LPF on LFE at 80hz, where does 80-120 go???? - AVS Forum
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post #1 of 36 Old 09-12-2010, 06:47 PM - Thread Starter
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Concerning LPF on LFE channel for the digital .1;

If you set it to 80hz, digital LFE channel contains sound up to 120hz, what happens to the sound information from 80-120hz?

I have read that is is discarded, but I have also been told it should be redirected to the mains, assuming they're set to large.

It appears this could be very receiver specific, or manufacturer.

Does anyone know where this sound goes?

I've searched and only found convoluted discussions...
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post #2 of 36 Old 09-12-2010, 07:21 PM
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It is lost. No processor that I know of re-directs it anywhere.

Set the LPF of LFE to 120 Hz.

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post #3 of 36 Old 09-12-2010, 07:34 PM
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The only time I know of when LFE is redirected to the mains is when they are set to large and sub is set to off/no. As Craig said, set LPF for LFE to 120. I really don't know why this setting is included.

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post #4 of 36 Old 09-12-2010, 08:18 PM
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Why then is THX spec'd at 80 hz for the LFE?
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post #5 of 36 Old 09-12-2010, 08:29 PM
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Quote:
Originally Posted by bsoko2 View Post

Why then is THX spec'd at 80 hz for the LFE?

I think mainly because frequencies above 80hz can be localized. If you are only using one sub localization could be an issue using the 120hz setting. With multiple subs becoming more common, this is less of an issue. Not an issue at all in my room. I personally have used the 80hz LFE setting with multiple subs, but have changed to 120hz with much better results using multiple subs. The bass seems to blend with the other channels better in my room with the 120hz setting.
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post #6 of 36 Old 09-12-2010, 08:38 PM
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Quick question, in my AVR menu I only have this listed for any crossover settings.

It says CROSS OVER, and then has all the way down to 40 and all the way up to 200 listed. It doesn't say LFE or anything else. On all of my subs I have their crossovers disabled, should I set mine to 120 or to 80?

I have the option of Large and Small for all of my speakers. I have them all set to Small. I guess in my particular situation, with my AVR, it will send all the lower stuff from 120 on down to only my subs, and then anything higher than 120, it will go to all my other speakers. Which is what I want?


EDIT : Looks like squirrel may have just answered my question?

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post #7 of 36 Old 09-12-2010, 08:48 PM
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Quote:
Originally Posted by yadfgp View Post

Quick question, in my AVR menu I only have this listed for any crossover settings.

It says CROSS OVER, and then has all the way down to 40 and all the way up to 200 listed. It doesn't say LFE or anything else. On all of my subs I have their crossovers disabled, should I set mine to 120 or to 80?

I have the option of Large and Small for all of my speakers. I have them all set to Small. I guess in my particular situation, with my AVR, it will send all the lower stuff from 120 on down to only my subs, and then anything higher than 120, it will go to all my other speakers. Which is what I want?


EDIT : Looks like squirrel may have just answered my question?

You are correct about the cross overs from 40hz to 200hz. Those are actual cross overs for your mains, center, and surrounds. The sub LPF/LFE is different. It really isn't a cross over. So look in your menu for LFP/LFE. In some receivers the LPF/LFE can't be changed. It is set at 120hz with no option to change it. You should leave the cross over on the back of your sub all the way to the max to bypass it. Or turn it off if it has a switch to do so.
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post #8 of 36 Old 09-12-2010, 09:10 PM
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Quote:
Originally Posted by Secret Squirrel View Post

You are correct about the cross overs from 40hz to 200hz. Those are actual cross overs for your mains, center, and surrounds. The sub LPF/LFE is different. It really isn't a cross over. So look in your menu for LFP/LFE. In some receivers the LPF/LFE can't be changed. It is set at 120hz with no option to change it. You should leave the cross over on the back of your sub all the way to the max to bypass it. Or turn it off if it has a switch to do so.

