Subwoofer speed is in the room, not the box
First, if you like swarm, that’s fine, please start a thread somewhere else about how much you like swarm.
I want to talk about the impression that subs are fast or slow compared to planar or line sources.
The concern, and it’s correct, is that adding a subwoofer to say a Martin Logan or Magneplanar speaker will ruin the sound balance. That concern is absolutely a valid one and can happen with almost any speaker, not just speakers with tight dispersion control.
What usually happens is that the room, sub and main speakers aren’t integrating very well. Unfortunately for most audiophiles, it’s very hard to figure out exactly what is wrong without measurements or EQ capabilities in the subwoofer to help you.
So, there’s the myth of a small sub being "faster." It isn’t. It’s slower has worst distortion and lower output than a larger sub but what it does is it doesn’t go down deep enough to wake the dragons.
The biggest problems I’ve heard/seen have been excessively large peaks in the subwoofer range. Sometimes those peaks put out 20x more power into a room than the rest of the subwoofer. Think about that!! Your 1000 W sub is putting out 20,000 watts worth of power in some very narrow bands. Of course that will sound bad and muddied. The combination of sub and main speaker can also excessively accentuate the area where they meet, not to mention nulls.
A lot is made about nulls in the bass but honestly IMHO, those are the least of our worries. Of course too many of them can make the bass drop out, but in practicality is is the irregular bass response and the massive peaks that most prevent any good sub from functioning well in a room.
Bass traps are of course very useful tools to help tame peaks and nulls. They can enable EQ in ways you can’t do without it. If your main speakers are ported, plug them. Us the AM Acoustics room mode simulator to help you place your speakers and listening location.
Lastly, using a subwoofer to only fill in 20 Hz range is nonsense. Go big or go home. Use a sub at least at 60 Hz or higher. Use a single cap to create a high pass filter. Use EQ on the subwoofer at least. Get bass traps. Measure, for heaven’s sake measure and stop imagining you know a thing about your speaker or subwoofer’s response in the room because you don’t. Once that speaker arrives in the room it’s a completely different animal than it was in the showroom or in the spec sheet.
Lastly, if your room is excessively reflective, you don’t need a sub, you need more absorption. By lowering the mid-hi energy levels in a room the bass will appear like an old Spanish galleon at low tide.
Agree completely with @erik_squires, @audiokinesis and others regarding treating the peaks with EQ, but not trying to boost nulls. Multiple subs helps with that (not wading into the swarm debate). One tradeoff I have not seen explicitly mentioned (although @phusis hints at it), is that setting a higher crossover point gives you more freedom in placement of the speakers vs. placement of the subs. Leaving the issues of room treatments aside, place your speakers for the best soundstage and imaging, and place your subs to minimize the problems associated with the long wavelengths of low frequencies (which create both nulls and peaks). Most room mode problems tend to occur with sub-125 Hz frequencies, although depending on room characteristics, they can go higher. But certainly, the lower you go, the more bothersome these tend to be. Flexibility of where you can place one or more subs helps tremendously. However, if you cross over at 35 Hz, for example, then you have pretty much lost that flexibility. You really can’t just move one of your main speakers 3 to 6 feet to deal with a peak at, say, 50 Hz, because moving them will ruin your soundstage. Crossing higher provides more options for sub placement to deal with troublesome modes. So, up to a point, the higher you can cross over, the better, up until where you can start hearing the directionality of the subs. This is room-dependent and person-dependent, but typically is around 80 Hz. I experimented with 50 Hz to 80 Hz, and for my situation, crossing at 70 Hz sounded best. The other issue sort of mentioned so far that could be stated more explicitly is phase-matching the mains and the subs at the point of crossover. This requires two things: (1) a continuous phase adjustment on the subs (like on those by Rythmik) or digital PEQ; and (2) a very steep and symmetrical crossover, typically implying an active crossover. That means both low-passing the sub and high-passing the mains are important. Because the wavelengths change quite a bit from 20 Hz (56 feet) to 80 Hz (14 feet), the mains and subs can only be in phase at a small range of frequencies. That is why the steep crossover is needed. Otherwise, even if the mains and subs are in phase at 70 Hz, with 6 dB/octave sloped filters there will be audible overlapping of the subs and mains from the lower audible limits all the way up to ~250 Hz or so. Because all filters have a frequency-dependent phase shift, most of that overlap is out of phase and contributing to "smudging" that translates to "slow bass." For my Dali Epicon 6’s, what has worked well for me is an active crossover (24 dB/octave) crossing at 70 Hz to a pair of Rythmik F12G-SE’s with the GR-Research drivers. Mains about 7 feet apart works well for my space; the subs are in diagonally opposite corners of the room. Since I exclusively listen to digital, I can use Roon’s PEQ on a per-channel basis to remove the peaks from the room modes (almost entirely in the range the subs operate), and then careful placement allows each sub to fill in the other’s nulls. After the digital is converted to analog, I want to retain my Denafrips’ sound signature, so I don’t use digital PEQ involving more ADC and DAC conversions. Instead, I am using a Sublime K231 active crossover; the Burr-Brown op-amps used in it don’t seem to color the sound much. |
Thanks. I love the speakers. I know some don't like the voicing (bump up at ~4 kHz), but I'm mostly a relatively low-volume listener. I have a very odd shaped room with many non-parallel walls; not bothering to post because I'm moving to Europe soon and will have a more normal-shaped room. Current room has a few modes (left sub has a deep cut at 68 Hz and a very slight boost at 130 Hz, right sub filter cuts a bunch at 55 Hz and a tiny bit at 350 Hz). But with the subs where they are, I get "glorious bass" in and near my listening position. Every room is different, so it is possible that, when I get to my new home, I may be in a position to place the subs more symmetrically with respect to speakers and cross them lower than 70 Hz. As Erik points out, that might allow crossing at a lower frequency. But every room is different, so I'll measure, experiment with various configurations, and listen carefully in the new location. And just in case, I am building an audio conduit to a location that allows flexibility in sub placement, and that location is part of the dedicated audio circuit to help minimize the chance of a ground loop. |
