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post #1 of 47 Old 06-25-2019, 06:16 PM - Thread Starter
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Calibrating dual subwoofers w/ Audyssey...

I'm trying to perform as much research as possible before running through Audyssey for the first time in my new theater room. One question I have is concerning the subwoofers. I have two identical Monoprice Monolith 10" subwoofers, and one will be near-field as depicted by the attached image. Subwoofer 1 is 12 ft. away while Subwoofer 2 is just 1-2 ft. behind the sofa. I have a Denon X8500H and I plan on using the two separate sub outputs.

From what I understand, the gain on both subs should be the same so that one is not working harder than the other, which makes sense. Is it necessary to use an SPL meter for this, or since both subs are identical, would having the gain dial at the same level on each suffice?

I've also read where the gain on the subwoofer itself should be adjusted such that Audyssey lands on a trim level of about -8 to -10. The subwoofer volume can later be increased via the receiver. How does this work when calibrating two separate subwoofers? If the gain/volume is the same on both subs, I would assume each sub will land on different trim levels with one being much closer to the MLP. I know it's recommended to take 1/2 of the difference of the trim levels and add it to the lower level and subtract it from the higher... should that final number be around -8 to -10 after adding/subtracting?

Hopefully my questions make sense. Thanks in advance for any advice.
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post #2 of 47 Old 06-25-2019, 06:31 PM
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Quote:
Originally Posted by Swoosh830 View Post
I'm trying to perform as much research as possible before running through Audyssey for the first time in my new theater room. One question I have is concerning the subwoofers. I have two identical Monoprice Monolith 10" subwoofers, and one will be near-field as depicted by the attached image. Subwoofer 1 is 12 ft. away while Subwoofer 2 is just 1-2 ft. behind the sofa. I have a Denon X8500H and I plan on using the two separate sub outputs.

From what I understand, the gain on both subs should be the same so that one is not working harder than the other, which makes sense. Is it necessary to use an SPL meter for this, or since both subs are identical, would having the gain dial at the same level on each suffice?

I've also read where the gain on the subwoofer itself should be adjusted such that Audyssey lands on a trim level of about -8 to -10. The subwoofer volume can later be increased via the receiver. How does this work when calibrating two separate subwoofers? If the gain/volume is the same on both subs, I would assume each sub will land on different trim levels with one being much closer to the MLP. I know it's recommended to take 1/2 of the difference of the trim levels and add it to the lower level and subtract it from the higher... should that final number be around -8 to -10 after adding/subtracting?

Hopefully my questions make sense. Thanks in advance for any advice.
Took a look at your AVR. Good news, it has XT32. According to this;
"Audyssey MultEQ XT32, Dynamic Volume, Dynamic EQ, LFC and Sub EQ HT: Delivers the ultimate equalization for your individual room including subwoofer EQ" meaning two real sub output.

Set both of your subs around 12 o'clock on the subs gain. Run your Audyssey. On the first run, it will tell you if the both subs volume are in range. Or some tweaking need to be done, as gain volume up or down. For both or one sub. Once in range, run the XT32 again. On the first sweep, the calibration system will adjust the phase correction/volume for each subs. Then do a full calibration for all speakers and the two subs as one, since there is only one bass channel (the .1).
Section II: Audio System Calibration and Subwoofer Levels:
II-A: Audyssey Calibration And Dolby Reference
II-B: Why We Add Bass After Calibrations
II-C: Where And How To Add Bass
II-D: Master Volume Levels And Sub Boosts
II-E: Gain Settings And Maximum Sub Output


Darth

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post #3 of 47 Old 06-26-2019, 04:14 AM
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Originally Posted by darthray View Post
Took a look at your AVR. Good news, it has XT32. According to this;
"Audyssey MultEQ XT32, Dynamic Volume, Dynamic EQ, LFC and Sub EQ HT: Delivers the ultimate equalization for your individual room including subwoofer EQ" meaning two real sub output.

Set both of your subs around 12 o'clock on the subs gain. Run your Audyssey. On the first run, it will tell you if the both subs volume are in range. Or some tweaking need to be done, as gain volume up or down. For both or one sub. Once in range, run the XT32 again. On the first sweep, the calibration system will adjust the phase correction/volume for each subs. Then do a full calibration for all speakers and the two subs as one, since there is only one bass channel (the .1).
Section II: Audio System Calibration and Subwoofer Levels:
II-A: Audyssey Calibration And Dolby Reference
II-B: Why We Add Bass After Calibrations
II-C: Where And How To Add Bass
II-D: Master Volume Levels And Sub Boosts
II-E: Gain Settings And Maximum Sub Output


Darth

Audyssey does "level-matching" which is certainly a valid approach if the user has no concerns about setting the levels of the two subs differently. However, as the OP points out, he does have this concern. He is asking about "gain-matching" which sets the two subs to identical gains, instead of identical levels. The approach can be done with Audyssey, but it requires some "intervention." I don't have time right now, but I will come back and explain how to implement gain-matching within the Audyssey routine.


Gotta go to work.


