The Bassmaxx B Zero is over twice the size of the Keystone and has a -3 dB of 42 Hz compared to 34 Hz.
If David's specs are correct, the B Zero should have more output than a Keystone above 42 Hz, as one would expect from a cabinet double the size that rolls off almost 1/3 octave higher.
I'd expect the dual 18" MTL 1X with a F3 of 50 Hz would be more sensitive above 55 Hz as well.
If 50 Hz response rows your boat, the MTL 1X is just fine as a design.
I only have a pair of Keystones,(which keep up with 28 horn loaded 8" and 10 EVDH1AMT drivers) but if you can get David to bring some BZeros to Madrid, New Mexico I'd be glad to do some comparison testing.
Art
So you have not literally tested your box against the Electrovoice MTL 1X. Are you going solely on what specification sheet state on the Electrovoice MTL 1X in an anechoic chamber?
The Electrovoice MTL 1X stands as tall as the Bassmaxx B Zero however is not as deep as the B Zero. Considering the last series offered a pair of EVX 180Bs in each cabinet which, are very efficient drivers on there own, more so when they are paired together, I don’t see how your box with a single driver is going to offer more SPL than a single Electrovoice MTL 1X when it is subjected with power.
Even at 40 Hz, the coupling effect of both EVX 180Bs should fall within the same region as your box since you mentioned your box will go down to 35 Hertz when subjected to a Powersoft K 10 or amplifier with similar power.
Maybe when someone in the States forms another Subwoofer Shootout you can bring your boxes to literally see how they compare amongst the likes of the Danely, the Bassmaxx, and the Electrovoice. Since one or all of the above brands have been in every Subwoofer Shootout held in the United States for the past decade or so, you will have proof that your design can indeed match or exceed the performance of the likes of the competitors once we go beyond the 1-watt/2.83-volt measurement with TEF results.
My interest is the Electrovoice MTL 1X using the EVX 180B since he claims one of his boxes will deliver more output than one Electrovoice MTL 1X using two EVX 180Bs below 50 Hz. So if you have seen any SPL charts higher than 1 watt/2.83 volt, pitting those two cabinets against each other in a real world scenario, feel free to post the link.
A lot of people copy the MTL 1X and put alternative drivers in the box. I am talking about the original Electrovoice MTL 1X using the EVX 180Bs. As a matter of fact, even if he can provide his box versus the current EV 2181 model it would be sufficient. That would hold more weight than copying Electrovoice's 1-watt/2.83 volt measurements and claiming one keystone box will offer more output than one Electrovoice MTL 1X or 2181 below 50 Hz once it is being fed with power higher than 1-watt/2.83 volts.
I dont understand. the EVX180b is a driver thats rated for 600 watts AES.. and an xmax of 6.4 mm.
the BC 18SW115 has well over twice the AES power handling, and 15 mm xmax (with an xlim of 60mm!). Whats so hard to understand about arts design? Yes the EV MTL is about 105 db 2.83volts/1meter (down to 50hz). Arts cab is not very far behind in sensitivity, and maintains it well into the upper 30s. Its a tapped horn loaded with a very nice driver, that can take as much if not more than 2 of the evx180b drivers can power wise.
the BC 18SW115 has well over twice the AES power handling, and 15 mm xmax (with an xlim of 60mm!). Whats so hard to understand about arts design? Yes the EV MTL is about 105 db 2.83volts/1meter (down to 50hz). Arts cab is not very far behind in sensitivity, and maintains it well into the upper 30s. Its a tapped horn loaded with a very nice driver, that can take as much if not more than 2 of the evx180b drivers can power wise.
Do you know why many participate in subwoofer shootouts? It is to see if the cabinet’s performance matches what the manufacture/designer states under real world conditions. One of the tests is taking a large amplifier playing audio tracks through various cabinets participating in the shootout to determine how they compare amongst one another at high sound pressure levels.
