gedlee said:
Point taken. The inverted rear wave is delayed on its path around the OB, and will find its way to the front no matter what you do. It's unrealistic to hope for anything like 30+ dB of absorption of the rear wave, since no absorbing material is that effective, and there is the additional risk of mass-loading the cone of the driver if the absorbing material is physically too close to the driver.
Since the rear wave is inevitably going to get around to the front - and will be diffracted around an edge as it does so - it makes sense to manage the delayed energy, rather than let it all arrive at once. I'm all in favor of time-dispersing it, spreading out the energy in the time domain as smoothly as possible (with a minimum of ripples). Felt-covered slots or resistive meshes seem like a good starting point - to be determined by measurement, of course.
Thanks for the interesting cross-cultural info in the other thread. Having grown up in Japan (went to Canadian Academy in the Kobe/Osaka area) and Hong Kong (King George the Fifth high school), I'm never too sure just how much Asian, Buddhist, and Taoist attitudes color my own. To some degree, at least.
The recent move to Denver has made me aware of how different the Pacific Coast is from the rest of the USA. Until the move two years ago, all of my time in the USA was in Los Angeles, the Bay Area, Portland (PSU grad), and Seattle, which are long-established port cities with a strong Asian orientation. Denver, by contrast, is more of a Midwestern city, and looks more towards the East Coast (lot of New Yorkers here, for example).
Graham,
Thank you for your comments. Who would have thought that oval speakers could run to 25 Hz? I wonder if any information much below 40Hz will actually be audible from the TL with the limited X Max of the Beta 8's?
Could you elaborate a little bit on the differing impedances the two Beta 8 drivers will be encountering. Will they be robbing one another of energy due to greater efficiency at different frequencies when hooked up in series?
Michael,
That is an interesting set of curves. I assume that it has to do with the back wave progressively canceling signal from the front of the baffle as the microphone point moves laterally? Is this effect aggravated by the presence of a baffle? I ask only because the recently treated Lowther PM6A's for Lowther America were to all intents and purposes perfectly omni directional, no portion of canceled sound detectable from 1 inch off of the frame edge to 10 feet away.
The sound, when standing behind the drivers, mounted on speaker stands with the magnet held to keep the front face perpendicular to the floor and at the front edge of the stand, was what you would find at the rear of a stage, during a performance, to a startling degree. As you moved adjacent to the frame, the front wave just painted itself onto that back side sound. Due to the way the Lowthers respond to the EnABL treatment, the front wave was pretty close to flat in frequency across the 180 degree front polar angle.
I will be interested in seeing if treating the baffle of an OB has the same effect that treating closed boxes and the entirely open, baffle less Lowther's, has.
Thank you both for your time spent on my project. Your thoughts and cautions are valuable to me.
Bud
Thank you for your comments. Who would have thought that oval speakers could run to 25 Hz? I wonder if any information much below 40Hz will actually be audible from the TL with the limited X Max of the Beta 8's?
Could you elaborate a little bit on the differing impedances the two Beta 8 drivers will be encountering. Will they be robbing one another of energy due to greater efficiency at different frequencies when hooked up in series?
Michael,
That is an interesting set of curves. I assume that it has to do with the back wave progressively canceling signal from the front of the baffle as the microphone point moves laterally? Is this effect aggravated by the presence of a baffle? I ask only because the recently treated Lowther PM6A's for Lowther America were to all intents and purposes perfectly omni directional, no portion of canceled sound detectable from 1 inch off of the frame edge to 10 feet away.
The sound, when standing behind the drivers, mounted on speaker stands with the magnet held to keep the front face perpendicular to the floor and at the front edge of the stand, was what you would find at the rear of a stage, during a performance, to a startling degree. As you moved adjacent to the frame, the front wave just painted itself onto that back side sound. Due to the way the Lowthers respond to the EnABL treatment, the front wave was pretty close to flat in frequency across the 180 degree front polar angle.
I will be interested in seeing if treating the baffle of an OB has the same effect that treating closed boxes and the entirely open, baffle less Lowther's, has.
Thank you both for your time spent on my project. Your thoughts and cautions are valuable to me.
Bud
Hmm ... I was in Hong Kong from 1961 through 1966, during the height of the Red Guard madness. The population of HK increased by about a million while I was there, which is pretty amazing for a city about the size of Manhattan (most of the New Territories were rural back then).
