Now if I had a paper bag, I'd put it over my head and find out if it works. 🙂 Or if I had a Japanese friend still living in a traditional paper house, I'd ask her. 🙂
I did once make a midrange horn from Styrofoam (aka EPS - expanded polystyrene foam) and cardboard. It worked quite well - the little midrange became ridiculously more efficient than the woofer - but I didn't care for the sound. It sounded a bit too much like speaking with hands cupped around your mouth. Yuck.
I almost brought this up earlier - while paper is heavy enough to be barely moved by the actual sound waves, a large sheet will certainly have resonant modes, lots of them, and may move much more at those locations and frequencies.
I still guess stiff cardboard (not paper) would probably get you most of the way - open-baffles don't have wonderful frequency responses anyway, so how much worse can a slightly floppy cardboard baffle be? But I have no actual solid data to show either way.
A relatively inexpensive alternative might be Coroplast - you know, the stuff that looks like corrugated cardboard, but is actually thin plastic rather than paper. Often used for throwaway election signs and so on. It has heavy internal mechanical damping, is reasonably stiff, and much heavier than similar-thickness corrugated cardboard. On the minus side, the edges can be sharp enough to cut skin, and most plastics are not particularly healthy to handle.
What audiophiles do, by itself, rarely convinces me of anything - there's so much nonsense in the world of audiphoolery, how can we trust any of it? This is a group that believes putting amplifiers on spikes changes their sound, that metal wires have directional response to electric current, that they can hear 0.0005% THD, et cetera. All of this is complete superstitious nonsense.
So how about massive beefy open baffles? Necessary or not? I've never seen any objective data showing a heavy rigid baffle is necessary, only proud audiophiles showing off heavy, expensive, waxed and polished carpentry. So what is one to believe without experimental data? The physics doesn't suggest much weight or stiffness is called for, and I'll believe in the physics any day, rather than in unfounded opinion. (I'll gladly believe in trustworthy measured data too, if anyone can find any.)
Back to beefy (or not) baffles. Certainly the part of the baffle that supports the speaker itself needs some mechanical strength, so using some minimal wood framework there makes sense. But one of the things that came out of the discussion on this thread is that the speaker basket probably couples vibrations into the baffle - so I think it would make sense to have a small wooden support structure immediately around the speaker, but connect that with soft closed-cell foam to a thin, light baffle, to minimize direct mechanical vibration transfer from the speaker frame into the baffle.
Has anyone tried this? As far as I can recall, I haven't run across this approach, ever. Anyone else?
The original open baffle concept died a natural death some seventy hears ago, because it worked so badly, and better alternatives had been discovered. Decades later the corpse was dug up and re-animated into a staggering zombie, using the black magic of vast quantities of cheap amplifier watts and easy active EQ thanks to op-amps or DSP codecs.
Nowadays, most people seem to build their zombies - err - OBs - the same way one should build a sealed or ported box, but the physics is very different, and the builders seem to be motivated by what looks beautiful or impressive to them, not by the actual science. Is that thick wood really needed? I doubt it, but have no measurement data to back up my guess.
Fair enough. I wasn't suggesting that cardboard was the ideal material for a permanent baffle - for one thing, it breaks down over time, for another, it doesn't tolerate humidity well. I do think cardboard is fine for a quick proof-of-concept experiment, though, before spending money on thin plywood or whatever.
If you go back and look at my post #10 in this thread, that's exactly the context in which I originally brought up cardboard on this thread: I suggested the OP do a quick test with a cardboard baffle to see if he liked the sound, before spending money on the plywood he was planning to use.
I have my doubts about an enclosure (as opposed to an open baffle.) At some frequencies, air pressure in a sealed or ported enclosure is orders of magnitude higher than in an open baffle.
When the air from the tuned port blows the hair on your forearm around, you know there's some significant air velocity (and corresponding significant pressure). Not the snail-slow air movement and negligible pressure you get in front of an open baffle.