Using a 1-watt/2.83-volt meter measurement and saying one box will be louder than the other below 50 Hz without literally testing them under high SPL conditions, is not how professionals conduct tests in the sound reinforcement market.
Omnifex,
Back in the 1980's and early 1990's when 200-400 watts per driver was the usual amplification, the sensitivity of the EVX speakers was a really big deal.
As you can see in the EV advertisement from 1990, I was both a large user and fan of the EVX.
There are 75 EVX speakers in that photo, and 72 EVM low mid, though the 36 HF drivers were actually JBL at the time.
You can see in comparing the dual EVX 180B loaded QRX-218S bass reflex cabinet to the dual 18 MTL-1X that the BR has better sensitivity and actual LF extension, 100 dB at 40 Hz compared to only 83 dB for the MTL-1X.
The QRX-218S has around +4 dB sensitivity at 40 Hz over the JBL SRX-728.
However, the JBL SRX-728 uses drivers with more excursion (2268 has 8mm Xmax, 23 Xmech) and better power handling than the 6.4mm Xmax EVX 180B.
Granted, the JBL requires more power to get loud, but given the power, it will go louder.
A speaker with double the displacement has 6 dB greater low frequency output, assuming it can handle the power.
How loud a speaker can go is not just determined by sensitivity, but by displacement and power handling, how well the driver dissipates heat.
The Polyimide voice coil former on the EVX will develop heat blisters when run much over it's 600 watt EIA RS-426A rating.
The BC18SW115-4 used in the Keystone has a 1700 watt EIA RS-426A rating, and Xmax of 14 mm (Xvar of 16mm), so it has the output equivalent of 2.5 EVX 180B.
I have tested it at double rated power, it has hardly any power compression, not so for the EVX.
The BC18SW115-4 loaded Keystone has very similar sensitivity to the SRX-728, but due to the more capable driver, can put out more level.
The measurements below were done with the same drive level at two meters using 25 Hz BR 125 Hz filters.
As an actual real world example, on side by side stages I compared the output of four of my dual Lab 12 BR cabinets to eight Meyers 650P subs per side.
The Meyers 650P probably has fairly similar output to the EV QRX-218S.
The headliner (Michael Franti & Spearhead) frequently pushed the 650P subs into TPL (TruPower limiting) and Excursion limit. The spectrum was 60 Hz boom boom, about 6 dB more 60 than 40 Hz, which corresponds with the cabinet’s continuous rating and spectrum.
At FOH, about 125 ft out, the system was hitting 108 dBC, the hard limit, no extra VU swing resulted in any more output, though it did sound crunchier..
My stage was doing dance groups with recorded music and one live act. On the last dance group, with some fairly heavy LF content, my four 2x12” front loaded subs were hitting 104 dBC, spectrum looking pretty equal from 40-80 HZ.
+2 dB at 40 Hz, -4 dB at 60 Hz. Not bad compared to sixteen 18".
One Keystone has similar sensitivity at 40 Hz as two of the dual Lab 12, but almost 6 dB more output at 100 Hz. It has far less power compression, and more excursion, so given the same power, even more level.
Having owned hundreds of EVX woofers, and having compared the actual output of thousands of cabinets at real world power levels in front of audiences ranging from 100 to over 100,000, I can guarantee that given more power, the BC18SW115-4 loaded Keystone will put out more SPL at far lower frequencies than the MTL-1X.
Art Welter
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Art,
The Electrovoice EVX 18 stemmed from the late 1980’s but was revised throughout the years. The original was the EVX 180 with a foam surrounding. Later came the EVX 180A with the accordion surround then, finally the EVX 180B, which rectified the problem of the burned tinsel leads due to receiving too much power. All three versions were rated 1000 watts program power. You may be mistaken the 400 watt to the Prolines which were modified EVMs from the 1970s.
