MT122 - Reverse the polarity

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Reverse the polarity

Printed From: Speakerplans.com
Category: Plans
Forum Name: MT122
Forum Description: Discussion / Questions about the MT122
URL: https://forum.speakerplans.com/forum_posts.asp?TID=96701
Printed Date: 27 March 2026 at 4:06am
Software Version: Web Wiz Forums 12.08 - https://www.webwizforums.com

Topic: Reverse the polarity

Posted By: Desert Storm
Subject: Reverse the polarity
Date Posted: 20 September 2016 at 6:35am

In setting up the sound system. Why does the compression drivers are need to reverse the polarity?

Need technical advice please, new member here.

Thank you

Replies:

Posted By: Finjby
Date Posted: 20 September 2016 at 10:35am

Not an easy question to answer briefly....but i will try.

Every 'order' of crossover slope (ie. 1st order (6db), 2nd order (12db), 3rd order (18db), 4th order (24db) etc.) introduces 45deg of phase shift.

So, if your 'top-box' has a passive 12db per octave crossover in it, then the low frequency driver and the high frequency driver will both have 90deg of phase shift at the crossover point.

When you 'sum' the combined output of both components, there is now an acoustic 180deg phase shift at the crossover point.... resulting in a cancellation (comb filter) between the low/high.

So, by reversing the polarity of the compression driver you effectively swap/invert the phase at the crossover point to eliminate the comb filter.

Your question could do with clarification, how are you measuring the system? Smaart etc? do you have a DSP crossover? what configuration are you running? further information from you, will help tailor the answers to give you more relevance and understanding.

Posted By: citizensc
Date Posted: 20 September 2016 at 11:16am

If you are using a DSP/active crossover does this apply? If im using a measurement mic + Ultradrive to do my time alignment do I need to think about this? Currently all my drivers are wired with normal polarity.

Posted By: Earplug
Date Posted: 20 September 2016 at 11:41am

With an active/digital crossover, this shouldn´t be a problem, but always best to check, some filter types will introduce more phase shift than others, eg a basic Butterworth compared to Linkwitz-Riley. FIR filters are the best, but usually only found in the more expensive DSP´s.

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Earplugs Are For Wimps!

Posted By: Finjby
Date Posted: 20 September 2016 at 11:57am

passive or active set-ups make no difference.... they are still filters and behave the same, be that in a DSP chip-set or passive network.

Plug a DSP into smaart directly (without a speaker attached) and see how the filters interact.

FIR does behave differently to IIR as the increase in latency enables you to 'bend time' and reduce the some of the traditional filter artifacts.

Always measure and decide from there, every variation of cabinet presents a different possibility of crossover interaction, you just need to be able to measure it first, then you can adjust to suit your needs.