THX surround speaker low frequency response questions. - AVS Forum
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post #1 of 19 Old 07-16-2009, 01:48 PM - Thread Starter
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THX mandates a setting a crossover at 80hz.
Many THX approved surround speakers have a -3db point of 100hz and a -6db point at 80hz.

Shouldn't all the speakers in a THX system have an 80hz -3db point?

The proper setting for sharpness is always0.
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post #2 of 19 Old 07-16-2009, 01:55 PM
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Its just guidelines....experiences may vary.

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post #3 of 19 Old 07-16-2009, 07:11 PM
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With THX certified products it isn't just a guideline they are supposed to meet certain parameters.

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post #4 of 19 Old 07-16-2009, 09:00 PM
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Originally Posted by fsrenduro View Post

With THX certified products it isn't just a guideline they are supposed to meet certain parameters.

The 80Hz recommendation is just a guideline...if you think different you will not maximize your setup.

Go ahead and just use 80Hz, if you think its not just a guideline the rest of us will maximize the potential of our systems

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post #5 of 19 Old 07-17-2009, 06:04 AM
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My surrounds have a -3dB of 88Hz, yet Audyssey set them at 150Hz. In your room, the actual cross may not be optimum at 80Hz.
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post #6 of 19 Old 07-17-2009, 06:45 AM
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Quote:
Originally Posted by Jim Hef View Post

My surrounds have a -3dB of 88Hz, yet Audyssey set them at 150Hz. In your room, the actual cross may not be optimum at 80Hz.

Jim, I posted in the audyssey thread about a similar issue with my speakers which are DIYs (12" woofers) they do down to 70Hz with authority.

Audyssey set my crossover @ 120Hz. I do lots of measurements on my own so I try to figure out why that was. I found out that I had a null @ 120Hz and it seems Audyssey uses that null to set my crossover. I didnt get much help on the thread but Chris (Audyssey) in the end did comment that if the null is deep/wide enough then Audyssey could mistaken it for the F3 point of the speakers. The wall behind my speakers was causing the null, I moved them around and noticed the null changing on the FR plot.

Long story short Audyssey is not perfect and it could mistakenly use a Null as the F3 point of your speakers. Its all okay though, crossovers can be changed and it will not disable Audyssey.

150Hz is way to high for any subwoofer IMO and the localization will suck if your subs are not close to your main speakers.

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post #7 of 19 Old 07-17-2009, 07:12 AM
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Penn we're arguing apples to oranges. I understand and agree that 80 Hz is a guideline set forth by THX to the general home theater public. Part of the original question was about THX certified Speakers which is what I was addressing. THX Speakers are designed to meet certain -3db points, among other things. I too thought that a THX cert speaker had to do 80hz at -3db but they may have softened that to 100 Hz to allow more speakers into the club.

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post #8 of 19 Old 07-17-2009, 07:14 AM
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Originally Posted by fsrenduro View Post

Penn we're arguing apples to oranges. I understand and agree that 80 Hz is a guideline set forth by THX to the general home theater public. Part of the original question was about THX certified Speakers which is what I was addressing. THX Speakers are designed to meet certain -3db points, among other things. I too thought that a THX cert speaker had to do 80hz at -3db but they may have softened that to 100 Hz to allow more speakers into the club.

ah, I understand what you are saying, sorry about the confusion. I agree with you.

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post #9 of 19 Old 07-17-2009, 07:53 AM
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Being able to use an 80Hz crossover is much less important for the surround speakers than it is for the mains. How many "main" speakers that are THX certified have -3db points above 80Hz? Similarly, for a crossover of 80Hz, the speaker should really be capable down to 60Hz as a recommended min, or 40Hz ideally. to maintain the purity of the rolloff being imposed by the crossover and not having the speaker's own integral rolloff interfering.
THX has many levels of certification, allowing for different product categories to play in the game.... Similar to a reviewer to says "this is a 5 star component for the budget category" THX says "this component meets best practices for this less-than-ideal-due-to-size/budget-constraints environment.

