2 different subwoofers for a 5.2 system? - AVS Forum
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post #1 of 23 Old 06-06-2012, 09:49 PM - Thread Starter
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hey guys ive been lurking here for a long time and this is my first post. I just bought a new JBL sub150p (10" 300w downfiring) and am going to use it with an older infinity ps12 subwoofer (12" 300w front firing). my speakers are the Pioneer SP-PK51FS speaker package. I was wondering if it was a mistake to get such a different subwoofer to use with my system or if its OK to mix and match subs. and would using 2 big subs be bass overkill for my modest system? I listen to a lot of electronic music and was just hungering for that extra impact.
thanks
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post #2 of 23 Old 06-07-2012, 03:01 AM
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Welcome to AVS. I'm going down this learning path as well. I have a second subwoofer in shipment right now that is a good bit more capable then my current one. Look forward to hearing some recommendations here. This will also be my first multi sub attempt so I'll be following.

I've found a ton of reading and approaches on this, perhaps tomorrow I'll dig all the links back up and throw some up here for you but you will find a ton of information.

Of course, there are multiple schools of thought here. One of the approaches places the more capable subwoofer up front in a sub sweet spot (see sub crawl) then the less capable sub (s) are used to tame modes placed along side walls or rear. They are recommending two less capable mode tamers only operating on certain freqs and not trying to match levels for those as they are just filling in the holes. This is the Geddes approach.

Another approach is a more textbook approach with perfect rooms, matching subs, geometrical placements... things like 4 equal subs along the middle of each wall. Works out great on paper from what I've read but the real world just isn't that tidy. This is the 'Welti / Devantier' approach

It should be an adventure finding the best setup. I do plan on using REW for measurements and a minidsp to help me out with PEQ. Highly recommend REW if you have not done so yet. My approach will be to try something, measure, try something else, measure... :-)

OKOK I'll dig up one link http://blog.acousticfrontiers.com/whats-new/2010/10/29/using-multiple-subwoofers-to-improve-bass-the-welti-devantie.html
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post #3 of 23 Old 06-07-2012, 09:33 AM
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Yes. You can run two different subs. It's optimal to run two of the same because in your case, the weaker sub may reach it's limits before the stronger one. To build on what dstew100 said, try for optimal placement of the bigger sub up front with your mains. Then look for a good location for the smaller sub much closer to your listening position. Then you can level match the two, and it won't have to work as hard to keep up.

And no it won't be too much for your setup with that much bass. You just need to adjust the gain (volume) on the subs to integrate in well with your speakers.

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post #4 of 23 Old 06-07-2012, 10:15 AM
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Yeah there seems to me more "actual implementation" schools of thought than just those two theory approaches. Strictly speaking, with the Geddes, you are not level matching the subs, you are just filling in the room modes with the extra subs. And the lesser sub can be at a lower volume (did I read 3 or 6 db down???).

It seems in implementation a lot of members do go with a level matching. Something along the lines of equal subs equal distance from MLP. Get the levels right, get the delays/phase right, and get the crossover right so it integrates well. If the second sub is lesser, this is the second time I've heard the recommendation to get it placed nearfield so it can keep up with the stronger sub. In this case I'd assume it's trickier to get the levels, delays, and crossover smooth... but that's the fun stuff. My second sub has been pumping the bass for something like 11 years, I'm sure it would look forward to some limited duties rather than try to keep up with the Rythmik FV15HP in route.

All of my inputs on this topic thus far are purely from reading, my first experiences will begin this weekend. So please, folks with the experience chime in.
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post #5 of 23 Old 06-07-2012, 10:27 AM
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I have used 2 different subs with great success. It's important to note that both subs were excellent performers.

Others use 2 different subs with great success.

IIRC, mojomike uses an SVS PB-13 Ultra in the 15Hz mode, along with a JTR Captivator built with 15hz tune. I think he is very happy with this combination.

