I moved from box speakers to open baffle a while ago and the hardest part still seems the fact that due to cancellation the low bass is a challenge and either requires very large baffles and/or very large displacement.
As a way to accommodate large baffles they are often folded (open box, H frame, Ripole) But this creates enclosed air spaces and parallel walls that create unwanted resonances.
One supposed way to deal with this is the Hartley "boffle" enclosure, something I want to test for myself in the near future.
But last night I got another idea that seems crazy..... I need someone with enough physics knowledge to tell me why this is a dumb idea......otherwise I have to try this as well.
Wat if you fastened a strong steel mesh to the back of an open back cabinet (and around the driver) and filled the cabinet with pebbles, marbles or gravel?
This would somewhat restrict the air flow....a bit like slot loading maybe?
There would be some resistance.....a bit like a aperiodic vent?
The path length from front to back would be larger?
The weight would kill all cabinet vibrations
Would it kill air column and/or quarter wave resonances?
Would it be worth trying? Or has it been done already?
Another variation would be to add some polyfill in between the stones/marbles
As a way to accommodate large baffles they are often folded (open box, H frame, Ripole) But this creates enclosed air spaces and parallel walls that create unwanted resonances.
One supposed way to deal with this is the Hartley "boffle" enclosure, something I want to test for myself in the near future.
But last night I got another idea that seems crazy..... I need someone with enough physics knowledge to tell me why this is a dumb idea......otherwise I have to try this as well.
Wat if you fastened a strong steel mesh to the back of an open back cabinet (and around the driver) and filled the cabinet with pebbles, marbles or gravel?
This would somewhat restrict the air flow....a bit like slot loading maybe?
There would be some resistance.....a bit like a aperiodic vent?
The path length from front to back would be larger?
The weight would kill all cabinet vibrations
Would it kill air column and/or quarter wave resonances?
Would it be worth trying? Or has it been done already?
Another variation would be to add some polyfill in between the stones/marbles
Anybody? Or is everyone eating popcorn looking at Trump and Elon and abandoning diyaudio?
A large force required to move air will load the rear of the driver like a sealed box with a leak. If the box is full of pebbles the "volume" of the sealed box will be tiny and not what you want. If the box is loosely filled with pebbles (not sure how) then it will likely act something like a box with stuffing but without a rear panel. Probably wouldn't be terrible but almost certainly worse than a cabinet with a properly designed aperiodic vent (if that is what you are seeking?).
I just found a research paper that compared the attenuation by frequency of gravel, pebbles and glass beads in a large diameter tube.
https://www.ideals.illinois.edu/items/16941
At 50hz the attenuation for pebbles(best performer) is only about 5db per meter....so 2.5db for a 50cm deep cabinet.
Would that be enough to prevent standing waves? Every bounce of the wave would lose 2.5db....so I cannot imagine enough energy can build for audible resonances.
Now that I think of it resonances for a large box would be in the vicinity of 100hz and there the attenuation is up to 7db per meter.....surely enough to kill resonances.
So it seems an open box filled with pebbles could be a very interesting open baffle bass solution.
-No cavity resonances
-Lots of added weight so also no box resonances.
-added path length virtually deepens the box(enlarge the baffle)....my guess would be around 30% extra path length.
-Possible lowering of bass driver fs due to a kind of slot loading effect? Not sure about that one.
-Attenuation rises with frequency so if a wider bandwidth woofer is used it progressively becomes more monopole so it could transition to a traditional monopole box arrangement for mid and top frequencies. In this case a little polyfill in between the pebbles could further attenuate the HF. Subwoofer speaker stands?
https://www.ideals.illinois.edu/items/16941
At 50hz the attenuation for pebbles(best performer) is only about 5db per meter....so 2.5db for a 50cm deep cabinet.
Would that be enough to prevent standing waves? Every bounce of the wave would lose 2.5db....so I cannot imagine enough energy can build for audible resonances.
Now that I think of it resonances for a large box would be in the vicinity of 100hz and there the attenuation is up to 7db per meter.....surely enough to kill resonances.
So it seems an open box filled with pebbles could be a very interesting open baffle bass solution.
-No cavity resonances
-Lots of added weight so also no box resonances.
-added path length virtually deepens the box(enlarge the baffle)....my guess would be around 30% extra path length.
-Possible lowering of bass driver fs due to a kind of slot loading effect? Not sure about that one.
-Attenuation rises with frequency so if a wider bandwidth woofer is used it progressively becomes more monopole so it could transition to a traditional monopole box arrangement for mid and top frequencies. In this case a little polyfill in between the pebbles could further attenuate the HF. Subwoofer speaker stands?
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Nothing good after the first half-wave. The simulator itself doesn't seem very suitable for such a task. You can download Hornresp and run the Wavefront simulator yourself.
