Many of my period-style timpani are refurbished drums made in the early or middle part of the 20th Cenutury that started out being much deeper. Hawkes are most commonly found, but there are many other makes such as Parsons, Besson, Boosey, Hards and Ajax. If you go to the Information page you can see the step-by-step process undertaken by Pete Woods of Henry Potter's. The result is an 'as new' timpani with a conventional 'half-round' classical shape, or a more straight-sided baroque shape. They vary in sizes from 22" and 24" as a pair with thick English calf heads for baroque music, up to a set of 4 (normally 22", 24", 26", 27.5") for classical repertoire. I usually use goat heads on these late classical / romantic drums.
Before
After (baroque shape)
After (classical shape)
Although there are limits on how much the shape of a bowl can be transformed, the photo below shows some of the different shapes that we are able to produce. The classical shape is on the left, and the baroque on the right. The baroque drum has straighter sides to increase the volume of the kettle. This is important when you consider that sometimes you will need to play a G at baroque pitch of A=415 (effectively a 'modern' F#) on a 24" drum.
I use these timpani both in period-instrument groups and modern chamber orchestras.
You can hear them in Beethoven's 4th and 7th symphonies with the Academy of St Martin-in-the-Fields directed by Joshua Bell. 
And in Berlioz' Symphonie Fantastique with OAE and Sir Roger Norrington
In rehearsal:
2nd timpani Scott Bywater. Percussion Glyn Matthews, Ben Hoffnung, Richard Horne.
1st Movement
2nd Movement
3rd Movement
4th Movement
5th Movement
2nd timpani Scott Bywater. Percussion Glyn Matthews, Ben Hoffnung, Richard Horne.
1st Movement
2nd Movement
3rd Movement
4th Movement
5th Movement
Here are some photos from my talk on the history and development of timpani at the 2012 Festival. Timpani were generously loaned by the Chamber Orchestra of Europe, Ben Hoffnung, Bill Lockhart, Sarah Stuart and Julian Fairbank / Majestic Percussion. Photos by Chris Christodoulou.
This film shows the Potter's workshop in West Street, near Leicester Square in London. Pete Woods (once again of Henry Potter's) began his apprenticeship here in 1968 and the men shown in this film were his major influences. The expertise that led Sam Potter to found the company using his son's name in 1810 has been passed down in just six generations.
With many thanks to the photographers and film makers who have allowed me to use their work; Stephen Tasker, Chris Christodolou (RCM), Tommy Pearson, Monika Rittershaus (Berliner Philharmoniker), Will Schofield, Glyn Matthews, Angus Bremner (SCO) and Zen Grisdale.