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#1 · (Edited)
The number of Devastator versions and the number of documented Devastator builds is multiplying, it would be nice if some of this information were kept more neatly in one place. This thread is a work in progress. I will add new variants to this thread and also builds and link them below. :cool:

As always, in the pursuit of performance from the use of wood! Wood is still cheaper than amps and sub woofers.... Let's not forget the other part of the Devastator formula, simplicity! (remember we are dealing with a band pass here, they are more complicated). No diagonals, all panels are on right angles to simplify the building process.

Note: there are also some guides linked below in this post. If you have questions about how to assemble a Devastator, there is a lot of good information in the builds, do this and do not this. That is on top of the build guide. Basic assembly works its way from the top and front panels, towards the back and downwards. Top hatches, rear panel vents, high compression fronts and Stepped fronts have all be added as the Devastator has evolved. Items are listed for the most part in Chronological order. Several members have put a lot of time in documenting the build process. Please check out their build threads!

Want to design a Devastator all on your own? The Hornresp tutorial is posted below. If you have design questions feel free to post them in that thread! There are tools for helping design cabinets in Google Sheets posted in that thread too.

With the addition of the Stepped front Devastators, responses can be mostly flat natively. Knowing your room and what can fit in a space are going to be key factors for selection vs trying to leverage the response shape in spot the suites the box well.

Suggestions for box selection: Devastators have seen evolutionary progress as time has gone on. The biggest factor for selecting a Devastator is the space available. That is one of the main driving factors for the wide array of designs beyond achieving more performance from the use of building material. Room size is another big factor. (I grabbed this from Audioholics)

Room
Dimensional Volume
Small Room​
< 1,500 ft^3​
Medium Room​
1,500 ft^3 to 3,000 ft^3​
Large Room​
3,000 ft^3 to 5,000 ft^3​
Extreme Room​
> 5,000 ft^3​

Small room, you can probably get away with a couple Micro 15" Stepped V1s. Medium room, you will need a couple 18"s at least. Large room - 21"s. Extreme, how many Fat Boy V5s can your marriage take? Other factors, is the room open to other areas and is it an odd shape? That can mess with the equation especially if sub placement options are limited.

Why bass physics suck:

Below is the Fat Boy Version 5 with the native 22Hz tune in gray and I tweaked the vent area down so it is now tuned to 18Hz. As you can see from the graph output takes a huge 5db hit from the lower tuning. In room that 22Hz box will probably stick with all the other Index Devastators down to 17Hz or 18Hz. That is a bit room dependent, so your mileage may vary. Also, remember 6db is the equivalent of doubling your sub system, amps, boxes and sub woofers, 3db from cone area and box displacement and 3db from the input power doubling.

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Now I am going to push this further down to 15Hz tuning on the rear chamber. As you can see we are down a solid 10db on the left corner from the original 22Hz tuning and another 5db from the 18Hz tuning.

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The important thing to know? Each octave (dividing a given frequency by 2) you descend in frequency will require 4 times the displacement to achieve a given level of output. Let's say when tuned 20Hz a box can hit 88db on 1 watt of power with 1mm of excursion. If we tune the box to 10Hz it would take 4mm of excursion from the woofer to hit 88db. This is an important fact when selecting a Devastator. There are three factors that will come into play. Output, Extension and Cost, those factors will always have to be balanced. You can chose 2, but you cannot get all 3 unless you are in a very small space that gains very well. A 7000 cubic foot room on a concrete slab is not a good place to chase extension. It would be better to go with higher tuned cabinets and gain the wobble effect from a BOSS platform. Unless you have the luxury of unlimited budget.

High Pass Filter Orders:

Real quick rundown, 6db of slope is an order. For example a 2nd order Butterworth filter will knock the response down 12db per octave. If set to 20Hz the response will be down 12db at 10Hz, assuming it is applied to a flat line. 2nd order filters can make integration easier in certain circumstances. Especially if the cabinet tunes have a wider range than just a few Hertz. Integration with sealed cabinets can be more tiresome and require a lot of trial and error. An 8th order 48db per octave slope on the sealed cabinet and then using a 2nd order HPF a few Hertz over tune on the Devastator can be a good starting point. Once again YMMV. If you do plan on using a 2nd order filter, go a little over tune with the filter to control driver excursion below tune.

