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Question about running two subs

cjf

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#1
Hello,

I've decided to finally take the leap into the world of subwoofer ownership with plans to purchase two of Rythmik's F18 Sealed Subs in the coming days. As I sit and plan on how best to configure them in my setup one thought came to mind that I'm unsure of the answer and was hoping anyone familiar with running more than one sub maybe could give some advise on.

My initial plan is to use my Benchmark DAC3 DX as the main center piece/connection point. The DAC3 DX has both XLR & Line Level Out jacks on it. Both of these connection points are labeled "Main" and are said to send the same signal out of both pairs of jacks at the same time.

I intend to use the Line Level "Main" Output jacks to feed my Pass Labs XA60.8 Monoblocks and the XLR "Main" Output jacks to send a signal to the two Subs. I will then use the built-in volume knob on the DAC to control the output level of all the speakers.

I have picked out a few places in the listening room that I will experiment with in terms of initial placement and its not likely that in their final resting place both subs will end up next to the main Left/Right speakers across the front wall (like seen in many sub owners systems).

So with that description out of the way my question is this. Since each Sub will either be receiving a Full Range signal from the Left or Right channel of the DAC3 am I required to at least attempt to follow a placement location for the Left Channel Sub somewhere on the Left side of the room and the Right Channel Sub somewhere on the Right side of the room? I believe that would be the expected general location of the subs given this configuration but maybe it doesn't matter?

A secondary question here is what kind of issues, if any, might I expect to run into if by chance the Left channel Sub ends up in the Front Left corner of the room and the Right channel Sub ends up in the Rear Right corner of the room fairly close the the listening chair (maybe 5ft)? To add to my uncertainty, what if also that Right channel Rear corner Sub also needs to have its Gain reduced by a decent margin (compared to the Left Sub at the front of the room) given its much closer proximity to the listening chair in an attempt to reduce location awareness?

My thought/concern which I admit ahead of time maybe unfounded is that since I am running Stereo Subs there may be some noticeable imbalance to the sound due to the signal feeding each sub channel not being "Mono/Summed Mono". I'm thinking along the lines of what it might sound like if you were to both reduce gain and tilt the balance of your main speakers to one side or the other.

With all this said I am aware of the concept of non-directionality in lower freq below 80hz but am unsure if that applies in all situations or if there are caveats involved when dealing with stereo subs not receiving summed mono signals.

Thanks for your thoughts on this
 

StevenEleven

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#2
Dang, no one has replied to you? Well I'm no expert, but I run two subs, so I'll meander a bit and the rest of the guys can bust my chops.

Point A: I run two subs. Price and brand not relevant for this discussion.

Point B: I have a receiver with surround sound and no doubt an $11 DAC chip and room correction and separate EQ for the subs, the towers, the center channel, and the surrounds.

Point C: If your subs are nice, 80 hz is a real nice cutoff frequency, a good rule of thumb. I let my receiver figure everything else out about the crossover and whatnot, because it's over my head. The subs are set to receive a full frequency signal and the receiver sends them what they need with some kind of 80 hz crossover.

Point D: I think a mono signal goes to the subs. Maybe if you have stereo outs to the subs and you have two subs it would be better to split them between channels. By my intuition is to send a mono signal to both. I think it would help better to deal with room modes or whatever you call them. I'm sure some folks have much more than an intuition on how to handle that but that's my unsophisticated methology.

Point E: I have one sub in the front right corner and one sub in the front left corner, a decent bit away from the walls, moved them around a little until I could relax about the sound,and level matched them with a decibel meter that was capable with low frequencies (not all of them are) from my listening position. I'm sure there are more sophisticated ways to handle it.

Point F: If everything else is humming (figuratively), in my experience adding a couple of capable subs makes for a huge upgrade in fidelity. It's one of the few upgrades I would say are exceedingly worth it. Getting full performance for that bottom octave or two adds a ton of enjoyment and realism to the sound.

