It's a near-field measurement aberration.
See here:
https://www.erinsaudiocorner.com/loudspeakers/dutch_dutch_8c/
-well, it won't be a Ripole anymore but you could do the same compound loading of a Ripole and still the get the resulting air-compression from the front along with an effective increase in Mms and lower of Fs while having the rear in a leaky enclosure designed to achieve a near-field cardioid pattern.
Apologies - haven't read the earlier posts, but the ideal bass driver for OB would have a very large diaphragm, made from very light material, and a very compliant suspension/surround for low resonant frequency. This way, the air load to moving mass ratio is maximised, which is what you want for highest efficiency.
Hi oneminde,
edit. sorry didn't notice ripole related links in post #46, will read those.
I think its edge diffraction to blame that takes the attention and makes poo sound, and not size of the system directly. No baffle system has very narrow bandwidth where edge diffraction makes secondary sound source and hence not so audible, while big baffle has much wider which ought to be more audible. Big baffle can work if it has equally big roundovers, or in other words any size would be fine as long as edge diffraction is considered and not making problem. I mean make speaker disappear. Size would affect directivity and how speaker interacts with room, but this is room and position dependent. Anyway, many things at play, careful not to lump too much stuff together especially without context 😉
Is there measurements for this? I cannot see how it would make cardioidish pattern, cancellation to only one direction. Construct of a ripole woofer looks to my eye it would be dipole and here are some measurements I found which show response is roughly equal on front and back and dipped 90deg to side, like with dipole. https://www.diyaudio.com/community/threads/21-in-a-ripole-subwoofer.377299/ Perhaps I don't get it how does it work? There is benefit of force cancellation though.
edit. sorry didn't notice ripole related links in post #46, will read those.
Not necessarily. More of the sound launches cleanly even before the edge. By the time the edge comes along there is not as much sound left there.
Hi,
your thinking seems logical except I'm not sure if it works that way. Why dipole has no bass and boxed speaker has not to do with mass but because there is no cancellation with boxed back wave. On a dipole both front and back sound interfere and cancel out as they are opposite polarity. Mass only affects the resonant frequency I think. If one wants bass with OB just use bigger "baffle" to isolate the front and back. Size and wavelength relate to each other. Even better, just use multiple drivers, enough cone area to have enough displacement to prevent high excursion and related distortion. Or use box as its room that dominates the low frequency response (peaks and nulls due to modes).
😆 size and Qts made bass I use OB form 14year my 8" fullrange made great bass with only
Hi,
TLDR; warning
yeah I'm not familiar how auditory system perceives diffraction, precedence effect and all, so I promote minimizing secondary sound source at the edge anyway possible, minimizing bandwidth, minimizing sound pressure relative to direct sound.
If you simulate edge diffraction its quite clear that at least on (some) axis, where bulk of the edge is equidistant to ear, the interference with direct sound is quite strong suggesting secondary sound source at the edge is pretty much as loud as direct sound. Frequency response of the edge differs from direct sound though, ever longer wavelengths don't make the secondary sound source (bafflestep) and possibly high frequencies get less to the edge as they beam, depending on transducer size. Here the distance from transducer to edge plays a role, or baffle size to transducer size, which basically determines the frequency response of secondary sound source and where "diffraction" IS loud. The shorter the distance from a transducer to edge, the narrower the bandwidth where edge diffraction secondary sound source is loud. Roundover would reduce the loudness on wavelengths that are relatively small to the radius. Directivity of a transducer would also rise with frequency and radiate less sound toward the edge in relation to direct sound.
You are right, if the edge is far enough, perhaps many milliseconds, the secondary sound source is no different to early reflections of room I think, except it would be opposite polarity than reflection would, not sure how this affects audibility. Its also debatable if early reflections in room are benefitical or not and I think the ones coming from direction of the speaker are said to be least benefitical, or even detrimental. Perhaps they are neutral at some point. Better not be guessing but try and eliminate as much as possible, both the edge diffraction and early reflections.