Remember, we are talking the Electrovoice MTL 1X using two EVX 180B versus your Keystone housing one B&C woofer. We are not talking about placing the Electrovoice EVX 180B in a traditional reflex.
All I am asking you is, if you literally compared a single Keystone to a single Electrovoice MTL 1X (both cabinets in the same location) feeding both cabinets power in order to draw to a conclusion that your single Keystone will offer more output below 50 Hz than a single Electrovoice MTL 1X loaded with the original EVX 180B drivers loaded in the box.
If you have, please post the comparison graph of both cabinets indicating the SPL from 100 Hz down.
I’m going to give you a scenario and, please tell me how is your Keystone is overcoming these objectives.
Placing one Keystone sub on the left channel of a Powesoft K 10 (2000 watts @ 8 ohms)
Placing one Electrovoice MTL 1X on the right channel of a Powersoft K 10 ( 4000 watts @ 4 ohms)
Driving the amplifier just below clipping with music material that offers a significant amount of SPL at 40 Hz and measuring the SPL from each box.
Now, I see a single Electrovoice MTL 1X will offer more output for the obvious reasons.
1. Coupling. Two drivers working together will offer a + 3 dB more than one working singulary.
2. Power. Moving from 2000 watts to 4000 watts is an additional + 3 dB
3. Surface Area. Two eighteens offers a larger surface area than a single eighteen
So how is your single Keystone box going to overcome those objectives and, offer more output below 50 Hz under the given scenario?
The Electrovoice EVX 18 stemmed from the late 1980’s but was revised throughout the years. The original was the EVX 180 with a foam surrounding. Later came the EVX 180A with the accordion surround then, finally the EVX 180B, which rectified the problem of the burned tinsel leads due to receiving too much power. All three versions were rated 1000 watts program power. You may be mistaken the 400 watt to the Prolines which were modified EVMs from the 1970s.
Remember, we are talking the Electrovoice MTL 1X using two EVX 180B versus your Keystone housing one B&C woofer. We are not talking about placing the Electrovoice EVX 180B in a traditional reflex.
All I am asking you is, if you literally compared a single Keystone to a single Electrovoice MTL 1X (both cabinets in the same location) feeding both cabinets power in order to draw to a conclusion that your single Keystone will offer more output below 50 Hz than a single Electrovoice MTL 1X loaded with the original EVX 180B drivers loaded in the box.
If you have, please post the comparison graph of both cabinets indicating the SPL from 100 Hz down.
I’m going to give you a scenario and, please tell me how is your Keystone is overcoming these objectives.
Placing one Keystone sub on the left channel of a Powesoft K 10 (2000 watts @ 8 ohms)
Placing one Electrovoice MTL 1X on the right channel of a Powersoft K 10 ( 4000 watts @ 4 ohms)
Driving the amplifier just below clipping with music material that offers a significant amount of SPL at 40 Hz and measuring the SPL from each box.
Now, I see a single Electrovoice MTL 1X will offer more output for the obvious reasons.
1. Coupling. Two drivers working together will offer a + 3 dB more than one working singulary.
2. Power. Moving from 2000 watts to 4000 watts is an additional + 3 dB
3. Surface Area. Two eighteens offers a larger surface area than a single eighteen
So how is your single Keystone box going to overcome those objectives and, offer more output below 50 Hz under the given scenario?
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Omni,
A: arts cab is loaded with a 4 ohm woofer. A 4 ohm woofer fully capable oftaking the full power a k10 can throw at it. This means both cabs are eating 4kw. 2000 watts per 180b might not be as fruitful.
B. A pair of drivers gain 3 db Because displacement is doubled. The 18sw115 HAS twice the displacement of the 180b, effectivly making it 2 drivers in itself (in fact it ha well over twice the displacement). This has nothing to do with surface area SD, its all about VD.
C: the horn is so short on the MTL 1x that it DEFINETLY does nothing to increase spl at 40hz, so in fact a typical reflex box loaded with 180bs probably has MORE output below horn cuttoff. making it a fair comparison.