I think cel4145 has some good ideas for you.
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post #6 of 23 Old 06-07-2012, 10:33 AM
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Does anything that had been said thus far change, if one of the two subs is sealed and other is ported?
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post #7 of 23 Old 06-07-2012, 11:55 AM
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^^

you dont want to do that because the phase difference between a sealed sub and a ported sub can be very different. For instance, a sealed sub at 20hz can have as little as 90 degrees phase shift (or group delay) while a ported sub with rumble filter turn on will have close to 270 degrees phase shift. If you can find the group delay of each sub, you know exactly the phase difference and can add rumble filter (which is HPF) to compensate. But that is a lot of research. If you don't have those plots, it will be a lot of trial and error.
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post #8 of 23 Old 06-07-2012, 12:32 PM
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Quote:
Originally Posted by Rythmik View Post

^^
you dont want to do that because the phase difference between a sealed sub and a ported sub can be very different. For instance, a sealed sub at 20hz can have as little as 90 degrees phase shift (or group delay) while a ported sub with rumble filter turn on will have close to 270 degrees phase shift. If you can find the group delay of each sub, you know exactly the phase difference and can add rumble filter (which is HPF) to compensate. But that is a lot of research. If you don't have those plots, it will be a lot of trial and error.

Brian,
I did not know that and may be getting myself into trouble. Can I not adjust the phase on the soon to arrive FV15HP or my current sub or my minidsp to correct the issue you noted? I'm reading and learning but I don't really really "get it" yet. My current sub is an ancient velodyne VA1512 which is a 12" front firing woofer facing forward and a 15" down firing passive radiator; my graphs are showing -3db around 28 Hz from 75 db REW test sweep. Is the passive radiator design considered sealed? I prolly should have got the F15HP if I had realized that. But hey, your shipment has been through Austin, Memphis, Knoxvile and Nashville on its way to Virginia tomorrow so it may be too late for that thought process.

I hope OP comes back soon or I'm really thread jacking here. Suppose it is on topic though.

EDIT: Also note the 12" woofer on the velodyne was replaced about 4 years ago with whatever woofer velodyne recommended at the time which was not the same as the original.
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post #9 of 23 Old 06-07-2012, 01:19 PM - Thread Starter
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thanks for the replies guys
the new sub just came in and im playing with it now. now that I have 2 subs i feel like for some reason my 1 is just not performing like it used to. it used to rattle the windows in my house used by itself but now when im playing it at the same levels its kinda wimpy. my receiver has 1 LFE out and im using a Y-splitter, could that be a reason for it? or is it just that im getting used to double the bass rolleyes.gif
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post #10 of 23 Old 06-07-2012, 01:31 PM - Thread Starter
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well i just tried swapping the cords back and forth on the Y-splitter and i did notice a difference in volume levels of my old sub. I have my sub set at LFE but when i connect the LFE to the L connector by itself it is very noticably quieter than if i were to connect both the L and R connectors on the back of the sub. So now im thinking i might need another Y splitter to get 3 sub out cords coming from my receiver (2 for my old infinity and 1 for the new jbl). could it be that the infinity sub is an older model that uses LFE with both L and R channels? or by using both L and R inputs im "doubling" signal?
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post #11 of 23 Old 06-07-2012, 02:14 PM
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Quote:
Originally Posted by thebeast1616 View Post

well i just tried swapping the cords back and forth on the Y-splitter and i did notice a difference in volume levels of my old sub. I have my sub set at LFE but when i connect the LFE to the L connector by itself it is very noticably quieter than if i were to connect both the L and R connectors on the back of the sub. So now im thinking i might need another Y splitter to get 3 sub out cords coming from my receiver (2 for my old infinity and 1 for the new jbl). could it be that the infinity sub is an older model that uses LFE with both L and R channels? or by using both L and R inputs im "doubling" signal?

http://www.audioholics.com/tweaks/get-good-bass/subwoofer-connection-guide

You want to use the Y splitter like you are doing. Depending on if your subs have stereo RCA inputs or mono, or both you may need extra Y splitters if the sub(s) only has the stereo input.

Could be a phase issue where the subs are cancelling each others output.
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post #12 of 23 Old 06-07-2012, 02:17 PM
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thebeast

Do you have an SPL meter? What test tones do you have available? Is it just the AVR test tone or do you have a CD or REW?
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post #13 of 23 Old 06-07-2012, 02:50 PM - Thread Starter
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never really used an spl meter before i still have to read up more on that. I guess ill try another y splitter and see what happens from there. Thanks guys for the help
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post #14 of 23 Old 06-07-2012, 04:02 PM
 
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Quote:
Originally Posted by thebeast1616 View Post

thanks for the replies guys
the new sub just came in and im playing with it now. now that I have 2 subs i feel like for some reason my 1 is just not performing like it used to. it used to rattle the windows in my house used by itself but now when im playing it at the same levels its kinda wimpy. my receiver has 1 LFE out and im using a Y-splitter, could that be a reason for it? or is it just that im getting used to double the bass rolleyes.gif