Hope this helps a little! Maybe people more knowledgeable than me will take a look at your questions and give you more informed advice. If so I'll be interested in their responses myself.
 

March Audio

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#3
Hello,

I've decided to finally take the leap into the world of subwoofer ownership with plans to purchase two of Rythmik's F18 Sealed Subs in the coming days. As I sit and plan on how best to configure them in my setup one thought came to mind that I'm unsure of the answer and was hoping anyone familiar with running more than one sub maybe could give some advise on.

My initial plan is to use my Benchmark DAC3 DX as the main center piece/connection point. The DAC3 DX has both XLR & Line Level Out jacks on it. Both of these connection points are labeled "Main" and are said to send the same signal out of both pairs of jacks at the same time.

I intend to use the Line Level "Main" Output jacks to feed my Pass Labs XA60.8 Monoblocks and the XLR "Main" Output jacks to send a signal to the two Subs. I will then use the built-in volume knob on the DAC to control the output level of all the speakers.

I have picked out a few places in the listening room that I will experiment with in terms of initial placement and its not likely that in their final resting place both subs will end up next to the main Left/Right speakers across the front wall (like seen in many sub owners systems).

So with that description out of the way my question is this. Since each Sub will either be receiving a Full Range signal from the Left or Right channel of the DAC3 am I required to at least attempt to follow a placement location for the Left Channel Sub somewhere on the Left side of the room and the Right Channel Sub somewhere on the Right side of the room? I believe that would be the expected general location of the subs given this configuration but maybe it doesn't matter?

A secondary question here is what kind of issues, if any, might I expect to run into if by chance the Left channel Sub ends up in the Front Left corner of the room and the Right channel Sub ends up in the Rear Right corner of the room fairly close the the listening chair (maybe 5ft)? To add to my uncertainty, what if also that Right channel Rear corner Sub also needs to have its Gain reduced by a decent margin (compared to the Left Sub at the front of the room) given its much closer proximity to the listening chair in an attempt to reduce location awareness?

My thought/concern which I admit ahead of time maybe unfounded is that since I am running Stereo Subs there may be some noticeable imbalance to the sound due to the signal feeding each sub channel not being "Mono/Summed Mono". I'm thinking along the lines of what it might sound like if you were to both reduce gain and tilt the balance of your main speakers to one side or the other.

With all this said I am aware of the concept of non-directionality in lower freq below 80hz but am unsure if that applies in all situations or if there are caveats involved when dealing with stereo subs not receiving summed mono signals.

Thanks for your thoughts on this
For 2 subs front and rear opposite corners are generally best for most effective room mode cancellation.

If the XO is set to 80Hz or below you are unlikely to localise the subs, even if one is closer. First try them both with the same volume setting as that will assist the mode cancellation.

Most low frequency stuff is mono so I suspect the amount of music stereo subs will be a problem with is minimal.

Having said all this I still think it is a better option to properly high pass filter the mains which you cant do in this configuration.

Hope that helps
 
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#5
Harman did research on using multiple subs. I don't have Toole's book right now, but I recall seeing diagrams that place them in each corner on the same side being the most practical choice.

Results were not room dependent.
 

Ron Texas

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#6
Harman did research on using multiple subs. I don't have Toole's book right now, but I recall seeing diagrams that place them in each corner on the same side being the most practical choice.

Results were not room dependent.
That's not my experience. Is that conclusion what Harmann reached or your interpretation of it? It's generally accepted that low frequency response is room dependent. In my room if the crossover is set low enough, a single sub can't be localized. I just love the internet. There is always someone out there who is willing to disagree with you.
 

andreasmaaan

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#7
For 2 subs front and rear opposite corners are generally best for most effective room mode cancellation.
Harman did research on using multiple subs. I don't have Toole's book right now, but I recall seeing diagrams that place them in each corner on the same side being the most practical choice.
The Harman research suggested the centres of two opposing walls were most optimal for room mode cancellation, IIRC.