Without specific knowledge how hearing system processes edge diffraction all I can do is thought and listening experiments, trying to minimize it all ways possible. Imagine baffle edge as sole sound source we have, lets imagine there is no transducer on the baffle, just the edge diffraction related sound source at the edge. A rectangular baffle would make four edges and thus four line sources, two vertical and two horizontal, delayed towards corners (if illuminating source was center of the baffle). We can simplify situation even more and imagine the vertical edges only, two line arrays if you will, spaced by baffle width apart. Similarly as any two speakers you have in your stereo setup there is sweet spot exactly equidistant from the speakers where phantom center forms and the speakers disappear, but as soon as you move head off center the phantom center is lost and attention snaps to the closest speaker. Moving your head some one can pretty much point finger where the speakers are, or in this case where the edge is. As you low pass the sound its less and less obvious where the speakers are, even with quite lot of head movement. Easy to test with stereo setup if you have low pass filter at hand. Well, all this is due to precedence effect, and we have the direct sound precede the edge so not sure if this has anything to do with edge diffraction. Fun experiment though. Low pass / mute / disconnect your tweeters and localization gets less precise: resolution of localization of speakers / phantom center seems to be related to wavelength. When baffle edge is no further than the transducer edge itself I would reason there is no difference to ear if there is edge or not, transducer we must have.
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That's not what I'm talking about, even though there's a discussion there as well.
If the wavefront stays on the baffle for longer, then more of it goes in front and away from the baffle and is guided by it. There is not as much to diffract by the time it gets near the edge.
Yeah you are somewhat right but the sound reduces very little toward the edge. You can inspect that with simulator, make worst case baffle and inspect the interference. You can estimate from the interference pattern how much attenuation there is with the edge source. You'll notice the ripple is strongest, edge is loudest, around where wavelength is ~baffle size and reduces slowly up in frequency until driver coverage narrows, beams ~drive size. Below and above this there is not much interference.
With simple VCAD sim worst case ripple seems to be around 8db peak to peak, and we can avoid math and estimate with two point source interference that the edge is ~8db down from direct sound near baffle dimension wavelength and slopes down from there.
If you make 100cm baffle you'll see interference starts ~343Hz and goes up to ~3.43kHz as its 10cm transducer 😉
Then simply by bringing baffle edge close to transducer edge the inteference disappears, no secondary sound source but only that of the transducer and its "self interference" which makes the beaming as well. Interpret as you like.
With simple VCAD sim worst case ripple seems to be around 8db peak to peak, and we can avoid math and estimate with two point source interference that the edge is ~8db down from direct sound near baffle dimension wavelength and slopes down from there.
If you make 100cm baffle you'll see interference starts ~343Hz and goes up to ~3.43kHz as its 10cm transducer 😉
Then simply by bringing baffle edge close to transducer edge the inteference disappears, no secondary sound source but only that of the transducer and its "self interference" which makes the beaming as well. Interpret as you like.
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Why does a waveguide work best when it is large enough to support the waves that it guides? There is diffraction at the end but you can round it over. Would it be better if the waveguide was as small as possible so there is almost none?
I'd imagine they would be roughly equal in diffraction performance, like any other transducer with roundover, but you'd lose the waveguiding part, directivity, like with reducing baffle size. Hence good waveguide profile and roundover is paramount to reduce secondary sound sources like edge diffraction and possible reflections. Good waveguide with good roundover seem to be able to eliminate secondary sound sources towards listening window and any ripple is seen at large off-axis angles. Just like reducing flat baffle and have as big roundover as fits and one is willing to fabricate. Any roundover is good, but no roundover is almost as good as long as there is no baffle either and very good solution for lazymen like me 🙂 Any roundover gets better and better increasing the radius until the system resembles a sphere for the wavelength. One can estimate this with simulator as well.
