If a subwoofer's frequency response is 28Hz on the low end, what does it really get to? - Page 2

An Atlantic Tech System 450e for the fronts + Quad Outlaw LFM-1EXs. Checked with other 450e owners who had Jeff Meier Calibrate their system and they too said that he set the xo at 110hz too:rolleyes: At first I thought something was wrong because my previous speakers (Energy RC-10s and RC-70s) were set to 80hz by Audyssey. So far I can't really localize my subs so I think I should just leave it as is. What do you think? Is there anything negative with an XO that high?

The xo for the sub in the avr should be 120 Hz and the xo on the sub should be turned all the way up or off. If the sub can be localized whe using a xo of 8--100 the sub is not setup correctly with the main speakers. Sub are playback devices. A xo of 80 on the sub leaves an audio hole from 80-120 Hz. Content in movies or music above 80 hz should not be a problem with a correctly setup system.

Room mode excitation may result in the sub having uable LF response below 28 Hz .

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kindly refrain from the bickering and personal attacks or you will be asked to leave the thread

The crossover in the AVR should be where it sounds the best. Depending on the capabilities of both the mains and subs that might be 40Hz, that might be 120Hz, or anywhere in between.
The same applies to the LP filter of the sub amp. Some AVR crossovers have adequate filter slopes to keep the directional frequencies out of the sub to the point that they're inaudible, but not all by any means. The cascading of both the AVR crossover and the sub amp LP filter will add their respective slopes and give far better filtering of above bandwidth directionally locatable frequencies. With a low crossover point, 60Hz or lower, most AVR crossovers will sufficiently filter out directional frequencies, but the higher the crossover the more beneficial it is to use both the AVR crossover and sub amp LP filter.

To become aware of it's location in the room by listening. You hear bass coming from the sub instead of all around where you are.

Directional cues come from above 100Hz. Ideally you can have subs anywhere in the room and not be able to tell where they are. They should seem to be in the same spot as your mains, because ideally you're hearing all the directional cues from them. But if for one reason or another you have enough above 100Hz content coming from the subs you'll get directional cues from them, messing up the works. With most AVRs crossing them over at 80Hz won't keep the above 100Hz content below the threshold of audibility, and if crossed at 100Hz none will. Cascading the sub amp LP filter can fix that issue.

Bill - With a single sub (relatively nearfield) and an 80hz xover, my subjective observation was that while I couldn't localize the sub audibly, I could localize it due to my perception of pressure felt in my ear on the side the sub was located on. Adding a second sub eliminated this and (again, subjectively), I can't localize the subs due to pressure difference.

Interested in your feedback on whether this is pure placebo on my part or a technically supportable observation. Thanks!

My sub is 18 inches behind me, and I can't localize it even at 115dB. As for feeling pressure in the left ear more than the right, that's not possible with ten foot and longer wavelengths, both ears will be equally pressurized with too little phase shift differential for you to discern any difference.
It's the difference in arrival time at the two ears, and the degree of phase shift that results, which allows us to directionally locate sound via triangulation. How low a frequency/long a wavelength we can do that to is based on the distance between our ears. They must be a significant portion of a wavelength apart, otherwise the arrival time/phase shift is too slight for us to detect. If you really can detect the sub location you're hearing content above 100Hz at a significant level, even though you can't tell that's the case. Most AVR crossovers only have 18dB low pass filters, so with an 80Hz corner content is only down 18dB at 160Hz, and that you can hear. Cascade another 12dB or more of slope with the amp LP filter and you're down at least 30dB at 160Hz, and that you can't hear. Adding a second sub will mask above bandwidth content, since even at 200Hz multiple arrivals from multiple sources is a bit much for your ear/brain to deal with. But from 300Hz on up your acuity is increased exponentially.

Interesting - thanks for the detailed response. Always good to learn something new.

Craig. Chris from audyssey had always recommended setting the x over to 120hz for the sub since there's content in the LFE channel way above 80hz. By setting it to 80hz you're throwing away information. You can see this in the charts from the bass thread where informations extends well beyond 120hz.

