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My previous Onkyo SR805 and now my Onkyo NR1007 both have a THX Subwoofer option to enable if you have attached THX certified subwoofers. The manual is pretty lean on information in what this actually does. I did actually have some THX Ultra certified subwoofers - the Jamo D7sub pair and they did actually sound better engaged in THX mode in my demoing back and forth. From what I can tell it seems this mode actually increases the voltage swings/dynamics supplied to the LFE subwoofer outputs, but that's in reading between the lines a bit between the subwoofer manual and the recevier manual and a couple forum posts through google searches. I'm curious if these swings would be too agressive for sub amplifiers not designed to accept these signals and would result in clipping or distortion instead of increased dynamics. For instance with the Jamo D7subs if you enabled THX sub mode you'd put the gains at about 1/8 gain on the knob and a light would turn on indicating the sub gain was set correctly for THX configuration, - change the setting in the receiver to enable THX subwoofer mode and you were good to go. The gain without THX sub mode enabled on the receiver would need to be set higher on the subwoofer to match the spl levels. Unfortunately I don't have any actual measurements to compare THX sub setting on vs. with THX sub setting off. Has anyone done any SPL or FR measurements to see what this setting is actually doing? I supposed it could be as simple as hooking up a multimeter to the subwoofer output and checking voltages to see what exactly occurs between the two settings. I may give multimeter a go later today.


I'm curious if it would possibly damage an amp if the voltage supplied is too high? I wouldn't think so, but figured I'd better ask before I tried it. I'm looking to see if it's worth enabling on my EP4000 amp and pair of passive JTR Captivator Pros after I get a bit of feedback.


Here is a article from Secrets of Home Theatre that talks a bit about the THX subwoofer mode settings.
http://www.hometheaterhifi.com/volum...06-part-4.html


Here is the Onkyo TX-NR1007 manual so you can see what I'm talking about for the THX subwoofer mode option if curious - (I'm not sure if other AVR vendors include this option or not?)

http://63.148.251.135/redirect_servi...En_webver2.pdf


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The LFE level output and gain (voltage) is higher then the other channels, which is what article talks about.Thx doesn't change that. Bgc(boundary gain control ) is the only THX feature that is an active correction that is relevant to output levels, and it is as it's name suggests compensates for corner or near wall loading.In short answer, engaging this feature won't damage your amp's input,especially a pro amp one,which needs high voltage to begin with.
 

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Sometime ago I used the built-in SMS-1 of my DD-18 THX Ultra 2 to measure what would happen if I turned on the THX mode of my Harman Kardon AVR8000 THX Ultra receiver. Surprisingly the curve changed despite leaving the Boundary Gain settings off. IIRC, the LFE started to roll off earlier at about 30hz. This is probably designed to save the subwoofer from damage trying to play at punishing THX listening levels.
 

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Quote:
Originally Posted by obsi /forum/post/20793451


Sometime ago I used the built-in SMS-1 of my DD-18 THX Ultra 2 to measure what would happen if I turned on the THX mode of my Harman Kardon AVR8000 THX Ultra receiver. Surprisingly the curve changed despite leaving the Boundary Gain settings off. IIRC, the LFE started to roll off earlier at about 30hz. This is probably designed to save the subwoofer from damage trying to play at punishing THX listening levels.

That's odd, Ultra 2's specs call for 20hz extension, which was lacking in the previous Ultra specs, which indeed was rolling off below 35hz.
 

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Quote:
Originally Posted by thehun /forum/post/20793798


That's odd, Ultra 2's specs call for 20hz extension, which was lacking in the previous Ultra specs, which indeed was rolling off below 35hz.

Not odd at all, cuz despite the Ultra2 DD-18's ability to plumb the low stuff, the receiver's post processing was still the earlier Ultra. Somewhat like the saying "The body is willing but the mind is weak."
 
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