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811B 2-way: OPA227 2nd order active x-over ...

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Posted on August 13, 2014 at 19:09:04






Got an active 2-way x-over with OPA227 op amps together for 811B/D250P-8 & 55-1220 mono speaker project.

Used target acoustic response in ARTA to set 2nd order 1.2KHz Butterworth HP LP slopes, then measured at listening position/ear level/9ft back from speaker.

The LP crossover was right on at 1.2KHz , but the 811B horn was crossing over at 800Hz.

I had to adjust the electrical HP to 3.18KHz to get the acoustic HP of 1.2KHz.

Not sure why the horn response was off by so much and the woofer was on target.

I moved the horn back 4" on the woofer box in a crude attempt to time align the drivers.

Just listened to some familiar music tracks until the woofer and horn seemed to blend together OK.

I would guess that the horn driver is about 8" back from the woofer voice coil.

I am aware there are more exact ways of doing this, but have not tried them yet.

Not sure the exact phasing at the x-over point either.

Electrically, the LP & HP are 180 out of phase at the crossover point as measured in ARTA.

Not sure what happens in room at the listening position.

Playing around with the comp. cap and padding. Using .47uF/25 ohm now.

 

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RE: 811B 2-way: OPA227 2nd order active x-over ..., posted on August 14, 2014 at 11:18:24
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
Hi DT,

As I recall, on a ALTEC A7-800, they usually move the 811B mounting bracket 4 inches back from the front face of the 825 enclosure, whereas on a A7-500, the 511B horn mounting bracket is positioned flush with the front of the 825 enclosure.

Have fun experimenting.

Jeff Medwin

 

RE: 811B 2-way: OPA227 2nd order active x-over ..., posted on August 14, 2014 at 14:17:32
Posts: 892
Joined: June 16, 2006
DT

How are you doing that with ARTA? I have ARTA but I can't get it
to do anything like that. But then I don't have a registered copy,
could that be the problem?

Your Sallen-Key is looking nice though, still working on mine,
waiting on parts.

Always parts:)

Cal

 

RE: 811B 2-way: OPA227 2nd order active x-over ..., posted on August 14, 2014 at 17:52:29
Page 62 in ARTA user manual.

You also have to set an overlay of your microphone measurements.

Make sure to set the preamp gain, amp gain and microphone sensitivity.

If you don't have a mic calibrator, try to use data from the user manual.

The main thing is to get a frequency plot of each driver against the target filter response.

 

Thanks I'll give it a try. nt, posted on August 15, 2014 at 11:49:33
Posts: 892
Joined: June 16, 2006
.

 

RE: 811B 2-way: OPA227 2nd order active x-over ..., posted on August 15, 2014 at 13:20:28
My idea was to do a scaled down 2-way similar to Model 19.

The MCM 55-1220 can produce some low notes for a 12" woofer as seen on the graphs.

I am tempted to order another one of those.



 

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