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Old 5th February 2013, 02:47 PM   #11
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Quote:
Originally Posted by flowwolf View Post
Well, then which subwoofers would you recommend me for low BL distortion @ hi xmax? prices around 300$.

maybe you have custom build subs. i would take a look at them then.
One of the best 18" in regard to low BL distortion and hi Xmax is the B&C18SW115, but it's price has gone up to more than double what you want to pay due to cost of the neodymium magnet structure.
A close second is the ceramic magnet BC18TBW100 at around $349.

You can see distortion results using the B&C18SW115-4 in bass reflex and tapped horn enclosures here:

Tapped Horn Vs. Bass Reflex Case Study

I have never pursued open baffle cabinets, but I can say that a pair of B&C18SW115 run open air driven to 15 mm excursion at 20 Hz have very little distortion and enough output to make me feel ill for quite a while after only a short exposure during break in.
The suspension did loosen up a small amount (perhaps 2 mm) after several hours running around Xmax.

Art

Last edited by weltersys; 5th February 2013 at 02:50 PM.
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Old 5th February 2013, 05:12 PM   #12
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Nice drivers! with good sensitivity.
(It would be great if manufacturers could share the details of copper wires, diameter etc..)

Thanks for the info.
Never used tapped horns, have to do some research before i can comment on it. Pretty backwards mounting

What kind of software is that you used there? If there are distortion measurements for pure sine waves, they are so interesting

p.s. this is the first time I saw h0 as "EtaZero" in a datasheet
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Old 5th February 2013, 05:32 PM   #13
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I continue..

One would try to use an underhung design, but have it's own deficiencies for extreme huge top plates, let's see a flux curve given by FEMM for a 45mm top plate design (average steels, magnets):

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very good indeed! but can you see that it's not entirely linear? what if you want a design with more than +-14mm?
It won't succeed unless you use high quality materials like pure iron. It start to saturate and you have to increase vcid this results in higher cost, but IMO still the best solution.

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Attached Images
File Type: png 2_uh.png (86.3 KB, 105 views)
File Type: png 2_uh_flux.png (8.3 KB, 105 views)
File Type: png 2_uh_blcurve.png (38.0 KB, 105 views)
File Type: png 2_uh_blcurve2 10mm.png (43.1 KB, 106 views)
File Type: png 2_uh_blcurve3 14mm.png (44.4 KB, 106 views)
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Old 5th February 2013, 05:43 PM   #14
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Next an XBL design:

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not bad, better than overhung but not as good as underhung. however, it is possible that it generates more high order harmonics than UH/OH. this is why the THD is not representative. It reveals that something has a certain degree of harmonic distortion, but what harmonics? 2nd 3rd? Here high harmonics are generated (in theory) but (i'm skeptical) i would be curious in real-world examples.
btw. i think the xbl is a clever one, but let's see what happens when the voice coil is 'mis-wound' :

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see the peak in the BL curve?
it requires careful engineering. IMO top plates should not be made of laminations like this:

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This might worsen the reluctance and more flux will flow on the low reluctance path.


The problematic part in a finished subwoofer that you won't be able to authentically measure BL distortion because of the suspension. It requires special machines. Therefore i'm trying to predict BL distortion as much as possible.

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Attached Images
File Type: png 2_xbl.png (84.0 KB, 104 views)
File Type: png 2_xbl_flux.png (10.2 KB, 103 views)
File Type: png 2_xbl_blcurve.png (45.5 KB, 103 views)
File Type: png 2_xbl_blcurve2 10mm.png (48.1 KB, 104 views)
File Type: png 2_xbl_blcurve3 14mm.png (49.7 KB, 103 views)
File Type: png 2_xbl_blcurve_bad.png (44.6 KB, 103 views)
File Type: png 2_xbl_bad.png (80.9 KB, 103 views)
File Type: png 2_xbl_flux_bad.png (12.5 KB, 103 views)
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Old 5th February 2013, 05:56 PM   #15
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p.s. please note that typical xbl BL curves are compared with the average BL curves of overhung designs.
at post #10 there is a BL curve for a well optimized sub:

Click the image to open in full size.
(i.e. if you compare the xbl with an average overhung, the xbl is winner)
Attached Images
File Type: png motor01.png (73.1 KB, 102 views)
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Old 5th February 2013, 05:58 PM   #16
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Quote:
Originally Posted by flowwolf View Post
Nice drivers! with good sensitivity.
(It would be great if manufacturers could share the details of copper wires, diameter etc..)

Thanks for the info.
Never used tapped horns, have to do some research before i can comment on it. Pretty backwards mounting

What kind of software is that you used there? If there are distortion measurements for pure sine waves, they are so interesting

p.s. this is the first time I saw h0 as "EtaZero" in a datasheet
OOps, gave you the wrong link. The distortion figures are in post #12 of this one:
Keystone Sub Using 18,15,&12 Inch Speakers

I used the Smaart program to look at the actual distortion speakers have when driven with a sine wave tone , an example showing 35 and 45 Hz at 77.5 volts(1500 watts in to a nominal 4 ohms) is posted below.
Using the distortion calculator harmonic distortion levels can be determined.
Slowly.
Attached Images
File Type: png Distortion Tests.png (99.1 KB, 16 views)
File Type: png Distortion Calculator.png (52.1 KB, 14 views)

Last edited by weltersys; 5th February 2013 at 06:06 PM.
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Old 5th February 2013, 06:17 PM   #17
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Super info.

