Bass-reflex loading a front loaded horn

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Uwe,

It can be done, but "a well designed vented box" will be larger than a "well designed" compression chamber for a front loaded horn.

The photo below shows an old (1979) system with ported compression chambers that attached to 45"x45"x30" deep straight bass horns, though the straight horns sealed the ports when used.

I only used the cabinet backs on one or two gigs without the bass horns...

Art
 

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Uwe, interestingly, I've been examining a similar idea recently, but regarding mid-HF speakers. My thought was to have a pair a high quality 90º cinical 12" coaxials, but when I need more energy out front (for instance, needing the low mids to carry more than 40 feet) I could maybe attach a custom-made 90 X 45º horn, with a 12" diameter throat.

Bottom line: For tops, while this might indeed help with throw, it would also cause phase artifacts that might make it non-feasible. (I still may try it)

Read this:

http://eaw.com/docs/6_Technical_Information/White_Papers/AX_whtppr_L.pdf

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Of course with subs, it may not be such a big deal. I would defer to Art's experience here.


Art, how does this possibly work, since LF is omnidirectional? I get the idea of doing it with a horn, as you did with the Keystone, because in that case you are literally extending the length of the horn.
With a vented box, there isn't that impedance, or whatever, right? So what would the front flare actually accomplish?
 
1) My thought was to have a pair a high quality 90º cinical 12" coaxials, but when I need more energy out front (for instance, needing the low mids to carry more than 40 feet) I could maybe attach a custom-made 90 X 45º horn, with a 12" diameter throat.

Bottom line: For tops, while this might indeed help with throw, it would also cause phase artifacts that might make it non-feasible. (I still may try it)

2)Art, how does this possibly work, since LF is omnidirectional? I get the idea of doing it with a horn, as you did with the Keystone, because in that case you are literally extending the length of the horn.
With a vented box, there isn't that impedance, or whatever, right? So what would the front flare actually accomplish?
1) With a 90º 12" coaxial, reducing the dispersion to 45º will cause internal reflections within the extension, which will actually degrade the upper frequency range coherency, effectively reducing "throw". A large 90º x 90º "waveguide" will give the lower end as much as a 3 dB increase in forward gain. The same "waveguide" can be integrated with a top elevation box and the LF cabinets also.
2) A large "waveguide", say double the frontal area of the LF cabinet, will also result in around a 3dB frontal gain, simply because the increased frontal area results in larger boundary area. This larger boundary area works equally well regardless of the cabinet design, whether sealed, BR, TH, or FLH.

Although the old fiberglass horns shown in post #2 had a horn cutoff above 60Hz, the rather huge frontal area of the stack allowed the direct radiator response below cutoff to provide a fair amount of frontal gain to below 40 Hz.

More information on the subject here:
Horn Extender/Wave-guide for TH

Cheers,
Art
 
1) With a 90º 12" coaxial, reducing the dispersion to 45º will cause internal reflections within the extension, which will actually degrade the upper frequency range coherency, effectively reducing "throw".
Art

Indeed. That's what that EAW white paper explains as well.

1) A large 90º x 90º "waveguide" will give the lower end as much as a 3 dB increase in forward gain. The same "waveguide" can be integrated with a top elevation box and the LF cabinets also.

Art

Now you have my attention!

I don't understand the physics of this (it doesn't make intrinsic sense to me) but I believe you.

I have posted follow-up questions on that other thread,
http://www.diyaudio.com/forums/mult...estions-diy-danley-th-mini-2.html#post5453433
- so as not to further hijack this one.
 
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hey Art - would a 0.7 scale Voice of the Theater front horn for 12pe32/Eminence 12 muck with stuff such as to render such a project
useless? what would it do if loaded with 12cx? (it would be a fun size for home :D)
A 0.7 scale Voice of the Theater front horn would be limited to around 160-1200Hz useful range, generally there is more than enough of those frequencies in the home without adding more low mid honk ;^).
The relatively narrow initial horn entry would mess up the dispersion of a co-ax.
 
@weltersys - re:12cx in ported with horn - how about a larger version of Frazier's CAT40 speaker? if that's viable (?) what size would you make it?
Freddi,

An increased size CAT40 would work OK with a 12" co-ax. The CAT40 is basically 18" x 18", pattern control around 120x 120 degree at 500 Hz- doubling the size would extend that pattern by about an octave.

I prefer the gain and better pattern control of a multiple-entry horn rather than a co-ax with a small horn inside of a waveguide, so would not be inclined to "scale up" a CAT40.

Art
 
thanks Art - its just I've already got Eminence cast frame 12cx with 80oz magnets and 2.5" coisl. Also lower sensitivity Eminence 12cx with 109oz magnets and 4" coils. Do you think 1/2" Baltic birch would suffice for the flare pieces? With the ~99dB 12CX - don't think one would want much reflex volume. How about just scaling the CAT40 1.5x? I'll also take a Karlson 12 if you can come up with one that
beats the original ;^)
 
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Thanks again Art. I wonder if it would port at the throat of the wavguide like
the CAT40? Tuning would be in the 60-70 region for some of those Eminence 12cx. Would you have a good sounding xover for a Martinsound 1144 12cx?
The CAT40 port around the mouth, not the best for diffraction, though it looks like the put foam in the waveguide to reduce the problem.

I don't have any crossovers for sale, and no experience with the 1144 12cx.
 
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