I've done that to all my subs, they are either set to max or just turned off. But that's the only cross over setting I have for my receiver. Isn't that setting for my subs? I can go as high as 200hz and as low as 40hz, if I had that set to 120hz, wouldn't it send all my LFE to the subs from 120 on down and everything else above 120 would go to all of my other speakers? The only other type of settings even remotely resembling a crossover settings are for Large and Small. Those are for my center, my fronts, my side, and my rear channels.

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post #9 of 36 Old 09-12-2010, 09:15 PM
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If you don't have an LPF for LFE setting, then you are sending the full LFE channel to your sub. The only way around this is to set the sub to off. Setting your other channels to small then redirects their bass to the sub channel below the AVR's crossover setting.

The LFE channel is only redirected to the mains if you set the sub to off and only if your receiver says it does that.

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post #10 of 36 Old 09-12-2010, 09:23 PM
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Quote:
Originally Posted by ransac View Post

If you don't have an LPF for LFE setting, then you are sending the full LFE channel to your sub. The only way around this is to set the sub to off. Setting your other channels to small then redirects their bass to the sub channel below the AVR's crossover setting.

The LFE channel is only redirected to the mains if you set the sub to off and only if your receiver says it does that.

So I'm good to go with how I'm setup? I do have a setting that says LFE/BASS OUT but my only options are for Fronts, Subs, or Both. I have it set to Subs.

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post #11 of 36 Old 09-12-2010, 10:01 PM
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What if the sub is located behind the listening position? Wouldn't the 120hz LPF make it very localized?
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post #12 of 36 Old 09-12-2010, 10:01 PM
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Quote:
Originally Posted by Secret Squirrel View Post

I think mainly because frequencies above 80hz can be localized. If you are only using one sub localization could be an issue using the 120hz setting. With multiple subs becoming more common, this is less of an issue. Not an issue at all in my room. I personally have used the 80hz LFE setting with multiple subs, but have changed to 120hz with much better results using multiple subs. The bass seems to blend with the other channels better in my room with the 120hz setting.

I have MCACC and when you set a sub crossover in the reciever it sets all speakers at what the sub is set to. So if you have 80 hz then all speakers are at 80 hz. Then, MCACC doesn't do 120 but jumps from 100 to 150 then to 200. I have multiple subs and have ran with a 150 crossover.
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post #13 of 36 Old 09-12-2010, 10:36 PM
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Quote:
Originally Posted by gpmbc View Post

What if the sub is located behind the listening position? Wouldn't the 120hz LPF make it very localized?

I had my sub right behind the couch. I used to have it set to 80Hz on the AVR, but for the last several months, it has been set to 150. I still don't hear sound from the sub. The bass sounds like it is coming from the mains.

So I guess the answer is, it depends. I think some people are more sensitive to sound direction as are some more sensitive to lower frequencies.

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post #14 of 36 Old 09-12-2010, 10:50 PM
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Quote:
Originally Posted by gpmbc View Post

What if the sub is located behind the listening position? Wouldn't the 120hz LPF make it very localized?


I don't think you should be too worried about this. Remember, the LFE channel is only for effects, like explosions, earthquakes, etc. True, above 80 might be localized but I doubt you'll ever get isolated 80-120 content from the LFE. It will most likely be blended with all other sorts of LFE data.

Very rarely will you get content that you should be worried about being localized (such as peoples voices) ever coming from the LFE channel. The general rule is set it to 120, otherwise you're going to get a premature rolloff of the LFE material.

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post #15 of 36 Old 09-12-2010, 10:56 PM - Thread Starter
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I didn't really want to get into a debate or talk about whats a better setup, just wanted a simple answer from those who know.

Sounds like the consensus is that the audio on LFE channel from 80-120hz is disregarded if you set the LPF of the LFE at 80hz.
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post #16 of 36 Old 09-12-2010, 11:07 PM
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Quote:
Originally Posted by jmilt13 View Post

I didn't really want to get into a debate or talk about whats a better setup, just wanted a simple answer from those who know.

