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Old 23rd December 2012, 09:49 PM   #21
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Re the wonders of a 'giant Cornu spiral... [with] lots of output up into 500Hz':

Output above about 300Hz from a back load = chronic group delay which is very audible for most people. Assuming, for e.g., a 6ft flare path length, then working on average SoS of 1.13ft / ms you've got a delay of 5.3ms up in the 500Hz BW: well above the 3.2ms audibility threshold for that frequency established by Blauert and Laws. A lower acoustic XO is needed, but without some help from the amp, Eq or whatever, the driver will need a short front horn to fill in the region between its mass corner and the practical upper corner frequency of the horn. I wouldn't advise taking any back load much beyond ~300Hz.
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Old 23rd December 2012, 10:21 PM   #22
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Default Sorry !

Sorry to interrupt you gentlemen , but can someone tell me if I'm wrong with my results (using the spreadsheet from Zillasspeak) to design a BIB (using the datas from the AN webpage?
The spec. :
Driver : Audio Nirvana Super 8 Cast Frame
sensit. : 97.3 db
equivalent diaghram radius : 88 mm
equivalent mass : 10.023
magnet weight : 1400 g
net weight : 3690 g
Fs : 44.63
Re : 7.2
Mms : 11.748 g
BL : 11.84 TM
Qts : 0.162
Qms : 3.836
Qes : 0.169
Vas : 66.495 ltre
Xmax : 1.0 mm
no : 3.379 %

My results :
Line length : 150,85
Zdriver : 32,73
Sm-terminus area : 110,60
Depth (internal) : 12,51
Width (int.) 8,84
Nominal Height- L/2 : 75,42

Thanks again !
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Old 23rd December 2012, 11:15 PM   #23
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Quote:
Originally Posted by planet10 View Post
All that does is indicate that the MArk Audio drivers have T/S curves that are closer to horizontal. Hae a look at these measurements of the same pair of FE127eN drivers by Mark & myself (and the factory's for reference (of stock drivers))

dave
That was the picture I was thinking of. I was wrongly remembering the results being closer than that!

If the factory specs are 'in doubt' which do you use to design? My measurements or the factory set?

sorry to OP for clogging up his thread.
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Old 23rd December 2012, 11:32 PM   #24
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Quote:
Originally Posted by gafhenderson View Post
That was the picture I was thinking of. I was wrongly remembering the results being closer than that!

If the factory specs are 'in doubt' which do you use to design? My measurements or the factory set?

sorry to OP for clogging up his thread.
No problem ! I was kidding. I will eventually ask one of my friend to measure the spec. of my drivers, but till then it helps me to have your opinion. I can figure more easily how I will do it and if the ceiling of my appartement are high anough !
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Old 24th December 2012, 01:26 AM   #25
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Quote:
Originally Posted by spartiate1952 View Post
..........but my amp is not very powerful, it's a SET tube 45 type 1,72 w.
For best power transfer with a SET amp requires the speaker be tuned to Fs, so to sim a BIB with the calculator requires inputting 2xFs and of course true Fs ideally should be known for each driver. Also, the amp's output impedance needs to be added as series resistance to calculate the driver's effective Qts.

Note that based on the published specs for Sd [~243.849 cm^2], Mms, BL, Fs, then Vas = ~91.785 L.

If there's no measurements, then use a ~0.4 Qts and if the amp's output impedance isn't high enough [DF = ~1], then some form of additional series resistance may be required to flatten out the speakers in room response.

GM
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Old 24th December 2012, 02:50 AM   #26
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Quote:
Originally Posted by gafhenderson View Post
If the factory specs are 'in doubt' which do you use to design? My measurements or the factory set?
I always start with the factory numbers.

dave
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Old 24th December 2012, 03:04 AM   #27
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I would go with a subwoofer instead.
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Old 24th December 2012, 06:25 AM   #28
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BIB is not really horn, both like classic TQWP....
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Old 24th December 2012, 07:40 AM   #29
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Both BIB & classic TQWP = Voigt are classified as tapped horns.

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Old 24th December 2012, 07:54 AM   #30
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Indeed. The BIB is a simple tapped corner horn. If it expands toward the terminus, some form of 1/2 wave resonant behaviour is present, ergo, it's a horn. As it happens, GM informed me some years ago that originally 'TQWT' was used in the opposite sense of how it is often employed these days, i.e. it was a pipe that narrowed toward the terminus. Although I suspect he & I are the only people here who continue to use that definition.

Last edited by Scottmoose; 24th December 2012 at 07:58 AM.
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