A: arts cab is loaded with a 4 ohm woofer. A 4 ohm woofer fully capable oftaking the full power a k10 can throw at it. This means both cabs are eating 4kw. 2000 watts per 180b might not be as fruitful.
B. A pair of drivers gain 3 db Because displacement is doubled. The 18sw115 HAS twice the displacement of the 180b, effectivly making it 2 drivers in itself (in fact it ha well over twice the displacement). This has nothing to do with surface area SD, its all about VD.
C: the horn is so short on the MTL 1x that it DEFINETLY does nothing to increase spl at 40hz, so in fact a typical reflex box loaded with 180bs probably has MORE output below horn cuttoff. making it a fair comparison.
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I know you are trying to help but my questions can only be answered under real world conditions. That means you would need to literally test both boxes at the same time to draw to a conclusion.
You are quoting everything off a specification sheet and assuming everything is going to be 100% guaranteed. Many of us have been through that stage and learned from those mistakes. This is why Subwoofer Shootouts, came about.
Keep in mind I am not knocking the Keystone box. I am merely asking has the Keystone been tested side by side against the Electrovoice MTL 1X using the EVX 180B drivers under high SPL conditions. If so, can someone provide the measured graphs?
I am very familiar with the EV line, have been using their drivers since the early 1970s.
The EVX series was a big step forward when it was released almost 30 years ago, but it has been far surpassed in output (and cost per dB) by other drivers.
1)The Keystone TH design is almost 6 dB more sensitive than a "traditional reflex" of a similar size.
2) It uses a four ohm driver.
3) It uses a driver with almost 3 times the displacement of the EVX 180B.
EV's QRX-218S "traditional reflex" beats the MTL-1X in both extension and sensitivity below 100 Hz. As far as scoops or horns, the MTL-1X is lame.
I have not directly compared the Keystone to the EV cabinets, but I have compared it to the JBL SRX 728, which has been featured in sub shootouts, so the relative levels can be compared, and you can draw your own conclusions.
In speed trials, if car "A" beats car "B", and "B" beats "C", we know "A" beats "C", same holds true for cabinets.
However, as we know from car racing, there is no replacement for displacement, for A B C to compete on a level playing field, they all need to use the same 426 cubic inch format.
Here is where the real difference comes in, the BC18SW115-4 has almost 3 times the displacement of an EVX180B, like comparing a single 426 Hemi to three of the same.
In post #29 you can see EV's measured response of the dual 18" MTL-1X and the QRX-218S.
You can see JBL's measured response of the dual 18" SRX728.
You can see my measured response of the JBL SRX728 and the BC18SW115-4 (the 4 is for four ohms) loaded Keystone. These tests were done using the exact same amplifier output voltage in the exact same place, the unused cabinets moved away and shorted to avoid any influence on the test.
All the cabinets are four ohm, both JBL and EV use a 2 volt output in to nominal 4 ohm cabinets for their one watt test. Both companies have reputable and repeatable test procedures. The cabinets have been in sub shootouts, so we can compare them to the factory specs, and we find them to agree.
From the above sensitivity information, all from actual tests, we see this:
EV QRX-218S 100 dB @40 Hz, 105 dB @100 Hz
EV MTL-1X 83 dB @40 Hz, 100 dB @ 100 Hz
JBL SRX728 96 dB @40 Hz, 99 dB @100 Hz
Keystone 98 dB @40 Hz, 103 dB @ 100 Hz
So at one watt, we can see the bass reflex EV QRX-218S clearly kills the EV MTL-1X.
The BR design is smaller with more output, simply a better design in all respects.
The Keystone uses a less efficient driver, but is only 2 dB less sensitive than the QRX-218S, and is between the two for size.
As we know, what happens at one watt has little to do with ultimate output, which is determined by displacement and power handling.
