The other factor affecting preferences is radiation pattern. Ideally, a speaker should radiate in a cardioid pattern - certainly above a certain frequency, dependent on room size. Hence Linkwitz's LX-mini.
Box speakers are omnidirectional at low frequencies, becoming progressively directional as each driver's radiating surface becomes comparable with wavelength - in other words, usually something of a mess when it comes to radiation pattern vs frequency.
OBs radiate as dipoles at the same frequencies that box speakers are omnidirectional (for a given diaphragm size). That can be useful in order to reduce room effects, but at lowest frequencies small rooms can't accommodate the long wavelengths, and at higher (middle) frequencies, the rear radiation may be counter-productive, particularly in "lively" rooms.
Both types are less than ideal in that they both suffer from variable directionality above frequencies whose wavelengths start to exceed diaphragm size.
But if you combine omni and dipole, you end up with cardioid (like radio direction-finding), and that's what Linkwitz's LX-mini does - at least for the vital middle frequencies.
Box speakers are omnidirectional at low frequencies, becoming progressively directional as each driver's radiating surface becomes comparable with wavelength - in other words, usually something of a mess when it comes to radiation pattern vs frequency.
OBs radiate as dipoles at the same frequencies that box speakers are omnidirectional (for a given diaphragm size). That can be useful in order to reduce room effects, but at lowest frequencies small rooms can't accommodate the long wavelengths, and at higher (middle) frequencies, the rear radiation may be counter-productive, particularly in "lively" rooms.
Both types are less than ideal in that they both suffer from variable directionality above frequencies whose wavelengths start to exceed diaphragm size.
But if you combine omni and dipole, you end up with cardioid (like radio direction-finding), and that's what Linkwitz's LX-mini does - at least for the vital middle frequencies.
Very few people make round open baffle speakers with the driver at the centre - a nude drive would be an exception. I made an open baffle a few years ago, and apart from a lack of bass it sounded very realistic, I've also made some mini line arrays that sounded awful, VERY beamy in the higher frequencies, but that's because I didn't do them right, I'm not against them; their uniform horizontal radiation, and uniform vertical linear dispersion gives them a potential advantage to those who know how to get it right. I've made two omnis, one with poor imaging ( possibly to falling high frequency response, possibly back wave reflection ), and some much smaller ones that imaged really well.
In my opinion, tattoos are for sailors and prisoners, but if people want them it doesn't bother me, I just hope that the realise that they may be in fashion now, but fashions have a habit of changing. It's easier to get " ink done " than get rid of it.
In my opinion, tattoos are for sailors and prisoners, but if people want them it doesn't bother me, I just hope that the realise that they may be in fashion now, but fashions have a habit of changing. It's easier to get " ink done " than get rid of it.
I frequently wonder the same thing.
Then I remember that there are also people who like face-tattoos, nipple-piercings, lutefisk, and kiviak. (Lutefisk is a gelatinous mass of whitefish preserved in lye. Kiviak is fermented dead bodies of decomposing Little Auks (birds) stuffed into a seal-skin bag, feathers, feet and all.)
Quite possibly there are Internet forums where people gather to show off their latest face-tattoo, and be congratulated on it. Quite possibly there are online forums where people discuss their enjoyment of nipple-piercings, lutefisk, and kiviak.
"There's nowt as queer as folk", as the old saying goes. (And "queer" simply means "strange" here. It has nothing at all to do with its more modern usage regarding gender identity or sexual orientation.)
To me, speakers mounted on open baffles are very much a case of "Throwing out the baby with the bath-water", to use another old English expression. Trading off most of the bass response and power handling, along with flat frequency response, along with low-frequency THD, in order to get rid of "boxy" sounds seems like a very poor trade off to me. On top of that, stereo imaging tends to be poor, in my experience, probably because of the big wash of uncontrolled reflected sound arriving from walls, ceiling, and floors in every direction, randomly delayed, and randomly attenuated...
Now, ponder this: put a smaller box speaker inside a large box speaker. Now play your favourite music through the small speaker. Just how little of the music do you expect to hear coming through the cone of the larger box's main driver?
