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I clicked into the Speakerboxlite page & see nothing about input levels, so it's a bit difficult to judge efficiency. That said, I'm not ready to give up on Hofmann quite yet.
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subwoofers with dual opposed drivers
- Thread starter Willem
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The point is to show the differences with the same driver(s) in the two different types of boxes under the same conditions. This might not be the case for every subwoofer though. With some woofers it is better to design a bass reflex box.
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Why isn’t it?
What project exactly? Link?
See post #167
Are you asking for my feedback on the SpeakerBoxLite simulator?
Do you think this simulator works right or are there factors that are missing?
I am not able to prioritize analysing the accuracy of that simulator any time soon, I am sorry. Not sure if I'm the right person to do it either.
Ok fair enough i find it very useful and easy to work with.
In case anyone is interested, Dynaudio told me that the 18s sub contains two completely separate sealed compartments, and that the core sub is essentially 2 18s stacked on each other, so 4 separate compartments. Dynaudio bills the 18s as using a "Dual opposing driver design principle." Does separate boxes defeat the purpose?
No. The movement of the opposing drivers cancel out the movement/vibration/effect on the cabinet. It will work with both separate and common compartments.
Awww, I wish I had spotted this discussion earlier.
I used to design and build my own speakers and subs. At some point I thought of the bipolar subwoofer approach (I am sure that I was not the first) and built a breadboard box to try it out. It was amazing! Plenty of nice deep bass in the room, but the sub cabinet was absolutely inert. Kind of freaky since most speaker cabinets have some level of vibration. It taught me that all of the cabinet vibes that I was used to were not from cabinet wall flexure, but from cabinet motion. Cool, but what are the benefits? Well, less energy loss is good. However we all have more amp power than we need, so not a big deal. Not shaking the mid and tweeter around is good. There is such a thing as doppler distortion. I have never tried measuring it. Just used the "less is better" approach. Besides, I always use subwoofers, which are decoupled from the other drivers. Then there is the re-emission of signal from the speaker cabinets that are shaking. Can't be good, but I do not know how much it is not good. Finally there is the transmission of vibration to room structure. For me this is the big issue. I hate when things vibrate. I just want sound, nothing else. This becomes a huge issue in a small room, or in a vehicle. I have tried various approaches for vehicle sound, and I like this one the best. I currently use an old sub by NHT (the W2, I think) in my truck system. No vibrations to cause buzzing, just nice deep low end. Not an ideal sub design, but I no longer have the time or tools to make cabinets, so that is what I must use for now.
btw, it is possible to shake a concrete slab under a house. I actually failed a water line when I got a bit overzealous with the volume control a few years back. These were big bass reflex subs downfiring. I built them for outdoor listening (design criteria was 120db at 18 hz) but had to try them indoors. I do not know how much was due to transmitted cabinet vibration and how much was due to air coupling. Either way, just coupling the subs to the concrete probably does not make the issues go away. All of my designs are now bipolar in the LF range.
I used to design and build my own speakers and subs. At some point I thought of the bipolar subwoofer approach (I am sure that I was not the first) and built a breadboard box to try it out. It was amazing! Plenty of nice deep bass in the room, but the sub cabinet was absolutely inert. Kind of freaky since most speaker cabinets have some level of vibration. It taught me that all of the cabinet vibes that I was used to were not from cabinet wall flexure, but from cabinet motion. Cool, but what are the benefits? Well, less energy loss is good. However we all have more amp power than we need, so not a big deal. Not shaking the mid and tweeter around is good. There is such a thing as doppler distortion. I have never tried measuring it. Just used the "less is better" approach. Besides, I always use subwoofers, which are decoupled from the other drivers. Then there is the re-emission of signal from the speaker cabinets that are shaking. Can't be good, but I do not know how much it is not good. Finally there is the transmission of vibration to room structure. For me this is the big issue. I hate when things vibrate. I just want sound, nothing else. This becomes a huge issue in a small room, or in a vehicle. I have tried various approaches for vehicle sound, and I like this one the best. I currently use an old sub by NHT (the W2, I think) in my truck system. No vibrations to cause buzzing, just nice deep low end. Not an ideal sub design, but I no longer have the time or tools to make cabinets, so that is what I must use for now.
btw, it is possible to shake a concrete slab under a house. I actually failed a water line when I got a bit overzealous with the volume control a few years back. These were big bass reflex subs downfiring. I built them for outdoor listening (design criteria was 120db at 18 hz) but had to try them indoors. I do not know how much was due to transmitted cabinet vibration and how much was due to air coupling. Either way, just coupling the subs to the concrete probably does not make the issues go away. All of my designs are now bipolar in the LF range.
