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Old 19th March 2013, 10:41 AM   #131
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Tony,
What would be really telling here would be a waterfall plot of the speakers decay over time. That is when you start to see a real resonance problem or even a termination problem with a surround or even a glue joint using the wrong adhesive. The impedance curves only show something at one place in time but not the mechanical decay times. That is why waterfall plots are so important when doing a network design at the level of accuracy you are attempting to approach. Resonant behavior of a cone or dome is something that is often overlooked or not well understood by most who are using simulation to do this development. That is part and parcel to why I said it is so important to measure real values in a real box.

Steven
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Old 19th March 2013, 10:57 AM   #132
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Have to agree on the measuring real values in real box, this is the first time I've seriously tried to simulate from published data. My simulations with real measurements were very successful. There are a number of variables here I don't fully know which makes it tricky. I think that the low frequency crossover seems pretty tolerant, but the tweeter is less so.

I may be trying to go too far, Others have reported this method working well, and I'm sure it should result in something much better than an off the shelf crossover which is what Steve was initially thinking of getting.

I can't seem to get better than 45deg separation on the phase for mid to tweeter with the 18mm offset. perhaps I should just live with that

Tony.
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Old 19th March 2013, 11:03 AM   #133
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Tony,
45 degrees mismatch is worlds better than most will ever achieve and most people would probably never have the hearing to tell what is happening. The time shift of 45 degree is not much. Remember that most people still listen to speakers with nothing but a single capacitor and one inductor in most commercial speaker systems.
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Old 19th March 2013, 12:21 PM   #134
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Me being my usual obsessive self I accidentally discovered if I use a 2nd order bessel on the mid lp and 4th order LR on the tweeter, both at 3Khz I get almost perfect phase tracking and pretty good FR as well. looks better than the symetrical 4th order LR at 3Khz.

Time for me to hang up my hat for a while though, I should post the schematics of what I have done so Steve can play with it some more

First pic is what I had got too with 2nd order bessel at 350Hz and 4th order LR at 3Khz. Second pic is the summed response.

Third pic is with 2nd order bessel at 350Hz and also on the mid at 3000hz with the 4th order LR at 3000Hz from the first pic on the tweeter. Fourth pic is the resulting FR.

Offsets used on the drivers were -18mm for the mid and -40mm for the SB23.

Tony.
Attached Images
File Type: png 350_3000_1.png (42.6 KB, 25 views)
File Type: png B2_LR4.png (21.1 KB, 24 views)
File Type: png accidental_discovery.png (45.8 KB, 24 views)
File Type: png B2_B2_LZ4.png (21.5 KB, 24 views)
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Old 19th March 2013, 12:34 PM   #135
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and here are the schematics. Knock yourself out Steve (for real world you will want to adjust to nearest standard values and see how it looks, if ok then you don't need to worry about coming up with strange values).

Third one is the one that has bessel 2nd order slope for both the high and low pass of the bandpass rather than 2nd order on the high pass and 4th order on the low pass.

z offsets to put into PCD are -18 and -40 for what I have simmed here the baffle position offsets didn't seem to make much difference but it doesn't hurt to put them in. I don't know if the Z offsets are correct however, they are my best guesses based on the cad diagrams of the drivers as to where the voice coils would be. edit: actually I haven't checked the impedance of these you have to put all of the networks into one in SW to get it to do the impedance, but you can only run the optimizer if you have a single driver (which is why I have separate networks for each driver) the optimizer in SW is great!!

Tony.

edit2: added pcd offsets screenshot.
edit3: added pcd saved file. tweaking the coil in the high pass to 140uH gives a better result I'm stopping now, I promise
Attached Images
File Type: png hp_lr43000.png (11.3 KB, 22 views)
File Type: png BP_B2_LR4_conventional.png (10.0 KB, 8 views)
File Type: png BP_B2_B2.png (8.6 KB, 7 views)
File Type: png lp_B2_350.png (5.9 KB, 8 views)
File Type: png pcd_offsets.png (25.5 KB, 9 views)
Attached Files
File Type: zip all_tweaks.zip (399 Bytes, 1 views)
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Last edited by wintermute; 19th March 2013 at 12:37 PM. Reason: add comment about impedance.
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Old 19th March 2013, 08:24 PM   #136
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Thanks Tony
Will go through in detail when I have more time later today, I am sure I will have some qsns!
Please PM me with yr address if you wish for that bottle of red.

Cheers
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Old 20th March 2013, 07:22 AM   #137
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No problem Steve, ask away and I'll try and come up with an intelligent answer, some may be a case of It just seemed to work best that way though

Tony.
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Old 20th March 2013, 07:46 AM   #138
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Tony,
When you used the Bessel filter section that didn't cause you any in band ripple in the response? That is what I understand from that filter topology. that it causes in band ripple around the crossover point. Just asking a hypothetical here,

Steven
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Old 20th March 2013, 09:26 AM   #139
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HI Tony
First of all, a big thank you for all yr work. Very much appreciated and way beyond anything I was expecting!
Interestingly, when I compared my own C, Z and L values with yours, they were very close on most components (but way off on a couple).
When I put your values into PCD with csp file, i get graph below (assuming I have components in right place on PCD circuit).
My last attempt at PCD is second graph which appears to have a flatter summed response.
Woofer LP = second order filter
Mid HP = second order
Mid LP = second order
Tweeter = second order parallel

Is this difference between the two the difference between SW and PCD?
So which is best to use?

Cheers
Attached Images
File Type: gif Graph2 PCD with SW values.gif (28.9 KB, 7 views)
File Type: gif Graph3 SN response.gif (29.3 KB, 6 views)
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Old 20th March 2013, 12:02 PM   #140
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Quote:
Originally Posted by Kindhornman View Post
Tony,
When you used the Bessel filter section that didn't cause you any in band ripple in the response? That is what I understand from that filter topology. that it causes in band ripple around the crossover point. Just asking a hypothetical here,

Steven
Hi Steven, You aren't thinking of a chebychev filter are you? Bessel does have a bit of a hump at crossover (similar to butterworth but not as much) which can be useful if you have a hole in your response.... The usual complaint about bessel is that the rolloff starts earlier (so you have a wider area of summation, but for 2nd order the rolloff actually starts later than for a LR. 4th order the bessel rollof starts earlier and is deeper. I used 4th order bessel on my MTM's and I'm very happy with it.

The main advantage of bessel is that it has perfectly flat group delay in the pass band, and has the best phase response out of LR, Butterworth and Chebychev filters.

Attached are two comparisons of bessel and LR slopes. Black is bessel and blue is LR. I find it interesting that the 4th order bessel still will sum with a hump compared to the LR, it seems that it would be the opposite when you look at the slopes (the second order seems intuitive that it will have a hump) unless I'm remembering incorrectly and 2nd order has a 1.5db hump and 4th order has a 1.5db dip, that would seem more intuitive......

Tony.
Attached Images
File Type: png 2nd_bessel_vs_LR.png (17.3 KB, 5 views)
File Type: png 4th_bessel_LR_comparison.png (17.6 KB, 3 views)
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Last edited by wintermute; 20th March 2013 at 12:04 PM. Reason: forgot attachments.
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