If 80hz is the minimum cut-off for non-localizable bass, why is the limit for the LFE channel as high as 120dB?

When the .1 channel was created, did engineers just not care about bass localization?

If 80hz is the minimum cut-off for non-localizable bass, why is the limit for the LFE channel as high as 120dB?

When the .1 channel was created, did engineers just not care about bass localization?

Most people don't care about sound quality or do not feel the need to put a lot of money into sound (or are incapable of putting a lot of money into sound), so they buy tiny htib-type speakers which require high cutoff. -- At least thats my take on the matter

small cheap speakers are not capable in most instances of reproducing bass below 100hz
that would be audible from the seating posistion.

You have to realize that for many applications an 80hz crossover is the recommended point in which the roll off begins. It's not a brick wall, but a slope that ends at 120hz. There is just more emphasis on those frequencys below the crossover point, regardless of what that setting may be.

Ian

Here are some good articles on the subject:
http://www.hometheaterhifi.com/volume_12_2/feature-article-slope-troubles-6-2005.html

http://www.hometheaterhifi.com/volume_13_1/feature-article-thx-1-2006-part-3.html

http://www.hometheaterhifi.com/volume_9_3/feature-article-multiple-crossovers-9-2002.html

You have to realize that for many applications an 80hz crossover is the recommended point in which the roll off begins. It's not a brick wall, but a slope that ends at 120hz. There is just more emphasis on those frequencys below the crossover point, regardless of what that setting may be.

Ian

ACtually, it is a digital brick wall at 120hz in the encoder, but recommended practice is to roll off by/at 80hz in the master (regardless of the brick wall at 120hz) to minimize or eliminate localization of bass in the LFE track. I assume they left that space to allow a more gentle crossover down there rather than just brick wall at 80hz or something which would not be very good at all because then you'd want to crossover well below that in the master.

For a lot of HT systems the 120 Hz LFE cut off frequency does not matter.

Many people seem to set their receivers to all small speakers plus a subwoofer. Most receivers tend to filter the LFE at the crossover frequency along with the redirected small bass. So, if you speakers are set to all small, and you use a subwoofer crossed at 80 Hz, the LFE is filtered in the receiver at 80 Hz. Your receiver may or may not do BM that way. My particular receiver has an adjustable LFE high cut filter (AKA low pass), and I leave it set to 120 Hz.

By the way, there is plenty of LFE signal recorded between 80 and 120 Hz. I have measured it with True RTA at the subwoofer jack output. There is an 8th order (48 dB per octave) low pass filter applied at encoding, and it is easy to see in the LFE FR curve of a DVD.

ACtually, it is a digital brick wall at 120hz in the encoder, but recommended practice is to roll off by/at 80hz in the master (regardless of the brick wall at 120hz) to minimize or eliminate localization of bass in the LFE track. I assume they left that space to allow a more gentle crossover down there rather than just brick wall at 80hz or something which would not be very good at all because then you'd want to crossover well below that in the master.


By the way, there is plenty of LFE signal recorded between 80 and 120 Hz. I have measured it with True RTA at the subwoofer jack output. There is an 8th order (48 dB per octave) low pass filter applied at encoding, and it is easy to see in the LFE FR curve of a DVD.


Well said!


Ian

There are a couple of reasons.First, you can take the stress off your mains and center by raising the XO point to 100hz or even higher to 110hz.

You can only do this if your subs are colocated with the center and mains. I use 100hz because my subs are capable (SQ wise) to go up that high and the burden of demanding bass is no longer on the mains and centers. One side effect is the lowering of the sound stage.There are very audible artifacts at 100hz, so you may be drawing your attention a little lower than your center channel.

Also it leaves you the ability to adjust the cutoff point at the sub, which may be a problem because the mains are fixed at the processor's XO point.

Also it leaves you the ability to adjust the cutoff point at the sub, which may be a problem because the mains are fixed at the processor's XO point.

That's a very good point. Also, many feel that it's best to just use the receiver's xo but that isn't always the case. Using a higher setting and implementing the the subs xo provides more flexibility. Most receiver crossovers offer a 12db slope which in some cases may not be steep enough to render the best results. Using both and staggering the settings may provide you with a cleaner response.

Ian

I'm running my mains as small with HSU 3.3 Turbo & MTX 100 (farfield 50 Hz low & nearfield 50 Hz high) and have the crossover fixed at 200 Hz. With this crossover I notice alot more detail in the bass. The nearfield sub does not seem to be that much localized.

. . . By the way, there is plenty of LFE signal recorded between 80 and 120 Hz. I have measured it with True RTA at the subwoofer jack output. There is an 8th order (48 dB per octave) low pass filter applied at encoding, and it is easy to see in the LFE FR curve of a DVD.

Thank you, J_Palmer_Cass!

Whatever 'low frequency transducer system' we connect to our 'sub out' jack on our front end has to be able to handle sound reproduction up to a little more than one octave below middle C -- this is still in the low end of male singing voice, as well as guitar, cello, Eb clarinet and sax, French horn, and many other instruments.
Hopefully actual recordings don't place these instruments in the LFE track, but the engineering problem remains: our 'subs' must be capable of reproduction up to 120Hz cleanly.