Port Holes on Horn Walls

Johnny Holguin

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Sep 23, 2016
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I'm sketching out a plan for a dual 8-inch horn. I wanted to port to get some lower frequencies - not wanting to use a sub for things like basic voice PA or wedding ceremony PA.

Is there a rule about putting ports on the horn walls? Would it even make a difference versus a port say on the side of the box?

I think Danley does this with some of their Synergy horns. Some advise would be grateful...
 

Johnny Holguin

Freshman
Sep 23, 2016
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San Antonio, TX
Hmm, views but no comment. Maybe a picture would help!
I want to use a B&C 8-inch coaxial. The problem I see now with putting a port on the wall is that I would have to include all that area between the horn wall and the outside wall.

I also thought about the 1/4 wave rule. If I wanted to say go down to 60Hz that port would have to be around 4-1/2 feet away and there's not enough room for that. Or do I have that wrong?

port-horn-wall.jpg
 

Peter Morris

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May 8, 2011
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I don’t think it’s a good idea to horn load a coaxial driver that way. The HF will bounce of the walls of the horn. The only way to get that to work is like what Danley does with their SM80 where the horn profile is more or less an extension of the speaker cone profile.

Yes it is possible to put port holes in the horn, but putting a large hole near the throat is not a good idea. What Danley (again) do in their synergy horns is put a small hole near the throat, its space at less than ¼ of a wave length relative to the crossover points so that the HF and MID can sum nicely without issues e.g. reflections from the base of the horn. As Chris said these are not bass ports, but inlets for the sound coming off the cone.

An example of a LF reflex port hole in a horn is Communities SLS920 (HF horn) and TW audio T24N (mid horn).
 
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Joris Wijgerde

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I'm definitely not an expert so please correct me if I'm mistaken but I have been building some synergies and most do indeed have reflex ports in the horn. This is different from mid injection ports as the location of injection ports are based the upper cutoff point of their passband. The reason for the spacing is twofold: for better summation and to keep the notch - created by sound waves that travel from the woofer to the apex of the horn (CD) and back - out of the mid's passband.

Since you want to keep the ports within 1/4WL of the upper cutoff point of their passband, anywhere down the length of the horn will do for a reflex port since the tuning is most likely way lower than an injection port. So in that case it would be preferred to put them close to the mouth of the horn to minimize diffraction, or in case the horn isn't large enough to provide loading at this frequency you could just place them outside of the horn.
 

Peter Morris

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May 8, 2011
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I'm definitely not an expert so please correct me if I'm mistaken but I have been building some synergies and most do indeed have reflex ports in the horn. This is different from mid injection ports as the location of injection ports are based the upper cutoff point of their passband. The reason for the spacing is twofold: for better summation and to keep the notch - created by sound waves that travel from the woofer to the apex of the horn (CD) and back - out of the mid's passband.

Since you want to keep the ports within 1/4WL of the upper cutoff point of their passband, anywhere down the length of the horn will do for a reflex port since the tuning is most likely way lower than an injection port. So in that case it would be preferred to put them close to the mouth of the horn to minimize diffraction, or in case the horn isn't large enough to provide loading at this frequency you could just place them outside of the horn.
The problem putting the ports near throat / the apex of the horn is the impact it will have on pattern control, reflections within the horn and horn loading of the higher frequencies.

1/4 wave length spacing for the operating frequency of the port would require the ports to be with in about a 1m or more in most cases ... so its not an issue.
 
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Johnny Holguin

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Sep 23, 2016
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San Antonio, TX
Thank you for the input. I learned a few things here. I went and looked at some other Danley products and their column speakers seemed interesting. They use coaxial drivers inside a horn but through a paraline system. Obviously, this works but a lot more complex.
 

Peter Morris

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May 8, 2011
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This is one trick that Danley does using coaxial drivers. Compression driver entrance at the apex + 4 small separate ports for the paper cone of that coaxial driver. They do not share the same volume behind the horn.

Plus 2 x LF driver entering mid way down the horn (4 ports) and the 4 x reflex ports near mouth.
 

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Johnny Holguin

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Sep 23, 2016
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San Antonio, TX
hehe wow. Ok, so is there some kind of extension connecting the compression driver to the horn? I'm imagining a pipe from the horn entrance to the dust cap. I would have never thought about doing something like that.