I think you´re contradicting yourself when using your analogy with the balloon burst in a closed (at one end) tube since this would result in an omni directional source at low frequencies.

Let’s focus on the first mode (01) of the drum head, presumably the fundamental of the drum somewhere around 40-50 Hz or so.

Here´s my take on a single head kick drum (only speculation but at least something):

At a low frequency (mode 01) of a single head open kick drum, the membrane should act as a dipole (since there’s no infinite baffle) for low frequencies and the “tube”, acting as a finite baffle, should actually makes the drum more omnidirectional at some frequencies than if it was not there since the tube separated the two opposite polarities of the dipole form each other somewhat at least for higher bass frequencies. At low frequencies, this separation is too small to prevent dipole behavior but might still attenuate (to some extent) the first positive cycle of the pressure wave in front of the drum since the negative pressure wave from the beater side will interfere more or less (depending on frequency and dimension of the shell) with the first positive front pressure wave after it has traveled around the finite baffle (the shell) so the second (negative) half of the cycle might be the one with the highest peak amplitude (assuming the receiver is positioned in front of the drum).

<SNIP>

When something hard and with weight behind it hits something large and flexible, the latter will move in the same direction. As the latter is a quite large membrane enhanced by a resonant tube, the result is a blast of high pressure originating in one place and travelling predominantly in the obvious direction. Per se directional. I believe it is this blast which stimulates the room resonance (and it's complex feedback into the source), in the way which is audible in the audio file I provided. Mere rotation of the drum caused this massive change in LF, I call this directional. This is to my mind incontrovertible, and well known to studio practitioners. Simply listening to the file is self evident proof. Reality does exist and is easily observed.

<SNIP in an attempt to get things back on track for the OP>
DD

I'd rather not have to close it...can you not just agree to disagree and offer advice to the OP based on your own philosophies, and let him choose? How much does this affect the original question?

No problem, once the studio is finished let me know. If it is possible to visit I would love it, I have been in other studios Marcelo built and they are really nice.

Last shot at this:


A pulse source in a tube closed in one end.

Sure André, you are more then welcome to drop by anytime!

OK guys.

Any more talk of kick drums/point sources without actual audio samples and you're booted off the thread...it's not helping the OP any and I'm pretty sure you'd agree if you were actually both in the same room with a kick drum and measuring equipment!

If Rod does find time to do his test (and I agree, it's the interaction with the room that's important, not "free field", since that was the original premise for the OP on this thread), we can return to the discussion.

In the meantime - any help for the OP?

Thank you and goodnight!

That just might work psycho, well done.
Rod may not live in a recording studio as I do, that is why I did the test and provided the audio file. 10 minutes work in the hope of world peace....;-)
Note the microphone was as far as possible from the drum and on a boundary, PZM style.
Thus this is a recording of drum/heads/room interaction.
Rod are you satisfied that this test demonstrates the directional nature of kick room interaction? I would be quite willing to do another or different test if you wish?

DD

Why not do the math?

Sabine equation in a reflective room & Eyring in an absorbent room?
This is what I did when I built my studio.

DD....... in my mind this brings too much of the "room play" into question......

Seeing as what we are discussing here is (essentially) "what is the acoustic LF plot of a bass drum compared to a speaker" - in a perfect world I would want to perform the test in an anechoic chamber - which is why (in my mind anyway) the suggestion was made to test outside....... as close as one is going to get (to anechoic conditions) without taking a trip and investing some hard earned cash to visit a certified lab (which is simply not worth the time, energy or investment - (for me anyway))

You could (however) produce what is essentially the same results (inside a space) by simply providing tests closer to the subject drum in question - and gating out everything after the initial impact - which would (essentially) take the room "out of the equation." - or at least it would up until the point where you run into a room boundary

For the purpose of this test let's say a pair of matching mics simultaneously capturing the data - one on the resonant side of the drum, one center-line on the body of the drum (at a right angle of course) ....... the resonant mic set at (say) 3' from the head - the other beginning at 1' from the body and moving (for each test) a distance of 6" away from the sidewall of the drum - if I found a distance that suggested a strong shift in amplitude I could always fine tune those adjustments to focus on the shift.

The larger the space (of course) the better the chance to gather meaningful data - so I would probably do this in my garage which is roughly 28' wide - 26' deep with a roof that runs from 8' on the back wall to about 14' on the front wall....

I live in a very quiet neighborhood - and given a calm day (so that wind did not become a factor) I could always run the test outside - but believe the garage would suffice for our purposes...

I could also run the test in reverse (leaving the mic on the side wall constant - while moving the one capturing the batter head further away from the drum - there would have to come a point of parity at some distance.. although testing outside I might well run out of property before I find it....... (I have about 4 1/2 acres - but only 1 acre of that is cleared - and trees would certainly skew the results )

Anyway - this is how I envision a test of this nature being performed with the resultant data being viewed as unbiased/valid.......

Rod

Please explain........

How would you derive the properties for the acoustic radiation of a bass drum in this manner?

Or are you speaking of something different with this reference? Perhaps back to the original question raised by the OP (I imagine as I reflect.........)

Rod

Guitarz,
sorry I did not observe the later pages of your studio diary..

The studio looks really beautiful

May I ask what kind of "reveberation figure" has the designer opted for?

Best

Ake

Thanks for the response Rod. In reply to the OP. I made the suggestion of using several tone sources throughout the room, including drums. One of these drums as commonly used stimulates the room quite differently with direction, thus I included this (IMO interesting) caveat.
This statement was directly contradicted so I provided waveform evidence of the asymmetry of a Kick Hit, and eventually, a recording of the room being stimulated by the same drum in two different directions. i.e. A continuance of my reply to the OP's topic. As such I see my work as done here. The audio speaks for itself don't you think?

The notion of comparing the Kick stimulus to others, real or hypothetical, is not mine, nor on topic here. I am afraid I cannot envisage any modicum of similarity between a resonant shell with two different types and tuning of heads, with a hole in one, and a single highly damped speaker cone.
Also gating out will prevent seeing LF developing. No cake and eating it I'm afraid.
So regarding testing that, I'm out, but if you do, vaya con dios and plse do share in a new thread.

As earlier, the room feeds back into the drum/heads. A close recording will show the increase in LF also. I could run the test again with a close mic if there is any doubt of that. But let's remember, my whole point in introducing the Kick drum source was to stimulate Room Decay at LF. i.e. OP's Topic.

I hope this has helped guitarz, and yes indeed nice kicks. I love my Orion, and if I remember correctly, earlier waveform was a Yamaha PHX. And yes, LOL, I did mix up the threads, I have since corrected the post to address your situation, thanks.

DD

What do you mean reverberation figure? The reverb time?

I asked him for a pretty live room for drums.

Thanks for the help Dan Dan, will try the kick measurement when I came back from holidays.

Will post the results of course

Yes, reverb time

Ake

Was responding to the OP.

Thanks,

Rod

This thread has kind of gone off the tracks, but wanted to know if you have any recordings from the room itself. It might help to do that and evaluate what "YOU" think. I would do a vocal, drums, acoustic guitar and or what ever to see if you "LIKE" the tone/sound.

I will fo that for sure really soon. Just went for a little vacations till the middle of the month

Sent from my GT-P3110