What are the pros & cons of high-efficiency horns?

[Folsom]

Duke, I think the problem would be that it might create a null at the listeners spot at the frequency. The dip may not exist directly in front of the speaker. So how off axis you are may determine whether it sounds wrong/right, if it plays those frequencies.

I'm imagining it like a dipole, except the cancellation begins at the lip of the horn.

But this all does depend on how ventilated it actually is... is it lossy or straight up passes sound?

 

[Duke LeJeune]

Duke, I think the problem would be that it might create a null at the listeners spot at the frequency. The dip may not exist directly in front of the speaker. So how off axis you are may determine whether it sounds wrong/right, if it plays those frequencies.

It looks to me like the horn's mouth is too small to have good directional control around the estimated dip frequency, and if such is the case, then I don't think the off-axis angle would matter very much, as far as whether the two outputs (front of woofer cone & mouth of horn) sum to a dip related to the effective length of the horn. The center frequency of the dip might move around a bit as the off-axis angle changes, but I wouldn't expect the magnitude of the dip to change very much.

 

[Folsom]

I suppose a measurement would tell a lot. Dipoles aren't always directional but you get a forward and backward. I don't know if this could beam or not.

 

[Duke LeJeune]

Dipoles aren't always directional but you get a forward and backward.

True.

But assuming a flat baffle, the directionality arises because the baffle separates the frontwave and backwave such that they meet, out-of-phase, at the baffle's edges. So there is a plane of cancellation (and partial cancellation as we near the plane) which causes the directionality.

If the baffle is folded straight back, I think the plane of cancellation is halfway between the outwide wrap-around distance and the inside path distance. I think this halfway point is not quite all the way back because the outside path length is longer than the inside path length. Thus the plane of cancellation is not quite all the way back.

Now if the baffle is folded into a two-fold dipole (reverse tapered in this case)... hmm, now it's no longer clear to me. I'm not sure where the plane of cancellation ends up, or if it even it's still a plane. The outside path length to the opening (woofer face to horn mouth) is much, much less than the inside path length to the opening so... is the plane of cancellation now inside the box? But inside the box, the SPL from the backwave will be much, much louder than the SPL from the frontwave energy which makes it into the opening, so I don't think there would be much if any cancellation there.

Anyway I think the net result is no significant directivity, as there would be with a "normal" dipole... just progressively greater cancellation (at least south of the 1/4 wavelength path length frequency)... but if I'm missing just one little point along the way here I could be completely wrong.

 

[bonzo75]

If I understand Leif's description if the "ventilated rear chamber" correctly, the front side of the woofer cone has no such long path length. Then the backside of the woofer is what has the long path length.

So far, so good.

But...

If the front of the woofer cone is indeed radiating into the room, then at the frequency where the 4 meter path length is equal to one wavelength - about 86 Hz - the output from the horn emerges 180 degrees out-of-phase with the output from the front of the woofer cone. So depending on the relative loudness of the two, there may be a cancellation dip in that region. If the crossover frequency is somewhat lower than that, any such dip may not matter.

Somebody please correct me if I'm missing something.

His bass horn comes in at 75 Hz

 

[Duke LeJeune]

His bass horn comes in at 75 Hz

That makes sense to me. The dip is probably pretty narrow, and if anything it probably works with the 75 Hz lowpass filter.

You can sometimes see the one-wavelength cancellation dip I'm talking about in the anechoic frequency response of speakers with a transmission line or something conceptually similar:

https://www.soundstagenetwork.com/measurements/pmc_gb1/

https://www.soundstagenetwork.com/i...&catid=77:loudspeaker-measurements&Itemid=153

https://www.soundstagenetwork.com/measurements/zucable_druid/

Out in the real home audio world those dips will probably be at least partially filled in by the reverberant field, which dominates perception at low frequencies because we don't hear the direct sound separate from the reverberant sound in the bass region, and dips are less audible than peaks anyway.

