Woofsorber - thoughts on an ultra-near-field subwoofer directly behind the head

[TheLastGerman]

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?

 

[Basic Channel]

I've never felt one, but have you thought about doing something similar to this sort of thing https://basspak.com/

I am not sure that minimizing vibration will do too much, but I am maybe wrong. If it was the vibrating the neighbours hated then they'd really hate washing machines.

 

[Elgrosso]

I like exotic stuff so I’d say it’s worth a quick & dirty try but I would not expect great ob sound.
Or is it just a fun project?

We know ob needs a lot of breathing space so you get enough of the front wave before it’s cancelled by the return of the rear wave, here you’re playing with the worst case.
Few cm of hemp probably won’t do anything, but I might be wrong since the waves will see more hemp “vertically”.
But I see the 9 cm spacing as detrimental here (contrary to typical bass trap).

You could treat the whole thing as a very lossy enclosure, or aperiodic, by extending the hemp thickness to touch the wall.
Basically a box with front wood, rear plaster, and 4 very thick sides made of hemps.
This way the rear waves will have to travel 50cm+ of hemp before reaching the front ones, might work.

To maximise output the woofer could be centered in the frame/box, and horizontally aligned to your ears.
But then it’s not a frame anymore, and with all these requirements volume will get close to the requirements for a very shallow sealed enclosure.

Otherwise you could build an H-frame / coffee table sub, placed right in front of you.

 

[DavidMcRoy]

I'm definitely intrigued. It occurs to me that you'll need an amplifier with extremely low noise in the driver's pass band since you'll be sitting so close.

 

[TheLastGerman]

I've never felt one, but have you thought about doing something similar to this sort of thing https://basspak.com/

I am not sure that minimizing vibration will do too much, but I am maybe wrong. If it was the vibrating the neighbours hated then they'd really hate washing machines.

Lounging on the sofa with that thing on your back? Well ...

Thanks!

 

[TheLastGerman]

I like exotic stuff so I’d say it’s worth a quick & dirty try but I would not expect great ob sound.
Or is it just a fun project?

No, its not (only) for fun. But yes, worth a try. Primary goal is to avoid additional boxes in my living room, but having good LF.

We know ob needs a lot of breathing space so you get enough of the front wave before it’s cancelled by the return of the rear wave, here you’re playing with the worst case. Few cm of hemp probably won’t do anything, but I might be wrong since the waves will see more hemp “vertically”.
But I see the 9 cm spacing as detrimental here (contrary to typical bass trap).

Sure. The absorber was never designed for this. I installed it long ago; it only serves to attenuate the reflections from the rear wall.

You could treat the whole thing as a very lossy enclosure, or aperiodic, by extending the hemp thickness to touch the wall.
Basically a box with front wood, rear plaster, and 4 very thick sides made of hemps. This way the rear waves will have to travel 50cm+ of hemp before reaching the front ones, might work.

Good point!

To maximise output the woofer could be centered in the frame/box, and horizontally aligned to your ears.
But then it’s not a frame anymore, and with all these requirements volume will get close to the requirements for a very shallow sealed enclosure.

I also had similar thoughts. My very first idea was to integrate a shallow sealed subwoofer with this or that driver into the absorber.

Otherwise you could build an H-frame / coffee table sub, placed right in front of you.

Nope! No more boxes!

Thank you!

 

[Basic Channel]

Lounging on the sofa with that thing on your back? Well ...

Thanks!

Perhaps better than having the neighbours on your back.....you can also sit (very) strictly in the MLP, win win!

 

[TheLastGerman]

I'm definitely intrigued. It occurs to me that you'll need an amplifier with extremely low noise in the driver's pass band since you'll be sitting so close.

Oh yes, you're right about that!

 

[TheLastGerman]

Perhaps better than having the neighbours on your back.....you can also sit (very) strictly in the MLP, win win!

It may be that the thing is good for tactile perception, but with the reproduction of a low double bass, for example, it is quite probably overwhelmed.

 

[Elgrosso]

Thinking more about it, the driver being so close to the wall you will certainly get some issues, unless it's very solid.
If the room behind is yours you could also try IB, you got your big baffle right there!
That would give you the best response, but will require a bit butchering, and some more paint work when you leave

 

[Vladimir Filevski]

In principle, what do you think of my idea - worth a try or nonsense?

Definitely worth a try!

 

[TheLastGerman]

Thinking more about it, the driver being so close to the wall you will certainly get some issues, unless it's very solid.
If the room behind is yours you could also try IB, you got your big baffle right there!
That would give you the best response, but will require a bit butchering, and some more paint work when you leave

The ultimate realization: Hammer, chisel, some cement ... That would also create a nice bass in the hallway.

Joking aside, you're damn right: Earlier while jogging I had the idea of hitting the wall with the heel of my hand, so I did and: BOMM! With a beautiful, harmonious fade-out. That was it. I will go back to my original thoughts regarding a flat sealed subwoofer.

Gentlemen, thank you for your contributions!

 

[TheLastGerman]

What has become of it so far? For now, a subwoofer that I can use in other ways if necessary:

An SB Acoustics SW26DBAC76-8 in a volume of approx. 10 liters powered by a Hypex FA251. The cabinet is made of 18mm beech MPX. The size is 42 x 42 x 13.6 cm, just finished (not yet sanded) and therefore still untested. More on this soon ...

 

[TheLastGerman]

What can I say - it works. I did a test setup, so I moved my listening position and the sub to an empty wall to avoid having to dismantle the absorber. With a little EQ, the level I calculated beforehand came out pretty much exactly the same. I'm quite satisfied.

 

[kemmler3D]

This is great! I think this is a clever idea, and the fundamentals are strong - use proximity so you don't need high output in bass frequencies, to avoid bothering neighbors. Until I got to the last post, my thought was that it should work fine unless you have a null right where you're sitting.

Of course it only works for one listening position, but it beats not having bass at all...

 

[TheLastGerman]

This is great! I think this is a clever idea, and the fundamentals are strong - use proximity so you don't need high output in bass frequencies, to avoid bothering neighbors. Until I got to the last post, my thought was that it should work fine unless you have a null right where you're sitting.

Of course it only works for one listening position, but it beats not having bass at all...

With that you outline my thoughts in a few words. Now there is still some tinkering to integrate the subwoofer into the absorber as described at the beginning. The subwoofer weighs 13 kilos, so I have to attach it to the wall behind, as the absorber itself is not strong enough to carry that much weight.

 

[TheLastGerman]

Done. I have made the wall mounting as simple as possible with attention to possible transmission of vibrations.

Damping material cut to fit

What it looks like behind the construction. There are three soft rubber dampers on the rear panel of the sub. The sub is not touching the absorber's frame.

Find the subwoofer ...

I am more than satisfied with the outcome. Sitting on the couch I have punchy and precise bass tone, but two meters away (and especially in the neighboring apartments, I may assume) you can barely hear any of it. I shouldn't praise myself, but I've really struck lucky with this.

 

[kemmler3D]

Very cool. Would love to see measurements from the head-in-a-vise position. Seems like a win, and it's really not even ugly once you put the absorber back.

 

[TheLastGerman]

Very cool. Would love to see measurements from the head-in-a-vise position. Seems like a win, and it's really not even ugly once you put the absorber back.

Measurements will follow soon, I promise ...

 

[anphex]

Looks cool! Kind of wary about the possible resonance distortion from the casing and absorber itself but we'll see