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After reading some of the threads on here and looking at my own equipment, I'm unsure about one particular crossover that gets mentioned. I'm curious about the one that is "built-in" to many receivers thats usually between 80-120Hz and is settable on some (i.e. denon)


I have a Sony STR-DE945 and am using the following settings


Subwoofer: on

Front: small

Front crossover >60Hz

Center: small

Center crossover >90Hz

Rear: small

Rear crossover >90Hz


My understanding is that these settings will send the LFE and the bass from the other channels below the crossover frequency to the subwoofer.


So where does that 80-120Hz crossover fit in to the picture? I find no mention of it in my manual or on the internet anywhere.


Also, my understanding is that if all speakers are set to Large they receive all bass information and only the LFE goes to the sub (again assuming the subwoofer is on...I know LFE goes to the mains if the sub setting is off). However, I notice that on sources without an LFE channel (i.e. CD Player, VCR, Prologic DVD's, etc) I still get output from the subwoofer with the speakers set to Large. How is that output generated? (i.e. is it a copy of the bass that goes to the other channels or something?)


Thanks in advance

Rob
 

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Rob,


Most receivers and pre-pros have much simpler crossover designs than your Sony. They use the same high-pass frequency for all of their speaker channels. 80Hz happens to be the crossover frequency chosen by THX for their recommendations and is used in equipment that they certify. Smaller speakers tend to have worse low frequency response, so using a slightly higher crossover is reasonable, too. There's nothing magic about any specific crossover frequency except insofar as it is appropriate for your own speakers.


Whether and how much of the lowest bass frequencies are copied to the receiver's subwoofer output when you have specified that your main speakers are large is a design choice in the receiver. I'm not familiar with the DE945, so I can't comment on its details. However, it is generally the case that a subwoofer will be able to reproduce much lower frequencies than any full-range speaker, so it is reasonable to use it.


Purists would probably object to such an uncontrolled crossover. There's no way to know how the large speakers roll off in the lowest octaves, so you'll get some enhancement in the frequency range where the subwoofer's output overlaps the mains'. Most people enjoy a slight bass enhancement, however.


Another concern is that the wavelengths of the lowest frequencies are comparable to most room dimensions. This means that they'll set up standing waves and interference patterns if several speakers emit the same sound at the same time. There will be particular locations in the room where the sound will be louder than normal and others where it'll be cancelled out. Optimizing your room's low frequency response is a topic that has been discussed in many other threads, however.


I hope this clarifies things a little.
 
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