I have looked through many BLH designs and almost all of them include so called coupling chamber. But I don't fully understand its role. It's mentioned that it acts as a low pass filter but even then I don't understand the purpose. Does it have something to do with baffle step? Or maybe it just attenuates high frequency output from the mouth to mitigate a comb filter effect?
The second reason and besides, we are more sensitive to issues with the higher frequencies such as this delay and displacement.
As noted above; it's an acoustical low-pass filter, so in most cases it's there to roll the horn off above a set frequency to reduce group delay and unwanted interactions -a 'typical' bass horn is really only practical up to about 300Hz (the actual frequency varies depending on the design and particularly the path length). There are (to a point) exceptions depending on the horn variant being used, but in the context of the above, that's the main one.
Thanks. So if I've understood correctly the document GM posted, the horn must have one/more acoustic low-pass filters to flatten upper resonances of the horn. The first one seen by the loudspeaker is the rear chamber seen as a helmholtz resonator (to dampen the strongest resonance I guess), then others downstream the horn are folds (where the area of the section changes) or abrupt and short restrictions (like the FH).
Correct, then there's getting the driver/terminus offset just right for good phase/time matching summed response that historically few get 'close enough' simply because it tends to waste too much space unless complex folded, though considering how much the room usually mods it, not a big deal in most HIFI/HT apps.
That said, I normally 'cheated' by adapting Olson's folded horn construction that with a little judicious internal damping worked a 'treat'. 😉
That said, I normally 'cheated' by adapting Olson's folded horn construction that with a little judicious internal damping worked a 'treat'. 😉
Thank you GM,
Is it needed to do more than dampen the sides of the chamber of the speaker with felt?
What are the sonic differences of a W configuration with expanding areas as shown in the article:
compared to straight angles with passages that increase their size after every fold (EG like what can be seen from the online images of Scott and Dave's Silbury)? https://www.wodendesign.com/Silbury.html
Is it needed to do more than dampen the sides of the chamber of the speaker with felt?
What are the sonic differences of a W configuration with expanding areas as shown in the article:
compared to straight angles with passages that increase their size after every fold (EG like what can be seen from the online images of Scott and Dave's Silbury)? https://www.wodendesign.com/Silbury.html
You're welcome!
One is a proper expanding horn with a flare factor, frequency, the other a stepped expanding horn, so not as smooth, efficient in theory, but have never done a comparison, so Scott would need to do sims for comparison.
That said, they're both parabolic flares since they each have a set of parallel sides, so not sure there would be much difference for a given acoustic pathlength except in the HF where it blends into the driver's output (baffle step) due to the slower expanding Olson flare.
Anyway, curious what Scott comes up with.
One is a proper expanding horn with a flare factor, frequency, the other a stepped expanding horn, so not as smooth, efficient in theory, but have never done a comparison, so Scott would need to do sims for comparison.
That said, they're both parabolic flares since they each have a set of parallel sides, so not sure there would be much difference for a given acoustic pathlength except in the HF where it blends into the driver's output (baffle step) due to the slower expanding Olson flare.
Anyway, curious what Scott comes up with.
Not the couple of Olson studio monitors I've been exposed to, the Mellow Monster I linked to comes closest in concept.......
Hmm, I don't have MJK's program anymore, only HR, but I can't make this simple formula line up even close to how/where I do it plus seems like I sent Scott a MJK sim long ago that he could have reverse engineered easily enough.
Sorry, missed this. Will put a few bits together (on laptop at the moment).
I read it as 'does the horn terminus have to be within a certain distance to the driver'. If I've read that right (apologies if I haven't) then: yes. The further away the terminus moves, the greater the group delay from that, and the internal pathlength of the horn, assuming the terminus is not positioned closer to the listening position than the direct-radiating driver.
Thanks @Scottmoose for the explanation, that’s the reason why huge horns (like the ones in Nelson Pass’ site) have the speaker concentric to the horn.
@planet10 now I understand (I hope correctly this time) that your post about the delay of the horn vs speaker was referred to the lenght of the horn and not the distance from the horn mouth to the speaker.
@planet10 now I understand (I hope correctly this time) that your post about the delay of the horn vs speaker was referred to the lenght of the horn and not the distance from the horn mouth to the speaker.