gedlee said:
I think its rather clear that the reason that "dipole's", (actually open baffle operation), raise further inquiry - is that some seem to prefer them, and the reasons for that preference has thus far been "illusive". (..which was the point for my questioning.)
If all you have to judge an OB by is a "two-way", then you may well be missing something. Perhaps, just perhaps, you haven't really expended enough effort to see what all the "hub bub" is about?
Additionally, (and I'm not intending to be argumentative or abusive) - I'm fairly certain that the "formula" you have found does NOT work for everyone who has heard it. I clearly remember "disenchanted" "auditions" of the Summa by others - in a variety of venues, including your place. I don't think I've ever heard your "formula" described as bad, but the undertone was sometimes: "good, and sometimes great, but ultimately not good enough". IMO though that's hardly a serious detractor, rather it appears that much is good, but that there is room for improvement (..and there ALWAYS is).
You of course don't have to enter the discussion on OB's.. BUT chances are that at least several of the qualities an OB provides can be done as well or better in a slightly more traditional design. IMO to dis-include yourself is to deny yourself the opportunity for expanded thought, and perhaps an eventual improvement to your "formula".
ScottG said:
Thank you for a response!
So (to you)..
#1: it provides a better sense of detail presumably because of linear decay below 1 msec.(millisecond)?
Note that you can radically improve linear decay with substantial "stuffing" near the driver - providing an even better *apparent* decay "pattern" than any open baffle can provide (..even within 1 millisecond).
I do however think you are correct (in result) - and I would also deem this to be the most significant feature in providing better image placement in the depth plane (vs. a traditional monopole).
Some questions then are:
What's different that is audibly better (to some) with an open baffle's decay signature over that of a heavily stuffed "box"? It almost certainly is measurable, but how can it be identified?
Moreover because its a measurable *result*, what MECHANICALLY is going on to the underlying process that makes an open baffle preferable to some (at least in this respect)?
#2: *How* is pattern control contributing to an audible improvement for you?
......................
You are of course absolutely correct that more space and money (for an open baffle approach) are separate issues to be reconciled with latter/on a different thread. (..something I also was trying to emphasize.)
Again, thanks!
#1: To my ears the subjective signature has more sense of freedom in the power range, say that the ''HF air'' does not stop abruptly as I listen to lower registers. It produces a natural rightness in front to back placement mainly, and more detail.
Friction/absorption takes time and multiple inner travel to work. Its progressively controlled clutter in a sense. It still bounces on the cone too.
Unhindered OB back dissipation (or damping filtered back exit) gives a different/lesser impulse response self 'noise'. Stuff a box a lot with Rockwool, listen, then stuff it again with as much is needed for same absorption using just a different material. It gives different midrange tone. So if you get differences between stuffing, then stuffing isn't a black hole.
Also, just a panel is far less total surface than a box (no structure is totally silent not even the 'heroic' ones). Another +, is fewer corners to diffract around or to treat (never well enough) with just a panel.
#2: In the power region many wall reflections occur with monopoles. Fig 8 gives less room signature.
*One system that I maybe like more above the modal region through the power region, that is less demanding in space needed from OB back to wall, and more readily controllable for reflection and coloration is cardioid.
ScottG said:
Scott
To my knowledge no one who came here and heard the Summas was not impressed. The reviews on my website were NOT select ones they were ALL of them - there weren't any bad ones. John VanOmmen liked the Summas that he heard at RMAF so much that he bought a pair, while others complained that the Amp sounded bad - no comments on the speakers though.
So your data here and mine don't agree.
I KNOW FOR A FACT that neither you nor anyone else exstolling the virtues of OB have heard the Summas.
Here is one to think about. OB has an inherently seveer diffraction at the baffle edge which is unavoidable - two waves of opposite polarity meeting up with one another. I go out of my way to reduce all diffraction in and near the sources and this has paid big dividends in performance. Why isn't the diffraction of the OB baffle objectionable? Maybe some like diffraction and some don't? I can however, see no justification for it being a "good" thing.
OB diffraction -
There were a lot of good discussions about OB diffraction on the early part of the "Beyond the Ariel" thread. One group believed that OB reduces diffraction, while another believed the opposite.
Last week, I performed some measurements on my OB speakers with a baffle of 280mm wide, 25mm thick and fully rounded edges. I knew a 2-3dB dip at 2kHz measured on axis had to be due to diffraction but was interested in knowing how severe the changes of diffraction in relation to the angles of axis. I rotated the OB panels to about 10 degree and that 2-3dB dip disappeared. So I did not bother to do further diffraction measurements. Diffractions seem to be rough as the baffle simulation programs indicate.
But how does it compare to a sealed box? I have not made a comparison. The BSD software, which does not include OB, shows diffraction effects ranging from 0 to 6dB.
My measurements can not conclude whether OB reduces or increases diffractions. But given that I have found diffractions from my measurement then OB is not free of diffractions. It may well be due to the asymmetry of the driver radiations, the directivity of the drivers, or others, such as the cancellation of the front and the back, or reinforcement of the front and back edge diffractions, ie. twice as bad.
But here is a question: The Nathan (or Summas) has a small rounded edge, as well as most commercial speakers. If the rounded edge is so small it can not possibly practically reduce diffractions - the radius of rounded edge curve has to be a significant portion of the wavelength to be effective. But looking at the speakers, the rounded edge may effect frequencies above 10kHz, but then even a dome tweeter would have no issue of diffraction at that frequency due to directivity, while in the 1kHz to 4kHz most sensitive region the diffractions may be at full swing, unless, of course, the waveguide eliminates the diffractions at its mouth.
There were a lot of good discussions about OB diffraction on the early part of the "Beyond the Ariel" thread. One group believed that OB reduces diffraction, while another believed the opposite.
