# Audio frequency allocation



## mikecd617 (Oct 19, 2012)

Hello, I'm just trying to wrap my head around audio in general. I find that information varies from one site to another. One of my questions revolve around how the receiver/sound system should be calibrated. I've read from a few sources that all low frequency should be directly sent to the subwoofer and to nothing else. Is this true? Or should low frequency be spread across other speaker such as towers etc.


----------



## rab-byte (Feb 1, 2011)

Welcome to the forums!

It depends. In general we can hear direction down to about 80hz below that we can't tell where a sound is originating. That's the reason only one subwoofer is needed, that's the .1 in 5.1

What you're asking about if I understand properly is crossover and roll off between a sub and a channel be it a tower or monitor. 

The goal is to have your system reproduce the whole frequency range from 20khz to 20hz at the same volume. This is what we call a flat frequency response. Even the best systems will have some variance in reproduction. That is the +/- 2db or the like you see on speaker and AVR spec sheets. And the reason people talk about the importance or timber or voice matching speakers. Since lower frequencies become more tactile and less audible voice matching your sub is less important. 

Back to your question. Some AVRs (Audio Video Receivers) will allow you to set the crossover (the point at which the sound is handed off to the subwoofer from the speakers) independently for each channel or speaker. Many will only give you one crossover point. 

If you only have one crossover you need to set it to the highest low frequency your speakers will reproduce. Often this is the lower end of your rear or center speaker. Doing this will allow you to have the same range playing out of all your speakers with your sub picking up the slack. If you have full range towers you can set the front speakers to "full" which will have them receive the full audio range from your AVR. Many towers can reach down to 50-40hz no problem but often they suffer from a significant drop in spl (sound pressure level or dB). Some AVRs will let you set crossover and LFE (low frequency effects/sub channel) to a different level. Doing this will allow you to direct movie effects differently from music. Giving you the oomph you may be looking for from movies while keeping your levels for music reined in. You may also see a subwoofer option for LFE labeled LFE+Main. Will send the subwoofer effects to both your tower speakers and the subwoofer. 

I guess the point is that your AVR can help fix certain problems with your audio but it can only do so much. Addressing issues in the room first will do more then the room AVR could ever adjust. Think of it like HDTV calibration. Calibration can go a very long way to optimizing your TVs performance but if the TV is getting glare from a window or isn't a very good display then calibration will not solve your video problems. 

My best advice is first to set your AVR to a direct or bypass the EQ. Play with speaker placement#. So the subwoofer crawl*. The after you have do that run your AVRs auto-calibration program. Then adjust your levels manually from there. There is a whole section in this forum dedicated to REW a free program that can really help you with equalizing or EQ'ing your system. 

#Speaker placement is very important too close to a wall and your base will often suffer too far into the room and you'll find the speakers get in the way of actually using the room. Your front speakers should be 1.5X the distance away from you as they are to each other. So if your speakers are 10 feet apart from each other you ideally want to be 15 feet back from them. Your center speaker should be centered with your TV at head level when seated and both the TV and center speaker should be directly between your two tower speakers. Your surrounds should be about 90-120 degrees around you (directly on each side of you or a little over your shoulder). Both DTS and Dolby's websites have good placement guides that are non-technical. 

*the subwoofer crawl is a simple non-mathematical way to identify the ideal placement of your subwoofer. You place the sub in your room's listening position (where you will be sitting day in day out) then play a track with ample amounts of base. You will get on all fours and crawl around the room listening to locations that have more or less base. Once you have found a location where the base is rich but not over powering place your subwoofer there. Now you've found the ideal location for your subwoofer! Simple right?


If anyone else would like to correct any mistakes or add their two cents I'd appreciate it. I'm sure I've missed something or gotten too technical about other aspects of setup.


----------



## JBrax (Oct 13, 2011)

It really comes down to personal preference and what sounds best to you. Many people set their crossovers at 80 thus sending all LFE to the subwoofer. Your sub was designed specifically for that task and it also takes a load off of your AVR. Not everyone chooses the THX recommended 80 but a number somewhere close as it really just depends on what your speakers can handle. To keep it simple 80 is a good starting point and from there tweak and go with what sounds best to you.


