It does look very similar to the B&G Neo8 though😕BAM said:
You can get the Neo8 down to 170Hz with higher order crossovers anyway.
Duck-Twacy said:
454Casull said:
From what I can make out, I would classify that as a flat diaphrgm. Pretty close, anyway. Perhaps a little rounded at the edges, but so what?
I wonder if we can get a 30º or 60º curve, so that we may compare Accutons to a cone loudspeaker and see if flat diaphragms have an advantage or disadvantage compared to empty cones in off-axis response.
1. Accuton probably qualifies as one of the stiffest cones in existence, wouldn't you say?
2. Aren't they well known to have a pretty severe ultrasonic breakup mode? I guess it is true that there is no free lunch.
2. Aren't they well known to have a pretty severe ultrasonic breakup mode? I guess it is true that there is no free lunch.
This is the point I am trying to get out. Filling in the cone makes it stiffer, since the outer edges will be structurally supported.
The intrinsic stiffiness will push the breakup region pas the region of interest.
An ultrasonic breakup mode would not be a problem with most people-yes I know some like to make sure about the frequency response between 20Khz and 40 kHz, but not everyone cares about that.
Now-about those off-axis curves....
The intrinsic stiffiness will push the breakup region pas the region of interest.
An ultrasonic breakup mode would not be a problem with most people-yes I know some like to make sure about the frequency response between 20Khz and 40 kHz, but not everyone cares about that.
Now-about those off-axis curves....
This thread is of great interest because I'm currently in the process of developing a new drive unit for Seventh Veil, with Doreen Bance of Bandor.
In our case, the drive unit is a full-range unit and has to cover 2/3rds of the audio bandwidth up to 20kHz. We have considered making a flat cone by having a flat piece of aluminium attached to the cone and using some filling in the hollow. However, this would add extra mass which is not a good idea when the cone is needed to perform high frequency duties. Also, I suspect that the flat cone may have problems through the breakup region (I prefer to have a controlled break-up at high frequencies rather than go for total stiffness with the corresponding dispersion difficulties).
I read with interest the difficulties that people have found in the mid-band and, to be honest, I don't know enough to understand the mechanism involved here, although I suspect that this may not be an inherent property of a flat cone.
We will be experimenting with the size of the dust-cap which performs the dual functions of adding stiffness to the cone and 'flattening out' some of the depth. The dust-cap will be convex to give strength to the structure. If we made the dust-cap flat and the same diameter as the cone we would, of course, have a flat cone.
Also, as you know, the depth of the cone effects its dispersion characteristics and this has to be taken into account.
I apologize for not being able to give any definitive rulings. My approach will be (as usual) to understand as much as I can about the theory and to use a mixture of rational thinking, intuition and experimentation to achieve the best sound for my particular application. I hope that this adds another useful 2 cents to the debate.
In our case, the drive unit is a full-range unit and has to cover 2/3rds of the audio bandwidth up to 20kHz. We have considered making a flat cone by having a flat piece of aluminium attached to the cone and using some filling in the hollow. However, this would add extra mass which is not a good idea when the cone is needed to perform high frequency duties. Also, I suspect that the flat cone may have problems through the breakup region (I prefer to have a controlled break-up at high frequencies rather than go for total stiffness with the corresponding dispersion difficulties).
I read with interest the difficulties that people have found in the mid-band and, to be honest, I don't know enough to understand the mechanism involved here, although I suspect that this may not be an inherent property of a flat cone.
We will be experimenting with the size of the dust-cap which performs the dual functions of adding stiffness to the cone and 'flattening out' some of the depth. The dust-cap will be convex to give strength to the structure. If we made the dust-cap flat and the same diameter as the cone we would, of course, have a flat cone.
Also, as you know, the depth of the cone effects its dispersion characteristics and this has to be taken into account.
I apologize for not being able to give any definitive rulings. My approach will be (as usual) to understand as much as I can about the theory and to use a mixture of rational thinking, intuition and experimentation to achieve the best sound for my particular application. I hope that this adds another useful 2 cents to the debate.
We have been here before !
Well to throw in some history we have been here before.
There was a fashion for flat square " high tech diaphragms"
a few years ago, Sony as one of the leading lights for this.
To answer 7V's speculations, the ideal "filler" must be stiff across
the section for classic sandwich construction, an example filler
would be short metal tubes glued together sideways.
Sony used a proper hexagonal "beehive" filler, seems difficult to
make, between two flat sheets. The tweeter was straightforward,
with a voice coil driving the sandwich directly.
However the 8" bass mid unit was driven at 4 points with a
complex lightweight gantry affair extending the bandwidth.
