No, the horn's BW is much too large, though as BW shifts up in frequency it becomes increasingly more important.
A horn is designed based on its BW, so the throat area = its HF cutoff and how large the driver is determines its CR, so choose the right driver for the app.
FWIW, the sim I did has a ~1:134 CR so a very good 'fit' for dual 15"/120 Hz regardless of flare factor/frequency. IOW, the CR is limited by the driver's design/construction with high power quality drivers having a ~3:1 max in a compression horn, but me n' others have loaded cheap drivers in up to 20:1 CR inverse tapered parabolic horns [TQWT], which your 'conical' will be if there's any straight sided walls plus will need to be tuned to 10 Hz, a full octave below 20 Hz for a 20 Hz.
Conical horns and bass don't seem to be such a good match unless you go for the 15m Dan solution:
As you will see later, a certain mini-
mum mouth area is required to mini-
mize reflections at the open end. This
area is larger for horns intended for low
frequency use (it depends on the wave-
length), which means that a conical horn
would need to be very long to provide
satisfying performance at low frequencies.
As such, the conical expansion is
not very useful in bass horns. Indeed,
the conical horn is not very useful at all
in applications requiring good loading
performance, but it has certain virtues in
directivity control.
https://www.grc.com/acoustics/an-introduction-to-horn-theory.pdf
In my mind it will act as an infinite horn if it were to have near perfect absorption, the absorber would serve the same purpose as the air mass inside the infinite horn, by dissipating(transforming) the energy.
More questions the better, more opportunity to seek answers and gain understanding. That is one important part of this whole endeavor for me. And if it works the way I think it will it's going to be an incredible experience.
I will leave few stones unturned before making this investment. Good idea, I'll ask on that thread.
I read that paper earlier today. I even tried a very long conical horn in hornresp and the response still suffered in the <30 range. Don't quite understand how that could be, maybe I'm not using the program properly. And the efficiency really suffers as well. The conical gets to just under 105 db, and the exponential gets up to 115-116 db.
What would be the difference between a horn radiating into a small room, where all the energy would end up dissipating anyway(albeit more slowly), transforming into heat, and a horn radiating into a "room" filled with absorber which just happens to be part of the horn? This is my big burning question.
You've got some great ideas. Using the high efficiency of the horn is so attractive. "Eliminating the room" definitely would get rid of lots of problems. Back on earth the only way to eliminate the room is to listen outdoors or use headphones.
Your current design means you will be building a room with a bass design that carries the risk of eliminating the basic horn action but not the room. That's the opposite of your wish. Your idea is very attractive and it may be hard to accept the issues.
If you can make a perfect acoustic absorber that is as transparent as air your concept will work. You are also going to be a multimillionaire. Dont go banking on it.
Id hate to see you do hard work and end up with a massive waste of time.
Let me dream with you. You want horn bass, high efficiency and a room with minimal issues that you can build with your good hands and adobe.
How about:
1. Exponential horns made from adobe
2. Adobe Horns will need special strengthening to prevent them crumbling with the pressure waves - maybe a very high cement adobe mix with lots of reinforcing wire?
3. Adobecrete horns can be rounded internally for less sharp corner boundary effects
4. Horns can be a stereo pair left and right and meet in the centre for lowest bass extension
5. Horns can join the side walls for 1/4 space efficiency
6. Side walls can splay out to visually integrate with the horns lateral walls and respect your idea of the room-horn continuity while preventing strong bass nodes in the room
7. With an exponential horn with a mouth you can now use hornresp and save years
Kind of like
Heres a link to a different French bass horn out of the room build with measurements to show it can work
http://vincent.brient.free.fr/bass_horn.htm Your design could be even better.
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A "disturbance to the wavefront" would result in a frequency response deviation, a well executed folded horn's response will be very similar to Hornresp simulations. With DSP, the frequency response can be tailored to your desired response.
With a 4th order BW filter at 20Hz, 75 volts input, about 940 watts into the average impedance, the single B&C18SW115-4 driver would just reach Xvar/Xmax rating, reaching 135dB at 20 Hz, capable of peaks above 140dB.
That much low frequency SPL will make your eyes flop around in their sockets, modulate your voice and breathing, and can cause things you never have thought would move to dance around. Window panes may resonate to the point of breaking.
Your hearing will distort to a greater extent than the 18SW115 before reaching it's limits.
Sounds like fun, but may be more than you will want 🤔
Having built many rooms, and a lot more horn systems, and hearing many others, my observation would tend towards the opposite conclusion.
As the builder of the huge horn system above succinctly said: "When done strategically and with the forethought of hindsight, a far simpler setup of far lower maintenance and for relative pennies on the dollar can be superior."
That said, hope you have fun with the project!
Art
Dan the builder made that quote possible, but to be fair its written by the 6moons reviewer, who is not known for being succinct.