Order: (typically you will not see a Dev go over a 4th order, just keep multiplying by 6 to go up)
1st 6db per octave
2nd 12 db per octave
3rd 18db per octave
4th 24db per octave

Why do we need High Pass Filters on a Devastator?

Below the tuning frequency of the Low Frequency(LF) resonator cone excursion goes out of control(see example below). The cone is no longer seeing a load like it would above the tuning frequency of the LF resonator. The cone movement would be similar to the sub being given power in free air. A pro driver can take several hundred watts in most cases in free air when sent a low frequency waveform. Doing that to a woofer frequently could A. damage the woofer over time and B. if sent a more powerful signal could bottom the woofer out immediately. The High Frequency (HF) resonator does present some load to the woofer below the LF tuning frequency, but it is not enough to control the cone movement. DO NOT RUN your Devastator without a protective high pass filter.

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As you see in the graph above, the cone motion with the 2000 watt input on this NSW6021-6 has the driver well outside of the 21mm xmax below 20Hz. Once a Butterworth 18Hz 4th order high pass filter is actived the cone is peaking around 19mm below 20Hz(light gray line) and that is inside the NSW6021-6's rated xmax.

Slang/Terms:

HCR - High Compression Ratio. This front has a bell curve, but is not quite as peaky as a lower compression front and uses less space. Good for shallow cabinets.
TR - Tactile Response
Stepped - A front quarter wave resonator with 2 or 2+ cross sectional areas. The response is typically more flat and they gain more low end output.
BR - Bass Reflex
QW - Quarter Wave resonator. These are typically referred to as horns. On a Devastator they do the high frequency lifting.
FPR - First Port Resonance
BB - Baltic Birch plywood. (not the veneer box store stuff, call a lumberyard)
BBv1 - Big Boy Version 1
MLP - Main listening position.
REW - Room EQ Wizard.
HPF - High Pass Filter.
BW - Butterworth.
LF - Low Frequency
HF - High Frequency
HO/SHO - High Output or Stepped High Output. Usually these cabinets have 22Hz tuning.
BMD - Beast Mode Devastator. Typically they are closer to 60" height vs 48"
FV - Finalizer. This cabinet started as a 48"x25.5"x34" cabinet with lower tuning. FV can be used for the 16Hz tuned rear chamber or the form factor
Dev - Devastator. Generally cabinets that are around 48" in height.
Mini - Typically this cabinet type is around 40" in height.
Micro - Usually in the above or around 30" in height.
Nano - Usually used for 12" cabinets.
FB - Fat Boy. Typically as deep as they are wide.
BAMF - Bass Ascension Module Five. Home music or PA cabinet with higher tuning and a Stepped QW resonator.
NSW - Eminence NSW6021-6
SAN - Lavoce SAN214.50 or the SAN215.30 is another good choice, but not usually that is referring to the 214.50.
DS - That could be a B&C 21DS115 or a 18DS100-4, both are great choices.
TBW - B&C 18TBW100 is usually the reference, but the 15TBW100 is another good woofer.
SAF - Lavoce SAF184.03
WAF - Should be the Lavoce WAF154.00
D21V6 - This would be an example the Devastator 21" version 6
M18V6 - This would be an example of the Mini Devastator 21" version 6
FB21V5 or FBv5 - Fat Boy Version 5
FV1 - Finalizer Version 1

Devastator response evolution:

The Devastator has seen developments over time. The examples below are on 48" tall cabinets to show the three main fronts and how they affect the response.

The Devastator 21" Version 1 is the first Devastator designed by John. As you can see the front HF QW resonator adds SPL across the entire frequency range, peaking in the mid bass region. Light gray is ported cabinet with the same vent length, vent area and chamber volume as the D21V1.

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Next up we have the Devastator 21" Version 5 with an HCR front. The HCR front has a smaller cross section area vs the lower compression front, but still adds output across the range and takes up less space in the cabinet. Once again dark gray is the V5 and light is just a basic BR chamber with the same specs.

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Finally we have the Fat Boy Version 5 with its Stepped QW resonator that has multiple cross sectional areas. The higher tuning coupled with the design of the QW resonator makes the cabinet very flat and efficient. The higher tuning also allows the resonators to be spaced 1 octave apart in frequency without cutting our top end short, so this design can still crossover at 80Hz into a sound system.