Speaking of oddball speaker cabinet materials, I will say that I was surprised when I tried Styrofoam for a sealed enclosure. The usual disposable foam cooler makes a not-bad speaker enclosure to my ears. A little brighter sounding than wood, but no objectionable ringing or unpleasant noises.
I'll stop there, I don't want to get too far from the thread topic - open baffle guitar speakers.
-Gnobuddy
You sand-fill a Briggs baffle because plain plywood has woody resonance.
If not resonant (and it probably will be), then the baffle need not be much heavier or stiffer than the speaker cone. However the baffle is bigger (the whole point) so it is bound to be less-stiff unless much thicker.
For guitar-amp accuracy, light plywood is probably excellent.
> ...If you know the ... ... ... ..., you can calculate cone acceleration....
Math??? Put the speaker face-up. Sprinkle a few grains of sand. Raise drive level until the sand dances off the cone surface. That is 1 Gee. Raise level to normal. Compare voltages. Now you know the Gee at normal playing level. (I estimate 5 or 10 Gee is normal for many speakers played loud.)
If not resonant (and it probably will be), then the baffle need not be much heavier or stiffer than the speaker cone. However the baffle is bigger (the whole point) so it is bound to be less-stiff unless much thicker.
For guitar-amp accuracy, light plywood is probably excellent.
> ...If you know the ... ... ... ..., you can calculate cone acceleration....
Math??? Put the speaker face-up. Sprinkle a few grains of sand. Raise drive level until the sand dances off the cone surface. That is 1 Gee. Raise level to normal. Compare voltages. Now you know the Gee at normal playing level. (I estimate 5 or 10 Gee is normal for many speakers played loud.)
you pump a giggawatt of power thru it to fuse it into a single solid mass!!!
but that's only after you sort thru it all to find the most uniform pieces....
but that's only after you sort thru it all to find the most uniform pieces....
Cardboard has the virtue of heavy internal mechanical damping - its pretty dead, acoustically.
Coroplast is very acoustically dead too, and free pieces of it are often found desecrating the roadsides after every election.
...but also has negligible driving force on it, particularly if the loudspeaker is soft-mounted...
Instead of the ancient philosopher's conundrum about the irresistible force meeting the immovable object, here we have the exact opposite: the negligible force meeting the featherweight object.
Thanks to differential calculus and L'Hospital's rule for limits of indeterminate forms, neither conundrum is a conundrum any longer. 🙂
Never mind the guitar amp or guitar speaker, open baffles themselves have absurdly bad frequency responses of their own, unless infinitely large...this was the main reason why they fell out of favour so very long ago, even in a time when their large size wasn't a major handicap.
The first attached image shows calculated frequency response of a point-source loudspeaker centered in a circular open baffle...it's far worse than the worst guitar amp frequency response I've ever seen.
Yes, a circular baffle with a central speaker is the very worst shape, and that horrid comb-filter frequency response can be improved a little bit by reshaping the baffle and offsetting the speaker from the centre, but it is still pretty horrid. The second image shows measured frequency response of a roughly 5" speaker in a rectangular baffle - and it's quite horrid too.
That's absolutely brilliant!
BL = 5 Tesla-metres and Mms = 50 grams (0.05 kg), plugged into (BL*I/Mms), immediately gives you an acceleration of 100 metres/second squared for 1 amp drive current. Since 1 g is 9.8 metres/second squared, 100 m/S^2 is about 10 g, as you say.
1 amp peaks into an 8 ohm speaker corresponds to 4 watts RMS power; very loud with a typical guitar speaker, easily over 106 dB@1m, and easily within reach of even small guitar amps like the Fender Champ.
However, for the truly insane guitarist, 5 amp peaks are certainly possible, and would produce 50 g peak acceleration. That's 100 watts RMS into 8 ohms, not unheard of in the glory days of loud rock music (and deaf and drugged guitarists.)
When I originally made that estimate, it was in order to find out what sort of cone-mounted acceleration sensor I would need to build a motional-feedback woofer. To make sure the sensor was never overloaded, I needed to make sure it could handle worst-case acceleration, which turned out to be maybe 80 g with the driver I was working with at the time.
