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  • Unbiasedsound
    replied
    Originally posted by Unbiasedsound View Post
    Plus the type of direct servo (Rythmik?) amps used by GR Research can enhance control over the driver for better quality bass.
    https://www.youtube.com/watch?v=1Q3QQPO7y04&t=27s

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  • wavefunction
    replied
    (From the OP): Thanks to everyone for their wisdom. After reading all this, and thinking about it, I have come to the preliminary conclusion that there are at least two main factors in the sound of open baffle or dipole bass:

    1. Because of the LF rolloff, the effective damping is typically higher than a boxed woofer, or equivalently, the effective Q is lower, resulting in a more Bessel type response shape than ported cabinets. As Bessel filters are known for having the best transient response, I think this helps account for some of the 'tight' or 'fast' descriptions I have heard about. Because of my experiments with listening to induced phase shifts via digital allpass filters through headphones, I believe Dr. Toole (JBL) when he says we can't hear non-linear phase as long as the group delay variation doesn't exceed something like 2 ms. At least in the mids and highs. But I think you can hear group delay variations in the LF region, since group delay typically varies widely "down there", especially with ported cabinets, and the periods below 100 Hz become long enough that the brain can begin to perceive such group delay variations as altering the waveform/transient response.

    2. The figure-8 pattern of dipole speakers interact with the room differently than the near omnidirectional pattern of a boxed woofer at low enough frequencies. And at low frequencies, these room interactions play a significant role in the perceived frequency response, as I'm sure most of you are well aware!

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  • bradley.s
    replied
    Originally posted by billfitzmaurice View Post
    By and large frequencies below 150Hz cannot be directionally located. Based on that one might think that crossing over from subs to mains at 150Hz would suffice, but there would still be a lot of above 150Hz content from the subs due to the harmonics created by the movement of the cones even at low levels, let alone at levels high enough to create high THD. For that reason 80Hz is the de facto preferred crossover frequency, as it minimizes the ability to directionally locate the subs.
    I believe there is a mid range where we lose our ability to interpret stereo. I read it in a research paper but didn't save it. It was odd because there was a gap in the middle of the mid ranges where our ability to hear in stereo degrades. We are good between upper bass and low mids, then our ability degrades in the mid mid ranges, then we're good at upper mid ranges. I can't remember if our ability to hear in stereo continued above upper mids.

    I can't remember how I found that paper in the first place so I've had a hard time finding it again. Wish I could because it might influence where we should locate our frequencies in the room. And it would be possible to do something like that today with DSP.

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  • billfitzmaurice
    replied
    Originally posted by bradley.s View Post
    Woofers play mid range frequencies (>250Hz.) In that case they are above the frequency threshold zone. Humans can hear stereo in the mid ranges. Although, I don't know which mid range frequencies we're best able to identify in stereo.
    By and large frequencies below 150Hz cannot be directionally located. Based on that one might think that crossing over from subs to mains at 150Hz would suffice, but there would still be a lot of above 150Hz content from the subs due to the harmonics created by the movement of the cones even at low levels, let alone at levels high enough to create high THD. For that reason 80Hz is the de facto preferred crossover frequency, as it minimizes the ability to directionally locate the subs.

    Leave a comment:


  • bradley.s
    replied
    Originally posted by johnk... View Post

    Dipole bass in a normal listening room really isn't dipole. It just multiple sources at slightly different locations with some having inverted phase. This configuration alters the way room mods are excited compared to multiple source with the same phase. The other issue is no room pressurization below the room fundamental with "dipoles".
    Why would someone want that? Other than experimentation. I understand why someone would want to experiment. Harman/JBL already worked out bass optimization in small rooms. Is there science or engineering available for open baffle bass sound field management? If not, Harman/JBL bass sound field management is the way to go.

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  • bradley.s
    replied
    Woofers play mid range frequencies (>250Hz.) In that case they are above the frequency threshold zone. Humans can hear stereo in the mid ranges. Although, I don't know which mid range frequencies we're best able to identify in stereo. I don't even want to say what I think I remember because I might cause someone else to mis-remember. I need a source to reference so I can remind myself. Thus, placing multiple woofers per channel to play the mids is fine. Bass, however, is a different story. Two to four 15" woofers used to play bass in stereo doesn't make sense to me.

    Here's a Harman paper on multiple subs with sound field management. Multiple subs placed in different room locations is the first step. The next level up is bass sound field management with measurements + DSP. JBL offers this service but they come to your home with mics and proprietary algorithms.

    https://pdfs.semanticscholar.org/00d...e976a1a72e.pdf

    Leave a comment:


  • dlr
    replied
    Originally posted by bradley.s View Post
    I don't know why anyone would specifically want dipole bass in a small room. You have long wavelengths that wrap around the enclosure anyway; 250Hz is a 4.5 foot wavelength. Also, why would you want 2-4 15"s per channel? You can't hear low bass in stereo and you'd make it impossible to control the low frequency small room modes. You wind up introducing problems rather than solving them.
    As long as you can have them positioned far enough from the walls, no reason why dipole can't be good in a small room. I've found dipole bass to be better than closed or ported systems in any situation. This is equalized dipole, not passive large, open baffle systems, that is.

