For days I've been racking my brain over all the possible (and impossible) options for a subwoofer for my particular listening situation. The room is unfavorably dimensioned and the neighbors are sensitive. So I think about how to minimize room excitation.
My latest brain fart looks something like this: An DSP-driven (so with appropiate equalisation and delay) open-baffle woofer (for example https://www.sbaudience.com/index.php/products/open-baffle-drivers/bianco-12ob150/) about 20 cm behind my head, integrated into a large absorber attached to the rear wall with 9 cm spacing.
The absorber consists of a 6.5 cm thick wooden frame covered with canvas on both sides. Behind the canvas are 5 cm thick hemp fiber insulation panels. My idea is to integrate the woofer into the absorber behind the front canvas so that it is as solid and vibration-free as possible (I haven't thought about the details yet).
I practically never listen to music louder than about 80 dB, so the woofer shouldn't experience much excursion.
In principle, what do you think of my idea - worth a try or nonsense?
My latest brain fart looks something like this: An DSP-driven (so with appropiate equalisation and delay) open-baffle woofer (for example https://www.sbaudience.com/index.php/products/open-baffle-drivers/bianco-12ob150/) about 20 cm behind my head, integrated into a large absorber attached to the rear wall with 9 cm spacing.
The absorber consists of a 6.5 cm thick wooden frame covered with canvas on both sides. Behind the canvas are 5 cm thick hemp fiber insulation panels. My idea is to integrate the woofer into the absorber behind the front canvas so that it is as solid and vibration-free as possible (I haven't thought about the details yet).
I practically never listen to music louder than about 80 dB, so the woofer shouldn't experience much excursion.
In principle, what do you think of my idea - worth a try or nonsense?
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Sounds good to me, maybe with some tweaks. The hemp fibers will not really absorb low frequencies but that does not matter. Your idea essentially is a dipole souce, with a dipole spacing of roughly 20 cm. At much larger distances, a dipole is an inefficient radiator. The front and rear contributions of the woofer have equal levels and they mostly cancel. There is no full cancellation, because of the difference in path lengths and therefore phase.
At much smaller distances however, the path length differences are relatively large. That mean that the front contribution is louder than the rear contribution - they do not cancel! More bass for you - or less for the neighbours.
Edit: I see I have written about this subject before. Check this post.
The vibrations transmitted into the wall have a good chance to bother your neighbours. You could either decouple the woofer from the wall, by suspending the wooden frame in springs, or you could actively counter the vibrations with a bass shaker, as done in the Sunfire Subrosa.
At much smaller distances however, the path length differences are relatively large. That mean that the front contribution is louder than the rear contribution - they do not cancel! More bass for you - or less for the neighbours.
Edit: I see I have written about this subject before. Check this post.
The vibrations transmitted into the wall have a good chance to bother your neighbours. You could either decouple the woofer from the wall, by suspending the wooden frame in springs, or you could actively counter the vibrations with a bass shaker, as done in the Sunfire Subrosa.
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I agree with TBTL's comment on the hemp not really doing much - passive sound reduction for lower frequencies/longer wavelengths requires significantly large structures if you're trying to absorb the sound.
The "best" solution, if you really want something loud for yourself but not for the neighbours, would probably involve 3 or 5 woofers arranged in a line (if 3) or in a plus shape if 5. The central firing woofer would be in phase with the others out of phase and attenuated. You'd get a thin/narrow lobe beyond which the sound would quickly die down. But woofer costs might become an issue.
A partial solution to this, would be to fold the back output of the single driver towards the front and bring it in from 2 opposite sides (like the 3 driver solution). You wouldn't need more than 1 driver, however there may be resonance issues, and you may need to be careful with the frequencies being fed to avoid it turning into a horn of some sort.
Btw I'd suggest looking into the ripole (also mentioned in the thread linked above), you can modify the side at which it is open to suit your cancellation needs. I'd also suggest playing around with simulations to make sure you're getting what you want, and how strong you want. Stronger cancellation = potentially quieter sounds/quicker drop off, and humans needs a lot of sound pressure for bass to sound even medium-loud (Fletcher-Munson graphs).
The "best" solution, if you really want something loud for yourself but not for the neighbours, would probably involve 3 or 5 woofers arranged in a line (if 3) or in a plus shape if 5. The central firing woofer would be in phase with the others out of phase and attenuated. You'd get a thin/narrow lobe beyond which the sound would quickly die down. But woofer costs might become an issue.
