Why should I cross my full-range speakers at 80hz in 2-Channel or Home Theater - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 15 Old 06-24-2020, 09:29 AM - Thread Starter
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Why should I cross my full-range speakers at 80hz in 2-Channel or Home Theater

I'm a DIY'er and see lots of talk about... "Just build it small because you're going to cross it over at 80hz to a subwoofer anyway".

This makes no sense to me, so I'm wondering what technical info I'm missing out on.
If you have the space for large monkey-coffin full-range speakers AND subwoofers, then why not have both and run the main [large] speakers full-range along with the sub?
Assuming the speakers can handle it of course.

I think I read somewhere that Dr Geddes configured his home theater that way.
Though his main speakers were not exactly true full-range capable.

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post #2 of 15 Old 06-24-2020, 09:30 AM - Thread Starter
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Quote:
Originally Posted by CZ Eddie View Post
I think I read somewhere that Dr Geddes configured his home theater that way. [full range main speakers + full range subwoofers]
No, I didn't read it. I watched the video.
I certainly don't want my subwoofers running full range.
But I can't think of any reason not to run my main speakers full-range.

"The boom is dead, long live the bass"
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post #3 of 15 Old 06-24-2020, 10:07 AM
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The way I setup/configure my system....... If I like the sound, I don't care what "experts" or anyone else says.
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post #4 of 15 Old 06-24-2020, 10:15 AM - Thread Starter
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Hahah, I "hear" you.
But if you have the ability to decide that you have fully vetted the pros & cons of a particular setup after just a few minutes of listening, then you're an audio God!

"The boom is dead, long live the bass"
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post #5 of 15 Old 06-24-2020, 10:18 AM
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Three reasons come to mind:

1) Speakers must be placed in the room where they provide the best imaging/soundstage and these locations are rarely the best location for bass reproduction.
2) Cancellations in the lower octaves caused by the interaction between the subwoofer(s) and speakers
3) Unless you plan on powering your mains with an insane amount of wattage, no "large" speaker can do what a subwoofer can do

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post #6 of 15 Old 06-24-2020, 10:23 AM
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Quote:
Originally Posted by Alan P View Post
Three reasons come to mind:

1) Speakers must be placed in the room where they provide the best imaging/soundstage and these locations are rarely the best location for bass reproduction.
2) Cancellations in the lower octaves caused by the interaction between the subwoofer(s) and speakers
3) Unless you plan on powering your mains with an insane amount of wattage, no "large" speaker can do what a subwoofer can do

All three of these are right, but #3 is 1,000% right.
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post #7 of 15 Old 06-24-2020, 10:26 AM
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Quote:
Originally Posted by CZ Eddie View Post
Hahah, I "hear" you.
But if you have the ability to decide that you have fully vetted the pros & cons of a particular setup after just a few minutes of listening, then you're an audio God!
No... but a few hours of changes and evaluation allows me to sit at the right hand of one.
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post #8 of 15 Old 06-24-2020, 10:34 AM
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Is a guideline, not an hard rule.

Paul at PS audio, favor a sub for 2 channels but never mentions crossing the mains.

^Ya, what he says, if it sounds good to you, leave it there never mind what everybody else say.
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post #9 of 15 Old 06-24-2020, 10:41 AM
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If you run a sub alongside VERY bass capable mains there is no reason to follow the 80hz guideline, instead you can still take advantage of your mains AND the sub by crossing over lower...maybe @ 60 all depending on the range of your mains. Let the sub do the heavy lifting.

If this is a 2 channel setup for music and not home theater then just go with the big @ss, bass capable mains and skip the sub.

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post #10 of 15 Old 06-24-2020, 11:07 AM
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Quote:
Originally Posted by CZ Eddie View Post
No, I didn't read it. I watched the video.
I certainly don't want my subwoofers running full range.
But I can't think of any reason not to run my main speakers full-range.
https://www.youtube.com/watch?v=L4Bm123cKAM
Earl Geddes has never understood Bass Management.
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post #11 of 15 Old 06-25-2020, 07:30 AM
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What do you consider actual full range speakers?

80Hz is a guideline and a better one might be double the f3 point (where the speakers dip -3dB) for bigger speakers.
A sub gives you options and can solve problems mentioned earlier in the thread.


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post #12 of 15 Old 06-25-2020, 08:53 AM
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Quote:
Originally Posted by Alan P View Post
Three reasons come to mind:

1) Speakers must be placed in the room where they provide the best imaging/soundstage and these locations are rarely the best location for bass reproduction.
2) Cancellations in the lower octaves caused by the interaction between the subwoofer(s) and speakers
3) Unless you plan on powering your mains with an insane amount of wattage, no "large" speaker can do what a subwoofer can do
Great post Alan! I will just add a little more detail to #3 .... relieving the amps of of the burden of the bass frees up wattage in the main channels that can more efficiently be used to drive the speakers. Every octave of extension requires a doubling of driver excursion, which requires a doubling of power output. To go from 80 Hz to 40 Hz requires a doubling of power. To go from 80 Hz to 20 Hz requires a quadrupling of power. Subwoofers, with their larger and dedicated power amps, can dig deeply much more efficiently. Adding powered subwoofers can free up all that amp power to drive the speakers, and allows the entire *system* to play back louder with lower distortion.

Bottom line, it makes a lot of sense to use "bass-limited" mains in conjunction with Bass Management and powered subwoofers. One more advantage is that the $$$ saved on large, expensive towers can be re-directed towards better, smaller speakers, or more and/or better subwoofers.

Craig
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post #13 of 15 Old 06-25-2020, 09:19 AM
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I use the AVR Audyssey microphone, for calibrating the room speakers. With my set-up and placement of MATCHED front speakers, the crossovers are 60HZ across the board, including the surrounds.

I use the LFE subwoofer input and set the subwoofer at half gain/volume, before speaker calibration. After calibration, I reduced the gain/volume to 1/4, for my overall listening. I have a button on the remote for DD surround for Netflix movies, and the music button is set for Multi-channel mp3 music.

Since I have this Audyssey calibration with my AVR, 60HZ crossover, it is where it is at.

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post #14 of 15 Old 06-25-2020, 07:35 PM
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Bottom line, use the right tool for the job. Subs are created to reproduce bass. Tower speakers reproduce bass as a side-gig to reproducing all the rest of the frequencies.

It's a VIRTUAL channel unless stated otherwise.
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post #15 of 15 Old 06-25-2020, 07:50 PM
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Heya,

Crossing over around 80hz is often to help with localization in movies (home theater) in addition to offloading a lot of energy and size needs and placement needs of a full range speaker set to do the same thing. It sounds like a great idea to skip the sub and just use full range mains if possible, but that assumes placement is excellent in the room and the bass range is not just a bunch of nulls that you cannot fix, since those bass ranges are placement dependent and you're seeing the room response, not so much the speaker's ability to create those frequencies at whatever SPL. So a sub helps since you can place it more ideally without destroying your imaging with weird placement of the mains. You can cross over lower if you want. Or higher if you want. It's all about how it works out in terms of room response and covering up any nulls at the listening positions. It may not matter at all for a lot of music that doesn't have a natural instrument or synthetically produces tones that drop as low as 20~25hz. But it matters a lot for movies/home theater where you will very often have 20hz~60hz tones on the regular, and more and more often with newer content.

Anyhow, cross them over where you wish based on listening position room response nulls to bass frequencies.

Very best,
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