Should I get one 18" or two 12" for my 3-Way?

Those SB 12s are hard to beat for extension and accuracy, plus they have really good xmax and sensitivity. In the right box they will take 500w for 2 pcs (mechanically limited) and play close to 120dB down to mid 20s. Almost every other pro 15 will have higher overall HD, especially over 100 hz and under 40 hz. You'll expect over 95dB@ 2.83V without extra acoustical gain of 2 drivers together. These have 3" VCs, which is pro audio territory.
So what would you use?
 
Well I thought its obvious from, my post. 2 SB34NRXL75s are overall better than most single 18s in regard to useful upper frequency limits and lower Fb once installed in an enclosure. The copper shorting ring helps with HD and lower Le. The motor asy is dead quiet too. You won't find many pro 18s that have true 3/4" of linear excursion with lower Kms and Rms too. Its alot of driver for the money, even if you are paying almost 700 bucks for 2 of them compared to one better 18" pro sound driver, which may have a minute Sd advantage compared to 2 of the SB 12s. The efficiency between the two drivers with the 12s being paralleled will be close if the 18 has comparable xmax after BSC is applied. The JBL2268hpl is also a good driver for your intended purpose, but it shouldn't be used higher than 200 hz, which isn't even remotely an issue for the SB 34NRXL75-8, which can be good to over 300 if the enclosure is optimized to deal with the midrange backwash.
 
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For consideration

Twin:

Dayton RSS315HFA-8
120L, 2pi sensitivity 92dB/2.38V, F3/F6/F10 36/28/21
Peerless XXLS-P830845
120L, 2pi sensivity 95dB/2.83V F3/F6/F10 40/32/26
SB Acoustics SB34RNXL75-8
75L, 2pi senstivity 98dB/2.83V F3/F6/F10 58/43/33
 
My use those SB34NRX75-6 12" drivers (actually 13" frame size). Just one woofer per side. My room is 20ft x 30 ft x 14 ft H. Those woofers FILL this space with bass. A 25 Hz sine wave at +/- 10 mm rattles the windows and causes small objects to danse on shelves.
 
Is there anything better than the 18LEX1600Nd?
Yes. https://d.precision-devices.com/products/all-products/pd1850-3/
It is all about power compression. The PD 1850/3 has a precision engineered 5 inch voice coil, hence just 1.6dB of power compression at 800 watts AES continuous power. Beyma used to publish their drivers power compression but they stopped that about 8 years ago... The Beyma 18 inch drivers all had between 4dB and 5dB power compression at AES rated power (not peak power).
Personally I only use drivers in sealed box loading and fine tune depending on room gain/placement using DSP as I believe time domain accuracy is the single most important aspect of any driver/loudspeaker design.
 
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Use a single 18" and place it as close to the mid-woofer as you can. This will give you the best directivity match and minimize lobes and nulls at your intended XO point. 1/4 wavelength at 260Hz is 13"

SPL is just one consideration here, get as close as you can to an ideal point source. You'll be listening to as much wall reflections as you will direct sound. Multiple drivers per passband will just muddy the waters at any volume because phase interactions will be multiplied as well.

Bonus: single 18" costs a lot less than 4x12 or 2x15.
 
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Yes. https://d.precision-devices.com/products/all-products/pd1850-3/
It is all about power compression. The PD 1850/3 has a precision engineered 5 inch voice coil, hence just 1.6dB of power compression at 800 watts AES continuous power. Beyma used to publish their drivers power compression but they stopped that about 8 years ago... The Beyma 18 inch drivers all had between 4dB and 5dB power compression at AES rated power (not peak power).
Personally I only use drivers in sealed box loading and fine tune depending on room gain/placement using DSP as I believe time domain accuracy is the single most important aspect of any driver/loudspeaker design.
Simulation in 60 litres sealed box..
PD1850 / V3
Performance at rated power with one driver before room gain in 61 liters (just over two cubic feet) = 105dB continuous SPL at 25Hz.

Performance at rated power with two drivers with 6db gain (3dB from floor plus 3dB from rear wall ie not in corners which would total of 9dB room gain per driver) = 114dB continuous SPL at 25Hz.
 

