You were probably hearing the stored energy in the horn blurring the decay time, as do all big horns/TLs/Tapped horns/ported loadings. With your sealed subs this effect is dramatically reduced. I find it difficult to listen to anything but sealed subs these days... Fast transient attack is easy to achieve as it is defined by the HF driver's upper end response, but equally important fast decay time at low frequencies is considerably more difficult to achieve, and downright impossible if the enclosures are huge since the stored energy is equally huge. Step response of some of these big folded horns shows 'ringing' continuing for over a quarter of a second after the signal has ceased.
https://www.diyaudio.com/community/threads/30-hz-easy-to-build-re-entrant-horn.332546/
You were a huge help with it, thanks!
You were a huge help with it, thanks!
That's interesting. Thanks for sharing. I'm very curious why you preferred sealed subs and hope you don't mind me trying to tease this out to see if there might be something beyond the stored energy group delay thingy?
- What are the frequencies covered by the horn vs the sealed subs? Did the sealed subs reach higher into the slam frequency band then the horn?
- What do you enjoy listening to with the subs?
- Was there any impact from special effects in movies missing.
- Did the horn do visceral, organ shaking, window flapping electronica bass that box sealed subs can do
- Do you like the feel of bass directly pressurising the room? Some find it exciting. Some hate it. It can activate the brains survival threat system with an adrenaline hit. Are you more the sort who avoids adrenaline or are you a guy who likes stimulation e.g. driving fast, sports, coffee, parties....
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Horn crosses to woofers at 500hz. When I crossed over to the new subwoofer, I didn't do it perfectly. I dropped the bass under 80hz down 6db, then sent that same signal into an analog low pass at 80, because I don't have a 3 way digital xo. I love electronic and pop music, but also listen to everything. Missing with the horn sub was the tight slap of the transients. It could however shake your inards with output. I do like the sensation of the bass pressurized the room. My 800 watt amps on the 12 inch subs flicker distortion lights often, even after I added a 3rd sub transmission line recently. Very much a fast car guy 🙂.
The horn sub moved to the theater was better for some reason than in the listening room. After I added a second very large vented sub to the theater just to even things out,, there was a huge improvement in bass tightness.. even though the same vented sub was awful in the listening room. I believe that was because there was only one position where it would fit.. I think multiple subs is the ticket and positioning them in the right spots is by far the biggest factor in performance. Trying to eliminate room with directivity and eliminating room with lots of absorption in rear was not something I could pull off. Ymmv.
The horn sub moved to the theater was better for some reason than in the listening room. After I added a second very large vented sub to the theater just to even things out,, there was a huge improvement in bass tightness.. even though the same vented sub was awful in the listening room. I believe that was because there was only one position where it would fit.. I think multiple subs is the ticket and positioning them in the right spots is by far the biggest factor in performance. Trying to eliminate room with directivity and eliminating room with lots of absorption in rear was not something I could pull off. Ymmv.
Looks like Mr Klinky nailed it with the timing thing. The other factor is <20Hz room loading. Its that range which seems missing from the horn. Its those infrasonic sounds that warn of impending disasters and activate the survival system. Looks like you enjoy the adrenaline rush but it might not be so good for the brain or heart.
This is the Hornresp modelling of your horn:
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Thanks guys for the insights. I have no doubt you're correct that the poor impulse response is a factor. Is OP planning an entirely straight horn?
Seems like I would have checked the group delay when I simmed but apparently not. It's been so long I can't remember.
Sheesh! That's going back to the days when 480p was the video 'hot ticket'! I was doing part time high end HT, trade show Sony FP HT systems and one of their EEs designed them and IIRC the channels, etc., were Owens Corning, but didn't find it in a quick search plus apparently has now been obsoleted with its latest 700 series bass traps, so best I can do is suggest researching diaphragmatic, limp mass, resonators.
I've been thinking about this. When I asked GM why I had so many squiggles in my response, this is what he said:
Because there's an impedance mismatch at every [poor] termination back to the throat, modulating the driver plus the straight section of pipe adds extra set of harmonic reflections.
