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Discussion Starter · #1 ·
On one thread I read here recently, someone alluded to a multiple sub setup where one would use two "ultra low frequency" subs, then rolled off (I'm assuming) to a couple sub seeing only the higher frequencies of the LFE signal.


Can anyone here give me a explanation or link to expand on this subject?


I am preparing to add a dual FI-318 IB sub to my HT room, to use along with my existing Rythmik 15" servo sub, which is placed next to the couch. But I also have two 12" (Rythmik non-servo) sealed subs that were built to be placed next to my main front speakers, which could be the "HF" subs. Plus I have a smörgåsbord of electronics that could be used to divide things up (Behr. DCX2496, Outlaw ICBM, etc.)


Or would the complications be more trouble then something simpler?
 

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I have something similar and think the complications are entirely worth it.


Here is the average response at the three seats on my sofa.



http://www.avsforum.com/avs-vb/showt...ht=ib+manifold


I can't recite all the settings by heart, but one IB manifold is LPed around 60hz, the other is about 80hz, and the maelstrom is around 100-110hz. No HP filter on the subs. The phase, slopes, levels were all set based on measurements and rather than recite them here, suffice it to say they are all over the map.
 

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You mean adding clean sounding sealed subs to your L/R/C channels to make them fullrange channels? Then dedicating good LFE subwoofers to your LFE channel? Mains subs are driven with L/R/C channels and LFE sub is driven by the LFE channel, receiver/prepro then set to Large L/R/C speakers.


Sounds like a normal practice to me. Just use the crossovers built in you mains subs, preamp, dedicated mains crossover, or L/C/R amps depending on what type of equipment you have or want to buy.
 

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Discussion Starter · #4 ·

Quote:
Originally Posted by amik /forum/post/18159322


I have something similar and think the complications are entirely worth it

Nice looking graphs. My project over at the Cult is labeled "Johnvb's IB". Since I am limited in the backwave area, it would be best to go with only one manifold, if I want vibration cancelling.
 

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jk, the idea is that by adding low frequency subs you get two benefits. first, modes from the main sub get smoothed out. second, you get more extension. the second sub only has to get to the level of the main sub in order to boost by a theoretical 6db. in reality, you might get 3-4db.


here is an example of two fourth order bandpass subs. the pink sub is smaller and tuned lower. it will help smooth modes from about 50hz down and add 4-6db around 20hz. in an average room, this would make the blue curve pretty much flat down to about 10hz.


 

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Quote:
Originally Posted by jkhome /forum/post/18159191


On one thread I read here recently, someone alluded to a multiple sub setup where one would use two "ultra low frequency" subs, then rolled off (I'm assuming) to a couple sub seeing only the higher frequencies of the LFE signal.


Can anyone here give me a explanation or link to expand on this subject?


I am preparing to add a dual FI-318 IB sub to my HT room, to use along with my existing Rythmik 15" servo sub, which is placed next to the couch. But I also have two 12" (Rythmik non-servo) sealed subs that were built to be placed next to my main front speakers, which could be the "HF" subs. Plus I have a smörgåsbord of electronics that could be used to divide things up (Behr. DCX2496, Outlaw ICBM, etc.)


Or would the complications be more trouble then something simpler?

Here is the link to the Geddes discussion on this topic.

http://www.avsforum.com/avs-vb/showt...ghlight=geddes
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by LTD02 /forum/post/18159435


jk, the idea is that by adding low frequency subs you get two benefits. first, modes from the main sub get smoothed out. second, you get more extension. the second sub only has to get to the level of the main sub in order to boost by a theoretical 6db. in reality, you might get 3-4db.[/IMG]

Thanks LT. I probably will first try using the one servo plus IB, and see how that goes.


OT... Have you dug out of the snow yet? I noticed the pile I created from the driveway 3 Saturdays (?) ago just disappeared yesterday, still lots of big piles in parking lots around the area. I know Richmond got slammed worst then the Southside.
 