-Gnobuddy
Attachments
Open back has merit when your amp+driver has bass Q over 1; also when you need bass Projection more than bass efficiency and size really matters.
Using cheap speakers and underdamped amplifiers to throw into a half-full club.
The argument is indeed weaker for home playing.
Using cheap speakers and underdamped amplifiers to throw into a half-full club.
The argument is indeed weaker for home playing.
I apologise if I'm telling you something you already know - the very clever thing about PRR's idea is that 1g of acceleration, downwards, will make any and every sand grain weightless - regardless of how heavy it is!
It's quite counter-intuitive, but heavy things and light things fall at exactly the same speed if you remove air resistance. More than four hundred years ago, Galileo made his reputation by demonstrating this, dropping balls of different sizes and weights from the Leaning Tower of Pisa in front of a crowd of watching university students and members of the public.
Galileo also made powerful enemies with this demonstration, enemies who believed he had committed sacrilege by contradicting Aristotle's teachings. Some of those enemies eventually got their revenge in his old age, costing Galileo his university position, his scientific reputation, and eventually, even his freedom, as he was placed under house arrest with the threat of being burnt alive at the stake always hanging over his head at the tail end of his life.
Thankfully, the Church no longer has the power of life and death over everyone, so PRR is unlikely to be threatened with torture and/or death for making his "All sand falls at 1g" suggestion. 😱
-Gnobuddy
"There is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss,"
Throughout my adult life, I've had the ability to throw myself at money and miss. Does that count? 🙂
-Gnobuddy
The 1 Gee observation comes from car rear-deck speakers. When old and dirty, they will play soft, or loud. But there is some critical medium level where they sound like a gravel storm. Grille off reveals dancing dirt. Soft, the dirt don't dance. Loud raises a cloud of dirt which rarely touches the cone. At the critical level the dirt dances with the beat.
Yes, all dirt dances different. You do not want rocks as heavy as the cone or you upset the relationships. You do not want dust too small to see (which also gets into physics of air). You do want dust which is "heavier than air" so it will settle quickly. Paper-fluff is a little slow. Ordinary beach sand is excellent (it has been segregated by water motion).
Yes, all dirt dances different. You do not want rocks as heavy as the cone or you upset the relationships. You do not want dust too small to see (which also gets into physics of air). You do want dust which is "heavier than air" so it will settle quickly. Paper-fluff is a little slow. Ordinary beach sand is excellent (it has been segregated by water motion).
Ever see a Chladni Plate demonstration? ( YouTube )
I've helped set these up more than once, vibrating the plate with a modified woofer motor and an audio oscillator, rather than a violin bow. The results are beautiful and fascinating to watch. But it never dawned on me that the critical vibration threshold for the sand (or salt) to start dancing was 1g peak acceleration.
Incidentally, at least in physics, lower case "g" is the acceleration due to the earth's gravity near its surface, approximately 9.8 m/S^2, while uppercase "G" is Newton's gravitational constant, about 6.674×10^(−11) metre cubed per kilogram per second-squared.
-Gnobuddy
Violin makers have long used Chladni figures to provide feedback as they shape the critical front and back wooden panels of the instrument’s resonance box.
This is to ensure the violin produces the richest and most beautiful tones.
Crucially, no one has ever made a violin with sand filled panels! 😉
A few year or two ago, I watched a documentary film on NetFlix called "Highly Strung". The film is about an Australian chamber orchestra, four almost priceless Guadagnini instruments, and the bizzare personality clashes, political machinations, and personal obsessions that follow.
But there was a sub-story about an Italian luthier who was charged with making a duplicate of one of the Guadagninis - a cello. One of the scenes in the film shows the luthier's work table, with an audio frequency generator on it, a loudspeaker facing up on the table, and either the cellos top-plate or bottom-plate positioned above the speaker.