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Other advantages to having the front QW resonator:

Cone protection from curious children, pets and sometimes friends that are tipsy. Less rear chabmer/motor noise, the panels dampen noise that would otherwise find its way through the cone and into the room. Obviously the QW resonator eats up more space vs having nothing in front of the woofer, but the QW resonator has a few things going for it.

Construction/material/tips:

The preferred building material is currently expensive. Baltic Birch plywood (not the veneer stuff at box store, call a local lumber yard) is the preferred building material. 18mm is close enough to 3/4" not to mess up the building process. MDF is heavy and makes a big dust mess and does not take screws well, tends to crack. ACX plywood is lightweight, but has voids and a tendency to warp. BB is lighter than MDF and does not make the dust mess and is less prone to warping and also voids. MDF also sucks for using Kregs.

If you have router with a flush trim bit, it is not a bad idea to add 1/8" inch on the side panels and then clean it up after assembly.

PL3X is the glue of choice due to how forgiving it is with voids and set time. When using PL, wear gloves, you do not want that stuff getting on your skin and it will mess up clothing. If you are a fluent wood worker, you do not have to say no to tight bond.

Marking panels before assembly is another pro tip. I would also suggest marking up the woofer cutout and drilling all the holes for fastening the woofer before assembly. Marking the panel alignments/positions on the side panel, front panel and baffle are all good ideas. Measure twice, cut once is another good rule to live by.

Air leaks around the access panel are usually the number one issue once the box is together. Especially if the measured response looks weak on the left corner. If you want to make sure you have a good seal, turn off the lights, put a flashlight in the rear chamber. Button the hatch up and look for light coming through the hatch seal. Weather stripping or the PE gasket tape will work.

If you have a question or are unsure of something when putting the cabinet together, feel free to post the question in the Index. This thread has large following that is happy to offer tips!

Bracing - here is a good example of a common bracing mistake. The wider dimension should be adjacent to the outside panel, like in the photo below.

Driver mounting - Chris made this write up for his technique for securing the sub to the baffle - link



Threaded Inserts (Sub woofer mounting solution)

Panel Names?


Below is a reference image
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Rear Chamber Resonance/dampening material

Chris when testing the JBL Quad Devastator did some measurements with different pillow configurations in the rear chamber. We also reached out to a few members for measurements they took. It would appear standing waves in the rear chamber start to encroach on the passband somewhere between 40" and 48" of rear chamber length. Boxes close to 48" on up need pillows tacked onto the side panels to alleviate near past band resonance. The goal is having a clear path from the back of the woofer to the vent inlet. Air restriction will hurt low end output. However, if there is minimal restriction in air movement, a minimal loss in low end output will take place. Here are the links to the Quad testing.

Resonance Testing Pt1
Resonance Testing Pt2

Does my UM18/IB/high Qts Sub work in a Devastator?

The short answer is no, it does not work in a Devastator. This is a UM18 in a Mini Devastator 18 Version 6.



As you can see the woofer gets a very sharp peak at the resonant point of the front horn of the cabinet. You might be thinking why not just EQ that peak? Here is the problem, the UM18 will ring when loaded in a Devastator, the cone stays in motion after a impulse. This is the UM18 vs the 18TBW100, pink is the UM18, green is the TBW. Notice how the cone on the TBW stops moving relatively quickly. Some subs are designed to work well in higher order band pass boxes, others are designed to work in lower order band pass boxes. There is a simple method for finding a good woofer using a specific metric. Efficiency Bandwidth Product (EBP), the woofers Fs value divided by its Qes value. The Devastator starts working once a value gets around 70 or so. Values closer to 100 are better, but not absolutely necessary. If you have a woofer with a value higher than 70 and are curios to see how it looks, just post a message in the thread :)



Any Devastators optimized for music?

Yes, the BAMFs are designed to handle music duty/PA use. There are currently three different versions available with different tuning depending on the needs of your system. If interested I have a smaller design meant for an 18" that will definitely make some loud noise that has not been released yet.

I bought a Crown amp that has a network card, how do I manage it???
Chris made a nice write up concerning this situation, you can find it right here. You will need the Harmon Audio Architect software installed on computer that is on the same network as the USP card.