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Aka "shoutiness". The simplest experiment is to place your hands on the side of your mouth and talk. Those elevated frequency (it becomes midrange hot) is why I despise large and wide baffles, it remind me of how horns sound since you get some of the effects, and I don't like horns. That deep nasally sound.
The other related issue which is connected, is the size of the midrange driver. Its duty is to do the human voice well and so, it stands to argue that it shouldn't be twice or trice the size of a human mouth. Too large of a driver, say 7-8" and the vocalist projection is too large. I've listened to 8" midrange in an OB and nothing sounded correct. It was like someone had put a magnifying glass on the recording...
I quote from troels :The launch of the Stradivari by Sonus Faber has created quite a debate and what has been argued against wide baffled speakers is some loss of pinpoint imaging. Here are some different views on the subject.
Mr. José Victor Henriques from his review of the new Sonus Faber Stradivari speaker:
"The Stradivari sounded like a live performance in a real venue, filling the room with sound and doing the proverbial vanishing act. Maybe less so because you just couldn't take your eyes off them. Given the larger than usual baffle, focus is not to the pin-point accuracy standard of, say, the Wilson Watts Puppies (their natural competition in this price range), suggesting some attention to “toe-in” to further sweeten the "spot". On the other hand I must confess I've never heard live “pin-point focus” as the instruments and singers usually energize the air around them creating a “bubble” of sound not just an “ideal” point source. In this particular aspect of sound reproduction, the Stradivari is closer to reality".
"Live pin-point focus": Has high-end HI-FI forgotten something here? The trend in recent years has been towards speakers with very narrow front baffles, trying to eliminate reflecting surfaces around the drivers, presumably enhancing pinpoint imaging. And with apparent commercial success. What is the trade-off? Because there's always a trade-off in speaker building. Well, by having a very narrow front baffle we will have edge diffraction at a rather high frequency giving delayed response subtracting from the target of pin-point imaging. We all know that a round sphere is the ideal surrounding for a speaker but for large speakers the sphere has to be large, very large and the WAF is close to zero. We never saw a commercial success from a sphere shaped speaker where the very narrow and slim line speakers can be rather deep (to give volume) and still appear smallish = high WAF.
Paul Messenger:
"Narrow speakers with a very wide radiation include more of the listening room and help create an illusion of bringing the musicians into the room; while more directional designs like horns and dipole panels give a precise view onto the recording itself. Neither one nor the other, the Stradivari is perhaps the ideal compromise between the two."
With narrow baffles we also run into serious baffle step compensation issues and we may have to apply large inductors to the basic driver in order to tilt the frequency response to be flat. Large inductors = large phase shifts. With a wide baffle the need for large inductors are reduced as we are dealing with a virtual 2pi situation. The "almost-infinite" baffle.
Henriques again:
"The virtual 2 pi radiating infinite baffle is based on the concept/surface of the “piano armonico” of the violin which allows the midrange unit to reach its lower frequency limit in a more poised and natural way, thus conveying to the listener a sense of better integration with the massive double bass drive units".
With a 66 cm wide baffle the Stradivari mid-drivers hardly need any baffle step compensation. It will be flat down to 200-300 Hz.
Roy Allison (former Acoustic Research and Allison Loudspeakers) in Stereophile, Jan/05) on the development of the Allison Model-1:
"I had emphasized dispersion in order to re-create as best as I could the performance-hall ambiance. I don't want to put up with a sweet spot, and I'd rather have a less dramatically precise imaging with a close simulation of what you hear in a concert hall in terms of envelopment. For that, you need reverberant energy broadcast at very wide angles from the loudspeaker, so the bulk of energy has to do multiple reflections before reaching your ear. I think pin-point imaging has to do with synthetically generated music, not acoustic music - except perhaps for a solo instrument or a solo voice, where you might want fairly sharp localization. For envelopment, you need widespread energy generation."