But cheaper units simply used a flat sandwich section driven
by a pretty much standard cone of somewhat smaller diameter,
not surprisingly they sounded no better than "normal" units.
Again regarding 7V's new unit I suspect the best you can do
is add a smallish convex metal dome and extend the voice
coil a little to directly drive / reinforce the added dome section.
🙂 sreten.
Well to throw in some history we have been here before.
There was a fashion for flat square " high tech diaphragms"
a few years ago, Sony as one of the leading lights for this.
To answer 7V's speculations, the ideal "filler" must be stiff across
the section for classic sandwich construction, an example filler
would be short metal tubes glued together sideways.
Sony used a proper hexagonal "beehive" filler, seems difficult to
make, between two flat sheets. The tweeter was straightforward,
with a voice coil driving the sandwich directly.
However the 8" bass mid unit was driven at 4 points with a
complex lightweight gantry affair extending the bandwidth.
But cheaper units simply used a flat sandwich section driven
by a pretty much standard cone of somewhat smaller diameter,
not surprisingly they sounded no better than "normal" units.
Again regarding 7V's new unit I suspect the best you can do
is add a smallish convex metal dome and extend the voice
coil a little to directly drive / reinforce the added dome section.
🙂 sreten.
Re: We have been here before !
As for extending the voice coil, I won't even go there now. It's a balancing act with coil wire material, power handling, length, diameter, excursion, impedance and mass.
Yes, we're going for a convex metal dome. The size will be partly determined by the need to add structural stability to the cone at its weakest point.sreten said:
As for extending the voice coil, I won't even go there now. It's a balancing act with coil wire material, power handling, length, diameter, excursion, impedance and mass.
Re: Re: We have been here before !
I actually meant extending the voice coil former, not the voice coil.
🙂 sreten.
7V said:
I actually meant extending the voice coil former, not the voice coil.
🙂 sreten.
SY said:
From the article "Loudspeaker With Honeycomb Disk Diaphragm", by Sakamoto, Satoh, et al in the Journal of the Audio Engineering Society, 1980:
"Another disadvantage of the cone diaphragm is the cavity effect....it is difficult to obtain a uniform frequency response because of the acoustic resonance of the front cavity and the path difference from each point of the diaphragm."
"For example, Fig. 3 shows the frequency responses of a rigid piston and a rigid cone, both 0.2 m [7.9"] in diameter. The sound pressure level of the cone has a peak at 1.3 kHz and a dip at 2.3 kHz. However rigid the cone may be, it is theoretically impossible to obtain a flat frequency response. On the other hand, for a disk diaphragm it is possible to achieve a flat frequency response by increasing it's flexural rigidity. This is the prime reason why the development of a disk diaphragm is so important."
Attachments
SY said:
Expanded material encased in a thin skin of aluminum or some stiff material might be heavier than a cone, but still, I feel, can meet the Mms requirements of 5.7 g or 7 g for a 4 inch cone. There will be more material, but most of the space will be taken up by light, expanded material. And then, there is the possiblilty of new materials like aerogels possibly encased in a skin of aluminum or some other stiff material.
I do believe something like the below can be done. The red is the aluminum, magnesium, or whatever coating. The grey inside is the expanded material, and perhaps different pieces can have different material for resonance cancelling purposes. Of course, all of them can be glued together-I just showed them separate prior to gluing.
I think a setup like this can easily meet the Mms requiremnts of a cone. Wouldn't such an arrangement would be inherently stiffer, since the outside diaphragm edge would be supported, as opposed to unsupported in an empty cone?
The first couple of pieces near the voice coil would have a donut hole cut into them for ventilation purposes.
Attachments
Wizard,
Although stiff cones are attractive for a number of reasons, I believe you're going to limit your frequency response. The KEF B-139, for instance, was only good--practically speaking--up to a few hundred Hertz. Part of that was due to a resonant spike at something like 1200-1500 Hz, but part of it was that the speaker simply didn't go that high.
Given that many drivers rely on cone breakup to extend the high frequency response, you're going to sacrifice an octave or three off the top end if you make the cone too rigid. Another factor, rarely mentioned, is that the cone itself forms a "horn" thus increasing the efficiency of the high frequencies being produced back nearer the voice coil. A more explicit approach to this was the whizzer cone, but it was also a horn. Then you get into flare rates and such, which have to be traded off against the cone stiffness, etc.
If you're willing to limit yourself to a couple of octaves per driver, then stiff cones may be the ticket, but crossover complexity will increase and you'll need five or six drivers, each covering a comparatively narrow part of the frequency range, blah, blah, blah...
