The following is from a tntaudio review. I would be interested in opinions.
The smaller Kerr K300 utilise a short transmission line (as in the Bailey approach to minimise overhang and dissipate cone rear energy. The larger Kerr Acoustic K320 uses a hybrid of transmission line and tuned third wave pipe. The familiar Tuned Quarter Wave Pipe (TQWP, often mis-described as a transmission line) has some of the power handling advantages of reflex loading (controlling cone excursion near the system resonant frequency) but fewer group delay disadvantages than reflex. This results in lighter but faster sounding bass and more placement flexibility in the room. The tuned third wave pipe trades some of that excursion limiting advantage in exchange for even lower Q bass tuning knee and deeper (quasi second order slope over 1 octave) extension.
The smaller Kerr K300 utilise a short transmission line (as in the Bailey approach to minimise overhang and dissipate cone rear energy. The larger Kerr Acoustic K320 uses a hybrid of transmission line and tuned third wave pipe. The familiar Tuned Quarter Wave Pipe (TQWP, often mis-described as a transmission line) has some of the power handling advantages of reflex loading (controlling cone excursion near the system resonant frequency) but fewer group delay disadvantages than reflex. This results in lighter but faster sounding bass and more placement flexibility in the room. The tuned third wave pipe trades some of that excursion limiting advantage in exchange for even lower Q bass tuning knee and deeper (quasi second order slope over 1 octave) extension.
There is no such thing as a 'third wave pipe' in this physical reality. A pipe sealed at one end and open at the other has a 1/4 wavelength fundamental defined by its axial length & taper, and any relevant end-correction. Closed form physical fact. Period. End of story. What they presumably mean is that they have used 1/3 wavelength of a desired frequency. That does not make it a 'tuned third wave pipe' though; it's a trifle ironic that they criticise the 'Transmission Line' term for questionable accuracy (that one rather depends how you wish to apply the term) yet proceed to use a term themselves that is technical nonsense. Oh well, nobody said audio was always very logical. 😉
Nothing against Kerr as a company BTW. While I certainly 'question' (ahem) some of the above, a friend sometimes uses their products at shows, and the ones I've heard have sounded pretty decent. Not how I'd do it, but enjoyable enough. Sufficient for a few of us a couple of years ago to have a bit of a session after the public had departed and spend an hour howling Welcome to the Pleasure Dome, The Power of Love, Bullet in the Head etc. (I'd been a few doors up with MA-Sota) Beer helped, obviously. It was a good room by show standards.
Nothing against Kerr as a company BTW. While I certainly 'question' (ahem) some of the above, a friend sometimes uses their products at shows, and the ones I've heard have sounded pretty decent. Not how I'd do it, but enjoyable enough. Sufficient for a few of us a couple of years ago to have a bit of a session after the public had departed and spend an hour howling Welcome to the Pleasure Dome, The Power of Love, Bullet in the Head etc. (I'd been a few doors up with MA-Sota) Beer helped, obviously. It was a good room by show standards.
Last edited:
I looked at the 300 and 320 and both are discribed transmission lines by Kerr website, the are just tuned to different frequencies. What a 3rd wave pipe is supposed to be I do not know
My guess is that if the Fs wavelength is 24 feet, they are using a pipe that is 8 feet long, instead of 6 feet. This would mean that the qw resonance of the pipe is lower than the resonance of the driver.
Having had a morbid moment to peruse the Kerr 'white paper', a small breakdown of its contents on the subject, FWIW:
No, it doesn't have to begin directly behind the main LF driver, nor does it have to gradually taper to the terminus, nor does driver Sd have any particular direct corrolation to line Vb [Vp] requirements, which for a given Fb [Fp] and gain are like any other vented enclosure dominated by Fs, effective Q and Vas.
A question of enclosure form-factor rather than anything else; folding is a matter of convenience rather than design, except in cases where it is actively used as a part of the acoustic low-pass.
To a point correct in the former case, complete twaddle in terms of extension (choking the terminus area aka mass loading typically lowers Fb with a given set of pipe dimensions [not that you'd be likely to design it in that way]. It certainly doesn't raise it). Some loss of outright gain at Fb will occur, but assuming your Vb is sufficient for the driver this will typically be beneficial in damping excess, and presumably (hopefully) you will adjust the amount of mass-loading / forcing to achieve a desired alignment rather than applying at random.
I'd be interested to know what interpretation of the physics they're applying to get this one.
