Crossover bass frequency ~ What are the advantages/disadvantages?

Holydoc

I searched for this answer but could not find it in these forums. The reason I am asking this question is that I want to be sure I am getting the best quality sound I can from my setup.

I know everyone has their own opinions about what frequency your bass crossover in your receiver should be set on. What I am searching for is technical reasons why it is better to set one frequency over another for MY system.

To give everyone background on my current setup:
• I have my receiver set to crossover at 80Hz.
• Subwoofer (SVS PB-12/plus) has its internal crossover turned off.
• All my speakers are set to small
• System is in a 7.1 configuration (see signature for speakers)
• Receiver has the capability to be set at 40, 60, 80, 100, or 120Hz.
• Only consider Home Theatre applications and not music applications

The reason I have it set at the above settings is that the THX spec is 80Hz with all speakers set to small.

IMHO, my reasoning, THX spec, for the configuration is not technically defendable. Why select 80Hz over 60Hz (remember we are just talking about my system and not systems in general)? What advantages/disadvantages am I getting for selecting 80Hz over 60 or 40Hz?

From what I have read, the 80Hz or below crossover setting makes technical sense since frequencies above 80Hz can be localized with our senses. Thus a crossover set to 120Hz on my system would allow my brain to determine that the bass came from the sub in the corner of my room and thus detract from the theatrical presentation. 80Hz and below are non-directional to our mind and thus the bass seems to radiate from all around the theatre. Is this assessment correct?

If the above assessment is correct, then between my choices of 80Hz, 60Hz, and 40Hz which would be the best for my system and why (don’t forget about the WHY)?

Please take in consideration that I have plenty of power to drive my speakers any way I want, the size of the RTi12’s and CSi5, and the quality of the SVS Sub.

Thanks again guys,

Sami

I have been experimenting with the settings and to me it's either 80 or 60 (it seems 80 is winning after 6 months). The reason being the LSi7's don't have much bass in them (SVS PCU is the sub). Too many things in the equation to say which one will be the best for you. How is the track mastered and how much db does it contain in the 60 to 80 region? Your SVS would most likely handle that area much better than the 12's. But if you can cut the SVS off at 60 it doesn't have to work as hard with scenes with bass from low to all the way to 80.

I think you will need to experiment like I did and decide which is the setting you like the most. One setting might work better with one movie while not being as good with another. I would think the heavy bass is directed to L/R channels so your centre shouldn't be of concern. Centre and surrounds I would leave to 80.

unc2701

Allegedly your -3db on the RTi12's is 30hz... personally, I favor having the mains handle as much as possible, then bring in the sub where the mains start to roll off. So without hearing the system, I'd vote for 40hz. A lot of people will tell you that you don't need a sub for 2 channel if your mains are good enough. I agree completely, but if you want that last octave it'll take a sub. To keep things as pure as possible, bring it in only where you truly need it.

Now, all that is talking about music. For HT, 80hz is your best bet, almost without question- Soundtracks are usually designed for the sub to get everything under 80.

Holydoc

unc2701 wrote:

For HT, 80hz is your best bet, almost without question- Soundtracks are usually designed for the sub to get everything under 80.

I guess I do not understand this statement. Soundtracks are designed for a subwoofer to play them at under 80Hz? Does a subwoofer speaker have a different sound than the woofer in a tower speaker of the same size? I do not mean to be difficult but if the sound mixer wanted all the sound from 80Hz and below to go to the subwoofer wouldn't he had removed all sound from the rest of the tracks except the LFE channel to ensure the replay was done correctly by the user?

I guess my real question is Unc, is if the soundtracks of movies are designed to send the 80Hz and below to a subwoofer, why technically did they select this range? Why not the 60Hz? I am trying to figure out the reasons so I can make an educated decision.

cnjvh

Another thing to consider is that everything below the crossover get mixed to mono so you lose the "stereo" effect of those frequencies. I found changing my crossover from 80 down to 60 seemed to create a much nicer front stereo experience. My opinon/theory is "lower is better" because of less localization and better imaging (assuming you dont go below the capabilites of the mains and create a dip in freq. response). However, the room characteristics can mess up a good theory pretty quick.

