Hi,
@#12 While I can second most of Roger's statements, I disagree with him regarding the use of a transmissionline as best suitable bass. In theory a TL would completely dampen the rear part acoustic output of the driver, resulting in a very good dynamc behaviour. In practise though we see that it rather follows the behaviour of an open pipe, or an BR box with an oversized thunnel.
Which simply means that the output port exhibits a high Q resonance behaviour. Secondly the TL bass performs like a monopole, while the ESL panel shows a dipolar response -and if tall enough even a cylindrical dipolar response.
If the transition between both responses were smooth it'd be ok, but thats just not the case with ESLs where steep acoustical flanks are almost the rule.
To achieve a truely smooth transition the polar responses of ESL and bass should be similar at least over +-1 oct around the xover point.
A dipolar bass utilizing electromagnetic drivers profits from their inherent damping, hence low Q behaviour and higher SPL/membrane area.
A dipole bass fits the ESLs sonic character the best.
Further down the frequency scale the bass may transit similarly from dipolar (lobed character) to monopolar by using a dedicated subwoofer.
The monopolar subwoofer not only works far more efficient, but may also profit from room gain, and it adds the slam, the dipole bass misses on.
@#14ff While the Qs of filters add in the electronic domain its my impression that this doesn't apply equally to mechanical Qs. Even equalized to same amplitude response a closed box will sound different to a BR box, different to a dipole. It also appears as if the mechanical Q dominates.
If the bass sounds boomy due to high Q behaviour, it still sounds boomy after electronic equing. On the contrary a very precise performing bass won't become boomy when equalized 'up', but just louder.
jauu
Calvin
@#12 While I can second most of Roger's statements, I disagree with him regarding the use of a transmissionline as best suitable bass. In theory a TL would completely dampen the rear part acoustic output of the driver, resulting in a very good dynamc behaviour. In practise though we see that it rather follows the behaviour of an open pipe, or an BR box with an oversized thunnel.
Which simply means that the output port exhibits a high Q resonance behaviour. Secondly the TL bass performs like a monopole, while the ESL panel shows a dipolar response -and if tall enough even a cylindrical dipolar response.
If the transition between both responses were smooth it'd be ok, but thats just not the case with ESLs where steep acoustical flanks are almost the rule.
To achieve a truely smooth transition the polar responses of ESL and bass should be similar at least over +-1 oct around the xover point.
A dipolar bass utilizing electromagnetic drivers profits from their inherent damping, hence low Q behaviour and higher SPL/membrane area.
A dipole bass fits the ESLs sonic character the best.
Further down the frequency scale the bass may transit similarly from dipolar (lobed character) to monopolar by using a dedicated subwoofer.
The monopolar subwoofer not only works far more efficient, but may also profit from room gain, and it adds the slam, the dipole bass misses on.
@#14ff While the Qs of filters add in the electronic domain its my impression that this doesn't apply equally to mechanical Qs. Even equalized to same amplitude response a closed box will sound different to a BR box, different to a dipole. It also appears as if the mechanical Q dominates.
If the bass sounds boomy due to high Q behaviour, it still sounds boomy after electronic equing. On the contrary a very precise performing bass won't become boomy when equalized 'up', but just louder.
jauu
Calvin
Hi all,
thanks for your replies, this really helps! Interesting to read about Roger his ideas, but the post by Bolserst about compression due to transformer core saturation is interesting as well. I've read all your replies and they contain a lot of information that keeps me going, hopefully progressing as well.
I'm busy with obligations at the moment, but as soon as I have time I will post more replies and findings. For instance, I own 3 different models of transformers right now, and I started to make measurements on when these start to saturate. I have a plan to make a simple led-circuit which start to glow as soon as the transformer core saturates.
So thanks for all your input and I have to report back soon new findings...
thanks for your replies, this really helps! Interesting to read about Roger his ideas, but the post by Bolserst about compression due to transformer core saturation is interesting as well. I've read all your replies and they contain a lot of information that keeps me going, hopefully progressing as well.
I'm busy with obligations at the moment, but as soon as I have time I will post more replies and findings. For instance, I own 3 different models of transformers right now, and I started to make measurements on when these start to saturate. I have a plan to make a simple led-circuit which start to glow as soon as the transformer core saturates.
So thanks for all your input and I have to report back soon new findings...
Just a thought. Roger's analogy of a bell under water brings to mind a possible(or maybe not) parallel solution using air against the diaphragm in the form of a steady stream through a tube of appropriate diameter and pressure, designed for quietest and best over all performance. Just a tube in close proximity blowing on the dia. in the center. Could this approach work?
Hi Sorry to be late on this discussion.
In addition to the list posted by bolserst, there is another dipole effect which can have a very strong negative effect on the bass of ESLs.
If you have an ESL handy, try this.... Place the ESL panel as close as you can to the wall and parallel to the wall. You'll find the bass will almost disappear. The closer the panel is to the wall, the worse the effect. This happens because of the acoustic reflection of the sound off the wall - imagine the wall as a mirror. As the membrane of the real ESL moves away from you, the membrane of the reflected ESL will be moving towards you. The sound pressure from the ESL and its image therefore have opposite sign and cancel.