Rubbish.
Possibly, depending on how the term is used. If it's a maximally-flat impedance line, then almost certainly. If not -more variable.
The frequency[ies] rather depend on the line tuning rather than an arbitary value like 80Hz, although this is probably a vaguely reasonable, if somewhat meaningless approximation in most cases.
True enough, they do tend to have larger volume requirements.
Historically considered, with at best questionable accuracy. Many TLs over the years (not all) have had heavily over-damped alignments if used for the purposes of LF reinforcement, frequently resulting from insufficient bulk or an excessively low tuning frequency.
Well, not as straightforward as a sealed box or a typical vented, but it's not a black art.
Potentially a fair point depending on type.
Twaddle, taken as a generalised statement. Some can. It's not invariable, and depends on the specific type being designed & the goals in question.
Ditto.
Possibly, depending on context, type & how you wish to define. Some do / can have the effect.
No, it doesn't have to begin directly behind the main LF driver, nor does it have to gradually taper to the terminus, nor does driver Sd have any particular direct corrolation to line Vb [Vp] requirements, which for a given Fb [Fp] and gain are like any other vented enclosure dominated by Fs, effective Q and Vas.
A question of enclosure form-factor rather than anything else; folding is a matter of convenience rather than design, except in cases where it is actively used as a part of the acoustic low-pass.
To a point correct in the former case, complete twaddle in terms of extension (choking the terminus area aka mass loading typically lowers Fb with a given set of pipe dimensions [not that you'd be likely to design it in that way]. It certainly doesn't raise it). Some loss of outright gain at Fb will occur, but assuming your Vb is sufficient for the driver this will typically be beneficial in damping excess, and presumably (hopefully) you will adjust the amount of mass-loading / forcing to achieve a desired alignment rather than applying at random.
I'd be interested to know what interpretation of the physics they're applying to get this one.
Rubbish.
Possibly, depending on how the term is used. If it's a maximally-flat impedance line, then almost certainly. If not -more variable.
The frequency[ies] rather depend on the line tuning rather than an arbitary value like 80Hz, although this is probably a vaguely reasonable, if somewhat meaningless approximation in most cases.
True enough, they do tend to have larger volume requirements.
Historically considered, with at best questionable accuracy. Many TLs over the years (not all) have had heavily over-damped alignments if used for the purposes of LF reinforcement, frequently resulting from insufficient bulk or an excessively low tuning frequency.
Well, not as straightforward as a sealed box or a typical vented, but it's not a black art.
Potentially a fair point depending on type.
Twaddle, taken as a generalised statement. Some can. It's not invariable, and depends on the specific type being designed & the goals in question.
Ditto.
Possibly, depending on context, type & how you wish to define. Some do / can have the effect.
Let me add to Scott’s comment. A “TL” can be designed such that the LF roll-off is anywhere between 2nd order and 4th order depending on how aperiodic it is pushed.
I should have data, but cannot find it, of an aperiodic TL pushed to a point where the roll-off was even slower.
The advent of modern TL modelers has greatly expanded what the “TL” desig space is and has brought considerably greater capability for a knowledgeable designer to fairly quickly & easily develop a target design.
These guys seem to be stuck in the “Bailey/Raford/IMF era of TL design. In terms of the quality of their loudspeakers i expect that is much more down to drive selection and getting the XO right. I do not doubt that teh same VOLT bas sdriver could be put into a number of different TLs, which depending on design goals, couls outperform these as a TL (i expect the simiar looking PMCs would face the same fate). PMC does have a lot of experience building TLs with this driver and that experience cannot be discounted.
It certainly is possible to improve the bass. And like a bad BR really screw it up. The missing midrange “distortion” is more specifically a reduction in time-smeared sound from the back of the driver coming back thru the cone (do they put the MR in an aperiodic TL?) because it is getting :sucked” down the line and absorbed instead. I expect an overlarge damped sealed box would do the same, but without being able to take advantage of the LF extension a TL can provide (if designed or that).
