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Old 7th August 2009, 08:00 PM   #1
krips is offline krips  Canada
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Default Lowest frequencies found in HT channels

I'm assuming that there is no content in left/center/right/surrounds below 20hz, but I was wondering if the lowest frequencies in these channels were even higher than that. ie - if you run your speakers full range, what is the lowest frequencies your speakers will see? thanks in advance.
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Old 7th August 2009, 08:33 PM   #2
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I think that is a far trickier question than you might think.

For one thing, the frequency being there is very different than you hearing it. At normal volumes I can't hear much below 28hz, and at high volumes, nothing below about 25hz. For me, anything below that isn't perceived as a tone, but just the 'foof' 'foof' 'foof' of the speaker moving.

Next, though just my opinion. I think a lot of what you feel in a action movie sound track, that which we perceive to be ultra-heavy ultra-low frequencies, are not frequencies at all, but phase shifts in higher frequency.

If a 40hz or 50hz tone is modulated with a phase shift of 10hz or 15hz, and a swept between channels that is timed with the phase shift, you will certainly feel that, but I don't consider the 10 to 15hz signal used in this manner a tone or a sound.

So, my point is, there can be subsonic frequencies that are not sounds at all, though you can feel them. I guess I would have to classify them more as effects.

I personally suspect there is really very little sound below 30hz, even though there may be some frequencies that are lower.

Like I said, answering your question gets tricky.

Steve/bluewizard
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Old 7th August 2009, 09:51 PM   #3
Paul W is offline Paul W  United States
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One of the chopper scenes in Black Hawk Down goes down to about 5Hz. Many/most newer action movies have content below 20Hz. If you have subs with clean output that low, the subsonic content can make quite an impact.

IB subs
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Old 7th August 2009, 11:55 PM   #4
fury is offline fury  Australia
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I think Krips is wondering if these low frequencies actually come out of the main speakers, or if they are sent to the sub channel.

I guess I am curious too, to know if it's really necessary to have say a center or rear surround channels playing down to 20hz, or if there is no information actually being sent to them in movies (as it is sent to the sub channel instead), and hence fine to have them only play down to ~80hz.
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Old 8th August 2009, 07:27 AM   #5
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Default Re: Lowest frequencies found in HT channels

Quote:
Originally posted by krips
I'm assuming that there is no content in left/center/right/surrounds below 20hz, but I was wondering if the lowest frequencies in these channels were even higher than that. ie - if you run your speakers full range, what is the lowest frequencies your speakers will see?
You assume incorrectly.

Idiots remix pieces of the theatrical LFE channel at high levels into the screen channels with some action movies having significant (-10dBFS?) subsonic (5-10Hz) energy.

Look for the Tom Cruise War of the Worlds remake spectral plots
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Old 8th August 2009, 07:49 AM   #6
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What are the THX specs?
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Old 9th August 2009, 02:59 AM   #7
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Someone posted on another thread that the lowest octave on a Bass Guitar is around 40hz and very musical. The lowest key on a piano is around 20hz and is not so musical but for effects is necessary. 20hz and lower would sure put a hurtin' on some small bookshelf sized center and surround speakers.
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Old 9th August 2009, 03:13 AM   #8
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There may be low frequency content in those channels, but if or how well you hear them depends on what speakers you are using there - if they are two-ways the midwoofers will start rolling off well above the lowest frequencies.

As an experiement, try hooking up a powered sub to any of the satellite channels and see what happens. Make sure you run the channels full range, or "large" on the speaker type selector.
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Old 9th August 2009, 03:47 AM   #9
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There were some spectra graphs posted on AVS a while back with surround channels showing a lot of high level and deep LF content, for some movies. Probably less of an issue in chick-flicks due to the lower explosion, gunshot, helicopter crash, meteorite and alien invasion to dialogue ratio.

Quote:
Originally posted by 901Fixer
Someone posted on another thread that the lowest octave on a Bass Guitar is around 40hz and very musical. The lowest key on a piano is around 20hz and is not so musical but for effects is necessary.
BG: E = 41Hz, B = 31Hz
Piano: Low A = 27.5Hz.

On a grand A sounds OK to my uncultured ear, but less good on smaller domestic uprights because of the shorter string length producing less fundamental, and the ear filling it in. Same is true with a 34" scale BG. Even E has insufficient length to produce a strong fundamental, and E is worse. E on a 41" URB is much fuller because of a higher fundamental content.
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Old 9th August 2009, 04:10 AM   #10
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So for music-ness, 30hz is really the lowest needed, not only to 40hz? This has been discussed some on other threads as to where does music end and effects begin. Low notes on Bass Guitar sound musical to me but the lowest key on even a Grand Piano is well into the seizmic clunk feel in my opinion.
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