There is a lot to unpack here, and there are a number of things that can cause the issues you describe. The best way for us to help you, (and/or for you to help yourself), is to take some measurements of the bass in your room. Until the root cause(s) can be delineated, we can only speculate.
Originally Posted by Artzilla
Thanks Craig. The issues I have will not be solved by gain matching but it's the first of other steps I planned to take. It is not intended to address what I list below, just a different foundation to start with vs level matching. It may turn out just to be a learning exercise but that's ok. I'll know what the results are and and will be satisfied with gaining the experience even if it is not an improvement.
***Midway through the next paragraph I realized a somewhat unique amp gain issue might make gain matching impossible or at least not optimal but I left the the info below in case you care to read it.
I agree about identical subs but if I recall a past conversation with SVS support they were not against it. Perhaps due to the similarity of the 2 cylinders, all 3 being ported and either native or tunable to 20 Hz, and all having 12" drivers. Gain structure however is different on all 3 units. Also, interesting fact I learned from SVS was that the amp in my pb12 plus will not drive that sub to it's full potential unless the gain on the amp is set to max. I was able to achieve that with a reasonable -10 or -12 trim for that sub in the receiver & keep it level matched with the cylinders which are running off the second sub channel then through an AS-EQ1. This did help with the dynamics but I'm getting a little off topic and that may render gain matching impossible if I want full performance from the pb12.
I can understand SVS saying these 3 subs will work together because they are all ported and they can all be tuned to have the same F3. However, I can't imagine them telling you the subs could be gain-matched when they all use dissimilar amps with significantly dissimilar gain structures. More importantly, I don't think gain-matching is the correct approach given your situation and it won't addrrss the problems you describe. It seems you have also come to the, (correct), conclusion that gain-matching won't work for your situation. In fact, with the significant dissimilarity of the gain structures of the amps in the cylinder subs vs. the PB12+, gain-matching would be contra-indicated.
The requirement that the PB12+ be set to its maximum gain setting might be really problematic for your setup. When you set the amp on the PB12+ to max output, and the receiver trim to 0, what SPL is read at the primary measurement position with just that sub connected? In general, you want this level to read between 75 and 80 dB, and you would use the subwoofer gain control to set the the measured level to this range. However, if the sub amp needs to be at its maximum setting to get full performance from the sub, it may not be possible to do this, and that sub will be set well above the other 2. More importantly, it may be set high enough that there is not enough adjustment capability in the receiver trim range to get it in line with the other two. Hopefully, that is not the case.
Originally Posted by Artzilla
1) Bass lacking unless I run my mains full range and double bass. I know - heresy - but a pro's youtube video indicated that solved a problem for a client that nothing else seemed to so I tried it. It was a significant improvement but I prefer not to run my gear that way and it is likely contributing to the next item.
2) Taughtness/attack/clarity of bass is not bad but not as good as I have achieved with mostly the same system in a different home with only the cylinder subs. Decay is also an issue but I want to try the steps below before looking into bass traps.
3) Pressurization. Inferior to the previous room running only the 2 cylinders.(much larger 23' x 28' x 8' - with tile and lots of glass-not exactly bass helpers) I think I should be able to achieve more than my current configuration is yielding.
My guess is I don't have the right time/phase alignment with the mains and likely have some cancellation going on. On the advice of Ed Mullen despite having 2 discrete sub channels and XT32 should run all the subs off a single output.
The plan was to gain match the subs. Replace the AS-EQ1 with a MiniDSP between the subs and receiver so Audyssey sees a "single sub". Then I can time align all as a single sub post Audyssey with REW. After typing through this however I think due to the PB12 amp Gain issue I will have to stick to level matching.
I think your suspicion of a mis-timing of the subs could be the culprit. However, I'm not sure the solution of putting all 3 subs on the same subwoofer output is the optimal approach. My suggestion would be to place the two cylinder subs on the Sub 1 output and then physically place those two subs equidistant to the LP. This will allow you to use the single Sub 1 Distance setting to time these two subs identically. Then place the PB12+ sub on the Sub 2 output and set its Distance appropriately, (remember that the "physical" distance of the subs is not necessarily the same as the "acoustic" distance due to the inherent latency in the subwoofer amplifiers, and the "correct" Distance setting for most any sub will virtually always be longer than the physical distance to take the latency into account.) Re-run Audyssey after making these changes and Audyssey will set the Distances based on the arrival times it measures. Those settings may or may not be the optimal settings for the speaker/subwoofer(s) splice, which I'll address later, but they should be correct for the relative Distances of the subs to each other.
Originally Posted by Artzilla
I may also play with the Geddes method for placement and try raising one of the subs off the floor. My best past sound in the previous home was achieved with the 2 cylinders colocated by stacking one on top of the other and running them sealed (since the top sub blocked the ports of the bottom sub). I initially thought it was just having both in the sweet spot for that room but recently considered the possibility that elevating the second sub addressed some room modes I could not affect with both subs on the floor. I did not have REW at the time so I cannot say one way or the other.
