Setting Up Multiple Subs - An interesting read... (1 Viewer)

[Brian L]

Here Here!

Putting aside single vs. multiple subs, even simpleton measurements techniques (discrete tones and an SPL meter) will give you enough information to position a sub and tweak an EQ. In my experience, the measurements always improve, as does the subjective results (note that I am talking a single sweet spot here....just call me Gary Reber Jr.)

If there are parameters at play that affect the sound, BUT, I can't do anything about them, then what do you do? Toss the EQ because it does not address all possible room interaction issues? No way.

I think down the road (well, there are some now) there will be some really cool products that will address room response in ways that we can't even begin to do now (DEQX, as well as some stuff that Meridian is doing, mentioned in a recent John Kotches WSR review).

But for now, is I can make my ears and my measurements agree, I am ahead of the game. Way ahead of the game.

BGL

 

[Mark Seaton]

Kevin- While your realization is very important, we do most certainly have tools to time and even frequency window acoustic measurements. This is most certainly why general EQ for full range speakers has so often gotten a bad rap. Above 200-500Hz, depending on the room and speakers, EQ can simply be the wrong tool and will not fix the problem you may be seeing on an RTA or with test tones. Above this range, you must use time windowed resposnes to look at the direct energy.

The interesting part comes in as you start looking at lower frequencies. If you try and use a time windowed measurement at lower frequencies, you find that you NEED to use a longer time window. Consider that you need to allow for most of a wavelength in your window. When we get to lower frequencies, the wavelength becomes very long, where the measurement, and our ears can no longer differentiate the initial arrival in terms of tonal balance.

Counter to your statement above, it is much more the decay of a sound signal by which we hear "detail" and differentiate instruments and other peculiarities. The systems you mention from Meridian and now Lexicon only differentiate themselves in how they determine what to EQ. Rather than looking at the pure magnitude response, they look at the decay time, and attenuate frequencies which have excessive decay times. The filtering is still parametric. Go back to the Harman white papers and read the earlier bass papers and they go through the measured and subjective results of EQ applied to subwoofers. In simple terms, even if we were outdoors, if the response has a large peak, it makes perfect sense that it will take longer for that frequency to decay or settle. Flattening the response reduces the initial energy at that frequency, which will bring the decay in check. In a room we are looking at it from the other end. These systems basically adjust the initial energy to better balance the energy supported by the room. Many MLS type measurments can easily depict such characteristics.

Without reading the earlier Harmon papers, the presumed inclusion and acceptance of EQ would not make sense to some readers.

 

[Wayne A. Pflughaupt]

Kevin,
You are correct. Equalizing doesn’t eliminate a node, it merely deprives it of energy. There is some debate as to whether or not this is the best means to address the problems, but generally it’s effective enough to produce satisfying results. As you noted, with proper parametric equalizing adverse effects of non-affected areas can be minimized.

Just curious - worries about “affecting everything else” aside, do you prefer the way things sound with or without the BFD?

Regards,
Wayne A. Pflughaupt

 

[dave alan]

Wayne,

If you don't mind me asking (been wanting to, but keep forgetting), what sub configuration do you use the BFD with?

I mean, ported, PR, sealed, front-firing, down-firing, single driver, multiple driver, etc.

Just curious.

Dave

 

[Kevin C Brown]

Wayne- The largest reason I took the BFD out of the loop, is that when I did my latest round of measurements (with ETF, a PC, and my trusty Radio Shack meter, time sliced and all... ), I actually have relatively flat freq response (I looked at 20 Hz to 200 Hz), with dips at 51 Hz and 134 Hz. In other words, there aren't any definite peaks to be mashed to get things any flatter than they are.

The initial freq response vs after the room nodes build up is just a supporting reason. (I do still have to look more at this. Kind of like a very multi dimensional space.)

Mark- Excellent info. Obviously, I am learning, and one piece of info does not necessarily make me an expert. But one piece at a time, and someday...

 

[Brian L]

If thats your in-room response, what in the hell are you doing worrying about this thread????

There are many that would look at that and declare game over, stick a fork in it, time to play a butt-kicking DVD and impress the neighbors!

