Things to check re. Denon 3805 AVR's SW Output, see fol. pages in Owner's Manual. It would help us to diagnose your problem if you could tell us how the AVR is set up NOW and also after you make changes, see pg26 & pg31:
1) pg26: Check of the measurement results. Be sure to STORE the RoomEQ Results, otherwise they are lost.....
2) pg27: 1-2 Setting the Manual EQ Setup. INITIALLY you can start with all EQ Settings = 0.0 dB, so you can quickly compare to RoomEQ Results. If you like the RoomEQ settings, you can transfer them across to Manual EQ Settings, except perhaps with different settings for 63 Hz and 125 Hz [Output by SW], per your "Personal Taste".
3) pg28: 1-3 Setting the Room EQ Setup. You can quickly change between Auto RoomEQ Results and Manual EQ Settings.
[Step 3: Recommend you select "ALL" and Step 4: Recommend you select "NORMAL.]
4) pg 32: 2-1 Setting the type of speakers. If you don't set Speaker Size for LF/RF [as per procedure in Manual] prior to running RoomEQ, then AVR will TRY to determine proper setting based on measured Freq Response. BUT, in many cases it will ERRONEOUSLY set it to LARGE, when actual speaker size is NOT 12-in or Larger. Unless you have LARGE Speakers that can hold their own against the Sub-Woofer, you should ALWAYS select SMALL for ALL Speakers. This prevents the LF/RF [et. al.] from TRYING to reproduce Low Freqs when ithey're just not up to the task of providing LOW-DISTORTION at High Power....and let the Sub-Woofer do what it's designed to do instead. This also prevents Low Freqs from LF/RF from INTERFERING with SW Frequency Response. You should do this BEFORE re-running RoomEQ.
5) pg37: 2-5 Setting the low frequency distribution: IF LF/RF are inadvertently set to LARGE, then SUB-WOOFER MODE = "LFE+MAINS" will result in Low-Freqs from LF/RF ALSO being routed to the SW Channel. This is important when listening to STEREO (and Synthetic Surround), since otherwise the SW Channel would have NO Signal. However, if you set LF/RF to SMALL, then LF/RF Low-Freqs are already being routed to SW Channel. You should do this BEFORE re-running RoomEQ.
6) pg40: 3-2 Setting the Ext. In Subwoofer Level. Allows you to adjust AVR's SW's Output level going to SW....note that DEFAULT is at Max = + 15 dB. You should do this BEFORE re-running RoomEQ.
7) pg34/35: 2-3 Setting the Channel Level. FINAL TWEAKS to SW (and other Speaker Levels) can be entered while listening to Test Signals being output from each Speaker.
Note that AVR only has TWO FILTERS available for the entire 20-200 Hz Bass Frequency Region, with actually only ONE Filter (centered on 63 Hz) available for Sub-Woofer when using typical 80 Hz LFE Crossover Frequency Setting. Since there WILL be one or more fairly narrowband RESONANCES in the 20-80 Hz spectrum due to ROOM MODES, this single Filter will TRY to ATTENUATE the primary Room Mode Resonance....resulting in the appearance of "Weak Bass" on other Low-Freqs. So you will probably want to BOOST the SW Level and/or REDUCE the 63 Hz Filter Attenuation so you can HEAR the OTHER Bass Notes. [BTW: Yamaha AVRs with YPAO PARAMETRIC Equalizer uses Filters with variable Center Frequency and "Q" (inverse Bandwidth).]
If you REALLY CARE about HEARING ALL of the Bass Notes, I recommend inserting a 1/3-Octave Equalizer in-between AVR's SW Output and SW Input which provides SEVEN Filters for 20-80 Hz SW Channel to attenuate MULTIPLE Narrowband Resonances while also reducing the NULL Depths, such as 2-Channel Unit from Monoprice...which can independently equalize up to TWO SW's: [You may also have some minimal controls on your Sub-Woofer you could try].
Room Equalization (via means other than AVR) for the 1/3-Octave Equalizer MUST be done PRIOR to running AVR's RoomEQ (which will Equalize from LFE Crossover Frequency and up. This can be done using a Calibrated Microphone and computer (or Cellphone) Software...or manually using a Sound Pressure Level Meter with integrated Calibrated Microphone and a 1/3 Octave Test Tracks (Download or Disc).....a LOT more on this subject is found here:
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