Sounds like bass cancellation to me.
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post #15 of 23 Old 06-07-2012, 07:16 PM
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Quote:
Originally Posted by dstew100 View Post

Brian,
I did not know that and may be getting myself into trouble. Can I not adjust the phase on the soon to arrive FV15HP or my current sub or my minidsp to correct the issue you noted? I'm reading and learning but I don't really really "get it" yet. My current sub is an ancient velodyne VA1512 which is a 12" front firing woofer facing forward and a 15" down firing passive radiator; my graphs are showing -3db around 28 Hz from 75 db REW test sweep. Is the passive radiator design considered sealed? I prolly should have got the F15HP if I had realized that. But hey, your shipment has been through Austin, Memphis, Knoxvile and Nashville on its way to Virginia tomorrow so it may be too late for that thought process.
I hope OP comes back soon or I'm really thread jacking here. Suppose it is on topic though.
EDIT: Also note the 12" woofer on the velodyne was replaced about 4 years ago with whatever woofer velodyne recommended at the time which was not the same as the original.

Adjusting phase at low frequency is difficult. For instance, the period of a 20hz signal is 50ms. Half cycle is 25ms. It is not something can be easily implemented. Now even say one way or another that we do acheive this 50ms phase shift at 20hz. For that say 50ms, the phase shift is even more severe as the frequency goes up. Others have suggested inverting the phase of one of the sub. However, that just moves the problem to crossover point to the front speakers where we really need those subs to be in phase.

But your case is actually not that bad. Passive radiator is similar to vented subs in terms of operation. So you are not as bad as mixing sealed and vented sub. If the velodyne does have a tuning frequency of 28hz, you should get good result with mixing it with FV15HP in 2 port mode. One port mode will give you more phase difference as the tuning frequnecy is much lower than the velodyne. Try and let me know.
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post #16 of 23 Old 06-07-2012, 11:55 PM
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Sounds like bass cancellation to me.

Or, and perhaps this is obvious, you just need to turn up the gain on your sub amp. You just dropped the amount of signal going to you old sub by hooking up to just the one channel.

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post #17 of 23 Old 06-08-2012, 01:27 AM
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Originally Posted by thebeast1616 View Post

never really used an spl meter before i still have to read up more on that. I guess ill try another y splitter and see what happens from there. Thanks guys for the help

Do not give up hope, these ninjas will get you there. As far as needing another Y splitter... On the sub that has two rca input's does the left one say LFE or Mono really close to it? If not you likely need another RCA splitter. This will help but is likely not the overall prob.

Good news is, those two subs are able to make a flat line tight response if you are willing to help them do it.

Will you please tell me more about the process you are doing? Did you just drop them down and plug them in and push play? Did you sub crawl? Have you sent raw test signals to the subs?
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post #18 of 23 Old 06-08-2012, 01:49 AM
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Originally Posted by Rythmik View Post

Adjusting phase at low frequency is difficult. For instance, the period of a 20hz signal is 50ms. Half cycle is 25ms. It is not something can be easily implemented. Now even say one way or another that we do acheive this 50ms phase shift at 20hz. For that say 50ms, the phase shift is even more severe as the frequency goes up. Others have suggested inverting the phase of one of the sub. However, that just moves the problem to crossover point to the front speakers where we really need those subs to be in phase.
But your case is actually not that bad. Passive radiator is similar to vented subs in terms of operation. So you are not as bad as mixing sealed and vented sub. If the velodyne does have a tuning frequency of 28hz, you should get good result with mixing it with FV15HP in 2 port mode. One port mode will give you more phase difference as the tuning frequency is much lower than the velodyne. Try and let me know.

Brian
Appreciate your feedback, UPS says tomorrow is the arrival day but I'm going to need some time to figure out if I can get both subs happy together. The ancient sub has served me well, but I look forward to the upgrade your design offers. I've tried to gather the tools to get them playing well together. I will not give up on that attempt lightly, but I will be upgrading significantly even if I have to retire the velo... But to be frank, folks across the street expressed their appreciation for 10pm shut down.

