I’ve been reading Linkwitz’s site and got confused about the shape of open baffle loudspeaker. His LX521 has a keystone, or keyhole, shaped baffle which makes sense if you read his page. However, most other open baffle loudspeakers have very simple sheets of rectangular plywood which are relatively huge. Some builders attempt to round off the corners or have sweeping curves resembling Samurai Jacks kimono. My question is, does it matter? I imagine a smaller baffle will allow for more cancellation of the lower frequencies requiring a larger speaker for lower midrange, or you can use a smaller speaker with a bigger baffle for the same effect. I get that. Also, as the frequency goes up the panel should narrow. -?
Does room size matter? If the baffle is too big it would be the same as installing speakers in the wall. I guess there is a baffle to room size relationship?
I also don’t understand how an open baffle woofer makes any sound whatsoever. I’ve played woofers, not in a box, and there is no bass. So what magic is going on if there is a minimal box with no front or back?
After all that, please post some links or references where I can study this.
Does room size matter? If the baffle is too big it would be the same as installing speakers in the wall. I guess there is a baffle to room size relationship?
I also don’t understand how an open baffle woofer makes any sound whatsoever. I’ve played woofers, not in a box, and there is no bass. So what magic is going on if there is a minimal box with no front or back?
After all that, please post some links or references where I can study this.
Welcome! The questions sound familiar. If you read SL already, stay on his site a bit longer, as a lot (or everything??) Open baffle related is explained there. I also recommend this writeup http://www.dipolplus.de/thema11.php (one Download is available in English)
Excellent! Thank you. I’ll be here, so much to learn. I’m working on an open baffle right now and will try out the theory. Well, as budget permits. 😉
There are freeware simulators that you can use to study baffle diffractions of boxed and open baffle speakers. Different baffle size and shape, different shape, size, location and number of radiators, movable mic.
Easy simple .exe for diffractions http://www.tolvan.com/index.php?page=/edge/edge.php
Multitool fullscale loudspeaker-xo simulator system https://kimmosaunisto.net/
Easy simple .exe for diffractions http://www.tolvan.com/index.php?page=/edge/edge.php
Multitool fullscale loudspeaker-xo simulator system https://kimmosaunisto.net/
It's all to do with the ability of long wavelength, low frequency sound waves to bend (or diffract) round an open baffle.
Long wavelengths from the rear of a woofer bend round the baffle and interfere destructively with the long wavelengths from the front of the woofer, resulting in bass cancellation.
By making the baffle larger, it becomes harder for the long wavelengths to bend (or diffract) round the baffle, resulting in less bass cancellation.
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Oh heck, now I need a PC with Windoes on it. Over the past ten years or so I’ve turned into quite the linux fan. Besides, who doesn’t like penguins?
Here's why you wouldn't make open baffles circular! https://www.hi-fiworld.co.uk/index....udspeakers-open-baffles-and-bass-part-15.html
You have a good grasp of the tradeoffs with OB. The LX521 is a sort of "smaller baffle" design. This has advantages off axis compared to large baffles. Some designers (MJK for example) only care about the front radiation on axis, and others (like me) are concerned with what is happening on and off axis, both in front of the speaker and to the rear, as well as how the loudspeaker's radiation interacts with the room and returns to the listener. A larger baffle will certainly have less low frequency loss than a narrower/smaller one, and this simplifies the design and makes it possible to use fewer bands in the loudspeaker sucessfully.
OB systems need some space to work best, so if the room is on the smaller size with any dimension less than 15 feet or so it is probably not a good choice. The speakers need to be located away from walls and the listening position must be away from the rear wall, so this implies that that room must be a certain minimum size.
At very low frequencies, a dipole source has a lot of cancellation. This is because the different pathlengths between the front source (front of cone) and the rear source (rear of cone) and the listener is much less than the wavelength of sound. Therefore the phase difference of these two sources at the listening position is not much different than at the source itself, and with the rear and front sources out of phase you get almost complete cancellation. But as you increase frequency, the two pathlengths are different by an amount (e.g. the width of the baffle) that becomes larger compared to the wavelength, eventually reaching half a wavelength. This flips the phase difference from 180 deg out of phase to in phase and the two wavefronts actually constructively interfere (add in phase) creating a +6dB SPL at that position and frequency. In general the SPL from a dipole source is dependent on distance from the dipole, and the listening angle. Linkwitz's web pages contain some models of the type of response pattern that this generates and that is a good source for info.