Holydoc

Sami wrote:

But if you can cut the SVS off at 60 it doesn't have to work as hard with scenes with bass from low to all the way to 80. .

Work as hard? I do not think this is a problem. The SVS is not straining nor near it potential. I am sure it could work from 120Hz without missing a beat. My concern is not whether I am pushing the system too hard, it is whether I am set up to get the most out of my system. In other words, would it make more sense to run the system at 40, 60, or 80Hz crossover given that I have the power?

Sami wrote:

I think you will need to experiment like I did and decide which is the setting you like the most. One setting might work better with one movie while not being as good with another. I would think the heavy bass is directed to L/R channels so your centre shouldn't be of concern. Centre and surrounds I would leave to 80.

I do not have the capability to set one set of speakers at a different crossover setting than the others. My receiver will only allow me to set a crossover that affects the entire 7 channels at the same time.

As far as experimenting for myself, that is what I am trying to avoid. I want to pull from this pool of knowledge that you guys have formed. I do not know enough about what to listen for to determine if I am getting the best experience out of my system's bass. For example it wasn't until I heard someone else's system play one of my CD's that I realized how much my old system lacked. I would of went on my merry way being satisfied with mediocrity. Of course after that I have spent several $1000 replacing all of my components and have surpassed his sound considerably.

unc2701

See this article:
http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe-channel-april-2000.html

They explain it better than I can, but the short answer is that the mains tracks usually get rolled off around 80 and all info under that gets moved to the sub track, so setting your sub crossover lower will leave a gap.

Holydoc

cnjvh wrote:

Another thing to consider is that everything below the crossover get mixed to mono so you lose the "stereo" effect of those frequencies. I found changing my crossover from 80 down to 60 seemed to create a much nicer front stereo experience. My opinon/theory is "lower is better" because of less localization and better imaging (assuming you dont go below the capabilites of the mains and create a dip in freq. response). However, the room characteristics can mess up a good theory pretty quick.

I had never thought about the fact that it is changing the effect to mono. Since the bass at 80Hz is suppose to be in the zone where localization is eliminated, it should not be a factor. However if the crossover is actually near the edge of that threshold, it may actually cause you to lose some imaging.

Good thoughts Cnjvh. I will have to test that theory about the imaging.

If I lower my crossover, am I losing anything? What am I sacrificing by going from 80Hz to 60Hz?

unc2701

Depends on how the onk works. some recievers will ignore the crossover for what it passes to subwoofer when it's got a 5.1 input (but still put a high pass on the mains). get a test CD and see what your onk does. If it sounds like you're getting a gap, then you know you need to put the xover at 80.

I run my system w/ unfiltered bass output, then set the crossover on the sub around 40 hz. My processor lets me send the .1 sub info to both the mains & the sub, so I don't get the gap.

Holydoc

unc2701 wrote:

See this article:
http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe-channel-april-2000.html

They explain it better than I can, but the short answer is that the mains tracks usually get rolled off around 80 and all info under that gets moved to the sub track, so setting your sub crossover lower will leave a gap.

Unc,

thanks for the link! That was exactly the type of information I was looking for.

If that article is true and "Dolby Digital's LFE channel carries additional bass information from 120 Hz on down. This is not a roll-off but a digital brick wall (i.e., no 121 Hz info), so the content is usually rolled off by the sound engineer starting around 80 Hz for a smoother blend ", then this is most probably the technical reason why THX has its standard at 80Hz. This 80Hz standard would give the sound engineers a starting point to roll-off the bass to the sub instead of making them do that determination on their own. By having this standard for roll-off, a theatre could be calibrated for one soundtrack and would work for any other soundtrack that was created using the standard.

Good stuff!

Sami

Holydoc wrote:

Work as hard? I do not think this is a problem. The SVS is not straining nor near it potential. I am sure it could work from 120Hz without missing a beat.