Both 2nd & 3rd harmonic @ -28dB and 4nd & 5th harmonics @ -40dB, 7th @ -51dB, close to inaudible above 400hz.
This is at xmax i suppose?
The tricky part is that you cannot tell the contribution from the suspension.
Does a Klippel reveals that?
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Old 5th February 2013, 06:58 PM   #18
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Quote:
Originally Posted by flowwolf View Post
Super info.

Both 2nd & 3rd harmonic @ -28dB and 4nd & 5th harmonics @ -40dB, 7th @ -51dB, close to inaudible above 400hz.
This is at xmax i suppose?
The tricky part is that you cannot tell the contribution from the suspension.
Does a Klippel reveals that?
I really have no Klippel experience, just have heard others write about it, and how the B&C neo drivers have the best BL charts.
They also use a very interesting coil winding topology, the details of which I have forgot.
I suspect B&C drivers are designed with simulations, then tested to see how they vary from the (proprietary) sim, after many tests the sim can be tweaked to closer match reality.
Fewer test iterations are probably required for each new model as the software is tweaked generation to generation.

The Keystone excursion maxima is right around 45 Hz, at 77.5 volts it would be around Xmax (Xvar), 30 mm peak to peak.
At 35 Hz, the excursion is probably only about 8mm peak to peak.
The suspension really puts the brakes on excursion above Xvar, the BC18SW115-4 would probably burn up before it hit Xlim.
Although I did not measure distortion, the driver sounded OK at 120 volts 60Hz, three times in a row (it was testing mistake), about 1 second per time.

Last edited by weltersys; 5th February 2013 at 07:00 PM.
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Old 5th February 2013, 07:38 PM   #19
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Interesting, Weltersys,
i will read through the Keystone Sub thread you posted before.
Understand. sure they have their proprieraty stuff for sims.

Progressive spiders are extensively used in subs.
According to Klippel's paper

http://www.klippel.de/fileadmin/klip...arities_00.pdf ) and Hutt's patent
https://docs.google.com/viewer?a=v&p...NTNiY2Y5MDUyMw

a regressive spider is better in linearity.


At worst case the distortion of the suspension could be measured separately. A spider compliance measurement machine may be present at manufacturers. I'm wondering whether it is able to measure distortions too.

I may have an idea about better coil winding topology, i will come up with the details in a few posts.

--------------------------

Here is a split-coil model.

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First I tried it on the existing flux curve of the optimized subwoofer and got worse results:

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was sceptical and did the Bl curve evaluation in FEMM, the result were the same:

mm BL
5 5.54122
4 5.70404
3 6.03851
2 6.35937
1 6.46567
0 6.48344

then I realized that a split-coil model is quite sensitive, it does matter were you put the coils and how:
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so, here is a newer FEMM model for split coils, and the flux curve, the result is generally good:

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Attached Images
File Type: png 2_sc1.png (66.0 KB, 91 views)
File Type: png 2_sc1_blcurve.png (43.5 KB, 91 views)
File Type: png 2_sc1_blcurve2.png (43.0 KB, 92 views)
File Type: png 2_sc2_flux.png (10.8 KB, 91 views)
File Type: png 2_sc2_blcurve.png (44.2 KB, 91 views)
File Type: png 2_sc2_blcurve2.png (50.2 KB, 93 views)
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Old 7th February 2013, 05:42 AM   #20
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Good work with that keystone design Art,
Since i'm not exclusively interested in OBs, i may build the design one day


---------------------------------------

Next a JBL differential drive structure:

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As expected, the even ordered harmonics are very low in level due to the symmetry,

Note that the flux curve is evaluated for 0A. If we set the current to 1A, we basically arrive to the same BL curve as would give by FEMM:

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The BL curve is no longer symmetric as well as the flux curve.
(at post #1 i mentioned that the BL curve evaluated by FEMM is not symmetric, and also depends on the direction of the current. however, in real world we never use loudspeaker drivers with DC current, therefore - IMO - evaluating the BL curve without taking the DC currents into account is not problematic. i.e. we can evaluate the flux curves for 0A. so the application won't take the the coil's own field into account, this is why it's simplified)
Attached Images
File Type: png 3_jbl.png (77.1 KB, 71 views)
File Type: png 3_jbl_flux.png (7.9 KB, 71 views)
File Type: png 3_jbl_blcurve.png (48.4 KB, 71 views)
File Type: png 3_jbl_blcurve2.png (46.4 KB, 71 views)
File Type: png 3_jbl_blcurve3.png (43.2 KB, 71 views)
File Type: png 3_jbl_blcurve2_1A.png (47.1 KB, 71 views)
File Type: png 3_jbl_blcurve3_1A.png (42.8 KB, 71 views)
File Type: png 3_jbl_flux_1A.png (7.9 KB, 71 views)

Last edited by flowwolf; 7th February 2013 at 06:01 AM.
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