 

[morricab]

Hi Brad,

Curious about the fastidious application of driver alignment by the Aries team with respect their subwoofer - I noted the specific citing of the sub very far in front of the drivers. Any further light about this would you know?

Only that I am in agreement with Stavros that it matters and I think it impacts realism...nearly all the speakers I have liked the most were time coherent.

 

[christensenleif@msn.com]

the driver front faces the horn
btw 18Sound 21LW1400
btw the side openings by the horn mouth are there to increase mouth area without shortening the horn

 

[kodomo]

Until a few months ago, I had a different bass solution and it had a folded full 20hz tapped horn. I placed it physically close to me etc. After having the new and completely aligned triple servo woofer h frame OB bass section from 20 to 120hz, there definitely is a difference. Of course I have a completely different solution and most of the difference comes from the different topologies of these solutions but one part of it is alignment too. This again is a pros and cons situation. I have tried tapped horn, and your once folded, vented chamber horn is a kind of tapped horn. They were ok for the last octave 20hz-40hz but my new solution already covers that and makes me have one lass channel and they really match the midbass horn, the integration is much better than my bass reflex boxes with dual tad 1601b's.

 

[christensenleif@msn.com]

they are not "kind of tapped horns"
they´re leaking from rear chamber to even out pressure and impedance and avoid air being pressed through membrane from rear chamber.....
Rune calculates the density of the compressed foam plug and have it custom made locally for each application....
after the positive experience with the vented sub chamber, we decided to test it on the midbass FLHs
after some calc and sims Rune came up with the "foam plugs" and we were very pleased to see and hear an even greater impact there...

 

[Duke LeJeune]

they´re leaking from rear chamber to even out pressure and impedance and avoid air being pressed through membrane from rear chamber.....

Very interesting!

In that case, my last few posts are probably not applicable.

 

[christensenleif@msn.com]

Rune has applied for a patent for this....whether it´s granted yet, I don´t know.
Rune was tutor for Bjørn Kolbræk when he studied for his Doctor degree in horns theory, yet Rune has more practical experience having built loads as in over 2 hundred horn subs...

 

[christensenleif@msn.com]

Rune´s new company...
https://nnnn.no/about-us/

Bjørn went to Celestion ...

 

[Audiophile Bill]

Rune´s new company...
https://nnnn.no/about-us/

Bjørn went to Celestion ...

Did you hear his new driver yet?

 

[christensenleif@msn.com]

no, unfortunately
maybe it pops up at ETF in Belleme, Normandie
though, the big excitement there is the Shearer horns they´ve built...

 

[bonzo75]

Did you hear his new driver yet?

Celestion axiperiodic driver with Bengal tiger horn loaded tweeter

 

[kodomo]

they are not "kind of tapped horns"
they´re leaking from rear chamber to even out pressure and impedance and avoid air being pressed through membrane from rear chamber.....
Rune calculates the density of the compressed foam plug and have it custom made locally for each application....
after the positive experience with the vented sub chamber, we decided to test it on the midbass FLHs
after some calc and sims Rune came up with the "foam plugs" and we were very pleased to see and hear an even greater impact there...

It looked like a tapped horn, I did not know it was a different design. Then I can not comment on it. It is great to have experienced engineers by your side!

My experience showed me that, if you can align for the whole frequency band it is beneficial. It is also better to have one channel instead of two, even if it is for bass. Also, the integration of new servo technology for bass and with the paper drivers I use in ob, integrates really good with horn mid-bass. This has been my own experience.

 

[christensenleif@msn.com]

acc to Rune , tapped horns have higher distortion, which given their construction, seems quite logical...

 

[morricab]

acc to Rune , tapped horns have higher distortion, which given their construction, seems quite logical...

I doubt at those frequencies a moderate increase in distortion will be readily audible.

 

[christensenleif@msn.com]

still I don´t seek higher distortion
what would the advantage with a tapped horn be instead of my solution?