In my last post about the tannoy cheviot I said that something was bugging me on piano reproduction.
Again that noise
Today I was listening to some music quite loudly and heard that problem again. It was really obvious that some distortion was happening, a noise of some sort mixed in the harmonics, when pushed a little too hard. This happened mostly on harmonically rich piano notes. I tough my love affair with tannoy was over …
Finding the problem
I made a small mono audio file looping this particular piano notes and used it to locate the problem. It was coming from a single speaker so I swapped the speaker cables trying to isolate the problem (musical server, dac, amplifier). It was still happening on the same speaker so I swapped the drivers from one enclosure to the other eliminating the rest of the components from the equation (cable connections, cabinets, cross-over). It was pointing to one of my drivers.
At that moment I was pretty sure it was about the foam surrounding job, and was pretty down about it, so I started inspecting the surround and spider and everything looked fine.
I played my audio file while disconnecting only the tweeter and the problem went away so I did the same thing disconnecting only the woofer and it was easy to pinpoint the problem to my high frequency compression driver.
I removed the back cap and the diaphragm, thinking that it should be pretty hard to find replacement parts now, everything looked fine and after re installation the problem went away. I figured out that the cause was the centering of the diaphragm. Problem I had before with lowthers.
I loosened the four screws holding the diaphragm in place and slightly moved it in the slot to reproduced the problem.
Now, it’s not an easy task to align diaphragms and I didn’t feel like doing complex measurements tonight so I did the adjustment by ear and also did the same thing to the second driver. Better centering the diaphragm seems to raise the efficiency and clarity of high frequencies. Too much movement and you get voice coil rubbing and, considering it’s sensitive parts you are playing with, you need to be very careful.
I’ve aligned my lowthers a couple of time in the past and it’s way easier to do compared to the hpds. With lowther drivers, you see what you are doing and listening to complex music in the same time give you clear indication for the adjustment. It’s not as easy with the dual concentric drivers because you can’t see what you are doing and positioning of the compression driver’s diaphragm prevent you from installing the driver on a table while listening to it.
After putting back everything in place I did some listening with complex piano musical pieces and the problem is gone leaving place to some beautiful music.
HPD in open baffle ?
By holding a hpd 315 in my hands while playing some music, I realized that they can produce an impressive amount of low end and I suspect they would works well in open baffle configuration. If used with low end reinforcement in narrow baffles, the cross-over point to the woofers could be quite low. With proper baffle configuration the hpds can possibly be used alone. That’s something I may try someday but my living room is not really OB friendly as it is.
I would need a proper alignment method for compression drivers, if someone have a “how to” of some sort it would be appreciated. You can leave a comment to the post or contact me by email.