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Discussion Starter · #9 ·

Quote:
Originally Posted by NJTEX /forum/post/18159369


You mean adding clean sounding sealed subs to your L/R/C channels to make them fullrange channels? Then dedicating good LFE subwoofers to your LFE channel? Mains subs are driven with L/R/C channels and LFE sub is driven by the LFE channel, receiver/prepro then set to Large L/R/C speakers.


Sounds like a normal practice to me. Just use the crossovers built in you mains subs, preamp, dedicated mains crossover, or L/C/R amps depending on what type of equipment you have or want to buy.

Actually I was referring to using an extra dedicated crossover (such as a Behringer DCX2496), after the main AVR bass management, to split the LFE channel into low and high frequency ranges, basically making a triamp setup.


I read an interesting mini article by Brian of Rythmik Audio posted on the "Rythmik owners thread" on the other AVS sub forum. Basically he stated that the LFE channel should not be thought as a channel per say, but an extra encoding process to extend the headroom of the other channel. So an explosion on a sound track is actually sent to whatever channels it's mixed into, then bass management occurs, sending the low bass to the LFE. Made sense to me.

http://www.avsforum.com/avs-vb/showt...1214550&page=3


Using that logic, I could see how in some systems, running some speakers full-range (even with "helper"subs) plus the LFE sub(s), could perform worst then setting all speakers to "small", and using multiple subs.
 

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Quote:
Originally Posted by jkhome /forum/post/18159621


Thanks, 60 plus pages should hold me over for a while.

The original is a HUGE thread over on DIYaudio.com



Geddes is a regular there and if you enjoy reading discussions involving him there are many over there
 

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Quote:
Originally Posted by jkhome /forum/post/18159671


Actually I was referring to using an extra dedicated crossover (such as a Behringer DCX2496), after the main AVR bass management, to split the LFE channel into low and high frequency ranges, basically making a triamp setup.


I read an interesting mini article by Brian of Rythmik Audio posted on the "Rythmik owners thread" on the other AVS sub forum. Basically he stated that the LFE channel should not be thought as a channel per say, but an extra encoding process to extend the headroom of the other channel. So an explosion on a sound track is actually sent to whatever channels it's mixed into, then bass management occurs, sending the low bass to the LFE. Made sense to me.

http://www.avsforum.com/avs-vb/showt...1214550&page=3


Using that logic, I could see how in some systems, running some speakers full-range (even with "helper"subs) plus the LFE sub(s), could perform worst then setting all speakers to "small", and using multiple subs.

Gotcha! I can't see where Brian's configuration would hurt but the level of benefits achieved are completely system dependant.


I can see with my system that it would help but it would still leave me with mains amplification power as my bottleneck. When I fix that, midrange headroom would become my next issue. On the positive side, at least for the time being, I like buying amps better than crossovers!
 

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Quote:
Originally Posted by LTD02 /forum/post/18159435


jk, the idea is that by adding low frequency subs you get two benefits. first, modes from the main sub get smoothed out. second, you get more extension. the second sub only has to get to the level of the main sub in order to boost by a theoretical 6db. in reality, you might get 3-4db.


here is an example of two fourth order bandpass subs. the pink sub is smaller and tuned lower. it will help smooth modes from about 50hz down and add 4-6db around 20hz. in an average room, this would make the blue curve pretty much flat down to about 10hz.

Curious what the phase looks like for these two? Assuming they're in phase throughout their passband the result would be flat down to 10hz but I suspect they will have some different phase shifts resulting in cancellation. Just trying to throw a wrench in



Fortunately for the OP all of the subs that would be used are sealed so they should all play together relatively well (no huge changes in phase - you should be able to adjust the phase of them one time and get them all in phase across their intended bandwidth for smooth XO's).
 

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"Curious what the phase looks like for these two?"


good point...phase depends on placement. not sure if i recreated things ideally. this appears to be the phase for a common location.


 

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Quote:
Originally Posted by LTD02 /forum/post/18160690


"Curious what the phase looks like for these two?"


good point...phase depends on placement. not sure if i recreated things ideally. this appears to be the phase for a common location.

Hmm, that doesn't illustrate my point very well
Looks like those track together fairly well. I was thinking more like mixing a sealed and ported sub where they track together pretty well until around tuning where the ported one moves 180 degrees out of phase...
 
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