In between very LF and the dipole peak, the relative phase angle is changing from 180deg out of phase to in-phase, and so there is a slow change in the SPL from the dipole source at the listening position vs frequency.
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The magic is eq. A driver on an open baffle will show a response that drops at 6 dB/oct below a certain frequency. Simply equalize that by means of some filter and you end up with a system that has a straight response. At the cost of course of max output of course, for an OB woofer 15-20dB correction at 20 Hz is not unusual. Eq can be done actively or by choosing driver parameters accordingly.
I hate to break it to you, but you can make a great OB with a circular baffle if the baffle diameter is less than about twice the driver diameter. In that case the responses on and off axis are very smooth. The diffraction problems arise when the driver is much smaller than the baffle, and the distance to the edges is the same from the driver center. In that case the driver is similar to a point source, and a round baffle reinforces the edge diffraction signature and causes strong peaks and dips in the frequency response. When driver and baffle are of similar diameter, the peaks and dips do not occur. There is a great paper on this topic by Mellow and Karkkanien called "On the sound field of an oscillating disk in a finite open and closed circular baffle" J. Acoust. Soc. Am., Vol. 118, No. 3, Pt. 1, September 2005.
Maybe if the author of that web page you linked to had more of a grasp of the subject they would have mentioned that the plot of a driver in a circular baffle is for a point source, like a tweeter in a large circular baffle (I think this was lifted from Linkwitz's study on that effect). It does NOT represent most OB systems and is an exaggeration of the typical level of this effect in a real loudspeaker just to make the effect stand out for the purpose of demonstration. See:
https://www.linkwitzlab.com/diffraction.htm
That was an excellent explanation of the physics of dipole cancellation - thanks.
Oh dear! Peter Comeau (Director of Acoustic Design @ International Audio Group IAG) usually knows what he is talking about!
I see now that I misinterpreted your statement. The reason why higher frequencies are audible was beautifully explained by CharlieLaub.
Back-wave wavelengths 1.2X to 6X the "path length" become constructive (vector addition), at 2X the most constructive (in-phase 0deg) as post #6 explained. This is quite a wide frequency range. For example, a "Transmission Line" or "Back-Loaded-Horn" with 2-meter-long folded "line", or an "OB-U" backless cab able to direct backwave to bounce off the wall 1-meter away, will each get a positive boost for 2.4-12m-long waves -- frequency range 28-140hz.
Looking for an interim project till my new amplifiers arrive.
I happen to have two disused satellite dishes and considering placing Lii audio f12 full range speakers in them. Being parabolic wondering if they be best placed on the convex side. Not knowing anything of sound waves and surface shapes for open baffle speakers does anyone have any thoughts or should I not let my imagination on the loose.
I happen to have two disused satellite dishes and considering placing Lii audio f12 full range speakers in them. Being parabolic wondering if they be best placed on the convex side. Not knowing anything of sound waves and surface shapes for open baffle speakers does anyone have any thoughts or should I not let my imagination on the loose.
Thanks AllenB.
I have been reading a lot re open baffle and wondered if the convex shape would act in some way like a horn diffuser although parabolic rather than ellipsoidal. I also wonder if the room features might come more into play as well.
No great cost outlay and if the sound was unbearable I could then revert to the more conventional flat plane baffle.
I read the Lii audio F12‘s have some good reviews.
I have been reading a lot re open baffle and wondered if the convex shape would act in some way like a horn diffuser although parabolic rather than ellipsoidal. I also wonder if the room features might come more into play as well.
No great cost outlay and if the sound was unbearable I could then revert to the more conventional flat plane baffle.
I read the Lii audio F12‘s have some good reviews.
It wouldn't act as a parabolic reflector if the driver wasn't in the focal point. It would instead lean toward a wider range of reflected sound scattered across the surface.
The interesting thing is that this might not be such a bad thing if used for the rear at the higher frequencies, before it reverts to dipole behaviour at lower frequencies. (Just speculating)
The interesting thing is that this might not be such a bad thing if used for the rear at the higher frequencies, before it reverts to dipole behaviour at lower frequencies. (Just speculating)