Evidently this luthier too had figured out that using a speaker and oscillator produces steadier and more repeatable results than a violin bow or "tap test". 🙂
LOL! Yamaha makes a "silent violin" (in fact, a whole series of "silent" band instruments) for players who cannot play normal-loudness instruments in their apartments surrounded by philistines. 🙂
Here's a link: SILENT™ SERIES - Strings - Musical Instruments - Products - Yamaha - Canada - English
-Gnobuddy
I have an idea: can we use the big peak in an open-baffle's frequency response to take a small midrange speaker, scale the baffle down to the right (small) size, and so give the speaker the peaky midrange response appropriate to a guitar speaker?
The midrange would then be married to a suitably larger woofer, and some sort of passive low-pass filter added to filter out the treble above the midrange peak caused by the baffle.
If it works, this might solve some of the severe treble dispersion problems that go with big 12" and 10" guitar speakers, while retaining the mechanical EQ curve they produce, which is part of good guitar sound.
-Gnobuddy
The midrange would then be married to a suitably larger woofer, and some sort of passive low-pass filter added to filter out the treble above the midrange peak caused by the baffle.
If it works, this might solve some of the severe treble dispersion problems that go with big 12" and 10" guitar speakers, while retaining the mechanical EQ curve they produce, which is part of good guitar sound.
-Gnobuddy
Attachments
Actually some of the large driver beaming is put to good use, being aimed at the back of the guitarist's legs. The tone may sound fine at ear level but harsh when the direct highs are heard. Sometimes the off-axis sound is preferable.
On Chladni patterns, I used tea leaves, less power needed to get the lines to form.
On Chladni patterns, I used tea leaves, less power needed to get the lines to form.
Invariably, in my experience - but this is precisely because dispersion is so poor, so that the on-axis sound has to be unbearably bright to make the off-axis sound bearable, no?
If there was better dispersion from the speaker, the amp could be less bright, and you'd get better sound at more listening positions, including on-axis. Just like the guys with their overpriced Kempers and Axe-Fxs using flat-response full range speaker cabinets.
Come to think of it, I've never seen a measured off-axis frequency response for a guitar speaker; I wonder if that enormous on-axis midrange peak mostly disappears off-axis, and the only reason for the on-axis peak is to try and get at least some treble off-axis?
-Gnobuddy
I thought about the beaming reflecting off the walls and becoming one with the sound (grasshopper) while writing that. It is just one of those things, in some situations it may apply, in others not. Even the high bump is bearable if the amp's tone controls adjust for it. I have two favorite speakers, a 10" out of a console stereo, and a 12" Yamaha organ speaker, both not guitar speakers originally. Would I like a Celestion Blue? Quite possibly. In the end do whatever gets the sound that you like.
I have a half-done project that's been lingering far too long: turning a pair of $3.99 Sony bookshelf speakers found at the thrift store into a small portable P.A. system for two vocal microphones and one acoustic or electric guitar. The kind of thing you can use for quick and easy solo or duo singing.
The speakers were originally part of one of those mini-component Hi Fi systems that were popular about twenty-five years ago.
One of the things I found out quickly was that feeding an electric guitar signal into this speaker sounds very dull and lacking in treble.
In my experience, Sony speakers tend to have a very sucked-out midrange, exactly the opposite of what guitar speakers have, and I think this is compounding my problems.
I'm in the process of building a preamp that will include filters that emulate a fairly typical guitar speaker frequency response. Hopefully that will make things sound better.
Just the filter by itself is more complex than a typical tube amp, as it includes an active treble boost stage (to provide the slow treble rise to 3.5kHz), an active third-order low pass filter (to drop response rapidly above 3.5 kHz), and an active second order high-pass filter (to cut out undesirable deep woofy bass from electric or plugged-in acoustic guitars.)
It would be nice if simply mounting a speaker to a too-small open baffle automatically produced most of the same features in the frequency response - the slow rise, the peak, and the rapid fall-off above it!
-Gnobuddy
Last week I came across a tweed case that would make a cool little busking speaker. I finally decided against it because I have enough stuff. It was heavy and when I opened it up inside was a typewriter. I probably should have asked how much they wanted, but my life is no worse walking away.