[theater_lover]

1) Why do open baffle H & W frame subs have one driver flipped around?  Is it to make the output equal on both sides (assuming the rear has less output due to the motor and frame)?

2) Isn't the acoustic center of most woofers closer to the dust cap than the front of the frame?  If so, doesn't that make having the drivers mounted on the same baffle face, with one reversed, not in phase?  Even "w" designs tend to have centers not aligned.

3) This one is an odd question.  If a driver relied on reflection, would position/phase need to compensate for the distance of the reflective surface from the acoustic center of the driver?

Thanks.

[Captainhemo]

You  can orientate the  woofers either way, just  adjust  wiring accordingly.  We've been sending out a lot of  cabinets with all woofers facing forwards

There was some concern over  cabinet balance with all the   weight onthe rear side, but with a decent sized base, it is not an issue.

jay

[theater_lover]

So the opposing drivers are purely for balance/weight distribution?

[Tyson]

So the opposing drivers are purely for balance/weight distribution?

Yes.

[Openly Baffled]

Hi theater_lover,

Please let me respond...

1) The flipped driver is intended to have an audible purpose.
Linkwitz and others proposed that due to the non-symmetrical construction of the woofer, cone, surround etc. they radiate distortion (non-linear properties) at different amplitudes front and rear. If both drivers are in the same orientation these sounds are reinforced. When one of the drivers is reversed, these artifacts are effectively cancelled.
I have tested this and measured a very small reduction in harmonic distortion at the  listening position but not enough for me to easily hear the difference. Our ears are less sensitive to very low frequency distortion. My systems now have both woofers facing forward for purely aesthetic reasons.

2) You are correct that the acoustic centres would not be so well aligned but due to the very low crossover frequency required (100-200Hz) the wavelength is much longer than the mis-alignment so it has little audible impact.

3) Not sure about your question. Are you referring to reflection in the cabinet or from rear room surfaces?

One of the biggest advantages of open baffle bass is the cancellation of sidewall and ceiling room modes. This requires equal (and out of phase) front and rear radiation. The back wall will always contribute a delayed reflection however this can be tuned by changing the distance between the rear wall and the speakers. Tuning this can produce excellent bass and is one of the joys of open baffle woofers.

Hope this helps,
Rohan

[theater_lover]

3- My reflection question was mainly about cabinet reflection in a theoretical design that orients the drivers so that their output is reflected off the cabinet and into the room.
For instance, say a "W" shaped cabinet had the drivers rotated so that one was pointed directly at the listener, and the other was pointed directly towards the floor.  The one pointed towards the floor is relying on an almost immediate reflection, while the one directed at the listener would not.

[Davey]

Linkwitz measured approximately 15db even-order distortion reduction owing to the "inverted" layout of one woofer.  (Confirmed by myself and others.)
It's fairly easy to measure with your microphone located close.  Even with the plane of the H-frame baffle opening.

Whether reducing even-order distortion in this way translates to an improved subjective evaluation is another topic.

Dave.

[Jaytor]

I built my triples with all the drivers facing forward. They sound fabulous and I haven't had an issues with the weight being all in the back. It's possible that distortion is slightly higher (I certainly don't hear any issues), but I like the way they look a lot better with them facing the same way, and it's a lot easier to wire them this way.

[rockdrummer]

I did the same thing. I had the super v with the servos facing opposite like the traditional plans. When I built the duals for my current set up, I faced them all forward purely for aesthetic reasons. My rookie ears can’t hear any difference. It’s as awesome as before.

Ben

[Tyson]

There's a tradeoff here - reversing the sub drivers does result in lower distortion (and this is how my OB subs are configured).  On the other hand, keeping both drivers facing forward means the air pressure coming toward you is generated directly by 2 forward facing cones which will result in a more forceful, punchy bass. 

Either way you configure them, it's still world class bass, leagues above a typical box speaker's bass.

[DThor]

I have a related question about the OB subwoofers.  How much does the H or W frame contribute to the sound?  If you were to mount the subs on a very thick baffle (similar to Spatial products), without the H or W frame, would you be giving up very much?  I'm guessing they might not go down as low in frequency.  Giving up a little there, as long as it wasn't too significant, might be worth it aesthetically.

[corndog71]

If a simple one piece baffle worked better then that’s what people would be using.  The h frame is much more space efficient while giving enough separation between the front and rear of the baffle.  You may not like the looks but Danny’s designs are all about sound quality.

[Tyson]

It also lets you get world class bass from a "stand" not much bigger than a small tower speaker. 

[Davey]

Well, one thing is for sure. When reversing one driver you know the radiation is symmetrical.
One thing you also know is that H-frame setups can have a force-cancellation issue with certain listening room constructions.  This can manifest with floor vibrations and/or significant vibrations into the rest of the speaker system (if it's attached.)