Sounds like the consensus is that the audio on LFE channel from 80-120hz is disregarded if you set the LPF of the LFE at 80hz.


Yup, that's correct.

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post #17 of 36 Old 09-13-2010, 01:04 AM
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Quote:
Originally Posted by bsoko2 View Post

Why then is THX spec'd at 80 hz for the LFE?

Besides beyond post #5,

Because there isn't much content above 80 hz on the LFE in most cases. The content amount and FR is entirely a creative decision.

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post #18 of 36 Old 09-13-2010, 02:51 AM
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Quote:
Originally Posted by jmilt13 View Post

I didn't really want to get into a debate or talk about whats a better setup, just wanted a simple answer from those who know.

Your question was answered in post #2. Doesn't mean it won't spawn other inquiries and debate. That's the way it works here.

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post #19 of 36 Old 09-13-2010, 06:50 AM
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Quote:
Originally Posted by yadfgp View Post

I've done that to all my subs, they are either set to max or just turned off. But that's the only cross over setting I have for my receiver. Isn't that setting for my subs? I can go as high as 200hz and as low as 40hz, if I had that set to 120hz, wouldn't it send all my LFE to the subs from 120 on down and everything else above 120 would go to all of my other speakers? The only other type of settings even remotely resembling a crossover settings are for Large and Small. Those are for my center, my fronts, my side, and my rear channels.

The crossover redirects sound from the mains and surrounds to the sub. So it rolls off the mains and surrounds below the crossover point, and rolls off the sub channel above the crossover point, typically having the two rolloffs meet where each is ireduced by 3 dB. So the crossover effects all speakers on which you utilize bass management. If you set the main speakers to large, there will be no redirection, so all the bass from that channel will go to the channel speaker, and the crossover will not roll them off. If you set your system up for double bass, as I understand it, the crossover setting only affects the sub channel, an you get too much bass in the frequencies where the main speakers' natural response and the sub's rolled off response overlap.
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post #20 of 36 Old 09-13-2010, 08:18 AM
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Quote:
Originally Posted by bsoko2 View Post

Why then is THX spec'd at 80 hz for the LFE?

THX is not "...spec'd at 80 Hz for the LFE". You might be confusing this with the THX crossover, which is spec'd at 80 Hz. However, this is completely different than the LPF of LFE.

The LPF of LFE and the THX crossover, (or any Bass Management crossover), are essentially unrelated. The Bass Management *crossover* is the combination of the HPF that is applied to the main channels that are set to "Small", (or in some Bass Management nomenclatures "have a crossover invoked"), and the LPF that is applied to the re-directed bass from those channels. The re-directed bass is then combined with the LFE channel, and the combined signal is sent to the subwoofer output. The LFE channel has been separately filtered by the LPF of LFE before being combined with the re-directed bass from the main channels. The LPF of LFE is not a "crossover" per se. It is *just* a Low Pass Filter applied *only* to the LFE channel. It should always be set to 120 Hz.

Only newer receivers even have a LPF of LFE. Before the advent of BluRay with Dolby TrueHD and DTS-MA, the LFE channel was filtered during the recording process at 120 Hz. There was no need to re-filter it on playback. However, TrueHD and DTS-MA are "full-range" in all channels, including the LFE channel. Therefore, there is the possibility of some content in the LFE channel above 120 Hz. Hence, the need for an LPF of LFE on receivers/pre/pro's capable od decoding TrueHD and DTS-MA.

Most recording engineers don't place any content above 120 Hz in the LFE channel, (and , in fact, not much above 80 Hz), so it's not a huge issue either way. However, to ensure you don't "lose" any LFE content, the LPF of LFE should always be set to 120 Hz.
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Some thoughts on the THX crossover:

The THX crossover is a very unique crossover designed to work specifically with THX speakers and sub. The HPF applied to the speakers is a 2nd Order, (12 dB/Octave roll-off) high pass. THX speakers are spec'd to have a -3 dB point of 80 Hz with a complimentary 2nd Order roll off. Add the two roll-offs together and you get a 4th Order, (24 dB/Octave) combined high pass roll off, with both starting at 80 Hz.