Even back then, HK was a first-world city, at the level of development of Japan, and far ahead of the rest of Asia. We saw first-run 70mm movies only a week or so after the Hollywood premiere, and there were lots of English-language theaters. Little did I realize when I saw throngs doing the mysterious Tai Chi exercises in the public parks that it would catch on in the West decades later.
I last saw Hong Kong during the summer of 1971, so it looks very different now. I was surprised to find that King George the Fifth is still around and has its own website, and the address looks like the same place close to the old Kai Tak airport in Kowloon.
It was interesting experiencing the Vietnam War from such a close vantage point. I routinely heard stories from servicemen on visiting US Navy ships that were suppressed in the US press - and didn't come out until a decade later. As a teen-ager, I was aware that the CIA influenced US opinion by planting stories in the foreign press - which is perfectly legal for the CIA to do - and then waiting for the US press to pick up on the planted story. Still technical legal - barely. If it was common practice back then, no reason to believe anything's changed some forty years later.
I heard enough about the CIA shenanigans in various countries that I wonder today about whether my father, who worked as Head of the Economic Section in the US Consulate, wasn't also a CIA analyst. My parents did meet in the OSS during WWII, which of course was the predecessor to the CIA. It was my father who showed me how to read articles in newsmagazines, to look for the portions that should be there and are instead omitted, as a sign of what the powers-that-be want to keep in the shadows. With enough skill in a given technical area, even technical publications in a tightly-controlled Communist country can be carefully deciphered to see what areas of research are classified.
I suspect my inherent skepticism about the "official story" may have come from that period, and very likely from the analyst techniques my father taught me. At the time of the Church Committee hearings in the mid-Seventies, I was already aware of the CIA-sponsored overthrow of Mossadegh in Persia, Allende in Chile, the death of Lumumba in a mysterious airplane crash, and the planting of CIA assets in the Los Angeles Times, the Washington Post, the New York Times, and Time, Life and Reader's Digest magazines. I had known that ten years before the rest of the US public, as colorful stories told 'round the dinner table at our house on Mt. Cameron Rd near the Peak on Hong Kong Island.
All in all, an interesting time. My parents passed on ten years ago, and we never discussed the CIA after they retired in Berkeley, California. One real hint about the CIA was that my dad made a pitch for me to join the CIA - just once, then let it drop. I found out from my sister he made the same pitch to her. Yet his offical position was an officer for the US Foreign Service, and all of the family carried diplomatic passports - in fact, we were well-versed in the emergency evacuation plans if the Communists suddenly came over the nearly-indefensible Hong Kong border.
I was appalled to how badly botched the 1975 Vietnam evacuation was - the whole thing was in gross violation of standard emergency-evacuation protocols for US Govt staff and families, nothing at all like the plans that were in place when I was in Hong Kong with the very real risk of Communist invasion. Mao at that stage was not the most rational actor, and we were all concerned he would do it just to show he could.
Even back then, HK was a first-world city, at the level of development of Japan, and far ahead of the rest of Asia. We saw first-run 70mm movies only a week or so after the Hollywood premiere, and there were lots of English-language theaters. Little did I realize when I saw throngs doing the mysterious Tai Chi exercises in the public parks that it would catch on in the West decades later.
I last saw Hong Kong during the summer of 1971, so it looks very different now. I was surprised to find that King George the Fifth is still around and has its own website, and the address looks like the same place close to the old Kai Tak airport in Kowloon.
It was interesting experiencing the Vietnam War from such a close vantage point. I routinely heard stories from servicemen on visiting US Navy ships that were suppressed in the US press - and didn't come out until a decade later. As a teen-ager, I was aware that the CIA influenced US opinion by planting stories in the foreign press - which is perfectly legal for the CIA to do - and then waiting for the US press to pick up on the planted story. Still technical legal - barely. If it was common practice back then, no reason to believe anything's changed some forty years later.
I heard enough about the CIA shenanigans in various countries that I wonder today about whether my father, who worked as Head of the Economic Section in the US Consulate, wasn't also a CIA analyst. My parents did meet in the OSS during WWII, which of course was the predecessor to the CIA. It was my father who showed me how to read articles in newsmagazines, to look for the portions that should be there and are instead omitted, as a sign of what the powers-that-be want to keep in the shadows. With enough skill in a given technical area, even technical publications in a tightly-controlled Communist country can be carefully deciphered to see what areas of research are classified.
