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In Reply to: RE: That makes sense for a woofer, not a subwoofer posted by Dave_K on June 01, 2016 at 10:12:21
The LXStudio and LX521 systems are suited for home listening purposes *and* for studio monitoring. They are true full-range speakers that do not require additional "sub woofers". Although they will provide "sufficient output" at low frequencies, they were not designed for HT LFE effects. Guess it depends on your expectations. For me, they will move as much low frequency air in my listening room that I require. (One can always double-up the woofers if more output is necessary.)
Anyway, my point is that dipole woofers excite room modes significantly less than monopole woofers and (IME) once one becomes accustomed to the quality of bass they provide in a "normal" listening room, there is no going back to listening to sealed woofers (even with a room loaded full of bass traps and DSP correction).
Follow Ups:
"Anyway, my point is that dipole woofers excite room modes significantly less than monopole woofers"
The OP states that this is a properly built out control room and should have little room modes.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
After several bounces around the room, the initial advantage dipoles have in the bass due to their directivity is reduced because all of the modes will eventually be excited. Still I concede that a dipole will generally have smoother in-room bass than a monopole.One solution is to use multiple monopole bass sources intelligently distributed around the room. According to Geddes, "the spatial variations, and to a certain extent the frequency response variations, will go down (get smoother) as 1/N, where N is the number of independent sources."
That is why, when I designed a subwoofer system specifically to blend well with Maggies and Quads (the original target market for the Swarm), I used four small subs instead of just two... in my experience, it takes four intelligently distributed monopole subs to match the in-room bass smoothness of two dipole main speakers. (In practice, thus far I have found that reversing the polarity of one of the four subs improves the in-room smoothness.)
Because a monopole can pressurize the room below the modal region, whereas a dipole cannot, monopole bass sources can potentially go deeper and deliver more tactile bass.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 06/02/16 06/02/16 06/02/16
The "swarm" approach recommended by Geddes (and used by many before then) has merits... and disadvantages. I personally feel that dipole bass radiators deals with room modes better because it does not excite them to begin with. It's also a much simpler approach, only requiring two "boxes" rather than six or more. Using many woofers requires a very low crossover point (greater group delay), etc. IME. YMMV.
I'm not being facetious Mike, I really do appreciate the opportunity. Lots of people have misconceptions about multisub systems, and you've just brought up several of them."The "swarm" approach recommended by Geddes (and used by many before then)..."
I'm pretty sure Earl Geddes was the first. Can you tell me who was advocating and/or using four subs asymmetrically distributed as a means of smoothing the in-room response before Earl did?
"...dipole bass radiators deals with room modes better because it does not excite them to begin with."
Dipole bass excites all room modes, some more than others.
Room modes ARE NOT BAD... and it is having TOO FEW room modes that degrades the bass in small rooms because the resulting widely-spaced peaks stick out like sore thumbs to our ears. In a larger room, the modal peaks in the bass region are bunched up much closer together (like what we get in the midrange region in our smaller rooms), so that they effectively form a CONTINUUM. A distributed multisub system essentially replicates this advantage of large rooms in the modal region. And perceptually it is the in-room frequency response that matters most in the bass region.
"[Dipole bass is] also a much simpler approach, only requiring two "boxes" rather than six or more."
In practice four monopole subs intelligently distributed is plenty, and Earl Geddes can deliver smooth in-room bass with three subs each independently equalized in the digital domain using his proprietary algorithm.
Practical dipole subs need a lot of displacement to get down to 20 Hz, and that usually takes its toll on system headroom. And as a longtime dealer of high-end dipole speakers (SoundLab and Gradient), in my experience dipole bass excels at pitch definition and clarity but is subjectively lacking in impact relative to a good comparable monopole system. In my experience a good distributed multisub system is the equivalent of a good dipole system in pitch definition and clarity but retains good impact.
"Using many woofers requires a very low crossover point (greater group delay)"
Group delay doesn't come into play as far as crossover frequency goes. What does come into play is the need to keep audible upper bass/lower midrange energy out of any subs that are located well away from the main speakers. For this reason I recommend lowpass filtering the subs no higher than 80 Hz, and using a steep slope, or using separate amps for the subs in the front and rear of the room if the subs in the front need to be crossed over north of 80 Hz.
Typical group delay in the bass region, in and of itself, is of negligible audible consequence, but its effect on in-room frequency response is of consequence. However since subwoofer + room constitute a minimum-phase system, when we fix the frequency domain, we have simultaneously fixed the time domain.
Maybe I'm not understanding what you mean by "group delay" in this context?
(from another post) "Also, unlike some who have commented in this thread, I have no financial motivation."
Just for the record, my dealer and manufacturer status is disclosed in my signature so that has been out in the open all along.
I mentioned my product only in replies to misinformation where I needed to cite a counter-example. In this thread I have been promoting an idea which can be implemented many different ways.
Note that in my initial reply to Noah I offered to provide him with a DIY solution that would be within his budget. Where's the financial motivation in that? I wouldn't be selling him anything, but instead would be my spending time helping him. This is because I really believe the idea offers what he is looking for, given his set of requirements. Gosh, that's almost the sort of thing Siegfried Linkwitz might do!Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 06/02/16 06/02/16 06/02/16 06/02/16 06/02/16
Yeah, I'll have to give that some thought.
