RS100-8 Transmission Line

[Einric]

The resonant frequency of the RS100-8 is 87.5hz.
That would put the 1/4 wavelength at 38.75".
I read somewhere that you should make the pipe slightly shorter than the 1/4" length and lightly stuff the pipe to dampen & slow the wave.
How short should I make the pipe? 36"? 30" anywhere in between?
Here is a picture of my design idea.

Any Thoughts?

[planet10]

That length calculation is for an untapered line (as yours looks to be), but does not include the end correction,

A good place to start is with Martin King's free alignment tables. It will generate the appropriate cross-section, length, and driver off-set.

dave

[Einric]

I will look those tables over later tonight.
What is End Correction?
Will a flare at the open end mess with this End Correction?
I plan on building a flare at the bottom end.

[kctess5]

Make sure to at least check out the the alignment tables and/or horn resp. Many times some kind of taper will result in flatter response. Also with what looks like a compression chamber on the front end it could further mess with the response if not specifically designed. Also a flare at the end will change response, possibly beneficially but its hard to guess.

Not sure exactly about end correction but I believe it is something to do with the pipe resonates, the maximum of air velocity will not occur exactly at the open end of the tube but a little beyond so the tuning will be not quite exactly the length of the pipe. I believe it is worse the larger the pipe is in diameter relative to length

Good luck!

[GM]

A pipe, tube, horn's acoustic length is longer than its physical length, so the end correction is how much the pipe is shortened for a given acoustic length.

Since the end correction is ~0.613x the effective terminus radius, flaring will affect it. In the scheme of things though, even it if alters tuning as much as a few Hz it won't be audible. That said, any line that requires damping won't audibly benefit from flaring unless it has a huge radius.

GM

[kctess5]

A pipe, tube, horn's acoustic length is longer than its physical length, so the end correction is how much the pipe is shortened for a given acoustic length.

Sounds like I was close

[GM]

Sure does! Resonances of closed air columns

GM

[Einric]

The compression chamber will only be as deep as necessary to give the driver a flat surface to mount to (an inch tops).
The pipe is actually a 3/8" wall cardboard tube with a 2.5" internal radius.

[kctess5]

If you have hornresp you should model it real quick, I would but I'm not with my pc

I suppose if you don't like how it sounds its not like it was a huge time investment with that tube

[GM]

Hmm, 8" driver firing into a 5" pipe........ Is this what MJK's tables calculate? If so, a TQWT is called for. Otherwise, a driver offset typically is required to deal with peaky pipe modes. That, or a high stuffing density.

GM