By setting it to 80Hz you send that information to the mains, where it belongs if they're capable to 80Hz. Only cross over above 80Hz if the mains won't go that low.

There may be some confusion as to receiver crossover and sub crossover. Generally you set the sub at 120 and the receiver at 80. This would be for theater that is 5.1 and has lfe content. For music it is much more complicated. That's why I use a different setup for each.
Edited by Bond 007 - 1/25/13 at 7:29pm

+1 That's why I use a different setup for movies than I do music.

There seems to be some confusion at times as to whether folks are talking about simple LF material (which can be played by either or both the subwoofer and mains depending on the crossover level) and the LFE channel material (the ".1"), which, as I understand it, cannot be redirected to or played through the mains.

Bill, I understand what you are saying. Some avr's , for example the Pioneer SC models don't let you set the LP filter. In that case should the avr be xo somewhere around 80 and the sub xo all the way up. Using the LPF and the sub xo may cause some interference and lower the sound quality?

Where you set the AVR crossover frequency is the sub low pass frequency. IME you get the best results when that's as low as possible, and where that is depends on the capability of your mains and center. If they won't work well below 120Hz then by all means set the crossover at 120Hz, but if they're happy at 80Hz or even 60Hz that's where you should set the crossover. If the sub doesn't pass any directional frequencies using just the AVR crossover then leave the sub filter set as high as it will go, but otherwise set it as required. The way to do that is to run your receiver channel level calibration test tone through the sub, close your eyes, see if you can tell where the sound is coming from. If you can lower the sub filter frequency until you can't, even if that frequency is the same or even a bit lower than the AVR crossover frequency.

OK, lets firm up the terminology here to be sure we're all speaking the same language. There is no such thing as a "sub xo" in the AVR. It is difficult to understand your question when you use this terminology.

Here is what there is:

1. Crossovers on the main channels. A crossover consists of both a High Pass Filter, (HPF), on the speakers and a Low Pass Filter, (LPF), on the sub(s). Both of these filters are set together; they CAN NOT be adjusted independently. For example, if you set an 80 Hz crossover on the L and R main channels, both the HPF and the LPF are set at 80 Hz. If you move the crossover to 100 Hz, they BOTH move to 100 Hz. The crossovers should be set based on the LF capabilities of the speakers, and the upper frequency capability of the sub(s).

2. LPF of LFE. This is not a "crossover" because it is ONLY a LPF, and it is ONLY applied to the LFE channel. It has NO EFFECT on the bass that is redirected to the subwoofer output. It ONLY affects the LFE channel. Older AVR's, (pre lossless codec AVR's), may not have this feature. Also, if the content you're listening to doesn't have an LFE channel, this filter will not be applied to anything. Even if you are listening in "stereo" with the Bass Management turned on, the bass that is re-directed to the sub will not be exposed to the LPF of LFE because it doesn't originate in the LFE channel.

3. Subwoofer Controls.
Hope that helps.

Craig
Edited by craig john - 1/26/13 at 6:50am

Same Ive been setting my LPF at 80HZ even my calibrator told me leave at 80Hz, though I was told 120hz by some friends on the forum I tried it for a couple of days but I went back to 80hz.
Edited by Franin - 1/26/13 at 7:02am

Thanks Bill and Craig John for the info.

I set mine @ 70hz.

Curious: If content in the LFE channel is non-existent above - or is rolled off starting at ~80Hz - what is the disadvantage to leaving the LPF of LFE set at 120Hz?
- If there's no content above 80Hz, nothing gets played anyway.
- If there is content, it does get played - which, presumably, is what one would want to have happen.

Thanks.

As I understand it, there is always the potential for sound above 80 Hz but below 120 Hz in the .1 channel. Whether or not there actually is any is going to depend on the mix. I don't see that there's any harm at all in setting the LPF for LFE to 120, as if the mix does contain the sound I want it, and if it does not, so what?