Why not pursue a bandpass design? Inherently low distortion, much of the benefit of dual opposing woofers. Low end extension is going to be the biggest hurdle. Many would prefer a shallower rolloff.
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I'm not sure that's audible with 10' wavelengths?
I am not sure if it is audible at all, but it would be at much shorter wavelengths. The idea is that the tweeter or mid gets moved fore and aft by large scale cabinet vibrations. Now that I think about it, it would not be that hard to measure. Not sure if it would show up in the traditional measurements. Maybe as IMD?
Really dug most of this thread, guys. Thank you.
With the talk of dual opposed, I am curious to open the can-of-worms (possibly) and ask about the Push-Pull style from MK and being used by Perlisten.
Can this be employed in a Ported Cabinet, or only Sealed?
Does it matter in which direction the drivers are mounted? (Same baffle, opposite baffles (effectively dual opposed but with one driver motor in, the other motor out), etc...)
Do you need 2x Vas when designing?
Any other tidbits that can be shared?
Many thanks!
With the talk of dual opposed, I am curious to open the can-of-worms (possibly) and ask about the Push-Pull style from MK and being used by Perlisten.
Can this be employed in a Ported Cabinet, or only Sealed?
Does it matter in which direction the drivers are mounted? (Same baffle, opposite baffles (effectively dual opposed but with one driver motor in, the other motor out), etc...)
Do you need 2x Vas when designing?
Any other tidbits that can be shared?
Many thanks!
Yes, push pull is what I did. The front woofer is mounted conventionally, and the back woofer is flipped magnet out. In theory this will cancel nonlinearities in the driver motors. In practice it makes one of the woofers really easy to wire ;-)
You can think of this whole idea as 2 mirror image subs mounted back to back. In fact, you can actually assemble one that way, even just as an experiment. You can also mount them face to face with spacers if you want to try slot loading. The only requirement is that the woofers are axially aligned and working in pressure phase but moving in opposite directions. Same for ports. Especially the same for passive radiators. Those things can really shake a cabinet.
You can think of this whole idea as 2 mirror image subs mounted back to back. In fact, you can actually assemble one that way, even just as an experiment. You can also mount them face to face with spacers if you want to try slot loading. The only requirement is that the woofers are axially aligned and working in pressure phase but moving in opposite directions. Same for ports. Especially the same for passive radiators. Those things can really shake a cabinet.
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I've been curious about the more practical aspect of putting this design to work. It seems I saw Alden or Dickason say that it can be done for a ported cabinet but neither go into details about it.
Hence my question about whether you treat it as any other Dual-Driver configuration.
You say "Axially Aligned." Perhaps I am hung up an an improper or incomplete definition of "axial." Wouldn't that be, for ease of description, ant either end of a Sonutube? Yet the MK and Perlisten Subs fave the drivers perpendicular two each other with one on the bottom of the cabinet and the other "forward facing." I've seen other examples where the drivers are mounted on the same Baffle (front-firing orientation) which of course.
Still, my main questions stand:
Can this be done in a Vented Design?
Are design parameters treated as any other dual driver configuration?
For the last 2 questions, Yes and yes. It is best to have an internal wall between the two chambers to eliminate strange effects due to channel imbalance. From that perspective it is just two of the same subwoofer design.
Yes, the sonotube with a woofer at each end is a good example. You want the axis of one woofer to go through the axis of the other. Same with reflex ports or passive radiators. Any misalignment will result in torsional vibrations.
There is a common old design where the cabinet is roughly cubic. Opposing woofers front and back, and opposing passive radiators side to side. This is a relatively compact design. You can isolate the 2 chambers with an angled internal baffle. If the chambers are not isolated (just one big box) then care should be taken to match all component pairs, and to have a matched mono signal to each active woofer.
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