I suspect my inherent skepticism about the "official story" may have come from that period, and very likely from the analyst techniques my father taught me. At the time of the Church Committee hearings in the mid-Seventies, I was already aware of the CIA-sponsored overthrow of Mossadegh in Persia, Allende in Chile, the death of Lumumba in a mysterious airplane crash, and the planting of CIA assets in the Los Angeles Times, the Washington Post, the New York Times, and Time, Life and Reader's Digest magazines. I had known that ten years before the rest of the US public, as colorful stories told 'round the dinner table at our house on Mt. Cameron Rd near the Peak on Hong Kong Island.
All in all, an interesting time. My parents passed on ten years ago, and we never discussed the CIA after they retired in Berkeley, California. One real hint about the CIA was that my dad made a pitch for me to join the CIA - just once, then let it drop. I found out from my sister he made the same pitch to her. Yet his offical position was an officer for the US Foreign Service, and all of the family carried diplomatic passports - in fact, we were well-versed in the emergency evacuation plans if the Communists suddenly came over the nearly-indefensible Hong Kong border.
I was appalled to how badly botched the 1975 Vietnam evacuation was - the whole thing was in gross violation of standard emergency-evacuation protocols for US Govt staff and families, nothing at all like the plans that were in place when I was in Hong Kong with the very real risk of Communist invasion. Mao at that stage was not the most rational actor, and we were all concerned he would do it just to show he could.
Lynn
A very interesting story. From my knowledge of history (which is my passion in literature) virtually anyone who was in the OSS during the war who worked in Foreign countries was involved in intelligence. As the war ended there simply were not enough "intelligence" people for the need and everyone in OSS was approached. the fact that your father did not actually mention this is very indicative of the likelyhood. And Hong Kong in the 60's!! What better place to be for some evesdropping on a critical country to the US.
I am not a big fan of the CIA, but on the other hand I cannot see how we cannot be without an intelligence capability. To think that the rest of the world is going to be fair, decent, honest and above board is simply ridiculous. To be that way ourselfes is simply hypocritical. The answer has to be somewhere in the more rational middle.
I've been to Cameron Road - you couldn't afford to live there now. I am going to Hong Kong in a couple of weeks. Too bad you have not been back - it is one of my favorite places. I really do love Asia. I was attracted to Lidia because she was Asian. I have always been fixated on any from the far east.
A very interesting story. From my knowledge of history (which is my passion in literature) virtually anyone who was in the OSS during the war who worked in Foreign countries was involved in intelligence. As the war ended there simply were not enough "intelligence" people for the need and everyone in OSS was approached. the fact that your father did not actually mention this is very indicative of the likelyhood. And Hong Kong in the 60's!! What better place to be for some evesdropping on a critical country to the US.
I am not a big fan of the CIA, but on the other hand I cannot see how we cannot be without an intelligence capability. To think that the rest of the world is going to be fair, decent, honest and above board is simply ridiculous. To be that way ourselfes is simply hypocritical. The answer has to be somewhere in the more rational middle.
I've been to Cameron Road - you couldn't afford to live there now. I am going to Hong Kong in a couple of weeks. Too bad you have not been back - it is one of my favorite places. I really do love Asia. I was attracted to Lidia because she was Asian. I have always been fixated on any from the far east.
It's taken me decades to realize to realize I grew up in a family of secrets, and how this must have affected my world-view.
My father used to take "business trips" about once a month, would be gone for two to three days, and would pick up souvenirs from Kuala Lumpur, Manila, Singapore, and Djakarta. It was the unwinding of the Valerie Plame case that was the real eye-opener. I didn't realize that the standard cover for most CIA agents was the diplomatic corps, for the very simple reason that a diplomatic passport is an automatic get-out-of-jail card.
I knew as a teenager the diplomatic passport was never to be abused - if we did any teenager capers, the local police might arrest us, but then we'd have to be immediately released, and my dad could lose his job after being recalled back to the USA in disgrace. This was quite forcefully drummed into me and my sister. Thus, we toed to the line as we grew up in HK.
