Sub Bypass compared to Low Pass Amp Setting (1 Viewer)

[bradlawson25]

Basically I have two 8" subs(with freq. response range between 20 to 400) connected to a Crown XLS1500 Amp which gets it pre-out signal from the sub woofer track. I have the HD 5.1 trailer for Mad Max. When i put the amp in "bypass" mode it doesn't have as much bass as when I put it in "Low Pass" mode set to 200hz. This doesn't make sense to me, Low Pass mode should only be allowing freq. below 200 hz, In bypass mode it allows anything that the subwoofer track is putting out. So if the sub track is putting out sound between ranges 300 to 20hz than the sub is getting all of it and there by more bass, but if the sub track is only putting out 200 to 20 hz, than bypass mode and low pass mode should sound the same.


So I can't see a situation where low pass mode should have more pass than bypass mode when the pre-out source is a subwoofer track.


Any thoughts or opinions?


Thanks

Brad

 

[Wayne A. Pflughaupt]

“Subwoofer track” as a pre-out source? What is that? What exactly is in front of the Crown, electronics-wise?


Regards,

Wayne A. Pflughaupt

 

[Al.Anderson]

What are your input connections? It looks like it Bypass mode it take a signal from both Input-1 and input-2, but in input mode it only takes input from input-1. So if you have one of your subs connected to output-2, it's not getting a signal.

 

[bradlawson25]

Sorry, the subwoofer track is what I call the "SUB" pre-out when the input is 5.1 dts, because the sub pre-out in a true 5.1 dts should ONLY be getting what the makers wanted the sub to play. I have the receiver "Sub pre-out" connected via RCA cable to the input 1 of the crown amp. The crown is in bridge mode. So the 2 subs are playing getting the same exact signal.


Thanks


Brad

 

[John Garcia]

What is the receiver's x-over set to? I'm guessing it is much lower than the 200Hz on the amp, so bypass is double filtering and causing the bass to roll off faster above the x-over.

 

[bradlawson25]

Now i am confused, bypass would not filter it at all right? Bypass just sends the signal as it is. The low pass would be filtering it. Also the receiver shouldn't be filtering it at all since it is a DTS 5.1 soudn track so it is just sending the entire SUB-Woofer Track via the pre-out to the amplifier for the sub right?

 

[John Garcia]

Sorry, yes, bypass would not add any filtering; I meant with the 200Hz filter. That doesn't explain the difference in output though.


There's a difference between LFE, the ".1" or "sub" track that you are talking about and BASS. Unless your mains are set to large and sub=yes, you are getting a filtered output, typically at 80Hz, from the receiver. The sub pre-out carries more than just the LFE audio track if you have speakers set to small with an x-over setting on the receiver. All bass below that x-over point (based on the x-over slope) from all the speakers set to small will also be redirected to that channel.


It is possible there is other circuitry involved when using the amp's x-over, which should not be necessary because the receiver should already be doing it. You want the receiver to do it as well because it will correctly blend with the mains using corresponding slopes as opposed to trying to manually blend the mains to the 200Hz x-over on the amp.

 

[bradlawson25]

The receiver is sending the same output to the amp. So the only change is the amp setting. If the amp is set to Low Pass at 200hz than it will not add any thing more than the receiver is sending it. So I don't really get why the receiver would have anything when the test is ONLY between setting the amp to LPE and Bypass mode.


After thinking about it, i am guessing the only thing is the is that the filter mode process the preout and makes it into a 4th order Linkwitz-Riley filters which uses the steeper 24 db/octave. I am thinking the processing using the Crown Amp software is why the bass sounds so much better.


But it was a good suggestion about the receiver sub pre-out setting, I differently don't want to double filter it, so i have to check that out when i get back home.