[THROWBACK]

I have seen this claim enough (the latest over in Audio Asylum) that I am starting to wonder about it. Do OB system inherently lack visceral impact compared to sealed or ported designs?

With my ignorance naked and fully on display, I would have thought the opposite was true. Consider the leading edge of a transient. In an acoustic-suspension design, the forward motion of the woofer has to be somewhat impeded by the resistance of the air spring behind it, or there would be no restoring force. Doesn't that affect impact? And wouldn't that be true to some degree  for all closed-box designs up to the true infinite baffle?

The OB, of course, has the problem of cancellation due to the sound wave rushing around from the front to the rear of the open baffle. But that takes time. Why would that affect the initial transient?

What am I missing?

[JohnR]

Put an OB sub in the nearfield and you won't wonder any more.

[THROWBACK]

Excuse me, John, but does that mean that I would hear a lot of impact in the near field but not in the far?

[JohnR]

Just try it. Seriously.

[AJinFLA]

Do OB system inherently lack visceral impact compared to sealed or ported designs?

No....thought some OB/room responses might, to some people, subjectively. YMMV.

cheers,

AJ

[Rocket_Ronny]

Depends on how much air the speaker can move. My super vs have great impact.

[Russell Dawkins]

I often wonder, when I read about one speaker having more 'slam' in the bass than another, whether what is being talked about is actually resonance—whether the box is sealed or ported, any box will be more resonant than no box. Resonance in this context could also be called overhang or settling behavior. When overhang is reduced bass energy is reduced but the bass range becomes more articulate so, for example, bass pitch and character is more easily discerned.

Hearing non-resonant bass was a revelation for me when I first heard it, although it wasn't open baffle, it was an obscure arrangement described in an old 1974-ish vintage English hi-fi mag where two bass drivers of identical free air resonance frequencies were mounted back to back in a sealed box. The idea was that when one driver approached its resonant frequency so would the other and each would control the other. The proof was the basically flat (±1-2 dB) impedance curve through what should have been the resonance zone. The sound of this stayed with me for the next year and made the bass resonance of all other speakers I heard laughably obvious!

[mcgsxr]

Agree that trying it is not hard and is the most likely to help you understand what happens.

Conventional wisdom states that it takes 4 OB woofers to equal a single boxed woofer in terms of output.  Likely only a concern if you are running the woofer off the same amp as the mains (as opposed to biamping with a dedicated sub amp where you can use the volume pot to account for the delta).

My first run at an OB sub was an older car 12 I owned.  I stuck with it for a long time after hearing what it could do biamped.

I am not sure about the "impact" thing.  It may very well indeed be the resonance of other subs vs clean OB bass.

[AJinFLA]

I often wonder, when I read about one speaker having more 'slam' in the bass than another, whether what is being talked about is actually resonance—whether the box is sealed or ported, any box will be more resonant than no box.

I took it to mean you "feel" the impact of kick drums etc in your chest, vs simply hearing the bass.
I myself have heard OB designs that are weak in this regard, but again, that is not inherent, as I have heard others with such impact.
It varies.

cheers,

AJ

[Russell Dawkins]

I took it to mean you "feel" the impact of kick drums etc in your chest, vs simply hearing the bass.
I myself have heard OB designs that are weak in this regard, but again, that is not inherent, as I have heard others with such impact.
It varies.

cheers,

AJ

I wonder if it might have something to do with the fact that, with OB, the net energy into the room, in bass frequencies especially, is approaching zero due to dipolar cancellation and thus energizes the room least. With a monopolar box what you hear, the room hears and the air volume in the room is maximally energized for the same on-axis response as the dipole. Put another way, for linear response on axis , dipole vs box, the room sound with the box has much more bass energy—it would be bass-shy with a dipole, even if response was flat on axis.

[JohnR]

No no no. Put a dipole sub near you - as in a meter. Then apply the theory.

[mcgsxr]

I have never tried what JohnR is suggesting.  Closest I had my OB 12 was 2m away.  And later 2 12's 2m away.

[JohnH12]

The difference is that the monopole speakers will pressurize the room so there is additional gain over a dipole.  The difference becomes less in larger rooms.  Jeff Bagby has a Diffraction and Boundary Simulator that will calculate the room gain difference.

