Here is a good video that goes into the differences between B&C and Eighteen Sound drivers. There is a lot of good information here.
Just skip to the part ( at 1 hour mark ) where they show the Klippel results for the 18NTLW5000 and the 18SW115.
The BL curve for the 18NTLW5000 is as flat and symmetric as they come. Very impressive stuff.
I will strongly consider the 15NTLW3500 as a state of the art 15" woofer.
i watched the whole video.
note at 43 minute mark the B&C guy says the DS woofers donât sound good above 120hz-160hz or so because of too much VC mass and inductance âŚ
this is what i was kind of alluding to before - the drivers with the most beastly motors that you like so much are really subwoofer drivers not optimized for midrange âŚ
as for Klippel measurements for NTLW vs SW they were much closer than i expected âŚ
only real difference i could see was inductance was symmetrical for NTLW while it was not for the SW
but the BL curve was almost identical - that was a surprise to me
keep in mind something else the B&C guy said though, namely that most of their efforts are focused on the neodymium lines. thatâs because those are the higher end, more expensive models. it makes no sense to waste development money on ferrite drivers since nobody in prosound wants heavy drivers so nobody will pay for ferrite drivers so why waste engineering efforts on them.
this means that the 15" ferrite Tetracoil is likely not on the same level as 18" neodymium Tetracoil
in fact i know it isnât because to get long stroke in a woofer you need a deep magnetic structure but with ferrite making the structure deep adds too much weight so you only see deep ferrite motors outside of prosound where people are willing to buy drivers that weigh 100 lbs. my TC Sounds LMS driver for example weighs 80 lbs to get its long stroke with ferrite magnet.
on other hand with Neodyium you can get longer stroke with less weight by using deep but narrow motor.
push pull designs like Differential Drive and Tetracoil further increase the amount of stroke you can get for any given weight of motor.
still the main point is donât expect to get great Xmax from a ferrite prosound driver, even a Tetracoil one.
Tetracoil offers an avantage in stroke to weight ratio so to speak, but perhaps not as much of an advantage as inside-the-voice-coil neodymium slug magnet does.
so between a Neodymimum B&C and Ferrite Tetracoil probably the Neodymium B&C would win when stroke is concerned. the Tetracoil may have advantage in inductance but that only matters if the driver was optimized for midrange to begin with which i donât think the 15" Tetracoil was, since Eighteen Sound calls it âsubwooferâ on the product page.
when youâre picking drivers i want you to pay attention to moving mass of the diaphragm as well as inductance. just because a driver is 15" and not 18" doesnât mean that it isnât a subwoofer. whether a driver is a woofer or a subwoofer is mainly down to inductance and moving mass as far as the spec sheet is concerned.
but also as the guys said the spec sheet doesnât tell the whole story. if the manufacturer calls their driver a subwoofer i wouldnât want to push that driver into the critical vocal range.
The DS isnât suitable as a woofer for sure. It uses a four layer voice coil like you would find in a car audio subwoofer. The inductance is too high for anything other than a subwoofer.
right so think of driver as a fighter or athlete and the design as a team or army
would you rather have one great fighter / athlete going at it alone - or have a team / army that works well together ?
the job of subwoofer is mainly compressing air inside a box. with a thick cone and multi-layer VC that job can be done well.
a woofer not having to do this then frees it up to have a thinner cone of material optimized more for damping than physical strength and motor optimized for better parameters at low excursions than for being able to maintain poor parameters for long excursions.
a symmetrical design, despite what the marketing guys were saying in the video, is more about being perfect at shorter excursions than about doing well at longer excursions. symmetrical designs automatically are flat in every curve around 0mm xmax - whereas non-symmetrical designs will tend to have a slope there.
if a symmetrical design has longer Xmax as in case of 18NTLW it isnât so much because thatâs inherent to push-pull motors but because push-pull motors are used in high end drivers and large Xmax is expected in drivers at that price point. what is inherent to push-pull instead is flat / horizontal region at the center of the BL and inductance curves.
i guess in the end itâs the Klippel results that matter though not how you got there. as the guys in the video said the push-pull type motor does most of the design optimization for you automatically, whereas with a regular motor you need to wrestle with finite element analysis to get it to behave. but in the end if they can make it work then it doesnât matter how it was done. all else being equal though a push-pull motor will be lighter but deeper which may matter in some cases.
you simply need a system that keeps drivers in their flat zone of BL curve. you donât need a system of drivers with huge linear strokes. for example in case of 3-way + sub that i suggested the 15" woofer is the JBL Differential Drive from PartsExpress and that one only has 7mm xmax, but what does it matter if all of the excursion will be handled by the subwoofer anyway ? That 15" woofer wonât move more than 1 mm under normal conditions and will remain in a COMPLETELY flat zone of the BL curve at all times.
by the way as far as JBL D2 compression driver it may not have a standard bolt pattern to match to horns. most drivers have one of several standard bolt patterns but because JBL doesnât sell drivers for profit and only as replacement parts they may not have standard bolt patterns as they only need to fit the original speaker they came with.
this is quite sad because the D2 is a very cool driver, albeit it is more optimized for array use which is to say for very long throw at high frequencies, rather than for hi-fi use where maybe it isnât so much about extreme output above 10 khz âŚ
the other point raised in the video was that it isnât about watts but volts and amps.
