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1/3rd Wave TL?
1/3rd Wave TL?
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Old 8th October 2019, 12:58 PM   #1
midrange is offline midrange  United Kingdom
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Default 1/3rd Wave TL?

This intrigued me.

[Listening test] Kerr Acoustic K320 Loudspeaker

It talks about 1/3rd wave loading in the design, rather than the usual 1/4 wave.

Has anyone here experimented with it?

I do like the tnt-audio site. There are loads of non-standard commercial speakers, and very small manufacturers. Makes a change.
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Old 8th October 2019, 02:31 PM   #2
Scottmoose is offline Scottmoose  United Kingdom
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There is no such thing as a 1/3 wave line in this physical reality. If a pipe is open at one end and sealed at the other, it has a 1/4 wave fundamental. Period. The actual resonant frequency & harmonic structure however is a function of length and taper for a given SoS / air density / humidity.

What they presumably mean is that they have selected a line length (physical or acoustical) of 1/3 a particular frequency. Meaning it's tuned to a lower frequency.
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Old 8th October 2019, 03:08 PM   #3
GM is offline GM  United States
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Jees, they're really desperate to appear unique!: Resonances of open air columns

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Old 8th October 2019, 04:16 PM   #4
Scottmoose is offline Scottmoose  United Kingdom
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'fraid so.

I'm familiar with their standmount K300. My friend Nick has been using them as part of his demo setup at UK hi-fi shows. Technically they might be a bit undersized on the old Vb front, and if you wanted to keep the crossover & ribbon tweeter I wouldn't shed a tear, but a few of us had a short 'session' one evening at the North West Audio Show after the public had gone for the day, ending up bellowing various tracks from Welcome to the Pleasure Dome (don't ask) and Rage Against the Machine at some fairly daft level. Beer helped, but to be fair, they were doing a good job in that modest space in terms of bass alignment. A bit more cone movement that I was expecting interestingly (well, I found it interesting), so possibly tuned a little higher (or the SPLs were more) than I thought. Reminded me of why I like QW speakers, and that Scan Revelator midbass though.

There's still no such thing as a 1/3 wave line though. Looking at their site, they don't appear to call it such, albeit stating equally incorrectly that "acoustic ‘transmission lines’ work on the basis of being tuned to 1/4 or 1/3 of the wavelength of the resonant frequency of the driver, and are heavily damped with absorptive material."
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Last edited by Scottmoose; 8th October 2019 at 04:42 PM.
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Old 8th October 2019, 04:25 PM   #5
GM is offline GM  United States
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Seems to me I last saw a similar explanation in a B0$3 patent application. :P

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Old 8th October 2019, 04:48 PM   #6
midrange is offline midrange  United Kingdom
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I did not put my question very well. I presume the design uses a line that is 1/3rd length, and not a 1/4 length (of Fs of driver?). So I was wondering has anyone tried this?
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Old 8th October 2019, 06:08 PM   #7
Scottmoose is offline Scottmoose  United Kingdom
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There's nothing to try. It's just a fixed ratio of Fs, in this case resulting in a line tuning < driver resonance, which as far as this type of pipe is concerned, is rarely a good idea.
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Old 9th October 2019, 11:46 PM   #8
cochleus is offline cochleus  United States
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The OP just asked a question about the TL tuning frequency in relation to the specified Fs of the driver.

Last edited by cochleus; 9th October 2019 at 11:59 PM.
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Old 10th October 2019, 01:37 AM   #9
GM is offline GM  United States
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Quote:
Originally Posted by midrange View Post
I did not put my question very well. I presume the design uses a line that is 1/3rd length, and not a 1/4 length (of Fs of driver?). So I was wondering has anyone tried this?
Don't know other than some docs I alluded to and now these folks playing on consumer ignorance.

Regardless and keeping it simple:

Scan-Speak Revelator 18W/4531G01: 34 Hz Fs, 0.35 Qts

T/S max flat vented:

Fb = 0.42*34*0.35^-0.96 = ~39.12 Hz

13543"sec/3/34 = ~132.77" 1/3 WL, but no such thing in my universe, so converting it to 1/4 WL:

13543/4/~132.77" = 25.5 Hz 1/4 WL is presumably ~what its base tuning is before stuffing.

39.12/25.5 = ~1.534x lower whereas I normally tune in 1/2 octave increments [~1.4142x = ~27.66 Hz], so an insignificant amount lower than me.

In short, not a bad alignment and is often preferable when near a wall or even lower when hard in a corner, so just one of myriad combinations of alignments required to blend a vented bass box in a room, but the way they advertise it, not cool, especially since I can't recall any manufacturer tuning based on 1/3 WL*Fs.

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