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post #4 of 47 Old 06-26-2019, 04:30 AM
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What I would recommend is to set the gain to about 12 o'clock on each to start out. Then, when you run Audyssey, it will check sub levels for each independently. During this step, try to get your sub to about 76-78 db's, but not more than 80 db's (you can use Audyssey or your own SPL meter if you like), which is a few db's hot according to the Audyssey. Once you do this for each sub, they should have around the same level from the MLP (where you put the Audyssey mic). Then will you run through the rest of the Audyssey setup, it will level the subs and set the distance for phase purposes. At the end, check your trim levels. They should be somewhere between -8 and -11. Then, if you want to add some bass boost back in, you can set them to something like -3 or -5, and you've got your 5db bass boost.
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post #5 of 47 Old 06-26-2019, 02:51 PM
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Originally Posted by Swoosh830 View Post
From what I understand, the gain on both subs should be the same so that one is not working harder than the other, which makes sense.

No, it doesn't "make sense," as the one closest to you will be much louder. You're negating the benefits of dual subs. You will not be using the sub by the TV to it's potential because the one closest to you will be way too overpowering.

Adjust the gains to match output levels and then let Audyssey run and set their distance and levels. Obviously, the nearfield gain will be much lower.
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post #6 of 47 Old 06-26-2019, 03:02 PM
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Originally Posted by m0j0 View Post
What I would recommend is to set the gain to about 12 o'clock on each to start out. Then, when you run Audyssey, it will check sub levels for each independently. During this step, try to get your sub to about 76-78 db's, but not more than 80 db's (you can use Audyssey or your own SPL meter if you like), which is a few db's hot according to the Audyssey. Once you do this for each sub, they should have around the same level from the MLP (where you put the Audyssey mic). Then will you run through the rest of the Audyssey setup, it will level the subs and set the distance for phase purposes. At the end, check your trim levels. They should be somewhere between -8 and -11. Then, if you want to add some bass boost back in, you can set them to something like -3 or -5, and you've got your 5db bass boost.
Again... this is the standard "level-matching" routine that Audyssey performs. Level-matching ensures that both subs contribute the same SPL at the Listening Position, (LP), irrespective of the gain settings of either sub. This can lead to significant differences in the gain settings of each sub, causing one sub to play at higher SPL than the other. This limits the overall "system output" to that of the higher-set sub and wastes some of the output of the lower-set sub. In addition, level-matching can only be "correct" at one position in the room, and will be incorrect at all other positions.

The OP is asking about "gain-matching" the subs, which is a different approach entirely. Gain-matching ensures that both subs are pushing the exact same energy levels into the space, and they are both outputting the exact same SPL's irrespective of the SPL at any one position in the room. See the OP's post below:

Quote:
Originally Posted by Swoosh830 View Post
I'm trying to perform as much research as possible before running through Audyssey for the first time in my new theater room. One question I have is concerning the subwoofers. I have two identical Monoprice Monolith 10" subwoofers, and one will be near-field as depicted by the attached image. Subwoofer 1 is 12 ft. away while Subwoofer 2 is just 1-2 ft. behind the sofa. I have a Denon X8500H and I plan on using the two separate sub outputs.

From what I understand, the gain on both subs should be the same so that one is not working harder than the other, which makes sense. Is it necessary to use an SPL meter for this, or since both subs are identical, would having the gain dial at the same level on each suffice?

I've also read where the gain on the subwoofer itself should be adjusted such that Audyssey lands on a trim level of about -8 to -10. The subwoofer volume can later be increased via the receiver. How does this work when calibrating two separate subwoofers? If the gain/volume is the same on both subs, I would assume each sub will land on different trim levels with one being much closer to the MLP. I know it's recommended to take 1/2 of the difference of the trim levels and add it to the lower level and subtract it from the higher... should that final number be around -8 to -10 after adding/subtracting?

Hopefully my questions make sense. Thanks in advance for any advice.
@Swoosh830 You've essentially described "Gain-Matching" which is a valid and useful technique, which can have some advantages over Level Matching.

Note: "Gain-matching" can only be used with *identical* subwoofers, which you have. (For those reading along, gain-matching can't be used with non-identical subs because they won't have identical amplifier gain structures, or identical driver excursions.)

Here is the process I use for Gain-Matching with Audyssey:

Prior to running Audyssey, if you have the capability of measuring Frequency Response, measure all the potential subwoofer locations and choose the two that have the least nulls, and/or the nulls that are least impactful. Place one sub in each of those two locations and measure the combined FR. Hopefully all nulls will be filled in and only peaks will remain. (Peaks can be EQ's by Audyssey. Nulls don't respond well to EQ and Audyssey has a much harder time EQ'ing them.) Here is an example of the different FR's that can be experienced from different locations of the subs:

Left Front Corner:


Right Rear 2/3 Wall:

Note that both subs have similar peaks but different nulls.

Combined Response of BOTH subs:


The combined response fills in the nulls and leaves only a few minor peaks for Audyssey to contend with. This is the primary reason why multiple subwoofers are virtually ALWAYS *better* than a single subwoofer... NO NULLS!!!

If you don't have measurement capability, us the "subwoofer crawl" method to determine the best sub locations: https://www.audioholics.com/home-the...ofer-placement
When doing the crawl method listen for the BEST bass response, not necessarily the LOUDEST bass response.

