Hi, here is a review of a problem I found in some of my HF drivers, and its repair.
I have these Eminence NSD2005 Neodymium 1" HF drivers in my top cabs. Lately I have noticed a strange kind of HF buzz added to the normal output of some of the drivers.
I naturally suspected something may have failed in the drivers. Being a careful (and the only) operator of the system I was very curious as to what may have failed so I pulled them out for inspection.
On the bench, fed from a sine generator I noticed that the buzz only appears at some frequencies and only starts at a certain level.
I used TrueRTA scope function to view the output of the driver as picked up by a measurement mic.
As the signal level was increased (at the offending frequencies) the waveform switched from nice and 'pure' sine, to an ugly and distorted wave.
This is what it looked (and sounds…) like above a certain (low) level:
I then opened the driver and closely inspected every part.
To my surprise, all looked in mint condition. gap and everything was clean. nothing loose, broken, burned or damaged in any way.
I was puzzled. There was defiantly something faulty causing this added distortion but it wasn't one of the 'usual' suspects.
I then noticed, as I was re-closing the back cover, that there wasn't any fastening feeling when tightening the cover bolts.
They just threaded nicely till the end of their travel and would reach a dead stop at the end.
I checked the packing spacer that sits between the membrane ring and the back cover and noticed it was completely pressed and lost its softness.
Measuring the actual space that this packing spacer was supposed to fill, I found it was in fact too thin.
The back cover is designed in such a way that its outer structure sits against the face of the membrane aligning ring,
so that when the above mentioned gasket is pressed and becomes too thin, it no longer presses the membrane ring and this enables the outer ring of the membrane to rattle.
I made an alternative packing gasket out of thicker 0.7mm cardboard. Re assembled the driver and the buzzing disappeared. The driver now sounds smooth and clean throughout its usable range.
Here is the original (pressed) gasket:
This is the new one:
Here in place, before closing the back cover:
I now have another 11 to upgrade…
N.W.
I have these Eminence NSD2005 Neodymium 1" HF drivers in my top cabs. Lately I have noticed a strange kind of HF buzz added to the normal output of some of the drivers.
I naturally suspected something may have failed in the drivers. Being a careful (and the only) operator of the system I was very curious as to what may have failed so I pulled them out for inspection.
On the bench, fed from a sine generator I noticed that the buzz only appears at some frequencies and only starts at a certain level.
I used TrueRTA scope function to view the output of the driver as picked up by a measurement mic.
As the signal level was increased (at the offending frequencies) the waveform switched from nice and 'pure' sine, to an ugly and distorted wave.
This is what it looked (and sounds…) like above a certain (low) level:
I then opened the driver and closely inspected every part.
To my surprise, all looked in mint condition. gap and everything was clean. nothing loose, broken, burned or damaged in any way.
I was puzzled. There was defiantly something faulty causing this added distortion but it wasn't one of the 'usual' suspects.
I then noticed, as I was re-closing the back cover, that there wasn't any fastening feeling when tightening the cover bolts.
They just threaded nicely till the end of their travel and would reach a dead stop at the end.
I checked the packing spacer that sits between the membrane ring and the back cover and noticed it was completely pressed and lost its softness.
Measuring the actual space that this packing spacer was supposed to fill, I found it was in fact too thin.
The back cover is designed in such a way that its outer structure sits against the face of the membrane aligning ring,
so that when the above mentioned gasket is pressed and becomes too thin, it no longer presses the membrane ring and this enables the outer ring of the membrane to rattle.
I made an alternative packing gasket out of thicker 0.7mm cardboard. Re assembled the driver and the buzzing disappeared. The driver now sounds smooth and clean throughout its usable range.
Here is the original (pressed) gasket:
This is the new one:
Here in place, before closing the back cover:
I now have another 11 to upgrade…
N.W.
