rms8
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Post by rms8 on Oct 24, 2012 10:51:47 GMT -7
Okay, I see now.
Filler subs have no effect on bass peaks, they really only help in filling in bass DIPS. I assumed (again) that the filler subs would peak as well and their peak would help reduce the peak from the front subs, not entirely, but somewhat.
Guess that was all wrong on my part.
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Post by pitviper33 on Oct 24, 2012 15:06:15 GMT -7
EQ is used to lower peaks. Rear subs are designed to help fill nulls and as such need to have approx the same output level as the front drivers I'm not sure whether you saw my questions above (post 16), but it's not obvious to me how the smaller displacement from the rear drivers would have the limiting effect you mentioned for the front drivers. I can definitely see how the limited displacement will limit the ability to fill extreme nulls. However in my own room there were no nulls that were complete. There were substantial dips, but none with true cancellation. I would think that in a case like mine, it wouldn't take equal power to the main drivers to eliminate the partial destructive interference. I don't have anywhere near enough experience to say whether my case is the norm or if it's more common to have more complete and narrow dips. Have you seen a large number of cases that exhibit near complete cancellation? Or are most rooms like mine and just have shallow problem spots? If the latter is true, couldn't adding a small (relative to the main bass drivers) amount of phase shifted energy in those problem spots correct the issue? Or is large displacement required to correct even less-complete cancellation? |
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genesplitter
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Linkwitz Pluto pvc pipe speakers + 18-inch IB manifold
Posts: 21
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Post by genesplitter on Oct 24, 2012 15:50:56 GMT -7
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rms8
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Posts: 48
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Post by rms8 on Oct 24, 2012 18:24:51 GMT -7
Starting to think I should just leave all the IB318's on the front baffle (as per my original idea) and not worry about "filler" subs. I'll let Audessey do it's magic, add my AntiMode if needed and hope for the best.
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Post by ThomasW on Oct 24, 2012 20:39:45 GMT -7
However in my own room there were no nulls that were complete. There were substantial dips, but none with true cancellation. A null doesn't mean zero output. Your 25dB 'dip', is a room induced null [aka mode]  |
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Post by pitviper33 on Oct 24, 2012 22:56:56 GMT -7
A null doesn't mean zero output. Your 25dB 'dip', is a room induced null [aka mode] Right. And had I attempted to fill that null actively instead of preventing it passively, it doesn't seem like it would necessarily require equal output from drivers at the back of the room. Sorry if I'm not making my question very clear. What I'm trying to understand is why rms's previous plan of using 2 15" drivers at the back of the room would limit his capabilities. It seems to me that they would not only not limit his 18s, but they might actually be very effective at improving room induced nulls such as I saw early in my build. What am I missing? |
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Post by ThomasW on Oct 25, 2012 6:41:36 GMT -7
Sorry if I'm not making my question very clear. What I'm trying to understand is why rms's previous plan of using 2 15" drivers at the back of the room would limit his capabilities............ What am I missing? If he's using 15"s to fill nulls, the output of the entire system is limited to the total output from the 15" otherwise the front/rear sub output won't be equal/balanced. |
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Post by pitviper33 on Oct 25, 2012 7:20:32 GMT -7
If he's using 15"s to fill nulls, the output of the entire system is limited to the total output from the 15" otherwise the front/rear sub output won't be equal/balanced. That's where I'm confused. Why is it necessary or even desirable to have the front/rear sub output equal and balanced? Is equal output really necessary to fill the nulls? |
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rms8
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Posts: 48
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Post by rms8 on Oct 25, 2012 7:21:01 GMT -7
There is plenty of room in the rear corners for a pair of 15" Titanics in a single sealed box on each side (provided i purchase two more). That would make it four "filler" subs in the rear. I get the concept that the rear subs are severely disproportionate to the front 18's, but I thought the concept was just assisting and not adding/supporting. If I was pushing the system as a whole to excessive volumes, then I would understand the disparity becoming a bigger problem, but at normal listening volumes for movies I would think/assume that the filler subs would simply help at reducing some peaks. Obviously this is all coming from no practical experience in an arrangement such as this  I appreciate all the feedback thus far and differing opinions!!!!! This is GREAT STUFF!!!!!!!!!! |
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Post by FOH on Oct 25, 2012 8:23:55 GMT -7
Sorry if I'm not making my question very clear. What I'm trying to understand is why rms's previous plan of using 2 15" drivers at the back of the room would limit his capabilities............ What am I missing? If he's using 15"s to fill nulls, the output of the entire system is limited to the total output from the 15" otherwise the front/rear sub output won't be equal/balanced. Isn't this only the case if he needed the broadband output of all 8-18s? One pair of 15s, or 18s could easily carry a room through the modal region, right? Thus the rears would be helpful. The huge displacement of the (8)18s is for the octaves below the modal region. This is the quick and dirty version, the detailed version is on page back. Nobody commented on my supposition, however I find it an interesting, and relevant topic. Plus, it makes sense to me.  |