Once you've optimized the locations of the subs, start the Audyssey EQ routine. The first process Audyssey performs is to measure the subs individually to set their levels into an approximate range for calibration. However, since you want your subs "gain-matched" after running Audyssey, you'll do this a little differently. For the first sub, set the gain control, (aka Volume Control), on the back of the sub so that the SPL meter of Audyssey reads 70 dB. Then apply that exact same gain control setting to the second sub, irrespective of what it measures at the measurement mic. The combined SPL of both subs will be 73-74 dB, which is at the low end of the expected range for Audyssey's calibration. Your subs will be gain-matched at this point. (From this point on, do NOT adjust the subwoofer gain controls at all. Leave them exactly where they're set. Any other adjustments will be made in the receiver to the subwoofer trim settings.)

Now, run the rest of the Audyssey routine, which will measure and set subwoofer levels and distances, and calculate the EQ filters for every channel of the system. When finished, go to the receiver's Manual Calibration settings. Check the crossovers for all channels. Ensure that all speakers are set to "Small". If the crossovers are set to anything above 80 Hz, do not change or lower them. OTOH, if they are set below 80 Hz, raise them to 80 Hz if you feel so inclined. (I always raise them to at least 80 Hz, no matter how "Large" the speakers actually are or what their -3 dB point is specified at.)

Next check the Level Trims for the subwoofers. In most instances, the trims will be set to different levels, i.e., they'll be "Level-Matched" at the LP, which is what Audyssey wants. However, since you want them to be Gain-Matched after running Audyssey, you'll need to set the subwoofer trims identically. Take the two subwoofer trim settings and "average" them. Add them together and divide by 2. Set each trim to that setting. IOW, if one sub is set to -2, and the other sub is set to -8, you have a 6 dB difference in output between the subs. 6 dB is the equivalent of double the amplifier power and double the driver excursion. That difference is huge and will cause the higher-set sub to work twice as hard as the lower-set sub. Therefore, in our example above, add -2 and -8, and you get -10. Divide that by 2 and you get -5. Set both sub trims to -5. Both subs will now be gain-matched through the gain structure of the entire system. Each sub will receive the exact same signal level, be set to output the exact same SPL and will be driving the room with the exact same energy. Neither sub amp will distort or run out of headroom before the other. Neither sub driver will be using any more excursion than the other. They may measure slightly different levels at the listening position, but that is inconsequential to the overall result. Once you've averaged the trim settings, there should be no localization of either sub, and the combined EQ settings should be impacted only trivially, if at all.

The combined subs should still be properly calibrated to the rest of the speakers, but if you want to ensure that the calibration is correct, play some 75 Hz test tones from an external source. (You can't use the internal test tones because Audyssey is disabled when the internal test tones are playing, even after running Audyssey! You won't get a representative test signal of the Audyssey EQ and calibration from the internal test tones.) When running the external test tones, ensure that you have Audyssey enabled, DEQ off, and both subs playing simultaneously while taking the measurements. If the trims are slightly off the 75 dB mark, and they need to be tweaked slightly, be sure to apply the same trim adjustments to both subwoofer trims equally. Do NOT adjust the subwoofer gains on the back of the subs to tweak the subs, as it is much harder to retain identical settings with the sub gains than with the receiver trims.

Your system will now be completely gain-matched, and properly calibrated for gains, (not levels), and distances, and Audyssey will apply the appropriate EQ filter taps to get the FR as flat as possible. If you want, you can now re-measure the FR of the subwoofer channel to see how flat Audyssey has made the system. This is typical of the FR I get with Audyssey and the above techniques:



And here is the time domain response I get:

Note that this is actually 3 Seaton Sound Submersive HP+'s and the Submersive DSP has been deployed to provide the rising response with decreasing frequency. Otherwise the graphs would show flat response instead of the rising response.

Here is the total system FR, (subs + speakers), with Audyssey:

Note that this is a 1/3 Octave measurement whereas the sub measurements above are at 1/48th octave. Therefore, there is much more detail in the subwoofer measurements. Also note that the subwoofer FR measurement extends to 5 Hz whereas the full range 1/3 Octave measurement only here extends to 16 hz. The same dip at 16 Hz can be seen in both graphs but the response rises below 16 Hz in the subwoofer-only graph, which is typical of my subwoofers.

You can also see the dip at 2kHz that Audyssey implements. That can be disabled using the Audyssey phone app, which I would encourage you to get and use.

At this point, you can enable DEQ. Use the Reference Level Offset if you find the bass too be too exaggerated with DEQ. I generally use RLO of -5 as that reduces the bass slightly, as well as reducing the bump in level that DEQ adds to the surrounds, which can also be over-exaggerated. Play around with those settings until you find what works best for you. I have had very satisfying results with gain-matching and Audyssey XT32. I get ZERO localization of either sub and a I get full, articulate and detailed bass response. Every note sounds like it's being reproduced at the same level and there is minimal overhang of notes, as seen in the time domain graph above. I've a number of listeners, (many of whom are very knowledgeable and experienced forum members), describe the bass as "the best bass response they've ever heard."

Good luck and enjoy your new subwoofers, gain-matched with Audyssey XT32!!!

Craig

PS. If you have any questions, please feel free to ask!

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post #7 of 47 Old 06-26-2019, 03:03 PM
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Originally Posted by zeus33 View Post
No, it doesn't "make sense," as the one closest to you will be much louder. You're negating the benefits of dual subs. You will not be using the sub by the TV to it's potential because the one closest to you will be way too overpowering.

Adjust the gains to match output levels and then let Audyssey run and set their distance and levels. Obviously, the nearfield gain will be much lower.
Actually, it does "make sense" depending on the goals one has for their "system." Also, you're not "negating the benefits of dual subs." See my post above for an explanation of why gain-matching works and how to do it.

