AudioCircle
Industry Circles => GR Research => Topic started by: Scott Joplin on 6 Oct 2020, 08:17 pm
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Hi. I recently watched Danny's YouTube videos called "Open Baffle Basics". I'm interested in acoustic solutions to obtain a smooth response and have come across "L-frames" before as a useful remedy to the problem of cavity resonance. What is the effect on the polar response of such a solution?
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This is really a great question that hits a fundamental design concept of "open baffle" speakers that's often glossed over (by ignorance or indifference). In the video he's really careful (?) not to mention the importance of uniform off-axis response across the entire frequency range; something that a properly designed dipole is capable of and is a main design goal.
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"Open baffle" is a very wide term and not all OB's are good dipoles, I agree this is the ideal goal for minimizing the effect of the room and getting the most out of the concept. I'd be interested to see measurements to get an idea of how much this ideal is compromised.
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This seems to open up more questions than it answers.
For the novice considering open baffle what is the best option? A plain baffle with no side wings providing a pure dipole, or a variation with side wings that is no longer a pure dipole?
Why would someone choose one of these over the other?
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A pure dipole is very difficult to achieve and not really something for a novice. https://www.linkwitzlab.com/models.htm
Wings are a way of effectively widening the baffle that further compromises dipole radiation, the question is, by how much and how much does it matter in a room?
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Ignoring for the moment the difficulty in achieving a pure dipole, what is the best answer in terms of sound quality and listener enjoyment? Pure dipole or modified polar response based on using wings?
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I believe the side wings also help with L/R stereo separation, as well as providing bass extension & acting more like a "waveguide" than a typical wide baffle or box side panel.
Thats radically simplifying things, but is kinda how I've come to understand it.
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So if side wings improve the sound and are better than a pure dipole why don't companies like Emerald Physics, Spatial Audio, and Magnepan include them in their products?
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Here's a link with measurements for the NX-Otica. Graphs for on-axis, vertical off-axis, horizontal off-axis, impedance, and a waterfall plot are in the first post.
https://www.audiocircle.com/index.php?topic=141654.0
As you can see, Danny's asymmetrical wing approach produces a very smooth response all around.
Mike
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So if side wings improve the sound and are better than a pure dipole why don't companies like Emerald Physics, Spatial Audio, and Magnepan include them in their products?
Simple - cost and complexity.
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I did think of that, but it doesn’t really have to be a lot more expensive or difficult. Looking at the cost to manufacture a speaker that sells for $3K to $5K or more per pair, two pieces of additional flat material for wings per speaker should not add a lot to the cost. And they could be very easily attached by the customer with a set of included screws using pre-drilled holes.
If that addition made a big difference in sound quality I would think that a manufacturer would want to offer it in order to gain an important advantage over competitors. Even if it created a slightly more expensive product than the wingless model. People are willing to pay for better sound quality if they can count on it really being there.
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Here's a link with measurements for the NX-Otica. Graphs for on-axis, vertical off-axis, horizontal off-axis, impedance, and a waterfall plot are in the first post.
https://www.audiocircle.com/index.php?topic=141654.0
As you can see, Danny's asymmetrical wing approach produces a very smooth response all around.
Mike
Thanks for the link but I can't see any diagrams, I'm new here, is there something I'm missing?
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I think Danny may have deleted his pics, cuz i have the same issue.
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I guess it's something to do with your browser...all his pics are shown here as before in the first post of that topic.
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I did think of that, but it doesn’t really have to be a lot more expensive or difficult. Looking at the cost to manufacture a speaker that sells for $3K to $5K or more per pair, two pieces of additional flat material for wings per speaker should not add a lot to the cost. And they could be very easily attached by the customer with a set of included screws using pre-drilled holes.
If that addition made a big difference in sound quality I would think that a manufacturer would want to offer it in order to gain an important advantage over competitors. Even if it created a slightly more expensive product than the wingless model. People are willing to pay for better sound quality if they can count on it really being there.
Well, OB speakers are a hard sell in general. And let's face it, the wings look weird. Way more weird than the flat panel a traditional OB uses. And thus have a lower WAF. And as a manufacturer, WAF is important because you want people to actually buy your speakers.
But from a pure performance standpoint, a speaker with a narrow baffle will out-image a speaker with a wide baffle, due to differences in edge diffraction.
