What do you want in a 6.5... Pick a FR any FR... A few targets inside - diyAudio
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Old 5th June 2007, 09:45 PM   #1
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Default What do you want in a 6.5... Pick a FR any FR... A few targets inside

Click the image to open in full size.

The frame in question, I was getting the measurement of the spider landing:
Click the image to open in full size.

Treated paper cone top, wool cone bottom. I'm leaning towards the wool. This is for a 6.5" midwoofer I'll fill you in a bit more as things unfold. I'm looking at a 31mm tall coil 1.5Ē dia coil, 7mm tall gap, 126mm diameter magnet 40mm tall with a short path inside the magnet at the least and a phase plug in addition to venting under the spider. I was playing with an ~7mm of xmax underhung design as well but I favor this one. This BL curve should be a bit more symmetrical believe it or not, saturating a pole this far makes the magnetic strength in the gap increase as you head deeper into the motor. You would have to combat that by rounding over the ID of the top plate and that sounds like trouble waiting to happen.

If you are thinking: WTF is he thinking with such a large magnet?
I want to test to see if its the magnet quality, or the steel quality that is leading to the lower than predicted BLÖ Not to mention this much xmax chews up a lot of magnetic strength (neo mags cost a lot more or I would use them).

E/M target:
Re 5.38 ohms
Rms ~2 NS/m or less
Cms ~.82mm/N
Mms ~21g
Le ~.6-.9 depending on how close I can get an off the shelf copper short...
Sd ~126 cm^2
Pe ~200W (Possibly over inflated butÖ I think it might take it)
SPL ~88.4dB/w, 87.13 dB/w, 84dB/w (see below)

Now the BL is where I'm a bit shaky. If everything is perfect 10.6 is what I'll get... I'm expecting more along the lines of 9.3 being most likely, and if it is like something out of my worst nightmare... were talking about 6.5 Tm. If the BL does end up this low, it is the steel causing the problem and I will be left with a lower sensitivity midwoofer that actually likes to be sealed, unlike the other versionsÖ It still looks rather nice though, although it is a bit power hungry.

I'm sure the suspension won't make it to 12mm so I won't even try calling it that... I guess we can hope and prey thoughÖ It never hurts to make the useable BL a little flatter and I donít see this unit being used

I'm going to also look into the price for Kertonite treatment through about 80% the thickness of an aluminum cone... I have a felling it would do pretty well, it is at least worth looking at and if its comparable to anodizing it should carry high value (especially if ceramic-like performance results). http://www.azom.com/details.asp?ArticleID=1438


Anyways back to studying for my last final. I'll get some more info up after this quarter is over. I can't wait to be distracted by feedback
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Old 6th June 2007, 09:19 PM   #2
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Default Re: What do you want in a 6.5... Pick a FR any FR... A few targets inside

Quote:
Originally posted by OlogyAudio
If you are thinking: WTF is he thinking with such a large magnet?
That's exactly what I thought the first time I saw the W17RC38 from Silver Flute.
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Old 1st July 2007, 10:37 PM   #3
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I should be done with the sample Tue if everything keeps on track and I'll see where this goes from there.
I'm trying the bottom cone (wool cone), that FR was with it using a dust cap so I'll see how it behaves with just the phase plug. It wouldn't be too hard to try some other different cones, just time consuming. I have high hopes for this variant though.

The dip at 350hz is an artifact of measurement by the way.
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Old 9th July 2007, 04:07 PM   #4
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Just one day away I hope...
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Old 9th July 2007, 06:09 PM   #5
MarkMcK is offline MarkMcK  United States
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Not quite sure I am following this thread . . . Perhaps the "FR" in the title means something other than full-range. Almost one Le indicated in the design specifications. Measurement graphs provided show high frequency limits at 6 or 7 kHz. A bit short of what most would consider full range.

Is this going to be a woofer in a two-way system? If so, then if the off-axis response holds, this is not a bad frequency to cross to a dome tweeter. Most dome tweeters produce frequencies below 9 kHz in the decay region. The highest frequencies and lowest frequencies are smeared in time (with the low frequencies lagging). I have seen a couple of dome tweeters that did hold together (onset and decay responses) down to 6 kHz.

This is always assuming that the response graphs provided are high resolution and have not been excessively smoothed. I am a little skeptical of the smoothness in the stop band. Very rare to see this even with wool cones.

Best of luck to you with your project. I applaud your diy reach and your skill at mounting cones and voice coils. Just curious, do you have access to a manufacturer's assembly jigs?

Mark
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Old 9th July 2007, 07:08 PM   #6
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Sorry about the confusion I was asking which frequency response (FR) was preferred. This is intended to be used as a midwoofer in a 2 way. Iím not sure what the extent of the smoothing is but given that the upper frequencies are fairly stable looking Iím sure there is some. I decided to use the wool cone (bottom graph) since under 2khz it is substantially flatter so Iím hoping this will translate into less linear distortion. I would guess the crossover point will need to be under 2.2khz just from the graph but its hard to tell with incomplete information. The frequency response is also likely to change quite a bit from that graph just due to the addition of a phase plug.

Iím toying with the idea of using some never before used in speaker cones (to the best of my knowledge) advanced plastics/composites for the cones but Iím sure that will be quite a challenge to get a company to work with me on that one and not charge a few arms and legs more than I haveÖ

The short path is under the top plate, on the outside of the voice coil windings and is 6mm thickÖ Iím not sure what that will do to the Le exactly (it would have more impact as a pole sleeve) but given that the pole was pretty close to saturated with this voice coil diameter I decided to opt with an extended pole and an extra thick external short path instead of a T pole and a 1-2mm thick short under the T and cap.

I canít wait to see my baby monster assembled so I just had to post more pics.

I have access to a manufacturer though for assembling jigs I find that square wire works great as a spacing gauge (round works too with a few more inserted into the gap to help get the better concentricity tolerance needed). I find that a 0.25-0.30 mm radius between the coil or former and the steel for midranges yields good results and Iím a bit paranoid and step it up to .4mm with the larger subwoofer designs Iím working with.

I donít have access to any powerful dynamic fluid and thermal modeling programs but Iíd love to see exactly how cooling of the coil changes as the gap width changesÖ Anyone out there have something like this in their lab?
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Old 10th July 2007, 04:38 AM   #7
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How do they damage a voice coil in shipping? I guess it got ran over by a truck?
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Old 11th July 2007, 04:59 AM   #8
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I can't hold back anymore... No t/s or FR yet but hopefully tonight...
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Old 11th July 2007, 05:03 AM   #9
sqlkev is offline sqlkev  United States
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Quote:
Originally posted by OlogyAudio
Click the image to open in full size.
I can't hold back anymore... No t/s or FR yet but hopefully tonight...

when you're done with these prototypes, I'll forward you my address


Are you thinking of releasing these drivers to the mass market any time soon? Target pricing?
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Old 11th July 2007, 05:23 AM   #10
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Soon (2-3 months?), if I could get 100+ out of the door before they can be put together somehow (1 month-ish)
I will have to take a look at the FR and t/s first though to make sure there isn't anything wrong.
Being a student puts a damper on things a tad with so much going on right now.

Can I discuss pricing here? I have a feeling that would be more suited for a group buy link? Iím almost always on AIM SN: OlogyAudio
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