Excerpted from the guide at https://www.avsforum.com/threads/guide-to-subwoofer-calibration-and-bass-preferences.2958528/ written by https://www.avsforum.com/members/mthomas47.7878709/.
Cliff Notes:
Several people have suggested having some abbreviated HT calibration tips, so I have added a few prior to the actual Guide. Anyone wanting more detail on anything from room and speaker setup, to setting crossovers, to the differences between sealed and ported subs, to selecting and positioning subwoofers in a room, can find the pertinent information in the Guide itself. There are some similar abbreviated tips, to selecting subwoofers, at the beginning of Section VIII.
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Try to position speakers and subwoofers strategically, doing a "subwoofer crawl" if necessary. Section I-A gives some good general advice on locating the speakers on the front soundstage. (The front three speakers will have the most impact on the overall sound quality for most of the frequency range.) You can Google how to do a sub crawl, or you can refer to Section VIII-E for instructions on how to perform the procedure.
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Set the subwoofer phase at 0, and the low-pass filter (sometimes labelled crossover) on the subwoofer at the maximum setting. Typically, the gain control (which is often labelled volume) should be set at or slightly below about the mid-way point. During the level-matching process, which occurs at the first mic position, you will actually want the subwoofer(s) to be slightly above the volume that Audyssey is telling you to achieve, for reasons which are explained in detail in Section II. (On newer Denon/Marantz AVR's, that means that you will want your subwoofer volume to be slightly in the red zone.)
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Allow your AVR to calibrate your audio system for you, using its automated routine. The first thing that will do is to calibrate your HT system to Dolby/THX Reference (which will correspond to 0.0 MV) , and it will provide a common basis for comparing listening levels and subwoofer boosts. That calibration process will insure that all of the channels are playing the same volume levels at the MLP (main listening position) and that all of the sounds will arrive at the same time. Those equal volume levels are also essential in order for the room correction process to occur.
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The second thing that the calibration will do is to set EQ filters, for all of the channels, to remove some peaks and dips in the frequency response caused by the interaction of your transducers (speakers and subwoofers) with the room. Those random peaks and dips in volume, at different frequencies, interfere with the quality of the sound we hear. With subwoofers, boomy, one-note bass is often the result of a random peak. After room EQ, the bass may sound smoother, but correspondingly less impactful, until the subwoofer volume is increased.
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It is important to understand that two different things are occurring during a calibration. The initial calibration process insures that equal volume levels, from all of the channels, will arrive at the MLP at the same time. The room EQ process (that is also part of the calibration) sets filters, for all of the channels, in an effort to improve the overall sound quality in the room. To do that, it needs to start with equal volume levels. From those equal volume levels, for each channel, room EQ will add or subtract volume at specific frequencies to get as close as possible to the target volume of 75dB. Where room EQ is successful, a measured frequency response will show a fairly flat line from the lower frequencies to the higher frequencies.
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There is a model calibration procedure shown in Section I-B which may help you to achieve an optimum calibration. It has a diagram of potential microphone positions which seem to work well for many listeners. Starting with good speaker setup, and a good calibration, can take some effort. But, doing those things can make an audible difference in the resulting sound.
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As noted, when an AVR calibrates your audio system, all of your channels including your subwoofer(s) will typically be set to play the same volume at the main listening position (MLP), and you will be listening to Reference volumes when you are at a listening level of 0.0 MV (master volume). Most people probably listen at an average volume of about -15 MV to -20 MV. Individual listening volumes, however, may vary much more widely than that. (Your master volume is the only AVR setting that will be unchanged after an Audyssey calibration. It will still be wherever you had set it prior to running Audyssey.)
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Since all of the channels are now playing equal volumes, and since we don't hear low-frequencies as well as other frequencies, after calibration most people will need to add more bass to their audio systems. That is particularly the case when we listen at below Reference volumes, where bass frequencies were designed to be in better equilibrium with frequencies in our normal hearing range of about 500Hz to 5000Hz. As we drop below Reference (0.0 MV), bass frequencies drop-out of our hearing much more quickly than other frequencies do. It is fairly typical to add +3dB to +6dB of subwoofer boost on top of DEQ, and much more than that if DEQ is disabled.
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We can compensate for the audible reduction in bass by turning-up the volume of the subwoofers, and how much volume to add is strictly a user preference issue. To state this in a different way, after an Audyssey calibration, very large subwoofers will be playing at exactly the same volume level as very small subwoofers would be, since all of the channels in a calibrated HT system are level-matched to play the same SPL at the main listening position. In order to use the greater headroom of more powerful subwoofers, it is simply necessary to turn-up their volume.
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After running Audyssey, it may be desirable to add most of your subwoofer volume increase with your subwoofer gain control, while not letting your AVR sub trim go above about -5, to avoid clipping the pre-out signal coming from your AVR. Typically, it is a good idea to raise the gain on the subwoofer high enough to achieve a trim level of about -10 or-11, during the initial level-matching process. After running Audyssey, we can raise the AVR trim to about -5, and continue to increase the subwoofer gain if we want even more bass than that. Section II explains the best ways to use the subwoofer gain in some detail, and explains why it is generally advisable to keep AVR subwoofer trim levels well in negative numbers.
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Some Denon AVR's have a feature called Subwoofer Level Adjust. If a Denon AVR has an On/Off control for that feature, it should typically be turned off, and any volume adjustments should be made either with the subwoofer's gain control, with the subwoofer trim control in the Audio menu, or with the trim control in the Speaker: Manual: Test Tone area of the AVR. Again, in making any subwoofer trim adjustments, it is desirable to keep the trim levels at -5 or lower. To add more subwoofer boost in excess of a -5 trim setting, it is always possible, and perfectly acceptable, to use the gain control on the subwoofer.
