There are a wide range of sources for sound equipment in London, but a limited amount are solely dedicated to sound equipment and offer specialist support to their customers throughout their shoot. Better Sound and Richmond Film Services are both experts in their field that provide a wide range of equipment and support if there are any problems on a shoot.
The choice between companies will come down to your requirements - for instance if you have a tight shooting schedule and are using complicated equipment it would be good to consider a company who offer substantial support. If you do not require this level of support and have more modest requirements then it would make sense to hire your equipment from an organisation that is convenient (who are close to your shoot or who you may also be hiring other equipment such as camera or lighting) and have a well maintained hire collection.
A notes on Sample Rates:
Sample Rate refers to the resolution of digital audio that determines its sound quality. Digital sound can be recorded at different sample ratings, the main two are 48kHz or 44.1kHz (although miniDV has the option of recording at 32kHz). It is important to choose one sample rate and work to this throughout the production and post-production stages as the two sample rates are incompatible. It is possible to convert sample rates if needed but best to keep this to a minimum. The sample rates will depend on the equipment that you use to record your sound. Below is a list of the sample rates available with different equipment:
DAT(Digital Audio Tape) - works at 44.1kHz and 48kHz
Minidisk- works at 44.1kHz
DA88(used for storage and mastering) - works at 44.1kHz and 48kHz
CD- works at 44.1kHz
DV(Digital Video) - works at 48kHz and 32 kHz (which is low quality and to be avoided)
Digital Betacam- works at 48kHz
DVD(Digital Video Disc) - works at 48kHz
Sound Equipment Hire Companies
The Film London Directory provides details of an extensive range of equipment hire companies dealing with sound, both specialists as well as general hire facilities which have well maintained sound equipment for hire alongside their other equipment.
See: 'Sound and Music > Equipment Hire Companies'