Wide baffles have their benefits, but also their failures. I believe it is important to keep 1st diffraction artifacts happen very quickly (based on the latest research probably below 5us). A wide baffle pushes the baffle step lower. One way of getting both is like this:
dave
I have some 1970 vintage Philips Application books, including "Building hi-fi speaker systems". It's fascinating to see how the theory and practice of speaker design has changed since then.
The books are from the period when wide baffles were in fashion... actually, they were never in fashion. They were wide because the cabinet was shallow, so wide was the only way to go to get cabinet volume.
The cabinets were shallow to get the most significant cabinet resonance (half wavelength, back of cone to rear wall of cabinet) out of the woofer's operating range. (Something that is largely ignored today.) Mid and HF drivers were deliberately offset on the panel for edge diffraction reasons, and to get the right distance between drivers (important at crossover) without making the cabinet too tall.
They were aware of the desirability of even polar response, including flush mounting the tweeter to avoid a "baffle step" at the edge of the tweeter. But they also considered a flat on-axis frequency response to be more important than an even polar response. The emphasis was on reducing in-room reflections and optimising the direct sound.
The books are from the period when wide baffles were in fashion... actually, they were never in fashion. They were wide because the cabinet was shallow, so wide was the only way to go to get cabinet volume.
The cabinets were shallow to get the most significant cabinet resonance (half wavelength, back of cone to rear wall of cabinet) out of the woofer's operating range. (Something that is largely ignored today.) Mid and HF drivers were deliberately offset on the panel for edge diffraction reasons, and to get the right distance between drivers (important at crossover) without making the cabinet too tall.
They were aware of the desirability of even polar response, including flush mounting the tweeter to avoid a "baffle step" at the edge of the tweeter. But they also considered a flat on-axis frequency response to be more important than an even polar response. The emphasis was on reducing in-room reflections and optimising the direct sound.
Interesting! This is something I've been looking at recently, too. When you go shallow enough, you reduce the 3-dimensional problem of interior reflection management to a 2-dimensional one--potentially a huge plus.
I suspect even deeper enclosures can benefit from internal baffles, or even basket restrictions, that don't allow the back-wall reflection any space to form behind the cone.
Trouble is, such things violate the false wisdom that audiophile marketing departments have been pushing that says drivers must have no restrictions or boundaries anywhere near their cones, front or back. This is silly, IMO, and discounts a host of acoustic benefits such things can bring to a design.
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Thanks much, Dave. It's on my christmas wish list now.
I went to Google Books and was able to glean some goodies between the redactions. This is pertinent stuff to the topic, found on page 76, 77.
(No OCR at hand, so I've attached screenshots of the text with a few of my comments.)
Attachments
If i am not mistaken on another thread it was suggested that the speakers be sited on their sides as a cure for the imaging problem. Not tried it myself as yet, but hope to do so very soon.
Different ways of controlling the same issue. Leaving the cone free to 'breathe' inside the enclosure does have the upside of decreased amplitude due to pathlength (and any absorbtion), so it's not so simple as optimizing the timing of enclosure reflections, though keeping them early is certainly one way of doing it.
True. I hope no one construes what I said to mean I don't believe in stuffing, too. The best of both worlds would be a combination of constrained path length/geometry and absorption.
The taboo that says, "The diaphragm MUST be left wide open to breathe," is far too limiting because it precludes the use of box geometries as mentioned above, plus a whole universe of useful acoustic filter elements that can be more effective than their electrical counterparts.
The taboo that says, "The diaphragm MUST be left wide open to breathe," is far too limiting because it precludes the use of box geometries as mentioned above, plus a whole universe of useful acoustic filter elements that can be more effective than their electrical counterparts.
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Hi Planet10,
My inspiration for large baffles comes from :
"Putting the Science Back into Loudspeakers" by John Watkinson.
http://www.celticaudio.co.uk/articles/science.pdf
My inspiration for large baffles comes from :
"Putting the Science Back into Loudspeakers" by John Watkinson.
http://www.celticaudio.co.uk/articles/science.pdf
Except for one major problem- how do you attenuate the backwave sufficiently without 'choking' the driver? Stuffing materials are most effective at velocity maxima (read: middle of the box). When the box is tight to the rear of the driver, the only way to get stuffing into these locations is to put it very close to the driver, which practically eliminates the ability to utilize the speaker effectively in a resonant enclosure, and in extreme cases, can raise the Q of the system.
In a large, 'free breathing' box, however, clearance can be provided such that the majority of the airspring can be left uninhibited, while periodic behavior (reflections) within the enclosure can receive superior suppression via increased pathlength and stuffing absorbtion (stuffing in this case can be placed away from the driver AND the sidewalls, maximizing efficacy).