All the cabinets are displacement limited below Fb (box tuning frequency), which for the EV MTL-1X is around 50 Hz (drops like a rock below), the BR and Keystone around 36 Hz.
At Fb, all the drivers are thermal limited.
The BC18SW115-4 handles 1700 watts, 1600 watts for the JBL SRX728, 1200 watts for either EV cabinet.
Roughly 1/3 octave above Fb, the cabinets run in to displacement limits before thermal limits. The JBL driver has only slightly more Xmax and power handling than the EV, so it has slightly more LF (excursion limited) output, but around 4 dB less output at 100 Hz (thermal limited).
Since the EV MTL-1X is the same sensitivity at 100 Hz, but less power handling, the SRX 728 has about a 1 dB advantage at 100Hz, and around 15 dB more output at 40 Hz.
Comparing the Keystone to the SRX728, thermal limits are similar, but the BC18SW115-4 has nearly double the excursion (2.5 times more than the EVX) and better sensitivity, it has more than 6 dB more output at low frequencies and about 4 dB more at 100 Hz.
Back to the EV MTL-1X, the Keystone has about 21 dB more output at 40 Hz, and 3-4 dB more output at 100 Hz.
By any metric, the Keystone beats the MTL-1X, but since EV's smaller bass reflex cabinet also does, not hard to do.
Art
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have a new bumper sticker for you...
"only milk, orange juice and subwoofer Vd comes in 2L"
At the stores around here (New Mexico, USA) booze comes in 1.75 liters, milk and orange juice come in 1.89 liters, but soda comes in 2 liter bottles.
The B&C18115 woofer has 1.936 liters one way displacement, the EVX180B has only .762 liter displacement.
You could say the EVX180B is about 2 pints low on juice
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Art,
Everything you have written is based on 1-watt/2.83-volt, 1 metre. I am asking what is the outcome when the cabinets are faced with more power that falls in the range of the Powersoft K 10.
You cannot guarantee the SPL of your design using a single B&C BC18SW115-4 woofer sitting on a Powersoft K 10 or an amplifier of similar wattage being fed a little under 4000 watts continuously, is going to beat the Electrovoice MTL 1X using two EVX 180 B woofers until, you literally test it.
The Keystone has two things going against the Electrovoice MTL 1X that is surface area (two eighteens versus one) and the coupling of two drivers working together as a team sharing the power.
You mentioned the B&C BC18SW115-4 offers nearly double excursion of the EVX 180B, which is correct it were competing against one EVX 180B. However, it needs to compete against two EVX 180Bs in the Electrovoice MTL 1X so the xmax, xlim, and, no% is times by two. For remember the B&C BC18SW115-4 in question is 4 ohms and the EVX 180B is 8 ohms each. Under those circumstances a single B&C BC18SW115-4 does not offer nearly double excursion against two EVX 180Bs under high SPL conditions.
This may not be apparent under 1-watt/2.83-volt measurements since that is not even enough power to make the voice coil warm. However, a lot of that SPL you are estimating at 1-watt/2.83-volt may not be the case once put to the test under a Powersoft K 10 or an amplifier of similar wattage being fed a little under 4000 watts continuously at 4 ohms.
But as you said, you have not literally test the Keystone against the Electrovoice MTL 1X. Possibly, your box will enter a Subwoofer Shootout in the near future. Hopefully the Electrovoice MTL 1X or the Electrovoice Phoenix 2181 will be present to make the comparison so we can see some measured charts under high SPL conditions.
Cheers!
Everything you have written is based on 1-watt/2.83-volt, 1 metre. I am asking what is the outcome when the cabinets are faced with more power that falls in the range of the Powersoft K 10.
You cannot guarantee the SPL of your design using a single B&C BC18SW115-4 woofer sitting on a Powersoft K 10 or an amplifier of similar wattage being fed a little under 4000 watts continuously, is going to beat the Electrovoice MTL 1X using two EVX 180 B woofers until, you literally test it.