5 edits and counting. Perhaps the 6th will be golden. :)
Ahem, yes well... I always do my best proofreading AFTER I hit "Post"...
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
I personally feel that dipole bass radiators deals with room modes better because it does not excite them to begin with.
While I agree that dipoles load the room differently, room modes are still excited. How could it possibly be otherwise? If the loudspeaker is putting any energy into the room at an eigenfrequency, its mode will be excited.
The links you shared to Linkwitz's experiments include measurements which clearly show that the bass response is dominated by modal peaks and cancellation nulls in either configuration. The pattern is a bit different, but it's hard to say based on frequency response that one is better than the other.
What's more relevant to this thread is the low bass, since the OP is looking for a subwoofer to cover frequencies up to 40 or 50 Hz. I still don't see how a dipole subwoofer could be a viable option due to the two drivers cancelling each other.
SL's dipole woofers are flat to 20Hz, so they do a fine job with 40 to 50Hz.
As I've mentioned, SL's summary section #3 clearly states the significant improvement that dipole bass radiation has on "small" room acoustics.
Until you have first hand experience with what I'm saying, please take my comments at face value and FWIW. Once you do have experience, perhaps you too can help educate those who do not.
Also, unlike some who have commented in this thread, I have no financial motivation.
Good luck to the OP with whatever solution he implements.
SL's dipole woofers are flat to 20Hz, so they do a fine job with 40 to 50Hz.
They are not flat to 20 Hz that I have seen. The measurements you linked to show a rapid dropoff of > 12dB per octave below the lowest room mode, which was at 50 Hz in the small room and 35 Hz in the large room. This is exactly what you would expect from the design.
As I've mentioned, SL's summary section #3 clearly states the significant improvement that dipole bass radiation has on "small" room acoustics.
I can't find any such statement in section #3. The closest I could find is this:
"The degree of these differences is difficult to predict and will depend upon the specifics of a room and the placement of woofer and listener. However, the dipolar source can be expected to interact less strongly with the room and will, therefore, on average convey greater detail and resolution of complex low frequency material."
But then that seems to be contradicted by the following bullets:
"* It is nearly impossible to predict the room transfer function from a prior knowledge of room dimensions, woofer and listener placement, radiator type and the room's eigenfrequencies."
and
"* No meaningful conclusions could be drawn from the steady-state room transfer functions about performance differences between dipolar and monopolar radiation."
Further, when I look at the differences between the monopole and dipole frequency response measurements, I can't say qualitatively that one is better than the other.
I'm not here to argue with you and not sure what measurements you are referring to. The woofers system used in the LX design is flat to 20Hz in a listening room.
- Response -3 dB at 30 Hz (Q < 0.5) on ground plane, free-field
The difference in my rooms between a dipole woofer system and conventional sealed woofers has always been enormous - the difference between listening to music Vs mud - especially after getting used to not hearing the room's effects, which does not take very long. While results will vary to some degree from room to room, a dipole woofer system will always excite room modes less.
"By far the perceptually most uniform response in the range below 200 Hz is obtained with an open-baffle, dipole or figure-of-eight radiating source. Because of its directionality, the dipole excites far fewer room resonances than an omni-directional source. The measured room response is not necessarily any smoother than that for an omni-directional source. But the perceived difference in bass reproduction is startling at first, because we are so used to hearing the irregular and booming bass of the typical box speaker in acoustically small rooms. Quickly one learns to recognize the distortion of this combination and it becomes intolerable."
http://www.linkwitzlab.com/rooms.htm
Whether or not any of this matters to you, who knows? Regardless, try to keep an open mind until you have had an opportunity to hear a system like the LX521. It will likely render discussions like this one moot.
I have not heard the LX521. I have heard the Orion and it was very good.
I just don't believe the claim of flat to 20 Hz though. And it seems to contradict Linkwitz's own measurements that you linked to.
I do believe the claim of -3 dB @ 30 Hz in a ground plane measurement. But an anechoic or free field measurement of a loudspeaker is not representative of its performance in the "pressure region" of frequencies below the lowest room mode. For a monopole, the free field response will understate the in-room response in that frequency range. For a dipole, the opposite is true, the free field response will OVER-state the in-room response in that frequency range.
Here's why: In the pressure region, which is the frequency range below the modal region, the longest room dimension is less than one half of the shortest wavelength. Therefore, there is no wave front and no radiation pattern to speak of. The pressure in the whole room just rises and falls. With a sealed monopole subwoofer, the room pressure increases on the outward stroke and the box pressure falls, and the room pressure decreases on the inward stroke and the box pressure rises. With a dipole, with one side pushing and one side pulling there is no net pressurization of the room. If not for air resistance, you wouldn't get any sound at all. The reason why a free field measurement is different is that the volume is infinite so there is no pressure region. In free space, the dipole will radiate a dipolar pattern even down to the lowest frequencies. That doesn't happen in a room.
If you don't believe me, you can see it in Linkwitz's in-room measurements.
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