I don't think it's the same situation.
A bending wave driver to work properly relies on almost perfect termination at the edge and also relies on special material properties that vary from the centre to the outside of the cone that cause the higher frequency bending waves to rapidly dissipate as they travel out to the edge, thus standing waves don't appear on the cone at higher frequencies.
The increase in dispersion comes from the higher frequency bending waves dissipating more quickly as they travel outwards thus limiting the effective radiating radius at higher frequencies.
This dispersion improvement is nothing to do with resonances because an ideal bending wave transducer won't have any discrete standing wave resonances occurring.
This is a completely different situation to a traditional cone driver with a uniform cone material and imperfect edge termination, where strong radial standing waves readily form due to the bending waves reflecting off the edge termination and travelling back up the cone, interfering with themselves and producing standing waves.
There is a big difference between a purely propagating and gradually dissipating bending wave (which looks like ripples travelling outwards on an infinitely large pond) and bending waves that form a standing wave pattern - like a stone being dropped in the middle of a round swimming pool.
The 1st radial standing wave on an 8" paper driver typically occurs at around 3-4Khz, and this mode has maximum excursion near the outer edge of the cone and minimum at the voice coil.
(This is why this resonance is best treated by damping near the edge of the cone, which is what I do with my staggered pattern of adhesive foam strips, as damping is most effective at the excursion maximum of the resonance mode)
At this particular resonance the driver is working more like a ring radiator where most of the radiation from that resonance is occurring at the circumference of the driver - because of this that resonance is somewhat directional and isn't as obvious off axis.
The 2nd radial mode (about 6-8Khz) will have an excursion peak at both the edge of the cone and half way down the cone, but as you're now at twice the frequency this results in it also being somewhat directional despite having a second peak at half the cone diameter.
Circumferential standing waves also radiate primarily from the edges of the cone, so they too are somewhat directional.
So until I see some measurements that unequivocally show cone breakup resonances to have wider dispersion (something like a normalised, high resolution directivity sonogram) then I just don't think it's the case.
The cone and surround matching is really a complicated issue. Depending on the shape of the cone and the weight of the surround, the first radial mode can have the node anywhere on the cone. The issue is how one can damp it out. I have patented a design that turns radial modes into circular modes creating radial bends that interactively damp out the radial modes. This works best when the radial modes are described above by DBMandrake.
I checked my measurements, but the problem is that I haven't used a wide test baffle, measurements have mostly edge interferences from baffles (or just the frame) Interferences have wide dispersion but lower amplitude than cone resonance.
This is Audax HM100z, polyamide cone and phase plug that fight against resonances and directivity ripples effectively. No xo applied. I don't remember baffle size and measuring distance. REW can't do normalization.
This is Audax HM100z, polyamide cone and phase plug that fight against resonances and directivity ripples effectively. No xo applied. I don't remember baffle size and measuring distance. REW can't do normalization.
Attachments
Interesting, have you published your damping approach ?
I discussed mine including some measurements and the layout of the damping strips I used in another thread here back in 2011:
http://www.diyaudio.com/forums/multi-way/192215-phase-plug.html#post2640803
Some discussion and measurements in another thread including measurements of the same damping technique used on some slightly different drivers:
http://www.diyaudio.com/forums/full-range/185012-whizzer-intelligibility.html#post2503393
I developed this technique experimentally around 2003/2004 without really understanding how it worked at first (although I think I have a good idea of exactly how it works now) and first described it on a full range driver forum around 2005, although I think that forum no longer exists.
The traditional approach of trying to provide all the damping at the edge termination with the surround just doesn't work very well - you can't get a close enough impedance match, nor can you absorb enough bending wave energy in the relatively small surround.
The interface between the cone and surround is ill equipped to absorb a bending wave. At most you can reduce the amplitude of the standing waves (and thus the resonances) but not eliminate them.
The approach I took was to damp them before they reached the surround, using self adhesive foam strips. When the cone tries to bend in the region the strip is stuck to it has to compress or stretch the foam block, this dissipates energy and thus directly dissipates bending waves without having to use a stiff lossy surround which is compromised at low frequencies and still doesn't adequately damp the bending modes.
Furthermore, instead of having a uniform cone and edge termination (where the bending waves in the cone occur at the same frequencies at every rotation around the cone and thus stack) the pattern I used divides the cone up into 8 sectors where the bending waves in the outer half of each sector are different to their adjacent sectors, so what standing waves remain tend to be cancelled out by their neighbouring sectors as adjacent sectors are moving in opposite phase. (This technique is also used by some kevlar drivers like the B&W FST midrange, albeit by using a material with differing propagation speeds in different axes, but the end result is very similar)
Higher modes are targeted by the inner ring of strips, as the frequency the damping targets goes up as you move towards the centre of the cone. (In fact the damping is tuned to the exact frequency of the resonance by moving it's radial position)
Finally this kind of damping configuration also both damps and "stabilises" any spurious circular modes travelling around the circumference - which conventional surround damping does absolutely nothing for.
