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Joe Rasmussen

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Joe Rasmussen last won the day on May 30 2017

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  1. Joe Rasmussen


    CORRECTION: The stupid spellchecker... "accentuation in the frequency response..." Exactly the opposite. the response it says is accentuated, not attenuated - I have also corrected/edited the original post.
  2. Joe Rasmussen


    Yes, it does go back further than Esa's book as my comment is 2007. The horn comment is on page 49 and context is the mid-bass or just midrange driver: "At high frequencies, the horn action of the cone causes easily an extensive accentuation in the frequency response..." It is also mentioned on page 48 as comment to Fig. 3.12a. It is easy to miss, so not surprised that you did. I have not heard anybody else describe it as a horn effect, but it does kind of make sense. But the important thing here is that a) it is caused by the cone profile, which does sort of look like a horn and b) a horn is an acoustic device, it is not about any physical breakup which is a mechanical issue. Do a CSD 'waterfall' plot and you will see exactly what you have, as cone resonances that don't even show up in the frequency response in any obvious way can be revealed. But some peaks in the FR can definitely be resonances. I have the facility here to do such measurements on any driver that can be brought here.
  3. Joe Rasmussen


    Even Esa Merilainen in his "Current Driving Loudspeakers" book, which I believe came out after I wrote it on my website article, called this a 'horn' effect, which is to say that it is a matter of shape of the cone. Lynn Olson also made a comment of what I said and made an interesting point, that bad speakers with bad high inductance can make the driver look good as the inductance will make them measure better, going some way to suppress this peak. So the better driver may well have a more pronounced peak and look bad. But in a good driver, look at the CSD 'waterfall' plot and often you can detect ridges where you may have minor resonances in the 3-10KHz range, but these do not coincide with the 4KHz peak. This is clear evidence that the 4KHz peak is not a resonance, not a cone breakup. Below is a quick but revealing comparison between the 6.5" HDS drivers using 1/6th Octave pink noise. Red is the multi-layer PP cone and the other is Black the Nomex cone as used by both Mike and myself (was used in the DIY Elsinore Mk5 speakers). PP on the right and Nomex on the left, other than cone they are identical. The two drivers are identical except for the cone material and the fact that the Nomex dustcap is a bit smaller. So the cone profile is very very close. So this is what it looks like: The similarity is not a coincidence, in fact if the Nomex dustcap had been exactly the same diameter, it would have been in more close. The slight difference in level, Black is the Nomex has a slightly lighter cone and hence about 1dB advantage. Note the slightly smaller dustcap of the Nomex, this means the 4KHz peak is broader, this I believe is logical to expect. Lynn Olson's comments below, I think lovers of speaker design might like to read it: Joe Rasmussen has a crossover design philosophy that overlaps with mine to a large degree. Not identical, mind you, but a lot of areas of agreement. I mainly use low-Q 2nd-order networks, but am quite partial to 1st-order combined with a notch filter as well, depending on what the driver wants to do. Linear phase I can take or leave, but the phase angles between the drivers are very very important and are quite audible as "phasiness" with pink-noise stimulus. A correctly designed crossover does not sound "phasey" and more importantly, sounds like a single driver, even when quite close-up to the loudspeaker. It is certainly true that high-quality cone drivers typically have a single well-defined peak at the top of the range, and this single peak is amenable to notch-filter equalization. I agree with Joe's comment these clean, well-defined peaks are not breakup, but are artefacts of the cone shape itself. They are especially evident in top-of-the-line cones with low inductance figures - in a more typical high-inductance driver, the peak is intentionally masked by voice-coil inductance. Since VC inductance is quite nonlinear, low inductance is a good thing - but it does make the FR look different than you might expect. It's the drivers with ragged responses above the top of the range that are more problematic to cross over and equalize - any driver with a whizzer or poorly designed dustcap or phase plug qualifies here. These are the notorious directional peaks you've seen me complaining about - the famous KEF B110, as used in the BBC LS3/5a, had three directional peaks 100 Hz apart in the 3.5 kHz region, as well as a single broad peak at 1.5 kHz (which was equalized in the LS 3/5a crossover).
  4. The brown pair is noticeable less sensitive.
  5. Again, have I? Have I even said there are no benefits in voltage drive. Please,. again, please, read my posts more carefully - before you put an oval peg into a round or square hole!
  6. You are not reading my posts very carefully. Is it not clear to you that I am in fact suggesting a THIRD WAY ???
  7. May I point out that you are misrepresenting my standing on this. You may well be right, that there are no such thing as a free lunch. As for something not being universally adopted is then a argument for no progress. There was once a time when horses and not cars were universally adopted, right? I think I have been very patient, but please consider intelligently the following, as this should surprise you very much and maybe rethink your fixed position... This is a speaker driven by zero Ohm voltage source: This is the same speaker driven by a current source: Looks similar? Let us overlay the two responses: Surprised? Where is the peak? Let us now look at the respective current phase angles: NOW PLEASE READ MY EARLIER POST WHERE I HAVE EXPLAINED HOW THE ABOVE CAN BE DONE. A SPEAKER SYSTEM THAT CAN BE DRIVEN BY ANY KIND OF AMPLIFIER. MAINSTREAM? WHO CARES?
  8. III i Take the "0.7" part of the graph. What if I could demonstrate that after calculating Vb to get Q = 0.707, then that is all that I need, right. Just know and build the volume of the box and Q =- 0.707 spot on. But if I increase series resistance by 41%, then the Q = 1.0, right? Absolutely right! Have we found common ground? I think so. BUT... Some years ago I approached a number of speaker designers, including Brad Serhan of Orpheus, Axis and Brigadiers Audio fame. Brad and I go back some thirty years. I showed Brad that I could build a 2nd order Butterworth alignment, Q = 0.707 and that we would agree that the alignment would only stay that way if it was driven by a zero source impedance. Unless we did something out of the box! I then showed him how our new box could be driven by any source impedance, even infinite source impedance. Yes, he was quite amazed. HOW: Use an LCR, tune the LC part to Fc and the Q of the LCR to match, adjust R for a flat impedance and it will also show a flat current phase angle. I AM NOT LYING: THAT BOX CAN BE DRIVEN BY ANY SOURCE IMPEDANCE AND WILL ALWAYS BE Q = 0.707 !!! If you use a voltage source, the Q will be preserved exactly as you say. But note that the current at Fc will likely be around 1/5th of the current compared to it seeing the DC resistance only. What about current drive? Now 1/5th of the current will still travel through the voice coil, but the other 80% will be absorbed by the LCR. The frequency response will be the same because it will obey Thevenin's Theorum in voltage terms, but the voice coil will now see current with zero degree phase angle. Not bad eh? THINKING FROM A CURRENT PERSPECTIVE LEAD TO LOOK FOR A SOLUTION THAT ACTUALLY WORKS!
  10. Off topic! I am not going to ignore the science. Please explain F = Bli and we can find common ground. That equation is at the heart of current drive.
  11. It was not meant as an insult originally, it was used by a scientist to explain why there is a tendency to ignore measurements that tended to prove a variable and not a constant. It is not an insult, it is a known factual shared mental condition. It is strange that social media always comes up with a comment being personal in nature, even when it isn't. This is a malaise of social media that I find disconcerting.
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