Last week, I performed some measurements on my OB speakers with a baffle of 280mm wide, 25mm thick and fully rounded edges. I knew a 2-3dB dip at 2kHz measured on axis had to be due to diffraction but was interested in knowing how severe the changes of diffraction in relation to the angles of axis. I rotated the OB panels to about 10 degree and that 2-3dB dip disappeared. So I did not bother to do further diffraction measurements. Diffractions seem to be rough as the baffle simulation programs indicate.
But how does it compare to a sealed box? I have not made a comparison. The BSD software, which does not include OB, shows diffraction effects ranging from 0 to 6dB.
My measurements can not conclude whether OB reduces or increases diffractions. But given that I have found diffractions from my measurement then OB is not free of diffractions. It may well be due to the asymmetry of the driver radiations, the directivity of the drivers, or others, such as the cancellation of the front and the back, or reinforcement of the front and back edge diffractions, ie. twice as bad.
But here is a question: The Nathan (or Summas) has a small rounded edge, as well as most commercial speakers. If the rounded edge is so small it can not possibly practically reduce diffractions - the radius of rounded edge curve has to be a significant portion of the wavelength to be effective. But looking at the speakers, the rounded edge may effect frequencies above 10kHz, but then even a dome tweeter would have no issue of diffraction at that frequency due to directivity, while in the 1kHz to 4kHz most sensitive region the diffractions may be at full swing, unless, of course, the waveguide eliminates the diffractions at its mouth.
it looks like this thread has become a sort of gedlee's own "Beyond the Ariel"
"discuss whatever interesting issues with Dr Geddes"
I have nothing against discussion of interesting issues with Dr Geddes
I think that it is great the He is here and presents His knowledgable and experienced point of view
but on the other hand it's a pity because this thread once had its own interesting topic
why not start a new thread with appropriate title, like for instance "Beyond Summa?"
the topic of this thread was on "stereo imaging", "phantom imaging" etc.
why change it?
is the original topic against somebody's agenda ?
best!
graaf
"discuss whatever interesting issues with Dr Geddes"
I have nothing against discussion of interesting issues with Dr Geddes
I think that it is great the He is here and presents His knowledgable and experienced point of view
but on the other hand it's a pity because this thread once had its own interesting topic
why not start a new thread with appropriate title, like for instance "Beyond Summa?"
the topic of this thread was on "stereo imaging", "phantom imaging" etc.
why change it?
is the original topic against somebody's agenda ?
best!
graaf
JPV said:
JVP, just for the record – it was Earl's suggestion to do an arrangement you'd like to explore further for homeFi.
http://www.diyaudio.com/forums/showthread.php?postid=1626226#post1626226
What Earl proposes is the wrong way IMO.
If you *always* play back in an concert hall ambience you *never* can play back an intimate recording – lets say a single close mic'ed singer, a small jazz group or a chamber ensemble – like intended by the producers.
This simply is because you cant get rid of the long decay from a big room you plan to do artificial - unless you switch it on and off , or – even more likely – create a multitude of setups that match for each and every record you have.
In this sense Earls statement
" that parallels the LFs in a large room - which ALWAYS sound good "
is misleading.
Nevertheless I would encourage you to try by yourself and hopefully you report back your findings.
This out of the way, back to your question.
Yes it is a challenge to do LF treatment for rooms.
Even more so for home sized rooms as absorbers are huge, heavy, expensive and you are not exactly fee in placement. In addition to that there isn't a "one fits all" solution.
http://en.scientificcommons.org/20359709
http://cat.inist.fr/?aModele=afficheN&cpsidt=17063274
(a very good reading to that topic)
Best way out are the plate absorbers mentioned back in this thread that can be DIY built – or – the new "compound panel absorbers" mentioned earlier in this thread .
Remember that this may apply more strictly for "European style" built houses. *If* you have a house where the rooms aren't separated by massive walls (>>50kg / m2) you may already have a acoustic environment – in the low frequency department – as big as your whole house.
I myself haven't experienced this but have heard so from different people.
Michael
HiFiNutNut said:
OB, like all enclosure will always have diffraction. There are tings that you can do in both cases to minimize this, but it can't be elliminated. A boxes limiting shape is a sphere and an OBs limiting shape is a torus - with teh sourec in the middle. These shapes have the lowest diffraction possible within the contraints. The torus is much higher than the sphere. But everything about diffraction depends on the details. The larger the baffle the later the diffraction signal arrives at the listener and the more detrimental it will be. But smaller baffles have LF limit problems. There is probably a "sweet spot" but I don't know where that would be. A torus would be great since it maximizes the dipole monemt while minimizing the diffraction. IF I were to do an OB, this is what I would try first.
Your numbers are off on the Summa line. Diffraction drops considerably when the radius is a 1/4 wavelength. On the Summas this radius is 2.5 " so there is little difraction above 1 kHz. On the Nathans and the Abbey this was forced to 1.25" which thus has little diffraction above 2 kHz. Of course the larger the radius the better, but this gets expensive. The large radius on the Summa dictated a molded cabinet which pushed the cost way up. Making these radi smaller allows for more common cabinet construction at a far lower cost. Notice that I DO NOT compromise on the radius on the waveguides - this WOULD BE unwarranted.
graaf,
While I appreciate and agree with your concerns, this discussion continues to enter and exit what is inferred in the title and to be honest, weeding through it to pluck the OT posts is a fair amount of work so how about we just let this one ride and ask the participants to try and stay on topic.
While I appreciate and agree with your concerns, this discussion continues to enter and exit what is inferred in the title and to be honest, weeding through it to pluck the OT posts is a fair amount of work so how about we just let this one ride and ask the participants to try and stay on topic.
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