But methinks your ears may not be in agreement with your measuements?

BGL

 

[BruceD]

Kevin,

I'd guess you were running the ETF with >200ms for the windowing time slice for the bass frequencies, correct? Were you were using 1/12 octave resolution or 1/3 octave?

 

[Kevin C Brown]

Bruce- The specific low freq test that ETF has. (Something like every 0.9 Hz. Even the high freq test tests every 1.46 Hz. But better s/n with the low freq test.) But so far, I haven't increased the windowing time more than the default yet. Next on my list. I also need to try and understand the phase plots more to see if that's another way to adjust phase throught the crossover.

Brian- That's just it. I really do like the sound of my system. I don't want to say it was a mistake to measure things, but it did get me questioning whether multiple subs might help with those dips...

I did watch Solaris over the weekend, but I don' think I'd put that in the "buttkicking" category...

 

[Chu Gai]

Oh come on now, you don't think Clooney should be kicked in the butt for that movie?

 

[Rutgar]

I think you're hitting the nail on the head. When I first got my DD-18 I worked diligently on getting the flattest response. I played with every setting possible until the response was smooth. Then, I played back a CD. The noise was awful! Everything sounded bloated, and hollow, all at the same time! The DD-18 out of the box sounded better than what I was hearing. I've since gone back and did as little eq'ing as possible. Basically, just pulling down the peaks a little, and not worrying about achieving a "ruler-flat" line. It sounds much better now.

 

[Wayne A. Pflughaupt]

Hmm, sounds like yet another flat response vs. house curve situation. Didja read up on house curve yet, Rutgar?

Regards,
Wayne A. Pflughaupt

 

[Rutgar]

Yes, and it's not the same thing I'm talking about. A house curve is basically a +6dB in the bass, sloping down until it reaches -6dB in the treble. I'm talking about the 20 to 200Hz region. Moreover, I believe the problem stemmed more from time domain problems than response, when adjusting everything to flat artificially.

Although I find that two subs help, I'm still not satisfied with my overall sound though. I'm beginning to consider massive amounts of bass traps.

Were starting to drift off topic. Maybe we should start another thread on bass response and electronic/physical corrections.

 

[BruceD]

Kevin,

This is critical, if you don't set the windowing to greater than 200ms, you won't get correct in-room bass response measurements. i.e. the graph results won't show what is truly going on.

This is the one point that isn't clear in the ETF examples for low-frequency measurements.

I'll be interested to hear your observations of your setup with the default setting vs. >200ms setting.

 

[Kevin C Brown]

Bruce- You're right. And basically, there was *some* but not a lot of difference between 0 msec up to 200 msec. (My meter is loaned out at the moment, so when I get it back... )

And, Mark's post turned on a light bulb in my brain after I thought about it for a while: a room node is like a capacitor. Stores energy which it then must dissipate. So not only does the eq'ing shape the initial response, *and* the formation and steady state of the node, but it also determines (and can improve) that dissipation. Neat.

 

[Wayne A. Pflughaupt]

Rutgar,
You’re on the right track, except there isn’t a set-in-stone figure for the slope. It’s entirely room-dependant; the smaller the room the more slope is needed. By the time you get to something as large as say, a civic auditorium, virtually no house curve is needed.

And it probably won’t be the same for the bass region as the upper frequencies. For instance, my slope rises 6dB between 20kH-100Hz. From 100-32Hz it rises another 9dB or so. That’s what it took to achieve what sounds like smooth octave-to-octave response from the highest to lowest frequencies.

The way I usually recommend determining your house curve slope is to play sine wave test tones at about 100Hz and 32Hz. Subjectively they should sound the like they’re at the same volume level. Of course, 32Hz actually measures higher, so when you get the two tones sounding the same you just shoot for a smooth measured slope between those two points. I prefer to shelve the slope at 32Hz, others prefer to keep it on the rise.

Naturally, if you happen to have a known notch or peak at 100 or 32Hz, you want to use another reference point as close to one of those as possible.

You might give this a shot and see what you think.

Regards,
Wayne A. Pflughaupt