Flanking the midranges puts two (major) lobes in the horizontal dispersion in the crossover range rather than one.
I'd choose half the problems over doubling them chasing "symmetrical directivity".
The horizontal directivity of the Radian ribbon is very inconsistent even without a second or third source added, ~120 degrees at 1.5kHz, widening to ~150@5Khz, dropping to ~90@7.5kHz, and "beaming in" ~35@20kHz.
The vertical dispersion is even more inconsistent
20% THD distortion of a (problematic) 2" full range run with no enclosure at 94 dB at 1m bears no resemblance to what the distortion of decent 3" drivers when enough are used to have "line" behavior at 250 Hz.
Even as few as eight 3" would have relatively low THD at 120dB SPL band limited from 250Hz-1.5kHz, most peoples hearing would be distorting far more than the drivers at that level.
A pair of 12NTLW3500 equaling that length would hit ~10% THD at 106dB, not loud at all in comparison to the mid/high output potential.
That said, you have not mentioned what line length, listening distance, dispersion, low frequency extension or desired SPL you'd like to achieve in your speakers.
Art
100% wrong.
please put any further comments here:
as that is the up to date thread with a closer to final design.
as for lobes in the linked thread check out the spec sheet for JBL VTX - it has the best directivity of any speaker with this exact design.
the two lobes CANCEL OUT ... but only with right crossover frequency.
this is why i had to swap 8" radian for 10" and push crossover down to 500 hz because i have determined that there are NO cone drivers smaller than 5" worth using and with a 5" driver now my radiating area was so wide that frequency had to go down to 500 hz and thus i had to go with a bigger planar mid.
well i have switched the design to the 10" and only using it to 3.5 khz. in this range the horizontal directivity is good.
vertical directivity is not a factor in a line array.
i haven't done the math but keep in mind that in a line array the SPLs only add in the FAR FIELD which is the distance at which the array behaves as a point source.
this is only realized at low frequencies and in large venues.
at high frequencies and in an average size room the output of multiple drivers will not add up using the usual +6db per doubling of drivers math. if it did then arrays would fall off at 6db / doubling of distance like line sources but they fall off at 3db / doubling of distance which actually means you get LESS output up close than you expect ... at least at high frequencies, which is why you want to use efficient drivers for highs, such as ribbons.
in fact in prosound line arrays it is considered IMPOSSIBLE to achieve adequate HF extension even with 3X 115 db / watt compression drivers per array element !
at low frequencies THD is not important and in my hornresp models the maximum output was on the order of 140 decibels, which is pretty loud.
as i specify in the new thread:
there would be four woofers per side, so 8 total. that's about 10 kilowatts worth of 95 db / watt efficient drivers.
as i said i used hornresp to model both power and excursion and this setup is good for about 140 decibels without leaving xmax or thermal limits.
EDIT: i see now why you thought it would only get to 106 db, it's because i didn't say that these would only be used down to 60 hz and then cross over to subs. yes you are right if the 12" woofers were to be run full-range they would be excursion and thus THD limited.
this is why i say refer to the new thread where the whole system is described not just one element of it then it will make sense.
NTLW3500 is not a subwoofer, and if it is then i will use something else like JBL HPL of which the NTLW3500 is a knock off. honestly i didn't check the specs of NTLW3500 i just assumed they would be similar to JBL HPL that is same price and same design but only available in 8 ohm and i wanted 4 ohm which NTLW offers.
the NTLW5000 is the subwoofer line but it only comes in 18" and 21" whereas NTLW3500 is a regular woofer and comes in woofer sizes.
don't send a boy to do a man's job - use real subwoofers for sub bass !
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i was going by price from usspeaker because i ordered from them before
since then i saw a lower price on another site but it's not a site i am familiar with and it had "customs" in the name so i guess it's some kind of import business and not a real retailer
the achilles heel of this driver is the basket, or more specifically the flange - it has no reinforcing rib of any kind. very questionable.
aside from that it's a unique driver in the category in that it has a vented pole and also under spider venting in a steel basket.
also very good combination of long xmax and high efficiency for such a small driver.
yet actually another problem with the driver is the terminals seem to protrude beyond cutout diameter.
basically should be good driver acoustically but a nightmare to actually mount into a cabinet.
The transition from near field to far field varies with frequency, there is not a single frequency at which the array behaves as a point source.
You can do the math on your proposed 90" line array using this:
From:
https://www.prosoundtraining.com/2010/03/17/line-array-limitations/
The near field distance can be defined by the following relationship:
D=1.57 L squared/λ
where
D is the distance to the far field transition
L is the physical length of the line source
λ = the wavelength of the frequency in question (all lengths in identical units).
Beyond this distance the listener is in the far field and there is 6 dB drop in level per doubling of distance. The transition distance can be quite long at short wavelengths, that is, high frequencies, but it is shorter at low frequencies. For each octave lower in frequency, the transition distance is cut in half.
In the near field the high frequencies are lost due to destructive interference.
At any rate, the design considerations of a line array for small room listening distances compared to large rooms will result in very different optimizations.
Best of luck with yours!
Art
