Buy a hand held scope or use your ears and pay attention to the sub and do it right. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
There are other ways to tune an amplifier that are valid. I'm not going to debate this with you because it's been discussed a thousand times. OP was looking for a shop, and he didn't come back to reply. Let this thread die.