Running 2 subs: Dual LFE outs vs. Daisy Chain (Y-cable) - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 10 Old 09-23-2019, 01:28 PM - Thread Starter
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Running 2 subs via Discrete LFE outs vs. Splitting 1 LFE signal (Y-cable)

Cheersen folks!

I found myself in a pickle: I have 2 subs (SVS SB-4000 and SVS PB 12 Plus) being driven by a processor that has multiple/distinct LFE outputs (4 as a matter of fact). It seems that, all of a sudden (literally overnight), the 2nd subwoofer output jack just died and it no longer outputs any LFE signals. Tried multiple troubleshooting techniques, such as swapping out the RCA cables, factory resetting, re-calibration, etc., but it seems that the LFE is now solely being outputted via SUB 1 only.

I've ordered a Y cable (1 RCA male to 2 RCA females) and I plan on daisy-chaining both subs from SUB 1 output only.

My question is this: if properly setup, would there be a sound quality difference between running multiple subs via dedicated Sub outs vs. daisy chaining them?

Cheerio!

Last edited by no_cure; 09-25-2019 at 10:39 AM.
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post #2 of 10 Old 09-23-2019, 02:03 PM
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The first question i have to ask is,,, if your processor has four separate LFE outs, why haven"t you tried the other ones, or are three of the four dead?

As for running two subs off of one LFE out,,,,, if they were identical and have built in DSP it would be pretty easy as you could adjust delay and phase manually, but with two different subs (not sure on how much difference there is in their port tune) that could be a bit more challenging vs having you processor make all the independent tuning adjustments for each sub separately. It can be done but likely not as well as your processor tuning each sub separately.

I also overlooked that 4000 is sealed vs the ported which just adds more difficulty to tune manually.

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post #3 of 10 Old 09-23-2019, 02:06 PM
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Originally Posted by indebtbassfreak View Post
The first question i have to ask is,,, if your processor has four separate LFE outs, why haven"t you tried the other ones, or are three of the four dead?

As for running two subs off of one LFE out,,,,, if they were identical and have built in DSP it would be pretty easy as you could adjust delay and phase manually, but with two different subs (not sure on how much difference there is in their port tune) that could be a bit more challenging vs having you processor make all the independent tuning adjustments for each sub separately. It can be done but likely not as well as your processor
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post #4 of 10 Old 09-23-2019, 02:21 PM
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Most dual sub outs are internal Y connectors. Some receivers with Audyssey have dual sub outs that can do individual levels & delays (but do EQ as a single sub). External Y connector should work fine. Results will depend on placement more than anything.

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post #5 of 10 Old 09-23-2019, 03:34 PM - Thread Starter
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Thanks everyone for responding...FYI, my pre/pro a Krell Evolution 707 3D.

Regarding using Krell's sub outs 3 or 4 instead of #2 , I believe that there is a way to over-ride the 'auto-system' and manually input that I have 3 physical subwoofers. Normally, I use the auto-calibration sequence to basically setup the distances and crossovers for each available speaker, and tweak from there (note = don't use the equalizer). I hooked up last night the 2nd sub to sub #3 out, but in the calibration process, if the system won't detect sub#2 , it will stop there and won't move on to 3 or 4...hence, besides Sub #1 out, no other LFE outputs will be active despite having a physical connection to other LFE outputs.

Until I figure this out, I was thinking of just leveraging a Y cable to daisy chain them from sub out #1 . To calibrate them both, I was going to manually input their distances by doing simple math:

Davg = (Dsub1 + Dsub2) / 2

And yes, the older PB12 Plus is ported (3 ports), while the newer one is sealed (SB-4000). Are you guys thinking that I might have phase issues because the subs aren't identical?

Do most people who only have 1 subwoofer out from their AVR, but daisy chain 2 (or more) physical subs, are the subs identical?
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post #6 of 10 Old 09-25-2019, 07:32 AM - Thread Starter
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Update: I can confirm that I can run both subs from LFE out #1 and 3, so sub out #2 digital card is caput (neither the RCA nor the XLR jacks work).

Now, since the auto-calibration process won't work (it will stop at 1 sub if it won't detect any signal from sub out #2 ), I had to manually set them up using a Radio Shack SPL @75db C-weighted (who remembers those eh??). This is fine and dandy, but am I missing out by not calibrating the system as such connected? Now, I do not use any EQ modes, I normally leave everything off and only use the calibration process to detect distances, offsets, crossovers, phase, gain, etc for all speakers.

Still, with that in mind, I just ordered a miniDSP UMIK-1 microphone and plan to use REW program to see my room's full spectrum frequency response. I will then see if I have any dips or spikes and can use the DSP on the SVS SB-4000 to correct them (the PB12 Plus is too old for DSP, but still kicking...pun intended).

FYI, both of my subs are centered around the front and back walls, but they ARE NOT equidistant from the MLP (the smaller sub, the PB 12-Plus is right behind the MLP sofa). If given the choice, is it advisable to run my subs via LFE's 1 & 3 separately or should I just daisy chain them from sub out #1 only?

Cheerio!
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post #7 of 10 Old 09-25-2019, 08:11 AM
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Quote:
Originally Posted by no_cure View Post
Cheersen folks!

I found myself in a pickle: I have 2 subs (SVS SB-4000 and SVS PB 12 Plus) being driven by a processor that has multiple/distinct LFE outputs (4 as a matter of fact). It seems that, all of a sudden (literally overnight), the 2nd subwoofer output jack just died and it no longer outputs any LFE signals. Tried multiple troubleshooting techniques, such as swapping out the RCA cables, factory resetting, re-calibration, etc., but it seems that the LFE is now solely being outputted via SUB 1 only.