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Originally Posted by zeus33 View Post
No, it doesn't "make sense," as the one closest to you will be much louder. You're negating the benefits of dual subs. You will not be using the sub by the TV to it's potential because the one closest to you will be way too overpowering.

Adjust the gains to match output levels and then let Audyssey run and set their distance and levels. Obviously, the nearfield gain will be much lower.
Unless the near sub is immediately at the listener, and usually away from walls, they all put deep bass power into the room, and at these frequencies and according wavelengths, there is much less difference in level from subs that are closer vs further, and much more determined by modal interaction with the dimensions of the room and the seat location. 2 locations equal distant but at front vs rear of a room might have 1/2 octave or more range that is 6-10dB more efficient with the identical sub placed in either location.

Unless you truly have a near-field subwoofer where the response is predominantly the direct/outdoor response, I would argue you don't want to turn down the louder sub. As mentioned by others, having the closer subwoofer turned down means the further subwoofers will hit their limits while the closer subwoofer still has more in the tank. If you need more headroom at the lowest frequencies, that's not the most efficient use of subwoofers. With careful planning and measurements, it is possible to separately EQ subwoofers with say shelving filters such that all subwoofers contribute equally at the lowest frequencies, but multiple subwoofers at the front wall are balanced with fewer rear subwoofers. It's not that hard, but requires separate, manual EQ and enough headroom that dialing back the front subs doesn't compromise the upper bass range. There's a system in the build out phase that I'm supplying 18 subwoofers, each having a sealed 18" woofer, where they are doing something like this with even more advanced modeling and management of the range above 25Hz to get ultra smooth response across 3 rows, with enough air movement to make 10Hz highly useful.

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post #9 of 47 Old 06-27-2019, 11:44 AM
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Originally Posted by Mark Seaton View Post
Unless the near sub is ..

I'm glad you responded Mark. I spoke with Craig John about this yesterday and he was explaining some points for it.

If you never come close to using the max potential of your subs, is it still really beneficial? I have very capable subs (Cap 2400s) and I don't think about reaching limits with those subs, because I don't. I forget that some are output limited.

Beyond limited sub outputs, what are the benefits? If you have posted this somewhere else (in your thread maybe?), can you link me to it? I would like to read more about it. I've tried gain matching before and I can make a pretty graph with it, but as far as actual sound goes, it doesn't sound as good. The bass is more enveloping when the subs are level matched.

If someone had multiple seating locations scattered all around the room, I could see it being beneficial, but most don't. Even the ones that do, usually only worry about their MLP.

Thoughts?
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Originally Posted by zeus33 View Post
I'm glad you responded Mark. I spoke with Craig John about this yesterday and he was explaining some points for it.

If you never come close to using the max potential of your subs, is it still really beneficial? I have very capable subs (Cap 2400s) and I don't think about reaching limits with those subs, because I don't. I forget that some are output limited.

Beyond limited sub outputs, what are the benefits? If you have posted this somewhere else (in your thread maybe?), can you link me to it? I would like to read more about it. I've tried gain matching before and I can make a pretty graph with it, but as far as actual sound goes, it doesn't sound as good. The bass is more enveloping when the subs are level matched.

If someone had multiple seating locations scattered all around the room, I could see it being beneficial, but most don't. Even the ones that do, usually only worry about their MLP.

Thoughts?
The answer depends greatly on the application and listener. All subs sound better well within their maximum limits. It is quite rare to never touch the upper capabilities of a subwoofer below 16-25Hz. Unless you don't want to add the hardware to apply separate EQ or take the time to do the manual measurements and calibration, I would only look at dialing down the upper range which is likely where the stronger response is an issue, leaving you the headroom to still work with the lowest frequencies.

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Originally Posted by Mark Seaton View Post
There's a system in the build out phase that I'm supplying 18 subwoofers, each having a sealed 18" woofer, where they are doing something like this with even more advanced modeling and management of the range above 25Hz to get ultra smooth response across 3 rows, with enough air movement to make 10Hz highly useful.

I know it's not all fun and games for you setting up these systems, but it has to be pretty cool getting to play with stuff like this. How does the saying go? “Choose a job you love, and you will never have to work a day in your life.”
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I’m surprised this doesn’t come up more often, Craig’s post should really be added to the Audyssey and Subwoofer guides.

I just came across this same issue as well, as I have one subwoofer in a corner and one mid wall. Sure enough the sub midwall was playing about 6db louder than the one in the corner.

My question is, if both subs are the same distance from the main listening position. Both on the front wall just outside of main L-R speakers in my case. Is there any advantage in measuring them as two subs in Audyssey and tweaking levels vs measuring as one sub with a Y-cable feeding both subs?

It seems like in this case measuring as one would provide more accurate EQ, as levels are not changing post EQ.
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I’m surprised this doesn’t come up more often, Craig’s post should really be added to the Audyssey and Subwoofer guides.

I just came across this same issue as well, as I have one subwoofer in a corner and one mid wall. Sure enough the sub midwall was playing about 6db louder than the one in the corner.

My question is, if both subs are the same distance from the main listening position. Both on the front wall just outside of main L-R speakers in my case. Is there any advantage in measuring them as two subs in Audyssey and tweaking levels vs measuring as one sub with a Y-cable feeding both subs?

