I am using a DA50, Slimline non-smoke Pitts muffler and Mejzlik 20x12 3-blade. A Mejzlik 23x8 is 2db louder (in general going from 3 to 2 blades adds 2 to 3 db at WOT.) At 6400 RPM from 7.5m over grass with the meter set to dbA and slow response I am at 90 db (our limint is 92db.) If you are over cement you will be at least 3-4 db louder. It will honestly be hard to make 86 at 7M... a canister will help but the prop is going to be an issue. On planes that just can't make the readings at our club we let people fly after coaching them to manage the throttle... if they rip the prop in the air and crack WOT too often they are grounded.

Make sure nothing rattles on the plane as that can make a huge difference - make sure all cables, hatches, cowl etc have been secured. Any hatches, cowl etc should have silicone, rubber or some other dampening material to reduce noise.

Interestingly enough my DA100, Slimline smoke in-cowl mufflers with Mej 25x12 3-blade at 6300 RPM is only 87 db! I believe vibration is the main difference - the airfame is not generating near as much noise as it's fully sheeted (Cap580.) The H9 Extra 260 is all covering - it resonates like mad. I also have a composite Sukhoi with a Evolution 58 that resonates so much it can't pass a sound test... its like 103db!!! I bet I could make 86 on the 580 with DA100 with a little work.

If you're going for quiet I believe Mejzlik is the best based on my testing (we tested a LOT of props.) The best way to get quiet is with a higher pitched carbon 3 blade. It will keep RPM's down and massively reduce tip speeds. I really like the performance of the 3-blades. Maybe they don't pull as hard but they are very smooth... one drawback is you'll have noticably less braking effect on downlines and when slowing for landing but you'll get used to it.

Chris.