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I'm new to this so dont hurt me please, be gentle


I'm thinking about building some sub cabinets for our rock/punk band and we play in clubs and outdoors and need to extend the bass guitar and kick drum, our bassist uses a 5 string so as low as 30hz


my thought was to build a 2 part cabinet, use half indoors and join together when outdoors


i know that you probally need lots of info on size and stuff but what do you think of my thought, ruff cabinet design attached


the red line indicates the join

 

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It would probably be much easier just to find one of Bill's plans that would fit your needs. http://www.billfitzmaurice.com/index.html All the hard work is done, you just buy the plan for $14 and build it following the directions and using the proper driver.


Great stuff, AutoTuba is a fantastic horn. But something like one of the Titans or Tuba 24s or something would probably be perfect.
 

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I agree with visiting Bill's site, or searching lilmike's designs here at avs. Not sure you would need the modular approach, as the extension needs would be the same indoors v out. You would just need more cabs for the latter.


JSS
 

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Well, the issue I see with such an extension is that the length sets the tune. The tune and the driver set the chamber size in a front loaded horn as you have drawn. Changing the length without changing the driver and the chamber means that the performance will be compromised somewhere.


Extensions are simply not an option with a tapped horn due to the design.


Sounds like you want 30 Hz. That's a reasonable goal. Lots of good options available, and you don't need super expensive drivers or huge cabinets.


Like maxmercy said - extension needs are the same whether you're outdoors or inside.


Now - how loud do you want to get? That determines how many cabinets you need to get there.
 

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Quote:
Originally Posted by lilmike  /t/1469097/thoughts-on-modular-front-loaded-folded-horn-cabinet-design#post_23233800


Well, the issue I see with such an extension is that the length sets the tune.
And that's why you don't see this done. If you do as the OP suggests, 'use half indoors and join together when outdoors', the half used indoors will only extend to an octave or so higher than the two halves. For the sub to function as a sub both halves would always have to be used.
Quote:
need to extend the bass guitar and kick drum, our bassist uses a 5 string so as low as 30hz
5 string bass doesn't actually go that low. I can virtually guarantee his stage rig doesn't.
 

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After playing bass for a while and wanting to someday build myself a Bass guitar rig your bassist wont need 30hz.(I play an 8 string bass) If he heard my bass on a pair of good headphones he would then realize his 5 does not go that low. In theory the B string fundamental does but not what he is used to hearing. More like 45/60hz. The T48 from Bill would be great for the bassist along with a top such as the DR series or Otop. Or if you want modular you could use Jack12's. Use a pair and be very happy also.


Just tell everyone what your wanting and others can guide you into what you need.
 

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Quote:
Originally Posted by lilmike  /t/1469097/thoughts-on-modular-front-loaded-folded-horn-cabinet-design#post_23233800


Well, the issue I see with such an extension is that the length sets the tune.
And that's why you don't see this done. If you do as the OP suggests, 'use half indoors and join together when outdoors', the half used indoors will only extend to an octave or so higher than the two halves. For the sub to function as a sub both halves would always have to be used.
Quote:
need to extend the bass guitar and kick drum, our bassist uses a 5 string so as low as 30hz
5 string bass doesn't actually go that low. I can virtually guarantee his stage rig doesn't.
I'm curious; Why does the pair go lower ? Improved directivity of the pair.

Thanks
Terry
 

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I'm curious; Why does the pair go lower ? Improved directivity of the pair.
The low frequency extension of a horn is based on its length and mouth area. Since the horn would be shorter and have less mouth area without the extension it would not go as low.
 

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Quote: 

And that's why you don't see this done. If you do as the OP suggests, 'use half indoors and join together when outdoors', the half used indoors will only extend to an octave or so higher than the two halves. For the sub to function as a sub both halves would always have to be used.Quote:need to extend the bass guitar and kick drum, our bassist uses a 5 string so as low as 30hz

5 string bass doesn't actually go that low. I can virtually guarantee his stage rig doesn't.
This is just wrong. There are a bunch of ways to look at this.

1. Barn door effect - something as simple as a wall built around the mouth of the horn can boost response, this is done quite a bit, and it works because it increases the frontal face of the sub to allow for diffraction effects (boost) to lower frequencies. In fact if you make the wall big enough, you've gone from 2 pi response (outdoors in a field) to 1 pi response (outdoors with a large wall around the subs).

Here's a thread that looks at the barn door effect through the context of multiple stacked speakers - http://www.diyaudio.com/forums/subwoofers/204472-multiple-cabinet-combined-response.html

And a very interesting and important quote from the first post - "The frontal area of the stack makes a significant difference in response shape, adding “wings”, flat pieces of plywood (AKA “barn doors”) to the stacks add 2 to 3 dB to the LF response when the frontal area is tripled."

So you don't even need a waveguide extension to boost low frequencies, you just need a large wall (which I suppose is a waveguide with no length) and this will work with any alignment - sealed, ported, any type of horn, etc.

2. Another way to look at this is to look at actual waveguides. First a sim - this shows 2 pi response with (red trace) and without (blue trace) the last segment shown in the schematic drawing. That last segment is huge - it takes the cab volume from 500 liters (without the last segment) to over 3500 liters, but as you can see, it does not change the cab tuning, it just adds a lot of spl above tuning. But it doesn't change excursion - with and without is almost a perfect overlay so it's a net gain with the only cost being the wood to build the massive flare, the cargo space to haul it and the few minutes it takes to strap the two pieces together.



So you could use this horn without the last segment inside and use it with the last segment extension outside and gain a bunch of db.