Dan the builder has been far more eloquent on this topic without writing a word.
suprised no one has linked Dick Burwen's system yet http://www.burwenaudio.com/Sound_System.html . Horns with a walk in closet!
Heres a hornresp attempt at modelling two side by side corner loaded horns. Each 4m long (Vol=3.3m3) bass hyperbolic-exponentential horns. Each horn has a single 18" woofer
Th efficiency of these horns is ridiculous. In this sim amp power was limited to 1W + 1W (yes thats one watt per driver) with 0.16mm excursion and impedance over 11ohms in series for a tube amp happy load.
Obviously 115dB (from 1+1W) is only sustainable by our ears for millisecond peaks before concerns of hearing loss arise.
Th efficiency of these horns is ridiculous. In this sim amp power was limited to 1W + 1W (yes thats one watt per driver) with 0.16mm excursion and impedance over 11ohms in series for a tube amp happy load.
Obviously 115dB (from 1+1W) is only sustainable by our ears for millisecond peaks before concerns of hearing loss arise.
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Take about 10% of the money it would take to render this "dream system" here in the real world and use it to buy tickets and spend some serious time listening to real, live music...jazz and classical being my favorites. The lowest octave plays a quite small role in actual music in actual venues and its absence or inadequacy has not much to do with the shortfall of music reproduction compared to actual live performances. Now if you just want to shake your belly and impress your buddies that's another matter altogether - that Cyprus system pictured ^^^ is a classic prepubescent big d**k dream run amok.
I don't have a belly, don't have much of an ego, and already have a big ****. What that leaves is passion. I know that it may seem strange, but I enjoy almost every aspect of bringing a project to life. Has little to nothing to do with other people. Audio is one of those things that keeps me up til 4 in the morning staring off into space, because it is fascinating.
In addition, I watch a lot of movies, and the lowest octave contributes a lot to feeling like you are in a film, and this horn would cover more than the bottom octave. This whole project is going to cost less than what some people pay for a single midrange horn. If it doesn't work, no big loss.
Kolbrek responded to my post on hornresp thread. From his response it sounds like it should work. He told me how to model it in hornresp. Will have to do that later, have to go work🙁
I need to do more research on absorbers, I used to have an awesome absorber calculator that could model various absorbers in various configurations but I can't find it.
Dusty,
As Kolbrek pointed out, if your absorber is perfect, the horn will work as it would into free space, outdoors.
Achieving 115-120 dB clean output with an F3 of 20Hz does not require huge horns.
By taking advantage of room gain, the level you stated you are looking for could be achieved with a fraction of the investment required for the horn/room/absorber project concept.
@dustman96 I know a lot of people are skeptical of your project, but I certainly hope you build it. I have dreamed of doing the same for over 30 years, ever since Jean Hiraga chatted with me about the idea of finding an abandoned railway tunnel in which to build such a system. That image has stuck in my head.
In my lava cave I had the room to build 32' long horns, as the cave was 70' long. Alas I lacked the time and the means to do so, but it could have been glorious. Although I've never had the chance to hear real front loaded horns that played down into 20s-30s, I have heard them down to about 120Hz and it was astonishing. The sense of space was like no other system. Who knew all that info was on the recording?
In my lava cave I had the room to build 32' long horns, as the cave was 70' long. Alas I lacked the time and the means to do so, but it could have been glorious. Although I've never had the chance to hear real front loaded horns that played down into 20s-30s, I have heard them down to about 120Hz and it was astonishing. The sense of space was like no other system. Who knew all that info was on the recording?
Rear wall high absorption looks pivotal to your horny room vision. Bass seems particularly problematic to absorb cleanly with its long wavelengths and penetrating powers.
This calculator http://www.acousticmodelling.com/ allows you to determine the frequency range and try heroic mixed absorption methods.
Good luck. With careful design you could pull this off!
Heres some quick modelling of excellent but heroic 78" thick absorption. Wood chips aint going to do it. 400Pa.s/m2 is going to be something very light and fluffy. Got anything like that which is a local waste product? You will need truck load of it. Especially with an exponential horn flare for the back wall so you get bass extension. Maybe there are better choices?
Sure, there are disturbances, but at the wavelengths you're working with, it won't make any difference at all at the listening position. Don't forget the impact of baffle diffraction on a subwoofer enclosure (which is to say, basically zero - and the edges are perfect 90s).
As for cost, I don't know how you build a room to be a bass horn, with at least 4 non-orthogonal walls, and expect that to cost less than 2 amps and 8-16 reasonably-priced woofers.
The response will no doubt be better. Theoretically, your bass response will be perfect with a DBA. And at higher frequencies, the sound is still bouncing around inside room. On the other hand, if you damp all reflections, you may as well just be listening outdoors.
https://en.wikipedia.org/wiki/Double_bass_array