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Author Topic: X-over and dB question  (Read 1282 times)

Immanuel Kuhrt

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X-over and dB question
« on: September 14, 2004, 03:08:34 PM »

Hi - I hope it is ok, that I ask this question here.

The thing is, that I am confused about x-overs. Why is the x-over point defined as the -3dB point - and not the -6dB point? Here is a scenario as I understand things:

I want to divide the workload between a woofer and a tweeter. Out of total luck (and to keep this simple) I have found 2 drivers with the same overall spl (90db 1w/1m) - and they really match well in the x-over area (again keeping it simple). So what I need is a simple frequency devision - no level adjustments. I want to cut at 1600Hz.

So now I make a 24dB/oct (so we don't have to talk about inverting the faze) lo-pass filter on the woofer. After this the woofer will play 87dB 1w/1m @ 1600Hz. Likewise I make a 24dB/oct high-pass filter for the tweeter. Now the tweeter also plays 87dB 1m/1w @ 1600Hz.

But 87dB + 87dB = 93dB ... I get a 3dB peak at the x-over frequency. Is this just an unavoidable evil - and a good reason to use an equalizer to cut out 3dB at the x-over frequency?

I have a real time digital environment (where I am going to do the actual x-over work anyway), so I tried to find the -6dB points @ 1600Hz (48dB/oct filters) by going lo-pass @ 1494Hz and hi-pass @ 1711Hz, but this didn't give me a flat total response either.

As you can see, I am a bit confused. What would you advice me to do? Use a -3dB equalizer at the x-over point? Or can you tell me, where I maybe am wrong in my way of viewing things?
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Immanuel Kuhrt

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Re: X-over and dB question
« Reply #1 on: September 14, 2004, 04:22:41 PM »

Well, I solved my practical problem by using 2 filters both set to 1600Hz in series. This gives me a completely flat frequency response from the filter. I am happy now Smile
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