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THX sub vs. non THX sub, pros & cons


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4 replies to this topic

#1 of 5 OFFLINE   VincentY

VincentY

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Posted April 11 2003 - 04:23 PM

I was told that if I were to use a non-THX sub that whenever I decrease the volume below reference (0 db), which is quite possibly quite often, that the only way to adjust the output of the subwoofer is to use the sub's volume knob on the sub itself, as oppose to using a THX sub, in which case when one lowers the overall volume on the pre/pro or receiver, the THX sub's volume decreases accordingly.

I am wondering if this is indeed true or is it untrue and based on THX marketing hype?

i thought that using any sub with a pre/pro/receiver would allow for proper volume adjustment (including adjusting the sub's volume) whenever one were to decrease the master volume on the pre/pro/receiver.

however, since i was told otherwise, that unless it is a THX sub, adjusting the volume down on the pre/pro/receiver would simply lower the volume of everything EXCEPT the output volume of the subwoofer, so it woun't work properly unless were to be willing/able to reduce the sub's volume appropriately by actually going to the sub itself and adjusting the output volume knob each time one were to go below reference (0 db).

am i totally confused? don't understand this bass management part for 5.1 systems on THX vs no THX.

Thanks.

#2 of 5 OFFLINE   Adam.Gonsman

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Posted April 11 2003 - 05:34 PM

Wow! That sounds really confusing. If I understand your question properly, this sounds like a salesman fed you a real line of bull hoping you'll shell out more bucks for a THX certified sub. I've never heard anything of the sort though. I have a non-THX receiver (would definately pass certification except yamaha doesn't seem to care and I don't blame them) and a non THX sub (again I'm sure would pass cert) and the volume for the sub goes up and down with the receiver just fine. Does the sub have a volume knob? Definately does. Is it to keep the sub in check with the receiver (pre/pro) volume as it changes? Definately not.

Every single receiver and pre/pro I have ever seen has variable output on it's sub pre-out. The volume knob on the sub is simply to bring the sub into balance with the other speakers in the system at any given volume. Once in check, the master volume for the receiver adjusts the volume of speakers (including sub) up or down across the board. The sub volume control is not meant to be adjusted for volume control during nurmal listening.

Hope that helps. Hope I understood you question correctly. Maybe I just don't understand either.

#3 of 5 OFFLINE   Jonathan M

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Posted April 11 2003 - 05:37 PM

Whoever told you that doesn't know what they're talking about.

No matter if your receiver is THX or not, it matters not. They ALL alter everything (Mains, surrounds AND sub) when adjusting the volume using the receiver's volume knob.

Many receivers conform to the bass management part of the THX specification anyway, whether they are labelled THX or not - this is due to the standard filters in Dolby digital and DTS chipsets (which most manufacturers use) conforming as standard to the THX spec.

As for THX subs, the spec likely is just regarding the xover in use. You will be using the receiver's lowpassed output signal anyway, so you don't need a xover on the sub (Most still have them, but you don't need them - either bypass it, or turn it up to it's highest setting.)

Verdict: You DON'T need a THX sub at all. Just get one that you like the sound of, or build one yourself (They're easy) if you're a little more adventurous and want to save some $$.
"Price and quality are not correlated"

DIY Home Theatre

#4 of 5 OFFLINE   Pierre G

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Posted April 11 2003 - 07:36 PM

Vincent, if you have the option to audition the subs don't pay extra for the THX certification.

You probably already know that I can't audition anything here because there are no decent dealers in my area. So I insist on THX as a guaranty, and I pay for it on this basis.

To qualify for THX, a sub should be able to do frequencies from 20Hz to 200Hz, and the crossover should be adjustable from 40Hz to 200Hz. My 400 watts THX Jamo D7 Sub has the knob to adjust the cutoff frequency which is useless IMO, because I'd rather bypass it and use my receiver's crossover, but I don’t have the option to bypass it in the Jamo case.

As for the 200Hz, any speaker, even my satellites play down to 80Hz, so there is an overlap of 120Hz, if a sub can play up to 110 Hz, it’s more than enough, but the lower it goes the better.

I don't know if Rel subs are THX but I consider the Rel to be the best subs, the Q series are cost efficient and monster performers, even the lowest in the series qualifies as a THX sub power wise. Check the Q150, Q200, Q400 series out.

The thing about having to adjust the volume from the sub everytime you lower the volume from your preamp is total nonsense, whether THX or not.

#5 of 5 OFFLINE   Lewis Besze

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Posted April 12 2003 - 05:44 AM

THX subs ratings have nothing to do with power per se, but output into certain size of room,and listening distance.
Also note that till THX 2 was introduced,THX sub's low end was reduced below 30hz per the THX standards,following the theatrical "trend".
Thankfuly THX 2 reckognise this outdated approach,and calls for full output to 20hz.

Vincent,

that explanation is "bologni".
Don't buy it!