The Valerie Plame case also explained deep cover - the most dangerous of all, since there's no diplomatic passport, and most countries do dreadful things to spies when they catch them. NOC work is usually conducted under cover of a high-profile, well-connected businessman, with the explicit permission of the top officers of the company.
What I didn't say in my last posting was my father left the Foreign Service under a cloud, not getting promoted in a timely way (he was due for an Ambassador position, and its up-or-out in the Foreign Service). So he ended up in a very low-status position in the US Agency for International Development (USAID), and suddenly gets a call out of the blue to work for Marine Midland Bank, which was a leading business bank headquartered in New York City.
For the first time in his life, he's wearing expensive suits, gets six months of training in Manhattan, and gets sent back to Hong Kong from 1970-72. He's once again mixing with the movers and shakers, going to all the cocktail parties, and meeting the same people as before (when he was head of the Economic Section of the Consulate). We didn't get the deluxe house on Mt. Cameron Rd (HK only had 800 houses when we there, so a Hong Kong house was a big deal) but instead had a full-size flat in the Mid-Levels. By then, I was going to college in Los Angeles, so was only able to visit for the summer, and say "HI!" to my old friends at KGV.
The Valerie Plame description of how Non-Official Cover (NOC) works certainly opened my eyes. Let's see - from OSS to Foreign Service (Ecuador, Algeria, Thailand, Japan, and Hong Hong) to USAID to becoming a banker that makes multi-million-dollar loans to Asian businessmen. I didn't think deeply about the call-out-the-blue that rescued him from the steel desk and windowless room at USAID, but it looks a little different now. He could well have been NOC in his last years before he retired in the early Seventies. This was during the time of the Nixon "Opening To China", with a lot of quiet negotiations going on behind the scenes.
I've heard from other kids whose families were CIA or Military Intelligence that the technique of looking for gaps in the narrative is the first thing taught at intelligence school - at the time, I thought every smart teenage kid thought that way. As it was, it came in handy during my years doing technical writing, since I could tell when engineers, particularly software engineers, were trying to be evasive. I'd zero in on just the area where they were being squirrelly, and ask just EXACTLY what they meant by procedure XYZ.
Looking at the broader picture, I can see how the intelligence analyst's way of looking at the world leads to looking for agendas whenever there's a distortion in the narrative. It's a good way of deconstructing marketing and political literature, as well as examining the larger reasons why some technologies fail and some succeed - the simple question, Who Benefits?
My father used to take "business trips" about once a month, would be gone for two to three days, and would pick up souvenirs from Kuala Lumpur, Manila, Singapore, and Djakarta. It was the unwinding of the Valerie Plame case that was the real eye-opener. I didn't realize that the standard cover for most CIA agents was the diplomatic corps, for the very simple reason that a diplomatic passport is an automatic get-out-of-jail card.
I knew as a teenager the diplomatic passport was never to be abused - if we did any teenager capers, the local police might arrest us, but then we'd have to be immediately released, and my dad could lose his job after being recalled back to the USA in disgrace. This was quite forcefully drummed into me and my sister. Thus, we toed to the line as we grew up in HK.
The Valerie Plame case also explained deep cover - the most dangerous of all, since there's no diplomatic passport, and most countries do dreadful things to spies when they catch them. NOC work is usually conducted under cover of a high-profile, well-connected businessman, with the explicit permission of the top officers of the company.
What I didn't say in my last posting was my father left the Foreign Service under a cloud, not getting promoted in a timely way (he was due for an Ambassador position, and its up-or-out in the Foreign Service). So he ended up in a very low-status position in the US Agency for International Development (USAID), and suddenly gets a call out of the blue to work for Marine Midland Bank, which was a leading business bank headquartered in New York City.
For the first time in his life, he's wearing expensive suits, gets six months of training in Manhattan, and gets sent back to Hong Kong from 1970-72. He's once again mixing with the movers and shakers, going to all the cocktail parties, and meeting the same people as before (when he was head of the Economic Section of the Consulate). We didn't get the deluxe house on Mt. Cameron Rd (HK only had 800 houses when we there, so a Hong Kong house was a big deal) but instead had a full-size flat in the Mid-Levels. By then, I was going to college in Los Angeles, so was only able to visit for the summer, and say "HI!" to my old friends at KGV.
