# Louder than a PK Sound CX 800



## Patrick Bateman (Sep 11, 2006)

Ever since I went to a show with the PK Sound CX 800s I have a renewed love of bass, and of going out to shows in general. I've become such a hopeless basshead that when I go to a show that lacks that bone crushing PK Sound, it's just not the same.

Last night I went to Excision in Portland, and it got me thinking:

*How can we make this LOUDER?*

I know this is a car audio forum, but I'm going to explore the question here for a few reasons:

1) The CX 800 is small enough, you could squeeze one of these into a SUV. (I believe they offer passive versions.)
2) In this thread I'll show you how you can trade size for efficiency, and I'll show you how you can improve the phase response of a sub
3) Car audio guys tend to appreciate re-donk-u-lous bass like no others


Not going to lie though - I'd love to see someone build the sub that I'm going to propose here. It's going to be BIG and it's going to be LOUD.



Also, 95% of you have never heard a CX 800. Even if you don't like dubstep, or EDM in general, it's still a blast. This is some serious next level ****, I've been going to shows for two decades and I've NEVER seen anything even in the ballpark of these output levels. These types of output levels were impossible a decade ago. In 2002 there wasn't a subwoofer in the world that had enough displacement AND power handling to do this. More importantly, in 2002 amplifiers weren't as efficient as they are now.

Combine those two things together, and you get a subwoofer so loud that the limiting factor becomes the electrical circuit of the building! (In my day job I do super computers, and I've heard of transformers exploding due to the juice that they require!)


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## Patrick Bateman (Sep 11, 2006)

Here's a sim of one half of a CX 800. In the sim we see the following:

1) with 2000 watts into 4ohms, we get about 131dB of output in the two octaves from 30hz to 120hz.
2) spec sheet says a single CX 800 does 139dB; my sims say about 137dB. (the pic above is only half of a CX800, you pick up 6dB when you add the other half.)
3) Even with 4000 watts, *the 18Sound woofer still has a lot of thermal headroom and a bit of xmax left.* I'm betting this is why these get so ridiculously loud, thermal compression is under control.

Also, the reason that my graphs don't look all smooth like you see with most sims is that I'm doing these in hornresp, so we're seeing the effects of various resonances in the enclosure. In the real world those peaks and dips will not be as pronounced.


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## Patrick Bateman (Sep 11, 2006)

My idea for a 'CX 800 Killer' is basically a sub that's part of the stage show. Similar to the Skrillex Cell, or the sets used by Deadmau5, Datsik, Excision, etc.

But instead of a big stage set with video projected on it, the subwoofer IS the stage set. The DJ is basically playing with the sub right in front of him.

(Obviously this wouldn't work if DJs actually played instruments or records, but DJs just hit a button don't they? Deadmau5 controversy: "All we do is press 'play'." - Los Angeles Times )



Hopefully my explanation makes sense. My basic idea is to take the subwoofer, and make it part of the stage. This gives you a lot of volume for the sub, which raises the efficency. And the sub will be white, so that the projectors that are used for the DJ's setup can project right onto the sub. (If one were clever they could make the sub a complex shape like The Skrillex Cell, but I'm not going to explore that here.)


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## Patrick Bateman (Sep 11, 2006)

In order to get louder than the CX800, we need one of two things:

1) More power

or 

2) More efficiency

The driver in the CX800 can only get about 1dB louder before heat puts the brakes on our output. So I'm going to crank up the efficiency. *I believe this is the only practical way to get louder than the CX800, unless you have the budget and the space for a whole pile of 'em.*



























The most obvious way to get louder than the CX 800 is to build a horn.

Here's a comparison of a CX800, along with a tapped horn that uses the same driver. *The cubic volume is exactly the same, and so is the tuning.* That helps us eliminate Hoffman's Iron Law as a variable.