Powersoft is very keen to point this out.
B&C iPal was co-developed with Powersoft and designed to be powered by Special Powersoft modules.
i didnât realize that Eighteen Soundâs iD series drivers like this one:
https://www.eighteensound.it/en/products/lf-driver/18-0/2/18iD
are also designed around the same Powersoft / iPal concept of very low VC resistance combined with high reactance ⌠thatâs something i learned from watching the video.
but it makes sense since 18 Sound and B&C are the same company now and this is some of their latest work plus also they and Powersoft are all from Italy. and as Powersoft said driver and amp is one system - at least when it comes to subwoofers.
so really, by doing a dedicated sub you wonât really be spending more per unit of deep bass output because even though you will have more amps the only amp that really costs $$$ ( the sub amp ) will have an easier time because you will be able to fully optimize the subwoofer both acoustically and electrically for the frequencies where most amp power is required.
only way you will save money by avoiding a subwoofer is by also giving up on some deep bass. if you try to get same amount of bass without a sub you will probably spend more.
in other words yes a system without a sub can be cheaper if you arenât targeting some specific performance level but if youâre not then why are trying to get ultra high end drivers ? yes i get it you already explained you want to build an amazing speaker rather than achieve amazing system performance. i can understand that as you are trying to make a statement piece / conversation starter rather than simply solve the needs of some venue that requires certain coverage.
still i have to point these things out and you can then ignore them 
i think iPal / iD may be a good choice if youâre only going to be running one driver per channel of a large amp.
normal drivers are meant to be paralleled into an amp channel so that perhaps you have an array of 8 ohm drivers driven by amp designed for 2 ohm load.
but as amp are going multi-channel and sub drivers getting more powerful perhaps weâre now looking more at a situation of one driver per amp channel at which point it make sense to use a driver of lower impedance âŚ
âimpedanceâ though consists of resistance and reactance and the idea behind iPal is very low resistance but still high reactance âŚ
thatâs because 100% of resistance is a loss to heat with no useful work done
while reactance may be a loss ( such as to inductance ) or may be converted to useful work ( EMF ) âŚ
with older amps most of the loss was in the amp itself due to class AB operation but with the latest class D design the losses are primarily in the driver ( which is why PowerSoft amps can use very small fans for a given level of power output ).
once youâre in this PowerSoft paradigm to further minimize system losses you will try to minimize the VC resistance without necessarily reducing impedance because your reactance comes from the BL and without the BL you will have to increase current which will melt the tinsel leads and burn your amp âŚ
thatâs where iPal and iD drivers come in with VC resistance in the range of 1.2 to 1.5 ohm or so ⌠yet still hitting peak impedance of almost like 100 ohms at resonance due to high BL âŚ
this kind of optimization is only possible with dedicated subwoofer drivers though âŚ
if i were you i would maybe take some more time to think about it, maybe save up a bit more, and build something that you will be happy with for at least 10 years rather than build something that maybe 2 years from now you realize wasnât as great an idea as you thought âŚ
on other hand maybe you would rather not wait 10 years between builds even if it means spending more money overall by building a new system every 2 years âŚ
i could understand that as well âŚ
finally want to mention my TC Sounds LMS is hard to get to Xmax with my QSX PLX amplifier
it simply takes a lot of power to drive these large subs to long excursions
i need to bridge both channels of the PLX into a single 18" LMS driver to extract the potential out of it âŚ
so this is kind of why the iPal things exists as well âŚ
i used to think the iPal was just about maximizing efficiency for the latest class D amps from PowerSoft but after watching your video and thinking back to my LMS subwoofer i realized that for a driver with the level of output of iPal there may not be any other way to even drive it to full potential âŚ
also to be honest when i was thinking of how i would build my ultimate system one reason i thought of NTLW over the iPal is simply the price !
the NTLW was about $700 while iPal was about $1,000 which is not trivial especially when you want to use four of them.
but i did suspect that durability may be an issue with NTLW because the force is transferred to the cone through 4.5" VC rather than 6" of the iPal âŚ
according to your video durability is the number one concern and also apparently itâs hard to get enough volts to drive a speaker like this ⌠if both those are true then iPal may be worth the extra $$$ over the NTLW for subwoofer duty even if it may not have as beautifully symmetrical a BL curve âŚ
the iPal also seems to have longer XMECH ( excursion before damage ) compared to NTLW
according to what i read harmonic distortion is not really that audible in subwoofers. with subs you may hear port chuffing or other non-harmonic type of spurious noises but harmonic distortion itself is not really that relevant there.
in other words an iPal may be THE driver to use for sub duty over the NTLW for pure slam and room shaking. then above 100 hz or so you transition to something like this JBL:
which should be more of a musical woofer than a sub-bass sledgehammer.