GM
It makes some sense that my subs performance seemed to increase in the theater, because in there, instead of having it oriented towards me, I installed a large bottom flange and stood it up on end and placed the mouth right down in the corner. The corner of the room may help smooth the exit somewhat. If the proposed horn does not have a rounded exit (the exit will be the damping material)will reflections back to throat affect performance similar to mine? Or at the mouth size in question, is it not relevant? And what percentage of the output will the wood chips/foam/insulation actually absorb? Won't there be huge reflection back to throat no matter what? As if so, how is that any different than a standard sub in room? Reverb continues in room way longer than my poor impulse response. Someone interested should model a room sized horn and the choke off part of the exit and see what happens to response. Could you not also model the damping material quite easily in hornresp? The other question is, what is the response INSIDE a horn? I am tempted to run a sweep inside mine to find out, but crawling back behind my rear projection mirror setup is a bit more than I'm willing to do. Very interesting stuff. Sorry I'm not qualified to give answers, just questions. Craig
Because there's an impedance mismatch at every [poor] termination back to the throat, modulating the driver plus the straight section of pipe adds extra set of harmonic reflections.
GM
It makes some sense that my subs performance seemed to increase in the theater, because in there, instead of having it oriented towards me, I installed a large bottom flange and stood it up on end and placed the mouth right down in the corner. The corner of the room may help smooth the exit somewhat. If the proposed horn does not have a rounded exit (the exit will be the damping material)will reflections back to throat affect performance similar to mine? Or at the mouth size in question, is it not relevant? And what percentage of the output will the wood chips/foam/insulation actually absorb? Won't there be huge reflection back to throat no matter what? As if so, how is that any different than a standard sub in room? Reverb continues in room way longer than my poor impulse response. Someone interested should model a room sized horn and the choke off part of the exit and see what happens to response. Could you not also model the damping material quite easily in hornresp? The other question is, what is the response INSIDE a horn? I am tempted to run a sweep inside mine to find out, but crawling back behind my rear projection mirror setup is a bit more than I'm willing to do. Very interesting stuff. Sorry I'm not qualified to give answers, just questions. Craig
Ah! Didn't re-read it, so maybe repeating; right, to somewhat compare, they would have to be oriented the same outdoors in that a false corner wall of similar dims is required and then only to compare near enough IB Vs in-room.
As I understand designing a sub bass horn, it ideally needs to be a truly full size hyperbolic [4pi, 1/2 WL rolled over to at least 180 deg], i.e. no pipe end correction required or at least some form of hypex depending on its cutoff, driver specs. Seal it into a room and it either needs to be long enough to include its 'throw' distance, while others have put it as 'x' loss over distance and/or at least some form of damped end correction [foam surrounds, inserts as required] like the OP plans to do.
That said, historically they're ~1/4 WL depending on room loading and use multiple drivers to truncate its throat's long/slow initial expansion and a 'fast' expanding one to truncate its terminus/mouth.
Right, regardless of mouth/terminus size, reflections back to the throat will modulate/comb filter with the driver's output at some amplitude and the larger it is, the lower in frequency the reflections, so can become a very big deal from a damping POV, though if there's a phase plug to randomize them into higher frequencies above the pass-band, then not an issue, ditto terminus/mouth damping.
Re room/mouth wall, if damping is via diaphragmatic [and presume limp mass] for LF, then no output, so will need a curtain wall? of damping in front of it to damp the higher frequencies. Anyway, best to research all this as I posted earlier.
If the room/horn is properly terminated and the horn expands properly with no parallel walls, then seems like it would sound more like a true outdoor IB or maybe a ~anechoic chamber when near its terminus/mouth.
As I understand designing a sub bass horn, it ideally needs to be a truly full size hyperbolic [4pi, 1/2 WL rolled over to at least 180 deg], i.e. no pipe end correction required or at least some form of hypex depending on its cutoff, driver specs. Seal it into a room and it either needs to be long enough to include its 'throw' distance, while others have put it as 'x' loss over distance and/or at least some form of damped end correction [foam surrounds, inserts as required] like the OP plans to do.
That said, historically they're ~1/4 WL depending on room loading and use multiple drivers to truncate its throat's long/slow initial expansion and a 'fast' expanding one to truncate its terminus/mouth.
Right, regardless of mouth/terminus size, reflections back to the throat will modulate/comb filter with the driver's output at some amplitude and the larger it is, the lower in frequency the reflections, so can become a very big deal from a damping POV, though if there's a phase plug to randomize them into higher frequencies above the pass-band, then not an issue, ditto terminus/mouth damping.
