Drum Sound Shield

[FLZapped]

Originally Posted by Les

Bruce,

I think what Chad's saying is a few points of a dB, ie 0.2, 0.3 above what was originally there.

So, if the drums without the shield is 101dB then at best, with a perfect parabola it might increase to 101.2dB or 101.3dB.

But, a drum shield is not a parabola, even if it's curved. And the standard 5-6 panel drum shields are most assuredly not exhibiting the effect of a perfect parabola.

What the drummer is hearing with a shield is reflected sound. Reflected sound cannot be louder than the direct sound (assuming the source is closer to you).

So, the drummers snare for example would be about 2'-3' from his ears, but the sound bouncing from the shield would be, say 6' away. The sound has traveled a greater distance and physics dictates that sound would be less loud.

It still approximates a parabola, and therefore, the physics involved can be applied.

Yes, the reflected sound can indeed be louder when it is summed with the direct sound, otherwise, there would be no need for parabolas in the world.

-Bruce

[FLZapped]

Originally Posted by Brad Weber

The way I interpreted the comments, and what seemed to have been pretty clearly stated, was that a shield or enclosure may make what the drummer hears louder but does not actually make the drums themselves louder. The source levels remain the same.

No, the source is still the same volume, but you no longer have an isotropic radiator, either.

Originally Posted by Brad Weber

Ironically, one would think that any increase in perceived level due to the shield or enclosure would make a drummer play quieter, yet what was noted occurred seems to be that they did not do so and thus experienced an increase in exposure.

It does seem obvious that they would play more quietly, but the real problem is that they were unable to hear the rest of the band and were left to guess at what level to play at.

Originally Posted by Brad Weber

This indicates to me that either there actually was no significant increase in exposure, that the drummer may have been incapable of altering their volume or that they were intentionally not reducing the volume of their playing, perhaps in an attempt to get rid of the shield.

See above. This was already explained several postings ago.

Originally Posted by Brad Weber

My view is that while the problems noted may have been caused by the shield, there were also potential solutions other than getting rid of the shield and any potential benefits it might offer. I run across many drummers that have bad impressions of shields or enclosures caused simply by their past experiences being with poor application and implementation of such devices. Just another example of being the right solution and properly implemented being critical to something's success in any specific application.

It was the right solution for us. It has also been the right solution for other worship drummers in my area. An unexpected realization was that they didn't realize how isolated they were from the worship aspect of the service.

-Bruce

[[Director] drew ryan]

While the AES types can debate the physics all they want, there is the perception that the drums are louder regardless of measured spl. I have observed this perception first hand. Without the drum shield the volume of the environment, the size of the space, not SPL, dissipates more of the energy. Put a shield in front of the drums and the energy is reflected back at the drummer. This creates the perception that the drums are louder because the volume of the environment just got a lot smaller.

Really, the best use of a drum shield is the reduce the SPL from the drums for the performers on stage and to keep the energy of the drums out of the microphones that vocals are using. An ISO booth is going to be a much better instrument for reducing SPL of the drums in the room.

[FLZapped]

Originally Posted by Gracetech

Actually the source will always be louder so the difference of the reflected sound will come within a few negative points maximum of the original source. Example: source is 100dB reflected level will usually be within -3dB possibly as loud as 99.9dB.

crt

This statement then nullifies the whole idea of gain from a parabola, or gain from any reflecting structure (Like a corner reflector) which folds back and sums the energy of an isotropic radiator. Where do you think "room gain" comes from with speakers placed in corners? Same exact principal.

-Bruce

[Brad Weber]

Originally Posted by drew ryan

While the AES types can debate the physics all they want, there is the perception that the drums are louder regardless of measured spl. I have observed this perception first hand. Without the drum shield the volume of the environment, the size of the space, not SPL, dissipates more of the energy. Put a shield in front of the drums and the energy is reflected back at the drummer. This creates the perception that the drums are louder because the volume of the environment just got a lot smaller.

I don't think that anyone is arguing that the drums may be perceived as being louder or that you may not even measure an increase in SPL at the receiver, it's purely the idea of people saying "the drums are louder" when, as you note, what they really mean is not that the drums themselves are louder but that what they hear is louder. So it is just clarifying that the drums aren't actually louder and rather that it is the reflected/indirect sound from the shield that causes any increase.

A detail, but unless it is a full enclosure rather than a shield then the volume and space into which the energy is dissipated does not change. In the case of a shield any increase in SPL or perceived volume is a result of local reflections and not of a change to the larger environment.

[Gracetech]

The only way that a parabolic could raise the sound level higher than the source would be if that parabolic was perfectly shaped and the frequency at which was reflected at the culmination point was within a 1/4 wavelength of the original source sound....Do you see the problem yet?

Only at the culmination spot would that sound be louder than the original source. Since with something the sound of a drum kit with multiple sources the culmination location would be all over the place so it would be hard to say that the kit is louder in any one location. You might be able under perfect circumstances to say this part of the kit is louder than it was but not the full kit.

With reflections time is working against you for coupling sound waves not to mention the direction of the sound wave.

In the real world you have a 99.9999999999999999999% chance that the source sound off of the kit will be louder than any group of reflections. Reflections will thicken the sound because of the early reflections but timing works against the coupling of the reflected sound and the original sound.

