SLA Pro X-over - in a tight, can i do this?

Short and Transmission Line Arrays for Pros
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tvent
Posts: 85
Joined: Sun Sep 26, 2010 4:29 pm
Location: Helena, AR

SLA Pro X-over - in a tight, can i do this?

#1 Post by tvent » Wed Sep 25, 2019 10:50 am

I have some off-the-shelf 12db 3.5k high-pass crossovers (Dayton Audio from Parts Express - $7 or so each... cheap but simple stuff.)

I'm in a time bind right now since EVERYTHING i've ordered since last Friday has either been delayed or just flat out not filled completely, which has me in a pickle.
Can I use these crossovers for the tweeters in the SLA Pro (2x6)?

I do have some 30 Ohm and 4 Ohm resistors I could wire into it to make it like the plans, but I don't have the crossovers in front of me as I type this to verify the Cap & Coil values of the pre-rolled crossovers.

My goal is to run the 2x6's with the 4x6's simultaneously if that makes a difference.

Help much appreciated.

Thanks,
Tim
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

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Bill Fitzmaurice
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Posts: 27418
Joined: Tue May 02, 2006 5:59 pm

Re: SLA Pro X-over - in a tight, can i do this?

#2 Post by Bill Fitzmaurice » Wed Sep 25, 2019 11:00 am

Off the shelf high pass filters will not work with the capacitive load of piezo tweeters. For temporary use you can run the tweeters without a high pass filter, but the 4 ohm resistor must be in place to protect the amp.

tvent
Posts: 85
Joined: Sun Sep 26, 2010 4:29 pm
Location: Helena, AR

Re: SLA Pro X-over - in a tight, can i do this?

#3 Post by tvent » Wed Sep 25, 2019 12:27 pm

Thanks Bill!
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

tvent
Posts: 85
Joined: Sun Sep 26, 2010 4:29 pm
Location: Helena, AR

Re: SLA Pro X-over - in a tight, can i do this?

#4 Post by tvent » Wed Sep 25, 2019 9:13 pm

Ran with it for rehearsal tonight.
The 4 ohm just inline seemed to really knock the piezos down and tame them very well.
Working great so far.
Thanks again!
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

User avatar
Bill Fitzmaurice
Site Admin
Posts: 27418
Joined: Tue May 02, 2006 5:59 pm

Re: SLA Pro X-over - in a tight, can i do this?

#5 Post by Bill Fitzmaurice » Wed Sep 25, 2019 9:44 pm

The 4 ohm resistor has no effect on the piezo response. The reason for having it is that the impedance of piezos decreases as frequency increases, to well below 1 ohm in the ultrasonic frequencies. That can cause potentially damaging oscillation in an amp that's doesn't have an inductive coupled output to protect it from that possibility. The resistor insures that there will not be less than a 4 ohm load at any frequency.

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