This reads a bit like someone who doesn't understand the love for Italian food, when all he has ever eaten is spaghetti out of a tin. He'd be right, it's not very good! 🙂
You have certainly pinpointed some major problems belonging to OB. The biggest being the loss of bass, and therefore the large loss of efficiency. IME this is a not only a problem, it's a problem that most OB builder just don't want to deal with. Or aren't even aware of the problem. They don't deal with the fact that even on a baffle that is large by home audio standards, bass loss can be 10dB or more. There is the baby gone with the bath water. But they want to keep the baby. With OB you have to give up bass efficiency or build giant baffles. Most people don't want to do either, they want a compact OB that still has efficiency >91dB@2.83 volts. Not an easy task. Because too many OB builders don't take this large bass loss into account, tonal balance is bad, very thin and sometimes shouty. I've stood in front of OB rigs where the comments were along the lines "The bass is so clean!" "Yes" I say, "so clean that it has completely disappeared." It doesn't have to be. Use a big baffle, large woofers and tame to rising response caused by the open back and OB can sound superb. There are other things that box builders don't understand when they start experimenting with OB, like the effects of rear radiation, driver placement on the baffle, baffle placement in the room, wings and some others.
Good OB speakers can image very well indeed, some of the best I've ever heard. As good as my giant horn systems? No, nothing matches those, but I've heard and built OB that were far better than most box speakers. Better depth, better width, more precise placement. OB isn't all about losing the box sound, that's just part of it. Do OB well and there are other sonic benefits.
Pano - the OB's bass efficiency issues can be minimised by using drivers with very large, light cones - which is pretty much the opposite of what's required for box speakers (which need relatively small, heavy cones). (Both types need highly compliant suspensions.)
One problem is that I don't think there are too many bass drivers available which have been designed specifically for OB. However, for all but the very lowest frequencies (and therefore largest of rooms), there are large-driver options out there - large enough to make baffle-less bass quite feasible...
One problem is that I don't think there are too many bass drivers available which have been designed specifically for OB. However, for all but the very lowest frequencies (and therefore largest of rooms), there are large-driver options out there - large enough to make baffle-less bass quite feasible...
Thing is, 18" woofers tend to be rather exotic, and over-engineered. They don't have to be (though the preference for a light cone that size may offer some challenges).
Yeah I don't know what makes good OB bass, point is the system size doesn't increase much so one can add as many woofers as needed for the SPL capability and extension. Its not cheap, but doesn't have to be expensive either.
Just to clarify: box speakers have to operate in conjunction with a compliance set by the air inside a relatively small box - so the driver's cone needs to be small and heavy, in order to keep system resonance low.
The OB driver merely has to deal with the air load, which is light in comparison with practical cones, even large ones. That way, efficiency can be raised by using a light cone.
The OB driver merely has to deal with the air load, which is light in comparison with practical cones, even large ones. That way, efficiency can be raised by using a light cone.
Yes, it can. Also drivers with a high Qts can help because they have a bass hump that will offset some of the bass losses. But you don't have to use a light cone or high Qts woofers, I've seen it done with rugged, low Qts pro woofers. But then you lose more bass. However it's a trade-off because you started with more efficiency in the first place. You just have to know and understand what your drivers and baffle are doing, then take steps to flatten the response. I've yet to encounter an OB bass that didn't have significant rising response (unfiltered) but I suppose it's possible with the right drivers and baffle.
Come to think of it, I did build an OB rig in my garage awhile back that used MCM 21 inch woofers on big baffles with deep wings. IIRC they played pretty flat from ~25 to 300 Hz by themselves. Almost the perfect OB woofer. Too bad the rest of the OB build sucked. 😀
The bookshelf speaker craze of 1968-1975 proved most people listen to sources from 300 hz to 4000 hz. Home Entertainment demonstrated bookshelf speakers with Simon & Garfunkle, which has source right in the efficient frequency zone of a bookshelf speaker. Neither performer even sang bass. Singer/songwriter material is popular now: a single soprano with a single nylon guitar typically. OB would fit right in with that listening habit. I play piano, at least down to 34.6 hz since age 11, and played bassoon, which went to 64 hz. I was not satisfied with bookshelf speakers. I would not, I suspect, be satisfied with OB.
