Room modes cease below the frequency where the bass wave is twice the length of the longest room dimension. For 18 feet this is 31hz. Smaller rooms, it is higher.
Subwoofer size has nothing to do with how boomy, fast, or slow it sounds. That is a function of qtc and group delay.
The largest effect on how a sub sounds is placement and the room. Room treatments help with ringing, dsp with frequency response at the listening position.
I ran velodyne subs for 25 years. F1000, ULD-12s in stereo, HGS-10, HGS-12. I have moved on to Rythmik. A L12 in my office and F15hp in my main system. The L12 is the equivilant of an HGS, the F series takes the HGS and wipes the floor. It is like a layer of crud cleaned off, nearly dry sounding, articulate, deep, and much higher output capability. It is a great step forward and well worth the upgrade. A pair is recommended to minimize room modes, the f12 probably being more than sufficient. |
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Two quibbles:
1 - Room modes ARE ringing
2 - Once bass traps are in place, DSP helps with ringing and nulls. .
Not going to argue this, plenty of professional acoustics literature out there. The bass traps help de-energize the rninging, and make DSP’s possible. You can even clean up nulls this way.
The combination of sub placement, room acoustics and DSP all contribute. Well done, they are lightning fast and completely organic sounding, and bigger = better.
However, poorly done, limited placement, no bass traps, no EQ, a small sub may often sound better.
Best,
Erik"
I think we fundamentally agree, but are not quibbling past each other. As I understand it:
1) Treating room modes by room treatments reduces decay time (ringing).
2) To optimize bass in a room takes a combination of setup, room treatment, and DSP. Just like a three legged stool, all must be applied properly to get a good outcome. |
"More important, IMO, is to have a SEALED sub for music."
Can anyone provide a supportable reason for this, or is this just an ad nauseum repeating of inaccurate information?
Subwoofer sound is primarly dictated by QTC and group delay. It is easier to build a sealed subwoofer with a low QTC and group delay (just throw a driver in a large sealed enclosure, the bigger the lower the QTC), but a vented subwoofer (whether ported, slot load, transmission line, or passive radiator) works just as well or better when properly designed. With decent quality subwoofers, the vast majority of issues people have are room and tuning related, not equipment related.
Just a few music focused manufactures using vented designs:
Vandersteen- Yep, slot load, including his $18,900 Sub Nine. Perhaps someone should let Richard know he isn't building his speakers correctly. After all, he is just a truck driver from Hanford, what does he know?
Wilson Audio- Yep, ported. But hey, David Wilson was just just selling speakers to deaf people.
Legacy- Passive radiators. I only heard Legacys once and was less than impressed, but it was 20 years ago and the room was less than optimal, so I really can't say they are good or bad. That said, they seem to be among the most liked brands. But again, perhaps Bill Dudleston doesnt' know what he is doing. Someone should let him know he should change his designs, as they are not audiophile approved as sealed.
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The Swarm and Debra subs are 'vented enclosure for correct roll-off to compensate for room gain (ports can be plugged with supplied plugs, if desired)'. I've tried my Debra subs both ways and preferred them unplugged.
The Swarm and Debra subs are an excellent example of using science and good acoustic theory to maximize the benefit for the minimum dollar. They have addressed the biggest issue, the room. It can be done with any 4 subs. You should see what some of the crazy home theater guys do, as the Swarm would never have enough deep bass for them (they want 120db @10 hz), things like quad JTR Captivators. Not to plug another forum, but AVSforums in the subwoofer section has some really great information on setup, tuning, and objective reviewing. The home theater guys have done more for good bass than just about anyone. |
"It’s nice to use subwoofers for theatre systems. The best option is to buy speakers for your audio system that do NOT need subs."
Why? The best speaker placement for imaging and bass are generally mutually exclusive!!!!! Are you willing to place 4 main speakers around your room at the optimal positions to minimize standing waves (ala a swarm setup)? Show me a full range speaker system that can go flat below 20hz that costs less than $10,000 a pair and is optimized for placement in the bass where the imaging is the best. The system in my office (a used set of Totem Mites and a Rythmik L12 for a total cost of $900) does that comfortably (when I say comfortably, it starts to roll off at 23 hz is and 1 db down at 20hz).
Even with "full" range speakers, good subwoofers with proper setup make a great difference. The problem is most people want to plop them down, spend no time setting them up, and then turn them up too loud resulting in a bloated, slow, plodding sound.
It takes time to get a sub properly setup and integrated. In my office, it took over 100 sweeps with REW with the sub in 3 different places to get a really good integration where it disappears. It can take a lot of playing with phasing, crossover and placement to get it right, but once you do, you can enjoy truly full range sound that lets you hear things you never knew existed.
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2. One Sub- With a single sub, unfortunately, the bass will be compromised because the bass will only be optimized at a single point in your room (your listening seat sweet spot) and the bass will not sound as good at other spots in your room. To optimally position a single sub, place the connected sub at your listening position/seat and play some content that contains several minutes of good and repetitive bass. Then, starting at the front-right-corner of your room, slowly walk counter-clockwise along the walls of your room until you find the exact spot where the bass sounds best to you. Lastly, locate the sub to this exact spot and then replay the bass content to verify the bass still sounds good to you when your seated at your listening position/seat.
mcreyn, Isuggest you may want to try this in your single sub office system."
Already did this. The sub started on the front wall, then the corner, and ultimately at the midpoint on the rear wall. Response from it is great there, and decay times are good. Since I am sitting at a desk, my listing position is always within a few inches making tuning easier as I only have to cope with one position.
The big issue I have is not sub related. I have a huge mode at 140 hz, followed by a suckout at 110 hz (and smaller ones at 65hz and 55hz). I am waiting to hear back from GIK acoustics, but will be trying some 244 bass traps to see if I can moderate this. Corner traps are not an option, but the 244 absorbs 16 sabins at these frequencies so should work well. |
Tim, We are going to have to disagree. The issue I have with my office is not a subwoofer issue, it is centered at 140hz, at which point a sub would be down over 20db assuming a normal 24db/octave low pass at 80hz. It doesn't matter whether I am using 1,2, 3 or 4 subs, the huge mode I have is way outside of that range. In my office, I have 3 potential spots to put a single subwoofer. I have measured all of them carefully and done the crawl, this is the best position of my choices. As far as room treatments, I believe that most rooms can benefit from them. The speakers and their interaction with the room are by far the largest determining factor in sound. I do believe in optimizing placement as a first step, but then what? Most rooms have long decay times and the first reflection points are too close, causing image smearing and brightness. $500-1000 in room treatments can transform how a system sounds. There is very solid science behind the reasons for and how to treat a room. You might find this article interesting: http://www.gikacoustics.com/room-setup-case-study/Finally, I think DSP is a great idea when placement and room treatments have not worked. I see the three all working together as a system. |