My ideal enclosure acts as a 'black hole' for periodic behavior, and leaves only the pressure/mass system intact for any resonant tuning. Optimizing the early reflections to a very short window is a fine way to minimize their effect within a small enclosure, but a larger enclosure seems to be a superior way to minimize the problems of enclosure reflections. Naturally, this limits us to discussing cases where a significant enclosure size is desired, but perhaps this is part of why larger, properly designed speakers tend to sound more dynamic- less early reflections leading to a cleaner transient response during a music playback situation. A test beginning at rest position wouldn't show this, however.
Again, I'm not trying to limit with my comments, but to remove limits.
I have no problem with big, open boxes if quarter-wave, helmholtz or a combination of resonances are desired to hit a design point.
I'm just calling for open-mindedness when it comes to other designs that go against the current orthodoxy.
Whereas "choking" is a verb rarely associated with a positive outcome, when you instead think of "choking" as "series flow resistance," maybe it can play a key role in any number of excellent designs. 🙂
edit: uh-oh, now I sound like a marketeer...
I have no problem with big, open boxes if quarter-wave, helmholtz or a combination of resonances are desired to hit a design point.
I'm just calling for open-mindedness when it comes to other designs that go against the current orthodoxy.
Whereas "choking" is a verb rarely associated with a positive outcome, when you instead think of "choking" as "series flow resistance," maybe it can play a key role in any number of excellent designs. 🙂
edit: uh-oh, now I sound like a marketeer...
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I think you'll find that the rule "baffle to back panel spacing should be between (and not too close to either) one quarter and one half wavelength at the driver crossover frequency" is not too limiting in terms of cabinet construction. The point is that if the resonance is above the driver passband, it won't be excited and thus won't have to be damped.
Regarding lining/stuffing, I've examined many of the Philips speakers of the period (the "Hi Fi DIN 45500" era). They were all 1/2 to 2/3 full of high density fibreglass batting. This filled all the space between the rear panel and the rear of the drivers. This was enough to provide useful absorption of front-back resonances, and provided high absorption of top-bottom and side-side resonances.
Driver complement was usually AD7066, AD8066 or AD12100 woofers, AD5060 midrange, and AD0140 or AD0160 tweeters.
Regarding leaving a large amount of room for the drivers to "breathe", my opinion is that this belief has little or no scientific validity. It is at odds with the body of practical experience gained from various woofer enclosure topologies, which can be summarised as "leave at least as much area as the driver's diaphragm area". Even if the back panel is hard up against the magnet (assuming no pole vent), the area of the cylinder around the driver that all the air has to pass through is still several times the diaphragm area.
So provided that the possible resonances (especially front to back panel) are well above the driver passband, where is the mechanism that could prevent the driver from "breathing"? Could it be that moving the rear panel further away from the driver, thus moving the resonance into the passband, alters the sound in a way perceived to be euphonic?
Another topic raised above is non-resonant reflections ("echoes") from the rear panel. Again, a small spacing is better, as the reflections will be closer in time to the original wavefront. The reflection timing in the classic "wide baffle / shallow enclosure" speaker will be in the same range as the baffle step timing. Proper dimensioning can make the reflection coincident with the baffle step, reducing its effect.
Note that I'm not advocating a return to the classic "large baffle". In my opinion, baffles should either be as small as possible or as large as possible. Their spatial and temporal effects should be minimised, and kept as far away as possible from the drivers when not avoidable.
Regarding lining/stuffing, I've examined many of the Philips speakers of the period (the "Hi Fi DIN 45500" era). They were all 1/2 to 2/3 full of high density fibreglass batting. This filled all the space between the rear panel and the rear of the drivers. This was enough to provide useful absorption of front-back resonances, and provided high absorption of top-bottom and side-side resonances.
Driver complement was usually AD7066, AD8066 or AD12100 woofers, AD5060 midrange, and AD0140 or AD0160 tweeters.
Regarding leaving a large amount of room for the drivers to "breathe", my opinion is that this belief has little or no scientific validity. It is at odds with the body of practical experience gained from various woofer enclosure topologies, which can be summarised as "leave at least as much area as the driver's diaphragm area". Even if the back panel is hard up against the magnet (assuming no pole vent), the area of the cylinder around the driver that all the air has to pass through is still several times the diaphragm area.
So provided that the possible resonances (especially front to back panel) are well above the driver passband, where is the mechanism that could prevent the driver from "breathing"? Could it be that moving the rear panel further away from the driver, thus moving the resonance into the passband, alters the sound in a way perceived to be euphonic?
