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Multi-Way Conventional loudspeakers with crossovers

Matching driver sensitivity in a two-way
Matching driver sensitivity in a two-way
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Old 10th August 2018, 01:54 AM   #1
luigi is offline luigi  New Zealand
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Default Matching driver sensitivity in a two-way

I'm trying to design a two-way speaker using a full range driver open baffle from 250Hz up and a 10-inch driver in a sealed enclosure for frequencies below 250Hz, with a passive crossover.

Presuming both are 8ohm drivers, can I simplify things by matching sensitivity of the two drivers, or is it preferable to have the output of the woofer slightly higher than that of the tweeter? Or does mixing open baffle with sealed enclosure screw that all up?
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Old 10th August 2018, 02:10 AM   #2
TMM is offline TMM  Australia
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The only requirement is that the tweeter/HF driver be no less sensitive than the woofer. This is because a tweeter can be easily attenuated in the crossover but a woofer can't. To pad down a large woofer requires large valued, expensive components with high power handling. The components to pad a tweeter (or small FR) are comparatively smaller and cheaper.

In reality the tweeter can actually be 3-6dB less sensitive than the woofer because the woofer needs 3-6dB baffle step compensation (BSC): mh-audio.nl - Home

In a large room with the speakers placed far out from the walls you need 6dB BSC. In a small/medium size room you can get away with less BSC, 2-3dB and achieve a balanced response in-room.

On OB as long as the full range driver operates above the baffle step frequency, it can be treated like a tweeter in terms of sensitivity. If the full range operates below the BSC frequency it needs additional sensitivity to account for diffraction/dipole losses.

Last edited by TMM; 10th August 2018 at 02:15 AM.
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Old 10th August 2018, 03:00 AM   #3
googlyone is offline googlyone  Australia
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Matching driver sensitivity in a two-way
Agreed. Do yourself a favour and pick a tweeter that is 3dB or more sensitive than the woofer.

You will find that the ability to tweak the tweeter output and crossover point / slope / "tuning" is extremely important.

If you are new to this, also do yourself a favour and read up on zobel networks (for the woofer) and LRC traps (For the tweeter) to deal with the woofers rising impedance and the tweeters resonance. Getting these right makes crossover design hugely less complicated.
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Old 10th August 2018, 05:39 AM   #4
Juhazi is offline Juhazi  Finland
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This kind of system is difficult to simulate right. Real world measurements in farfield including off-axis are needed, and still also listening tests in the room where they are intended to be used. Bondary reflections are challenging between 100-400Hz especially when you have different radiation patterns for bass and FR.

Please consider making a proto with minidsp first, so you can try various xo points and slopes, even delay matching! I am quite happy of the sound of sealed 10" bass and dipole upper drivers! I found LR2 slope around 180Hz best, but it depends pretty much of the OB driver's lower end capability/distortion.
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Last edited by Juhazi; 10th August 2018 at 05:41 AM.
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Old 10th August 2018, 09:13 AM   #5
googlyone is offline googlyone  Australia
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Matching driver sensitivity in a two-way
If the OP has a minidsp, then sensitivities and crossover design is pretty much a moot point.

While I am a massive DSP XO advocate, I don't think this was the point of the question. Implementation of a passive XO does introduce design drivers around sensitivities that you just have to consider.
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Old 10th August 2018, 11:28 AM   #6
waxx is offline waxx  Belgium
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I do a similar WAW design (altough the Fr and woofer are in ported boxes) and i found while experimenting with a minidsp i borrowed from a friend in mono (same stereo amp, one channel for top and one for bass) that the bass needs to be 3dB louder than the top to have an equal response in my room. Now i'm building a 1st order passive crossover for that based on the test at 180Hz with a zorbel network on both drivers and i pad down the FR till 3dB below the sub.

But i think it's speaker and setup depending, that's why the minidsp test is a good id. So you can test and measure (i use a Behringer ECM800 microphone, a studio audio interface (even a cheap one is good) and the free REW software for that) and adapt untill you got the right setup. I'm not fond of dsp's in hifi installations (i prefer all analog), but for finding the right crossover setup this minidsp is a genious thing. I'll order one for myself soon just for that i think.

Also, measure your drivers on frequency response (.FRD file) and impendance (.ZMA file), and use that in a program like Xsim or similar software, so your electric circuit is right for your specific drivers. Without that it's a bit guessing wich circuit will be right.

Last edited by waxx; 10th August 2018 at 11:33 AM.
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