Calling a 50-60 cm wide baffle an infinite baffle is a truth with some modifications. Having an infinite baffle would mean mounting the drivers on the wall, creating a true 2pi environment. By making a wide and curved baffle cabinet, edge diffraction is avoided and a virtual 2pi radiation pattern is produced. Any driver mounted on a baffle will have an f3 = 11,600/width of baffle in cm. A driver mounted on a baffle of 20 cm with will be down 3 dB at 11,600/20 = 580 Hz. Making the baffle 50 cm wide the f3 is reduced to 232 Hz. Enough for a midrange driver working from 300-400 Hz to release its full potential without baffle step compensation. To read more about baffle step compensation and cabinet edge diffraction, try the following links:
http://sound.westhost.com/bafflestep.htm#bafflestepresponse
http://www.t-linespeakers.org/tech/bafflestep/index.html
http://www.speakerdesign.net/understand.html
Ken Kessler writes in his report on the Stradivari that it sounds like a dipole, so whether the midrange here will have to work as a true dipole is to be seen. Prototype baffles will have to be flexible to accommodate both vented midrange boxes and dipole arrangements. The sketches shown here are purely made to start thinking in curved, wide baffled constructions. No dimensions or calculations at this stage. A truly curved front panel is not an easy task and will probably require gluing several layers of thin MDF or plywood sheets over curved internal bracing.
Diffraction is why you need a smooth acoustical cabinet, not an EDGE that can kill a man... LOL, aka look at what Laurence did with the Vivid loudspeakers.
So are we saying, collectively: Either a narrow round edge cabinet or a relatively wide curved cabinet - both have their advantages. The vanishing act expressed differently. I have not listened to the S.S Stradivari but since its not a flat panel like most OB, it might hide some tricks.
Hi, you are right but mind the scale, if you listen 10 wavelengths away and edge is at 10 wl away as well, so that path length of diffracted sound to listening spot is about double it will be attenuated 6db. (linesources attenuate 3db with doubled distance?🙂. On practical sized speakers, say from 20cm to 1m wide and listening 3 meters away they would be roughly as loud no matter what the width. You can use the size to attenuate the secondary sound source, make speaker similar to room size and thats it.
About clean wave (direct sound before diffraction), as you suggest I'm sure there are some time thresholds that apply to edge diffraction audibility like to any other early reflections. I guess worst is somewhere when edge is from 0-5ms from the source 0 being special case as good as it gets, no different from direct sound. Psychoacoustics stuff. Early reflections are said to integrate with direct sound and affect timbre if they arrive roughly 0-2ms or so, then up to 10-15ms bother with localization cues in the recording, typical early reflections times of studios or something. I'm guessing similar rules apply to diffraction related secondary sound sources, like reflection related secondary sound sources, I mean how would auditory system differentiate between those?
tmuikku: But that is the trick, fooling the listener and blending the direct and diffracted sound. Even the driver basket will generate some diffraction, so its not a matter of no diffraction, its a matter of how much and when and these are all tuneable. I can see a place for both a wide and narrow round baffle. The idea is to come close to the orb like it was mentioned 🙂
Yes if its badly implemented system, and / or bad horn like cupped hand with reflections and edge diffraction then yeah. Waveguide is something that can make coverage angle less than 180degrees if its something that is benefitical on an application like too reflective room, or if the listener is looking to reduce direct to reverberant sound ratio, increase clarity or imaging or what adjectives everyone wants to use, to further distance from the speakers. Good waveguide and well implemented system is not shouty if power response is smooth, similar through whole bandwidth. Shoutyness is result off directivity jumping up I think, power response falls down and lows and highs are having separate coverage angle and perceived separately. Perhaps reflections from horn mouth, edge diffraction, can make it too, a horn sound. Believe or not this is thing of the past, see ATH4 thread. For sure one can use direct radiating tweeter to prevent any such concerns. On the other hand 1" dome on standard 4" flat flange needs >4" radius roundover to get rid of diffraction ripple on its pass band to same extent as any sized waveguide can 😉 So, its just easier to get better performance in this regard with waveguide, just don't put the waveguide into any baffle.
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