The Keystone has two things going against the Electrovoice MTL 1X that is surface area (two eighteens versus one) and the coupling of two drivers working together as a team sharing the power.
You mentioned the B&C BC18SW115-4 offers nearly double excursion of the EVX 180B, which is correct it were competing against one EVX 180B. However, it needs to compete against two EVX 180Bs in the Electrovoice MTL 1X so the xmax, xlim, and, no% is times by two. For remember the B&C BC18SW115-4 in question is 4 ohms and the EVX 180B is 8 ohms each. Under those circumstances a single B&C BC18SW115-4 does not offer nearly double excursion against two EVX 180Bs under high SPL conditions.
This may not be apparent under 1-watt/2.83-volt measurements since that is not even enough power to make the voice coil warm. However, a lot of that SPL you are estimating at 1-watt/2.83-volt may not be the case once put to the test under a Powersoft K 10 or an amplifier of similar wattage being fed a little under 4000 watts continuously at 4 ohms.
But as you said, you have not literally test the Keystone against the Electrovoice MTL 1X. Possibly, your box will enter a Subwoofer Shootout in the near future. Hopefully the Electrovoice MTL 1X or the Electrovoice Phoenix 2181 will be present to make the comparison so we can see some measured charts under high SPL conditions.
Cheers!
EV's measurements clearly show the EV MTL-1X to be less sensitive than their bass reflex cabinet using the same drivers.
The Keystone tapped horn design is about 6 dB more efficient than a BR, which equals the +3 dB in doubling cone area and +3 dB power of a dual BR design.
My observations are not based just on one watt sensitivity ratings, they are based on high powered real world testing and comparisons to other commercially available cabinets as well as my own designs using EVX speakers.
You can see the results of sine wave testing at 77.5 volts (1500 watts in to 4 ohms) in post # 12 here:
http://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html
Distortion averaged only 5.438 % at that power level.
I have fed the Keystone 120 volt 60 Hz sine waves (3600 watts). With music or pink noise 4000 watt peaks are no problem for the B&C 18SW115, though I have seen DJs take out the EVX drivers with 600 watt amplifiers.
The B&C driver gets rid of heat far better than the EVX, it has less power compression, so at high power the advantages become more pronounced.
Between Electro Voice's tests and my tests the evidence clearly show that the B&C loaded Keystone has a higher sensitivity below 100 Hz than the EV MTL-1X.
Given the fact that the B&C loaded Keystone is 15 dB more sensitive at 40 Hz and 3 dB more sensitive at 100 Hz than the EV MTL-1X , and has more than double the excursion (+ 6 dB) handles more power, and has less power compression, it is a no- brainer to guarantee that it can go much louder.
What makes you think that a cabinet with higher sensitivity, more power handling, and almost double the excursion would not have more output than the lesser rated speaker?
Art
"The Keystone has two things going against the Electrovoice MTL 1X that is surface area (two eighteens versus one) and the coupling of two drivers working together as a team sharing the power."
You mentioned the B&C BC18SW115-4 offers nearly double excursion of the EVX 180B, which is correct it were competing against one EVX 180B. However, it needs to compete against two EVX 180Bs in the Electrovoice MTL 1X so the xmax, xlim, and, no% is times by two"
Didnt we cover that? the number of drivers is moot, surface area is moot. Its all about Volume displaced, which the bc 18sw115 4 does better than TWO EVX 180b (it STILL has almost 20 percent more displacement than a pair of EVX 180b). The only reason drivers "couple" is because they gain double displacement. The only added benefit would be in the case of Front loaded horns gaining double the mouth area (the MTL 1x is not a front loaded horn, so this is moot again). The B&C is the product of nearly 20 additional years in driver technology, its cooling capabilities are immense, and compression is low.