It seems like in this case measuring as one would provide more accurate EQ, as levels are not changing post EQ.
Generally it's best to EQ the combined response of both subs, as you *listen* to the combined response of both subs. If you're using a Y-cable feeding both subs, you are, by definition, gain-matching the input signal. Then, if you set both subs to the same gain/volume, you'll be gain-matched through the entire system chain.



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Originally Posted by craig john View Post
Generally it's best to EQ the combined response of both subs, as you *listen* to the combined response of both subs. If you're using a Y-cable feeding both subs, you are, by definition, gain-matching the input signal. Then, if you set both subs to the same gain/volume, you'll be gain-matched through the entire system chain.



Craig
Sorry, it seems I wasn't clear in my question.

Audyssey Sub Eq HT can eq 1 sub or 2 subs, when measuring 2 subs it will set individual delays delays and levels for each sub. As these should be the same in my case. Would there be any advantage to running Audyssey in two sub mode vs one sub mode with a Y-cable spitting the signal to two subs. In both scenarios Audyssey would be EQing both subs combined.

I wasn't sure if there was some phase magic or anything else going on behind the scenes in 2 sub mode, that would be lost in 1 sub mode.
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Sorry, it seems I wasn't clear in my question.

Audyssey Sub Eq HT can eq 1 sub or 2 subs, when measuring 2 subs it will set individual delays delays and levels for each sub. As these should be the same in my case. Would there be any advantage to running Audyssey in two sub mode vs one sub mode with a Y-cable spitting the signal to two subs. In both scenarios Audyssey would be EQing both subs combined.

I wasn't sure if there was some phase magic or anything else going on behind the scenes in 2 sub mode, that would be lost in 1 sub mode.

Hi,

Unfortunately, XT-32 with SubEQ doesn't do anything with respect to phase-matching the subs, and you already know that Audyssey EQ's the subs as one, regardless of how they are connected to the AVR.

Mark Seaton may come back to this thread. If he does, he will tell you that, where subwoofers are on the same wall and reasonably equidistant from the MLP, he recommends Y-connecting them into a single sub out. That gives Audyssey one less variable to deal with. Whether there would be a measurable difference in the frequency response that way, much less an audible one is another question, but I would recommend following Mark's advice.

Regards,
Mike
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Hi,

Unfortunately, XT-32 with SubEQ doesn't do anything with respect to phase-matching the subs, and you already know that Audyssey EQ's the subs as one, regardless of how they are connected to the AVR.

Mark Seaton may come back to this thread. If he does, he will tell you that, where subwoofers are on the same wall and reasonably equidistant from the MLP, he recommends Y-connecting them into a single sub out. That gives Audyssey one less variable to deal with. Whether there would be a measurable difference in the frequency response that way, much less an audible one is another question, but I would recommend following Mark's advice.

Regards,
Mike
Thanks Mike,

You might want to add a subsection to the subwoofer guide regarding Audyssey Sub Eq HT when using 2 subwoofers and the issue of losing subwoofer headroom. I understand why they do it the way they do, but in many cases what they are selling as a feature can substantially handicap your system.
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Hi,

Unfortunately, XT-32 with SubEQ doesn't do anything with respect to phase-matching the subs, and you already know that Audyssey EQ's the subs as one, regardless of how they are connected to the AVR.

Mark Seaton may come back to this thread. If he does, he will tell you that, where subwoofers are on the same wall and reasonably equidistant from the MLP, he recommends Y-connecting them into a single sub out. That gives Audyssey one less variable to deal with. Whether there would be a measurable difference in the frequency response that way, much less an audible one is another question, but I would recommend following Mark's advice.

Regards,
Mike
Do you know if this is true if your room isn't a a square or rectangle? My room is basically a fat L, that is, a squarish room with a much smaller squarish room inset in a corner. It is sealed(ish). I'll probably finally do some experimenting and serious reading this summer, but I only have six spots to play with and up front are two of them. I'll probably try it regardless, but I was curious.

Spoiler!

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Do you know if this is true if your room isn't a a square or rectangle? My room is basically a fat L, that is, a a squarish room with a much smaller squarish room inset in a corner. It is sealed(ish). I'll probably finally do some experimenting and serious reading this summer, but I only have six spots to play with and up front are two of them. I'll probably try it regardless, but I was curious.

I don't know for sure, but FWIW, I can't see why the geometry of the room would make any difference. If having two subs on the same wall and equidistant from the MLP is an inherently good subwoofer placement, then using a Y-connector to eliminate another variable should still be a valid concept.

Regards,
Mike
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I have found this to be much less problematic when using the "2-sub" mode. Audyssey is able to measure each sub's arrival time independently and set each sub's Distance appropriately. Therefore, if one has no ability to measure and adjust the subs, the 2-sub mode will most likely provide a more beneficial result. Having said that, if one is using more than one subwoofer, it is virtually always beneficial to be able to measure the FR in order to provide the most optimal result, whether using Audyssey or any other Room Correction or EQ device.
I need to edit this for clarity:


"...the 2-sub mode with gain-matching will most likely provide a more beneficial result.



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I don't know for sure, but FWIW, I can't see why the geometry of the room would make any difference. If having two subs on the same wall and equidistant from the MLP is an inherently good subwoofer placement, then using a Y-connector to eliminate another variable should still be a valid concept.

