Any of you Hartke owners out there have the the spf switch set to the off position? Its supposed to block out harmful sub sonic low frequencies to protect your cabinet. Ive been wanting to set it to off to see if it will alter my tone any, but im paranoid to for fear of blowing my 4x10 cab. If I had a 15 or 18 to go with it Id have done it. Any of you 4x10 or even 2x10 guys ever play with that switch. If so what were the results?