Drums suck!

Andy

Honorary Member
Completed a piece of R&D this morning that I've been working on for some time. Without some pretty advanced diagnostics, I can't take it any further, but I don't need to - I've got ears. What I haven't got is complete answers, just pieces of real world evidence & some theories.

Now here's the really crappy bit, I'm not going to share most of the detail with you, it's too "hard won", & you don't really need to know anyhow. I will leave you with these basic thoughts though:

Venting - many of our drums aren't vented. In most cases, they benefit positively from this, except in some thicker/more rigid shell forms. I set about building some test drums from ply shells (mostly Keller, if you're interested, but also a couple of Pearl & an old Gretsch 3 ply too), removed all variables, then compared them to several of our solid shell forms in both snare & tom formats. The results were very revealing, with some startling differences in performance affects. In almost all cases, the ply forms were better with venting, as without, they tended to choke both dynamically & in terms of useable upper tuning range. The common thread seems to be rigidity, but I'm not completely sure.

The biggest deal for me is the missing half of the equation, drums suck as well as blow. The theory is that a vent is necessary to dispel air pressure & allow the drum to "breathe", but what if the vent can't suck air back into the drum fast enough such that it doesn't put the brakes on the head movement. Does that cause a phase delay between the heads? I found evidence that it may well be the case. There's no point in breathing out if you can't breathe in. I'm convinced that the combination of more readily excited shells with a larger resonance amplitude in some way mitigate choking on some unvented drums too, but I can't prove the mechanism.

This is all nerdy stuff that nobody really needs to know except the drum builder. It's not a better or worse factor, it just is. Drums do really suck though :)
 
From an acoustical/mechanical perspective, the mass of enclosed air acts like a spring (since air is not compressed easily and therefore work has to be done on it). As such, it can be thought of as a device that alternately stores and releases energy in much the same way as a capacitor behaves in an electrical circuit. It is quite possible therefore that you could see a phase delay (not saying that it's appreciable, just that it could exist). The proof is fairly straightforward: position two mics close to the batter and reso heads, say an inch off of each, precise positioning is imperative, and look at the waveforms on a digital sampling oscilloscope.

The idea of the air mass and the associated venting affecting the sound is not at all odd. It is this very idea that is behind vented (AKA ported) loudspeaker systems where the mass of the air in the vent is used to "tune" the enclosure/driver combo to extend low frequency response (at the expense of a few other parameters). In this case, drum vents would be too small to have the same effect and they would probably be best modeled as a resistive loss (reducing the effectiveness of the vent for a loudspeaker).

The thing is, I don't see why a drum vent would behave in an asymmetrical manner. It should "suck" as much as it "blows". Not unless you attached some manner of "one-way doggie door" to it. (A little flap might be an interesting means of controlling damping.) A vent can be too small and be driven into turbulent flow (making a noise and reducing effectiveness) but that would be a two way street.


You have opened up a series of questions that I would like to explore in lab (phase issues, volume and velocity of air passing through a vent, etc.) I wish I wasn't so busy at work right now or I'd bring a tom in and do some tests. Got me curious though.
 
Just thinking from the shirt sleeve, I can think of ways to measure the phase change from the batter to the resonant head. Of course you can measure it in both states with the vent and without the vent. There are Piezo disk vibration sensors that you can hook up to the heads, then use an oscilloscope, watch and record the vibration, make adjustments for the amplitude being different from the batter to the resonant heads.

I guess, even using two microphones would show the differences, but that amplitude differential may be significant and hard to control and isolate.

Also another way would be to use two vent holes, one at the bottom and the other at the top. Of course this method could only measure the effect when using the vent holes. Use adjustable check valves on both holes, and set one for intake and the other for exhaust, then use flow meters between the two and watch and record the phase shift. In this method the amplitude should be closer to the same, and the air movement would be measured instead of the head vibrating as in the above experiments.

Placing vent holes at different locations using two vent holes, may reveal enough data to mathematically predict the optimum location for the vent hole in any drum based on a few experiment parameters such as depth of drum, diameter, heads, shells.

If you were to combine the two experiments using Piezo and flow, then you can check the difference between the head vibration and the gas flow.

Intuitively, I would think there would always be a phase shift between the batter and the resonant head no matter how small, and that would be dependent on the speed of sound in an oxygen nitrogen gas (air). So, just for fun, what would happen if you sealed the drums and filled them up with helium. You can tune the drums higher by the mixing of helium to air ratio. Or, you can tune them lower by filling them with a carbon dioxide to air ratio.

Anyway, thanks for the thought experiment.
 
When I put my finger over the vent hole of a drum, then strike it, why don't I hear any difference? The science may say this and that, but if I can't hear a dif, it means nothing. Right?
 
I hear the difference on a snare, of course with the snares off, and also on my 10, and 12 inch toms, but I can not hear the difference in my 13 tom and 16 floor and bass drum.
 
Very interesting drum science !

Let me get this straight.
My drums suck. But buying a set of Guru's won't help.
Because Guru drums also suck.

.
 
