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Old 6th September 2013, 05:37 PM   #11
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Quote:
Originally Posted by RayCtech View Post
Most possibly caused by a short between two or more folds, but when playing the movement of the diaphragm may cause it to "un-short" intermittent or it can be your ohm meter that puts out a DC voltage so the diaphragm move and creates the short. Try to measure with the opposite polarity - then the diaphragm folds will move the opposite way....
No short. Looks more like an issue with the conductive coating thickness consistency. Have seen a few others post about this Re issue also. Some post on PE forum (i believe) saw where another had similar issue almost to a tee, wished he had bought 3 or 4 instead, tho sounded fine (to his ear). Mine sound different to me and by measurement. Could have been diaphragms from two different batches, use up all the prototypes, toss in a bin. That's where the old addage "Waste not, Want not" comes into direct contradiction with given specifications and profitability > pssst the DIY crowd won't notice if we pawn off some crap.
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Old 13th September 2013, 08:21 PM   #12
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Quote:
Originally Posted by SpinMonster View Post
Can the AMTPRO-4 really able to cross at 800hz like the ad says?

If I bought a pair does anyone want to do testing on them?
I'd love to see the results.
I have one for testing. I'm wondering, do I need to protect it with a capacitor for testing purposes?

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Originally Posted by Greebster View Post
Not with an Fs of 900
I'm not sure if the "fs" they list is meaningful? You don't see a bump in the impedance at 900Hz, do you?
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Old 17th October 2013, 12:16 AM   #13
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anyone tested the little mini 8 yet? wondering what x/o they wd need.
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Old 17th October 2013, 02:16 AM   #14
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Unhappy RE: Mini 8? Yes: FR looks pretty rough...

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Originally Posted by Bill poster View Post
anyone tested the little mini 8 yet? wondering what x/o they wd need.
Mini AMT - free air and waveguide.PNG

I think that's 5 db per box...

Here's my thread over on TechTalk: http://techtalk.parts-express.com/sh...ed-by-Critofur
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Old 17th October 2013, 12:24 PM   #15
Baldin is offline Baldin  Denmark
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Quote:
Originally Posted by critofur View Post
I have one for testing. I'm wondering, do I need to protect it with a capacitor for testing purposes?



I'm not sure if the "fs" they list is meaningful? You don't see a bump in the impedance at 900Hz, do you?
1. Depends on the test equipment, and the level (how loud you do the test) ..... I would always place a large cap in series to make sure nothing bad happens

2. Though you don't see a big bump on the impedance curve, it will still be it's resonance frequency (free air), and you will see the output fall below this freq ....
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Old 5th June 2014, 01:29 AM   #16
DcibeL is offline DcibeL  Canada
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Quote:
Originally Posted by Greebster View Post
Not with an Fs of 900
Old post but just want to point out that ribbons, planars, AMTs, do not have an Fs. No coil you see...That should be obvious looking at the impedance graph...flat line without resonance...
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Old 5th June 2014, 01:50 AM   #17
a.wayne is offline a.wayne  United States
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Thats not entirely true , there are Resonance peaks, not much but there is and its really a case of motor Strength vs diaphragm mass .
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Old 5th June 2014, 03:15 AM   #18
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It is measurable, small but there. Mass, and tension are key to this minor inflection if I'm not mistaken. The RT4001's I have has an fs of 2100, crossing them above 2.2k. Optimum would be above 4.5k as distortion is rather high below this and peaks at resonance. The standard rule of thumb is to cross at least 1 octave above fs and this holds true with measurements. Same is true of my Monsoon PM9 planars. Best crossed an octave above resonance.

Am looking into waveguides as a partial fix. The Vifa XT25/ Pellegrine Waveguide combo does a marvelous job at both extending the low end and reducing distortion. Would think similar results could be had with an AMT
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Old 5th June 2014, 06:11 AM   #19
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Quote:
Originally Posted by DcibeL View Post
Old post but just want to point out that ribbons, planars, AMTs, do not have an Fs. No coil you see...That should be obvious looking at the impedance graph...flat line without resonance...
Not so. Ribbons, planars and AMTs are just specail cases of a electrodynamic speaker. They all have a coil in a magnetic motor structure.

In pure ribbons the coil have only on turn. In a planar and in ribbons like the ones in Apogee duetta, there are multiple turns, on a plane diaphragm, suspended over on between a magnetic field. In an AMT the diaphram is just folded into pleats, but can have either on or more turns in the coil.

The coil effect on the impedance, will be a rise towards high frequencies. For planar the coil effect is very low, due to very low number of turns, therefore seemingly flat towards high freq.

The resonance freq is dominantly mechanical, determined by moving mass and spring effect. The degree of the resonance effect on the electrical impedance, is determined by the transformation factor Bl, that is magnetec field strength times length of wire in the field (coil). As Bl is normally very low in a planar, ribbon or AMT, the effect on the impedance is not strong and therefore the curve seems flat.

So the resonance is there, and so is the coil.

Best regards Baldin
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Old 7th June 2014, 06:18 PM   #20
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So what is your recommend lowest crossover point and crossover type you recommend for this driver. Do you think 1000hz will bypass the resonance of the amt.. or 800hz is doable without to much effect on the sound..
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