The Valerie Plame description of how Non-Official Cover (NOC) works certainly opened my eyes. Let's see - from OSS to Foreign Service (Ecuador, Algeria, Thailand, Japan, and Hong Hong) to USAID to becoming a banker that makes multi-million-dollar loans to Asian businessmen. I didn't think deeply about the call-out-the-blue that rescued him from the steel desk and windowless room at USAID, but it looks a little different now. He could well have been NOC in his last years before he retired in the early Seventies. This was during the time of the Nixon "Opening To China", with a lot of quiet negotiations going on behind the scenes.
I've heard from other kids whose families were CIA or Military Intelligence that the technique of looking for gaps in the narrative is the first thing taught at intelligence school - at the time, I thought every smart teenage kid thought that way. As it was, it came in handy during my years doing technical writing, since I could tell when engineers, particularly software engineers, were trying to be evasive. I'd zero in on just the area where they were being squirrelly, and ask just EXACTLY what they meant by procedure XYZ.
Looking at the broader picture, I can see how the intelligence analyst's way of looking at the world leads to looking for agendas whenever there's a distortion in the narrative. It's a good way of deconstructing marketing and political literature, as well as examining the larger reasons why some technologies fail and some succeed - the simple question, Who Benefits?
Hi Bud,
Your FR Beta will have a single Fs related impedance peak; your TL Beta a broadly damped characteristic tending towards a spaced double peak with a little line damping. As you say;- in series one will rob the other over different frequencies and the amplifier will be unable to directly drive / control either cone individually.
It is line length and output which extends the response below Fs, thus making good use of a small driver, but the effects of rear of cone line pressure variations remain audible through the line driver cone and these can 'colour' (UK) forward output compared to the plain baffled version. This is why I use my line driver as the bipole rear to mask that upper bass / low mid colouration.
Actually this is why I am following Lynn's thread, to see a design which will not be similarly affected by any cabinet induced reflections / pressure / delay effects etc.
Cheers ......... Graham
Your FR Beta will have a single Fs related impedance peak; your TL Beta a broadly damped characteristic tending towards a spaced double peak with a little line damping. As you say;- in series one will rob the other over different frequencies and the amplifier will be unable to directly drive / control either cone individually.
It is line length and output which extends the response below Fs, thus making good use of a small driver, but the effects of rear of cone line pressure variations remain audible through the line driver cone and these can 'colour' (UK) forward output compared to the plain baffled version. This is why I use my line driver as the bipole rear to mask that upper bass / low mid colouration.
Actually this is why I am following Lynn's thread, to see a design which will not be similarly affected by any cabinet induced reflections / pressure / delay effects etc.
Cheers ......... Graham
Graham Maynard said:
It's really weird how Dr. Geddes and I are travelling on almost-parallel tracks. Spooky.
Anyway, returning to the world of loudspeakers, I think it's important to focus on mechanisms that create reflections, diffraction, and standing waves. The problem with any kind of box - bass horn, vented, resistive-vent, transmission-line, etc. - is that there are many, many reflections inside the box, and that damping materials don't absorb all that well at low frequencies. Most bass boxes in fact rely on the crossover to dump the response before the modes get too annoying and intrusive.
The box modes are in the awkward region of 200~800 Hz, where the driver itself is actually quite well-behaved (with the exception of spider modes). This is the center-of-energy of the spectrum, and resonances in this region have a substantial effect on voice colorations.
But the crossover isn't going to help that much - the higher the slope, the more problematic phase distortion is going to be, so you're trading off box coloration suppression vs the phase distortion of the crossover. I'm not one of those absolute-phase absolutists, but I do think 24 dB/octave or higher-slope crossovers in the 200~800 Hz region need to be treated with a bit of caution. If phase distortion is audible anywhere, it's audible in this region.
This, to me, is the real merit of the OB design - it can clean up the 200~800 Hz region, letting you hear the driver as it really is without those annoying high-Q box modes. Yes, diffraction around the edge of the OB needs to be accounted for, but this is a one-shot error, not a long-term standing wave that is only partially alleviated by damping materials.
But - the desire for deep bass can throw away all this goodness, leaving you in the worst-of-all-worlds scenario of dipole excursion requirements and increased emissive area that dipoles require, while leaving behind a residue of box coloration from the purported "sub" woofer. The whole point of putting up with all the downsides of OB design is getting rid of box modes.
