Crossover Question

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Banthapudu
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Joined: Tue Feb 16, 2021 12:33 pm

Crossover Question

#1 Post by Banthapudu » Thu Feb 18, 2021 12:01 am

My First Post!
I built an Omni15 (2 12's, no tweeter) and did my best to follow the instructions to the letter. This is the first speaker cabinet I've attempted, and so far I'm very pleased with the results, but I'm not sure I've got it 100%. I've played bass through it full volume maybe 4-5 practices, and then the first issue showed up. The midrange speaker was buzzing. I figured it was breaking in and cone excursion was increasing, making contact with the baffle, so I installed a spacer ring to give some clearance, and it solved the issue. But I started to feel like the mids and highs were lacking, like it wasn't keeping up with the low end. So I ran a sine wave tone generator through it, sweeping across the frequency spectrum, expecting the mid horn to disappear around 3-500 hz, but I can hear a response all the way down to 50 Hz and lower. I'm pretty sure I wired it up correctly per the directions...omitting
the .45mH coil and 5.6uF cap, making the midrange filter a high pass. Could I have fried the crossover somehow? Maybe that's when the buzzing started, since it started playing the low frequencies? But it seems like blowing a cap would just open the circuit and no sound at all would happen through the mid speaker?
Any help would be greatly appreciated...

Grant Bunter
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Re: Crossover Question

#2 Post by Grant Bunter » Thu Feb 18, 2021 2:16 am

But I started to feel like the mids and highs were lacking, like it wasn't keeping up with the low end
Is this in your plans in the on the first page?
the 4 ohm impedance gives 3dB higher sensitivity from the woofer section
That will give the woofers some advantage over the mid driver from the outset.

What mid driver did you use?
Adding a spacer ring changes the relationship of the phase plug extension relative to the driver (unless you also added a slightly smaller 1/2" phase plug extension as well) which alters the mid driver performance I would have thought.
When you had it apart, where there any marks on the mid driver from where it was contacting the mid horn?

Pics showing how you laid the boards out and what they look like would be also be handy...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

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Bill Fitzmaurice
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Re: Crossover Question

#3 Post by Bill Fitzmaurice » Thu Feb 18, 2021 7:51 am

If you play sine waves through the cab it may seem like low frequencies are coming from the mid because they radiate omni-directionally below 300Hz. The only way to be sure of what's coming out of the mid driver is to disconnect the input to the low pass filter.

Banthapudu
Posts: 5
Joined: Tue Feb 16, 2021 12:33 pm

Re: Crossover Question

#4 Post by Banthapudu » Thu Feb 18, 2021 8:03 am

Great points, all...thanks for the replies and the good ideas.
The drivers are 2 Deltalite II 2512's, and the 6" is the Eminence Alpha 6CBMRA.
I don't remember seeing any marks on the 6" driver when I installed the spacer.
I didn't add anything to the plug, as I was trying to ensure clearance.
I'll post pics of the boards soon.
Bill, excellent point...I'll disconnect the low pass input and try again

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Bill Fitzmaurice
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Re: Crossover Question

#5 Post by Bill Fitzmaurice » Thu Feb 18, 2021 9:12 am

Buzzing could be coming from cabinet parts vibrating as well. You'd trace that with a sine wave at a frequency that causes the buzzing.

Banthapudu
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Re: Crossover Question

#6 Post by Banthapudu » Thu Feb 18, 2021 10:18 am

Curious about what frequency the rolloff should start attenuating low end response for the midrange...
I'm using the high pass crossover for the mid-only (no tweeter) configuration, 22uf and 33uf caps, and 5 mH inductor...
high pass for mid horn.png
high pass for mid horn.png (14.3 KiB) Viewed 262 times
Same question I guess for the woofer crossover point...1.1mH ind and 66uF cap...
Low Pass for Woofers.png
Low Pass for Woofers.png (11.43 KiB) Viewed 262 times

Banthapudu
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Re: Crossover Question

#7 Post by Banthapudu » Thu Feb 18, 2021 11:36 am

I isolated the woofer and horn sections and checked them separately by ear..no spl meter..
I believe the high pass is working as it's supposed to ...rolls off quickly around 200Hz, blocking low end as it should.

Woofer section doesn't seem to roll off the highs until around 2khz...speakers are good to 4khz per the published curves, so the crossover is doing something, I just expected it to be lower, around the crossover point of the horn.

Does this sound like it's functioning as expected?

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Bill Fitzmaurice
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Re: Crossover Question

#8 Post by Bill Fitzmaurice » Thu Feb 18, 2021 12:27 pm

It looks OK. The low pass is around 500Hz, the high pass around 300Hz. The low pass is higher than 300Hz to compensate for where the woofers are placed, which itself acts as a low pass filter. The reason you still hear them at 2kHz is due to their rising sensitivity in the mids.

Banthapudu
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Joined: Tue Feb 16, 2021 12:33 pm

Re: Crossover Question

#9 Post by Banthapudu » Thu Feb 18, 2021 1:19 pm

Thanks for all the help!

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