For some time I have also tried the "cover the vent" test to hear if there is a difference. I have done this on snare drums, snares off and on. No hearable difference to me. Ronn Dunnett did not vent his snares for a long time. His thoughts are also that the sealed system allows quicker response between the two heads. I tend to agree.
 
I found that I needed to add vent holes to the toms of my 65 Slingerland kit in order to tune the drums better for Jazz. The kit is in Jazz sizes. 18, 12, 14.
I found this by accident. The 12" tom had an extra 1/2" hole in it from a previous mount. I blocked the hole with a tight plastic plug and I didn't like the drum as much as I did before I plugged it up. I installed a vent in the 12" tom where the hole was and I then installed a vent in the 14" FT.
I get less unwanted overtones while playing fast rolls at tight tunings with the vents. Sympathetic snare buzz is also reduced slightly.
 
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From an acoustical/mechanical perspective, the mass of enclosed air acts like a spring (since air is not compressed easily and therefore work has to be done on it). As such, it can be thought of as a device that alternately stores and releases energy in much the same way as a capacitor behaves in an electrical circuit. It is quite possible therefore that you could see a phase delay (not saying that it's appreciable, just that it could exist). The proof is fairly straightforward: position two mics close to the batter and reso heads, say an inch off of each, precise positioning is imperative, and look at the waveforms on a digital sampling oscilloscope.

The idea of the air mass and the associated venting affecting the sound is not at all odd. It is this very idea that is behind vented (AKA ported) loudspeaker systems where the mass of the air in the vent is used to "tune" the enclosure/driver combo to extend low frequency response (at the expense of a few other parameters). In this case, drum vents would be too small to have the same effect and they would probably be best modeled as a resistive loss (reducing the effectiveness of the vent for a loudspeaker).

The thing is, I don't see why a drum vent would behave in an asymmetrical manner. It should "suck" as much as it "blows". Not unless you attached some manner of "one-way doggie door" to it. (A little flap might be an interesting means of controlling damping.) A vent can be too small and be driven into turbulent flow (making a noise and reducing effectiveness) but that would be a two way street.


You have opened up a series of questions that I would like to explore in lab (phase issues, volume and velocity of air passing through a vent, etc.) I wish I wasn't so busy at work right now or I'd bring a tom in and do some tests. Got me curious though.

Jim, I did not see your post while I was writing mine, so that although it appears that I was copying what you said about the microphones, it was not intentional.
 
Just like the human ear has a eustachian tube to normalize pressure with atmospheric within the middle ear so the tympanic membrane can respond. If your eustachian tubes are blocked you feel like your are listening with your head in a drum-that too and you will often extravasate fluid into your middle ear from the vacuum formed.
I wonder if having smaller more numerous symmetrically place vents would affect it, and the position relative to batter and resonant heads considering depths of shells? Theoretically it should but I don't know if the human ear would distinguish it?
 
Just like the human ear has a eustachian tube to normalize pressure with atmospheric within the middle ear so the tympanic membrane can respond. If your eustachian tubes are blocked you feel like your are listening with your head in a drum-that too and you will often extravasate fluid into your middle ear from the vacuum formed.
I wonder if having smaller more numerous symmetrically place vents would affect it, and the position relative to batter and resonant heads considering depths of shells? Theoretically it should but I don't know if the human ear would distinguish it?

Tthis brought to mind the concept that Evans has with their Genera dry heads. There are 20 equi-distant very small vent holes around the head which help dry out the overtones.
 
For some time I have also tried the "cover the vent" test to hear if there is a difference. I have done this on snare drums, snares off and on. No hearable difference to me. Ronn Dunnett did not vent his snares for a long time. His thoughts are also that the sealed system allows quicker response between the two heads. I tend to agree.

My brain tells me that with the vent there would be more response between the heads but not any faster than non-vented. The reso head would move less vented but not necessarily faster since the distance is still the same between heads. my 2 cents. I have seen drums with 6 or 8 1.5 inch holes around the perimeter. That would suggest the reason would be a lot delayed.
 
Simple solution: We all need to switch to concert or roto toms!!!
 
Jam an earplug in there and see how it goes.

I haven't paid much attention to vent holes or how they work. I have a Ludwig snare that one vent hole way at the top of the shell and my Sonors all have two vent holes. Two badges. One on each side.

Do most toms have two vent holes?
 
Very interesting drum science !

Let me get this straight.
My drums suck. But buying a set of Guru's won't help.
Because Guru drums also suck.

It doesn't really matter... my playing suck on any drums, vent or no vent, it's so bad it really sucks... so, my drums suck and I suck... we kinda choke each other to death, but sometimes we get along just fine, we don't suck at all... it's like a bit of fresh air, it makes me scream of joy so loud until I'm out of breath (sigh)
 
I agree that drums do suck, but they can suck less if they have silver sparkle wrap under good stage lighting.
 
I've got some Yamaha BCAN drums. The 16X16 Fl. tom has 3 vent holes on the reso end,and the 18x20 has 5 (4 reso and 1 batter). The 14x14 and all the smaller toms have 1 near the reso end. I can't remember what Yamaha claims about the extra holes, but I do remember reading in their adds, that there was a reason for them.
 
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