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It is important to understand that Audyssey will measure your speakers, at their specific positions in your room, and your AVR will set preliminary crossovers in accordance with its own programming. For instance, if a particular speaker pair, or center channel is capable of playing below 40Hz, at its specific position inside a room, your AVR will set the speaker to "Large". Or a 40Hz or 60Hz crossover may be set, if the speakers can't go quite low enough for an initial setting of Large. Those aren't actually recommendations. They are just observations, based on the measured response of your speakers. After an Audyssey calibration, reset crossovers as suggested below.
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If there is a subwoofer in the system, speakers should typically be set to Small, and crossovers should typically be set at 80Hz or higher. The LPF of LFE, in the AVR, should typically be set to 120Hz (which is usually the default setting in our AVR's). There are exceptions to that, which are explained in Section III, but this is typical best practice advice for starting-out with an HT system.
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It is always acceptable (and often desirable) to raise crossovers from their initial calibration setting, but it is not generally desirable to lower them from wherever your AVR set them. Among other things, Audyssey will not be EQing speakers below the crossovers set during the calibration process.
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If you have Audyssey, you can add subwoofer boosts on top of Dynamic EQ, or turn off DEQ and add your own subwoofer boosts. Section V explains DEQ in detail. Experimenting with it on, and with it off, may be helpful. Turning it off will probably require you to add more subwoofer volume, but for some people, it may change the sound in a positive way. There are also RLO settings, associated with DEQ, which may be helpful in some cases.
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You can turn Audyssey off, to hear how things sound without room EQ, and then turn it back on without changing the room correction filters that it set for any of the channels. And, you can experiment with Audyssey Flat. Audyssey (Reference) and DEQ are always the default settings after a calibration. Audyssey Flat and/or DEQ off are user preference options, and both are explained in Section V.
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After an Audyssey calibration, you can change any settings in your AVR without affecting the room correction filters that Audyssey sets. Changing AVR settings prior to running an Audyssey calibration will not be helpful. Audyssey is designed to ignore and override prior settings when it calibrates an audio system. The only setting that will remain unchanged after an Audyssey calibration is the master volume. But now, your original setting of -15 MV, or whatever it is, will be calibrated to correspond to Dolby/THX Reference when the MV is set to 0.0.
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If you make a significant change to a room, such as moving a speaker or a subwoofer; changing to different speakers or subwoofers; adding new subwoofers or other channels; or adding room treatments or making significant furniture changes; you should recalibrate.
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It may be important to recognize that virtually all settings, including your master volume level, are listener-preference settings. There is no universally correct way to listen to music, or to watch movies or TV shows. Even the use of room correction, in whatever form, is a user-preference feature. Some people prefer listening without room correction, or limiting its effect to just the lower frequencies. And, that same idea applies to all of the settings associated with room EQ, or with our AVR's in general. There are default settings that may help us to get started, and there are some best practice principles which we may want to follow. But, we will all define audio quality in slightly different ways, and we will all have slightly (or profoundly) different listening preferences. Informed experimentation can be the key to discover what we really like.
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When you try different calibrations, or different settings, remember that you will ultimately have to trust your own judgment with respect to sound quality. The Guide, and other sources, can offer options and explanations, and make suggestions about things that you can try. But, in the end, everyone will have to decide for himself what he actually likes.
Each of us decides for himself how much, or how little, he wants to experiment with his audio system. Some of us may just be looking for a plug-and-play approach to our HT's. That is perfectly fine too! After all, the goal here is simply to please ourselves with our entertainment hobby. And, for those of us who do want to experiment, each of us also decides when he is satisfied and wants to stop experimenting. It is not unusual to stop and just enjoy our audio systems for a while, and then to experiment again weeks, months, or even years later.
The way in which you experiment and listen can be important though. Take your time! Try a particular setting for several days, unless you are absolutely sure that you don't like it, before trying a completely different one. Ideally, you want to let your hearing adjust to one sound quality before trying something different. What you don't want to do is to introduce several new variables all at once, because you won't be able to separate them, and you may not have really learned anything about your own listening preferences.
You also don't want to overload your own hearing, and your brain's response to what you are hearing, by trying to pack too many changes and too many concentrated listening sessions into too short a period of time. I referred to them as "concentrated" listening sessions, but that is really the wrong word. They really need to be as relaxed and natural listening sessions as you can make them.
Your brain will tell you what you do and don't like, if you relax and give it some time. You don't have to 'concentrate' to decide whether something tastes good or not, or how much seasoning you prefer, or whether you like a particular color. Concentrating on trying to hear specific things in your sound can actually be counterproductive. Just relax and enjoy the process of experimenting, and of making gradual, incremental improvements in your sound quality.
If you listen for two or three days, your hearing will adjust somewhat to that particular sound. Then, when you do try a different setting you will have an audio benchmark with which to compare any changes in the sound. You won't necessarily have to concentrate there either. Just let the listening sessions happen naturally. If there is no audible change in the sound, then you may not need to worry about that particular setting. If you feel that a new setting has a positive effect on the sound, make a note of that setting, and of your reaction to it. Keeping track of which settings work best for you, and why they seem to improve things, will help as you continue to experiment.
If a setting seems to have a negative effect, you might cross that one off your list, or perhaps return to it later. Above all, be patient and take your time. Impatience will only take you in circles! There are just too many different ways to achieve improved sound quality, and too many variables, for us to try to go too fast. But, if we are patient and systematic in our experimentation, almost everyone will get to a final result that is most appropriate for that particular listener.