With all this said I am aware of the concept of non-directionality in lower freq below 80hz but am unsure if that applies in all situations or if there are caveats involved when dealing with stereo subs not receiving summed mono signals.
It's a question of degree, i.e. we find it increasingly difficult to localise as frequency decreases, with the freequency at which localisation becomes impossible depending on many factors. Having said that, in a typical room and with music, it will be very difficult to impossible to localise below 80Hz, so I wouldn't worry if I were you.

So with that description out of the way my question is this. Since each Sub will either be receiving a Full Range signal from the Left or Right channel of the DAC3 am I required to at least attempt to follow a placement location for the Left Channel Sub somewhere on the Left side of the room and the Right Channel Sub somewhere on the Right side of the room? I believe that would be the expected general location of the subs given this configuration but maybe it doesn't matter?

A secondary question here is what kind of issues, if any, might I expect to run into if by chance the Left channel Sub ends up in the Front Left corner of the room and the Right channel Sub ends up in the Rear Right corner of the room fairly close the the listening chair (maybe 5ft)? To add to my uncertainty, what if also that Right channel Rear corner Sub also needs to have its Gain reduced by a decent margin (compared to the Left Sub at the front of the room) given its much closer proximity to the listening chair in an attempt to reduce location awareness?

My thought/concern which I admit ahead of time maybe unfounded is that since I am running Stereo Subs there may be some noticeable imbalance to the sound due to the signal feeding each sub channel not being "Mono/Summed Mono". I'm thinking along the lines of what it might sound like if you were to both reduce gain and tilt the balance of your main speakers to one side or the other.
All vinyl recordings and most modern studio recordings have monaural bass anyway, so this question will only come into play with certain modern live acoustic recordings and some older remastered pan-pot recordings (with odd exceptions of course).

For recordings in which the sub-bass is stereo, there will probably be some cases in which you'd want the sub for each channel on the same side of the room as its corresponding main. But so long as that criterion is fulfilled, whether the sub is at the front or rear of the room is not going to be a concern in probably 99% of cases.

Note that for stereo bass recordings, the subs will not cancel room modes if placed optimally for this purpose (e.g. in opposite corners or midway along opposing walls). But as I said - subject to your taste in music - this will not be an issue you'll encounter very often IMO.
 
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March Audio

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#9
The Harman research suggested the centres of two opposing walls were most optimal for room mode cancellation, IIRC.



It's a question of degree, i.e. we find it increasingly difficult to localise as frequency decreases, with the freequency at which localisation becomes impossible depending on many factors. Having said that, in a typical room and with music, it will be very difficult to impossible to localise below 80Hz, so I wouldn't worry if I were you.



All vinyl recordings and most modern studio recordings have monaural bass anyway, so this question will only come into play with certain modern live acoustic recordings and some older remastered pan-pot recordings (with odd exceptions of course).

For recordings in which the sub-bass is stereo, there will probably be some cases in which you'd want the sub for each channel on the same side of the room as its corresponding main. But so long as that criterion is fulfilled, whether the sub is at the front or rear of the room is not going to be a concern in probably 99% of cases.

Note that for stereo bass recordings, the subs will not cancel room modes if placed optimally for this purpose (e.g. in opposite corners or midway along opposing walls). But as I said - subject to your taste in music - this will not be an issue you'll encounter very often IMO.
Not to argue with the Harman data (havent disagreed with anything they do so far), but when I did try it the results were not as good, sorry dont still have the measurements. Not sure of any reason for this, could have been something specific to how I did it. Thanks for spotting my dodgy advice :)

Just for info here is the REW sim results for my room and listening position. Very similar, 2 major differences highlighted, one worse one better. Diagonal corner is a bit flatter below 60Hz.