I say all this knowing that I've got quite a few B-139s at the house, and love them. I also have a quad-amped system. So, yes, using drivers to cover narrower parts of the audible spectrum comes naturally to me.
Go for it.
Grey
Although stiff cones are attractive for a number of reasons, I believe you're going to limit your frequency response. The KEF B-139, for instance, was only good--practically speaking--up to a few hundred Hertz. Part of that was due to a resonant spike at something like 1200-1500 Hz, but part of it was that the speaker simply didn't go that high.
Given that many drivers rely on cone breakup to extend the high frequency response, you're going to sacrifice an octave or three off the top end if you make the cone too rigid. Another factor, rarely mentioned, is that the cone itself forms a "horn" thus increasing the efficiency of the high frequencies being produced back nearer the voice coil. A more explicit approach to this was the whizzer cone, but it was also a horn. Then you get into flare rates and such, which have to be traded off against the cone stiffness, etc.
If you're willing to limit yourself to a couple of octaves per driver, then stiff cones may be the ticket, but crossover complexity will increase and you'll need five or six drivers, each covering a comparatively narrow part of the frequency range, blah, blah, blah...
I say all this knowing that I've got quite a few B-139s at the house, and love them. I also have a quad-amped system. So, yes, using drivers to cover narrower parts of the audible spectrum comes naturally to me.
Go for it.
Grey
Aerogel?
What about aerogel? Stiffness and low density seem to indicate that some form of aerogel would be one of the best materials for a filled-in "cone". Audax does make aerogel drivers but these are in the conventional cone form.
What about aerogel? Stiffness and low density seem to indicate that some form of aerogel would be one of the best materials for a filled-in "cone". Audax does make aerogel drivers but these are in the conventional cone form.
Re: Aerogel?
I couldn't possibly agree more.
Maybe aerogel exclusively is the answer, perhaps aerogel as one of a series of wafers of different materials glued together-it looks like it could be the answer, one way or the other.
One of the things about aerogel is that it has to be one of the most quickly commercially marketed things I have ever seen, as least as regard loudspeakers. Things go slowly in the loudspeaker field. I mean, it took about 10 years from the publication of Thiele's and Small's paper for the vented box to be accepted as something no longer revolutionary.
But I remember reading in the Tuesday Science supplement of the New York Times about these new substances called aerogels, and how they might have commercial uses. A couple of years later, Audax is making commercial cones out of them, and not charging very high prices for them either, (most new materials are introduced in models with very high prices, and the feature works it's wy down the price hierarchy gradually).
Yes, I agree. Aerogel would be one of the first places to look on this.
freelancer said:
I couldn't possibly agree more.
Maybe aerogel exclusively is the answer, perhaps aerogel as one of a series of wafers of different materials glued together-it looks like it could be the answer, one way or the other.
One of the things about aerogel is that it has to be one of the most quickly commercially marketed things I have ever seen, as least as regard loudspeakers. Things go slowly in the loudspeaker field. I mean, it took about 10 years from the publication of Thiele's and Small's paper for the vented box to be accepted as something no longer revolutionary.
But I remember reading in the Tuesday Science supplement of the New York Times about these new substances called aerogels, and how they might have commercial uses. A couple of years later, Audax is making commercial cones out of them, and not charging very high prices for them either, (most new materials are introduced in models with very high prices, and the feature works it's wy down the price hierarchy gradually).
Yes, I agree. Aerogel would be one of the first places to look on this.
kw, couldn't agree more, especially since I've had excellent results with Audax's aerogel drivers. I'm also a big advocate of structured cones (or flats or whatever), using more than one material to work around conflicting requirements, and using various shaping processes to optimize material behavior.
Aerogels were already old news when the NYT article ran. I worked with them as aircraft materials back in the mid-'80s, and they weren't new then.
Aerogels were already old news when the NYT article ran. I worked with them as aircraft materials back in the mid-'80s, and they weren't new then.
One thing to consider if you're talking about filling a cone to any depth is that most materials (including aerogel, I imagine) have a certain amount of compressibility. As you thicken a compressible diaphragm, I believe you'll begin to see some mechanical lowpass filter behavior as the material's compressibility couples with its mass. IOW, the finer excursions of the VC might be absorbed before reaching the surface of the diaphragm.
I know that in full-range drivers, even the stiffnes of the glue formulation used between the VC former and the cone/whizzer is an important consideration for treble response.
Though I recognize that you're discussing the mid/midbass band, I wonder if you'd encounter this lowpass phenomenon.
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