Oops

Re: Oops

:-)... I know a guy who designed power amp heat sinks and he used cigarette smoke to help see air flow patterns inside power amps and power modules.

You might want to be careful about putting a lit cigarette down inside a speaker cabinet. Maybe something like an incense stick?

JR.
 
Re: Oops

Just thinking out loud here. Would smoke, or something like it with larger features, in combination with stroboscopic illumination at a small frequency offset from the excitation frequency do it? The air motion gets aliased down to a frequency where you can see it. The trouble is that you're looking at "different" smoke with each successive sample, which may blur it all out. I bet aeroelasticity folks know how to do this. Maybe look at their literature. I'll go have coffee now. -F
 
Re: Oops

Tim McCulloch said:
So... uh... where did Josh put the chicken? er.. feathers?.... Or was he wearing a chicken suit under his clothes?

/laughs at your 11Hz chicken!
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We have PLENTY of chickens around here. I am not sure about now-but for a long time, Gainesville (where Danley is located) was known as the "chicken capital of the world" due to how many were processed.

We even have a chicken statue near downtown--------------
 
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It is very hard to study actual real life port flow due to the back-and-forth motion of the air. Smoke, strings, Floviz, it all quickly becomes a smear that tells you nothing.
 
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I wonder if you could replace a woofer with a large piston and watch the port flow in one direction at a time.
would that data be relevant to the cyclical flow from audio?

Jason
 
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With the speaker laying on it's back there would be some convection flow that could eventually clear the port.

If a single narrow stream of smoke like incense was coming out of a port, some turbulence could be seen disturbing a coherent smoke stream, while probably not enough detail to see laminar flow.

A friend of mine from back when I worked at Peavey got a patent for directional biased port air flow, so one of his speakers would reveal smoke coming out of one port and clean air being sucked into the other.

JR

PS: Back in the 60's my brother's PhD thesis was about particle size/formation inside a supersonic nozzle and he fired a laser into the particle stream to get results. I suspect port behavior has been studied and something along the lines of chicken feathers is not all that crazy while a little too MacGuyver for me and messy to clean up.
 
Re: Oops

Per Søvik said:
It is very hard to study actual real life port flow due to the back-and-forth motion of the air. Smoke, strings, Floviz, it all quickly becomes a smear that tells you nothing.
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I agree, that is why we look at it with FEM tools and then test for sound 'quality'.

Jason Lavoie said:
I wonder if you could replace a woofer with a large piston and watch the port flow in one direction at a time. would that data be relevant to the cyclical flow from audio?
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I don't think the info would be that helpful since you really care about, at least in this box, 30Hz and above.
But it would be fun to try, I never have. We have large boxes with sealed plungers for each driver size to test different port design/box volumes.

I came up with a 'more clever' title though: "Things that happen while it's raining in Seattle"
What we were really looking at was how distortion as measured in driver displacement compared to distortion as measured in SPL and then the effect of properly tuning the box on the displacement distortion.

Mark
 
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John Roberts said:
A friend of mine from back when I worked at Peavey got a patent for directional biased port air flow, so one of his speakers would reveal smoke coming out of one port and clean air being sucked into the other.
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I had thought it was another major loudspeaker mfg who had patented that.. but it must have been licensed.
http://www.google.com/patents/US6549637
 
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Yup Jon Risch, still working there last time I bumped into him at the super market a few years ago.

Peavey has a pile of patents... I got 7 or so myself while working there.... (none of mine are related to speakers).

JR
 
Re: Oops

Frank Koenig said:
The trouble is that you're looking at "different" smoke with each successive sample
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Not as much as you think, hence Jon's patent for directional ports. We were working with some really high power woofers which got really hot inside the box. Jon measured that with normal ports you end up sucking most of the hot air you blew out right back into the box and don't end up exchanging much air at all. So he came up with a cute and simple little port treatment that give you an "in" port and an "out' port. It was first used in the Versarray 218 subs.

Anyway, I was disappointed to watch the video. I was expecting something like the famous frozen chicken test used by the Air Force:)
 
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