Another topic raised above is non-resonant reflections ("echoes") from the rear panel. Again, a small spacing is better, as the reflections will be closer in time to the original wavefront. The reflection timing in the classic "wide baffle / shallow enclosure" speaker will be in the same range as the baffle step timing. Proper dimensioning can make the reflection coincident with the baffle step, reducing its effect.
Note that I'm not advocating a return to the classic "large baffle". In my opinion, baffles should either be as small as possible or as large as possible. Their spatial and temporal effects should be minimised, and kept as far away as possible from the drivers when not avoidable.
I work mostly with full-range drivers, so perhaps a worst case situation. I have found that if i do not allow sufficient space to the sides of the driver cutout, or if the back panel is too close to the driver, i get colourations that i vcan remove by giving more room to "breath".
I have also found that an angled rear wall has some positive benefit, althou not always commensurate with the extra effort involved.
If you are doing a multiway, then one has to consider the wavelengths involved. In a woofer cabinet the wavelengths are such that almost any box is small. In these thou transmission-lines tend to reduce time-smear by "sucking the back wave down the line".
dave
Concern about the passband is all well and good.... except that we're talking about real-world speakers here, not brickwall filters. So in many cases a few octaves away is still quite audible
Yes, my remarks don't apply when the driver's passband includes the front-rear resonance. In that case you need to move the walls back far enough to allow sufficient damping material to minimise the reflections. Note that just moving the walls back is not enough - there has to be damping, because the amount of energy reflected back is constant regardless of the distance, for any practical enclosure size. In other words, you get just as much reflection if you give the driver room to "breathe", it's just delayed in time. That will certainly alter the sound character, but is it better?
You do indeed have to consider the wavelengths. And when you do, you will find that the dimensions are not as free as you think. For example, in a two-way, you need to allow for frequencies up to 1 or 2 KHz in the passband. For 1 KHz, that means the front-rear distance should be less than 17 cm (about 6 inches). Keeping well away from 1/4 and 1/2 wl, and allowing for out-of-band response as pointed out by badman, means you should aim for about 4 inches front to back. For a 2 KHz crossover, the situation becomes almost hopeless - better to go for a deeper cabinet and damp the resonance.
All of this assumes that the amount of energy reflected back through the cone is sufficient to cause problems. It depends on a number of factors. For example, I would expect the problem to be worse with full-range drivers with their light cones. I propose a simple experiment:
Take a driver in an enclosure. Mount an identical driver over it, face to face, with its terminals shorted together. Listen to what comes through the back of the second driver. This is a "worst case" scenario, but it will give you an idea of the magnitude of the problem. Remember that all of the energy radiated from the back of the driver in an enclosure has to go somewhere. Absorbed by the walls and damping in the anclosure, or back out through the cone of the driver.
Take a driver in an enclosure. Mount an identical driver over it, face to face, with its terminals shorted together. Listen to what comes through the back of the second driver. This is a "worst case" scenario, but it will give you an idea of the magnitude of the problem. Remember that all of the energy radiated from the back of the driver in an enclosure has to go somewhere. Absorbed by the walls and damping in the anclosure, or back out through the cone of the driver.
Today i placed the 1000's on heavy stands on there side with the tweeter facing in with a slight toe in.... This created a more stable image with voices being more central instead of the wall of sound effect. Not holographic spooky imaging but acceptable, the weakest point in an otherwise outstanding speaker.
Brilliant speaker, im going to try a diy high end bookshelf with some seas metal drivers in the future to see if they can out perform the yamaha's. To me i cant see any speaker at a resonable price outclassing them completly but maybe im wrong?
Brilliant speaker, im going to try a diy high end bookshelf with some seas metal drivers in the future to see if they can out perform the yamaha's. To me i cant see any speaker at a resonable price outclassing them completly but maybe im wrong?
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I think the Yamaha's will have much better dynamics than a system based on Seas metal drivers, but if well executed the latter will have much lower coloration in the upper bass / lower midrange area.
I don't think anything will ever beat the Yamaha Beryllium midrange
I find it quite ironic that other speaker manufacturers have only cottoned on to this material in the last few years where as Yamaha was using it nearly a quarter of a century ago 😀 Still haven't seen anything other than tweeters us it yet though - they are miles ahead of the curve.I'd tend to agree, there really is quite a bit of cone on the 12" bass to allow reflections from the rear baffle through. The carbon fibre bass unit of the NS1000X (also similar to the NS2000) does a better job in that area. On the NS2000 thay also added extra bits of wood at the side with 3/4" or 1" rounded edges to, which certainly helped with imaging 🙂
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