Re room/mouth wall, if damping is via diaphragmatic [and presume limp mass] for LF, then no output, so will need a curtain wall? of damping in front of it to damp the higher frequencies. Anyway, best to research all this as I posted earlier.
If the room/horn is properly terminated and the horn expands properly with no parallel walls, then seems like it would sound more like a true outdoor IB or maybe a ~anechoic chamber when near its terminus/mouth.
Regarding the room's reverberant energy vs loudspeaker impulse response times, there is a strong psychoacoustic effect to consider; we should not forget that the brain processes direct sound very differently to the later arrival of reverberant/reflected sound. This is evidenced by listening to recordings in ordinary, untreated domestic rooms (YouTube videos, etc.) where very obvious/unpleasant room artifacts are clearly audible in the recording, but of which we would not usually be aware if we were present in the room listening to the person speaking. A microphone is a dumb pressure-sensing device whereas our ear/brain combination employs some pretty smart processing! In conclusion, I would have to politely disagree that one can compare or conflate the relative durations of speaker impulse response with reverberation.
Perhaps I should fire up my old CARA room design software. CARA did not provide for modeling of horn speakers in a room, but in this case the room is the horn. Making an exponential or other curved shape room might not be possible, but conical should be. Then the back wall could be treated in various ways to see what the reflections, nodes and standing waves might be.
This is something that has been suggested to me: https://www.diyaudio.com/community/threads/simple-corner-speaker-reasonable.379883/post-6862585
that you could find interesting to use your room as part of this "Möbius" subwoofer.
that you could find interesting to use your room as part of this "Möbius" subwoofer.
So I'm hung up on the absorber. It seems as though unless I use some super low density absorber I'm never gonna get full absorption under 30-40 hz. Perhaps using giant wedges of porous absorber combined with diaphragmatic absorbers is a better approach?
Couple other queries:
At low bass frequencies, the expansion rate of the horn is just a matter of area increasing at a certain rate? Meaning I could have two parallel walls and two curved walls and as long as the expansion rate of area is appropriate for the frequency range then the actual shape of the walls doesn't matter much?
At 20-150 hz would having two parallel or straight sided but expanding walls introduce any distortion, resonances?
Couple other queries:
At low bass frequencies, the expansion rate of the horn is just a matter of area increasing at a certain rate? Meaning I could have two parallel walls and two curved walls and as long as the expansion rate of area is appropriate for the frequency range then the actual shape of the walls doesn't matter much?
At 20-150 hz would having two parallel or straight sided but expanding walls introduce any distortion, resonances?
The best achievable absorption would be the equivalent of one end of the room/horn open to the outside, like a garage door the width and height of a garage.
Diaphragmatic absorbers could occupy less space than porous absorbers alone, but material cost won't be wood chips 😉
Yes, cross section area plotted against axial length.
The curved walls can also be approximated by straight sections.
In the upper range, parallel walls may be problematic for a high aspect ratio horn expansion, as the large dimensions vs wavelength could promote "standing wave" resonance. You'll be dealing with those in any practical room functioning as a portion of a horn.
If you were to use room walls for the final expansion as in Klipcshorn or Tom Danley's "Bdeap 32" designs, resonances < 150 Hz shouldn't add any problem that won't be in the room.
Scaling up the 45" x 45" x 22.5" "Bdeap" from 32Hz to 20Hz would be relatively easy, as would it's construction.
Making one end of a room anechoic down to 20 Hz won't be so easy..
Art
Not sure what is meant by high aspect ratio expansion in this context. ?
If the distance between the parallel walls is small compared to the wavelength, such as in a standard folded horn cabinet, does that cause resonances in the actual output of the horn(disregarding room resonances)?
A cross-sectional area of 8 square feet could be square, 2.83' x 2.83', 1/1 being a low aspect ratio, or 8'x1', 8/1 being a high aspect ratio.
The wavelength of 2.83' is 399 Hz, out of your chosen 20-150Hz pass band, the wavelength of 8' is 141Hz, within the pass band.
No.
I like the idea of using wood chips because in my mind's eye it seems as though it would act as a porous absorber, act similar to a diaphragmatic absorber, as well as a diffuser. And it seems the relatively large pore spaces would allow low frequencies to penetrate deeply.