In the sims we see the following:

1) The shape of the output is very similar, due to both being tuned to the same frequency
2) The F3 of the two boxes is virtually identical, but the tapped horn has more output above the tuning frequency. This is because the output from a helmholtz resonator is narrow in bandwidth, while the output from the rear of the cone in a tapped horn is broadband. So the TH is a bit more efficient up high, but at the cost of some deep nulls where the front and the back are 180 degrees out of phase.
3) The group delay of the tapped horn is arguably superior
4) The tapped horn has much lower displacement at 70hz


One big 'x factor' with the vented box is the efficiency of the port. Loudspeaker ports compress pretty quickly, and that compression can add distortion and reduce output at high power. The tapped horn will suffer from these problems at a much lower degree, as the air faces much less resistance as it 'flows' through the TH, due to the larger dimensions of the duct


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## m R g S r (Oct 1, 2009)

What driver is in these CX800's? The 2400? Or the 9600 long throw?

Just checked it out. Looks like its a 9000 series neo or 9600c possibly? 

So one could use the 18sw115 as well. It's a bit cheaper than the 9600c...

That 28mm x Max figure is wrong. (For one way) that's either x mech or x max peak to peak. Not one way...


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## Patrick Bateman (Sep 11, 2006)

In this post, I'll show a 'box' that's louder and more efficient than the CX800.

I put 'box' in quotes, because this isn't really a box. It's basically a wall, ideal for projecting videos onto.










In the sim above, I've compared the output of the CX800 against my 'box'. We see the following:

1) F3 is about the same - so both of these boxes can dig deep into the 20s
2) My 'box' is much much more efficient. One of my 'boxes' has as much output as two of the CX800s, at the same voltage
3) The displacement on my box is a little better, as I'm using a 21 instead of a 18








Here's what my 'box' looks like. As promised, *it's a monster.* Twelve feet tall and twenty four feet wide.

Due to it's simplicity, it can be assembled in about an hour, with the help of three other people.

I hope the pic makes it clear how this 'box' works. *This is a radial back loaded horn.*

In my pic, it might not be obvious how the sound radiates.
Basically, the sound radiates radially, like the pulse from an explosion. *The horn would be circular, if it wasn't for the fact that I folded it over.* (That's why the mouth is an odd shape.)

















​JBL's "smith horns" from the 70s worked in a similar fashion, except they're a segment of a circle, whereas my horn is a full circle, which is folded over.


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## Patrick Bateman (Sep 11, 2006)

Assembly of the 'box' is dead simple. It's literally a circle folded over. *If you know how to build a wall than you can build this horn.*

In the image above, I've shown how many pieces of plywood you need.
Ideally, you'd use 27 pieces but you could likely get that down to sixteen pieces if your careful.

Also, if it's not obvious, *there's no box for the 21s.* They're just radiating into the air. This is a back loaded horn.










You don't see a lot of back loaded horns in prosound, but they operate a lot like a tapped horn. Rhino Acoustics used to sell one called the 'Bassmaxx'

For our application, the primary advantage of a back loaded horn over a front loaded horn is simplicity. Because there are no back chambers for the subs, assembly of the bass wall is easy.

Another cool thing about the bass wall is that the wavefront of the subs is distributed across an enormous mouth. 24 feet wide! If you've followed any of Geddes or Toole's writing about room nodes, it's safe to assume that a very large mouth like this will improve the sound in the room/club.

I really need to draw a cross section of the horn, to show how the sound radiates.
















The sound path in the subwoofer is very similar to a Paraline. I have some threads descrbing how they work : http://www.diyaudio.com/forums/multi-way/217298-square-pegs.html

The easiest way to visualize this is to cut out a circle in a piece of paper, and then fold that circle. That's how this horn works.


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## Patrick Bateman (Sep 11, 2006)

One obvious question -

*What's the depth of the horn?*

That depends! 

One of the neat 'features' of this horn is that *it scales.* You can build it with one driver, or four drivers, or even eight drivers. *That's up to you.* Response shape won't change a whole lot, adding drivers just increases efficiency and output.


If you use one driver, then the spacing between the plywood sheets is 3/4".

If you use two drivers, then the spacing is 1.5"

If you use eight drivers, the spacing is 6".








In the example here, with four of the B&C 21SW152s*, the gap between the two plywood sheets is 3".

Note that there's no taper or anything funky like that. *It's literally a flat plywood wall, seperated by a 3/4* divider, with another wall in front of it. The funky shape of the cutout forms the horn mouth.* Because the sound is expanding radially the area is constantly expanding. (IE, this is a very natural expansion, even if the shape looks unorthodox.)


