Hi,
A thought came to me.
The reason we want to have open baffles is the mids that are reflected off the back wall enriches the sound. However for bass the reflected bass will cancel out the bass from the front. The purpose of using OB for bass is that it does not have cabinet resonance and no back reflection to colour the sound.
One way to increase bass output is the use of slot loaded OB bass. To create an imbalance between the front and the back.
My thoughts are, what if we put a bass trap like this wedge bass trap directly behind the woofer, placed directly behind the magnet.
Super Wedge Acoustic Wall Tile 5" x 12" x 12" (UL 94) Each 300-895
This would absorb a significant amount of bass radiating from the back and create the imbalance with the front. Reducing the canceling power of the bass from the back.
This would increase the bass output from the front.
I would probably try it out one of these days.
Does somebody have any thoughts on this?
Oon
A thought came to me.
The reason we want to have open baffles is the mids that are reflected off the back wall enriches the sound. However for bass the reflected bass will cancel out the bass from the front. The purpose of using OB for bass is that it does not have cabinet resonance and no back reflection to colour the sound.
One way to increase bass output is the use of slot loaded OB bass. To create an imbalance between the front and the back.
My thoughts are, what if we put a bass trap like this wedge bass trap directly behind the woofer, placed directly behind the magnet.
Super Wedge Acoustic Wall Tile 5" x 12" x 12" (UL 94) Each 300-895
This would absorb a significant amount of bass radiating from the back and create the imbalance with the front. Reducing the canceling power of the bass from the back.
This would increase the bass output from the front.
I would probably try it out one of these days.
Does somebody have any thoughts on this?
Oon
No, its not the reflected sound that cancel out the bass, its the rear wave that diffracts around the baffle.
I think the main purpose of using dipole bass in a small room is due to the loudspeaker-room interaction.
It's both, diffracted and reflected sound, forming a second order system. Of course it depends on the distance to the front wall.
- Elias
Real bass traps are big. Really big. A stack of home insulation rolls floor to ceiling is a good example.
I find my well made sealed and stuffed boxes do just fine for the subs. The only way to really eliminate the backwave is the true IB design. If I had a place, it is a most attractive idea. Basically you are using another room as the box. The "box" is large relative to the drivers resonance. If that room is so large as not to cause reflection problems, so the better.
I find my well made sealed and stuffed boxes do just fine for the subs. The only way to really eliminate the backwave is the true IB design. If I had a place, it is a most attractive idea. Basically you are using another room as the box. The "box" is large relative to the drivers resonance. If that room is so large as not to cause reflection problems, so the better.
Hi Melon Head,
Just curious what did you use to absorb the backwave? The idea behind a wedge absorption system is the sound that is reflected of the triangle reflects into the valley of the wedges and it is this multiple reflection that actually absorbs the sound. For it to work on bass it has to be very tall structures because bass frequencies have long wavelengths. Hence the one i have chosen is 5 inch high. Normal sound absorption wedge foam is only 2 inch. Did some reading, trying to control the bass nodes of my room..
And as for the bass trapping. I intended for it to be placed immediately behind the magnet. That would allow it to absorb at the source rather than after the bass have left the speakers.
I suppose if one were to build it in a u frame then the sound will be somewhat halfway between a sealed box and OB. Which could sound pretty good, getting the best of both worlds..
Oon
Just curious what did you use to absorb the backwave? The idea behind a wedge absorption system is the sound that is reflected of the triangle reflects into the valley of the wedges and it is this multiple reflection that actually absorbs the sound. For it to work on bass it has to be very tall structures because bass frequencies have long wavelengths. Hence the one i have chosen is 5 inch high. Normal sound absorption wedge foam is only 2 inch. Did some reading, trying to control the bass nodes of my room..
And as for the bass trapping. I intended for it to be placed immediately behind the magnet. That would allow it to absorb at the source rather than after the bass have left the speakers.
I suppose if one were to build it in a u frame then the sound will be somewhat halfway between a sealed box and OB. Which could sound pretty good, getting the best of both worlds..
Oon
The reason to go with dipole bass is to reduce the excitation of many room modes. However, when a dipole woofer is placed close to a wall the reflected wave cancel the low bass response. This is in contrast to a monopole woofer which has the bass reinforced by placing the woofer close to a wall. A correctly damped U-frame or cardioid is not affected by reflections from the wall behind the woofer.
Damping the rear wave of a dipole to produce asymmetry between front and rear will make the woofer behave more like a monopole. While it will tend to increase bass response it will also increase room mode excitation making the response potentially more irregular.
Also, slot loading doesn't produce much in the way of asymmetry at low frequency, as I have shown through measurements several times.
Here is a link to a discussion of woofer ype and rear wall reflections.
Damping the rear wave of a dipole to produce asymmetry between front and rear will make the woofer behave more like a monopole. While it will tend to increase bass response it will also increase room mode excitation making the response potentially more irregular.
Also, slot loading doesn't produce much in the way of asymmetry at low frequency, as I have shown through measurements several times.
Here is a link to a discussion of woofer ype and rear wall reflections.
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Hi John K,
That was quite informative. So putting on something at the back will make it a bit more like a monopole speaker. How would one execute such a procedure. I was looking at the 5" wedge acoustic foam as something that would absorb bass well. Would that be a good technique? Or do you have a better idea.
Say a u-frame with the 5" wedge acoustic foam?
Oon
yes they do, but im not stating any level of attenuation either. The method i used, perhaps not entirely correctly, is what ive seen referred to in architectural noise reduction, and attenuation is also dependant on the absorbent Sabine rating. Also those traps are more than 6 inches deep at their greatest point, so they would perform slightly better.
Perhaps i shouldve said that absorption begins to become 'useful' at frequencies where the thickness is greater than the quarter wave. Once we get to whole wavelengths it is much more effective. Of course the value in traps like those could lie in the diffusion of the serrated shape. They may well work to high bass region, im not saying i know it all. However, i wouldve thought that attenuation BELOW 125hz wouldve been the goal.
BUT, i have used similar traps and of much larger size, with little improvement.
Perhaps i shouldve said that absorption begins to become 'useful' at frequencies where the thickness is greater than the quarter wave. Once we get to whole wavelengths it is much more effective. Of course the value in traps like those could lie in the diffusion of the serrated shape. They may well work to high bass region, im not saying i know it all. However, i wouldve thought that attenuation BELOW 125hz wouldve been the goal.
BUT, i have used similar traps and of much larger size, with little improvement.
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I am hopping by putting it at the source before the sound spreads it would be significantly more effective. I would agree that if you wanted to reduce nodes in the room you will need to fill up the wall. But in my case, you can view it as lining up the insides of a sealed speaker cabinet with bass trap. That is how i intend to use it.
Has anybody ever tried using 5 inch wedge as cabinet stuffing.
Melon head, u have seem to have tried everything under the sun. Tried this before in your audio nirvana 15inch cabinet before?
Oon
Has anybody ever tried using 5 inch wedge as cabinet stuffing.
Melon head, u have seem to have tried everything under the sun. Tried this before in your audio nirvana 15inch cabinet before?
Oon
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