A partial solution to this, would be to fold the back output of the single driver towards the front and bring it in from 2 opposite sides (like the 3 driver solution). You wouldn't need more than 1 driver, however there may be resonance issues, and you may need to be careful with the frequencies being fed to avoid it turning into a horn of some sort.
Btw I'd suggest looking into the ripole (also mentioned in the thread linked above), you can modify the side at which it is open to suit your cancellation needs. I'd also suggest playing around with simulations to make sure you're getting what you want, and how strong you want. Stronger cancellation = potentially quieter sounds/quicker drop off, and humans needs a lot of sound pressure for bass to sound even medium-loud (Fletcher-Munson graphs).
Just a cheap thought here?
And off the top of my head
A thick dense panel mounted to the back wall with green glue just behind the big woofer and use the fibre behind the driver.
My second thought is that as this woofer is so close to you a driver such as the SBA might be overkill and a couple/trio of cheap old school woofers or a quad slightly angled towards the ears would work better, you might only need 10 to 20 watts power each
Maybe something like the Peerless 830667 while they are still available
And off the top of my head
A thick dense panel mounted to the back wall with green glue just behind the big woofer and use the fibre behind the driver.
My second thought is that as this woofer is so close to you a driver such as the SBA might be overkill and a couple/trio of cheap old school woofers or a quad slightly angled towards the ears would work better, you might only need 10 to 20 watts power each
Maybe something like the Peerless 830667 while they are still available
Sure. The absorber was never designed for this. I installed it long ago; it only serves to attenuate the reflections from the rear wall.
Roger that.
Interesting stuff - food for thought. But my ideal situation is to manage without any additional boxes in my living room - that is the core of my considerations.
Well - I have made a calculation based on my average listening level:
In order to achieve 75 dB at a listening position 2.5 m away, the main loudspeakers have to produce about 83 dB at a distance of 1 m.
To generate 75 dB at a listening position 0.2 m away, the woofer in the absorber must generate around 61 dB at a distance of 1 m.
The cone movements and thus the mechanical excitation of the absorber construction attached to the rear wall with only 3 narrow steel brackets and the wall behind it should therefore be very low. Moreover, the rear wall is located inside my apartment and does not border on the neighbor's apartment.
The Sunfire Subrosa has an interesting concept, but it would be a bit over-engineered in my case, especially as I can imagine there would be a lot of trial and error involved to achieve something like that.
Thank you for your comments!
Also very interesting considerations, but as I wrote before: I want to get by without additional boxes in my listening room. As soon as I hit the lottery jackpot and am freed from the lowlands of earning money, I'll come back to it when it comes to furnishing my opulently equipped room, which then was built especially for the purpose of listening to music. On the other hand - do I still have neighbors to consider in this case?
I have already experimented with some solidly built ripoles. I have already experimented with ripoles, which have been lying dormant in the attic for a long time now, but these are also additional boxes.
Thanks to you too!
If my ideas were to become reality, I would first try out whether the back wall really needs treatment. I will certainly try out fiber behind the driver. Several drivers require more sawing and milling, which I don't have the time or inclination to do at the moment.
I can get the SB Bianco here for about € 90.00, the Peerless for about € 70.00. The few bucks won't make the difference and I certainly won't go wrong with the SB Bianco.
Thank you!
Funny stuff ... If I wanted to acoustically reproduce the impact of a 10-megaton hydrogen bomb in my town, then this is certainly a good technical implementation that should also make a lasting impression on my neighbors in the apartment below mine.
Thanks!
Earlier while jogging I had the idea of hitting the rear wall with the heel of my hand, so I did and: BOMM! With a beautiful, harmonious fade-out. That was it. Now I am considering a solution with a flat, closed subwoofer with either this or that driver.
Gentlemen, thank you for your contributions! 👍🏻
Gentlemen, thank you for your contributions! 👍🏻
I knew about bass shakers but that's new to me! Rather than cinema it looks great fun for video games!
Waves being 'large' from 4 to 17 meters ( 1 cycle) and nearfield? Pfff...
Neighbors and walls? The latter are the only ones to guarantee 'soundproofness', and are part of sound diffusion in a room, at least they are boundaries.
And boundaries reflect those 4-17m waves ( say 20-100 Hz) that eventually would reach you
Neighbors and walls? The latter are the only ones to guarantee 'soundproofness', and are part of sound diffusion in a room, at least they are boundaries.
And boundaries reflect those 4-17m waves ( say 20-100 Hz) that eventually would reach you