4355

[hanad400]

Hello forum

I´ve read most of the 4350, 4635 threads, but can´t find anywhere the length of the ports of the 4355. I´m trying to build a pair, but this one is missing. Please help me.
Thanks, Gunther

[hanad400]

Sorry for my confuse, I mean the length of the ports of the 4355.

[Mr. Widget]

I am sorry, I don't know what the actual port length is, but realize that they are curved and not simple straight lengths of tube, so you would want to trim them to the final length to achieve the desired resonant frequency. Having a curved tube complicates the math significantly.

If you do not know how to measure tuning frequency do some google searches, it is fairly simple. The desired frequency is somewhere between 30 and 35Hz... I imagine the actual target frequency is posted here somewhere if you search our site...


Widget

[hanad400]

Thank you Mr. Widget
Regards, Gunther

[Ruediger]

... Having a curved tube complicates the math significantly. ...
Widget

The mass in the tube without any end corrections can easily be estimated, it's the same as that of a straight tube:

1.) The volume of a torus (ring) is 2 x pi**2 x R x r**2 (complicated calculation, see Wikipedia)

2.) The area of the torus cross section is r**2 x pi (easy)
3.) The "length" of the torus (wrong word, I know) is 2 x R x pi (easy)

"2" x "3" = "1 (easy calculation supplies proper result).

Finally add the end corrections, as for a straight tube.

Ruediger

[BMWCCA]

The volume of a torus (ring) is 2 x pi**2 x R x r**2...
Do you design intake manifolds for Audi in your spare time? ;)

[Mr. Widget]

"2" x "3" = "1 (easy calculation supplies proper result)."3"...i.e. length is the tricky part.

Widget

[Ruediger]

"3"...i.e. length is the tricky part.

Widget

I don't think so. In the calculations "R" is (inner radius + outer radius) / 2, and the length is that of a circle or part of a circle. I thought it was more complicated, but it is not.

Try it this way: take the complicated formula for the volume of a torus. That is the result of a proper integration. Now consider that as cross "section x length". Divide it by the cross section of the torus. What remains is the length, and that leads You to the radius.

Ruediger

[Mr. Widget]

I don't think so. In the calculations "R" is (inner radius + outer radius) / 2, and the length is that of a circle or part of a circle. I thought it was more complicated, but it is not.

The air in the tue shall behave like a lumped mass, all dimensions must be small when compared to the wavelength.

RuedigerI get that, and I suppose the drawing is confusing my point. I am not sure that the port is based on an actual radius. From what I have seen it appears to be a slightly accelerated curve.


Widget

[Ruediger]

I get that, and I suppose the drawing is confusing my point. I am not sure that the port is based on an actual radius. From what I have seen it appears to be a slightly accelerated curve.


Widget

Okay, then estimate how an equivalent port with a proper part of a torus would look like, and take the dimensions of that fictive (imagined) tube. length = (inner length + outer length) / 2.

It's all estimates, as You know Yourself: the end corrections are, the assumption of a certain temperature (speed of sound), the assumption of a certain DC resistance of the voice coil.

[Mr. Widget]

It's all estimates, as You know....:)

That was basically my initial point... make the ports as close as you can by guessing and then measure the response to dial them in to the correct value. Calculations are great for determining the distance between galaxies, but sometimes working empirically is the best and easiest approach.


Widget

[John]

Sorry for my confuse, I mean the length of the ports of the 4355.

The I.D. is 5,1/4"

The actual port is made up of 2 lengths of tube with mitred ends forming a angle not a curve. :blah:

[Woody Banks]

The I.D. is 5,1/4"

The actual port is made up of 2 lengths of tube with mitred ends forming a angle not a curve. :blah:

Something like this?

[Mr. Widget]

The I.D. is 5,1/4"

The actual port is made up of 2 lengths of tube with mitred ends forming a angle not a curve. :blah:I don't remember them that way, but then I don't really remember much. ;) Do you have a pair? In today's desire to avoid air turbulence, that wouldn't fly, but with such a large diameter, I am sure the acoustic compromise is minimal if at all.

Widget

[grumpy]

Something like this?

Interesting look, but I like them better mounted to the front baffle :)

[Mr. Widget]

?

Interesting look, but I like them better mounted to the front baffle :)Well, they're just not finished yet... when they get the veneer on them they will look fine. ;)


Widget

[John]

Something like this?

Yup! :cheers:

[Woody Banks]

?

Interesting look, but I like them better mounted to the front baffle :)

This is to prevent the wife from placing that fern on top of your fresh veneer. :D