    WRT multiple woofers per channel, outside of the driver numeric "overkill", multiple drivers per side could have an ameliorating effect by having sources from multiple locations in the room, especially floor/celiing reflections and possibly a small amount of room mode change as well, probably more in the lateral room mode range rather than longitudinal. Not quite the multiple subwoofer approach promulgated by Geddes, but may still have some benefit. Call it a possible smoothing effect. I suspect the smaller the room, the more effective that might be.

    dlr

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  • johnk...
    replied
    Originally posted by bradley.s View Post

    I don't know why anyone would specifically want dipole bass in a small room.
    Dipole bass in a normal listening room really isn't dipole. It just multiple sources at slightly different locations with some having inverted phase. This configuration alters the way room mods are excited compared to multiple source with the same phase. The other issue is no room pressurization below the room fundamental with "dipoles".

    Leave a comment:


  • Unbiasedsound
    replied
    Plus the type of direct servo (Rythmik?) amps used by GR Research can enhance control over the driver for better quality bass.

    Leave a comment:


  • billfitzmaurice
    replied
    Originally posted by bradley.s View Post
    you could have two guys listening to bass enclosures in the same room and one guy might love it while the other guy hates it because they're standing in different locations.
    That applies to all low frequency speakers, not just OB.

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  • bradley.s
    replied
    I can see how someone might read my statement and come to your conclusion. So I'll add, you could have two guys listening to bass enclosures in the same room and one guy might love it while the other guy hates it because they're standing in different locations.

    Less energy means lower volume, which is why I'd place one open baffle in the near field. As an alternative, one could place a single bass enclosure in the near field.

    I don't know why anyone would specifically want dipole bass in a small room. You have long wavelengths that wrap around the enclosure anyway; 250Hz is a 4.5 foot wavelength. Also, why would you want 2-4 15"s per channel? You can't hear low bass in stereo and you'd make it impossible to control the low frequency small room modes. You wind up introducing problems rather than solving them.

    I don't know why Magnepan does what they do. If I'm not mistaken, they use large panels for physically short high frequencies and delicate lightweight panels to generate bass. They seem like the worst of all worlds. You get beaming with high frequencies and weak bass. Plus, the large ones are ginormous.

    Leave a comment:


  • johnk...
    replied
    Originally posted by badman View Post

    So, you seem to be implying that open baffle is more sensitive to room modes. The opposite is true, there's less overall energy to excite the modes and the rearwave reflections tend to smooth out room performance somewhat relative to monopoles.

    No. open baffle woofers, depending on position, may excite fewer room modes. Is that good or bad? The result is they are more sensitive to listening position ( and speaker placement) because it is very easy to move on or off a position of modal reinforcement or cancelation.

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  • badman
    replied
    Originally posted by bradley.s View Post
    So you could have two guys listening to open baffle bass in the same room and one guy might love it while the other guy hates it because they're standing in different locations.

    Personally, if I wanted to have open baffle bass I'd use only one speaker and I'd place it in the near field of my listening position so I didn't get stuck in a bad room mode. And, you would play it at lower volume in that case which would be helpful.
    So, you seem to be implying that open baffle is more sensitive to room modes. The opposite is true, there's less overall energy to excite the modes and the rearwave reflections tend to smooth out room performance somewhat relative to monopoles.

    The much, much bigger issue in dipole bass is displacement, baffle size, and power. Smaller baffles perform better but need more power, displacement, and EQ, much moreso than the more efficient monopole systems. It's not uncommon to use 2-4 15"s per channel in a serious dipole setup (or just look at how Magnepan scales their systems) because of all the loss.

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  • bradley.s
    replied
    Here's JBL's wavelength chart so you can see the physical length of bass frequencies.

    https://www.jdbsound.com/art/frequen...art%202013.pdf

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  • bradley.s
    replied
    wrt to the original post. I understand "hi-fi" setting as a small room, or, typical home audio. In small rooms, bass (<250Hz) frequencies are physically large so the interactions between the low frequency waves and the small room cause standing waves. So you could have two guys listening to open baffle bass in the same room and one guy might love it while the other guy hates it because they're standing in different locations.

    Personally, if I wanted to have open baffle bass I'd use only one speaker and I'd place it in the near field of my listening position so I didn't get stuck in a bad room mode. And, you would play it at lower volume in that case which would be helpful.

    https://www.jdbsound.com/art/frequen...art%202013.pdf

    Leave a comment:

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