Transmission Line Questions

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I do not know anything about transmission line speakers (is that how they are described? :scratch: ). i first got the idea from planet10 here. i have seen, and read the page about, El-Pipe-O. i would like to see, and read about, any other exapmples (maybe on a smaller scale :D) of transmission line speakers.

i would like to know how i work out the box size, tube diameter and tube length for a set driver. can i use normal speaker software and input the tube as a port?

thank you very much for any info.
 
Hi Matttcattt,

I have recently added some classic transmission line alignment tables to my www.quarter-wave.com site. You can use these tables to quickly scope out a design for any applicable driver.

If you want more TL theory, there is a series of documents that derive the basic equations I use to model TL's in my MathCad worksheets. I have included a link to a free downloadable MathCad Explorer program which will run any of my MathCad Version 8 worksheets.

Also, there are four "quarter wavelength" loudspeaker projects that I have designed and built along with a gallery showing a number of other speakers DIYer's have built based on one of my designs or their own original design based on the MathCad worksheets.

Hope that helps,
 
frugal-phile™
Joined 2001
Paid Member
i looked at all the links posted, but i could not find any explination of how i work out the box volume, and tube length and diameter. i could not understand any of the graphs as they were not explained. can i use winisd or any other speaker calculator program to work out the box size, classing the tube as a port? i am interested in a box, with a tube, like el pipe-o.
 
Right, that's just it. Transmission line design frees you from volume and such. It has to do with surface area and line length. Again, it's all about the quarter wavelength of the Fs of the driver. You want to design an enclosure that best supports that frequency while damping all the resonant frequencies. That's it! No more boxes! It's miraculous and so liberating.

Download the mathcad worksheets and start fiddling. Pick a driver, enter its attributes, then mess with the two Sd parameters, the stuffing density and the line length. And keep posting back here.

The graphs are hard to explain. I'll let someone else contribute.

Dave
 
can someone help me put the driver parameters into the mathcad worksheet?

the parameters are:

Eminence Model No. Beta 15
Nominal Chassis Diameter: 15", 318mm
Impedance: 8Ohms.
Power Rating: 350Wrms
Resonance: 35Hz
Usable Frequency Range: 35Hz to 4kHz
Average Sensitivity 1W @ 1m: 98dB
Magnet Weight: 34oz.
Magnet Gap Depth: 0.312", 7.94mm
Voice Coil Diameter: 2", 50.8mm
Mounting Information
Overall Diameter: 15.15", 384.8mm
Baffle Hole Diameter: 13.77", 349.6mm
Front Sealing Gasket: fitted as standard
Rear Sealing Gasket: fitted as standard
Fixing Holes Diameter (8 off): 0.25", 6.4mm
Fixing Hole P.C.D.: 14.56", 369.9mm
Depth: 6.05", 153.6mm
Weight: 9lbs, 4.08kg
Shipping Weight: 11lbs, 5kg
Thiele-Small Parameters
Resonant Frequency (fs): 35Hz
Impedance (Re): 6.32Ohms.
Coil Inductance (Le): 1.10H
Electromagnetic Q (Qes): 0.63
Mechanical Q (Qms): 8.10
Total Q (Qts): 0.58
Compliance Equivalent Volume (Vas): 334.6 litres
11.82 cu.ft
Peak Diaphragm
Displacement Volume (Vd): 327cc
Mechanical Compliance
of Suspension (Cms): 0.35mm/N
BL Product (BL): 11.5 T-M
Diaphragm Mass inc. Airload (Mms): 60 grams
Equiv. Resistance of Mechanical
Suspension Loss (Rms): 1.61N*sec/M
Efficiency Bandwidth Product (EBP): 55
Voice Coil Overhang (Xmax): 4.0mm
Surface Area of Cone (Sd): 823.7cm=
Impedance at Resonance (Zmax): 88Ohms.

here is the mathcad worksheet:
 

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Fs 35 goes in Fd
Re 6.320 goes in Re
Lv 1.10 H goes in Lvc
BL 11.5 goes in Bl
Overall Diameter 15.15 goes in Sd
Vd 327 goes in Vd
Qes 0.63 goes in Qed
Qms 8.10 goes in Qmd

At that point, adjust SO and SL to 1Sd each, set density to 0.01, then fiddle with the line length until the first graph begins to show a bump at 35 Hz.

That's the resonant frequency of your driver in an empty 1:1 Sd T-Line.

As soon as someone can explain the other graphs, then you'll know what to adjust for. In the meantime, adjust the stuffing parameters from extreme to extreme, and study the changes in all the graphs. I learned a lot by doing it that way.

Dave
 
Lets try again :

Fs = 35 goes in Fd
Re = 6.320 goes in Re
Lv = 1.10 H goes in Lvc
BL = 11.5 goes in Bl
Sd = 823.7 cm^2
Vas = 334.6 goes in Vd
Qes = 0.63 goes in Qed
Qms = 8.10 goes in Qmd

Qts = Qtd = 0.58

I would start by going to the alignment tables and picking a SL/S0 that yields a length that looks reasonable from Table 1 in the 35 Hz column. Then select a consistent value for Znormalized from Table 2 again from the 35 Hz column. For Zelectrical I would assume 0.625 after extrapolating the data in Table 3. Finally select the driver offset from Table 4 that again is consistent with the SL/S0 assumed. You can now calculate S0, then SL, and see how big of an enclosure is produced. Iterate this process until you have a design that looks good for size. Plug this design into the "TL Offset Driver.MCD" MathCad worksheet and see what the SPL and impedance curves look like, this is when you can start playing with the stuffing density to tame the ripples.

Hope that helps,
 
There is a standard notation for the Theile-Small parameters. Typically the "s" subscript is used in every other puplication. But 20 years ago, when I started studying speaker design, I decided that the "s" subscript made no sense to me and that I wanted the "d" subscript instead. All of my notes and programs use my own unique notation. I never anticipated that my work would ever be used by other people. So the translation is as follows :

Correct ----> Martin "the idiot non conformist" King

fs ----> fd
Re ----> Re
Qms ----> Qmd
Qes ----> Qed
Qts ----> Qtd
BL ----> BL
Vas ----> Vd or Vad
Sd ----> Sd
L ----> Lvc

My appologies if this has been confusing but I am totally convinced that the rest of the world will one day see the beauty of my superior subscript notation.
 
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