Should my 2nd sub be sealed or ported?

Some people claim that the two subs have to match exactly or you're asking for integration issues. I personally disagree and think as long as the subs are similar in the range of frequencies covered and loudness, the particulars of the sub don't matter.

Read about gain matching vs level matching. If gain matching is for you, then you would want another of the same sub: http://www.avsforum.com/t/1282064/two-subs-gain-matching-vs-level-matching

If one is blessed with terrible room acoustics that don't blend well with their current subwoofer based system, I say, get another room.

My opinion, to best answer your question, one needs to see a measurement graph of the room so as to see how the single sealed sub is interacting with the room's acoustics.

If you can EQ them independently it shouldn't matter. If you can't it still shouldn't matter much IMO. While it would be nice to have identical subs, in practice I would guess the main issue is seriously overdriving one sub, and that is as likely to be a placement issue as due to the sub itself.

Virtually all rooms are going to have several LF peaks and valleys. Google room modes.

59Hz corresponds to wavelength of around 19 feet.

What are the distances between...
a) The subwoofer and the measuring spot?
b) The measuring spot and the wall behind it?

One needs a graph so as to see how one can knit the one together with the other.

FWIW, a 59Hz dip corresponds with the cancellation a 60Hz appliance will make. The added energy conflicts with the existing energy, hence the cancellation. In my opinion, 60Hz is the worst offender of the bunch. Also, your dip is going be a range, say from 52Hz to 65Hz as it's not just a straight drop like one would physically see when looking down a well pipe. It's going be more like a shoulder-to-shoulder dip one would see when crossing a small creek running parallel to a hillside, one shoulder a bit higher than the other. Overall, typically, a dip can be a quarter to half an octave wide and ten to twenty dB deep. Again with the need for measurements as without measurements, one can't be sure of the severity of the dip or null.

A bit more on the matter can be found at this website.

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Edited by BeeMan458 - 3/7/13 at 12:09pm

I hate the facts.

One can add a DSPeaker, Anti-Mode. I've been playing with mine for several months and overall, despite the negatives I've posted, with effort, coupled with Audyssey, MultEQ XT, in an untreated room, up to 73Hz, I've been able to reach the ideal of +/- dB. I did have to add an isolator to eliminate the gain a ground loop was adding to the sonic signature. If one has a ground loop hum in their system, this will squirrel up your readings by about 3dB as the ground loop hum acts as sonic gain.

Today's graph: no smoothing.



Note the dip around the +72Hz range. The good news, pretty much, anything after 80Hz in the LFE channel, don't matter and the crossovers recommended by Audyssey for the Mains and the Center Channels is 40Hz.

My new thought, is the +/- 3dB ideal, too strict of an ideal for our purposes. Would a +/-5dB be a more appropriate standard to shoot for?

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Edited by BeeMan458 - 3/7/13 at 12:34pm

A soft dip is sometimes correctable; a true (deep, narrow) null caused by cancellation (room mode) is very difficult. The usual solutions are to (a) move the listening position or (b) get another sub to use near-field to bolster the response at the listening position.

Speed of sound is roughly 1127 ft/s so 59 Hz is a wavelength of about 1127/59 = 19.1 ft as previously stated. However, the quarter-wave number is where cancellations start, or about 4.8' and multiples.

FWIW, in my experience, changing the LPF on one of the subs, or the phase of one of the subs will cause a sharp dip to come and go. In order to see this phenomenon is real time, one mush have at their disposal, room measuring capability. Most here have taken the time to acquire measuring capability so just for giggles, I suggest, if one is interested in what I posted, setting up their measuring gear and do what I suggest if their subwoofers have continuous potentiometer capabilities.

Based on what I posted above, one can only so so much as it's not a end-all procedure but doing what I suggest, does have beneficial acoustical possibilities.

As to room dimension measurements, room measurements don't take into consideration the WAF which is a much more powerful acoustical force in our living room.