My main question at the moment is how much attenuation is needed to kill cavity resonances. Would a 3db attenuation per "bounce" kill any resonances?
What would open baffle and dumping rocks into a speaker be considered?
Being that normal woofers work just fine?
Most the " open baffle" experience is midrange
If I say it is not a good idea would you still pursue it anyways.
Being the easy solution gets mentioned many times. Mount a high Qts woofer to a wall
Then make it " open" to the next room. How easy is that.
Being the next room is just another big box or the room it is in also a big box.
Since dipole cancelation seems to be incredibly misunderstood these days.
Besides a very large wall to reclaim bass, maybe firgure out the size of a IEC test baffle.
The test standard for speakers, good to 100 Hz. probably a little big.
So wall or bend the baffle to a wing.
Being that pebbles and marbles dont offer much absorption.
Why not use just normal absorption material? the endless materials mentioned for 100+ years now.
Or just use " wings" to reduce the dipole cancellation and not have a huge baffle.
Absorption can be attached to that too.
Eventually you want the blur from the room anyways, more suitable with midrange as mentioned.
Being that normal woofers work just fine?
Most the " open baffle" experience is midrange
If I say it is not a good idea would you still pursue it anyways.
Being the easy solution gets mentioned many times. Mount a high Qts woofer to a wall
Then make it " open" to the next room. How easy is that.
Being the next room is just another big box or the room it is in also a big box.
Since dipole cancelation seems to be incredibly misunderstood these days.
Besides a very large wall to reclaim bass, maybe firgure out the size of a IEC test baffle.
The test standard for speakers, good to 100 Hz. probably a little big.
So wall or bend the baffle to a wing.
Being that pebbles and marbles dont offer much absorption.
Why not use just normal absorption material? the endless materials mentioned for 100+ years now.
Or just use " wings" to reduce the dipole cancellation and not have a huge baffle.
Absorption can be attached to that too.
Eventually you want the blur from the room anyways, more suitable with midrange as mentioned.
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I would argue the opposite. Clayton Shaw said in an interview the most important advantage for open baffle is in the bass, below the Schroeder frequency and I tend to agree. I am sure if you were to measure your box speaker response at several different locations in your room you would have to conclude it's a total mess, unless you have multiple subwoofers meticulously placed around your listening room.
Open baffle bass surely is a challenge but if done well it solves many bass problems.
But yes, if you want easy and/or cheap solutions stick to boxes.
I would choose open baffle bass with a monopole mid/high over a open baffle with box subwoofer.
Been using subs in cars , clubs and homes for 30 years
Never a problem
Just the greatest times of my life with any guests that attended.
Including the car club or home.
First open baffle claims magical no box sound, then magical " soundstage"
now it works for non directional frequencies ( which get cancelled anyways)
It is the mids that create the sound.
Been around open baffle speakers for 30 plus years.
And it was before the no box sound was the romantic push
I can calculate the baffle needed for 100 Hz...its big
Wont be any rocks in it.
You do know that Western Electric figured this out for their theatre systems
over 100 years ago? maybe look at a Western Electric baffle and note the size
for calculated 50 Hz. Being they were using high Qts underhung speakers
another important aspect often left out by modern approach.
But used exclusively by people that knew what it takes to make a system work.
Which carried out well into the 30's 40's 50's 60's 70's etc etc
Using open baffles
Never a problem
Just the greatest times of my life with any guests that attended.
Including the car club or home.
First open baffle claims magical no box sound, then magical " soundstage"
now it works for non directional frequencies ( which get cancelled anyways)
It is the mids that create the sound.
Been around open baffle speakers for 30 plus years.
And it was before the no box sound was the romantic push
I can calculate the baffle needed for 100 Hz...its big
Wont be any rocks in it.
You do know that Western Electric figured this out for their theatre systems
over 100 years ago? maybe look at a Western Electric baffle and note the size
for calculated 50 Hz. Being they were using high Qts underhung speakers
another important aspect often left out by modern approach.
But used exclusively by people that knew what it takes to make a system work.
Which carried out well into the 30's 40's 50's 60's 70's etc etc
Using open baffles
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2.5dB attenuation for a 50cm deep cabinet filled with pebbles would be hard to detect in a room.
No, the slots between pebbles are not like slot loading, and if they were, would cause resonances.
Not much, an aperiodic vent attenuates the output of the Helmholtz resonator, making the cabinet in between sealed and ported.
Slightly, which would distort the dipole figure of 8 pattern.
No.
Considering it would have virtually no effect on the low bass you wish to regain, can't see the worth of it.
That would have hardly any effect at low frequencies, and would simply increase the rear attenuation, which can be much more effectively be done with a box.
I have a naked 21 pro woofer that goes below 50hz without EQ and 30hz with eq....in a medium sized leaky room. I haven't tried it on a baffle yet but I think a not ridiculously sized baffle will make it go below 40hz without EQ