So - the question is, how to pick up the bass region where the OB is running out of excursion without a major penalty in box coloration getting re-introduced? That's why I'm advocating something as unfashionable as deliberately small closed-boxes.
I know it looks ugly, linking together a latter-day AR-1W woofer to the wonderfulness of OB's. We all know where that leads, the murky sound and disastrous system-integration of electrostats yoked to slow-sounding paper-cone woofers in little closed boxes. I agree, that sounds terrible.
The trick is a low-distortion closed-box woofer in a small, very rigid, multi-partition bulkhead-construction box. Trust me, the RELs work very well with electrostats - the secret is the monitor-grade ATC woofer. The Rythmik just takes this further, using servo-feedback and fairly exotic woofer.
What I don't like about closed-box systems is a zero in the response around 1 Hz or so. The LF zero is caused by small box leaks, and these are significant enough that test-boxes must correct for the loss in order to measure compliance accurately. I don't know if the servo system compensates for this, but I'm guessing it does, since the frequency response is directly synthesized by the feedback module.
Anyway, in terms of BudP's dipole, I'd suggest the twin drivers work in parallel (not series), and the driver that's in the TQWT, transmission-line, or bass-horn has a sharp-cut low-pass filter no higher than 120 Hz. If you have the courage to hear the awful truth about your bass box, listen to the thing full-range, with no crossover at all, and no HF radiator to mask what it's doing.
Graham & Lynn,
So it appears that if I choose to use two different lengths of 4" plastic pipe I can average out the twin peaks with two more and perhaps swamp most of that back emf from the TL driver.
The "box" is going to be fabricated from some pretty smooth components, primarily split plastic tubes, rejoined in an as yet undetermined small chamber behind the driver, with four exit holes and automotive carpet underlayment filling the half tubes up to a flat surface. Perhaps, as that material seems to work by trapping the energy and dissipating it through making it vibrate millions of interlocked, kinked fibers of differing diameters and lengths. You certainly need less of it to damp a box than you need of any other material I have used.
The pipes themselves will not be straight, will have open weave mesh glued into them to stabilize the damping material, which may well also be the carpet underlayment and will have very smooth surfaces.
We shall see if any of this thought experiment works out. At least the cost will be nominal and the parts easily disassembled when my wife discovers drain pipe lurking in the living room..... Maybe I can hide the straight bits under faux woodgrain sticky backed vinyl for an even more profound response.
Bud
So it appears that if I choose to use two different lengths of 4" plastic pipe I can average out the twin peaks with two more and perhaps swamp most of that back emf from the TL driver.
The "box" is going to be fabricated from some pretty smooth components, primarily split plastic tubes, rejoined in an as yet undetermined small chamber behind the driver, with four exit holes and automotive carpet underlayment filling the half tubes up to a flat surface. Perhaps, as that material seems to work by trapping the energy and dissipating it through making it vibrate millions of interlocked, kinked fibers of differing diameters and lengths. You certainly need less of it to damp a box than you need of any other material I have used.
The pipes themselves will not be straight, will have open weave mesh glued into them to stabilize the damping material, which may well also be the carpet underlayment and will have very smooth surfaces.
We shall see if any of this thought experiment works out. At least the cost will be nominal and the parts easily disassembled when my wife discovers drain pipe lurking in the living room..... Maybe I can hide the straight bits under faux woodgrain sticky backed vinyl for an even more profound response.
Bud
Karlson Coupler
Hi Bud:
If you want to consider different length pipes to distribute the bass response, you may want to consider the Karlson Coupler modified for a tube. Interesting way to avoid a single, large node in the bass response.
http://www.silvercore.de/index.php?id=35,79,0,0,1,0
Hi Bud:
If you want to consider different length pipes to distribute the bass response, you may want to consider the Karlson Coupler modified for a tube. Interesting way to avoid a single, large node in the bass response.
http://www.silvercore.de/index.php?id=35,79,0,0,1,0
Hi
BudP, well I am coming more from the practical side – doing measurements or simulations, listening to the OB experts here, asking questions and trying to make up my mind – there are passionate brilliant thinkers here that may explain MUCH better.