The periodic positioning of the strips around the perimeter as well as providing damping also "phase locks" the circular modes in step with the damping strip locations rather than letting them "free run" around the circumference in a chaotic, semi-random phase relationship with the radial modes. This elimination of chaotic circular modes I believe helps to eliminate the "random" cone breakup hash that many cones suffer from and cannot be corrected for with EQ.
Certainly the cones I have treated with this arrangement subjectively do not have any "random" cone breakup noise/sound to them at all, even if the radial modes are still partially present and not perfectly suppressed.
Last edited:
This SB has a really nice aluminium cone with dents to kill wibes
SB Acoustics SB15NAC30-8 5" Aluminum Cone Woofer
SB Acoustics SB15NAC30-8 5" Aluminum Cone Woofer
My patent has been in force for a few years now, lost track of how many. I think the main difference from other applications is that strips are not damping material. They have to be stiffer than the cone material, and they have to be at an angle to the radial lines. I showed a Klippel scan playback of the result to Peter Larsen when he came to Taiwan, hoping there could be a quick way to see some results using his Fine Cone software. Application of this is quite tedious.
Last edited:
From the response curves, I don’t see anything suggesting that the design works.
Frankly, I think it might Soongc. I don't see a violent break up mode, just a gradual rising of the response beyond a certain point. This generally speaking implies that the cone stays pistonic right up till break up. I don't see any reason not to use this SB Acoustics speaker (although I haven't and won't, but for other reasons).
The rise in the response I significantly high, and the following series of peaks are pretty obvious higher order modes. Yes, you could filter this out with heavy filtering, but then that is more parts and thus more cost. For a 5” device, I am not sure how much if the bandwidth you could use, normally 5” devices can have quite a wide band giving you more usage options. I guess each person may decide differently.
The impedance curve suggests they might have wanted a full range driver.
The dust cap breakup mode could also be mixed in there are well.
The impedance curve suggests they might have wanted a full range driver.
The dust cap breakup mode could also be mixed in there are well.
Last edited:
I got everyone chi-fi ear buds this year and got to listen to some different ones (yes I opened the gifts and tried them all first). The boarseman kr25d are awesome. So are the kz-es3. Qz in another good brand.
I also got to listen to the new apple airpods that someone else had. They have impressive bass, but otherwise didn't impress me. I think they might have exaggerated the bass and treble to impress inexperienced consumers (I am biased against apple btw).
As far as distortion goes, After listening to some decent ear buds (which can be equalized flat) its interesting what makes speakers better.
I don't put much creedence in the idea of euphonics but its a hard thing to rule out. There might be some masking and also softening effects from certain kinds of distortion that can be relaxing, especially as the cone moves into and out of its break up. Theres also a possibility that there are complex interactions between room, dispersion, frequency response, etc. that can create a euphonic coherency. Coherency is something that we look for that matters and is hard to quantify or measure.
I still think the big difference is dynamics. The ear has some way of judging scale and feeling the intensity of sound, the same way that the eye can judge scale. Its that palpability to the sound that helps trigger emotion. Is it worth spending thousands on? Depends on the person.
I also got to listen to the new apple airpods that someone else had. They have impressive bass, but otherwise didn't impress me. I think they might have exaggerated the bass and treble to impress inexperienced consumers (I am biased against apple btw).
As far as distortion goes, After listening to some decent ear buds (which can be equalized flat) its interesting what makes speakers better.
I don't put much creedence in the idea of euphonics but its a hard thing to rule out. There might be some masking and also softening effects from certain kinds of distortion that can be relaxing, especially as the cone moves into and out of its break up. Theres also a possibility that there are complex interactions between room, dispersion, frequency response, etc. that can create a euphonic coherency. Coherency is something that we look for that matters and is hard to quantify or measure.
I still think the big difference is dynamics. The ear has some way of judging scale and feeling the intensity of sound, the same way that the eye can judge scale. Its that palpability to the sound that helps trigger emotion. Is it worth spending thousands on? Depends on the person.
Last edited:
with all this talk i have to assume that driver distortion is inevitable and not much can be done about it so now i have to wonder if it simply comes down to picking a "distortion flavor" i can live with.
There is a tendency to be way too pedantic about this stuff. Just make some sawdust and and use your ears to listen to what sounds good. With some experience you can almost predict in your mind what a driver sounds like just by looking at it and knowing the specs.