Soundman2020 - Studio Design Forum

Very helpful - thanks guys!

Hi, I am not an expert in the physical aspects of acoustics. My complements for the details you try to bring in here. Hi Frans - thanks for posting your comments! I've been dormant for a while with deadlines and other projects picking up more momentum than I expected. I'm still interested in the ph...

Here are the frequency response curves obtained by varying the neck length of the "Hubble Space Telescope" (as I am calling this now huge assemblage of tubes) in 1/2" increments: HR 4in Pipe Flared - Different Neck Lengths.jpeg Resonance at the lowest frequency of 44Hz was achieved wi...

Ok now we are getting serious... HR 4in Pipe with Flared Couplers.jpeg This gives the orange frequency response curve (cyan is the previous test with a chamfered 3/8" hole in a pipe cap): HR 4in Pipe with Flared SPL.jpeg HR 4in Pipe with Flared Couplers Spectro.jpeg Recalling the strong resonan...

5710 note that one thing we like to do is to force the mode distribution into higher frequencies since those tend to be easier to mitigate with plain old absorption. so having the pipe create some harmonics higher up is usually easier to deal with in exchange for more reactance in the target freque...

Another way to visualize the striking effect of HR neck geometry is to look at the spectrograms in REW. The figures below are from the 3' length of 4" pipe. Here is the spectrogram for the 3/8" hole with sharp edges. You can clearly see the long decay tails for the two pipe resonances, but...

So there's a bit more progress to report (I really should have started a new thread). Based on what I've learned so far, I wanted to build something that actually had an acoustic effect at my room's nasty modal frequency around 44Hz. It didn't have to be the final practical solution, but I just want...

gullfo wrote:Qr Bbpost well, since we're going to down the rabbit hole.. fluid dynamics is a good start: https://en.wikipedia.org/wiki/Fluid_dynamics

Yes it could be interesting to play around in OpenFOAM with some of these hole geometries (with all the other rabbits lol).

5704 nicely done. i was going to mention "ported speakers" a while back ;-) :idea: Yes it seems like I've rediscovered "port chuffing" :geek: . This is said to happen at high SPLs in ported subs and is audible. Interesting that it crops up silently (unless you're a candle) in th...

If you've been following this thread, you'll have noted a lot of head scratching in regards to different Helmholtz resonator neck profiles (ie sharp corners vs flared vs chamfered etc). I found time to do a few more tests, and think there might be something to this. To recap, resonators with smoothl...

5697 as far as positioning - yes, targeting the modal points is more effective than (example) simple stacking into a corner -- where modes terminate is not as effective as a mid-point in the room to attenuate a length mode. however, depending on the room space, a 2ft deep box in the middle of the r...

Despite my ramblings about mass-spring systems and the failings of MDF boxes, they do appear to resonate as indicated by the "candle test". Apparently the candle effect is related to something called "vortex shedding" which seems to be more pronounced when sharp-edged holes are u...

5677 Would it be possible to compare the results with the same bottle, but with stoppers made from different material? One could be a "cork" made of mdf with a hole drilled through the middle. Another could be a plastic "cork", or perhaps one of those rubber stoppers with a hole...

I added a tiny bottle, which has a neck volume similar to that of the MDF perforations. It resonates like crazy around 360 Hz (can get a nice pure tone blowing across mouth, and it interacts with a frequency sweep as shown in the red curve above).

I've been reviewing the physics on harmonic oscillators (driven, damped, etc) and one point came to mind that may or may not be relevant. Helmholtz resonators are equivalent to a mass-spring system, where the mass is the air in the neck (with corrections) and the spring is the compressible air in th...