Re: Cutting a hole in the bass drum...How big, etc...
I found this on the net:
Holes in Your Head or Not
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.
Thicker heads tend to stay in motion longer. With loose tension they will vibrate at a lesser rate, which all translates into lower pitch and a longer resonance. This assumes no internal muffling, or other devices to make the head stop its vibrating motion sooner.
Some want the different feel created by having air relief but still want maximum bass affect. As you remove more head area you trade off deep bass for a different feel. A solution is using smaller holes placed around the perimeter of the head. If you want the mic to capture sound from inside, you either have to resort to say the May mic system or revert to a larger hole to get the mic into the drum as you require. What you ultimately do will be based upon the balcance of all the factors that are important to you.
It is the area of the hole that counts. Where it is located matters little for the affect on sound (as long as it isn't on the batter side). If you want maximum tone out of the head, then the size of each hole needs to be in the 1-2” size, and they need be placed closer to the perimeter, but not placed so the edge of the hole is closer than about 1” to the break for the bearing edge. In other words, for the best tone, you need to keep as much of the center of the resonant head intact as possible. And again, it’s not the number, it’s the area displaced that can make a big difference and where that area is removed. You can make any number you want, in the following example to illustrate the concept we'll make two holes to represent the maximum area displaced by a common 7 inch hole.
The math is simple. We first need to calculate the area of a 7” hole. To do this we use the formula Pi(R˛). So first find half of the diameter of the 7" hole (the radius), which is 3.5”. Now multiply that times itself. So 3.5 x 3.5 = 12.25. Then take this result of 12.25 and multiply it times Pi, which is 3.142. So we now have 12.25 x 3.142 = 38.5. So the area of the 7 inch hole we started with is 38.5 square inches. This 38.5 sq. in. is important. We will simply round it up to 40 square inches, cause close is enough.
Now we can use any number of holes as long as is does not cumulatively exceed 40 square inches of total area. Yet at the same time does equal 40 square inches. This will be the same air relief as having one 7” hole and the end result will be more center surface are and a stronger bass affect.
Now take the 40 sq. in. and divide by 2, 3, or 4, what ever. Let’s say you want 3 holes. 40 ÷ 3 = 13.33. So 13.33 is the maximum area for each of the 3 holes. So we now take the 13.33 ÷ Pi (which is 3.142) = 4.24. Now extract the square root (from a math table or calculator) of 4.24 and you get 2.06. So 2 x 2.06 = 4.12. This means 3 holes of 4.12 diameter will give the same acoustic result as a single 7” hole.
Let’s say you have1 hole of a diameter of 4.5”, a common bass drum hole. Let’s compute the area displaced by that single 4.5” hole. (Math: 4.5 ÷ 2 = 2.25, THEN 2.25 x 2.25 = 5.0625, THEN 5.0625 x 3.142 = 15.9). A 4.5” hole has an area of 15.9 sq. in.
In the above example we show that if we were to use 2 holes of 4.5”, the cumulative affect will have less area (31.8 sq. in. total) than that of a single 7” hole, whichj we learned was about 40 sq. in. The 2 – 4.5” holes will therefore be a little more bass heavy than will a head with a 7” hole because they do not remove as much of the heads surface, although you probably will not hear it.
As the bass drum is equipped with a solid resonant head, it will always sound warmer or more bass heavy. The smaller holes are designed to allow relief yet still allow the resonant head to resonate. As you cut away more of the head there is less to resonate.
More large holes will make the drum a little louder and more present out front. Smaller holes around the perimeter gives better feel but the drum retains warmth.
So if you want more acoustic impact from the resonant head itself, create less “hole” area