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Post by ThomasW on Oct 25, 2012 9:43:41 GMT -7
There is plenty of room in the rear corners for a pair of 15" Titanics in a single sealed box on each side (provided i purchase two more). That would make it four "filler" subs in the rear. The rear subs aren't and will never be "filler" subs. They're just rear subs One calculates the amount of air that can be moved by the full stroke Vd (aka volume of air displaced) of a driver by multiplying the Xmax times 2 times the driver's SD. Do this for the 15"s and compare that to the 8-18"s Isn't this only the case if he needed the broadband output of all 8-18s? It doesn't need to equal the total output of the fronts, but IMO he needs to be a lot closer than 2 or 4 modest 15"s |
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rms8
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Posts: 48
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Post by rms8 on Oct 25, 2012 9:47:25 GMT -7
If he's using 15"s to fill nulls, the output of the entire system is limited to the total output from the 15" otherwise the front/rear sub output won't be equal/balanced. Isn't this only the case if he needed the broadband output of all 8-18s? One pair of 15s, or 18s could easily carry a room through the modal region, right? Thus the rears would be helpful. The huge displacement of the (8)18s is for the octaves below the modal region. This is the quick and dirty version, the detailed version is on page back. Nobody commented on my supposition, however I find it an interesting, and relevant topic. Plus, it makes sense to me. Makes sense to me too, but I guess until someone has actually implemented it in real time, it's all speculation at this point. Regarding what you suggested " One pair of 15s, or 18s could easily carry a room through the modal region, right? Thus the rears would be helpful. The huge displacement of the (8)18s is for the octaves below the modal region" I was planing on setting a HP filter on the filler subs at 20Hz since (from what I've read [thx for the docs] and experienced) there shouldn't be any crazy peaks in that region. Make sense?? |
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Post by FOH on Oct 25, 2012 10:48:47 GMT -7
There is plenty of room in the rear corners for a pair of 15" Titanics in a single sealed box on each side (provided i purchase two more). That would make it four "filler" subs in the rear. The rear subs aren't and will never be "filler" subs. They're just rear subs One calculates the amount of air that can be moved by the full stroke Vd (aka volume of air displaced) of a driver by multiplying the Xmax times 2 times the driver's SD. Do this for the 15"s and compare that to the 8-18"s Isn't this only the case if he needed the broadband output of all 8-18s? It doesn't need to equal the total output of the fronts, but IMO he needs to be a lot closer than 2 or 4 modest 15"s What's the differnce between these and filler subs? I don't know the distinction. Now, on to the displacement; if the playback needed all the displacement that the 8, 18s had in the modal region (~25hz on up), then I could see your point on needing 8, 18s to "catch", or whatever. But all but a couple of the IB drivers are merely there for excursion control for the deep stuff. Again, mere supposition on my part. I've seen many successful HT's with quite modest filler subs. |
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Post by FOH on Oct 25, 2012 10:56:58 GMT -7
Thinking aloud here;
How's this different than if he actually re-config'd, 2 channel stereo and the system had a single 18, per side, as a sub for that channel.
The rear 15's tasked with acoustic balancing duties. The remaining six 18's up front tasked with augmenting the extreme bottom end, ....low passed at 20hz.
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All that is hypothetical, back OT.
I don't understand, .. if the rear 15s can keep up with the mains, then I'd think they could work fine in response smoothing duties.
Thoughts?
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Post by ThomasW on Oct 25, 2012 12:05:45 GMT -7
I don't understand, .. if the rear 15s can keep up with the mains, then I'd think they could work fine in response smoothing duties. I suppose he could run the 15"s in a narrow passband then they wouldn't be asked to keep up with the 18" if there were major infrasonic signals. Were this my build, I'd have 4 IB3-18"s in the front (single bass array if there's an AT screen available) and a pair of Fi .Q18"s in each rear corner. Do we know what the main speakers are |
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rms8
New Member
Posts: 48
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Post by rms8 on Oct 25, 2012 13:05:20 GMT -7
I don't understand, .. if the rear 15s can keep up with the mains, then I'd think they could work fine in response smoothing duties. I suppose he could run the 15"s in a narrow passband then they wouldn't be asked to keep up with the 18" if there were major infrasonic signals. Were this my build, I'd have 4 IB3-18"s in the front (single bass array if there's an AT screen available) and a pair of Fi .Q18"s in each rear corner. Do we know what the main speakers are I've toyed around with altering the rear walls of the room to incorporate two IB318's in each corner, but it just doesn't seem to work out very well design-wise due to the volume they would need since they're IB's only. Unless something changes, I'll be using my Phase Tech and Niles speakers : Front L/R = Phase Technology PC-500Front C = Phase Tech PC-3Side Surround = Niles Stage Front Pro770FXRear Surrounds = Phase Tech PC-SurroundWide Chnl = Niles PHD42Height Chnl = Polk M3 |
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