Horn Frequency Tuning

[Pawel66]

Can anybody help me with it?

I know the procedure is in PW 21/2017 - I do not have it. I have the two volumes that were put together, but Volume II ends at PW 20 - 

I have my horns refreshed, operating, but the frequencies are wrong. I am turning the screws, cannot get it right, I am apparently missing something.

[Pawel66]

Ok, I kept digging in the forum and found a very helpful document.

There is no frequency adjustment, it is the membrane thickness that determines frequency.

I could not figure out how turning of the screw in the middle of the membrane can affect the frequency...

Or I am missing anything?

[BobH]

Thanks for finding this Pawel, i'm always amazed when people take the time to put together documents like this, that are so helpful to others

I've added it to the tech manual so it doesn't get lost

[Pawel66]

Thank you Bob. I thought we were missing this info in the Tech Manual. Reference to PW is great, but may not be easy to access.

Yes, robust study there, great job!

[Pawel66]

Thanks to Michael's kindness I got hold PW 21 and I see the missing link - it is the bushing inside the clamping collar that turns and changes the distance of the entire sound post from the spring.

This bushing is not shown separately in other places - I will need to look into it and separate it from the collar so that it can turn.

[Pawel66]

Having fixed some issues that I have come across with the two horns from my Ponton:
1. Broken off insulator plate covering the points lever - cut one from a teflon sheet I had at hand
2. Seized threaded bushing in the collar - the one that is use to tune frequency - a famous mixture of 50/50 ATF and acetone and heating made it move

I progressed with attempt to tune the frequency, where I failed.

Too little adjustment range - when adjustments started going the right direction, I was coming to the point when horns went dead. Could not compensate with the other screw. I landed ca 30Hz below targets on both horns.

I may come back to it, I lost patience for now.

Many thanks to Michael for his help.