How to convert a tapered port to a straight port?

[DeanP]

Just as the header says,"How do I convert a tapered port to a straight port?"

I have a port that is 5" long and 1 3/4" at one end and 1 1/2" at the other end.
Do I just split the difference and make it 1 5/8 x 5 long? Or is there a formula I could use? ( I'm assuming that I would only require the same internal volume as the tapered port??)
Or is there someone who sells these type of ports in the USA? I know they have them in Europe.
Thanks in advance...
Dean

[ThomasW]

How did you come by these?

I've never heard of them. They can't be very popular even in Europe. A pretty extensive google search turned only two hits. One was in reference to a M&K prosound speaker, the other referenced the Jan/Feb 2002 issue of the AES Journal.

Maximizing Performance from Loudspeaker Ports
Alex Salvatti, Allan Devantier, and Doug J. Button 19
The low-frequency performance of a loudspeaker is significantly enhanced by the use of tapered ports, but there are numerous trade-offs involving the size of the port and the input and output tapers. Design issues include the effectiveness of heat transfer, amount of turbulence created, air velocity, smoothness of the taper, symmetry of the two tapers, effective mass in the port, and the contribution to the frequency response. Suggested design rules are based on extensive empirical studies.

If I was going to use them I'd model them as a 1.5" port.

When I get a chance I'll ask Jon, maybe he's heard of them.....

[DeanP]

I'm going to start from the beginning so everyone understands what I am trying to do.
I have Athenas for my rears and centre, then I rebuilt a set of Sound Dynamics 100s and am using them as my fronts. A problem came about as now they don't match, in tonal sound,with the center. So I thought that I should build set of fronts and a center so they all match. Well, in order to build something worth while(hence my thread on Audax surround and eventually the M8as) I found that I wouldn't have enough money to do that. Plus even if I went the Audax route, which would be cheaper(than M8as), you,Thomas, explained that they won't be around much longer to provide me with parts later. So that went down the tubes. So later on, I will build some high quality speakers, but right now I wanted to build something cheaper for fronts and a centre. So...
I figured that the only way to get a "match" was to buy another set of Athena AS-B2s and because I'm into building speakers, I would build a set. The parts are only $215CAN for x-overs, tweets and woofers, which is a perfect budget for now, plus I'll save $70 from the retail speaker. I am also in the process of rebuilding my 54L sealed shiva to a 95L vented and would like a "bookshelf" speaker for mains as the 95L shiva is quit big and the WAF will be low on this. So I will off set this WAF by using "bookshelf" size speakers instead of floor standers that I have now.
So I measured up the Athenas AS-B2s I have now for box dimensions but the port thru me as it was this tapered thing.(5" x 1 1/2" - 1 3/4") They sell tapered ones hereMonacor but of course this one isn't what I need so I would like to make it a straight port but I need to convert its size.

Thats it in a nutshell. :amen:

Any suggestions?

Dean

[ThomasW]

Okay.....

It appears that they're basically trying to increase the effectiveness of the 'flare.' So I'd do as you said and model it as a 1-5/8" port. I think you'll find that 1/8" changes in diameter don't have a big impact on the tuning.

In the real world 10% variance in the design of ported boxes has little effect on the overall performance.

[Andrew Pratt]

That makes sense...play around with one of the modeling packages and see what effect that small a difference really has...i.e its very small and that assumes you're dead on accurate for your net internal volume.

[DeanP]

Thanks for the help!
Just after I posted , I went downstairs to my "stock" and found I have a tapered port from Solen but it 1/2" shorter but with the same diameters. Although the end which should be 1 1/2" is about 1 9/16" which precludes that if it was a total of 5" in length, it would be the 1 1/2" desired. Would this have any major effect on the design?(BTW I don't have the specs for the driver as they are from Athena)

Dean

Maybe I could just make the port a little longer using a piece of mdf and a router. :W

[DeanP]

Case closed! thanks for the help! :T