Huh?
Any quarter wave resonator, by definition would be a resonator, unless it's closed at both ends, at which point yes it's a transmission line, but also effectively equivalent to a sealed box, minus a reduced impedance peak which I honestly fail to see the value of to anyone not using wimpy tube amps.
That quarter wave resonator will also eventually be out of phase with the forward wave of the driver, just like a passive radiator or a port, leading to an ultimate 24db/octave rolloff.
If what you're saying, is that the impulse response is very clean, then yes, TLs can have very clean impulse response unlike the conventional vented box, but only because the conventional vented box' impulse response wasn't modeled in the design process.
Likewise with a properly damped helmholtz enclosure... designed with clean impulse response as a goal and with a tuning behaviour appropriate for a given room.
The open end of a TL is a point source bass radiator. Not sure how this makes it couple "excellently" to the room. It's effectively identical coupling to the vent in a vented box. The difference is that TLs are modeled to factor in internal ringing / upper harmonics and most ported boxes are thrown together haphazardly. This of course has nothing to do with coupling. Neither will couple to room modes like a cardioid or dipole source. I think what you're calling coupling, is a shallow ~3db/octave rolloff of an extended bass shelf alignment, which most TLs effectively resemble. This shallow slope appropriates room gain behaviour.
I would greatly appreciate in-room measurements to show this phenomenon, of a single one of your TLs and how they load the room evenly from 20hz to 400hz or what have you. Else I don't see how their radiation is desirable over any other monopole. The closest thing you get is that the upper harmonics of lines also contribute output as a secondary source, which is a very narrow passband, and only useful if the open end is far away from the radiating driver.
Likewise with any properly damped ported box. The damping and frequency response of the ported box determines its coloration characteristics or lack thereof, and likewise with a TL. Neither requires amplifier boost like a sealed box.
Not if you want infrasonics. The 24db/octave rolloff of a resonant system like any TL with open end output won't get you subsonics below the knee. MJK's research indicates there's no such thing as the mythical 12db/octave TL, unless you completely stuff it and turn it into an oversized sealed box. The only advantage of such an approach is to get a flatter impedance peak; a goal which is beyond me for usefulness, as such a TL would again require the same type of boost as a sealed box, and have the same F3 as a sealed box of the same volume.
Of course, if you don't care about what's going on below 20hz, it's irrelevant. Go with a vented box or a TL. TLs are optimal for the same types of program as well designed, well damped ported boxes. Any differences between them will be evident in the various models using MJK's worksheets.
As is the case with a well designed ported box, along with the requisite 24db/octave rolloff of both. If one wants bass down into infrasonics with a gradual rolloff, they need multiple 18s as you said. If one only needs bass down to 20hz, then they need superior modeling software like MJK's quarter wave worksheets, which analyze damping properties of enclosures in general. Whether it's a TL or a vent or passive radiators or sealed, they will still require many spaced sources if they want truly measurably flat frequency response. That, or cardioid subs, which have the caveat of, being gradient systems, worse efficiency than sealed and thus more need for response shaping.
TLs are non resonant if properly damped and they do not roll off at 24 db/octave but at 12 db per octave. They have to be damped to the point were there is only one peak of impedance and not two, like an undamped quarter wave pipe has or a Qb4 ported box.
The port of a TL has a large area, unlike a reflex enclosure. There is large non turbulent air movement.
An organ builder showed me long ago that pipes couple to the room evenly. In a church were there was an electric organ being replaced by a pipe organ, he showed me the effect.
The speakers of the electric organ were loud up front and quiet at the back. The spl fell as the square of the distance. The pipe organ on the other hand filled the church pretty much uniformly. Organ builders use the term encircling for the phenomenon.
This is why a congregation will sing much more lustily with a pipe organ then an electric organ. The pipe organ builds confidence in a fashion that no speaker driven instrument can.
Now a TL will support the driver over about 1.5 octaves, so if the pipe is tuned to 40 Hz there will be support to 100 Hz. If tuned to 20 Hz then there will be support to 60 Hz. You will not get support to 400 Hz. However it is below 100 Hz that speakers become progressively poor couplers to the room.
The late John wright showed that if you build dual TLs tuned half and octave apart you get a particularly even driver support and in room response. These systems are highly unusual and exceedingly uncommon. As far as I know he was the only individual to make a commercial design available not long before his untimely death.
I took these readings with a calibrated microphone.
Now the large line has good assist from 20 to 60 Hz and the smaller line from 40 to 100 Hz, although there seems some assist to 120 Hz.
I took readings from one meter of the top ports from 20 to 60 Hz and 1 meter from the division of the 10" woofers and also 1 meter from the tweeter axis. I took readings across the front row seats and the back row seats. From 70 to 200 Hz I took readings from the port of the smaller TL. These readings are bracketed. Drive was constant throughout the frequencies sampled.
From 40 to 60 Hz there is overlap from the ports of the 7" and 10" drivers and the the ports of both lines. So in this region the tweeter axis response is probably the most significant as well as the far field response.
Freq Hz TL port Tweeter axis Front row seats Back row seats.
20 92 db 94 db 86 db 94 db
25 98 db 98 db 94 db 96 db
30 97 db 96 db 92 db 96 db
40 96 db 96 db 92 db 86 db
50 100 db 100 db 97 db 90 db
60 94 db 96 db 90 db 84 db
70 (102) db 101 db 92 db 95 db
80 (102) db 98 db 90 db 94 db
90 (100) db 98 db 84 db 100 db
100 (99) db 95 db 95 db 94 db
110 (96) db 96 db 97 db 94 db
120 (96) db 96 db 94 db 90 db
200 (90) db 96 db 86 db 86 db
400 -------- 90 db 90 db 85 db
500 -------- 98 db 87 db 85 db
Readings from calibrated Shure condenser Mic.
The bass of from TLs is certainly very different in character from other loading systems.
I had a client here last week, who had just had a CD mastered at Greg Rierson's studio. He has large PMC lines. That was this individuals first exposure to TLs. He got his second here. He said both these systems were the best he had ever heard and he had heard a lot. He said he heard numerous features in the bass line he had never heard before.
He is going to decide whether he will contract Walberswick studios to archive the bands reel to reel archive and master it to CD. Unfortunately it is rock music, but a job is a job!
If you want to hear large lines you will have to come here or find some large PMC speakers. They are not plentiful. Greg's were $27,000 per pair and they are a long way from the top of the PMC offerings.
