Why use Hi-Pass on amplifiers for motorcycles

Nocage

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I have got several emails from folks asking why to use Hi-Pass when setting up theirs Arc Audio MPAK 11-12 setups. One guy had a car audio company do his install and they set it up with full pass, he was not happy with the sound or volume. He took it back to them and they called me and after setting it up correctly for a motorcycle...everybody is now happy and smiling.

I did a write up on this and wanted to post it to help folks understand whats happening and what it affects.

Why Hi-Pass rather than Full pass?

Setting the amp on Full Pass is going to hurt both the sound quality and the volume.

The reason it will hurt sound quality is that Full Pass amplifies all of the signals to the speakers (20HZ to 20k HZ) The Moto 602 has a Frequency Response of range of 65Hz - 20kHz. In real life though they effectively and efficiently reproduce sound in the 100Hz to 14kHz range. (the human ear does not hear much of anything above 14kHZ) So your sending signals in the 20Hz to 90Hz (sub bass sound) range to your speakers to reproduce and they cannot reproduce these sounds correctly and what you are going to hear is a muddled sound on the lower end, not the crisp mid bass and upper bass that these speakers will produce (100Hz to 400Hz) It's going to cause distortion that will affect the entire sound range, not just the lower end. So you want to set your amp to Hi-Pass and set your Freq. to 100-110. That will stop the signals lower than 100-110Hz from being amplified and sent to your speakers.

The reason it will hurt Volume is that your amp applies the wattage it produces to whatever range of Freq. you tell it to reproduce. 20Hz thru 20kHz. Reproducing sounds in the sub bass range 20Hz to 80Hz takes 4-5 times more power to reproduce than sounds in the 100kHz and up range. (There is a reason Sub Woofers eat so much power to really sound good) So in full pass your wasting a good portion of your amps power on sub bass Freq. that your speakers cannot reproduce and that you cannot hear at speed on a bike. That mean that the power to reproduce sounds that you can actually hear at 80 MPH on a sled is going to be considerably less.
 
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Very well stated and explained! NICE JOB! Makes a good understanding of the reasoning for these settings.
 
Thanks for that info. I'm in the process of upgrading my audio system. The new amp has 3 settings, and everywhere I looked it said to put it on the HP setting, but no one explained why. Thanks for the post.
 
Great info. Question though this is all for the amp set up. What about teh HP/LP filters on the head unit? Sony 5000 with Arc Audio MPAK 11? Should they just be off and let the amp do the cross overing?
 
Great info. Question though this is all for the amp set up. What about teh HP/LP filters on the head unit? Sony 5000 with Arc Audio MPAK 11? Should they just be off and let the amp do the cross overing?
Use either one... personally I would use the head unit... let the amp work free of its filters/crossovers.... I use my DSP for crossovers and run the amp at full range

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