The THX LPF, (not the LPF of LFE, but the LPF applied to the re-directed bass), is spec'd at 24 dB/Octave, staring at 80 Hz. The combination of a 4th Order HPF and 4th Order LPF result in a perfect "Linkwitz-Riley" crossover with minimal phase issues.

The THX crossover is always included in THX receivers and pre/pro's, and it is always set at 80 Hz, with the HPF and LPF slopes pre-determined as above. However, in non-THX receivers and pre/pro's, unless the manufacturer specifies the crossover slopes, (and virtually none do), the slopes are unknown. They could be anything from 1st to 4th Oder, and they could be the same or different above or below the crossover point. In addition, the speakers being used with the crossover can vary in their low frequency roll off, as can the HF roll off of the sub. Whether or not the built-in crossover works "correctly* with the given speakers and subs is a total crap shoot.

The THX crossover plus THX speakers and subs is the *only* setup I'm aware of that is designed as a "system", where the components are designed to work together to yield a specific result. Say what you will about THX, their crossover is the best designed crossover "system" available, IMO.

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post #21 of 36 Old 09-13-2010, 05:11 PM - Thread Starter
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Originally Posted by ransac View Post

Your question was answered in post #2. Doesn't mean it won't spawn other inquiries and debate. That's the way it works here.

Sorry, I'm use to forums that are strict on staying on subject.

Why can't dolby and dts just get with THX since it's obviously a better choice?
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post #22 of 36 Old 09-13-2010, 05:18 PM
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Quote:
Originally Posted by craig john View Post


Only newer receivers even have a LPF of LFE. Before the advent of BluRay with Dolby TrueHD and DTS-MA, the LFE channel was filtered during the recording process at 120 Hz. There was no need to re-filter it on playback. However, TrueHD and DTS-MA are "full-range" in all channels, including the LFE channel. Therefore, there is the possibility of some content in the LFE channel above 120 Hz. Hence, the need for an LPF of LFE on receivers/pre/pro's capable od decoding TrueHD and DTS-MA.

My previous AVR had a selectable LPF for the LFE channel and it was made in 2002. Harmon Kardon AVR525. I could filter stuff above 40hz if I wanted to with this baby.

Also, the .1 channel has always been full range. It just isn't used like that very often. There are few isolated music releases that used the LFE channel as an auxilary channel. I think there was a few that were heights and then something else but I can't find the link I was looking for just now.... I remember some Widescreen Review articles that mention the use of channels not in the norm of regular surround setups. IIRC, it was most recently mentioned in an article about 7.1 surround at home.

Anyway, you are correct but I just wanted to point out that it isn't new to HD audio codecs.

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post #23 of 36 Old 09-13-2010, 05:31 PM
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Quote:
Originally Posted by jmilt13 View Post

Sorry, I'm use to forums that are strict on staying on subject.

Why can't dolby and dts just get with THX since it's obviously a better choice?


Not sure in what sense you find THX a better choice but in the context of the original question, DBX and DTS have zero control over what movie mixers put into any channel. They simply encode what they're fed so it can be stored in less space than PCM would take. So there's not really anything for them go get with THX about.
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Originally Posted by jmilt13 View Post

Sorry, I'm use to forums that are strict on staying on subject.

Here, we have trouble stay on topic for more that two posts.

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post #25 of 36 Old 09-13-2010, 09:17 PM
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In essense does that mean that its better to set crossover at 80Hz especially for receivers that do not have separate option for LPF for LFE or it does it matter where the croosover is set.

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post #26 of 36 Old 09-13-2010, 09:36 PM
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Originally Posted by vinodk View Post

In essence does that mean that its better to set crossover at 80Hz especially for receivers that do not have separate option for LPF for LFE or it does it matter where the crossover is set.

