Here are the basic concepts:
· Any hole larger than 7” is like having no head at all on the drum.
· A 7” hole creates the feel of a one-headed kick drum, feeds more beater attack direct to an audience and provides some of the tone of the resonant head. Further, it’s easy to position a mic and change internal muffling devices, if used.
· A 4-1/2” or 5” hole, or even 2 such holes, offset, allows some relief for rebound control of the kick beater, contains more of the drums resonance so that the resonant head is more pronounced in the tuning of the drum. A 4-1/2” hole is difficult to get large mic’s positioned within (but can be done) and/or internal muffling altered.
· No hole, very resonant, creates more bounce or rebound from the kick beater. It can become difficult to get the “slap” of the beater and resonance of the drum both when miced with one microphone. The muffling remains inside. The resonant head is very predominant in the overall sound.
There are usually four reasons why drummers want a hole (or multiple holes) in the bass drum:
· It looks cool.
· They do not like the feel of the beater on the batter head surface, it bounces as a result of not enough air relief.
· They need to mic the drum from or capture the sound from the inside.
· They want more projection without using a mic (less bass impact, more beater attack presence).
For those who want it because it looks cool, there is an acoustic impact on the sound by placing a hole or holes in the resonant side. By acoustic impact I mean that the removal of head material does affect the bass portion of the note coming from the drum.
Allot of the “bass” portion of what you hear is based upon the surface area in the center of the drum. That surface area is a diaphragm working much like a speaker radiator might work, in that it will aid in moving air. Remember that pitch is dictated by the tension and the surface area in movement. So if you remove a large center portion, you lose a large portion of the bass reinforcement that gets emitted by the heads movement and tension usually has to increase to compensate for the removal of the center area. Adding holes does not increase bass content as might be the case on a tuned vented speaker cabinet would.
all from this excellent web site http://home.earthlink.net/~prof.sound/
a drum tuning bible, i would recommend everybody to read/download/print this.