As far as frequencies bouncing around inside a box and reflecting through the front, at the 1/8 watt I use there wouldn't be much of that. HD chart of spec sheet of my boxes don't show a problem at 5 W. The bass reflex speakers I own are stuffed with large folds of some soft rubbery compound. Seems like the designers saw the internal reflection problem coming. As far as bass leaking out the back, I've measured that by backing my boxes up against a 1" thick plaster wall, the bass response at 30 hz (6' forwards on axis) is only 8 db lower than 54 hz (tuning freq) compared to 28 hz of the spec sheet freq response chart. I use them that way, and don't want a subwoofer for adequate piano & organ response.
True, at least as far as general operation.
Not true (in total).While the radiation pattern and room interaction is different, there are other key differences to the result as previously mentioned - and they are very much "real"/audible differences when comparing to a typical closed box design.
In fact I'd argue that other than the very obvious lowest room note excitation (where a dipole does not do this very low in freq., though few dipole designs extend that low in freq. anywhere near the average), that
Those other differences have greater subjectively importance.
I know this from having compared typical large open baffle designs to *large-volume/large-baffle enclosure designs with a specialized design used to substantively reduce reflections coming back through the cone. The radiation profile and room interaction is certainly different, but the sound is remarkably similar. 😉
*similar to Sonus Faber's Stradavari Homage
Whether at 1/8W or 5W is irrelevant - the point is that the unwanted sounds from within the box will come through the main driver's cone as if it wasn't there. Meaning, nearly as loud as if they were being played by the main driver itself (despite attempts at internal sound absorption, I'd suggest), and competing with it.
Scott G - what were the design features which were most successful at reducing the effect of internal reflections? Baffles/labyrinths, stuffing and thick felt?
I'm interested in any info you might be able to point to that supports your statement(s) here.
I thought that the inside of a sealed enclosure, driven by a woofer, would basically become a pressure zone. Any "sounds" that we'd hear are the harmonics/resonances developed by the enclosures' geometry ... and the exterior panels driven by the pressure inside the enclosure. How much of that is actually transmitted through the cone while it is working? I've not seen a definitive answer to that ... just some speculation based on how thin the cones are ... so they must leak a lot.
Or/And, if I place another driver within the enclosure you'd hear that driver through the inoperative cone. Kind of like placing a woofer inside a paper bag. ... but I don't think that's what is happening and would be a poor test of the cone leakage theory.
Indeed. It's much talked about - and I've done some work in my speakers to reduce the effect, but just how big is the leakage and how hard is it to fix? I haven't seen any good measurements of that. It's probably not easy to measure.
1. The wide baffle/rear-panel design has fairly distant and small side-panels (that were also not parallel),
2. I used a large (about 15" diameter) funnel-like (about 40 degrees) reflector behind the *fullrange driver's magnet (extending from the magnet's outer edge),
3. I also used several 1/4" round dowels irregularly placed between baffle and rear panel with a 2" thick wrap of Ultra-touch insulation (glued) around the dowels EXCEPT within a few inches of the baffle and rear panel (..basically the insulation was not resting on the interior panels, nor was it within several inches of the driver or reflector). This absorptive material was good for freq.s above 300 Hz and basically blocked-out most reflections without adding much additional suspension loss.
*The Fostex FE166ES-R is exceedingly "finicky" when it comes to its air-load/internal-loss character AND reflections through the cone, just a bit of stuffing near the driver will "shrink" the sound-stage both laterally and to a greater extent: depth-of-field. I specifically used this driver as a "litmus test" because of its finicky nature.
With both my large open baffle and large baffle sealed box testing I used a high-pass above 90 Hz, and both were eq.ed flat (..all digitally). Note: the rear-output of the fullrange driver goes surprisingly high in freq. near the average when used on an open baffle. I didn't "push" the drivers very hard (..they were below 80 db).
When a wave encounters the rear of the cone, part of the wave is reflected from the cone and part is transmitted through the cone.
The exact ratio of reflection to transmission depends on the material of the cone - the denser the cone, the less the amplitude of the transmitted wave.
The animation shows what happens when a wave travels from a low density (high wave speed) region into a high density (low wave speed) region.