1562645627581.png


1562645996334.png
 
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jmontoya21

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#10
I run two subs and i would agree that most likely they will not end up left right of the mains, based on my research four subs is the ideal set up, but two is a lot better than one, i would stay away from putting them in the corners because based on my research they create problems, i would do one in between the mains and the other across at the listening position, as far away from the walls as you can live with. i see your point on the stereo vs mono signals and have wondered the same thing, i think it may come down on how the music was recorded, i would like to try to feed the subs both left and right signals at both locations but i’m not sure if the experts would agree, as far as the loudness of the closer sub goes, yes, you would want to turn down that one some, but my bests results came when i first shifted phase on one sub and then even better when i added time delay via minidsp and dirac live.
 

March Audio

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#11
I run two subs and i would agree that most likely they will not end up left right of the mains, based on my research four subs is the ideal set up, but two is a lot better than one, i would stay away from putting them in the corners because based on my research they create problems, i would do one in between the mains and the other across at the listening position, as far away from the walls as you can live with. i see your point on the stereo vs mono signals and have wondered the same thing, i think it may come down on how the music was recorded, i would like to try to feed the subs both left and right signals at both locations but i’m not sure if the experts would agree, as far as the loudness of the closer sub goes, yes, you would want to turn down that one some, but my bests results came when i first shifted phase on one sub and then even better when i added time delay via minidsp and dirac live.

Multiple subs are really essential if you want smooth bass. Corners are fine and you benefit most from boundary gain, lowering necessary power and resultant distortion.

Take a look at this thread.

https://www.audiosciencereview.com/...subwoofer-selection-criteria.7080/post-163945
 

andreasmaaan

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#12
Not to argue with the Harman data (havent disagreed with anything they do so far), but when I did try it the results were not as good, sorry dont still have the measurements. Not sure of any reason for this, could have been something specific to how I did it. Thanks for spotting my dodgy advice :)

Just for info here is the REW sim results for my room and listening position. Very similar, 2 major differences highlighted, one worse one better.

View attachment 29107

View attachment 29109
Haha no worries :)

To be fair to the Harman research findings, they are not suggesting that the centred/opposed arrangement will necessarily produce the smoothest response at a given single point in the room, but rather that it will be most likely to produce the closest to optimal combination of all of the following:
  • the smoothest response at the widest range of likely listening positions in a rectangular room
  • the smallest variations in response between those positions
  • the highest sound power per input, on average, at all those positions
The arrangement you went with was also found to be an good one, although slightly less optimal on average. These charts from the document neatly sum it up:

1562663114500.png
 

PierreV

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#13
In my limited experience either 2 rooms (dual subs) or 3 rooms (1 dual, 2 single) depending on the mood...

* stereo imaging never an issue.
* manufacturer suggested settings are usually awful.
* if one doesn't have a microphone calibrated DSP in the amplification chain (Audissey and the likes), DSP in the sub is essential, or at the very least precise phase and filter adjustments.
* some sub crawling required but room dependent.
* bigger is better - the SB16 Ultra is supposedly way too large for my office, but I am very happy with the result running it at -25 or -23 dB. It's probably overkill for the room and not cost efficient but it gives me the freedom to move it and use it elsewhere.
* best strategy if one wants clean FR is to measure (REW for example) and adjust. If you can't measure, even listening to a frequency sweep should help: it should be as 'stable' as possible by ear. In a way, this is the best test for audibility - if the sweep level doesn't fluctuate at the listening position you are all set - but it is a bit hard to use one's ear to tweak the parameters.

The difference in SQ between a sub thrown at some place per manufacturer instructions or theoretical suggestions found on the net and a properly set up one is massive. I can A/B test by turning my sub dsp parameters on/off from a phone and the result goes from a boomy molasse of excessive bass to a tight, as it should be, punchy and well defined one.

