Attention: TDR Forum Junkies 
Just got 3 air horns from a boneyard from wrecked trucks and thought I'd share with you how these are constructed and how the quality stands up to age. Please do not turn this into an ''oil war'' and just accept this as one man's opinion. After taking off the horns and as much valving and air line as I could get ,here are the impressions I came away with.
*Reeds-- the reed system in both horns is driven by the venturi [suction effect] the air comes in the base of the horn at 90 degrees to the reed and rushes past it and exits the bell. The reed is about the thickness of an aluminum pie pan and vibrates against a 'donut hole' as the air is being drawn through the donut hole. The reed on the Hadley is thinner and is easier to drive at lower pressure and lower air volume than the Grover.
*Machining-- The Donut hole is a casting and appears to be machined to a higher degree on the Hadley than the Grover,which looks like simply cast and then plated
* Reed pressure-- The reed must be held against the 'donut hole' of the venturi and this is where the horns differ the most. The Hadley is held close to the venturi by the back -up plate [the back of the horn] with only a machined-in tolerance. The Grover is held in place with a spring pushing against the reed. BTW this is the reason the reed is thicker on the Grover-it has to be stiffer to withstand the constant spring pressure and increased wear this would generate.
* Volume and sound --All three horns were pretty much similar volume if you put enough air to them. As you bring the pressure up,there is a squeal,then a soft tone ,then louder and louder with increased pressure. A little synthetic grease between the reed and the venturi makes the tone louder and easier to drive at lower pressure. IMO, the Grover sound was a little more ''breathy'' than the more solid sound of the Hadley.
* Valves -- the pull valve on the hadley was more beefy,but no idea if that makes it better
* price-- all three horns cost me $25. 00 :-laf .
*Reeds-- the reed system in both horns is driven by the venturi [suction effect] the air comes in the base of the horn at 90 degrees to the reed and rushes past it and exits the bell. The reed is about the thickness of an aluminum pie pan and vibrates against a 'donut hole' as the air is being drawn through the donut hole. The reed on the Hadley is thinner and is easier to drive at lower pressure and lower air volume than the Grover.
*Machining-- The Donut hole is a casting and appears to be machined to a higher degree on the Hadley than the Grover,which looks like simply cast and then plated
* Reed pressure-- The reed must be held against the 'donut hole' of the venturi and this is where the horns differ the most. The Hadley is held close to the venturi by the back -up plate [the back of the horn] with only a machined-in tolerance. The Grover is held in place with a spring pushing against the reed. BTW this is the reason the reed is thicker on the Grover-it has to be stiffer to withstand the constant spring pressure and increased wear this would generate.
* Volume and sound --All three horns were pretty much similar volume if you put enough air to them. As you bring the pressure up,there is a squeal,then a soft tone ,then louder and louder with increased pressure. A little synthetic grease between the reed and the venturi makes the tone louder and easier to drive at lower pressure. IMO, the Grover sound was a little more ''breathy'' than the more solid sound of the Hadley.
* Valves -- the pull valve on the hadley was more beefy,but no idea if that makes it better
* price-- all three horns cost me $25. 00 :-laf .
