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Old 18th July 2013, 02:00 PM   #21
GM is online now GM  United States
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You're welcome! Please keep in mind that while GD increases with decreasing tuning, human hearing is ~inversely proportional as best I can tell from mine and some others observations, so what seems to really matter is an individual's GD threshold higher up, which IME, sufficiently long [ML]TLs are on a par with BRs with very large area vents [often > Sd in a simple reflex, a no-no according to the pioneers of audio], so as long as vent mach is < ~5%, it's never been an issue AFAIK; though there are folks who swear they can tell that any vented alignment is audibly inferior/unacceptable to a sealed alignment even after I’ve easily fooled them! In such cases, literally ‘stuffing a sock’ in the vent solves the ‘problem’.

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Old 18th July 2013, 02:27 PM   #22
IG81 is offline IG81  Canada
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I caught a few references as to GD<~30ms being acceptable and not generally noticeable, though I don't have solid sources for this.

Most GD values seem to be quite reasonable if the alignment also is, or so do I gather from some WinISD sims. My TD15M in a 5cu.f GR box Fb=32Hz stays below 12ms within its f10 pass-band for example. Sounds fast and tight to me.

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Old 18th July 2013, 02:31 PM   #23
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Quote:
Originally Posted by PET-240 View Post
Hey GM,

Can you advise any differences between the two regards sound, speed, decay etc please?
Also what size diffrrence are you thinking for the TQWT?

Thanks,
Drew
Greets!

Both are essentially 4th order alignments same as a BR and as I noted, mainly just a difference in shape, not net Vb, so the inversely tapered TQWT is normally limited to alignments where a low vent mach requires a very long vent. The difference between a simple BR and these is increased acoustical damping of the vent, i.e. increasing the cab’s acoustical path-length decreases the vent length, ergo when it gets < than baffle thickness, the vent area must increase for a given tuning.

This extra damping is similar to ‘critically’ damping a BR’s vent with some form of resistance, such as [layers of] cloth or similar stretched over it to quell any under-damped ‘ringing’ at Fb.

What makes the MLTL, etc., superior though is that it doesn’t trade away vent efficiency like the BR does plus it can allow a lower tuning to be chosen with less loss in efficiency, though it will be larger. No ‘free lunch’ in reproducing large WLs, size matters!

As such, AFAIK there’s no advantage of using a TQWT when a MLTL will suffice and in each case, the amount of internal damping and where along its path-length it’s concentrated will determine its Qt[p]; though due to the TQWT’s HF harmonic ‘ripple’ it needs more damping if used over a wide BW, so would by necessity be the ‘tighter’/‘faster’ of the two unless a similar amount of damping is used in the MLTL also.

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Old 18th July 2013, 02:58 PM   #24
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Quote:
Originally Posted by IG81 View Post
I caught a few references as to GD<~30ms being acceptable and not generally noticeable, though I don't have solid sources for this.
This was debated ‘ad nauseam’ on the late basslist and with my copy of it currently inaccessible, these posts saved by John Murphy is all I have: Discussion of Group Delay in Loudspeakers
Discussion of Equalizers and Group Delay in Loudspeakers

Again though, due to us all hearing the same, yet not so much, it’s up to the individual to determine what sounds best overall in their system, so for me, the rest is just about finding a starting point for experimentation.

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