The Crossover — Why such a division between methods? - AVS Forum
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post #1 of 9 Old 07-26-2012, 10:31 AM - Thread Starter
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On the most simplistic level as I can get, I feel I must ask this question; partly because I've never really seen it posted anywhere to get any type of response arguing for or against either method I'm about to introduce, nor has there ever seemed to be a consensus on the matter.

Background:
I'm running an SVS SB12-NSD with my 2-channel rig and loving the results. I have it running with an Anti-Mode unit and am experiencing good results there, too. My speakers begin rolling-off around 50Hz, thus after experimenting and running the Anti-Mode, I currently have my crossover set at around 75Hz. Now, I have read that it might be favorable to set it 1 octave from the speaker's limitations, so to speak (i.e., 100Hz); other interesting reads waxed about the effects of going the other way and setting it as low as possible (so, maybe around 35 to 40Hz). Hmmm...

The Question, Relatively Pure & Simple:
So with that, it begs the question (without getting into REW, EQ-ing of any kind/bass management techniques, or differentiating between setting the crossover yourself versus letting a Receiver do it for you after one has done the initial setup...speakers to 'small', et cetera):

Why does it appear that there is such a vast, cavernous difference between camps when it comes to setting crossovers on a sub? I've ID'd that there are mainly two, as somewhat illustrated above: Those who cross low, and those who cross above (as I am doing).

I'm not looking to get responses that say for me to set at what sounds best to me. I am looking for comments as to why there doesn't seem to be a hard-and-fast rule overall; why such a discrepancy exists between higher versus lower. It seems very odd to me; and it's a question that's been eating at me for some time...nothing more.

Why is there such a discrepancy?
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post #2 of 9 Old 07-26-2012, 11:13 AM
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Because it is a summing effect. Sometimes putting the crossover right at the point where your speakers "give up" gives you a nice 4th order roll-off instead of 2nd order and this can help for your room. Sometimes this might create a null. It all depends how the summing occurs around the crossover point.
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post #3 of 9 Old 07-26-2012, 12:30 PM - Thread Starter
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Quote:
Originally Posted by Sdiver2489 View Post

Because it is a summing effect. Sometimes putting the crossover right at the point where your speakers "give up" gives you a nice 4th order roll-off instead of 2nd order and this can help for your room. Sometimes this might create a null. It all depends how the summing occurs around the crossover point.

That is an outstanding answer. It makes total sense. I've seen it mentioned about the summing effect, but was uncertain how it pertained to the differences in methods. So, again, it has more to do with the room with regard to how you end-up setting it...

Thanks!
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post #4 of 9 Old 07-26-2012, 12:35 PM
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There are so many variables with speakers and subs. Here are some reasons people use either higher or lower crossover points:
  1. Phase relationship between mains and sub: There are many combinations: sealed speaker/ported sub, ported speaker/sealed sub, sealed speaker/sealed sub, ported speaker/ported sub, horn speaker/sealed sub, etc. These combinations combine differently depending on the phase relationship between the speaker and sub.
  2. Speakers and subs vary in their frequency response: Some subwoofers are linear up to 200 Hz and work well with higher crossovers. Some very low bass subwoofers need lower crossovers. Most speakers don't have loud enough output without distortion below 80 Hz and need the higher crossover. Some speakers have more output down low and or the owner doesn't listen as loud and a lower crossover with a shallow rolloff provides more sources for the midbass resulting in a smoother frequency response.
  3. Speakers and subs vary in their decay: Either the subwoofer or speaker has better natural decay and will work better with either a higher or lower crossover. This is shown in a waterfall measurement of each and can be used when determining crossover. The frequency response may be the same with either a high or low crossover, but the decay will differ.
  4. Variations in reflections: Both a speaker and subwoofer have reflections in the room. A lower crossover keeps the reflections more the same through the audible range of localization. This can help provide a better soundstage and is the reason two channel guys will sometimes prefer the lower crossover for music listening.
  5. Variations in room interaction: Due to their different locations, the speakers and subs will interact with the room differently. Changing the crossover can help optimize the speaker/sub/room interaction.
  6. Voicing: A speaker and subwoofer driver can sound different at the same frequency. Change the crossover gives the listener the preferred sound of either his speaker or sub.
  7. Calibration: Someone might not have their distance settings set properly for the type of subwoofer (it can vary depending on alignment type). This causes a timing differences and can result in being able to localize the subwoofer with a higher crossover. Some then lower the crossover instead of fixing the timing issue.
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post #5 of 9 Old 07-26-2012, 01:24 PM - Thread Starter
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Quote:
Originally Posted by desertdome View Post

