Male cat yowling

I was wondering if anyone would know what to do to stop a male cat from yowling. When our females are in heat our male cat downstairs yowls for about 20 hours a day. I would think he would get tired of it himself. I have tried a few different things but it is just the way God made him I guess and he can't help it. Does anyone have any ideas. I am a breeder for 20 years and you'd think I would know everything by this time but I learn new things every day and have new experiences. It pretty much drives us nuts at night. My other males did not do that and that is why I have never experienced it before and he just started it this year. He is now 4 years old.
Spraying him with water gives him an eye infection so that doesn't work and shaking the can of pennies, that doesn't work, he just gets used to it. WE just have to shut our doors.

I think shutting your door is the best your going to do. Since calling for a female is a natural thing for them to do, you be pretty hard pressed to get him to stop. If he can smell them, he's gonna call. We have one that does the same thing. The only way to get him to quiet down is to make sure that (as much as possible anyway) he can't smell them. Do you hold you males in cages? If so you can use acoustics to keep the sound from traveling.

I'd get him fixed. Obviously, he's going to go thru this everytime a female is in heat. He's not your only breeding stud is he?

I would have him neutered as soon as possible, if he's had his litters that is. Fertile males do yowl, and spray and act very disturbing at times, that's their nature. Maybe Feliway would work, but I wouldn't bet on it.