Trade offs exist regardless.  Even dipole setups with the woofers in force-cancelling opposing configuration create their own issues.

It's quite a bit more complicated than opposing the drivers for balance/weight distribution. 

Dave.

[Captainhemo]

It is,  but  at the same time,  I'm betting you couldn't tell the difference acoustically if a say dual 12 with both woofers   facing forward  were swapped with a dual 12 with opposing  woofers.  I've listened to both  numerous times and at first,  I thought the    both facing forward provided a bit more impact but after  numerous swaps... it's almost impossible to tell.

We've done this with both dual and triple setups

AFAIK,  Danny is still running an all forward set of triples  we sent him to try  the in  this configuration  and I'm betting  anyone who has  been up there for a demo/listening  session lately was not disappointed.

I never try and steer anyone either way when they  are ordering cabinets,   I  just   explain that  they  aren't likely to notice  a difference  either  way and that they should go with what  works for them appearence wise.

jay

[Danny Richie]

Playing one way verses the other has some effect, but not what people think.

The woofer itself, meaning the motor structure and frame, will take up some air space. So the amount of compression on one side verses the other side is different. So flipping one woofer around equalizes the pressures.

So have claimed it can cancel out some even order distortion, but that is still almost theoretical at best. Measuring any distortion outside of an anechoic chamber is nearly futile. Room noise levels typically exceed the levels actually being measured.

It is like measuring the level of one persons voice in a crowed room among a hundred others.

You can move the microphone close to the speaker to change the differential, but rest of the room noise is still in the response.

So it is like moving the microphone closer to the one persons voice that you are trying to measure while the rest of the people are still talking.... It is still a mess.

To measure any real effect (if there is any) one need to be far enough away for the woofers to sum as a single unit. And you again can't really do that and get any meaningful distortion measurements outside of an anechoic chamber.

And on top of that, distortion is really nothing. By that I mean it is a drop in the bucket compared to the settling time of a woofer being played hard. That is where real audible differences take place and where the servo control system really sets itself apart.

Another myth involved in flipping one woofer around is that there is some kind of force cancellation. That is not true. When a woofer is flipped around you also flip the polarity on that driver. So it still moves in the same direction as the other woofer. So all of the force is moving in the same direction.

Flipping one does separate the acoustic centers a little bit, but the wavelengths being played are so long that it doesn't matter too much.  Even at 200Hz the wavelengths are still five feet long.

I have a related question about the OB subwoofers.  How much does the H or W frame contribute to the sound?  If you were to mount the subs on a very thick baffle (similar to Spatial products), without the H or W frame, would you be giving up very much?  I'm guessing they might not go down as low in frequency.  Giving up a little there, as long as it wasn't too significant, might be worth it aesthetically.

The H frame and W frames allow greater separation of the front and back waves while also loading the drivers. This extends the low end response and allows for more impact.

A flat baffle allows cancellation to occur much more quickly reducing output and extension. 

[Davey]

Danny,

There's not a myth (that I'm aware of) that force cancellation results from flipping one woofer around in an H-frame.  As you mention, reversing one driver in an H-frame setup would necessitate reversing the electrical connection as well.  Regardless, an H-frame system has no force-cancelling effect in either configuration. 
To achieve a force-cancelling effect the woofers require an orientation such that the cones are always moving in opposing directions on the same axis.  I would think that's obvious.  (Even a 90 degree configuration doesn't come close to that.)

Theoretically speaking, you've reduced asymmetry as much as possible with a flipped driver in an H-frame.  That, is an inherently even-order reducing mechanism.
Non-theoretically speaking, meaningful woofer system distortion outside an anechoic chamber is easily doable....under the right conditions.  This was demonstrated to me in person by Siegfried Linkwitz about twenty years ago.  Klippel has an interesting process for this as well.....although quite convoluted.

Anyways, whether this reduced even-order distortion contributes to a net audible benefit (or detriment) is, (as I mentioned above) a subjective evaluation and another topic.
Servo-control is a different topic as well.

Dave.

[Danny Richie]

Danny,

There's not a myth (that I'm aware of) that force cancellation results from flipping one woofer around in an H-frame.  As you mention, reversing one driver in an H-frame setup would necessitate reversing the electrical connection as well.  Regardless, an H-frame system has no force-cancelling effect in either configuration. 
To achieve a force-cancelling effect the woofers require an orientation such that the cones are always moving in opposing directions on the same axis.  I would think that's obvious.  (Even a 90 degree configuration doesn't come close to that.)

Correct, but as soon as someone starts talking about force cancellation that's what people think.