Regards,
Mike
The geometry of the room might actually play a significant role as the FR of each sub will be different depending on how each sub's in-room position interacts with the rest of the room, and how the combined response of both subs interacts with the room AND the speakers. This could be impactful whether the subs are on the same wall or different walls, and whether the room is symmetric or asymmetric. Using the Y-connector method, (aka the "1-sub" method above), would still need to be verified using post-Audyssey FR measurements as described above. Short of that, it's just a guess as to whether gain-matching or level-matching is most appropriate, and whether the Distance setting is appropriate or not. IME, Audyssey does a less-than-ideal job of getting the later correct. YMMV.



Craig
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The geometry of the room might actually play a significant role as the FR of each sub will be different depending on how each sub's in-room position interacts with the rest of the room, and how the combined response of both subs interacts with the room AND the speakers. This could be impactful whether the subs are on the same wall or different walls, and whether the room is symmetric or asymmetric. Using the Y-connector method, (aka the "1-sub" method above), would still need to be verified using post-Audyssey FR measurements as described above. Short of that, it's just a guess as to whether gain-matching or level-matching is most appropriate, and whether the Distance setting is appropriate or not. IME, Audyssey does a less-than-ideal job of getting the later correct. YMMV.

Craig

Hi Craig,

I agree with what you are saying, and I think it is important to understand the full context of a statement like the one you quoted. This a key phrase from my statement:

"If having two subs on the same wall and equidistant from the MLP is an inherently good subwoofer placement, then using a Y-connector to eliminate another variable should still be a valid concept."

I completely agree that placement matters, but it matters irrespective of room geometry. So, starting with good subwoofer placement is extremely important in all instances. But, if the FR is inherently good with two subs equidistant on the same wall, then I believe that Y-connecting the subs should still be just fine in a non-square or non-rectilinear room.

Regards,
Mike
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Do you know if this is true if your room isn't a a square or rectangle? My room is basically a fat L, that is, a squarish room with a much smaller squarish room inset in a corner. It is sealed(ish). I'll probably finally do some experimenting and serious reading this summer, but I only have six spots to play with and up front are two of them. I'll probably try it regardless, but I was curious.
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The geometry of the room might actually play a significant role as the FR of each sub will be different depending on how each sub's in-room position interacts with the rest of the room, and how the combined response of both subs interacts with the room AND the speakers. This could be impactful whether the subs are on the same wall or different walls, and whether the room is symmetric or asymmetric. Using the Y-connector method, (aka the "1-sub" method above), would still need to be verified using post-Audyssey FR measurements as described above. Short of that, it's just a guess as to whether gain-matching or level-matching is most appropriate, and whether the Distance setting is appropriate or not. IME, Audyssey does a less-than-ideal job of getting the later correct. YMMV.

Craig
What works best or is most likely to work will depend on where the system, listener, and subwoofers are oriented within the L. There are always some exceptions, but IMO exceptions should be verified with real measurements, not "let me try this and listen," with the caveat that broad cancellations that go away when one sub is turned off quickly tell you to dig deeper even before measurements.

In my experience which aligns with the physics of what is going on, if 2 subwoofers are along one wall or both at the same width or depth of the room (say left & right sides at 1/4 or 1/2 depth of the room), you are better off driving the 2 subs identically as you are looking to use the differing interactions on the common dimension with hopes that one has strengths where the other has weaknesses, and/or the symmetrical placement doesn't energize certain modes. As an example, symmetrical 1/4 width spacing left & right should keep from exciting the 1st & 2nd modes of that dimension (in this case width).

A very important bit to digest is that every drywall boundary is not the same. Quite often one wall will have a solid foundation wall behind it or exterior brick wall, and an opposite wall might be drywall with another room or utility space behind. This is most certainly not an acoustically symmetrical condition for the subwoofer. Accordingly, general rules of thumb work on assumptions, and this case often blows apart those assumptions.

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What works best or is most likely to work will depend on where the system, listener, and subwoofers are oriented within the L.
Just as in real estate... Location, location, location! It's always about location first!

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There are always some exceptions, but IMO exceptions should be verified with real measurements, not "let me try this and listen," with the caveat that broad cancellations that go away when one sub is turned off quickly tell you to dig deeper even before measurements.
Measurements!!! Anything less is just a guess!

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In my experience which aligns with the physics of what is going on, if 2 subwoofers are along one wall or both at the same width or depth of the room (say left & right sides at 1/4 or 1/2 depth of the room), you are better off driving the 2 subs identically as you are looking to use the differing interactions on the common dimension with hopes that one has strengths where the other has weaknesses, and/or the symmetrical placement doesn't energize certain modes. As an example, symmetrical 1/4 width spacing left & right should keep from exciting the 1st & 2nd modes of that dimension (in this case width).
"...driving the two subs identically" = "gain-matching"!

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A very important bit to digest is that every drywall boundary is not the same. Quite often one wall will have a solid foundation wall behind it or exterior brick wall, and an opposite wall might be drywall with another room or utility space behind. This is most certainly not an acoustically symmetrical condition for the subwoofer. Accordingly, general rules of thumb work on assumptions, and this case often blows apart those assumptions.
Excellent point, and it reinforces why measurements are almost mandatory to optimize multi-sub systems.

