Celestion cdx1-1445 mod | audiobymartin

13/64" flat end drillbit

carefully drilled hole in cover

before and after

in free air.

13/64" flat end drillbit

1/4

In my limited experience, most compression drivers perform better when the rear cover is removed.

In the case of the Celestion CDX1-1445, you can't remove the rear cover, as the diaphragm is glued on.

Experimenting about "venting the rear of diaphragm" then hit my mind.

After all, the Radian 760PB neo does have a vent hole in the rear cover as do many other CD’s.

The Radian 950PB’s however didn’t have a rear hole, which was a surprise when I received them.

I listened to the 950PB’s without the rear cover installed, I preferred without the cover, so drilling a hole in the cover didn't cross my mind. I also had to consider the resale value of those pricey 950PB.

Given the CDX1-1445 is a small diaphragm format (35mm), I arbitrary selected a 13/64" diameter hole size. (0.5 centimeter)

spl

no smoothing, microphone placed 3" from horn mouth

phase

not much difference

step

quicker setting with hole

spl

no smoothing, microphone placed 3" from horn mouth

1/3

The impedance result in the Dats (Not shown)

The impedance peak became narrower, which is a good sign.
The phase flattened out a bit, this is good also.
Counter-intuitively, the FS increased a bit, but was still well below the 1445’s optimal operating range. No issue here.

Still… here’s a rough idea of the rear cover hole mod.

Measured on the STH100 horn.

Purple is 13/64" hole in the rear cover
Blue is me blocking the hole with my finger
Step response show great improvement