Now if you had a Concrete parabolic then you would have a good chance to see coupling in action. With a concrete parabolic it could bounce the lower frequencies instead of just transmitting them and because they are longer wavelengths then they could possibly make it to the culmination location within a 1/4 wavelength and headed in the same direction.

crt

[Les]

Originally Posted by FLZapped

It still approximates a parabola, and therefore, the physics involved can be applied.

Yes, the reflected sound can indeed be louder when it is summed with the direct sound, otherwise, there would be no need for parabolas in the world.

-Bruce

No, the physics don't apply. I don't see how a drum shield really approximates a parabola.

I can take a bunch of trap boxes fly them sideways and call it a line array, heck it might even approximate the look of a line array. But, just because it approximates it in looks does it mean that the physics of the line array apply? I wish, but it doesn't.

Even then, a parabola is spherical but a drum shield is not. It's a series of "curved" panels (and even then it's not a perfect curve!).

So, I'm failing to see how a 2D curve, that's not even a perfect curve, could match the physics of a 3D perfectly shaped parabola.

Also, you're right that you could have 2 sounds couple together to in effect become louder. But, take a look at the reality of that happening and you'll quickly see that practically this isn't going to happen, and it's certainly not going to happen across the frequency spectrum. The timing, phase, etc, would have to be almost perfect... I don't see it happening with a drum shield.

[Les]

Originally Posted by FLZapped

This statement then nullifies the whole idea of gain from a parabola, or gain from any reflecting structure (Like a corner reflector) which folds back and sums the energy of an isotropic radiator. Where do you think "room gain" comes from with speakers placed in corners? Same exact principal.

-Bruce

It's late and maybe I'm not thinking clearly, but wouldn't room gain (corner loading, boundary loading, etc) effect the lower frequencies and have greatly diminishing effects as we move up the frequency charts?

[Les]

Originally Posted by FLZapped

It was the right solution for us. It has also been the right solution for other worship drummers in my area. An unexpected realization was that they didn't realize how isolated they were from the worship aspect of the service.

-Bruce

It may very well be the right solution for the drummer/band and more preferred to them, but you typically don't use a drum shield for the drummer or the band, you use it because it's a tool that ultimately benefits the audience/congregation and benefits in their worship.

Whether that's because the drums are too loud on their own, or they bleed to much into other mics, etc doesn't really matter. You use one because something is needed to be done and that is a tool to use.

If I don't need a shield then I don't use a shield. I prefer to not have one, however, they sometimes become necessary and/or a good tool to utilize to solve another problem.

And it can happen that they feel isolated and that's a legitimate concern, but with correct implementation of both the monitoring and visualization elements much of that can be overcome.

The same argument about isolation can be made for in-ear monitors as well. You can feel isolated in those, but there are tips/tricks to lessen that feeling.

It sounds to me after re-reading the threads that what you needed was a screwdriver, but you were using a hammer. Once you use the right tools then everything goes much more smoothly.

I understand that it may not have worked for you and that you prefer without the shield, and that's fine. It's just another tool in the belt.

[Brad Weber]

Originally Posted by Les

It's late and maybe I'm not thinking clearly, but wouldn't room gain (corner loading, boundary loading, etc) effect the lower frequencies and have greatly diminishing effects as we move up the frequency charts?

Not in the truest sense as theoretically space loading occurs when the source is physically located at an infinite boundary and affects all frequencies. However, what many people think of as space loading for real world sources typically relates to a source located near an often limited boundary, and in the case of side walls and floors a boundary somewhat shared by some of the listeners. This creates a much more complex scenario that is source location, receiver location and frequency dependent.

And while the effects for a drum shield would likely differ with frequency, they would not necessarily diminish. Remember that even at high frequencies you would still get some frequencies that acoustically sum. At the same time, while I agree that the typical drum shield is not a parabola, however it very well could provide multiple reflections with different arrival times to any receiver point. Add these two points together and at a point you likely get multiple reflections that arrive at different times with each summing at different frequencies. So while you may get a larger increase at lower frequencies, it is still possible to get increases at higher levels.

Basically, think of the combfiltering resulting from the direct sound and multiple reflected paths. The sound from paths A and B may be 180 degrees out of phase and cancel at one frequency but the sound from paths B and C may arrive in phase and sum at that same frequency. Get enough paths with different path lengths and the result is multiple interactions with an overall increase.

FWIW, we need to be careful of the references to specific wavelength or phase differences as one must account for the relative signal levels and any resulting gain. For example, two sine waves of the same level with 90 degrees (1/4 wavelength) of relative phase sum with +3dB gain, however the same two signals could have up to 1/3 wavelength difference and still have some net gain. Conversely, if the two signals were of different levels then the resulting gains and losses might be lesser. You could have two sine waves with sufficient level difference that the net result is effectively the higher level signal regardless of the relative phase.

But beyond all the technical issues, I think Les hit on the bigger issue. In many churches, as well as other performance spaces, there are often two acoustical goals related to the performers on stage. One goal is providing an appropriate environment for the performers to work effectively while the other is to provide an appropriate result for the listeners. Sometimes achieving one goal may conflict with achieving the other. The challenge in those situations is to determine the best overall balance and compromise for the church.