Dual opposed Slot Loaded Port

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mattlong8

mattlong8

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Joined 2011
#1
Greetings Bass Lovers,
I've been having a hard time finding any president for a design idea I have. I may just not know what to call it. I can think of several reasons why this design may be problematic but I keep coming back to it for some reason. The design takes a dual opposed slot loaded subwoofer and integrates the slot as the last part of the port.

This is a quick model I made to demonstrate the idea.
An externally hosted image should be here but it was not working when we last tested it.

My thoughts are that this will provide significant low end extension while not taking up a lot of extra room. The port is lengthened lowering Fb or allowing larger port area for the same Fb, reducing turbulence; the front of the woofers are loaded to improve impedance matching and theoretically lowering Fs; cabinet vibrations are reduced by the opposing drivers(which I would have facing each other); and sharing the slot loaded area with the port mitigates the volume increase.

Has anyone tried this? Does it have a common name? Could this a beneficial trade-off when trying to optimize for low extension and space conservation? I'm imagining some strange resonances/standing waves causing big peaks or dips in the response. This is why I threw that little triangle section where the ports meet. I think the geometry of this area could be a critical factor and any insight would be appreciated. I wonder if the long wavelengths will tend to propagate more towards the lower impedance path, so less energy will pass from the port on one side through to the other.

Please bear in mind this model is just to present the concept and is in no way refined...and yes I searched extensively for an existing thread, please pardon me if I missed it😉. If this hasn't been done, I do not authorize it's use by others for commercial purposes:lock: but DIY away 😀

-Matt Long
 
#2
Hi, this is basicly a tapped horn - bandpass horn hybird, without much actual horn action, so I suppose it's more of a tapped quarter wave tube - bandpass hybird. Certainly stands a chance of working, and could be modeled in hornresp. I would look at the CUBO series of subs, they are tapped - bandpass horns.

Acutally, on 2nd thought, this is pretty interesting for me because I could take my two existing slot ported boxes and strap them together like this. Maybe I'll run a model.
 
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#4
Rigtec is correct, the OP's design is functionally the same as the EAW SB1001, a ported box with the port exit plenum also housing the speakers.
Of interest, the previous version of the cabinet also included smaller ducted ports on the side front panels in addition to the central port.
 

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#6
turbodawg said:
A "bandpass tapped horn" would be much closer to describing this:
Click to expand...
A "tapped horn" gets larger from throat to mouth, the OP's design seems to maintain a uniform cross section, as such would fall into a "pipe" category.

Whether the OP's design is a BR or a pipe or a TH depends on ratio of duct to enclosed volume and the taper of the duct.

Regardless of what it is called, it is not conceptually new, and can be modeled with Hornresp 🙂.
 
#8
weltersys said:
A "tapped horn" gets larger from throat to mouth, the OP's design seems to maintain a uniform cross section, as such would fall into a "pipe" category.

Whether the OP's design is a BR or a pipe or a TH depends on ratio of duct to enclosed volume and the taper of the duct.

Regardless of what it is called, it is not conceptually new, and can be modeled with Hornresp 🙂.
Click to expand...

I called it a tapped tube in post #2.
 
#10
mattlong8 said:
Greetings Bass Lovers,
<snip>
Click to expand...


Yes, I am familiar with that design.

The cabinet uses a combination of a reflex and band pass. Anyone can mimic the design by merely having two reflex cabinets facing each other while having the proper spacing in order for the sound to escape.

EV X-Array Subs follow a similar principal. These have no characteristics of the EAW SB 1000 or the 1001.

Nevertheless, the biggest obstacle will be the amount of pressure build up the cabinet will need to endure for the exit area is very small (based on the photograph) compared to the surface area of the drivers.


As it is a band pass, you will be limited in the upper frequencies due to exit of the port/vent the sound must escape through. They perform okay for an extension to your bass bins if your bass bins can’t offer anything meaningful under 50 Hz, but tend to sound too limited to cover a full bass range on their own.
 
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#11
any advantage over building two cabs with one driver each ?
(and I mean real advantage that is clearly heard)

for pro use I can see the advantage of pushing most possible driver into smallest possible space
and small cabs are most likely not very practical either

but if we look at in a smaller scale ?
 
#12
I've been searching my aged memory for any other instance in mechanical design where the whole game of design hinges on a single troublesome factor that pushes the limits of design abilty. For readers of this forum, loudspeaker design (even ESLs... but maybe not horns) is twisted out of shape by the need to eat the rear wave.

That is what is driving this imaginative design, just like almost all other speaker designs.

Sad.

For myself apropos cone drivers, I like sealed boxes (kind of a crude solution but it introduces the fewest new resonances and modes) and OBs (kind of a non-solution). But this design does introduce all kinds of acoustic bits and pieces and, by the precepts above, is not too desirable.

Ben
 
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#13
tinitus said:
any advantage over building two cabs with one driver each ?
(and I mean real advantage that is clearly heard)

for pro use I can see the advantage of pushing most possible driver into smallest possible space
and small cabs are most likely not very practical either

but if we look at in a smaller scale ?
Click to expand...

I can't think of any advantage other than having size of the slot operate as a means of a low pass filter.
 
#19
Hi Paul,
I have not made any progress on this design. To have an idea how it would behave with out building one would require modeling in hornresp(as mentioned above) or akabak. I'm currently waist deep in (gasp!) a lighting project (don't shun me please!) but I might be able to test a few geometries next month.

Given appropriate drivers this design seems well suited to your application due to the long port length relative to the enclosure size. The other reason why I feel like there may be something in this is the close and rigid coupling of the two drivers in a partially closed space will give a boost in some frequencies. I think this boost is the same thing that bento is talking about above albeit from a problematic perspective.
There may be a way of using this with a particular bass reflex alignment to decrease the cabinet size while maintaining output and bandwidth. A chip off the old Iron law so to speak.
In reality it may amount to little but I enjoy the occasional indulgence in to the conceptual.

Thanks for chiming in paul.

-Matt
 
#20
Hi Matt, let's see if we can make this work albeit on either side of the Atlantic and mainland USA. If it turns out to be too high to go under my rack it could go above the ceiling. I am also thinking about infinite baffle in that position. Not sure how to model it other than in two separate bass reflex cabs joined together but what effect will having the drivers opposite each other in close proximity have. It works for infinite baffle but the bass reflex port joining the front wave may have some bearing on the outcome.
 
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