Reference Port Plug Design - link

Performance data (HR Estimations GP1m):
The Big Boy Family 21"s
The Fat Boy Family 21"s
The Finalizer Family 21"s
The Alpha Family 21"s
The BAMF Family 18"s + 21"s
The BMD Family 21"s
The Mini Devastator Family 21"s
The Devastator Family 21"s
The Mini Devastator Family 18"s
The Devastator Family 18"s
The BMD Family 18"s
The Micro Devastator Family 18"s

Shallow + Narrow 21" + 18" Devastators

Common 21 Comparison Graphic (shoutout to Chris for his help with this)
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Common 18" Comparison Graphic
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Current (9-1-22) top picks!
Colorfulness Slope Purple Rectangle Font

Note: The Alpha III and IV have narrow clones. The FBv6 has a narrower clone and the 18BMDSV2 has a clone.

PLEASE SHARE BUILDS IN THIS THREAD!!! (including pictures)

Designs (Guide is near the bottom of this post and see build links, a lot of go information in there.)

Broken down by woofer size:

24"
21"
18"
15"
12"
Build threads/other
Guides
 

Attachments

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18
#5,387 ·
Would anyone be kind enough to run a hornresp graph for me? I’ve got 2 BMD 21” Stepped Version 4 (Alpha IV Clone) that I’m using co-located behind my screen. However, I also have an SKHorn that I could use instead to give me some more room since things are getting a little cramped with the devs. Trying to find out how much output I’d lose and how the response might look different. Both devs are using B&C 21’s and those same drivers would be used in the SKHorn. Thanks in advance.
 
#5,390 ·
This is normalizing power for both since the situation involves two subs for each, should be a watt into the SK and a watt into the pair of Alphas. If you are doing movies the Alpha IV clones are a must in my opinion. I am assuming 21DS115-4s are in use.

Alpha IV clones

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The SKHorn

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#5,392 ·
No, that is .5 watt into each Alpha. Since it was colocated I wanted to keep it as apples to apples with the SK. Each system is getting the same voltage in the sim. I am away from HR to verify that, but yes, I believe it should be a 3db bump.
 
#5,398 ·
It was not a dumb question.
I used to run one of my Devestators upside down when I had my room configured a different way, the two of them worked great like that.
Yeah, it sucked in a way because I had put casters on the bottom, which became the top on the one, so I removed them which just left a bunch of holes.
When I reconfigured the room I wound up having to flip it over once again.

I had also inverted the signal using the MiniDSP since that is what GSG recommended since day one.



That was my old configuration. I switched the room 90* and removed the couch and put a single chair in there. Shotgun is put away. :)
 
#5,400 ·
I had one of the 2 alpha IIIs cut and ready to assemble. Fast forward from last fall to now and all the edges touching the garage floor have swelled and are unusable. I have no idea if this is just from moisture or water getting in the garage. There is no indication I have had any water in there. The 7 full sheets of MDF on the opposite wall are fine which is good cause the price per sheet is a bit high. Now I need to buy one more sheet of MDF to get them both built. Anyone else ever have this happen?
 
#5,406 · (Edited)
When I built my Alpha 4 clones, the recommendation was to put a cheapo pillow on the two tallest side panels.

Mine ended up on each side down here. That way they were still on the long walls, yet also out of the way of the woofer and vent. Hopefully this image makes sense:

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As for what pillows: I used something similar to this. Just the cheapest normal size pillow available. Pillow
 
#5,407 ·
I think 2 standing pillows are standard for all Devastators.
 
#5,420 ·
finished the build. its loud. tried some tech nine on it. movies will come later. i have the marantz out to a minidsp and into the crown xls2502. its enough to move some serious air out of the ports.


How did that candle hit the deck? :LOL:
 
#5,413 ·
So, I might have been running my Shallow Mini Hybrid 21" HCR (SAN 4-ohm) a little too hot during a screening of Interstellar, and it sounded like it was being driven too hard. At least my pant legs were ruffling, some things in the room might have been shaking (like a bifold closet door), and there were some unhealthy-sounding resonances. That's the best I can do with my newbie vocabulary.

And it got me thinking: I want to ensure this speaker is okay long term. Should I be running a voltage limit on the NX6000D? If so, what should the limit be?
 
