As many of you know by now, I’ve been on a decade-long pursuit of solid mid-bass performance in my rig, as it is required to balance the amazing output of the ESL panels and my equally capable low-end from the Infinite Baffle Sub + the 18” sealed sub at the rear of the room.
To me, mid-bass is the range from ~60Hz to 350Hz and is fundamental to a good sense of ‘dynamics’ and ‘power’ in most modern music. It is also where critical fundamentals and harmonics for live instruments like drums and bass guitar (and acoustic Bass and cellos). This also happens to be a range I find many panel speakers to be deficient in due to several factors, the first being their dipole nature in the upper end of this range, with attendant natural cancellation. In addition, blending a large line source to a dynamic woofer system is a tough trick to pull off with analog passive crossovers. Additionally, the power curves are different between the panel and woofer, leading to an ‘unbalanced’ sound at high volumes.
A few of these issues were addressed by replacing the passive crossovers in the Monoliths with DSP-based active crossovers, where we can also time-align the panel to the woofer, fixing a key challenge in the impulse response. Steeper slopes help protect the panel from resonances caused by overdrive at low frequencies, and PEQ allows us to fine-tune the response blend across the x-over region.
Since I custom-tune the speakers in their final location and room, we also do minor PEQ to compensate for location-based artifacts, like floor bounce.
Further improvements in mid-bass came from replacing the stock woofer with one designed more for the range they cover in my setup. I covered that in this thread regarding their replacement.
Nothing, though, comes close to the mid-bass capabilities of the line array of mid-bass drivers I built for the SL3XC center channel; that’s how to really augment this frequency range for a line-source system. Someday I’ll build four more of those for the rest of the ESLs.
But even after all of that, there was still a lack of ‘impact’ during movies and certain musical passages that left me wanting a bit more in this region, which led to the investigation and deployment of something known as ‘Mid Bass Modules’ or MBM’s as I’ll refer to them from here on.
First, a bit on room acoustics realities. So even with plenty of woofage in the room, there is, unfortunately, a room-induced resonance in the 60 to 80Hz range (a couple, actually) at my main listening position (MLP), and no amount of EQ will truly fix that. So, we need a ‘fix’ that can offset that as well as deliver a more tactile sensation of ‘impact’ in this range.
As a regular AVSforum denizen, I read the DIY subforums where several bass-heads on there discuss the benefits of augmenting mid-bass with dedicated MBMs. Most were in locations along with the other speakers, but some investigated their use in the nearfield (like as in really close to the MLP) to leverage the particle velocity a ported enclosure can create at these frequencies. This was documented as delivering a high degree of tactile sensation that augmented the ‘chest-thump’ and other motion-borne feedback along with the acoustic output that was not as impacted by the room.
Having a couple of spare 12” woofers (HiVi M12) that could be deployed for this purpose, all I needed was a suitable enclosure, which thankfully, Parts Express had (Goldwood E-12SP). Along with some stuffing and foam, I was able to assemble my MBMs in about 30 minutes each. Oh, and yet more amplification is needed, so I bought a QSC GX5 500w / ch stereo amp. This is a class H amp with great specs and perfect for the MBM duty. All it needed was a fan mod to quiet it down.
The amp is driven by an output from my DriveRack 4800 speaker processor, where I can adjust delays and EQ to align and optimize the MBMs for integration with the rest of the rig. Adjustments primarily focused on achieving a consistent impulse response so that sharp transients, such as drum hits, aligned well with the front speakers and the sub. The feed is the Sub1 output from the pre-amp and has content from the second-order low-pass from the nine other channels as well as the 120Hz and below LFE channel, so its effective range is 0Hz to 240+ Hz.
Placing the MBMs just behind the MLP and adjoining seat maximizes the tactile impact, and since these speakers are so close, they’re hardly affected by room modes and really put out the sound in their range. Even though the high-pass crossover is a sharp one (48dB/Octave) at 45Hz, the cone of the woofers still moves a good bit. So the MBMs operate from 45Hz through 240+, but mainly 45 to 180Hz.
OK, enough about rationale and setup; how do they sound? I tell you, it’s such fun to hear concert videos with the same kind of physical sensations as one has at real venues, with pants legs flapping and real chest thumps. Action movie soundtracks now have seriously impressive realism, explosions shake the chairs, and you feel the hairs on your arms move. This setup has impressive, deep bass, but now with this mid-bass range filled-in from the nearfield woofers, it has power in the sub-bass harmonics that were not quite there before and tactile feedback beyond the floor shaking; your body now feels the air moving around you.
I’ve been to live Blue Man Group concerts multiple times and have all their DVD-Audio and BluRay discs, playing those now, and they sound much closer to the live sound I recall from the events. Everything from the large drum whacks to the richness of the PVC-pipe instruments has an impact that resonates in the body like never before. The chair arms vibrate along with the music in a way that you feel.
Even classical sounds much more realistic. I have a great BluRay concert video with immersive audio (Dolby Atmos) soundtrack, and the piano sounds like it’s right there in the room, with all the fullness in lower octaves that makes it more ‘real’.
An interesting side effect is that since the mid-bass is now filled in, I can lower the overall volume setting on the system when playing ‘loud’, and it still sounds loud enough. A good 4 or 5dB lower!
In conclusion, this was very much worth the effort, and I’m extremely pleased with the results.
Even though that’s >1,000 words, I’m sure you have questions, so fire away.