80Hz is the THX recommendation and is a good starting point. It really depends on the capability of your satellite speakers. If you're running small cubes, you probably need to set it higher. If you're running satellites that all dig to the 40s or below, you might want to set the XO lower.

Are you sure you don't have and LPF for LFE? It may be labeled differently and may not be in the settings where you'd think it should be. If you don't have it, it is probably fixed at 120. That's fine as that's where you should set it anyway.

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post #27 of 36 Old 09-14-2010, 07:27 AM
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Quote:
Originally Posted by jmilt13 View Post

Sorry, I'm use to forums that are strict on staying on subject.

Why can't dolby and dts just get with THX since it's obviously a better choice?

The THX crossover is only a "better choice" when it's used with THX speakers and subs. (Remember I said they were designed as a "system"?) Without THX speakers and subs, (or, at least, speakers and subs designed according to THX speaker and sub spec's), the THX crossover is just as much a crap shoot as any other crossover scheme.

Besides that, what do Dolby and DTS have to do with the crossover? They are encoding/decoding schema, and they have no idea what the playback system will consist of. It is completely up to the end user to optimize their system for playback. In terms of the crossover selection, that means knowing how your speakers and subs are designed, and selecting the crossover setting that best matches them.

What *would* be nice is if the receiver/pre/pro manufacturers gave users the option of selectable crossover slopes. Then users could more easily optimize the crossover to their particular speakers and subs. Of course, this would also allow for a lot more error on the part of users who don't understand and/or mis-use the settings.

Do you own THX speakers and/or sub(s)? A THX receiver or pre/pro? If not, maybe we can help you optimize your settings. What BM settings are you currently using, and how did you decide on them?

Craig

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post #28 of 36 Old 09-14-2010, 08:21 AM
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In my Pioneer Elite there's only a universal crossover. If I pick 80Hz, the LFE is "cut" there and I lose the above information - a major bummer, imho. It doesn't get redirected to the mains, even if set to full range/large. Although 80Hz in my experience is great to avoid localizing, there 's a lot of information above 80Hz in the LFE channel from my experience, particularly in concert DVD's. I know Craig said the opposite and that there isn't much above 80Hz (post #20), but my ears tell me otherwise with my content I tend to listen to. If you set the sub x-over to 120Hz, you'll lose the impression of the deep thuds, but only because they're being masked by higher punches now produced from the sub. On my friend's new Denon 1611 unit, there's a Sub crossover and then separate mains/surrounds crossovers. This allows great flexibility.

I've also noticed while may speakers claim or do digg into the below 80Hz range, most do much better and play cleaner if left to only play 100Hz and up or even 120Hz and up - particularly 2 way designs. It's hard to compete in the sub 120Hz range using a couple 6" drivers powered by a receiver or amp that's also producing up to ~20,000Hz, versus a sub with a dedicated 10", 12" or so driver and a dedicated amp, when it comes to producing physically impactful bass.
This is just my experience in my room. YMMV. Best thing to do is experiment with lots of different content and let your ears do the deciding, or your gut if the bass is deep and loud enough.

Why do all of my threads suck? Is there an internet posting school somewhere? -wes k
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post #29 of 36 Old 09-14-2010, 02:18 PM
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Originally Posted by boarder1995 View Post

In my Pioneer Elite there's only a universal crossover. If I pick 80Hz, the LFE is "cut" there and I lose the above information - a major bummer, imho. It doesn't get redirected to the mains, even if set to full range/large. Although 80Hz in my experience is great to avoid localizing, there 's a lot of information above 80Hz in the LFE channel from my experience, particularly in concert DVD's. I know Craig said the opposite and that there isn't much above 80Hz (post #20), but my ears tell me otherwise with my content I tend to listen to. If you set the sub x-over to 120Hz, you'll lose the impression of the deep thuds, but only because they're being masked by higher punches now produced from the sub.