#5,414 ·
If there wasn't clunking noises coming from the woofer, it's probably fine. Stuff in the room rattling and your pants legs shaking are just the subs way of letting you know it's working fine. The whole house moves up and down enough for my wife to notice the motion two floors above the subs at my house. All sorts of strange things rattle and shake, and anything hanging on the walls might fall down. Interstellar does have VERY low frequencies, so hopefully you have an appropriate High Pass filter on the signal going to the Devastator (or any ported sub). If you don't, then you were probably hearing bad sounds from the sub, it is running is nearly free air at certain points of that movie due to the very low frequency content there.
 
#5,422 · (Edited)
BMD 21" Alpha V Flex Tune

The goal for this design is an everything box. Depending on the needs of the room or personal preference of the builder. Not sure what to build? This is a good one if it fits into the space available! With zero ports plugged this thing is very similar to an Alpha III, but the vent is longer and there is an additional rail added to the vent, that is where the flexible tuning comes in. All ports open is roughly a 22Hz tune for the LF resonator. Drop a plug into one of the vents and the tune should drop to 19Hz. Adding an addition plug will push the tune down to just over 15Hz. I am assuming the plug will eat about 5 inches of the vent length and we get the rest of vent back in the form of added displacement. For this math to work, keep the rail spacing to spec. The simulation order will be - all open, 1 plug, 2 plugs. The NSW 6021-6 is the driver used in the simulation.

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1000 watts with a BW 18Hz 4th order HPF active. MaxSPL 92 volts (2.23kw) 21mm (xmax) over LF tune.

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1000 watts with a BW 17Hz 4th order HPF active. MaxSPL 86 volts (1.95kw) 21mm (xmax) over LF tune.

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1000 watts with a BW 14Hz 4th order HPF active. MaxSPL 78 volts (1.6kw) 21mm (xmax) over LF tune.

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#5,423 · (Edited)
Commencing work on the BBv11 Flex Tune! This should be another go to option if you are unsure of exactly what it is you want, but you know you want it loud.

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I am throwing the Alpha V in here for reference.

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#5,425 ·
I am running a simulation with the BMD18SV3 loaded with the NSW4018. There a few things to note on the NSW4018, the motor force is pretty low at 147.6 Bl2/Re for an 18" woofer. Motor force is important for driving through the resonance created by the bandpass enclosure. The resonators creates acoustic resistance which the cone must work against. Designing the resonators to work with less motor force results in a larger box and less power handling to name a two things that are not desirable. We also have to look at the native resonance of the subwoofer, which is pretty high on the NSW4018 at 38Hz. Excursion will rise and efficiency will fall the further below the woofer's Fs we go on the LF tune. Efficiency will fall in a non linear fashion, once you drop below roughly 67% of Fs the rate it which it falls increases and excursion will also quickly increase. With the higher Fs on the NSW4018 that number is 25.5Hz. You can see with the 1000 watts of input power on the simulation excursion is 4mm over rated xmax. The BMD18SV3 has a tune a little over 20Hz and is optimized for things like the NSW4018, the TBW and the SAF that do not have the crazy motor force of something like the 18DS100-4. If you want to use the extra wood for something cool, I would take a look at the BMD18SV3 or the SV2, depending on the space requirements.


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#5,426 ·
I have been circling the drain on doing 2 Devs (thinking Mini V3 as I have a 40" height limit and want a lower tune), and am about to pull the trigger and buy some plywood. With that, I was curious about lining of the cabinets. In testing, everyone is doing pillows now, general recommendation just dont block the ports -got it-, but compared to many typical sealed or ported enclosures these are not damped as much.

Looking at B&Cs sites on sample speakers and sub designs they have, I see they have a 6th order (dual 18") sub enclosure and it shows both the rear chamber and even the throat in the front getting treatment. Would this help tame the low 100/120/140's hz resonance a bit that could impact a higher XO? Just wondering if there would be benefit in doing so. It looks like the cover the area directly in front of the woofer from the pics in the diagram.

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#5,427 ·
I have been circling the drain on doing 2 Devs (thinking Mini V3 as I have a 40" height limit and want a lower tune), and am about to pull the trigger and buy some plywood. With that, I was curious about lining of the cabinets. In testing, everyone is doing pillows now, general recommendation just dont block the ports -got it-, but compared to many typical sealed or ported enclosures these are not damped as much.