Oh, and pics, got to have pics
And a side view of the two, with the 18" rear sub visible to the left (between rear Sequels):
And floor view:
To me, mid-bass is the range from ~60Hz to 350Hz and is fundamental to a good sense of ‘dynamics’ and ‘power’ in most modern music. It is also where critical fundamentals and harmonics for live instruments like drums and bass guitar (and acoustic Bass and cellos). This also happens to be a range I find many panel speakers to be deficient in due to several factors, the first being their dipole nature in the upper end of this range, with attendant natural cancellation. In addition, blending a large line source to a dynamic woofer system is a tough trick to pull off with analog passive crossovers. Additionally, the power curves are different between the panel and woofer, leading to an ‘unbalanced’ sound at high volumes.
A few of these issues were addressed by replacing the passive crossovers in the Monoliths with DSP-based active crossovers, where we can also time-align the panel to the woofer, fixing a key challenge in the impulse response. Steeper slopes help protect the panel from resonances caused by overdrive at low frequencies, and PEQ allows us to fine-tune the response blend across the x-over region.
Since I custom-tune the speakers in their final location and room, we also do minor PEQ to compensate for location-based artifacts, like floor bounce.
Further improvements in mid-bass came from replacing the stock woofer with one designed more for the range they cover in my setup. I covered that in this thread regarding their replacement.
Nothing, though, comes close to the mid-bass capabilities of the line array of mid-bass drivers I built for the SL3XC center channel; that’s how to really augment this frequency range for a line-source system. Someday I’ll build four more of those for the rest of the ESLs.
But even after all of that, there was still a lack of ‘impact’ during movies and certain musical passages that left me wanting a bit more in this region, which led to the investigation and deployment of something known as ‘Mid Bass Modules’ or MBM’s as I’ll refer to them from here on.
First, a bit on room acoustics realities. So even with plenty of woofage in the room, there is, unfortunately, a room-induced resonance in the 60 to 80Hz range (a couple, actually) at my main listening position (MLP), and no amount of EQ will truly fix that. So, we need a ‘fix’ that can offset that as well as deliver a more tactile sensation of ‘impact’ in this range.
As a regular AVSforum denizen, I read the DIY subforums where several bass-heads on there discuss the benefits of augmenting mid-bass with dedicated MBMs. Most were in locations along with the other speakers, but some investigated their use in the nearfield (like as in really close to the MLP) to leverage the particle velocity a ported enclosure can create at these frequencies. This was documented as delivering a high degree of tactile sensation that augmented the ‘chest-thump’ and other motion-borne feedback along with the acoustic output that was not as impacted by the room.
Having a couple of spare 12” woofers (HiVi M12) that could be deployed for this purpose, all I needed was a suitable enclosure, which thankfully, Parts Express had (Goldwood E-12SP). Along with some stuffing and foam, I was able to assemble my MBMs in about 30 minutes each. Oh, and yet more amplification is needed, so I bought a QSC GX5 500w / ch stereo amp. This is a class H amp with great specs and perfect for the MBM duty. All it needed was a fan mod to quiet it down.
The amp is driven by an output from my DriveRack 4800 speaker processor, where I can adjust delays and EQ to align and optimize the MBMs for integration with the rest of the rig. Adjustments primarily focused on achieving a consistent impulse response so that sharp transients, such as drum hits, aligned well with the front speakers and the sub. The feed is the Sub1 output from the pre-amp and has content from the second-order low-pass from the nine other channels as well as the 120Hz and below LFE channel, so its effective range is 0Hz to 240+ Hz.
Placing the MBMs just behind the MLP and adjoining seat maximizes the tactile impact, and since these speakers are so close, they’re hardly affected by room modes and really put out the sound in their range. Even though the high-pass crossover is a sharp one (48dB/Octave) at 45Hz, the cone of the woofers still moves a good bit. So the MBMs operate from 45Hz through 240+, but mainly 45 to 180Hz.
OK, enough about rationale and setup; how do they sound? I tell you, it’s such fun to hear concert videos with the same kind of physical sensations as one has at real venues, with pants legs flapping and real chest thumps. Action movie soundtracks now have seriously impressive realism, explosions shake the chairs, and you feel the hairs on your arms move. This setup has impressive, deep bass, but now with this mid-bass range filled-in from the nearfield woofers, it has power in the sub-bass harmonics that were not quite there before and tactile feedback beyond the floor shaking; your body now feels the air moving around you.
I’ve been to live Blue Man Group concerts multiple times and have all their DVD-Audio and BluRay discs, playing those now, and they sound much closer to the live sound I recall from the events. Everything from the large drum whacks to the richness of the PVC-pipe instruments has an impact that resonates in the body like never before. The chair arms vibrate along with the music in a way that you feel.
Even classical sounds much more realistic. I have a great BluRay concert video with immersive audio (Dolby Atmos) soundtrack, and the piano sounds like it’s right there in the room, with all the fullness in lower octaves that makes it more ‘real’.
An interesting side effect is that since the mid-bass is now filled in, I can lower the overall volume setting on the system when playing ‘loud’, and it still sounds loud enough. A good 4 or 5dB lower!
In conclusion, this was very much worth the effort, and I’m extremely pleased with the results.
Even though that’s >1,000 words, I’m sure you have questions, so fire away.
Oh, and pics, got to have pics
And a side view of the two, with the 18" rear sub visible to the left (between rear Sequels):
And floor view:
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