This is a lightweight plastic practice mute for double horn bass trombone, made in Japan by Toshio Okuda. Its sound is very soft, it fits securely inside the bell, and its small size allows it to be stored inside the bell while the instrument is in the case.
For 2018 these are mutes available in black, but not other colors at the moment.
Professional trumpet player & the Okura mute builder
Many brass players have talked about practicing with a practice mute. As a trumpet player I am also one of them and would like to introduce how I think of practicing with the mute.
When talking about our air stream, I believe that we often tend to play by using different angles of the air at the middle register and the high. Meanwhile, at the low it is exceedingly required to blow straight into the mouthpiece.
While practicing with a practice mute, we are able to feel some resistance against the air that you exhale. This resistance may often help your embouchure stay focused, without the lips widened by strong air stream.
My practice mute "okura mute" is made of plastic and that makes its advantage of comfortable resistance that is not too strong.
I would recommend that you practice mainly your low register with the biggest sound possible first. Imagining the feelings of that, you may try to make the angles for your middle/high register closer to the angles for your low, you may learn more effectively how to blow depending on different registers.
The "Okura+mute" has been named with "+" (plus) by me as the mute builder, wishing that everybody can learn something extra (=plus) by using my mute, in addition to what you may learn with your ordinary mute-practice. Of course you may have your own unique way of using the mute as well.
I sincerely hope that these mutes assist many brass players from all over the world to have fun with instrument playing!