In fact I'd say doubling the displacement of a single driver is likely more advantageous than doubling drivers (cant get much more coupled than a single diaphragm)
". For remember the B&C BC18SW115-4 in question is 4 ohms and the EVX 180B is 8 ohms each. Under those circumstances a single B&C BC18SW115-4 does not offer nearly double excursion against two EVX 180Bs under high SPL conditions.""
what does that have to do with anything? 2 evx 180b wired in parralel equal a 4 ohm unit. how does this change the excursion of the drivers? even if we consider twice the xmax for the evx 180 (which gives us 13mm), its still outdone by the 15mm of the BC (which STILL has more xlim than even 2x xlim of the evx).
Just because the EV charts are at 1 meter, doesnt mean any magic happens at 40 hz in the MTLX when fed considerable amounts of power. In fact, being below horn cut off, the only magic that likely happens is mechanical failure of the driver.
You mentioned the B&C BC18SW115-4 offers nearly double excursion of the EVX 180B, which is correct it were competing against one EVX 180B. However, it needs to compete against two EVX 180Bs in the Electrovoice MTL 1X so the xmax, xlim, and, no% is times by two"
Didnt we cover that? the number of drivers is moot, surface area is moot. Its all about Volume displaced, which the bc 18sw115 4 does better than TWO EVX 180b (it STILL has almost 20 percent more displacement than a pair of EVX 180b). The only reason drivers "couple" is because they gain double displacement. The only added benefit would be in the case of Front loaded horns gaining double the mouth area (the MTL 1x is not a front loaded horn, so this is moot again). The B&C is the product of nearly 20 additional years in driver technology, its cooling capabilities are immense, and compression is low.
In fact I'd say doubling the displacement of a single driver is likely more advantageous than doubling drivers (cant get much more coupled than a single diaphragm)
". For remember the B&C BC18SW115-4 in question is 4 ohms and the EVX 180B is 8 ohms each. Under those circumstances a single B&C BC18SW115-4 does not offer nearly double excursion against two EVX 180Bs under high SPL conditions.""
what does that have to do with anything? 2 evx 180b wired in parralel equal a 4 ohm unit. how does this change the excursion of the drivers? even if we consider twice the xmax for the evx 180 (which gives us 13mm), its still outdone by the 15mm of the BC (which STILL has more xlim than even 2x xlim of the evx).
Just because the EV charts are at 1 meter, doesnt mean any magic happens at 40 hz in the MTLX when fed considerable amounts of power. In fact, being below horn cut off, the only magic that likely happens is mechanical failure of the driver.
Sorry Sine, you are mistaken.
Doubling drivers doubles SD, which increases efficiency by three dB when the drivers are within 1/4 wavelength.
Increasing displacement requires a longer, heavier voice coil and a stiffer, heavier cone, which reduces efficiency.
Given limited power and unlimited space, using two drivers with 1/2 the Xmax will in general be at least 3 dB louder than one with double the Xmax. When power compression and the lowered sensitivity of the long throw driver is taken in to account, real world results are more like 5 dB.
The EVX 180B is more efficient than the BC18SW115, the fact that the Keystone is more sensitive than the EV MTL-1X is because of the cabinet design, not the driver.
Hornresp sims say the EVX 180B in the Keystone is 2 dB more efficient at 40 Hz, but ultimate output is 8 dB less at Xmax ( 6.46mm vs 15mm). The sims don't reflect the upper response of the Keystone correctly, the real cabinet show more SPL in the 100 Hz region than at 40 Hz.
That said, the sims predict the EVX 180B only requires 37 Volts (171 watts) to hit Xmax, while the BC18SW115-4 requires 82V (1681 watts), 10 dB more power for 8 dB more output.
If you used a pair of EVX 180B loaded Keystones, they would come within 2 dB of the LF output of one BC18SW115-4 Keystone, and would only require 1/5th the power.
And they would probably smoke a pair of EV MTL-1X in the LF, even in Jamaica, mon
.Art
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