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Multi-Way Conventional loudspeakers with crossovers

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Old 18th March 2013, 12:49 AM   #121
Stevenn is offline Stevenn  Australia
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Hope i got this right, using plane of speaker front panel surface as 0 and measuring to top of dustcap:
Tweeter +2.5mm
Mid -11.5mm
Woofer -25.5mm

Thanks

Last edited by Stevenn; 18th March 2013 at 12:55 AM. Reason: Error
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Old 18th March 2013, 04:17 AM   #122
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Thanks Steve, I should have read the docco in the link I posted earlier a bit more carefully. the splview program is to be used to "normalize" the various frd files. Once you do that the phase data is much more consistent I'll upload some new ones later on, maybe this evening. That was the bit that was bugging me.

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Old 18th March 2013, 05:08 AM   #123
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Tony,
Where do I find a copy o speaker workshop? I am not sure if it has been updated in years and I looked at sourceforge and it showed no results?

Thanks for any help, just wanted to take a look.
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Old 18th March 2013, 01:16 PM   #124
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Hi Steven, it hasn't been updated for years, but is still available for download at the audua site Speaker Workshop It is also on sourceforge now Speaker Workshop | Free Audio & Video software downloads at SourceForge.net , I'm hoping someone with an interest will pick it up and start developing it again.

The crossover simulation in speaker workshop is very powerful and quite accurate (with a few caveats) I did checks of simulation versus actual final implementation and the results were very close (especially considering the final measurement was done at a different distance, in a different location on a different stand to the measurements used for designing the crossover). My Morel MTM Project

Steve, I've attached new frd files. These ones are MUCH better with respect to the phase. I'm pretty confident that these ones should be ok.

I used the splview program from Jeff's site and normalised the data from 20Hz to 30,000Hz with 2048 points for each driver. I had to cheat a bit with the SB23 and I put in the 20Hz level manually, and also two points at 15Khz and 20Khz 9db lower each than the 10Khz measurement. Without doing that it just never made it to 30Khz and the phase went crazy. It's not really that relevant past about 2K anyway.

Give those a try and also put in the offsets in PCD and see what you get. I haven't tried them yet.

Tony.
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Old 18th March 2013, 02:18 PM   #125
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OK I had a play in sw with the new measurements. Attached is what I have at the moment. Still going with the original 300Hz/3000Hz crossover points, but note no driver offsets used, just the basic frd's. This is with 2nd order bessel on the 300Hz and 4th order L/R on the 3000Hz...

The black curve is the result of the sim. The blue curve is what you get if you put that into Frequency response modeller and apply 44% baffle step (3.1db loss) with an 11" wide baffle. note that I suspect that if I do the actual baffle diffraction sim that it will have a bit of a hump around the 1Khz area where there is currently a dip, which may work to our advantage.

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Old 19th March 2013, 03:21 AM   #126
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Hi Steve, I've done a bit more playing. I've now also put baffle step data into each drivers frd's using response modeller, and put everything back into pcd including offsets.

The vertical and horizontal offsets make a little difference but not much, SW models came accross well. Z offset data is a different matter. it has a small but not bad effect for the lower crossover point, enough to be ignored, however it has a much bigger effect for the High pass cross between mid and tweeter. enough to need to consider it. SW does allow Z offset to be used so I can play around with it.

I changed the low frequency crossover point to 350Hz after comparing the non-baffle step corrected and baffle-step corrected plots. Cursor in the screen shot is around 350Hz. Blue trace is uncorrected, black is corrected.

Both non baffle step corrected and baffle step corrected files in the attachment.

note that with the new data the zobel on the tweeter may not be necessary saving a big coil if not. edit, scrub that it didn't look like it was making much difference in PCD but when I took it out in SW the difference was more obvious due to the bigger graph.

Tony.
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File Type: png baffle_step_compare.png (24.7 KB, 30 views)
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Last edited by wintermute; 19th March 2013 at 03:25 AM. Reason: add comment about zobel making difference.
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Old 19th March 2013, 05:30 AM   #127
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Thanks Tony

The problem seems to be more the initial peak in SB23NRX45-8 at about the 140Hz: i have not been able to remove this whatever I did. An L-Pad is just not practical, either.
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Old 19th March 2013, 06:45 AM   #128
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hi Steve, I wouldnt worry about it. You will probably find it is artifect of the factory measurements. They do them usually in a standard box which is not optimal for the driver. You are better off using modeled response under 200 hz. Try the baffle step adjusted frds you should notice a difference

By the way, is your plan for sealed or vented?

Tony.
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Old 19th March 2013, 08:48 AM   #129
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Stevenn,
Just remember that if a mechanical device has a mechanical resonance there is no way to electrically remove that resonance. It does not require and electrical impulse to excite that frequency and no amount of notch filtering will stop that mechanical resonance. It is just the physics of the devices we are working with. That is why we always try to keep the resonant area of a device out of band for how we are using a device, but even then all you are doing is lowering the level of excitation, but it is just lower down in db out of band, it is always there.
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Old 19th March 2013, 10:10 AM   #130
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Hi KH, do you think that the anomaly showing in the response attached is a mechanical resonance?

I'd interpreted it as a rising response typical of being in too small a box, but I guess if anything it would be more likely to be in too large a box for manufacturers measurements.

There is a tiny glitch in the impedance curve around the same place as the dip in the middle of the hump, but nothing particularly obvious.

On another note, putting in the z offset (relative to the tweeter) for the mid certainly makes it a lot harder to get decent phase matching! Looking at the cad drawing for the drivers (mid and tweeter) I estimated the offset to be around 18mm (a bit more than Steve's 14mm) This is an area I'm a little uncertain of, as my measurements took care of this (and I had pretty much time aligned drivers as well which makes it easier!)

Steve, are the tweeters flush mounted? how about the mids?? did you get 14mm because the mids are not flush?

Tony.
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