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Use a single 18" and place it as close to the mid-woofer as you can. This will give you the best directivity match and minimize lobed and nulls at your intended XO point. 1/4 wavelength at 260Hz is 13"

SPL is just one consideration here, get as close as you can to an ideal point source. You'll be listening to as much wall reflections as you will direct sound. Multiple drivers per passband will just muddy the waters at any volume because phase interactions will be multiplied as well.

Bonus: single 18" costs a lot less than 4x12 or 2x15.
Most studies favour multiple subs distributed in room as you can even out room nulls/nodes more easily than on single location ... Dr Geddes has written extensively on this subject and had many AES papers published which were positively peer reviewed.
 
Most studies favour multiple subs distributed in room as you can even out room nulls/nodes more easily than on single location ... Dr Geddes has written extensively on this subject and had many AES papers published which were positively peer reviewed.
yes, but if OP is going to cross at 260Hz it's not a sub

there's two paths here: run it like a big 3-way like he is planning or
run it like PA mains crossed at 80hz to subs which could be placed anywhere

it it better to stretch the mid-woofer lower in frequency, or stretch the "sub" higher?
that depends on the drivers used, vented vs. sealed alignment, max SPL wanted.

I think both are valid approaches.
 
yes, but if OP is going to cross at 260Hz it's not a sub

there's two paths here: run it like a big 3-way like he is planning or
run it like PA mains crossed at 80hz to subs which could be placed anywhere

it it better to stretch the mid-woofer lower in frequency, or stretch the "sub" higher?
that depends on the drivers used, vented vs. sealed alignment, max SPL wanted.

I think both are valid approaches.
Yes, good point I didnt read the OP wanted a 260Hz crossover... In which case a big 3 way with two 15 inch (or two 18 inch!) subs forming the base of the speakers would be the way to go.
 
I did some simulations in WinISD ( 9cuft, 24hz and 28hz).
the two 12" have exactly the same SPL, Cone Excursion, Group Delay... compared to a single 18".
While having 1/2 the Mms per driver.
Lower Qts (0.28 vs 0.43)

I'm not sure if inertia is a thing to consider?
Seems like the 12s are easier to drive.

If 1/4 wavelength at 260Hz is 13", I have basically 12-13 inches between the mid and the first woofer,
What's gonna happen to the second one being 24+ inches away from the mid?
 
Hi there,

Let's start from these assumptions:
  • F3 is tuned at ~24hz for both.
  • Xmax within range.
  • Fully active 3 way, no passive crossover.
  • The 18" has +3db compared to the two 12" below 28hz, so it get's lower... but again, DSP here.
  • box size doesn't matter.
  • they will cut at 260hz.

pros/cons?
Anyone experienced both?
Modern speakers have multiple woofers, I get that, commercial thing, the general public likes them more for the look and space vs the fridge sized speaker... but would they sound "better" with a bigger woofer?
The short answer is Yes! 'There's no replacement for displacement' 😉, though down low it's more about physical impact than SPL, i.e. more compression horn like performance with its lower distortion too.

Anyway, based on actual 12" Sd (10" dia., 2 = 14.14" dia.), 18" Sd (15.55" dia.) specs, 1 mm Xmax, this piston calculator 'says' dual 12" = ~83.04 dB, 18" = ~84.69 dB

Done this way you're 'forced' to choose based on acoustic radiation efficiency, which in turn works out to less power required = less distortion/higher SQ.

Coming from a horn background, I'd choose ~0.81x 260 Hz = ~210.6 Hz = ~ dual 18" = ~ 24", but these apparently have fallen out of fashion, so few choices and exorbitant prices! 🙁 A single then requires 4x more power handling.
 
Alright alright, I ordered the 12s... otherwise by page 3 I'll need 4x21" per speaker.

Quick photoshop... that thing is 5'10" or 6' high.
CustomDouble12.jpg


  • WTMW or MTWW ?
  • Front or back reflex?
  • Shared volume or separated (for the low)?

I already got the tweeters and mids, two woofers this weekend and more on backorder, still waiting for the horn.