The Geddes approach might be your best option, but you absolutely NEED to use measurements to make it work. Unfortunately, the description of the Geddes technique, ( https://mehlau.net/audio/multisub_geddes/
), doesn't specifically address how to use the Distance settings in the Bass Management processor, or how to connect multiple subs to a processor that has dual subwoofer outputs. It assumes you'll connect them all to one output, which may or may not be the optimal way to use the processor. If you want to go this route, I would probably use the PB12+ as the "primary" sub. Set its gain at maximum, then place it where it is most optimal, (see below, but most likely in the front left corner.) Then use measurements sweeps of the subwoofer and the CC to optimize/maximize the SPL at the crossover point. Once that is done, then add the 2nd sub on the Sub2 output and measure the same sweeps as before. You're primarily looking to fill in the nulls that existed in the first set of measurements. Slowly turn up the gain on the 2nd sub until you start to see an improvement in the frequency response. You may need to play around with both Levels and Distances to optimize this. Then repeat the process with the 3rd sub. In this scenario, you may be better off with the 3rd sub in a position that is not symmetrical to the listening position, but try as many positions as possible.
Remember that the Geddes technique is not used to maximize system headroom. It is used to optimize the frequency response, and it assumes that the combined output of the three subs will provide all the "needed" headroom. Since it generally results in different gain settings for each sub, you may find that the highest set sub is the sub that hits its max output first and therefore limits the system output to that level. If that level is all the output you'll ever need, you're done. If not, you're back to the drawing board.
Since the issues you have described can all be explained by frequency response anomalies, the solutions are best handled by adjustments that affect the frequency response, and with frequency response measurements. Without measurements, any suggestion made by anyone are just based on speculation and guesswork.
Here's one such speculation: Your subs and speakers are not timed properly to each other. I have found that Audyssey often fails to get this parameter right, especially in systems with multiple subs, and even more frequently when the multiples subs are all run off of one subwoofer output but the subs are placed at different distances from the LP. The best way to correct this problem is to measure the response and adjust the subwoofer Distances accordingly using the measurements in real time. Here's an example of this phenomenon:
This is a system with 3 subs connected to one subwoofer output, and therefore just one setting for subwoofer Distance. The cyan trace is with the Audyssey set subwoofer Distance. Note the 20+ dB cancellation centered on the crossover frequency of 80 Hz. This is what happens with the speakers and subs are mistimed relative to each other. The green trace is the exact same system, the only difference being an addition of 3.6 feet to the subwoofer Distance setting. The speakers and sub are now correctly timed to each other and the cancellation is eliminated. On these fora, this process is often referred to as the "Subwoofer Distance Tweak." The difference in sound between these two measurements is stunning. The first setting is lifeless and dull with seemingly no bass energy. The second setting adds power and weight to the bass with pressurization and tactile impact, and articulation. It is certainly possible that this is your biggest, and possibly ONLY problem with your bass response. Frequency response measurements will definitely tell the tale.
Originally Posted by Artzilla
Regarding Craig's inquiry about the room:
This is a multi-use living, HT,music room - we do everything here except cook and sleep. MLP is just off center of the long wall of a 13' x 19' x 8 room. Mains B&W 803s towers, 6' & 7' or so from side walls on the opposite wall with baffles about 32" from the back wall. There is a low rise Sanus stand between them as well as a 65" tv set back as far as I can get it.
Windows and doors do not work well for a lengthwise configuration. To be sure the room is compromised, but fairly well damped with carpeting, furnishings & wall hangings. It does have 3 openings one being a stairwell (maybe that should be considered a 4th) so it is far from ideal.
I've attached an image as the room is and another with placement options I've considered "if" I decide to cover or seal some windows. I'd be curious if you have any input.
Neither of these configurations will result in an optimal listening position. The first has the seating against the back wall. This will generally result in large peaks or nulls, (mostly peaks), due to the close and high intensity reflections from the back wall. The second configuration places the LP in the virtual center of the room which is generally the weakest point for bass response in any room. A more "optimal" listening position is placed at one of the odd number divisors of the room length, (i.e., thirds, fifths, etc.) If you can move the seating in either drawing to 2/3's or 3/5's of the room length, you'll be in a much better position for your starting bass response.
In the first diagram, the PB12+ is placed on the right side next to an opening to a stairwell and a doorway to the kitchen. That sub will receive little, if any, room reinforcement. Can it be moved to the left corner in the spot where you currently have a small cabinet? That placement would provide nearly optimal room reinforcement. It will also actuate all the modes in the room, which can then be addressed by the other 2 subs.
You have the option of different tunings of your subwoofers. I suggest you tune them all the same, whichever tuning that is. All 3 subs in "sealed" mode may work for you, especially on the lowest bass, where room-gain can provide more output in the lowest frequencies, (below 20 Hz). OTOH, all 3 subs set to 20 Hz tune can also work well, with output optimized at 20 Hz and above, but sacrificing the output below port tune. Either way, avoid tuning one sub in sealed mode and the other sub or subs in ported mode. A sealed/ported configuration will be very difficult to optimize and is not recommended.
So, now you have a lot of work to do...
If you want to post some measurements of your subs, please start with the baseline response of each sub in each possible placement within your room. We can go from there.