James,
Are you speaking about diaphrams? If so, go to NWTF's website, listen to the purr and cluck and try to imitate them with your natural "voice". This way you could call them with the slate, then as they get closer, use your "voice" to bring them closer; without having to move a 'see-able' muscle. I did this for several years before I was able to confidently use a diaphram call.
To purr, natural voice, is akin to gargling, varying the opening of your lips and vocal cords. Clucking is acheived by 'popping' my tongue OFF the roof of my mouth, varying the amount of air applied and using my vocal cords to achieve the pitch wanted. Don't worry about being to loud with these methods; unless you have huge lungs and a huge mouth

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Good luck this year!