There are so many variables with speakers and subs. Here are some reasons people use either higher or lower crossover points:
  1. Phase relationship between mains and sub: There are many combinations: sealed speaker/ported sub, ported speaker/sealed sub, sealed speaker/sealed sub, ported speaker/ported sub, horn speaker/sealed sub, etc. These combinations combine differently depending on the phase relationship between the speaker and sub.
  2. Speakers and subs vary in their frequency response: Some subwoofers are linear up to 200 Hz and work well with higher crossovers. Some very low bass subwoofers need lower crossovers. Most speakers don't have loud enough output without distortion below 80 Hz and need the higher crossover. Some speakers have more output down low and or the owner doesn't listen as loud and a lower crossover with a shallow rolloff provides more sources for the midbass resulting in a smoother frequency response.
  3. Speakers and subs vary in their decay: Either the subwoofer or speaker has better natural decay and will work better with either a higher or lower crossover. This is shown in a waterfall measurement of each and can be used when determining crossover. The frequency response may be the same with either a high or low crossover, but the decay will differ.
  4. Variations in reflections: Both a speaker and subwoofer have reflections in the room. A lower crossover keeps the reflections more the same through the audible range of localization. This can help provide a better soundstage and is the reason two channel guys will sometimes prefer the lower crossover for music listening.
  5. Variations in room interaction: Due to their different locations, the speakers and subs will interact with the room differently. Changing the crossover can help optimize the speaker/sub/room interaction.
  6. Voicing: A speaker and subwoofer driver can sound different at the same frequency. Change the crossover gives the listener the preferred sound of either his speaker or sub.
  7. Calibration: Someone might not have their distance settings set properly for the type of subwoofer (it can vary depending on alignment type). This causes a timing differences and can result in being able to localize the subwoofer with a higher crossover. Some then lower the crossover instead of fixing the timing issue.

This is just great...so informative! This really helps spell it out for me.
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post #6 of 9 Old 07-26-2012, 03:26 PM
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To expand a bit further on things beyond desertdome's post:

What your first post describes is common audiophile rules of thumb or more accurately folklore. Most of this comes from plug-n-pray experimentation and anecdotal cases which might be common, but are certainly not a rule.

Remember that most such recommendations originate to a time when measurements were a black art and full range speakers ruled. The mindset of recommending as low a crossover as possible comes from a past reality where enthusiasts had at most 3 dials to play with when dialing in a sub woofer (Level, XO, and phase). They were generally trying to combine with their main speakers which were still running full range with no high pass crossover, and the speakers were voiced to sound balanced on their own, no subwoofer needed. The recommendations tended to revolve around theoretical ideals of speaker behavior which is only observed outdoors or in a textbook. In past times with 2ch systems there also were very few who had expectations of dynamic playback levels anywhere near what we now know is possible and expect in modern home theater and 2ch systems.

If you did get lucky and achieve a very nice extension to the bottom of most bookshelf speakers, it sounded a little thick because the factory voicing accounted for a lack of deep bass which you just added back in. There is also the very significant factor of in-room response. If you limit the upper response to ~40Hz, you have a little better chance of not having a big modal peak in the upper bass range which can be very audibly offensive. One of the most significant keys to utilizing a higher crossover frequency is smooth in-room frequency response. In your own case, the use of the AntiMode immediately provides you options those just twisting a few knobs don't have.

Finally we get to the behavior and capability of various speakers. Today you can find everything from compact speakers extending to near 30Hz and monstrous speakers intended for use with subwoofers with huge output to their low end cut off of 60-80Hz. The appropriate crossover implementation for each will be very different, and will differ still on the application (room and playback expectations). Most of the simple crossover rules of thumb stem from a blissful & idealistic approach which has little basis in reality. The approach of crossing at least an octave above the lower extension limit of a speaker comes from such an ideal view. It can be a workable approach, and for speakers with deeper extension, even desirable, but is certainly not a requirement.

Here are a few guidelines off the cuff:
  1. Are you able to high pass your main speakers?
  2. If yes to #1, choose a crossover high enough for desired playback capabilities and above any major holes or peaks observed in the response at your seat.
  3. If no to #1, make your best estimate at how low the speakers extend in room and experiment with a subwoofer crossover near that frequency.
  4. Do you have EQ available on your subwoofer?
  5. If yes to #4, you are more flexible with higher crossover frequencies if desired, but still subject to room response limitations.
  6. Either you can see the measured EQ'd result or you make a best guess and are left to listen to check how effective the correction was.
  7. If no to #4, measurements in room can be even more valuable to find the best subwoofer location and possible crossover frequency. If not, it's a plug-n-play effort.