The effect is complicated - if the wall is a perfect reflector, the effect is similar to a comb filter (notches at regular frequency intervals - with the interval determined by the spacing of the ESL from the wall.
When the gap between the ESL and its reflection is half a wavelength, the cancelation is close to perfect. So if the ESL is 0.5 m from a wall, the distance to the reflection is 1m, so frequencies of 170 Hz (340 m/s divided by 2 x 1m) cancel, and all frequencies below this frequency are severely attenuated.
The cancellation effects are not perfect because the distance between listener and the two sources are different, and any angle between the ESL and the wall helps. At 45 degrees to the wall, one ESL is located in the plane of the other where no sound is produced so there is no cancelation at all.
If you put the ESL at right angles to the wall, the bass will improve - a lot.
It is also possible for the sound from the two ESLs to add constructively - and this happens when the distance between the ESL and its reflection is equal to one wavelength.
Some might recall Walkers famous experiment, he put two of his Quad 57s face to face, and there is a very strong cancellation effect. Same effect.
To get the best bass response from the ESL, it should be well separated from the wall and it helps if it is not parallel with the wall.
Hope this helps
In addition to the list posted by bolserst, there is another dipole effect which can have a very strong negative effect on the bass of ESLs.
If you have an ESL handy, try this.... Place the ESL panel as close as you can to the wall and parallel to the wall. You'll find the bass will almost disappear. The closer the panel is to the wall, the worse the effect. This happens because of the acoustic reflection of the sound off the wall - imagine the wall as a mirror. As the membrane of the real ESL moves away from you, the membrane of the reflected ESL will be moving towards you. The sound pressure from the ESL and its image therefore have opposite sign and cancel.
The effect is complicated - if the wall is a perfect reflector, the effect is similar to a comb filter (notches at regular frequency intervals - with the interval determined by the spacing of the ESL from the wall.
When the gap between the ESL and its reflection is half a wavelength, the cancelation is close to perfect. So if the ESL is 0.5 m from a wall, the distance to the reflection is 1m, so frequencies of 170 Hz (340 m/s divided by 2 x 1m) cancel, and all frequencies below this frequency are severely attenuated.
The cancellation effects are not perfect because the distance between listener and the two sources are different, and any angle between the ESL and the wall helps. At 45 degrees to the wall, one ESL is located in the plane of the other where no sound is produced so there is no cancelation at all.
If you put the ESL at right angles to the wall, the bass will improve - a lot.
It is also possible for the sound from the two ESLs to add constructively - and this happens when the distance between the ESL and its reflection is equal to one wavelength.
Some might recall Walkers famous experiment, he put two of his Quad 57s face to face, and there is a very strong cancellation effect. Same effect.
To get the best bass response from the ESL, it should be well separated from the wall and it helps if it is not parallel with the wall.
Hope this helps
Okay, strike that thought. Here's another.. what about stretching/sandwiching the dia. in a perimeter of for example 00-10 hardness rubber? How well could that serve as a dampening solution?
While a soft adhesive/mount might improve reflections back into the diaphragm caused by rigid edge termination, this isn't a significant contributor to the behavior of an undamped fundamental diaphragm resonance. If the same tension is achieved in a rigid and soft mount, differences are likely to be quite small.
That one is harder to predict. How large an area the tube covers (not sure if you are talking about a small diameter here or something large), how much pressure is applied, internal resonances of the tube, etc., will all influence things to varying degrees. If taken to extremes, the idea would create a displacement in the diaphragm and likely distortion similar to a single-ended ESL (though lower level), since the air flow is only coming from one side. Whether a more restrained approach could provide useful improvement is hard to guess about. Sometimes it's easier to mock up and measure an idea like this than it is to try to accurately model it.
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Yeah, I'm imagining the equivalent of touching the dia. with my finger. So I suppose it's trial and error to arrive at the best balance between pressure and noise. But the question firstly is whether it's even worth considering. The fact you didn't shoot down the idea encourages me to try it. I have several sets of Acoustats. Hypothetically speaking, if it was 100% effective, how would it change the sound? What improvement would/should I readily hear?
Hi,
I think the analogy Roger Sanders used to decribe the ´dampening´ leads to misunderstanding.
He says that the mass of the surroundings of the diaphragm swamps the resonance, which after my opinion is not what happens here.
It rather seems to me that its the grossly differing force/mass relationship that hinders the membrane to move in a way to generate any considerable output at all.
Also, fluids and gases behave differently regarding viscosity.
Finally a effective damping should apply to a considerable fraction of membrane area to be effective. Applying some force or damping at only one point rather only changes the modal behaviour of the membrane, splitting it into several sections, each with its own behaviour. The extreme is seen when a single membrane is fixed by a soft, dampening surrounding. Mattstat already explained that´s behaviour.