I've ordered a Y cable (1 RCA male to 2 RCA females) and I plan on daisy-chaining both subs from SUB 1 output only.

My question is this: if properly setup, would there be a sound quality difference between running multiple subs via dedicated Sub outs vs. daisy chaining them?

Cheerio!
If the processor has discrete sub-outs, that - by definition - means they will be different than splitting the same signal and sending it to both subs. Usually a discrete sub-out will offer an individual level and distance setting. I have yet to see a mainstream discrete sub-out offer an individual EQ curve, but some fringe processors may offer it.

Splitting the signal at the subwoofer pre-out is not technically the same as 'daisy-chaining'. Daisy-chaining means the line level output of subwoofer #1 is used to send a signal to the line level input of subwoofer #2 . I generally don't recommend daisy-chaining any subwoofer because the line-level output is often high-passed and/or undergoes some sort of AD/DA conversion. There are exceptions of course, but overall you're better off avoiding a true daisy-chain.

If it's more convenient to connect to subwoofer #2 with a shorter cable from subwoofer #1 , then simply use the 1M-2F signal splitter at subwoofer #1 . This will avoid any potential for line-out shenanigans from sub #1 .

Agree with above that integrating a PB12-Plus and an SB-4000 will pose challenges with respect to different FRs and phase responses and you can expect at least some level of phase cancellation between them over certain bandwidths which wouldn't otherwise exist with two of the same model.
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post #8 of 10 Old 09-25-2019, 10:11 AM - Thread Starter
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@Ed Mullen : I appreciate your detailed input! Your SVS subs rock - as a testimony, the oldest gear in my setup is the SVS PB12-Plus sub (coming up on 11-12 years I think) and it's still working!

Apologies, I improperly referenced 'daisy-chain' terminology: what I meant to say was to use a Y cable (1M – 2F) to split one LFE signal into 2 subs, not physically daisy-chain the two subwoofers.
However, it seems that you recommend that I run my dual subs via 2 discreet LFE outputs from my Krell EV 7073D processor. Given that I can run both of my SVS subs via LFE out # 1 & 3 (LFE #2 is dead), and manually configure distance and gain for each sub…I’m leaning towards that choice.

Now, on the matter of properly configuring/calibrating 2 subs of different specs - how would one go about doing that?
My thinking was to leverage REW software to identify where my low frequency dips and peaks are; measure freq. response via 3 distinct tests: SVS SB400 alone, PB 12-Plus alone, then both subs together – then compare the graphs and try to correct any low frequency dips via the DSP app that comes with the SB-4000 sub. Now, I’ve never used REW in the past (just ordered the miniDSP UMIK-1 mic) so, admittedly, my thinking may have some flaws in it.
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post #9 of 10 Old 09-25-2019, 11:32 AM
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Originally Posted by no_cure View Post
@Ed Mullen : I appreciate your detailed input! Your SVS subs rock - as a testimony, the oldest gear in my setup is the SVS PB12-Plus sub (coming up on 11-12 years I think) and it's still working!

Apologies, I improperly referenced 'daisy-chain' terminology: what I meant to say was to use a Y cable (1M – 2F) to split one LFE signal into 2 subs, not physically daisy-chain the two subwoofers.
However, it seems that you recommend that I run my dual subs via 2 discreet LFE outputs from my Krell EV 7073D processor. Given that I can run both of my SVS subs via LFE out # 1 & 3 (LFE #2 is dead), and manually configure distance and gain for each sub…I’m leaning towards that choice.

Now, on the matter of properly configuring/calibrating 2 subs of different specs - how would one go about doing that?
My thinking was to leverage REW software to identify where my low frequency dips and peaks are; measure freq. response via 3 distinct tests: SVS SB400 alone, PB 12-Plus alone, then both subs together – then compare the graphs and try to correct any low frequency dips via the DSP app that comes with the SB-4000 sub. Now, I’ve never used REW in the past (just ordered the miniDSP UMIK-1 mic) so, admittedly, my thinking may have some flaws in it.
You don't necessarily have to use the two discrete sub-outs from the Krell. In fact, sometimes allowing a dual discrete AV processor to set the actual distance for sub #1 and sub #2 actually results in phase cancellation between them, particularly if they are in any sort of opposite wall config.

If you have REW, you may get better results with running both subs off pre-out #1 using a splitter and then measuring the FR of sub #1 , sub #2 and then sub 1+2. This will allow you to see if the starting locations for sub #1 or #2 are inherently bad (i.e., nulls) and also if sub 1+2 needs some phasing to optimize the combined response.

After you've done all that - then you can run set-up and it will think there is only one sub in the system (which are actually duals that you have already optimized and phased).

Ed Mullen
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post #10 of 10 Old 09-25-2019, 01:44 PM - Thread Starter
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Much obliged @Ed Mullen ! I don't completely yet understand (see) how I can use REW to bring both subs in phase with each other (and my mains). I understand the general theory of excessive/cancellation of modal peaks or nulls given multiple source points, so my goal should be to calibrate all subs and rest of speakers such that they all move forward/backward in sync at the subs' crossover frequency (which I always ignore the auto calibration and set it at 80 Hz across the board).

With that said, I DO have some external help: along with absorption panels @ early reflection points, I've recently installed bass traps in the 4 lower trihedral corners (floor-wall-wall)...

Upon further pondering about, it makes sense why in the past when my dual subs were being driven via pre-outs #1 & 2 discretely, the auto calibration mode always notified me that 2nd sub is out of phase. And yes, both subs are mid-way the front and rear walls (which for dual sub setups I understand it's ideal), but they aren't equidistant from the MLP.

Nevertheless, should be a fun weekend as my REW learning curve levels off (lots of reading to do...).

I appreciate everyone's input - cheerio!
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