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## Patrick Bateman (Sep 11, 2006)

Here's a quick comparison of the weights of my 'subwoofer wall' versus the PK boxes:


Eight PK Sound CX 800s weigh 1520lbs
My subwoofer wall, with four B&C 21s, weighs 835lbs. That calculation is based on the weight of four B&C 21s (160lbs) along with 27 sheets of plywood (675lbs)


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## Patrick Bateman (Sep 11, 2006)

m R g S r said:


> What driver is in these CX800's? The 2400? Or the 9600 long throw?
> 
> Just checked it out. Looks like its a 9000 series neo or 9600c possibly?
> 
> ...


Based on the specs, I believe it's this:

Eighteen Sound Speakers - Eighteen Sound 18NLW9600 - Eighteen Sound 18NLW9600 18" woofer handles 1,800 watts AES. Eighteen Sound 18NLW9600 18" subwoofers are available here. 18 Sound speaker components.

The PK spec sheet says they're using a driver with a 5" voice coil, and this is one of the few available.

For my subwoofer wall I opted for a 21.

If someone wanted to build one of these in their back yard, there's no reason you couldn't use a more 'common' driver, like a simple car audio 12 or 15. The main reason that I opted for the $$$$ B&C driver is because of the power handling.









The subwoofer wall accomodates a 321" video projection. So it would be a hell of a projector screen for a back yard theater.

Obviously this thing is too big to fit in the average home, but there are some ways to fold it so that it would. But I wanted to make it as dead simple as possible to assemble, as the whole idea is that this thing would be assembled on-site. Basically set it up before a show, and tear it down after. The shape isn't orthodox, but the efficiency gain is the real deal, and the parts weigh less than a conventional subwoofer.


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## danno14 (Sep 1, 2009)

Hmmm..... Perhaps i could use My four Fi ib18's to "get back" at those annoying wakeboard boats this summer....

"no honey, it's just for the kids outdoor movie night!"


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## co_leonard (Aug 14, 2009)

Patrick, this will be for home audio, right?


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## 454Casull (Nov 6, 2005)

Sorry, still not seeing the design of the horn. Can you draw a cross-section?


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## lionelc5 (Oct 31, 2011)

TC Sounds LMS Ultra 5400 18" DVC Subwoofer 293-666

Here is another 18" option.


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## lionelc5 (Oct 31, 2011)

danno14 said:


> Hmmm..... Perhaps i could use My four Fi ib18's to "get back" at those annoying wakeboard boats this summer....
> 
> "no honey, it's just for the kids outdoor movie night!"


Do you have those FI 18s in a box or IB?

Do you want to sell them?


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## chad (Jun 30, 2005)

It's been a long time since I got down and dirty with horns. But I think there is something missing here.

Horns generally, as pictured with the bassmaxx(freakin awesome subs BTW) and Servodrive rely on a certain amount of driver to adequately drive the air in the horn. When using multiple horns (unlike front loaded cabs) the F3 of the SYSTEM lowers with appropriate coupling as the mouth dimension gets larger. You are also multiplying drivers to effectively excite the air in each horn to combine this effect also.

So yes, a horn that large WILL (hopefully) exhibit directivity control to the frequencies dictated by it's mouth dimension. but I firmly feel that you are not going to do it with 4 18-21" drivers and equal what you can with the mass quantity of front loaded devices coupled as you see in these events.

Gary Stewart Audio (from the studio 54 days too) was notorious for putting flare extensions on conventional W-bins to decrease the F3. May be good to dig around and look at his stuff too.


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## danno14 (Sep 1, 2009)

lionelc5 said:


> Do you have those FI 18s in a box or IB?
> 
> Do you want to sell them?


Sorry, not for sale

Pending my own home theater setup


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## Patrick Bateman (Sep 11, 2006)

chad said:


> It's been a long time since I got down and dirty with horns. But I think there is something missing here.
> 
> Horns generally, as pictured with the bassmaxx(freakin awesome subs BTW) and Servodrive rely on a certain amount of driver to adequately drive the air in the horn. When using multiple horns (unlike front loaded cabs) the F3 of the SYSTEM lowers with appropriate coupling as the mouth dimension gets larger. You are also multiplying drivers to effectively excite the air in each horn to combine this effect also.
> 
> ...