It is certainly possible that there is content above 80 Hz in the LFE channel. It's even possible that there is content above 120 Hz in the LFE channel on Dolby TrueHd and DTS MA soundtracks. In fact that is the reason there is an LPF of LFE in the first place, so that, if the higher-frequency content is detrimental, (i.e, makes the sub localizable), it can be filtered out.

Still, you selecting a higher crossover than 80 Hz, and preferring it, doesn't necessarily mean that there is content in the LFE channel above 80 Hz. It could mean that having the sub reproduce the re-directed bass from 80 to 120 Hz sounds better in your room, on your system than it does being reproduced by the speakers.

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Originally Posted by boarder1995 View Post

On my friend's new Denon 1611 unit, there's a Sub crossover and then separate mains/surrounds crossovers. This allows great flexibility.

This may seems minute and picky, but I believe words are important, and when used incorrectly can cause confusion. The Denon AVR-1611 does not have a "Sub crossover". It has an LPF of LFE; see page 50 of the online manual:
http://www.usa.denon.com/AVR-1611-OM-E_005.pdf

The Low Pass Filter, (LPF) of the Low Frequency Effects, (LFE), channel, or "LPF of LFE", (which is what you are referring to when you use the words "Sub crossover"), is *not* a crossover at all. A crossover separates frequencies at a certain frequency and sends one set of frequencies to one speaker and another set of frequencies to another speaker. The LPF of LFE is just a single filter than removes frequencies above it from the single LFE channel. It does not send anything anywhere else.

When referring to the LPF of LFE it should be referred to as such and not as a "crossover" because it's not a "sub crossover" and it can cause confusion to call it a crossover, (as evidenced by first post in this thread.)

Quote:
Originally Posted by boarder1995 View Post

I've also noticed while may speakers claim or do digg into the below 80Hz range, most do much better and play cleaner if left to only play 100Hz and up or even 120Hz and up - particularly 2 way designs. It's hard to compete in the sub 120Hz range using a couple 6" drivers powered by a receiver or amp that's also producing up to ~20,000Hz, versus a sub with a dedicated 10", 12" or so driver and a dedicated amp, when it comes to producing physically impactful bass.

This is just my experience in my room. YMMV. Best thing to do is experiment with lots of different content and let your ears do the deciding, or your gut if the bass is deep and loud enough.

Agreed! However, in addition to my ears, I prefer to use measurements to verify what my ears tell me.

Craig

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Perfection is not attainable, but if we chase perfection we can catch excellence."

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post #30 of 36 Old 09-14-2010, 09:05 PM - Thread Starter
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Originally Posted by craig john View Post

The THX crossover is only a "better choice" when it's used with THX speakers and subs. (Remember I said they were designed as a "system"?) Without THX speakers and subs, (or, at least, speakers and subs designed according to THX speaker and sub spec's), the THX crossover is just as much a crap shoot as any other crossover scheme.

Besides that, what do Dolby and DTS have to do with the crossover? They are encoding/decoding schema, and they have no idea what the playback system will consist of. It is completely up to the end user to optimize their system for playback. In terms of the crossover selection, that means knowing how your speakers and subs are designed, and selecting the crossover setting that best matches them.

What *would* be nice is if the receiver/pre/pro manufacturers gave users the option of selectable crossover slopes. Then users could more easily optimize the crossover to their particular speakers and subs. Of course, this would also allow for a lot more error on the part of users who don't understand and/or mis-use the settings.

Do you own THX speakers and/or sub(s)? A THX receiver or pre/pro? If not, maybe we can help you optimize your settings. What BM settings are you currently using, and how did you decide on them?

Craig

Ok, maybe I meant more along the lines of;

If the LFE is a limted channel, which by its very purpose it is, why hasn't there been a standard developed as to what audio data it will contain?

Seems to me things get directional above 80hz and it should be a digital track 0.1 standard....(screw anyone with bose style mains) Could movie theater setups have anything to do with this standard not being developed?

... or why isn't the LPF a proper "inverse crossover", redirecting to the mains, so nothing is disregarded.
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