^^^ If it is a room null it might not help much. Not all dips are true nulls. However, one of the most important uses of a continuous phase control is to get the mains and sub in phase at the crossover frequency so the sound works together instead of cancelling each other out. This is easy to hear; play a test tone at the crossover frequency and adjust the phase. Best if you can sit in the LP and have a friend do it, or a simple one-person scheme is to set up an SPL meter at the LP (preferably on a tripod) with the meter facing the sub, then adjust the knob whilst kneeling behind or beside the sub with the tone playing.

I am fortunate to have a dedicated media room, and an understanding wife (to a point...)

That's not being fair as the above is trying to have it both ways. Cancellation is cancellation and removed cancellation, no matter what the phenomenon is that removes the cancellation, is still removed cancellation.

Once one is set up to measure their room's acoustics, it costs nothing but valueless time and enhances the play time experience and harms nothing in the process to twist and play with the subwoofer's potentiometers; measuring in the process, to the good or bad, how small parametric changes interact with a rooms acoustics. Experiment, live, play, enjoy.

What I don't understand is why some folks here are so adverse to measuring how small parametric setting changes affect acoustic measurements when doing so costs and harms nothing.

My recommendation, one should set their measuring gear up and play for a few days with subwoofer placement and parametric settings. And in doing so see first hand how small subwoofer placement changes and parametric setting changes affects both dips and nulls. Doing so doesn't hurt anything and costs nothing. It's all about adult playtime and in doing so will help one better understand how their subwoofer's output interacts with their room's acoustics.


I have an understanding wife.....as long as it meets with her approval, she's understanding.

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Edited by BeeMan458 - 3/8/13 at 5:53am

Room nulls are caused by sound waves reflecting off a surface, which inverts them, and then cancelling (destructively interfering with) the direct signal. They tend to be related to room dimensions and can be very deep. The standing waves build at frequencies based on room dimensions and adjusting the phase does not help them since you cannot change the fundmamental frequency with phase control. The sound waves still cancel each other out at all points no matter the phase. Another way to think of it is that adjusting the phase knob moves the direct and reflected signal's phase, but they still cancel in the room. Dips caused by other effects, such as multiple reflections and reflections off soft surfaces, are more amenable to tuning out.

I have no issue doing measurements and encourage it; not sure where you got that idea from my post. My meaurement system is a bit more than most audiophiles (the measurement mic alone is worth around $1200), but I like to suggest easy experiments anyone can do. I didn't say anything about turning the pot to see what happens, just that it might not help a true room null. The Rythmik's single-band PEQ can help; I use mine to help flatten a peak (peaks can only build up so far since the energy can do no more than double; nulls from signals cancelling can be very deep and are much harder to compensate).

Changing the LPF changes the frequencies the sub is putting out so may help or hurt depending upon how it interacts with the room and other speakers.

There is certainly no problem just playing around, my point was and is that a room null caused by signal cancellation is not impacted by adjusting the phase knob.
Edited by DonH50 - 3/8/13 at 7:11am

A suggestion, try it before knocking it.

What happens, if one has two equal waves cancelling each other they have zero. If one wave is attenuated, the other wave becomes dominant then one has a corresponding increase. It's all very rational and one can easily see the changes taking place on their computer screen as changes and remeasuring takes place. But if one has a single subwoofer, then what I post has no meaning but if one is using two or three subwoofers, then what I post has all the meaning in the world.

Maybe the aversion is because as youth's, people were taught that it's wrong to play and have a good time. I'm okay with someone not wanting to play but I'm not okay with people telling others that life is set in stone and they shouldn't play with their parametric settings and measuring gear. I say to everybody, play, measure, have a good time. If it don't work for the person, then it costs them nothing and hopefully they had an entertaining good time in the process. No matter what anybody says or tries to do, they can't change reality and in my case, reality is empirically based REW measurements. Don't know why the argument.


And one will never know if they don't play.