When you array a pile of front loaded horns, the F3 of the array gets lower as the array grows larger. This is because the devices in the array sum constructively. The reason that they sum constructively is that the back wave of the driver is sealed off.

Back loaded horns don't see this affect, for the most part. This is because the radiation is much more complex (since there's output from both sides of the cone, *and* there's multiple cones.) On top of that, the output from a BLH is dropping like a rock below the F3, and one should use a highpass filter to keep the driver from exploding.



I know this wall of subs looks a bit odd, but it's just a plain of back loaded horn. Albeit a BLH with an unusual (but very simple) folding scheme.


I hadn't considered directivity, but this would have quite a bit. Heck, that might be the best reason to do it. In the horizontal axis, this wall of woofers would maintain pattern control down to 46hz. (IE, the wall basically acts like a waveguide with a beamwidth of 180 degrees and beamwidth control down to 46hz.)


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## chad (Jun 30, 2005)

Patrick Bateman said:


> I hadn't considered directivity, but this would have quite a bit. Heck, that might be the best reason to do it.


LOL well duh  :laugh:


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> eyes on the goal.
> 
> louder than PK Sound, builder friendly and modular design.
> 
> ...


I'm looking at 4000 watt amplifiers as we speak 

Behringer Stereo Power Amplifier - Walmart.com


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## danno14 (Sep 1, 2009)

Patrick Bateman said:


> I'm looking at 4000 watt amplifiers as we speak
> 
> Behringer Stereo Power Amplifier - Walmart.com


I have one you may borrow if you like..... Purely for scientific test purposes


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## Patrick Bateman (Sep 11, 2006)

danno14 said:


> I have one you may borrow if you like..... Purely for scientific test purposes


Lynnwood *is* in the Pacific Northwest...

(My location in my profile is fake, I actually live near Seattle)


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## danno14 (Sep 1, 2009)

Mmmhmmmm. I live in sumner with an office in issaquah. Want me to toss it in the trunk tomorrow? Figuratively tossing that is


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## chad (Jun 30, 2005)

LOL Walmart sells Behringer... a whole new low.


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## Patrick Bateman (Sep 11, 2006)

My first idea with this thread was a sub that could double as a projection screen. Would be very cool/different for live venues.

One problem, I don't build subs for live venues.

So, lets see what we could do to scale this down a bit?









This is the backyard home theater of an enthusiast in California. That's Mark Seaton from Sound Physics Lab in the pic, gives you an idea of the scale. (Fairly similar in size for what I'd proposed for a club-type setup.)

























This is a Sound Physics Lab BDEAP. Basically it's front-loaded horn that's designed to use a boundary to extend the horn mouth. It's an odd beast; it's very room dependent and it really needs to be used in sets of at least two, and ideally four. But if you meet it's requirements, you can get 10hz bass and big SPLs.

The BDEAP is kind of interesting in the context of this thread for three reasons:

1) Danley is preparing a new line of subs that seem very similar, the "BC" series
2) The BDEAP could be re-configured so that it becomes the theater screen. Basically change the foot print so that four of the BDEAPs become the screen. (Note that the mouth of the horn goes *away* from you, so you won't be staring at it while you watch a movie.)
3) All of my 'clones' of Danley designs, and we have the plans for the BDEAP right here:


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## Patrick Bateman (Sep 11, 2006)

I was pondering how the BDEAP works, and why you want a gap between the cabinets and the wall. I believe I have it pretty well sorted. Here's what's going on:

1) In a conventional horn, the last 25% of the horn length may be as much as 50% of the cabinet volume. This is because the volume of the segments grow very fast as you reach the mouth
2) In the BDEAP, the wall and the airspace between the cab forms the last segment
3) The sound radiates radially. My quick illustration shows how this works; the red square is the horn mouth, the grey square is the BDEAP cabinet, the orange and white rings are how the sound radiates once it exits the mouth of the BDEAP. If you had four BDEAPS it would radiate in a ring; but as you go from four to two to one you change the radiation shape.
For instance, with two BDEAPS, like in the photo above, you get *half* a ring, not a full ring.

This isn't the end of the world, as long as you have a good solid boundary.