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I guess it's something to do with your browser...all his pics are shown here as before in the first post of that topic.
That's interesting. I don't see them either, on my flat phone using Chrome.
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That's interesting. I don't see them either, on my flat phone using Chrome.
Same here, so maybe that's the issue?
I can see most recent images, but those in older posts don't appear?
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That's interesting. I don't see them either, on my flat phone using Chrome.
I see a bunch of pictures and plots, but no polar plots.
Love the duct tape !!! No shop is complete without it.
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I've a chromebook. Polar plots would be nice but a range of off axis measurements would be useful
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I've a chromebook. Polar plots would be nice but a range of off axis measurements would be useful
Not sure why some folks can’t see the graphs. The horizontal off-axis graph has plots at 0, 10, 20, 30, and 40 degrees off axis
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I can't see them either. It would be nice to see the full range of responses through 180 degrees to really see how the wings effect the dispersion.
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Only up to 40 degrees? I've done some simulations with a similar approach and the nulls look promising, it's a bit of a mess to the rear but I don't think that should matter too much.
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At 90 degrees there are nulls. This allows the speakers to be placed close to a side wall
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Well, OB speakers are a hard sell in general. And let's face it, the wings look weird. Way more weird than the flat panel a traditional OB uses. And thus have a lower WAF. And as a manufacturer, WAF is important because you want people to actually buy your speakers.
But from a pure performance standpoint, a speaker with a narrow baffle will out-image a speaker with a wide baffle, due to differences in edge diffraction.
So the trade-off appears to be that an OB speaker with a narrow baffle will image better, but with a wide baffle it will produce stronger bass. Is that the main reason to choose one baffle width over another?
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The Linkwitz Lab page I linked to earlier should answer that question, it's well worth reading if you haven't already. Edge diffraction can be mitigated on a large baffle by rounding the edge but means a reduced null but over a larger area.
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So the trade-off appears to be that an OB speaker with a narrow baffle will image better, but with a wide baffle it will produce stronger bass. Is that the main reason to choose one baffle width over another?
Correct, a narrow baffle baffle with no wing will image better than a wide baffle but it will have less bass.
But, if you add wings to the narrow baffle, it will NOT lose bass and will still have better imaging.
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Regarding measurements, perhaps someone can post a -90 to +90 degree measurement to visualize how the "L" frame baffle affects the polar response. Never seen any provided by the manufacturer - maybe just an oversight that can easily be rectified.
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Regarding measurements, perhaps someone can post a -90 to +90 degree measurement to visualize how the "L" frame baffle affects the polar response. Never seen any provided by the manufacturer - maybe just an oversight that can easily be rectified.
Maybe I'm dense, but what type of useful information would a graph from 40 to 90 degrees provide? It seems that even at 40 degrees off-axis you will mainly only be hearing one speaker and, unless you're in an extremely large room, will be up against a sidewall. Curious minds want to know.
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It would show the depth and spread of the nulls
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It would show the depth and spread of the nulls
So what you are trying to do is visualize the figure 8 pattern?
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Exactly
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The ear hears an average of direct and reflected sounds, and the reflected sounds are primarily characterized by the off axis response. Dipole cancellation also reduces the audibility of some early refections, so it'd be nice to see how far down in level and in what frequency range the cancellation covers.
The figure 8 pattern is theoretical, real world implementations will vary.
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The figure 8 pattern is theoretical, real world implementations will vary.
Yes, as I say, I've done sims but in reality there are many variables, that's why I'd like to see actual measurements, there aren't many of these speakers about and it's an interesting idea.
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Are you looking to buy a set Scott?? Would you like some referrals?
Don
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That would be useful.
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That would be useful.
Check out these videos of the NX-Oticas from New Record Day
https://www.youtube.com/watch?v=prwyd7XlqVI
https://www.youtube.com/watch?v=8xxFKVC2Xro
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Thanks for those. However there's no measurements of the off axis nulls which are also important with an OB speaker, it's not just about the on axis response.
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There may be some misconceptions here, but there are some good questions too.
Instead of just answering the questions I will take some measurements for you guys to help better explain. So I will get back to you guys on this as soon as I get caught up on orders, special projects, and emails.
And then I'll set something up and take measurements. But it will be limited to ranges above 200Hz. Unless I try to move my entire measuring system outdoors. Ugh.
So hang on.
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Above 200Hz would be very informative, thanks.