The Importance of Chamfering
Copyright 2009 © Troels Gravesen
This study has been on the to-do list ever since I saw the first Avalon clones with the middriver stuck into a very narrow and deep rectangular hole. I always thought the midrange would suffer congestion but I never had the chance to hear any of the clones.
As often as possible I
stress the importance of chamfering the driver holes to
allow free ventilation for the rear energy coming from
the driver. Obviously the energy coming from the rear of
the driver is exactly the same as what comes from the
front and as most drivers have very thin and acoustically
transparent membranes we need to do all we can to get rid
of the rear energy in order not to have that energy being
reflected back towards the membrane. The reflected rear
energy will be delayed and hitting the membrane it will
cause smearing of detail and increased (subjective)
Before we go to the study below, here's a scary example of a ScanSpeak 15M midrange driver:
I was sure the differences would show up on CSD (cumulative spectral decay) and step response, but it didn't. Much to my surprise! But what surprised me even more was that it had a significant impact on frequency response. What I already knew from mounting a small middriver into a narrow tube (A) was the impact on sound (TJL3W and Classic 3-Way). Comparing A and C on pink noise leave no doubt of the importance of chamfering driver holes. On C we hear a full-bodied sound with deep and wide low-end response where A will make the sound thin with an unpleasant presence. It sounds congested.