When I was toying with the BDEAP configuration, it occurred to me that you could use *one* BDEAP if you but it in a corner.

Does that description make sense? As crazy as this sounds, *over half of the horn length is provided by that gap between the BDEAP cabinet and the wall.* Similar to the ol' Klipschorns from the 60s.


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## Patrick Bateman (Sep 11, 2006)

Okay, in my last few posts I detailed the idea of a sub that you can use to project an image onto. And that evolved into something that's similar to the old SPL BDEAP, which uses a room boundary to flatten and extend the response.

I'd prefer NOT to do a BDEAP for three reasons:

1) front loaded horns generally have a higher cutoff than back loaded and tapped horns. By a LOT. For instance, you can pretty easily get a twelve down to 25hz in a TH but the same driver in a FLH it might crap out at 50hz.
2) FLHs are harder to build
3) Based on some things I've read, it looks like THs have an advantage in the time domain. (See my thread http://www.diymobileaudio.com/forum...n/144111-up-front-bass-new-way-new-post.html‏)

Closest thing to a BDEAP that's a tapped horn is the Danley TH-50. So let's figure out how it works.









Here's my 'guesstimate' of what the cabinet looks like if you took it apart









I used the pics from diyaudio user 'tundraltd'









Here's the driver in the TH-50. It's a car audio driver, the MTX 9515. Same woofer that's used in the most powerful sub in the world, the Danley Matterhorn. AFAIK those are the only two designs from Danley that use a car audio driver.









Here's the simulated response of the TH-50, versus the TH-Mini. (mini is grey.) Basically the sonic 'character' of the two is practically the same, the TH-50 just plays an octave lower. No real efficiency gain, though the TH-50 does require a bigger driver due to the higher displacement requirements.









Excursion of the two is basically the same above 40hz; TH-50 goes an octave deeper. (If you don't highpass the TH-Mini you'll run into some serious problems.)


In my next post I'll see if I can come up with something similar to the TH-50 using an Alpine Type S.


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## Patrick Bateman (Sep 11, 2006)

One 'neat' thing about horns of all varieties is that the horn basically dictates the response shape. IE, you can often sub one driver for another with little ill effect. Cone area and motor strength play a big role; so you can't put an eighteen into a box designed for a twelve.

Nonetheless, the TH-50 is a great example of this. The graph above shows the response of the $500 MTX 9515, versus *four* of the Alpine Type S tens. (The enclosure is exactly the same; it's my guesstimate of the TH-50 footprint from the earlier post, based on the pics from diyaudio.)

We see the following:

1) output is almost identical. I'd be willing to bet that you couldn't even tell them apart without seeing the woofers. Response curve tracks each other within one dB in most of the passband

2) The Alpine is a bit smoother, likely due to lower VAS

3) Maximum output is about the same. The MTX has higher xmax, but four of the Alpines have a cone area that's comparable to a 20" woofer.

Besides being cheaper and smoother, the quad Alpine setup also give you the advantage of distributing amplifier heat over four 2.6" motors, which is basically like a 20" woofer with a 5.2" voice coil. (IE, it should handle 1000 watts with ease.)

Neat huh?


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## thehatedguy (May 4, 2007)

Make me one that I can put into my spare tire well.


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## BP1Fanatic (Jan 10, 2010)

Lol! Check out the foam core thread in diyaudio for ideas of putting a horn sub in a spare tire well.


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## T3mpest (Dec 25, 2005)

So Patrick I actually have 2 of the b&c woofers your modeling.. anyway to scale down one of these horns. I want to do a build where I.lose the back seat of my suvd do a wall right there in an suv, but.not taking up the cargo area Can you shrink anything down to that size or is a conventional ported box the best way here


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## keep_hope_alive (Jan 4, 2009)

Patrick, you would get along with a buddy of mine who has been doing live sound for over 20 years and designs/builds his own point source arrays. the best live sound i've heard has been from his rigs. 

Rexroat Sound - www.rexroatsound.com - home of the MPT series

Rexroat Sound - www.rexroatsound.com - home of the MPT series


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## chad (Jun 30, 2005)

Those intrigue me as the cabs are all full range.

Kinda followed them around on facebook a bit because they posted on "PA a Day."

Odd finding them as locals.


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