----------



## gdstupak (Jul 13, 2010)

JBrax said:


> ... Many people set their crossovers at 80 thus sending all LFE to the subwoofer.


Not trying to step on your toes, but to be technically correct...
All of the LFE (Low Freq Effects) is already going only to the sub (unless you have told the AVR to mix it into the mains also).
Setting the crossover for the mains at 80hz has the AVR send all frequencies below 80hz to the sub.


----------



## JBrax (Oct 13, 2011)

I apologize for not being technically correct. Just trying to provide a little non technical guidance so the OP can begin with a generalized starting point.


----------



## Owen Bartley (Oct 18, 2006)

Mike, it is really a matter of personal preference in the end. As has been mentioned, different receivers have different capability and different ways of handling crossovers and LFE, so it might help to know what you're working with. Personally I have my system set up for"large" and "LFE+Main" so the mains play full range, but also send low frequency information from the L/R channel to the sub. It works for me because I don't always turn the sub on for watching TV or listening to the radio, and I still have decent low end. When I turn the subs on, they might get a little help from the mains.


----------



## DanTheMan (Oct 12, 2009)

IMO, the more LF sources the better, but only if the LF sources are capable. My speakers, though large can't really keep up with my subs in that department. So there's a handoff. 

Essentially, get several subs(the better, the better;the more the better IMO) Audyssey multiEQXT32, EZEQ from Harman--well, or TACT and forget it. 

Dan


----------



## gdstupak (Jul 13, 2010)

Re-evaluating my settings this past weekend reminded me of a point to make....
Just because your main speakers can play full range doesn't mean you will get the best integration with your sub by playing them full range. 
My main tower speakers play confidently down below 40hz (Onkyo/Audyssey usually sets my mains as full). But there are many lower frequencies which my mains and sub play out of phase with each other which causes lower output at those frequencies. 
Setting my mains crossover at 80hz integrates my system best which gives me the flattest frequency response.

My in-ceiling surround speakers also play pretty low (Onkyo/Audyssey usually sets these at 50-60hz crossover). But they do not sound good playing those lower frequencies, so I usually set the crossover at ~90hz.


----------



## 3dbinCanada (Sep 13, 2012)

Whether to allocate bass frequencies (80Hz and below) to just the sub via the receiver's crossover is a function of several things, first and foremost, the room's acoustics, the 5 speakers bass capabilities, and lastly the receivers ability to drive multiple speakers full range simutaneously. 

Most receivers, even the higher end models still do not have the capability of driving a surround system suite of speakers full range at decent volume levels without beginning to clip. They simply don't have a large enough power supply to drive the entire suite full range despite being sonically very good. However, they can easily drive the main speakers full range with the rest of the bass in the remaining channels going the sub.

Most surround and center speakers are not capable of producing lower than 50 to 60 Hz so sending bass to these speakers would be a waste of time and possibly damaging them as well depending on how loud they are being played. 

Supposing though that you had 5 full range speakers in your surround system and the amplification to provide the power required. Your last hurdle will be room acoustics due to speaker placement. Its much easier to get clean bass from one or two sources in a room them 5 or 7 sources depending on room size. 

I hope this helps.


----------



## DanTheMan (Oct 12, 2009)

It should actually be easier with more low frequency sources to get a good bass response in your listening area. Dr. Geddes and Todd Welti have documented different approaches for multisubbing as well as a few others.

In acoustically large rooms--think gymnasium--this doesn't hold up.

Dan


----------



## 3dbinCanada (Sep 13, 2012)

DanTheMan said:


> It should actually be easier with more low frequency sources to get a good bass response in your listening area. Dr. Geddes and Todd Welti have documented different approaches for multisubbing as well as a few others.
> 
> In acoustically large rooms--think gymnasium--this doesn't hold up.
> 
> Dan


One is more likely to find multiple bass nulls in a large room compared to that of a smaller room. Furthermore, speaker placement that works for Home Theater may not be ideal for the bass reproduction..ie speakers maybe located to close to side or back walls cause excessive booming etc. Its much easier to place a sub for eveness of bass response than multiple full range speakers.


----------

