So/Sl ratio?

[Tomac]

I've been reading about tl construction and browsing martin's and planet10 sites lately.I learned things about tl that i didn't know before but there is one thing that I failed to understand.How do you determine So/Sl ratio?I know that it's equal 1 in straight pipes, but i just can't find the right explanation about determing it.Lot of people use 4 for So and 0.5 for Sl in their construction,but i can't see the logic connection.I know that it can be 1 in round pipes because there are no standing wawes and, for the same reason,it can't be 1 in "normal" boxes.
thanks in advance

p.s. MJK,have you received my mail with problems I have wiith mathcad worksheets?

[MJK]

The definitions in my worksheets are as follows :

S0 = area at the closed end (x = 0)

SL = area at the open end (x = L)

SL/S0 is just a ratio of the two (= 1 for a straight pipe, > 1 for a TQWT, and < 1 for a tapered pipe). Most TL builders go a step further and express S0 and SL as ratios with Sd the driver area. This is a way of normalizing the enclosure and transfering the enclosure description to drivers of different sizes.

There is no best value for SL/S0, for a given tuning frequency there can be an infinite number of SL/S0 values and lengths that will produce different response plots. I typically start with an assumed value and by trial and error focus in on an optimization that gives a nice response. There will probably be many different geometries that work well for a given driver.

p.s. MJK,have you received my mail with problems I have wiith mathcad worksheets?

I get between 5 and 10 e-mails a day and participate on a couple of forums. I try and respond to all e-mail questions within 24 hrs. People use different names on forums and in e-mails so it is hard to keep track of who is who. I believe I am caught up on my e-mail questions as of yesterday so if I have not answered your e-mail from several days ago, it probably means I did not see it.

My appologies if I missed something,

[Tomac]

thanks for your fast reply,Martin! Actually the mail was sent some 7 days ago or even more,can't recall now.I've sent it through e-mail service on this web.it has the same nick as one i'm using here.
Regarding the Sl/So ratio-is there any general rule that states something like "if So is bigger than 1 Sd it will lower down FR.or if the Sl is below 1Sd there will be some loss in bass"?What is the minimum for the So? is it 1 Sd?I've noticed some people make Tlines with Sl/So=1 as it is case with Visaton vib 130 tl design: http://www.visaton.com/cgi/VisatonFr...Artikel_ID=585
isn't it causing standing waves in the tunnel?
thanks again!

[MJK]

Tomac,

Yes, I remember getting an e-mail through this site and I am pretty sure I responded.

There are no hard rules about the areas S0 and SL for a TL. Try the MathCad worksheets and see what works best for your driver. Take a look at my alignment tables to scope out the size of an enclosure for different tuning frequencies and area ratios.

When I am designing an enclosure, I like SL/S0 = 1 since it is probably the easy design to build. Nice square shapes which are easy to cut and assemble. My next preference is a tapered TL, SL/S0 < 1, since this probably is the smallest enclosure and speads the fundamental quarter wave and three quarter wave the furthest apart in the frequency domain. This is the lowest risk approach. My least favorite enclosure to build is a TQWT (SL/S0 > 1), did one of these and it was big and difficult to build. I like easy since I am lazy and not a skilled woodworker.

I've noticed some people make Tlines with Sl/So=1 as it is case with Visaton vib 130 tl design .... isn't it causing standing waves in the tunnel?

Exciting and controlling the standing wave is kind of the hole idea behind a transmission line enclosure. The standing wave resonances produce the bass response.