I know where your thread is and I also have one going in the theory area. I'll be posting my graphs, failures, and hopefully some multi sub gains. I'm convinced multiple subs is the way to go... I'm not convinced my 11 year old sub can participate in the sound quality folks describe the Rythmik as providing. My goal is to grab another FV15HP, it's just going to be another year or three.

Attempting to digest the technical aspects of your post... Geeze mad calculus and computer science should get me there, I'll get there hopefully soon.
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post #19 of 23 Old 06-08-2012, 08:37 AM
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Will there be a big audible difference in these setup, even if you can get smooth frequency response for bass?

Setup A: Rythmik FV15HP + a cheap sub such as Klipsch SW450
Setup B: Rythmik FV15HP + Rythmik FV15HP

Movie playback volume will be about -15 to -10 dB.

Setup B is definitely my dream. I'm wondering if it's worth to pump my cash for dual FV15HP in my large area (living room opened to kitchen, dining, and the rest of the house through stairs, space >8000 cu ft). I presume setup B will give better REW waterfall due to its tight response, faster decay maybe.

I'm currently having Setup A.
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post #20 of 23 Old 06-08-2012, 08:32 PM
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I have a Rythmik FV15 that just beats my old Paradigm into dust. But I do have the Paradigm (PS1200) set up in a two sub system. It helps a little bit. Funny how when I adjust the Rythmiks cross over it seems to help the Paradigm. Will I get another FV15? Maybe someday..

Jeff
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post #21 of 23 Old 06-09-2012, 05:08 PM - Thread Starter
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Originally Posted by dstew100 View Post

Do not give up hope, these ninjas will get you there. As far as needing another Y splitter... On the sub that has two rca input's does the left one say LFE or Mono really close to it? If not you likely need another RCA splitter. This will help but is likely not the overall prob.
Good news is, those two subs are able to make a flat line tight response if you are willing to help them do it.
Will you please tell me more about the process you are doing? Did you just drop them down and plug them in and push play? Did you sub crawl? Have you sent raw test signals to the subs?

Right now i have the infinity PS12 and JBL sub150p subs, 2x pioneer SP-FS51-LR for mains, 1x pioneer sp-c21 for center, and 2x pioneer SP-BS21-LR that arent hooked up yet. Im using a pioneer vsx821k receiever. my audio source is just my laptop playing mp3s and internet radio. My set up is in a temporary location so i didnt want to spend the time do all that set up/subcrawling yet.

the inifinity ps12 sub it says "for LFE use L or R" under the inputs and theres a "LFE/normal" switch above it which i set to LFE. I just have 1 LFE out from my reciever so im using a Y-splitter (1 cord to each sub). I am planning on using another Y-splitter so i can get a total of 3 cords running from LFE out (1 for the JBL and 2 for the infinity).
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post #22 of 23 Old 06-10-2012, 01:51 AM
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Originally Posted by thebeast1616 View Post

Right now i have the infinity PS12 and JBL sub150p subs, 2x pioneer SP-FS51-LR for mains, 1x pioneer sp-c21 for center, and 2x pioneer SP-BS21-LR that arent hooked up yet. Im using a pioneer vsx821k receiever. my audio source is just my laptop playing mp3s and internet radio. My set up is in a temporary location so i didnt want to spend the time do all that set up/subcrawling yet.
the inifinity ps12 sub it says "for LFE use L or R" under the inputs and theres a "LFE/normal" switch above it which i set to LFE. I just have 1 LFE out from my reciever so im using a Y-splitter (1 cord to each sub). I am planning on using another Y-splitter so i can get a total of 3 cords running from LFE out (1 for the JBL and 2 for the infinity).

Given you description of the connections, sounds correct to me.

Clearly the benefits of multiple sub woofers are documented with real science and measurements behind it. However to get them playing nice is not easy. Position, Phase, Measurement, Trial and Error, these are some of the tools to getting there. If it is a temp set up you may try a couple different things but if it sounds better with just one sub, then maybe wait to get them playing nice until they get to the real spot.

Perhaps if you post pictures or a room diagram we/they can suggest some positions to try? Is it still sounding weaker as a pair than your single sub did? How are you trying to get the phase set?
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post #23 of 23 Old 06-10-2012, 09:17 AM
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Yatzee, New Rythmik FV15HP plugged in!!!
Not playing with the multiple subs right now, just got the Rythmik running with the music at -20 to break her in a bit before we crank it. Prolly start toying with the multi-sub and measurements next week. Definitely much more musical then my velo.
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