Straws in port tubes

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aceinc

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Straws in port tubes
« on: 13 Apr 2019, 04:02 pm »
In my center channel speaker which I threw together a number of years ago I used WinISD to calculate everything and built it to the specs. However in the ports (I used flared ports from PE) I stuffed a bunch of plastic drinking straws to the point they were individually polygon shaped. I believe I got my original idea from North Creek Audio's web site. I have found the overall performance of this speaker to be quite good.

I did no empirical measurements just thought I would mention it in case others had tried it and had some insight into its plusses & minuses.

Peter J

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Re: Straws in port tubes
« Reply #1 on: 13 Apr 2019, 04:12 pm »
In my center channel speaker which I threw together a number of years ago I used WinISD to calculate everything and built it to the specs. However in the ports (I used flared ports from PE) I stuffed a bunch of plastic drinking straws to the point they were individually polygon shaped. I believe I got my original idea from North Creek Audio's web site. I have found the overall performance of this speaker to be quite good.

I did no empirical measurements just thought I would mention it in case others had tried it and had some insight into its plusses & minuses.


Laminar airflow.

 A much talked about "thing" some years ago in the audio world. I built and still have some North Creek Rhythms with the straws George Short was recommending at the time. Like you, I never tried them without, so couldn't point to performance differences other than theory.

nickd

Re: Straws in port tubes
« Reply #2 on: 13 Apr 2019, 05:45 pm »
I have been thinking about port air flow for a few years. Constraints are mostly not having the equipment to test theory in actual applications.

I noticed at a young age how water would not fill a round culvert and the creek would over flow a road with the culverts 2/3 full. So the engineer would need oversized culverts to get the flow needed due to those unbreakable laws of physics.

Some 30 years later after reading Bose patents on the oval shape of their ports, I knew some speaker designers were aware of the weakness of round ports too.

In time I bought a high end muffler and exhaust pipe for a Honda trx400. I was trying to squeeze a bit more power out of the dated engine design. It ended up way too loud. Couldn’t ride with out hearing loss danger. But I liked the increased power from the improved air flow. I found they made a “quiet pack” for the muffler and ordered one up.

It turned out to be 3 different size steel tubes welded to a flange to seal the empty space between the tubes. Then the side of the tubes inside of the muffler is cut at an angle. The results are impressive. Very little loss of air flow (power) but the system is now suppressing almost all of the harsh noise.

 I’m guessing they are on to something here. I think an oval port is the easy answer, but different size PVC pipes with gaps sealed with silicone and glued into a flange is on my list to try for sure. An angle cut on the “inside” will no doubt make the port do its job over a wider frequency range.

 Good luck finding box tuning software to model that though. It will be trial and error for sure.
« Last Edit: 13 Apr 2019, 09:57 pm by nickd »

aceinc

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Re: Straws in port tubes
« Reply #3 on: 13 Apr 2019, 08:40 pm »

Laminar airflow.

 A much talked about "thing" some years ago in the audio world. I built and still have some North Creek Rhythms with the straws George Short was recommending at the time. Like you, I never tried them without, so couldn't point to performance differences other than theory.

I built a pair of his entry level speakers, the Echo's. I still use them as my rear speakers. At the moment I have each of them them running in parallel with a Dayton 10" Titanic in a sealed enclosure. I actually have the components to make a 12 db 80 hz Xover, I have been too lazy/busy to build the boxes for them.

But I digress. I have read some "straw" posts lately which appear to be naysayers, which having never really tested them, I can not discuss intelligently. Perhaps I should ask my son (an aerospace engineer) to model the differences in airflow. Then try to correlate this to low frequency sound.

poseidonsvoice

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Re: Straws in port tubes
« Reply #4 on: 13 Apr 2019, 11:00 pm »
North Creek brings back nice memories. Nearly a decade ago I still had my North Creek Okara’s, a gutsy little 2way using the famous Vifa P13WH 5.5 inch woofer and Scan Speak D2905-9500 tweeter in a rear ported EBS alignment. I did try both stuffing the port with straws (dipped in shellac) and without the straws as well. The straw version definitely cleaned up the midbass (the speaker really never played “bass” ie <50Hz). Strangely enough I never went after the science for why, I just assumed. The floor standing OKARA in this link with rosewood veneer and a black front/rear baffle was mine: http://www.northcreekmusic.com/OkaraII/OkaraII.htm

I never really played with ports thereafter, only OB,  passive radiators and sealed enclosures as my low frequency setup currently is a multisub sealed swarm which of course I could only dial in with didactic measurements. I often wonder what mid bass anomalies I once had with the Okara’s that I was largely ignorant of since I knew nothing about acoustics or the importance of in room measurements.

Sorry I can’t contribute anything scientific...but the concept of laminar flow seems logical.

Edit: My sale post about 9 years ago!: https://www.audiocircle.com/index.php?topic=77973.0

Best,
Anand.

aceinc

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Re: Straws in port tubes
« Reply #5 on: 22 Apr 2019, 02:33 am »
Regarding the "Echos" from North Creek and Titanics. I built the boxes for the crossovers, and put them together. I listened to a few hours of Jazz and other mellow stuff using Youtube as the source and an Adcom GFA555 II for amplification. I would have no problem using this combination for front speakers in a less robust system than I currently have.

Hijacking my own thread again.