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Edited by BeeMan458 - 3/8/13 at 7:54am

+1. Few really understand what the purpose of the phase knob is. When one sub alone is operating all by itself it does nothing audible. It does help prevent cancellations where more than one source is operating in the same pass band, which would be the bandwidth close to the crossover frequency with respect to the mains, and across the sub passband where more than one sub is running.
As for running two different subs, that limits your system to the capabilities of the lesser of the two. I don't know what you've convinced your wife/girlfriend of that which constitutes a 'monster', but a 5 cu ft sub is no monster.

When you have a "real" null, it is caused by the sound directly from the sub combining with, in effect, the reflections of the same sound from walls, ceiling and/or floor, and they subtract from each other. In a perfect, rectangular, enclosed room you could calculate where the nulls would be for any listening position because they depend on nothing but time (which boils down to distance for this purpose - - the reflected sound comes later. If I'm thinking straight this morning, for a 50 Hz wave a strong reflection that comes 1/25 of a second behind the direct sound would be 18 degrees out of phase and the two would "combine" to yield, theoretically, zero at that listening point.

Phase is essentially the same as delay. The waves from the sub interact with the room the same way whenever (or in whatever phase) they are originally emitted because it'sall about how the different audio paths put WHATEVER the original sound was out of phase with a reflection.

The reason you cannot EQ out a null is like this. Think of the initial wave from the sub, then a perfectly out of phase wave from a wall. The out of phase wave's strength is close to the strength of the initial wave. That's true whether the initial wave is very quiet or very loud. The reflection causing the problem simply gets louder when you EQ up the frequency. So instead of, say 1-1=0, you have 10-10=0.

My question morphs into, what can we hear in a transient sound recording like that of an action based sound track where one is concentrating on visual as well as acoustical?

Example; a quarter octave null, from 72Hz to 90Hz, that's fifteen dB in depth, over that of the overall ideal, +/- 3dB.

I'm going use the James Bond movie, "Casino Royale" parkour chase scene. How much would one notice the described null while watching this scene at +80dB? And is anybody noticing the null in their sound system with this type of fast paced action in front of them?

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Edited by BeeMan458 - 3/8/13 at 8:38am

Phase will have no effect on a null if it's the only sub in the room (Assuming the null is below the crossover to the other speakers). If there's more than one sub, it can effect the null, but it's a crappy way to solve the problem. You're basically fixing the null problem by making your subs out of phase with each other at the null location. The more out of phase, the greater effect on the null.

To the OP,
If your room is about 20' deep, the null can be easily explained.

Well that's not fair. Crappy is such a subjective term. In a perfect world with unlimited resources, sure but if one is limited to their own devices over that of the ideal, then it's fair to say that one person's crappy is the best another can expect.

I really am being made to believe that some here only want to work with that what's set in stone.

Just for the record, my last diversion from the status quo was to invest in a couple of isolator to eliminate the 3dB gain a ground loop was adding to the signal.

I measured the output before and I had a reading of 13.1mv and after the isolator was added, the reading dropped to 00.1mv. One's system can benefit if one is willing to think omni-directionally when trying to get the best out of their system.

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Edited by BeeMan458 - 3/8/13 at 11:57am

I have no idea how you got the idea I am against trying things from my post. Here is what I said that started all this angst in response to your suggestion to adjust the phase knob:

How you got from there to the idea I am against trying things is beyond me. I am an engineer, experiments are what I live for!

And in this specific case, I have indeed "tried it", and many other things, over the past few decades. However, the well-known science behind room acoustics says cancelling a null from a room mode with just the phase knob is not possible. It can affect many other things, my post was meant to clarify the one thing often discussed in subwoofer threads.

In any event, I'll bow out, not worth the pain - Don

Well known to engineers, but not so much to the average consumer. Everyone's entitled to an opinion, but if you're going to give an expert opinion you first must become an expert. That doesn't happen in nine months. Nine years, maybe.
The OP deserves to get a correct answer from someone actually capable of giving him one. Don't bow out, just use your block button to separate the wheat from the chaff.