couesnon was even more impressive.
This Couesnon has a 285xx serial number. Amazingly, though the Woodwind.org forum I was able to get in touch with another clarinetist who has a Couesnon only 6 serial numbers away from mine. Even more amazing, he is the original owner and still has his Couesnon's sales receipt. This enabled us to date our 285xx Couesnon clarinets to 1960.
After playing my Couesnon for a year I decided that I needed to have another Couesnon as a back up. Happily, I stumbled upon a 70's model Couesnon on ebay being sold by a repair tech I recongized from the Woodwind.org forum. The starting bit was only $450. Remarkably, it turned out that I was the only bidder. My repair tech found several things that needed to be fixed on the clarinet. This added $200 to the ebay price. Still, it boggles the mind to think of getting a pro-level grenadilla wood clarinet for $650! This Couesnon has a 348xx serial number. Since it appears that there are no Couesnon serial number lists in existance, I have not been able to determine the exact production year for this clarinet. 1970's seems to be a reasonable ballpark estimate.
Comparing my 285xx and 348xx Couesnon clarinets, I quickly discovered that their parts are not interchangable. Therefore, Couesnon made some design changes between the two models. I asked my repair tech to measure their bore sizes. The 348xx Couesnon has a smaller bore than my earlier model and is more Buffet-like in terms of its bore size. Performance-wise, it's my impression that the 348xx Couesnon has a bigger sound, more "ring", and a greater level of projection. My initial comparision was done with a Grabner K14 mouthpiece. I've recently discovered that a Grabner K11e gives the 285xx Couesnon a greater amount of ring and projection. So, it's a matter of experimenting and finding the mouthpieces that are an especially good match for the particular Couesnon model.
I've come to use the 348xx Couesnon as my primary clarinet. Happily, a few months ago the same ebay seller put a 65 mm Couesnon Monopole barrel for sale, I was able to get it, and it fits my 348xx Couesnon.
For me, vintage Couesnon clarinets have characteristics in common with 1930's Buescher saxopohones....which I also dearly love. I've come to feel a special bond with vintage Couesnon clarinets. For whatever reason, it seems to me that Couesnon is a perfect match for what I'm looking for in a clarinet.