In the end the appropriate effort and approach to executing a sub-speaker crossover depends greatly on the options and adjustments available to you.

Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." Daniel H. Burnham
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post #7 of 9 Old 07-27-2012, 09:26 AM - Thread Starter
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Quote:
Originally Posted by Mark Seaton View Post

To expand a bit further on things beyond desertdome's post:
What your first post describes is common audiophile rules of thumb or more accurately folklore. Most of this comes from plug-n-pray experimentation and anecdotal cases which might be common, but are certainly not a rule.
Remember that most such recommendations originate to a time when measurements were a black art and full range speakers ruled. The mindset of recommending as low a crossover as possible comes from a past reality where enthusiasts had at most 3 dials to play with when dialing in a sub woofer (Level, XO, and phase). They were generally trying to combine with their main speakers which were still running full range with no high pass crossover, and the speakers were voiced to sound balanced on their own, no subwoofer needed. The recommendations tended to revolve around theoretical ideals of speaker behavior which is only observed outdoors or in a textbook. In past times with 2ch systems there also were very few who had expectations of dynamic playback levels anywhere near what we now know is possible and expect in modern home theater and 2ch systems.
If you did get lucky and achieve a very nice extension to the bottom of most bookshelf speakers, it sounded a little thick because the factory voicing accounted for a lack of deep bass which you just added back in. There is also the very significant factor of in-room response. If you limit the upper response to ~40Hz, you have a little better chance of not having a big modal peak in the upper bass range which can be very audibly offensive. One of the most significant keys to utilizing a higher crossover frequency is smooth in-room frequency response. In your own case, the use of the AntiMode immediately provides you options those just twisting a few knobs don't have.
Finally we get to the behavior and capability of various speakers. Today you can find everything from compact speakers extending to near 30Hz and monstrous speakers intended for use with subwoofers with huge output to their low end cut off of 60-80Hz. The appropriate crossover implementation for each will be very different, and will differ still on the application (room and playback expectations). Most of the simple crossover rules of thumb stem from a blissful & idealistic approach which has little basis in reality. The approach of crossing at least an octave above the lower extension limit of a speaker comes from such an ideal view. It can be a workable approach, and for speakers with deeper extension, even desirable, but is certainly not a requirement.
Here are a few guidelines off the cuff:
  1. Are you able to high pass your main speakers?
  2. If yes to #1, choose a crossover high enough for desired playback capabilities and above any major holes or peaks observed in the response at your seat.
  3. If no to #1, make your best estimate at how low the speakers extend in room and experiment with a subwoofer crossover near that frequency.
  4. Do you have EQ available on your subwoofer?
  5. If yes to #4, you are more flexible with higher crossover frequencies if desired, but still subject to room response limitations.
  6. Either you can see the measured EQ'd result or you make a best guess and are left to listen to check how effective the correction was.
  7. If no to #4, measurements in room can be even more valuable to find the best subwoofer location and possible crossover frequency. If not, it's a plug-n-play effort.
In the end the appropriate effort and approach to executing a sub-speaker crossover depends greatly on the options and adjustments available to you.

Hi Mark. I'm both excited and honored that you, personally, took the time to talk about this. You and the others have really made this as informative as it could possibly get. Cannot thank you enough.
I thought about purposely experimenting with both sides of this coin, but after taking crude measurements and 'dialing it in', I've pretty much been settled on the 75Hz or so crossover point for my Paradigm Signature S2s. I can detect absolutely zero localization (the SVS sits just behind and to the left of the right speaker), and the bass is highly nimble, 'musical' and layered when it's called for.

Anyway, I appreciate your chiming-in, really!
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post #8 of 9 Old 07-27-2012, 04:59 PM
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I guess it comes to preference and what gears you have, those with big a$$ main speakers would generally want to cross it very low to to avoid a bump at the crossover point. Those with puny mains would like to set the crossover a bit higher to provide a fuller bass response
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post #9 of 9 Old 07-28-2012, 08:48 AM - Thread Starter
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Originally Posted by qguy View Post

I guess it comes to preference and what gears you have, those with big a$$ main speakers would generally want to cross it very low to to avoid a bump at the crossover point. Those with puny mains would like to set the crossover a bit higher to provide a fuller bass response

It does seem to appear that way, doesn't it. While I wouldn't say my speakers would ever be considered puny, the higher 70-ish range does reap great benefits; just as it seems someone with super-tiny surround speakers benefit from a 125Hz and above kind of crossover setting.
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