[grsimmon]

I often wonder, when I read about one speaker having more 'slam' in the bass than another, whether what is being talked about is actually resonance—whether the box is sealed or ported, any box will be more resonant than no box. Resonance in this context could also be called overhang or settling behavior. When overhang is reduced bass energy is reduced but the bass range becomes more articulate so, for example, bass pitch and character is more easily discerned.

Hearing non-resonant bass was a revelation for me when I first heard it, although it wasn't open baffle, it was an obscure arrangement described in an old 1974-ish vintage English hi-fi mag where two bass drivers of identical free air resonance frequencies were mounted back to back in a sealed box. The idea was that when one driver approached its resonant frequency so would the other and each would control the other. The proof was the basically flat (±1-2 dB) impedance curve through what should have been the resonance zone. The sound of this stayed with me for the next year and made the bass resonance of all other speakers I heard laughably obvious!

The type of woofer arrangement you describe above - is this what the Martin Logan subwoofers are doing?  Do you think it matters if it's 2 opposing or 3 opposing woofers?   Curious if you still think this design set-up is worth pursuing?  I've never heard it myself, but am very curious.

[Russell Dawkins]

The type of woofer arrangement you describe above - is this what the Martin Logan subwoofers are doing?  Do you think it matters if it's 2 opposing or 3 opposing woofers?   Curious if you still think this design set-up is worth pursuing?  I've never heard it myself, but am very curious.

I'm not familiar with the Martin Logan subs you mention. Googling yielded only single sided subs with plate amps on the side opposite the driver.
I have seen some manufacturers using woofer arrangements which would seem to fit the criteria I described and have always paid particular attention to comments regarding the bass quality of these speakers in reviews. Often the bass is singled out as being good, but never have I read a review which suggested the reviewer was hearing what I heard with mine. I suspect that even reviewers, having been brought up on a diet of what I consider to be boingy bass, consider that sound to be normal—which I guess it is, by definition.
I even went so far as to approach the designer of a successful high end studio monitor (Barefoot: http://barefootsound.com/) about the advantages of his opposed woofer design, but he didn't answer directly. I think that for the few manufacturers who use this configuration, they don't want to draw attention to it, because it is probably not patent-able and so easily done, the only downside from the manufacturing point of view being a little more complication—it's easier to mount two woofers on the same side with one grill cloth, plus I believe that accurate pair matching (of the opposing drivers) is important.

Three drivers would not work; what is needed is symmetry across the plane defined by the backs of the woofer magnets. In my box, the 12" woofers' centers were about about 18" from one end and 30" from the other end of a 48" long box which was about 16"wide and 14" high. I'm just guessing on the dimensions—this was in 1974. The box was wrapped in 2" thick cedar if I recall which formed the basis of a coffee table. It was a sub/satellite system with the sub being mono and crossed at around 125Hz. The satellites were open baffle with wide range drivers. Yep, I was ahead of the game!

I do plan to continue my experiment with this design in the near future with a pair of the Jordan Eikonas.

[grsimmon]

The subs from MartinLogan I was thinking of are here:

http://www.martinlogan.com/balancedforce/index.php


They use 2 identical and opposing drivers in a sealed enclosure.   I think there's other companies that do a similar setup, but the ML's are the ones I've been curious about. 

[maplegrovemusic]

Seaton Sound makes the type of sub what you are describing

[rodge827]

Put an OB sub in the nearfield and you won't wonder any more.

JohnR
I have two Hawthorne Augies I'm experimenting with, each in its own 22"X 18" baffle. When you say 1m would that be 1m from my seated position which is about 2m from my ears? Or 1m to the right and left of my chair?

[JohnR]

Cool 

As near as seems to make sense - to get any closer than a meter from the center of your listening chair though I think you would need to raise the sub(s).

There are two effects at work here. One is the intuitive "more sub less room". The other is that dipole cancellation reduces the closer you get. You may need to adjust your dipole EQ.

A W-baffle (opposed drivers) would work better, but give it a try anyway Also, for impact don't use too low a crossover - maybe try a steep filter at 100 Hz.

[Early B.]

There are two effects at work here. One is the intuitive "more sub less room". The other is that dipole cancellation reduces the closer you get.

I have OB monitors sitting on top of dual stereo OB subs. I never thought about placing the monitors on stands and moving the subs around the room. I don't have an "impact" issue, but placement changes might be a good thing for aesthetics alone.

Conventional wisdom says to place OB speakers away from the walls as much as possible. Not sure if the same holds true for OB bass modules.