But forget about sims, let's look at an ACTUAL real waveguide extension with measurements. http://www.diyaudio.com/forums/subwoofers/184986-horn-extender-wave-guide-th.html

As you can see, the waveguide does not change the tuning but it does add a bunch of dbs. And even though it's strapped to a tapped horn it doesn't mess up the response curve.

3. Horn theory shows that "extensions" and variations on the extension concept are valid and very useful.

For example, let's say you wanted to play a small sub inside, and you have wall reinforcement (1 pi environment) when the sub is inside. But you also want to play it outside in an open field and you want it to have the same tuning in both situations. Is this possible? Of course, and it's right in the basics of horn theory.

Here's a quick sim showing situation 1 on the left and situation 2 on the right. As you can see, the closed box volume is the same, the throat area is the same, the horn flare T is the same. The ONLY thing different in these two horns is that the 2 pi (outside) horn is longer. It's an extension of the SAME HORN and it's necessary to keep the same tuning when you remove the wall reinforcement (go from 1 pi to 2 pi). I didn't even design this horn, I used Hornresp's System Design With Driver (Leach's math) to give me a horn for this particular driver with bandwidth from 23 - 230 hz for 1 pi and 2 pi situations. The only thing I changed in the sims is I halved the power in the 2 pi sim. As you can see, the frequency response is almost identical and the excursion difference is self explanatory (I halved the power in the 2 pi sim). The bottom response graph shows both frequency responses overlaid so you can see how close they are, they don't overlay perfectly but it's close.



So I've shown a bunch of examples in which you can add barn doors or waveguide extensions to a sub and add some dbs without changing the tuning, regardless of whether you are staying in 2 pi in both situations or whether you go from 1 pi (wall reinforcement) inside to 2 pi (open field) outside. You can also go from 0.5 pi inside (corner loaded in a very rigid concrete corner) to 2 pi outside with the same response, you just need a much larger extension.

Not only that, but this is done all the time, both barn doors and waveguide extensions. And the whole theory of extending a horn flare is horn theory basics. So yeah, it will work just fine if you design it properly. None of these 3 examples are similar to the pic in post 1 but with proper design you absolutely can achieve more spl and the same low knee frequency with waveguides or even flat boards.
 

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The low frequency extension of a horn is based on its length and mouth area. Since the horn would be shorter and have less mouth area without the extension it would not go as low.
Wrong. The low frequency extension of a horn is based on every aspect of it's design AND environment. Waveguides don't have to change the low knee frequency, even if you change the environment.
 

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Nice post "diy speaker guy"

Something to take off my "Hornresp" to do list". Well thought out.
You are increasing the baffle step function of the speaker/horn to re-enforce the bottom end, with a wall (barn doors).
I've done this with heavy poly tarp, which is lighter/more portable and can be made to look good.
You might then consider a corner load, which "lilmike" points out in "Offset driver Hornresp tutorial", is as
much as a 12db gain over the open field.
"maxmercy" points out the middle ground; more cabs gets you higher efficiency and a bigger wall, which yields
a lower step function and still more gain.
I think Bill was referring to the simple case of cutting a horn in half, which I misunderstood.
and finally the post sketch appears to be a front loaded bass horn; aka "LTD02's" "SubMaximus"
I aim to please.
 

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I think Bill was referring to the simple case of cutting a horn in half..
+1, because that was the question posed. As for using horn extensions to realize both a longer pathway and larger mouth for extended LF response, my Tuba and Titan pro-sound sub designs have incorporated that feature for 15 years.
 

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Regardless, your answer is still wrong. I showed both a case of adding a waveguide segment that would increase spl in the same 2 pi environment (whether used inside or outside) AND a case where you can switch from 1 pi (or 0.5 pi, not shown) to 2 pi and maintain the same frequency response. And in both cases the low knee frequency does not change. And if you look at the example 3 sim in my last post, the 2 pi horn is almost exactly 2x larger than the 1 pi horn, so technically it is cutting the horn in half. I could show the same thing with the example 2 sim, I could make the last segment exactly the same size as the original horn, in which case it wouldn't have as much gain but it would be half the horn and tuning would not change. in both these cases the last segment will be relatively short in comparison to the rest of the horn but it will be large and if you want to you can size it to be exactly the size of the original horn so when the last segment is strapped on it exactly doubles the horn size. So yes, you can cut a horn in half (in terms of volume, not path length) and maintain the same tuning regardless of whether you are staying in the same environment or moving to a different environment with less boundary reinforcement. So no matter how you look at it your answer is wrong.

You can intentionally make the last segment of a size and shape that it does NOT maintain the same tuning, but you certainly can make it to maintain the same tuning even in different environments, as shown.
 

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The low frequency extension of a horn is based on its length and mouth area. Since the horn would be shorter and have less mouth area without the extension it would not go as low.
This statement is the problem. If you don't consider the flare shape (and size) and environment you absolutely cannot say that the low frequency extension of a horn is based on length and mouth area. There's a HUGE difference between a conical and exponential expansion and they will give remarkably different low frequency extension even if the length and mouth area are the same. And if you put the horn in an open field you will have a remarkably different response than in a rigid concrete corner. (In the last case the low frequency extension won't be remarkably different but the overall response will be.)

If the goal is to maintain the same low knee in the same environment but to add spl by adding a waveguide equal in volume to the original horn, this is easily achievable. And if the goal is to maintain the same frequency response (including the low knee) in different environments with a waveguide equal in volume to the original horn (per boundary reduction) this is also easily achievable.
 
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