At this point, it can be pointed out that there is another approach to multi-subwoofer setup. It is based on the approach used by Earl Geddes and described here: https://mehlau.net/audio/multisub_geddes/ It doesn't use gain-matching or level-matching. It uses one sub as the "primary" sub and the additional subs are added only to impact the frequency response. The gains on the additional subs are turned up only as loud as they need to be to impact the FR. More importantly, the subs are randomly deployed throughout the space.

In my own system, I use a "hybrid" approach. My 3 Submersives are randomly deployed throughout my space to provide a relatively smooth FR. More importantly, the FR is quite consistent over multiple listening positions. They're gain-matched, and the combined output is EQ'd as one sub with Audyssey XT32. Since the FR is consistent over multiple LP's, the applied EQ is also consistent over multiple LP's. I then employ the port-Audyssey tweaks I described above to set the trims identically and tweak the Distance settings.

This is nowhere near as elaborate as some of the systems Mark is setting up, (18 subwoofers EQ'd with DSP-based RC systems like DataSat and Trinnov!!!), but it still works pretty well. As you can see from the graph I posted previously, I get 115 dB at 10 Hz with no compression, which ain't bad!



Craig
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What works best or is most likely to work will depend on where the system, listener, and subwoofers are oriented within the L. There are always some exceptions, but IMO exceptions should be verified with real measurements, not "let me try this and listen," with the caveat that broad cancellations that go away when one sub is turned off quickly tell you to dig deeper even before measurements.

In my experience which aligns with the physics of what is going on, if 2 subwoofers are along one wall or both at the same width or depth of the room (say left & right sides at 1/4 or 1/2 depth of the room), you are better off driving the 2 subs identically as you are looking to use the differing interactions on the common dimension with hopes that one has strengths where the other has weaknesses, and/or the symmetrical placement doesn't energize certain modes. As an example, symmetrical 1/4 width spacing left & right should keep from exciting the 1st & 2nd modes of that dimension (in this case width).

A very important bit to digest is that every drywall boundary is not the same. Quite often one wall will have a solid foundation wall behind it or exterior brick wall, and an opposite wall might be drywall with another room or utility space behind. This is most certainly not an acoustically symmetrical condition for the subwoofer. Accordingly, general rules of thumb work on assumptions, and this case often blows apart those assumptions.
Thanks Mark. If one has two identical subs symmetrically placed behind MLP and already has dual sub cables routed from an XT32 AVR back to the subs, is there any disadvantage in using both independent outputs? All I see here is it “removes one more variable.” But what is the risk exactly that would ultimately make the results worse vs using a Y cable? Thanks.
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Thanks Mark. If one has two identical subs symmetrically placed behind MLP and already has dual sub cables routed from an XT32 AVR back to the subs, is there any disadvantage in using both independent outputs? All I see here is it “removes one more variable.” But what is the risk exactly that would ultimately make the results worse vs using a Y cable? Thanks.
Not Mark, but...

If you use both sub outs, the subs will still be EQ'd as one sub. Therefore, the only differences would be that the two subs could have different trim levels and Distance Settings. If you use the previously described gain-matching technique, then the only potential difference left would be different Distances. If they're equidistant to the LP, there should be no difference in Distance settings. Therefore, as long as you "gain-match" there should be no difference between using 1 sub output or 2.

However, I will say this... putting 2 subwoofers on the same wall is usually not the best utilization of dual subs, especially if the 2 subs are placed close together. When two subs are co-located, or located close together, they "mutually couple." IOW, the two subs combine, and their wavefronts propagate as if they were one subwoofer. This results in more total output, but it also means that there is only one "transfer function" of frequency response to the listening position. The benefits of null elimination and FR smoothing that can occur with dual subs is reduced or even eliminated with co-located dual subs. Placing dual subs disparately around the room works much better for these purposes. Harman showed this to be the case, and their recommendations were:
Quote:
One subwoofer at each wall midpoint is the best in terms of Std, Max-ave and Max-min but does not support low frequencies particularly well. Two subwoofers, at opposing wall midpoints, performs very nearly as well as four at the midpoints and gives a much better LF factor. One subwoofer in each corner also has good low frequency support, but does not perform quite as well as one subwoofer at each wall midpoint, in terms of Std, Max-ave and Max-min. If cost and aesthetics are considered, subwoofers at 2 wall midpoints is preferred.

https://www.harman.com/sites/default...multsubs_0.pdf
(See Page 28 for diagrams of the optimal placements.)

In my own experience, placing 2 Submersives up front on either side of my CC did not result is a good FR, and Audyssey did not do well EQ'ing that one response. Things worked much better with one in front and one in back. When I added the 3rd, I placed it as far from the other two as I could, and this resulted in the smoothest FR, and had the highest seat-to-seat consistency. Audyssey had a very easy time getting a flat FR and and an EQ'd curve that worked very well when spatially averaged.

If you need to place your subs on the back wall, I suggest you try to separate them as much as possible, even going to the corners. Corner placements will provide more output,and will maximally excite the room modes. Hopefully you'll have enough differences in FR's from each corner to provide adequate smoothing. Of course, placing them in the corners can result in bigger differences in levels, and in that case, gain-matching will become even more beneficial.

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great read, this thread...really good stuff. thanks guys

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I really appreciate all of the information shared in this thread. Having little to no experience with subwoofers, the information on this forum has helped a great deal and I've learned a ton over the last few months.