-Greg
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post #10 of 19 Old 07-17-2009, 07:59 AM
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Originally Posted by glaufman View Post

Being able to use an 80Hz crossover is much less important for the surround speakers than it is for the mains. How many "main" speakers that are THX certified have -3db points above 80Hz? Similarly, for a crossover of 80Hz, the speaker should really be capable down to 60Hz as a recommended min, or 40Hz ideally. to maintain the purity of the rolloff being imposed by the crossover and not having the speaker's own integral rolloff interfering.
THX has many levels of certification, allowing for different product categories to play in the game.... Similar to a reviewer to says "this is a 5 star component for the budget category" THX says "this component meets best practices for this less-than-ideal-due-to-size/budget-constraints environment.

Your last statement is so true and THX should be taking with a grain of salt. I have never found THX certified speakers to be better then Danley, JBL, Mark Seaton or any DIY speaker designs so in the end its all just user specific.

I have high end sealed DIY speakers that roll off naturally at 70Hz...I have never read about a recommended min of 60 Hz being set in stone if the sub system does up to atleast 80Hz very well.

I guess my main point is that anyone hung up on THX specs, THX speakers are the people that need to understand a little more about overall audio performance. THX label and standards has nothing over some of the best systems I have heard...Heck some THX label stuff is not what I consider good at all when compared to custom HT systems.

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post #11 of 19 Old 07-17-2009, 08:14 AM
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Quote:
Originally Posted by penngray View Post

Your last statement is so true and THX should be taking with a grain of salt. I have never found THX certified speakers to be better then Danley, JBL, Mark Seaton or any DIY speaker designs so in the end its all just user specific.

But it can be useful for J6P who doesn't want to learn enough to make his own decisions, to simply buy THX stuff in his price range and have a warm fuzzy... not so much for me, however...

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I have high end sealed DIY speakers that roll off naturally at 70Hz...I have never read about a recommended min of 60 Hz being set in stone if the sub system does up to atleast 80Hz very well.

Well, "recommended min" and "set in stone" are two different things. Bottom line is that if the speaker starts adding it's own rolloff to that of the crossover at a frequency where the the output of that speaker is still required to make the crossover smooth, it's easy to see that that there will be a little dip... whether or not it's audible will depend on the person, the sub, the room, the material etc... OTOH, if we're talking DIY, you can have a speaker with a 1st order rolloff, and crossover with a first order rolloff on the speaker side but a second order rolloff on the sub side where a -3db point of 80Hz on the speaker would be just peachy, and then anything else would cause dips or bumps... like you said above, it all depends... rules of thumb...
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I guess my main point is that anyone hung up on THX specs, THX speakers are the people that need to understand a little more about overall audio performance. THX label and standards has nothing over some of the best systems I have heard...Heck some THX label stuff is not what I consider good at all when compared to custom HT systems.

I happen to agree with you there, but some of that comes from misunderstanding their different logos. Some equipment carries a THX logo indicating that they license certain technology from THX, such as Re-Eq or BGC or the like, and have nothing to do with being THX certified... except for that particular circuit meeting THX's requirements for that particular circuit. Also, what's THX certififed for one environment may not sound very good in another environment, but the different classes are very ambiguous except for anyone who does some homework. I blame THX for this. At a min, they need to do a better job marketing themselves to the public.

-Greg
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post #12 of 19 Old 07-17-2009, 08:15 AM
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Good points!

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post #13 of 19 Old 07-17-2009, 09:14 AM
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Originally Posted by penngray View Post

...150Hz is way to high for any subwoofer IMO and the localization will suck if your subs are not close to your main speakers.

The 150Hz was only for the side surrounds and not the mains. My dual subs are closely aligned with the front mains, so I have no problem with those. I agree though that Audyssey could have found a problem with my very bright room and the placement of the surrounds. It's not a simple room configuration.
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post #14 of 19 Old 07-17-2009, 09:42 AM
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Things go beyond Xover frequency. The original THX satellite speaker was supposed to be a sealed design so the 12 dB/octave slope on the electronic Xover combined with a 12 dB/octave mechanical slope of a sealed design result in 24 db/octave. This matched the 24 db/octave ellectronic slope on the low pass subwoofer channel. All the original THX speakers were sealed. Then at some later time ported THX speakers appeared! I think that the technical considerations eventually gave way to profits.

Ed
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post #15 of 19 Old 07-17-2009, 02:02 PM - Thread Starter
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I think under THX surround speakers are supposed to be -6db at 80hz.
So they don't cause phase issues with a sub or something.