That's why I said it's impossible to say which would work best for you. Those are just things to consider when you experiment with the system.

Holydoc wrote:

I do not have the capability to set one set of speakers at a different crossover setting than the others. My receiver will only allow me to set a crossover that affects the entire 7 channels at the same time.

Then your weakest links are the centre and the surrounds but I don't think the soundtracks have much below 80 for them.

Holydoc wrote:

As far as experimenting for myself, that is what I am trying to avoid. I want to pull from this pool of knowledge that you guys have formed.

Then I would think 80Hz is good setting for you.

Wouldn't frequency sweeps give you a good idea of what setting works for you? Get a microphone, SPL metre and do some measuring. That would solve the problem of not knowing what to listen for but then again it would create other problems (like how to get the measurements). Is there a guide for us dummies that tells step by step how to do this? I have all the stuff but haven't had enough time to actually look at the procedure.

Maybe I'll need to consult some of the audio gurus from our lab, and see if I can borrow some pro equipment...$10k SPL metre, wonder how much better it would perform vs. RadioShack's.

izafar

unc2701 wrote:

See this article:
http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe-channel-april-2000.html

They explain it better than I can, but the short answer is that the mains tracks usually get rolled off around 80 and all info under that gets moved to the sub track, so setting your sub crossover lower will leave a gap.

If the receiver has proper implementation of bass management then you shouldn’t experience any hole.

Eric W

It depends on the receiver if each individual channel can have its crossover frequency adjusted, or if you have a "global" setting, where all the channels are set at once. If I remember right, H/K's usually do the individual, while Denons use the global, but I'm not sure about Onkyo.

Anyway, for that system, I would use no higher then 80 Hz for any of the speakers. 80 Hz is a great starting point (yes the reference to THX applies, they chose wisely for their 80 Hz spec).

If you have individual crossover capability, then I would put the rears to 80 Hz. For the fronts, I would use either 60 Hz or 80 Hz, depending on which one you think sounds better. Personally I think 40 is a bit low, if you have a SVS sub, which is a good quality sub, I would want it to reproduce more then just 40 Hz down. Then, set the center to 80 or 60 as well, and then the rears also to 80.

If you have a global crossover setting, then I would use 80 Hz. The primary reason, is any information that may be recorded in the rears, or the center that is in the upper bass range will be either lost or not produced too well if the system is crossed over too low.

Holydoc

Eric Wong wrote:

If you have a global crossover setting, then I would use 80 Hz. The primary reason, is any information that may be recorded in the rears, or the center that is in the upper bass range will be either lost or not produced too well if the system is crossed over too low.

Onkyo has global settings. I had not considered the back and center speaker before in the equation. With the center speaker basically falling off at 55Hz and the surround speakers falling off at 60Hz, it makes good sense to consider placing the crossover at some setting above these thresholds. In my case 80Hz is the only setting above 60Hz that I can select.

Thank you very much Eric for your words or wisdom. That reasoning can be easily defended and supported with documented truths. I like that!

Sami

Holydoc wrote:

Onkyo has global settings. I had not considered the back and center speaker before in the equation. With the center speaker basically falling off at 55Hz and the surround speakers falling off at 60Hz, it makes good sense to consider placing the crossover at some setting above these thresholds.

That's what I've been saying.

How much of the 40-80Hz range is coded to surrounds and centre, that's another matter so they just might be ok with lower setting as well. L/R most of the time are the most capable speakers in the system for bass so it would make sense to code them to receive the bass (or just the LFE).

aaharvel

Personally I like the 60hz (actually 62hz) setup all the way around. 80hz blares too much for music. While it may be desirable for home theater, I put my musical priorities first.

Holydoc

Sami wrote:

That's what I've been saying.

Sorry Sami if I did not give credit where credit was due. Sometimes you have to hit me with a really big hammer before I truly understand.

Thanks so much for everyone's input in this learning session for me. Excellent, EXCELLENT feedback!