Looking at B&Cs sites on sample speakers and sub designs they have, I see they have a 6th order (dual 18") sub enclosure and it shows both the rear chamber and even the throat in the front getting treatment. Would this help tame the low 100/120/140's hz resonance a bit that could impact a higher XO? Just wondering if there would be benefit in doing so. It looks like the cover the area directly in front of the woofer from the pics in the diagram.

View attachment 3449532 ?
Heavy handed dampening is not required for dealing with chamber resonances, but if it gets heavy handed, you will start sacrificing low end potential. Use as little as you can get away with. @a77cj7 was kind enough to do some testing on this. You can find the results below.


 
#5,429 ·
For a dual sub enclosure I think it needs to grow. Also port compression is going to be a deal, that's a lot of energetic cone area+motor.
 
#5,430 ·
Mr. 5,
After all this time, whats it been, like 4ish years or so, and all the work, how many of these things have you got to actually hear and play with? With sooooo many out in the wild now of all the different designs, has anyone had you over to spend any real time with your babies?
As for me, you Sir are welcome any and every time you like. Granted, I'm only running the original design and I'm in west MI. but the offer stands. I think it would be fantastic for you to see and for us to show you what all those arrant keystrokes and hour's upon hour's researching and computing have manifested into.
How knows......it may even lead to an even greater level of awesome.
 
#5,432 ·
I appreciate the offer! I have my two cute little Minis, they are pretty fantastic for music, but the size of the room requires mega firepower for movies. It will be awhile before I get any big guns down there, but that is okay got now, I barely have time to utilize the current subs. Seems to come with the young kids. The oldest does get a kick out of sitting on top of the minis during the action scenes in the kid movies, the current status quo will change...
 
#5,436 ·
Would the B&C iPal driver be a better driver vs the ds in a dual configuration

Obviously this is end game build
We do have a dual Dev, but that is for the JBLs for a few important reasons. Shoving two drivers in the cabinet has the main advantage of saving a piece of wood, but at the cost of your back telling you to take a hike. Also there is a good strong potential for the woofers not accepting the loading, since the distance from the end of the QW resonator to the center point of the woofers is far greater and a fixed metric as far as nature is concerned. The distance past a 18 or 21 is much greater than the distance past a 12". The greater distance is going to mess with the pressure wave front causing undesirable load variances between that woofers. We had to test the 12"s to make sure it would work before sending it out there into the wild. The M.A.U.L. had this issue on its first run. Anything would be very experimental and pretty niche. Then there is the darn problem of nature only letting us get so much more out of displacement. 20 cuft would be enough for one single 18" to work well in a Devastator. In order to get two 18"s cranking to their potential without shredding them, you will need another 20 cubic feet. Which brings the question of why not just stack them or stick them together vs making an absolute monstrosity? If you want the most violence out of a volume of space, just keep adding sealed subs until it gets what you want. Ideally TD18s from Acoustic Elegance. If you want to save a lot of money then Alpha IVs for Vs would be an excellent approach. Keep adding until violence levels meets preference. Nothing is saying you cannot build a second Devastator on top of the side panel of the other Devastator to make it a dual. That would skirt around a lot of problems and result in the same thing as them sharing a cabinet, but without having the issues with driver destruction or time domain issues with the impulse response.
 
#5,438 ·
Slot ported sub will not have the issues with time. You still have to make it large enough for the vent to handle the stresses the DS18s will put on it. 20cubic feet is getting started.
 
#5,441 ·
So I have 4 devs in my room but I only play as loud as 7dB max and I do have very smooth FR across the seats. I know that Devs are output monsters but does it matter if 4 devs are used just to put out a total of 7dB boost in bass? I mean I can't any amp to show more than 1 light :).
So my question is: Does using Devs in such application where major output isn't required still beneficial?
 
#5,442 ·
So I have 4 devs in my room but I only play as loud as 7dB max and I do have very smooth FR across the seats. I know that Devs are output monsters but does it matter if 4 devs are used just to put out a total of 7dB boost in bass? I mean I can't any amp to show more than 1 light :).
So my question is: Does using Devs in such application where major output isn't required still beneficial?
In theory turning half of them off, to simulate spending half as much money, would be a valid test. It would show the differences between two playing louder, and four with less output per unit.

One of the Devastator advantages is usually more chest kick due to higher particle velocities, along with greater output per watt/dollar.
 
#5,446 ·
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