@mitchco 's experiments https://audiophilestyle.com/ca/revi...ker-comparison-with-binaural-recordings-r768/ and e-book https://www.amazon.com/Accurate-Sound-Reproduction-Using-DSP-ebook/dp/B01FURPS40 are very helpful.

disclaimer: I optimize for my listening position and don't care much about a large sweet spot.
 

cjf

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#14
Hello,

This is great info everyone and I appreciate the responses.

Well to start with it looks like I lied about the Subs I was going to purchase. Instead of two Rythmik F18's I decided to go for two Rythmik E15HP2's. Main reason was the slightly smaller footprint of the E15HP2 which in turn will allow me a few more placement options within the room over the bigger F18's. The room itself is about 6500cu/ft and very "Open". Its a new room and in a different house so I'm starting from scratch here with no history to go on. I don't think I will be disappointed with the smaller E15 Subs either way since they have the same onboard amp as the F18 model. My main usage for them is 99.9999% music anyway.

After reading thru the replies here I've also decided to resurect my old Lynx Hilo back from the dead and into the mix. This in addition to the DAC3 will allow me to have full control over the two Sub channel's separately from the two main speakers. The main speakers will run from the XLR outs of the DAC3 and the Subs will run from the Hilo XLR Line Outs. The AES/EBU Out of the Hilo will feed the DAC3 and I will use USB from the Hilo to the media server.

I considered this setup early on also but my main problem with it was that it introduces the need to mess with two separate volume controls which is not a big deal for those that only use their system for dedicated listening sessions at a preset output level most of the time. That level of course probably being chosen after careful measurements where taken within the room with an eye on the balance and gain levels between Sub/Main Towers at some predetermined SPL level.

But for my usage, I play my rig all day long which resides in the main living area at various output levels depending on the situation. Turning down the Mains Vol still leaves the Subs output at their previous dedicated "listening session" level. Then when you go and fiddle with the Sub Vol level to compensate I can imagine it wont be too long before both Vol levels are out of whack from where they once were when you setup the whole rig using REW and other DSP software.

Anyway I'm sure this isn't new info to anyone here but I wanted to mention it. For me having one volume control to handle all speaker channels and more importantly maintain their individual levels in relation to each other all at once is a necessity. So with that said in order to achieve the common gain control mentioned above I will need to configure/use a software based Vol control (ie..JRiver 64Bit) at the media server level as a wrapper around all the gear and its various knobs which control each individual output.

Using the software Vol control will allow me to disable all the other VOl control knobs in the chain. Finding a good/transparent VOL control is no small feat IME. The DAC3 DX has a very transparant VOL control in IMO and I have no complaints with it at all. But, the Hilo is a different story. As an example, I have found reasons in the past to be somewhat scared to add the Hilo back into the mix as a center piece. I know its a well respected piece of kit and without it some of the stuff being discussed here wouldn't even be possible but IME its placement in the chain needs to carefully considered for these reasons:

1. It doesn't do Linux AT ALL (if that's your thing, Windows/MAC Only...Blaah)
2. its Digital Inputs (except for USB) seem to be intolerant to automatically changing Bit/Rates from upstream external sources and I've yet to get them to pass any DSD streams at all sourced from upstream devices (ie..Bricasti M5 as an example)
3. Its Analog Vol control (for the Monitor/Headphone outs) is anything but transparent. An easy test here was to feed the Analog Outs from Benchmark DAC3 back INTO the Analog Inputs of the Hilo. Then without any AD/DA conversion involved, simply routing the Analog back out of Hilo via monitor outs, lots of details are lost when using the Monitor out and its Analog Vol control. Its not even subtle. Anyone who doesn't believe me please give it a try for yourself.

But I see I've gone off topic a little here so I will reserve my gripes about other gear for another day. In the meantime, I will break out the measurement gear I have and do Before/After measurements using REW to see how the main systems measures now in mthis new space before the Subs are in place and again after they are installed. Looking even further ahead, I will also most likely dust off the Audiolense software and put it to use to fix what needs fixing.

Thanks again for the info/responses
 
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