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811B D250P-8 : 2nd order x-over graphs ...

24.140.98.34
Posted on July 27, 2014 at 10:02:49
deathtube 667






Been trying to come up with a decent sounding x-over for 811B Altec horn D250P-8 driver and MCM 55-1220 12" woofer.

The recommended x-over for the D250P-8 is 2nd order 1600Hz, so I used that and a 2nd order 500Hz crossover for the woofer.

I selected the crossover values based on the impedance at the x-over frequencies and used Zobels on the horn & woofer to get a flat impedance curve.

There is a compensation circuit and 12dB series padding resistor on the horn.

The speaker was measured at the listening position ear level.

Been listening to this for a few days and it sounds alright.

Subjectively better than my previous efforts.




 

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RE: 811B D250P-8 : 2nd order x-over graphs ..., posted on July 27, 2014 at 15:09:48
John Sheerin
Audiophile

Posts: 524
Location: PA
Joined: July 28, 2003
 Nice work. If you want to take the next step and get a better transition through the crossover (looks like you could use a few more dB of output as well as some phase adjustment), I'd suggest creating a target curve for each driver and try to tweak the crossover to match the measured curves to the target curves. If you have measured curves of the drivers, you're half way there - now you just need measured impedance curves. I don't know Arta, but I know in Speaker Workshop and a lot of other measurement / xover simulation software you can create a target, create a network, have your measured response and impedance of the raw drivers and then have the program optimize the network to try to get the response after the xover to match your target. Then you can sum the drivers together and tweak a bit more try to get the best match between the drivers. Then you go back and change everything to the closest values of components you can buy and see how close you can get.

Or, if you have the drivers' voice coils aligned at the moment you might try pushing the tweeter back from where it is and seeing how the response at the crossover changes - might help fill in some output and smooth the ripple you have at the moment.

 

RE: thanks ..., posted on July 27, 2014 at 15:43:03
deathtube 667
 ARTA does have a target response function, but I have not tried it yet.

I have the impedance plots for the woofer and horn measured free air and in the enclosure/horn.

Part of the issue might be the quality of my woofer test box.

I'll try your suggestions and see if I can improve the results.

 

RE: Good to see you back here ..., posted on July 28, 2014 at 08:37:22
Paul Eizik
Audiophile

Posts: 2120
Joined: September 15, 2001
 John

...still bringing Big Science to the wild frontier!

Regards from the Chicago Horn Club

Paul

 

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