Originally Posted by m0j0
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:
Originally Posted by Swoosh830
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.
You've essentially described "Gain-Matching" which is a valid and useful technique, which can have some advantages over Level Matching.
"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!!!
PS. If you have any questions, please feel free to ask!