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Young Croc
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    Posted: 03 December 2022 at 12:00am
I don’t think Rog uses the forum anymore  
This is a 14 year old thread aswell. Smile
Originally posted by Lammbock Lammbock wrote:

Hallo Rog,

I`ve found this thread on a research we are doing at the moment to get benchmarks concerning subwoofers, their freqeuncy responses, spl etc. Have you measured the Stasys X subwoofer with 2.83V ot 2V as an impedance correction due to 1W@1m. Do you have a waterfall or burst decay plot for the subs?

An answer would be really nice, either here as a pm.

Thank you in advance, greetings Marcus
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Hallo Rog,

I`ve found this thread on a research we are doing at the moment to get benchmarks concerning subwoofers, their freqeuncy responses, spl etc. Have you measured the Stasys X subwoofer with 2.83V ot 2V as an impedance correction due to 1W@1m. Do you have a waterfall or burst decay plot for the subs?

An answer would be really nice, either here as a pm.

Thank you in advance, greetings Marcus
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http://news.harmony-central.com/Product-news/Fohhn-Announces-the-PS-9-Subwoofer

this one and the martin audio ASX ... 152db they write there ... has anyone an idea how this is possible ?
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ceharden View Drop Down
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Ok, the mass/spring analogy is fine, in a basic helmholtz resonator (blowing over the top of a bottle is a good example) you have the mass of the air in the neck and the spring of the volume of air in the bottle.

However it's not quite that simple because the tuning is related to the area and length of the port and what you're actually interested in is the momentum of the air.  You can get the same tuning from a long wide port (large mass of air) and a short narrow port (low mass of air) because although the larger port will have a larger mass of air it will be moving slower.  Have a read up about Helmholtz resonators.

Yet again I'm really annoyed I must have thrown out my uni notes where we did the derivations from first principles of driver parameters, enclosure tunings etc.
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Old Croc
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did someone just mention SPRING COMPLIANCE?
 
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Old Croc
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Originally posted by ceharden ceharden wrote:

I think the point tb_mike is making is that sound waves behave very differently to just a flow of air

Yes but at low frequencys like the 30Hz tuning of the stasys X port the wavelength will be something like 11 or 12 meters, so i would say that for the purpose of my drawing at the top i would have thought that picturing a quick puff / blast of air would be sufficient.
 
(this conversation is very quickly rising above my head LOL)
 
All i was thinking is that a chamber acts as a spring and a port acts as a mass (is that right or wrong?) so to make a port have the same mass as a larger port you would need an intermediate chamber (to add mass) but somehow stop it from adding any "spring"/compliance....
 
....oh i dont even know what im on about anymore Wacko
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I think the point tb_mike is making is that sound waves behave very differently to just a flow of air.

Here's my take if I can explain it properly.  Now we all agree that what we're dealing with are driven resonant systems, specificially helmholtz resonators.

In the case of the StasysX the rear chamber isn't large enough to properly support a resonance at the tuning frequency required/ports required would be too big etc.  In fact a few years ago I tried to build a cab with a port of almost the same volume as the cab.  Although the maths said it would resonate where I wanted it, there just wasn't enough air in the cab to support the resonance in the port.

So, instead you add another chamber on and tune that to the frequency desired.  The driven part then comes from a port to the rear chamber containing the drivers.  Now I don't know how the tuning would work regarding the port between the rear chamber and the 'port chamber'.

I think it would be interesting to draw an electrical equivalent circuit to the StasysX, I suspect that the rear chamber porting arrangement would appear as a Pi network LC low pass filter.
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Old Croc
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Is this not correct?
 
Volume of air in cabinet = spring (compliance)
Volume of air in port = mass (inductance)
 
Picture something like an 8th order bandpass design with 2 chambers (one on each side of the driver) and both chambers are ported into a 3rd chamber, are you saying that (as compression is only at the source) the air in the 3rd chamber does not act as a spring of air?
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Old Croc
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Originally posted by Jake_Fielder Jake_Fielder wrote:

Originally posted by tb_mike tb_mike wrote:


Jake
you didnt include wavelength of sound and object involved. At bass frequencies youl find they do the same thing.
 
Sorry, i dont get you? When i drew those pics I was just picturing a blast of air and whether or not it would compress.
 
 
 

compression only occurs at the source.

What I see are filters/EQ in your diagram. I could be wrong.


Edited by tb_mike - 19 April 2008 at 8:12am
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Old Croc
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From the Unity horn thread in New Projects...

Originally posted by Steve B Steve B wrote:


If you consider a horn with zero flare rate, i.e. a tube, and connect a side chamber to it you end up with something like a silencer box on an an exhaust. The electrical analogy is an inductance and capacitance in series, in shunt with a line. Transmission will dip at the resonant frequency.
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My uni Library doesn't have Olson in it....But as soon as I get back I'm geting out 'Acoustics  - Beranek' I believe it was a lot of acoustical/mechanical/electrical equivalents in it, a lot of discussion recently has made me really understand them more!
 
 
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Old Croc
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Originally posted by tb_mike tb_mike wrote:


Jake
you didnt include wavelength of sound and object involved. At bass frequencies youl find they do the same thing.
 
Sorry, i dont get you? When i drew those pics I was just picturing a blast of air and whether or not it would compress.
 
 
 


Edited by Jake_Fielder - 17 April 2008 at 12:19pm
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