Perhaps it will be reviewed in stereophile and some sort of objective measurements will be available. I like the idea of top two planars though.
Obviously they wouldn't whether OB or tiny sealed nor nothing HIFI per se since they would only be an octave wide at most, but just wondered if they used a sub harmonic synthesizer like I did long ago to make non existent sub-bass for 'fill' when listening to pipe organ symphonies, action movies with explosions.
I am just starting to look at open baffle designs but as there is no magic in physics and following the Occam's razor, is it plausible that a 6dB slope compensation let say up to +20 or even 24dB makes the job based on the 91dB sensitivity (see in post #19) to reach a "reasonable" power handling (value not mentionned in the paper #19)? Is it possible to put more figures on that thanks to the loudspeaker excursion in open baffle (very long excursion driver?)?
two 6" per channel works fine ported or sealed. But OB I doubt. See what SL did : minimum two 10" OB per channel with hard cone and long Xmax !
I am sure you know it already. However I found there is a fine filter tunning at cheating and make a tigth bass : filter tunning and passive parts (dunno for active) are importants. The coil (you know that) but also the decoupling and precise amount value of the // cap (if second order and...).
Do not hesitate to play with distance of the listening chair to find if you are in a high or low pressure node according the room where you are listening to (but you know this).
You know it already. low size = cut off below 150 hz (my experience with low sized -aka hifi reviws- loudspeakers but not OB
I am sure you know it already. However I found there is a fine filter tunning at cheating and make a tigth bass : filter tunning and passive parts (dunno for active) are importants. The coil (you know that) but also the decoupling and precise amount value of the // cap (if second order and...).
Do not hesitate to play with distance of the listening chair to find if you are in a high or low pressure node according the room where you are listening to (but you know this).
You know it already. low size = cut off below 150 hz (my experience with low sized -aka hifi reviws- loudspeakers but not OB
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again : room size and litening distance but no magic with bass. Decay quality though can be a question of sources and parts matching... tunning ime.
There is no mention of any active EQ being used on this speaker. But even if it was, adding 20 dB could extend the response to 40-50 Hz. The penalty is of course a massive increase in amp power and cone excursion.
The problem is not so much that the required power will be unreasonable but that the driver is simply not able to operate nicely when the gain is increased by 20dB or more to equalize the dipole response to be flat. One issue is the increased excursion demand. To check this, model the driver as if it is in a closed box with a volume that is very, very large, e.g. enter 999999 liters or whatever for the box volume. Check out the cone displacement for 1W. Now increase the power by 20dB to 100W. Does the cone excursion remain within the acceptable limit (e.g. Xmax)? Keep in mind that this 20dB boost is just to equalize the low frequencies up to the 1W SPL level at some higher frequency. It's not making it "loud" - the equalized dipole speaker will just be operating as if you applied 1W to a closed box speaker!
The other problem with trying to use too much boost is what I call "distortion amplification". Distortion products such as harmonic distortion will appear at a higher frequency than the fundamental. Let's say driver X in a closed box has -40 dB of 4th order harmonic distortion at 100Hz. This means the distortion component at 400Hz is -40dB compared to the level of the fundamental at 100Hz. Now make this a dipole. If we are far below the dipole peak, the response is falling at 6dB per octave. 400Hz is two octaves higher than 100Hz, so the level at 400Hz is 12dB higher than the level at 100Hz. This also "magnifies" the distortion product by the same amount, changing what was a -40dB distortion level (1% distortion) into a -28dB level (about 4%). Taking this further, if the response is 20dB below the level at some higher frequency then there will also be a 20dB magnification (10x) of the distortion product there. One side effect is that higher order distortion products will be magnified more than lower ones, and higher order HD is typically thought to lead to bad sound.
In my own systems I try to limit the bandwidth of any driver used as a dipole, especially when the baffle area is relatively small, to no more than about 2.5 octaves when possible. 3 octaves is pushing it IMO. This helps to reduce the power lift required and will minimize the distortion magnification problems.
Ok. I got it confirmed in a youtube video that they are using Acoustic Elegance woofers. 12" means that it's the Dipole 12 model.
I've got a spreadsheet made by Linkwitz that calculates max SPL in open baffle and closed box. Here's the results for two AE Dipole 12 with no baffle and in closed box.
It's quite possible to get down to 40-50 Hz with decent SPL level with these drivers and some giant series coils in the crossover, I think.
But 20 Hz? Not gonna happen.
I've got a spreadsheet made by Linkwitz that calculates max SPL in open baffle and closed box. Here's the results for two AE Dipole 12 with no baffle and in closed box.
It's quite possible to get down to 40-50 Hz with decent SPL level with these drivers and some giant series coils in the crossover, I think.
But 20 Hz? Not gonna happen.
With a big inductivity on the woofer they make it current driven. Minimizes some distortion.
Now it depends how you listen to music.
Rock music listeners are not prefering this speaker.
Limiting to 50hz is a good idea. Active filters would help.
Drivers which are not masked by music in the upper frequencies - sometimes you can hear the material itself (surround and spider, air noise) making noises while large excursions take place. Something like single voice with some deep bass.
Now it depends how you listen to music.
Rock music listeners are not prefering this speaker.
Limiting to 50hz is a good idea. Active filters would help.
Drivers which are not masked by music in the upper frequencies - sometimes you can hear the material itself (surround and spider, air noise) making noises while large excursions take place. Something like single voice with some deep bass.
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The result is of course dependent on room and placement, but less so than with boxed speakers.
I gave up dipole sub a long time ago. Even sixteen 21" in very large H-frames was not up to the task of reaching 20 Hz with low distortion and high enough SPL.
The problem is that the required cone excursion for a given SPL increases 8 times for each octave below the dipole peak. Two octaves = 8^2 = 64. Three octaves = 8^3 = 512. Four octaves = 4096. You get the idea....
I gave up dipole sub a long time ago. Even sixteen 21" in very large H-frames was not up to the task of reaching 20 Hz with low distortion and high enough SPL.
The problem is that the required cone excursion for a given SPL increases 8 times for each octave below the dipole peak. Two octaves = 8^2 = 64. Three octaves = 8^3 = 512. Four octaves = 4096. You get the idea....
Thank you for the simulations and all the other comments/opinions that help me to understand open baffle. Some terms remain unclear to me...
- Monopole : which real situation is it?
- Dipole : open baffle in free space conditions I guess. Meaning without the effect of the room
- The excursions in the table in #36, is it peak (so to compare to the 15mm peak in #31)?
Feel free to discuss whatever you desire.
My original question was already answered.
Two naked 12" woofers without any baffle can hardly provide clean deep bass to 20Hz. Something is fishy.
My main system has four 15" woofers on sort of H frame dipole. Still require eq to be flat to 20Hz.
My HT has closed boxes for 15" woofers, so not applicable. But my bedroom system has two 15" on H frame, still require eq.
There is no way to cheat physics.
My original question was already answered.
Two naked 12" woofers without any baffle can hardly provide clean deep bass to 20Hz. Something is fishy.
My main system has four 15" woofers on sort of H frame dipole. Still require eq to be flat to 20Hz.
My HT has closed boxes for 15" woofers, so not applicable. But my bedroom system has two 15" on H frame, still require eq.
There is no way to cheat physics.