This of course is quite different from the crossover frequency (or frequencies), which should depend entirely on your speakers and room.

"...so what?"

The harm is locatibility. Within personal sensitivity differences, it's generally accepted that the human threshold of locatibility of a sound is around 80Hz. A sound mixing engineer has no way of knowing where subs are going be placed in a room, so there's no way to spacially place sound in a LFE sound track above 80Hz. Yes, THX specs the LFE channel at 20Hz to 120Hz and others spec the channel all the way from an infrasonic 3Hz up to 20kHz and I'm sure, beyond. The rub is the ability for humans to locate reproduced sound above 80Hz.

That's my understanding regarding the question: "So what?" And no, I don't like it either.

Oddly enough, in doing some frequency sweep measurements and comparing sub frequency limit potentiometer settings, I've found that personally, in our room, having the limit potentiometer turned up, exasperates nulls in the 80Hz to 90Hz range and for what ever reason, probably harmonics, lowering the potentiometer setting has a reciprocal affect on the lower frequencies. Is there such a thing as reverse or negative harmonics?

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Edited by BeeMan458 - 1/27/13 at 5:12am

As my "so what" was tied to "and if it does not [contain the sound]", I reiterate: So what? If there's no sound, there's no sound to locate.

And I still say that if the engineer put some 100 Hz sounds on the LFE track, I want to hear them, not filter them out, despite the fact that I might notice that it's coming from my right.

Yeah, that's sort of how I figure it, too.
Agreed.

My comment was tied to the part of the comment of there being content in the sound track above 80Hz.

Agreed, if there's no content above 80Hz, there's no need to set your subwoofer's limit potentiometer above 80Hz and setting the other speaker's LPF above 80Hz is only going introduce sound location confusion. And yes, if there's content above 80Hz in the LFE channel, I too want to hear the recorded material. But in our case, like your situation, the sound will be coming from both the left and the right corners. In our place, like a ventriloquist, the sound will be coming from behind a large easy chair placed in the front right room corner and from the deep right side of the big easy chair on the left, will come more of these random >80Hz sound waves.

Now we have possessed easy chairs. Please, have a seat, the chairs will be with you in a moment.

As I explore the issues of subwoofers, I can see why many subwoofer directions are nothing more then how to plug them in and make AVR connections with additional language as to where the power function switch is located and maybe a bit more if the sub comes with added PEQ features.

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Edited by BeeMan458 - 1/27/13 at 5:41am

LFE content is strictly for movies and has absolutely nothing to do with 2 ch music. Therefore locatability is really not an issue. Its surround sound! Are you really going to notice that the minute amount of sound above 80 seems to be coming mostly from the direction of the sub while you are watching an explosion on tv? There is no harm in setting the lpf at 120 FOR MOVIES. MUSIC IS DIFFERENT!

Just answering the why behind the answer to the question as the question addressed 0.1 LFE, movie channel information as opposed to two channel recordings with no LFE, 0.1 channel, content.

Agreed and have posted as much regarding the locatibility of >80Hz (blending) in a complex action based recording. Again, I'm just giving the best response I'm able to, based on information found while researching this question.

In regards to this question, my notice was grabbed when I did room measurements to see how changing a sub's limit potentiometer to 80Hz or less affected measured room nulls as energy levels in the offending frequencies were attenuated. In our case, a huge, positive reduction at the null point of ten dB.

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Edited by BeeMan458 - 1/27/13 at 5:52am

Multi-channel music, (DVD-A, SACD, and BluRay Music), can have an LFE channel also. In fact, MC music is where the biggest problems with the LFE channel are found. I listen to a LOT of MC music, and that is the primary reason I set my LPF of LFE to 80 Hz.

Craig

Edit: I have attached a file that may be useful. It describes Dolby's suggestions for how MC music is to be recorded. An understanding of the recording process can help with the understanding of the playback process:

dolby5.1music.pdf 545k .pdf file
Edited by craig john - 1/27/13 at 8:00am