and you wonât have to worry about things like Xmax with that 100 hz crossover.
so perhaps:
BMS 5530ND Compression Driver on Horn
2.5 khz crossover
18 Sound 8NM610 Bucket Midrange on Waveguide
600 hz crossover
JBL 2265 HPL vented, tuned to 60 hz
120 hz crossover
21" B&C iPal vented, tuned to 24 hz
the only amp that will cost you anything is the one driving the iPal. Crown seems to be a good value in US while Powersoft a good value in Europe. Dynacord seems a good cost no object option.
the rest of the amps you can get used on Ebay without taking out a mortgage.
or you can drive the subs with cheap Ebay amps as well but you may have to do what i do which is use a 2-channel amp bridged into a single driver for every sub. this will definitely be a lot cheaper than buying new amps.
remember the installation guys often have to use new amps under warranty and the mobile DJs are looking for light weight amps that can power multiple cabinets. nobody wants big heavy amps that need to be bridged to drive a single sub so you will be able to buy those for cheap used on Ebay.
one guy on AVS Forum had an entire wall of cheap Ebay amps like that driving his subs. itâs actually a pretty smart way to save money. pro guys have to let those go for next to nothing because they are unable to use them even though they still work.
watch out for fan noise though. newer class D amps may not need a lot of cooling but older class AB amps like my QSC sure do and the fan are loud as fuck. you can swap the fans but only if you donât plan to load the amp. so you can swap the fans for a Noctua on the amp driving the mids and highs but definitely not on the amp driving the subs.
i also wouldnât swap fans on any new amp that is worth anything. only on cheap disposable Ebay amps.
maybe iPals arenât the best idea after all if youâre going to drive them with used eBay amps âŚ
and the amps designed to drive something like iPal will cost you an arm and a leg âŚ
these are the types of things i would be thinking about rather than simply trying to get the âbestâ 15" woofer âŚ
AVS Forum is a good place to get help on high end DIY subwoofers and mediocre subwoofer amps ( mainly Chinese knock-offs of Lab. Gruppen )
SpeakerPlans:
is a great place for help with prosound amps but they focus on lightweight mobile amps and also on European market
Diy Audio is a great place for things other than subwoofers so long as you ignore the Danley hype. The problem with Diy Audio is even though they have some great people there are even more total idiots.
AudioScienceReview great as well but they are too focused on tiny low-output speakers even though their own founder said you havenât lived until you heard a dynamic speaker like a large JBL âŚ
finally there is Prosoundweb but they donât allow discussion of non-professional use and are very protective of companies sponsoring the forum. i was able to get help from very high level industry pros there but shortly after many of my threads were deleted.
there is also data-bass forum run by Ricci:
https://data-bass.ipbhost.com/
i never used it but me and Ricci used to be buds in the early days of AVS before i stopped posting and then he went to start data-bass âŚ
it seems data-bass would be a good forum to ask about drivers like iPal especially as Ricci literally tested the iPal for data-bass âŚ
the most important amplifier companies or brands IMO are:
Crown
Lab Gruppen
Powersoft
Dynacord
Crown: big in US, part of Harman umbrella so can have presets for JBL speakers. recently has switched to class D for most new amps.
Lab Gruppen - known for their high end âclass TDâ amps, was recently purchased by Behringer. still uses class TD but recently starting to use class D as well. Class TD is a more musical type of amp than D, but D is more efficient.
Powersoft - known for their lightweight subwoofer amps. Powersoft always made only class D amps, which is why people looking for class D amp usually look to Powersoft first.
Dynacord - brand name ElectroVoice uses in US. EV itself i think is part of BOSCH. only negative thing i heard about them is that they are expensive.
QSC used to be all the rage with their SMPS Class H amps at the time i got my PLX. but these days they are more known for their Q-Sys DSP system than their amps. their amps lately are second rate to be honest while Q-Sys is the king of DSP now.
used QSC amps on E-bay may be a great value though because QSC was the amp to get back in the day and now theyâre flooding the used market.
basically if youâre either an institution or a mobile DJ you buy a new switching amp for big bucks
institution will buy it for efficiency and warranty and a mobile DJ will buy it for light weight power for the subs
Lab. Gruppen and Powersoft have their own unique back story so donât fit the general pattern ⌠but Crown and Dynacord do
Crown and Dynacord have converted their higher end models to switching ( class D ) while keep the lower end models linear ( Class AB / H )
and itâs no a subtle difference in price. weâre talking $500 for the linear amp versus $5,000 for the class D amp âŚ
they probably both cost the same to make. the price simply reflects the market conditions where linear amps flood the used market and canât sell for more than a few hundred while people will pay almost any price for a light weight efficient amp.
i also like the latest and greatest as much as you but in this case maybe it isnât worth the premium for the time being, until the market is saturated and prices come down.
itâs like the early days of flat screen TVs when people paid huge money for 32" sets with 720p resolution. now you can get 65" 4K TV for the same price.
class D amps will probably follow the same pattern - better not to pay for them unless you need that power and light weight efficiency RIGHT NOW.