The proper setting for sharpness is always0.
Also my Oppo BDP-103D is region free.
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post #16 of 19 Old 07-02-2012, 06:39 PM
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I realize this thread is old, but this is a rather long conversation without mention of the most important factor; DOLBY (or DTS or THX), remember them.
The guys who encode the movies and send audio to the surround speakers, at WHAT FREQUENCY ? Seems to me you should be worried about how low the the frequency is for the audio being sent to the surrounds (by Dolby or DTS); So you can build or buy speakers that can reproduce it all.
I found my way to this thread looking for the answer to that question. "Who's on first - What's on second" You make a valid point when I can't find a speaker salesman who knows the answer to this question. There is nothing vague about it! At some point in time somebody, somewhere, decided how low in frequency the audio track to the surrounds would be! And maybe THX does something different from Dolby (or DTS) WHAT IS THAT NUMBER. Thats how low I will build my surrounds to go ! (or buy) Phase issues with the sub, good point; but that can happen at any point in this crossover region. what we need first ,is the NUMBER. How low do THX surround audio tracks go!?!
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post #17 of 19 Old 07-03-2012, 07:22 AM
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Quote:
Originally Posted by terryaaa View Post

I realize this thread is old, but this is a rather long conversation without mention of the most important factor; DOLBY (or DTS or THX), remember them.
The guys who encode the movies and send audio to the surround speakers, at WHAT FREQUENCY ? Seems to me you should be worried about how low the the frequency is for the audio being sent to the surrounds (by Dolby or DTS); So you can build or buy speakers that can reproduce it all.
I found my way to this thread looking for the answer to that question. "Who's on first - What's on second" You make a valid point when I can't find a speaker salesman who knows the answer to this question. There is nothing vague about it! At some point in time somebody, somewhere, decided how low in frequency the audio track to the surrounds would be! And maybe THX does something different from Dolby (or DTS) WHAT IS THAT NUMBER. Thats how low I will build my surrounds to go ! (or buy) Phase issues with the sub, good point; but that can happen at any point in this crossover region. what we need first ,is the NUMBER. How low do THX surround audio tracks go!?!

It doesn't really matter how low of a frequency the mixers mix into the surround channels.... that's what a sub is for. Now if you are going to have a dedicated HT room and you are going to have powerful amps sending hundreds of watts to your speakers and not just an AVR then maybe you would want to know that answer. But I believe they could mix 20 hz or below into any speaker in a surround system, so for most ppl that is a ridiculous thing to try to accomplish. So most ppl buy or build speakers that have a -3db of 60hz or lower and then use 80hz or 60hz as a crossover to the sub. And then you can have a sub that will play down to 20 hz or 16 hz or even 10 hz.

IMO (which I don't have by the way) the best to have for 7.2 for example is 7 identical speakers all capable of 60hz -3db and have 2 subs capable of -3db into the teens somewhere.

Shawn
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post #18 of 19 Old 11-20-2012, 06:07 AM
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Originally Posted by penngray View Post


The 80Hz recommendation is just a guideline...if you think different you will not maximize your setup.


Go ahead and just use 80Hz, if you think its not just a guideline the rest of us will maximize the potential of our systems

im just asking so that i can learn

what if your front LR speakers and your center speakers go down to 22hz and 56 hz?

wouldn't it be better if all the speakers played all the frequencies that they can handle? or would that cause overlapping issues?
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post #19 of 19 Old 11-20-2012, 08:12 AM
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In general the right location for your left right and center speakers is very unlikely to be the best location for a subwoofer. Room effects are dramatically different in teh bass range and maximizing location can give significant benefits.

plus, unless your manufacturer lists limits for their specs, it's best to assume that low frequency extension is -10 dB, not -3 or even +/- 3dB *(shich you should take to mean -6 unless yousee a graph to the contrary). And speakers that can happily make 30 Hz sound at say 90 dB may run out of steam (compress) when you get into louder playback, which is another reason to use bass management.

Finally for us mere mortals who use middle of the road receivers to power our systems, taking the bass out of the main channels greatly relieves the power requirements on the receiver, making it more likely that even at very loud volume we are not getting audible distortion from the receiver's amps.
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