Much of my daily practice is away from home and in a situation where loudness is not an issue. I would like to practice more at home but am wondering if there is a practical way to mute a flute to an extent without affecting the playability and airflow? When I played saxophone I used to place a cloth loosely in the bell and that was an effective mute.
I could experiment, but if there is a tried and tested method it would save me time.
You could build a DIY sound booth like I did for playing in my apartment! You’ll never achieve 100% soundproof, but you can take the volume down to an acceptable (and ignorable) level. I essentially just went to the hardware store, got PVC pipe and dowels for extra support, and made a little skinny box over my computer desk.
Put a dowel through each pipe, join them up with the connectors, and boom! Frame.
Next, I went to Amazon (because I didn’t have time to visit rummage sales) and bought a bunch of really heavy moving blankets. It’s much harder to find quality moving blankets these days, and likely way cheaper to go to a rummage sale. Start with the top, and get a good firm ceiling on your booth. You can punch holes in the blankets and use zip ties, or buy greenhouse clamps (get them a size bigger than your PVC to account for the bulk of the blanket) like I did.
Next, hang the blankets on the sides, with any overlap going up top. you want these to hang like curtains that seal against the floor but don’t bunch up with a load of extra material. Use two blankets that overlap as a “door” on the side you’ll be entering and exiting out of. Turn off any desk lamp inside and check for “leaks” by looking for exterior light from the room. You want this to be as airtight as possible, as sound will escape through the smallest crack. Put an LED light in your desk lamp to control heat, and maybe a small fan, and you’re done!
For extra sound reduction, hang two blankets per wall, one on each side of the horizontal pipe, and throw a comforter or something big and fluffy over your “ceiling” blanket. You can also throw some acoustic foam on any hard surfaces nearest to your booth to help reduce echo and reverb. IMO reverb is really what makes a sound irritating when you’re trying to tune it out.
Edit: I can send you some pictures if that would be helpful. Total cost, maybe 120 USD? That’s because I spent 60 on acoustic foam and more than I should have on moving blankets.
Another option is to play softly, which strengthens the embouchure.
That may not be true in every case. I used to play (very) softly and it wrecked my tone when I went out to sessions or concerts. I think the degree to which one WANTS to quiet the flute doesn’t match up with what is achievable by playing softly but still with good tone.
[quote=“MadmanWithaWhistle”] >You could build a DIY sound booth like I did for playing in my apartment! You’ll never achieve 100% soundproof, but you can take the volume down to an acceptable (and ignorable) level<
In England we refer to that technology as ‘a shed’. My wife’s been hinting for some time that storing me out of sight and out of mind down the garden with the potato fork and old tins of paint would be the perfect solution. 
Alas, living in Seattle means being crammed in an ugly “modern” pillbox with a bunch of other lousy drooling specimens of humanity. A nice insulated shed (perhaps with a woodstove?) would be lovely, but instead I’ve got my little blanket Fort Cameron. It’s ok though, the hamsters don’t seem to mind the flute 
Have you tried the “blob of blue-tac” approach? You make a sausage of a blob of bluetac (poster putty) and lay it along the audience-side of the embouchure hole. The closer to the hole and the bigger it is, the more it reduces the volume. You won’t enjoy playing as much, but at least it will let you.
Or you could buy a really bad flute!
I was going to post MadmanWithaWhistle’s answer but he got there first. I’ve heard of whistle players using 'blue-tac" (putty) to quiet the fipple, but I can’t help but think that doing that to the flute embouchure would mess you up, when you do want to play at full volume. As it is, I have trouble calibrating my solo home practice volume to what I need to do when playing with others.
The nice thing about flute is that it’s high-pitched, and those frequencies are more easily damped with the kind of ad-hoc “vocal booth” mentioned above. It’s a tougher problem to solve with low-pitched instruments like bass or drums that need more extreme acoustic treatment.
For a cheap alternative to a full booth, try hanging some packing blankets, rugs, or plastic bubble wrap packing material in the corner of your practice room, with a soft rug on the floor. Make sure the rug extends around and behind you. Play with the flute facing into that absorbent material in the corner of the room, and you’ll kill a lot of the volume for anyone outside the room.
I would appreciate some pictures. It sounds like a great idea, but I can’t quite picture it all in my mind. 
It sounds like the original poster will continue to play at volume outside of home.
It wouldn’t be all quiet. Playing softly is recommended as a way
of improving tone and strengthening embouchure. I play softly at home a good deal
and I’m very loud when I want to be, FWIW. It might be worth a try.
Yes I can practice during the day where volume is not an issue.
I don’t really want to cultivate habitual soft playing; I’m interested in ways to occasionally knock some of the volume off while playing ‘normally’ in terms of air when playing in proximity of others.