The seemingly two most effective and easy to apply measures so far are to electronically notch-out the amplitude peak and to mechanically add a flow resistance.
The first is more of a workaround while the latter atually adds the required resistive component to the resonant circuit.
jauu
Calvin
I think the analogy Roger Sanders used to decribe the ´dampening´ leads to misunderstanding.
He says that the mass of the surroundings of the diaphragm swamps the resonance, which after my opinion is not what happens here.
It rather seems to me that its the grossly differing force/mass relationship that hinders the membrane to move in a way to generate any considerable output at all.
Also, fluids and gases behave differently regarding viscosity.
Finally a effective damping should apply to a considerable fraction of membrane area to be effective. Applying some force or damping at only one point rather only changes the modal behaviour of the membrane, splitting it into several sections, each with its own behaviour. The extreme is seen when a single membrane is fixed by a soft, dampening surrounding. Mattstat already explained that´s behaviour.
The seemingly two most effective and easy to apply measures so far are to electronically notch-out the amplitude peak and to mechanically add a flow resistance.
The first is more of a workaround while the latter atually adds the required resistive component to the resonant circuit.
jauu
Calvin
re post # 23. I doubt it will make any difference at all.
At high frequencies, the membrane is already very highly damped and there is no resonance.
The main membrane resonance occurs because of air sloshing around the ends of the frame between the front and rear of the membrane, instead of being compressed by the membrane. The sloshing air gives the membrane mass - (in the same way that a shaken ballooning sheet seems heavier). The combination of the air mass and the tension in the membrane causes the resonance. To damp the resonance, the easiest solution is to force the air through a resistance - a tightly woven mesh. Screen printing mesh is good.
At high frequencies, the membrane is already very highly damped and there is no resonance.
The main membrane resonance occurs because of air sloshing around the ends of the frame between the front and rear of the membrane, instead of being compressed by the membrane. The sloshing air gives the membrane mass - (in the same way that a shaken ballooning sheet seems heavier). The combination of the air mass and the tension in the membrane causes the resonance. To damp the resonance, the easiest solution is to force the air through a resistance - a tightly woven mesh. Screen printing mesh is good.
This makes the most sense to me. From the Book AUDIO by Mario Rossi, ISBN 978-2-88074-653-7 (in french) a nice graph illustrating this issues. The graph illustrates the acoustic power radiation into space by three types of acoustic radiators: A monopole (such as a boxed speaker), a dipole normal to the wall, and a dipole parallel to the wall. So dipoles are much more cricital than monopoles at lower frequencies.
Dipole_Monopol_Leistungsabstrahlung.jpg
It depends strongly on ke if the parallel or the normal dipole is the more powerful one at the distinct frequency. Forget about bass for a normal dipole at ke<=1.
Nota Bene: The terms "Normal" and "Parallel" relate to the radiation pattern of the dipole. So the a dipole speaker screen which is physically placed parallel to a wall results in a "Normal" dipole radiating pattern in relation to the wall.
This graph also explains why it is wise to toe in dipole speakers by 30°... 45° in relation to the surrounding, vertical walls of the room: Toeing in will partially and mutually cancel out the both parallel and normal, antilogic radiation effects.
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The mesh does cost a little in output, a bit less than 1 dB, typically.
What happens is that as the frequency falls, there comes a point where the air starts sloshing around the speaker instead of being compressed. When this happens, the air starts behaving like a mass added to the membrane- as described above.
The normal damping effect of the air occurs because the air is being compressed and energy is radiated away as sound. When the sloshing occurs, the natural damping also falls away very quickly. In the finish, the resistance required to damp the membrane resonance is actually quite small, about a 1/10 of the normal damping due to the air at higher frequencies, so it has quite a small effect on sound production at higher frequencies.
What happens is that as the frequency falls, there comes a point where the air starts sloshing around the speaker instead of being compressed. When this happens, the air starts behaving like a mass added to the membrane- as described above.
The normal damping effect of the air occurs because the air is being compressed and energy is radiated away as sound. When the sloshing occurs, the natural damping also falls away very quickly. In the finish, the resistance required to damp the membrane resonance is actually quite small, about a 1/10 of the normal damping due to the air at higher frequencies, so it has quite a small effect on sound production at higher frequencies.
Does this entail covering the entire surface of the dia.? In the case of the Acoustats, I take it the mesh needs to be between the stator and dia. on both sides, so close proximity which may limit excursion. I'm surprised Jim Strickland didn't implement this instead of the felt pads on the backs of the panels.
On my speakers, I've glued the mesh to the ribs on the outside of the rear stator covering the entre area of the membrane. On the Quad ESLs, it is glued to the inside surface on the rear stator.
I use a pair of JL F 212 with ML CLX ESL crossed at 55 hz.
The CLX run full range with no low end crossover, the JLs have their own internal x over
The CLX run full range with no low end crossover, the JLs have their own internal x over
Can you please give a comparative description with/without? Did you retain the felt? To what extent does it restore bottom end response? Or, I should say eliminate resonance. Have you taken measurements?