I just want to provide a quick update. I finally had some time to install (and learn about) REW on my laptop, connect each of my Monolith subwoofers, and fire up the X8500H for the first time. I don't have any other speakers setup yet, but I wanted to take some measurements with each subwoofer to get an idea of what I'll be dealing with in my room. The gain on both subwoofers was at about 2 o'clock and the receiver volume was at -22.0db.

I don't have many options for placement for Subwoofer 1. Subwoofer 2 wound up being the best on the same side (opposite end) of the room as Subwoofer 1. The final graph is after tweaking the phase of Subwoofer 2. This is with no room correction or acoustic treatments of any kind.

Subwoofer 1:



Subwoofer 2:



Both subwoofers:



I'll have to see what I can do about that null at 40Hz.

Thanks again for all of the input!

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post #28 of 47 Old 07-07-2019, 01:31 PM
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I really appreciate all of the information shared in this thread. Having little to no experience with subwoofers, the information on this forum has helped a great deal and I've learned a ton over the last few months.

I just want to provide a quick update. I finally had some time to install (and learn about) REW on my laptop, connect each of my Monolith subwoofers, and fire up the X8500H for the first time. I don't have any other speakers setup yet, but I wanted to take some measurements with each subwoofer to get an idea of what I'll be dealing with in my room. The gain on both subwoofers was at about 2 o'clock and the receiver volume was at -22.0db.

I don't have many options for placement for Subwoofer 1. Subwoofer 2 wound up being the best on the same side (opposite end) of the room as Subwoofer 1. The final graph is after tweaking the phase of Subwoofer 2. This is with no room correction or acoustic treatments of any kind.

Subwoofer 1:



Subwoofer 2:



Both subwoofers:



I'll have to see what I can do about that null at 40Hz.

Thanks again for all of the input!
First of all, congratulations on getting and using REW. It will take you from "guessing" to actually KNOWING you've found the optimal response. Great move!

If you look at the overall "shapes" of the individual graphs below 40 Hz, you'll see that they are more similar than different. Both have peaks around 20 Hz, recessions between 20 and 30 Hz, peaks at 30 Hz and large dips at 40 Hz. Therefore, you don't have one sub filling in the dips of the other. This is most readily apparent with the deep, wide null at 40 Hz.

Above 40 Hz, Sub1 has a broad recession that is somewhat filled in by Sub2, and the deep, narrow nulls above and below 80 Hz are completely eliminated in the combined response. This is the kind of "complimentary" response you want across the entire subwoofer bandwidth. I suggest you keep looking for subwoofer positions that give you similar benefits above and below 40 Hz. When evaluating individual responses, look for a flat or peaked response on one graph that counteracts a dip on the other graph. This will give you a flatter combined response with fewer and less problematic dips/nulls.

Good luck!!!

Craig

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First of all, congratulations on getting and using REW. It will take you from "guessing" to actually KNOWING you've found the optimal response. Great move!

If you look at the overall "shapes" of the individual graphs below 40 Hz, you'll see that they are more similar than different. Both have peaks around 20 Hz, recessions between 20 and 30 Hz, peaks at 30 Hz and large dips at 40 Hz. Therefore, you don't have one sub filling in the dips of the other. This is most readily apparent with the deep, wide null at 40 Hz.

Above 40 Hz, Sub1 has a broad recession that is somewhat filled in by Sub2, and the deep, narrow nulls above and below 80 Hz are completely eliminated in the combined response. This is the kind of "complimentary" response you want across the entire subwoofer bandwidth. I suggest you keep looking for subwoofer positions that give you similar benefits above and below 40 Hz. When evaluating individual responses, look for a flat or peaked response on one graph that counteracts a dip on the other graph. This will give you a flatter combined response with fewer and less problematic dips/nulls.

Good luck!!!

Craig
Thanks for the feedback, Craig. I will certainly try more positions. For subwoofer 1, the only other position would be on the other side of the TV stand, assuming I want to have one sub at each end of the room (a small storage room prevents any other location at that end).

For subwoofer 2, the closer I moved it to the other side of the rear wall, the worse the response got. That is the side of the room that eventually opens up to the staircase that leads to a landing, which then leads to my entry if you go down, and my living room if you go up. It's not a completely open side of the room, though it is definitely not sealed off. The closer subwoofer 2 got to that side, things went South. I could try putting it right next to the end of the sofa on that side or slightly more forward than I had it in my tests yesterday, but responses were worlds better in the back corner with full length walls. Subwoofer 1 is currently farther away from this opening... moving it to the other side of the TV stand would put it pretty close. However, I'll never know the results unless I test!

I also plan on getting acoustic panels and possibly bass traps for my room. The "nook" behind the TV is dead space other than the A/V equipment I have behind the TV stand. I was considering GIK Acoustics monster bass traps on the front wall and soffit bass traps in the nook corners. I plan on hanging 4" thick panels on the rear wall behind the sofa. I could even fit triangle bass traps in the rear corners if needed. However, I don't know enough about bass traps to speculate whether or not they would help the nulls in my graph... or if they are better suited at eliminating peaks (though from what I've read, room correction/EQ does a decent job at eliminating peaks).

Thanks again.
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post #30 of 47 Old 07-09-2019, 10:36 AM
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Just a Quick One, after audyssey My subs are set to -8.5

If i whant more subs, like i get with DYN EQ

should i raise in subwoofer trim or in test Tone.

Have a Marantz sr7012
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