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Pashley 8th December 2012 10:33 PM

Compact Transmission Line equivalent?
Transmission line designs have a number of nice properties, but they are often inconveniently large, especially for subs. e.g. the Perfectionist Audio coffin woofer (Coffin TL Plans) claims high efficiency with <1% THD 10-200 Hz (I'm skeptical, but exact values are not important here) but it is 6x2x2 feet which is not convenient.

One way to design a passive radiator speaker is to first do a ported design, calculate the mass of the air in the port, and then use a passive with that mass.

Could that approach be applied to a compact pseudo-TL design? Work out a TL design, then use a very large heavy passive radiator as an equivalent to the long pipe? This is superficially plausible, but I am not at all sure it would actually work. What do others think?

planet10 9th December 2012 12:10 AM

Compact, Transmission-Line, and Subwoofer are 3 words that are incompatible in the same sentence.


Bjohannesen 10th December 2012 09:19 PM

Compact Quarter Wave Sub
2 Attachment(s)
Hi Pashley

TL, or Quarter Wave do need a certain length to define the tuning frequency, which can be higher or lower depending on the driver Qts. However the shape of the cabinet can shorten the length of the cabinet. Volume is a parameter to optimise the SPL, expecially the controbution from the opening. "More volue, more Bass". Thise has to be thmed by stuffing.

MJK´s models are excelent to simulate the result of a given design.

Havind said this, my own constructions are often not the best cabinet for a drvier, as sizes does matter.

My Hide Away is an example of a compact sub doing pretty weell and is fullfilling my needs. It has just been upgraded with SCANSPEAK 26W/4558T00.

You might find some inspiration in the documents enclosed.

Hi from

schmeet 11th December 2012 03:02 PM

I guess you could Mass-Load a Transmission Line with a passive radiator but it is all one big compromise, there is no beating the laws of physics.

There are 3 elements:

- Frequency Response
- Efficiency
- Size

You can have two of these. Horns/TLs tend to go all out for FR and Efficiency at the expense of size.

If you want small and low then go for a Passive Radiator, Isobaric, Bass Reflex enclosure. But make sure you have plenty of power to hand!

djn 11th December 2012 08:55 PM


Originally Posted by planet10 (
Compact, Transmission-Line, and Subwoofer are 3 words that are incompatible in the same sentence.


Not for Bose Dave.

Telstar 25th December 2012 04:25 PM

TLs are underrated.

Kindhornman 25th December 2012 05:15 PM

Those Bose devices are simply two tuned tubes, or transmission lines with the device at the center of each tube length. As with anything Bose they are not what we would call accurate devices and produce two fairly high "Q" bass notes. This gives a semblance of base but it is fairly rough sounding and counts on you accepting this lumpy response to simulate a wider bass frequency response. You can make a TL with small devices but you are going to be limited in SPL output by the devices limited Xmax factor. Line length is the critical factor for tuning the device for the cutoff frequency, but cross sectional area will be a function of the device size you start with. So if you aren't looking for thundering bass levels but are only trying to supplement a system that is used at a lessor volume you could design a TL. I personally would just build a bass reflex or sealed enclosure and get a bigger power amplifier if size is the issue.

planet10 25th December 2012 10:10 PM


Originally Posted by djn (
Not for Bose Dave.

You misspelled that. B$%@ doesn't build hifi, they build lifestyle products.


dangus 26th December 2012 11:50 AM

I believe the answer is a stuffed sealed box.

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