dave
I get so tired of claims about TLs, both good and bad but incorrect, that come up so often and I'm glad to see Scottmoose and Planet10 address them here. I did a similar thing with a letter to the editor about a review in last November's Stereophile of the Alta Audio's Alyssa speaker. Alta calls the design an XTL, meaning bass extended by its TL. Well, what they claim is untrue, plain and simple. The review article showed a cutaway drawing of the cabinet. It's a 2-way that has a long port and a multi-fold line. Considering the line only and based on the listed cabinet dimensions, the line was about 48" long and essentially had a constant CSA its whole length. Therefore, the line's 1/4-wavelength resonant frequency was about 70 Hz, not nearly low enough to tune the system properly, much less to extend the bass (and the likely correct system tuning should have been around 40 Hz based on the midwoofer's likely spec's. The 9" long port tuned the system to the low 30's, yet the system was described as having the bass response extended by the TL. Not only that, but the locations of the midwoofer and the port's internal entrance within the line were just plain bad. Oh, and the port was stuffed (although Alta forgot the stuffing in the speakers reviewed by Stereophile). I also corrected a comment John Atkinson made about TLs in general. In case you're wondering, my letter was never published and Alta Audio's advertisements about this design continue to have these untrue performance claims.
Paul
Paul
I emailed Scott about that one after seeing the cut-away. Whatever he said i tossed it out of my head.
You can certainly see the convoluted performance in the measured frequency response. Anyone need a red rake?
dave
That doesn't sound pretty. Will take a look if I can ensure my starting blood-pressure is at a low-enough level. 😉
They forgot the damping? How in the name of sanity does a company producing loudpeakers manage to forget the damping, above all for a QW variation which they are sending to Stereophile of all places for review? That's stark, staring incompetence. Who built and production QC checked them, Long John Silver's parrot?
Probably for the best, I doubt Thumper's Mother would have approved. 😉 Either way, far as I can see, Paul's spot on -a folded end-loaded QW with an offset, rather [over] lengthy mass-loading port. Not exactly what you'd call screaming novelty taken as a broad concept. I'll be charitable and say nothing about the execution.
edit... OK I will. It's 'not very good'.
What I said in my letter about Alta's claims is that they were not supported by physics or the math. That's about as nice as I could be.
Paul
Paul
As best as I could tell from the Manufacture's Response to the review in that same issue, they boasted about not using stuffing in the line itself (I think) but then stuffed the port (even though they left out that stuffing in the review pair)! I've never heard of anyone intentionally stuffing the port in any TL.
Paul
Paul
Bud Fried did stuff the vents in his restitive lines. He called them TLs.
Above is the Fried Model R. You can see the 3” high piece of foam (not unlike what you would buy for a bed) in a slot that reached to near the back. The smaller Fried Q used the same technique in a smaller 2-way.
dave
Above is the Fried Model R. You can see the 3” high piece of foam (not unlike what you would buy for a bed) in a slot that reached to near the back. The smaller Fried Q used the same technique in a smaller 2-way.
dave
Attachments
Stretching a point, Ferrograph's S1 and TDL's 'Reflex Transmission Line' did more or less the same, but we're really then in the business of vented boxes with oversized ducts that would require damping to kill the self-harmonic modes even if it wasn't wanted for shaping the alignment to whatever is being targeted.
In the more abstract sense, damping vents was relatively common for classic BR boxes; traditionally you fine-tuned either by stapling damping over the back of the driver, or over whatever vent you settled on using the old click test. In principle no reason why you can't do the same with MLTL variations, although if designed properly they're unlikely to require it in the first place, short of a band-aid to address a problematic room interaction etc.
In the more abstract sense, damping vents was relatively common for classic BR boxes; traditionally you fine-tuned either by stapling damping over the back of the driver, or over whatever vent you settled on using the old click test. In principle no reason why you can't do the same with MLTL variations, although if designed properly they're unlikely to require it in the first place, short of a band-aid to address a problematic room interaction etc.
Okay, Scottmoose and Planet 10. I didn't know that in the old days TLs had their termini stuffed or that technique was used for BRs and ported boxes. That said, I don't believe the "designers" at Alta Audio had any idea of what they were doing and simply ended up stuffing the port in the Alyssa to try to make up for all of the problems inherent in their TL design (more like a guess than a design IMO).
Paul
Paul
Oh, absolutely. I've just read the manufacturer comments in the Stereophile review -drooling nonsense of the first order. Let's be honest -dodgy physics aside, a speaker that has a 'proprietary' construction material that they have named (cough) 'DampHard' is enough to set the alarm bells ringing.
Last edited:
I have never heard or seen an S1 but many years ago Scott brought it up and we had a bit of discussion on it and i made this picture which might be useful to the discussion.
dave
Attachments
