Planar Speaker Asylum

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Planar Speaker Asylum

RE: Cascade on frame ...

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In Reply to: RE: Cascade on frame ... posted by JBen on August 09, 2010 at 00:35:28

The phono cartridge is a great idea that could actually measure diaphragm deflection, but if you do try it, I'd use something wickedly tough and disposable like an old Stanton, because while you can get meaningful results at a low volume level if you slip up you could mangle the cartridge. You could also cut up a cheap microphone and stick the electret diaphragm to the speaker.

Follow Ups:

RE: Cascade on frame ... - JBen 12:56:09 08/10/10 (8)
As a matter of fact, it was and old Stanton that I was searching for! It is over 20 years old. The only remaining piece of my LP days [sob]! The whole thing got lost in a move. My wife thinks it's in the black hole of our storage. Of course, she only said it after 2 hours of me searching in vain!

The plan was to use it on the MDF frame itself. For vibration sensing rather than sound. The idea was to somehow measure behaviors of the MDF plain, MDF with P-Frames, MDF with HALF-Razoring (no PF) and MDF+PF+HR. This was on the initial phase of testing, just before I started sticking the stuff on.

I did think of a microphone but since it just picks up sound, I dismissed the idea. Still, your idea does suggest to me that the coil of a cheap common mic alone may have worked. Removing most of the diaphragm would filter out sound and capture more of the low vibrations. Does this make sense?
- RE: Cascade on frame ... - josh358 14:42:48 08/10/10 (7)
  Yes, that could actually work. The idea is to make the permanent magnet a fixed reference, and then attach the coil to the frame without a diaphragm that would pick up airborne vibrations. Essentially, you're removing the impedance matching. However, I think an electret element would make more sense, since it doesn't even have to be attached to the microphone.
  
  That being said, doesn't someone make an inexpensive accelerometer? That would be the right tool for the job, if you're interested in measuring the frame vibrations.
  
  Another thing you could do is to get an LED and a photocell, and attach a "wiper" on the frame that would slide between them as it was displaced. Then just look at the output of the photocell. Years ago, I used a unit that had both separated by a slot in the middle to make a shaft encoder. I used the photocell output to drive a digital circuit, but no reason you couldn't calibrate it and use it for analog vibration measurements. It cost practically nothing and it would be easier to calibrate than the other options because it would respond to DC.
  - RE: Cascade on frame ... - pictureguy 16:05:11 08/10/10 (6)
    An accelerometer can be made using an inexpensive phono cartridge.
    Fix the cartridge to the thing to be measured. Since the cantilever / tip is suspended there will be a bit of lag in its motion when the cartridge is vibrated.....inertia....which will produce an output current.
    To add sensitivity, add weight to the cantilever tip.....certainly 100mg would make a big change.
    I have no idea if you'd want to run it thru RIAA equalization or how you'd calibrate your home brew unit to a standard.
    I've seen plans for using a phono cartridge in a home brew earthquake detector.
    
    Also, my Ipod touch has an accelerometer in it as do my Nintendo controllers....and those are 3 axis and pretty darn amazing....especially when you consider the cost!
    Too much is never enough
    - RE: Cascade on frame ... - JBen 18:52:31 08/10/10 (0)
      Yes, a cartridge may do the trick. I may even get one of the cheapies from Best Buy. I lost the ability to measure a PLAIN MMG (mine are already FULLY-Contaminat...errr Razored : - )) but it may serve to better represent what happens when I add the P-Frames. It ain't subtle to the ear. Plus my measurements of recorded sound strongly suggest that it is impulse-driven. On one hand, a constant smooth frequency sweep will not show a difference. OTH, grab some comparative samples of dynamic music and the difference is quantified and clear.
      
      This, still, does not say "why" it happens. I am more focused on "what works", "how to replicate it" and "sharing". Better measurements that support any findings may help to do this....and the theorists, as well. I am glad that they are having a ball these days!
      
      You made my day with this one. "I have no idea if you'd want to run it thru RIAA equalization " I am not making fun of you. I did have my laugh of the day thinking that the thought also crossed my mind. In any event, we would have to shoot the signal through a phono input anyway...unless we used a ceramic/piezoelectric...hmmm, there's a thought! They can take more weight. Come to think of it, any piezoelectric minipanels out there?
      
      In my case, I would then transfer to the PC. In this system, Cool Edit's ability to represent and quantify the amplitude variations may help.
      
      Standards are likely out of our reach on this. However, some consistency of method could yield relatve readings that may do the trick.
    - RE: Cascade on frame ... - josh358 16:53:42 08/10/10 (4)
      That was JBen's idea, to use a phono cartridge. Unfortunately, his old Stanton is missing.
      
      You'd definitely want to disable the RIAA correction, since that compensates for the preemphasis that's added during mastering. I'm thinking that a mic input or a low-level tape head input on an old preamp would probably do the trick. Or even a high level line input, you're going to be blasting the thing and overload is more of an issue than SNR.
      - RE: Cascade on frame ... - pictureguy 18:30:28 08/10/10 (3)
        
        In Reply to: RE: Cascade on frame ... posted by josh358 on August 10, 2010 at 16:53:42
        
        I'd try to avoid overload if possible.
        I remember an input called 'tape head'. I wonder if it was equalized?
        
        I'd also try to find either a REAL chart recorder or the equivalent for a laptop.
        I don't know what the state of the art is in this regard.....laptop instrumentation and metrology.
        Too much is never enough
        
        RE: Cascade on frame ... - josh358 19:31:19 08/10/10 (2)
        
        In Reply to: RE: Cascade on frame ... posted by pictureguy on August 10, 2010 at 18:30:28
        
        Of course, I'm getting senile. It would have deemphasis, presumably for 7-1/2 IPS tapes.
        
        So much for that . . .
        
        RE: Cascade on frame ... - pictureguy 23:58:15 08/10/10 (1)
        
        In Reply to: RE: Cascade on frame ... posted by josh358 on August 10, 2010 at 19:31:19
        
        First person to write an Iphone / Ipod Touch app to use 'em as an accelerometer wins the PRIZE.
        
        Yep, an all expense paid vacation to the nut house.
        Too much is never enough
        
        RE: Cascade on frame ... - josh358 05:20:04 08/11/10 (0)
        
        In Reply to: RE: Cascade on frame ... posted by pictureguy on August 10, 2010 at 23:58:15
        
        Hey, why not? You could tape it to the frame, and hope it holds.

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