Hissing noise from horn speaker

[Ron Burgundy]

Just finished my second Smart Pie External Controller rear hub kit install. Same kits with the exception that my bike has the brake sensor installed instead of the brake lever. For some reason I think the brake sensor is causing the hissing because if I activate the sensor (Break the magnetic connection), the hissing stops.

Should I be concerned about this noise? 

[Bikemad]

I have not come across this hissing noise before so it is difficult to say what might be causing it.

Try plugging in each brake sensor independently (one at a time) to see if one sensor causes more noise than the other?

Try pulling the brake lever very slowly to see if the hissing noise changes slightly before it eventually stops?
I'm wondering whether a magnet is positioned slightly too far from the sensor and is just on the point of switching even though the brake lever is fully released. 

I don't think it is anything to be concerned about, and if you didn't have a horn fitted you would not even have been aware of it.

Alan
 

[Ron Burgundy]

The noise does in fact change tone when I apply the sensor brake. It actually only stops for a split send while applying the brake but then returns. It has a different tone while idle vs under brake use.

In the alarm business, we place a 1k resistor at the siren to prevent a similar issue. I wonder if I can do that on the horn?

[Bikemad]

It might be worth trying just to see if it works.

I presume the horn will be powered from a low voltage supply instead of full battery voltage on the external controllers, but you might want to put a voltmeter across the two horn terminals and see what it reads when the horn button is pressed to find out for sure.

If it is full battery voltage, the 1.3 Watts going through the 1k resistor could generate a lot of heat if the horn button was depressed for too long. 

Alan
 

[Ron Burgundy]

  Well you know what... I can't hear it when out riding and if it not representing a problem that needs tending to then I will likely let it be. Just that my wifes bike does not have the noise and only difference between them is I have the Brake sensor and she has brake lever.

Thanks for the thought and answers though