But to give it a try – there is ALWAYS both with OB – the plain interference of the front and the back wave ( comb filter effect ) AND the additional interference with the "second sources" created at any discontinuity in a surface the sound wave travels along especially at the edge of the baffle ( JohnK put already great light on that ).
Taking this together, the baffle gets more and more invisible when moving the mic more and more off axis right into the baffle plain, except for the delayed "second sources". These "second sources" created at the baffle edge don't radiate into the baffle plain IF the edge is symmetrically as they then ( ONLY ! ) form a dipole with its axis aligned with the speaker with zero SPL at 90 deg off axis.
An other way to reduce the interference of the edge was discussed earlier with the zero thickness baffle edge – which revealed that the " second sources " in fact HELP to smooth FR.
An other way to approach the interference of that " second sources " is what Earl does with his OS wave guides. Basically replacing ( or at least altering ) the " second sources " at the baffle edge ( not seen by the FRONT sound wave due to the WG ) by the second sources at the mouth of the WG.
Bottom line :
The " presence of a baffle " does have a multitude of effects depending on the point of view.
---------------
Your experience of almost flat FR with the EnABLEed Lowther - even at 90 deg off axis if I understood right - is ( almost ) beyond my understanding.
With the " entirely open, baffle less Lowther " you SHOULD have got a FR change roughly like below (on-axis reference, 30-45-60 deg off axis)
Maybe the overall sound image including all the room reflections was that superb / convincing that the speaker gets virtually invisible / absent – even when listening very close to it.
To some degree years ago I got a comparable effect from my vintage SONAB speakers having had a full range speaker roughly the same size than the Lowther in a BR box, firing straight to the ceiling.
You literally could swim in an ocean of sound (and yes, they were Alnico IIRC).
One interesting design detail not found on more modern loudspeakers was that SONAB used damping material all over the rear side of the speaker pressed against the basket
-----------------
Lynn, sharing your background here is at least as thrilling as sharing your points of view to the audio topic !
Greetings
Michael
BudP, well I am coming more from the practical side – doing measurements or simulations, listening to the OB experts here, asking questions and trying to make up my mind – there are passionate brilliant thinkers here that may explain MUCH better.
But to give it a try – there is ALWAYS both with OB – the plain interference of the front and the back wave ( comb filter effect ) AND the additional interference with the "second sources" created at any discontinuity in a surface the sound wave travels along especially at the edge of the baffle ( JohnK put already great light on that ).
Taking this together, the baffle gets more and more invisible when moving the mic more and more off axis right into the baffle plain, except for the delayed "second sources". These "second sources" created at the baffle edge don't radiate into the baffle plain IF the edge is symmetrically as they then ( ONLY ! ) form a dipole with its axis aligned with the speaker with zero SPL at 90 deg off axis.
An other way to reduce the interference of the edge was discussed earlier with the zero thickness baffle edge – which revealed that the " second sources " in fact HELP to smooth FR.
An other way to approach the interference of that " second sources " is what Earl does with his OS wave guides. Basically replacing ( or at least altering ) the " second sources " at the baffle edge ( not seen by the FRONT sound wave due to the WG ) by the second sources at the mouth of the WG.
Bottom line :
The " presence of a baffle " does have a multitude of effects depending on the point of view.
---------------
Your experience of almost flat FR with the EnABLEed Lowther - even at 90 deg off axis if I understood right - is ( almost ) beyond my understanding.
With the " entirely open, baffle less Lowther " you SHOULD have got a FR change roughly like below (on-axis reference, 30-45-60 deg off axis)
An externally hosted image should be here but it was not working when we last tested it.
Maybe the overall sound image including all the room reflections was that superb / convincing that the speaker gets virtually invisible / absent – even when listening very close to it.
To some degree years ago I got a comparable effect from my vintage SONAB speakers having had a full range speaker roughly the same size than the Lowther in a BR box, firing straight to the ceiling.
You literally could swim in an ocean of sound (and yes, they were Alnico IIRC).
One interesting design detail not found on more modern loudspeakers was that SONAB used damping material all over the rear side of the speaker pressed against the basket
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Lynn, sharing your background here is at least as thrilling as sharing your points of view to the audio topic !
Greetings
Michael
Hi Michael,
I agree. My experience with conventional cone drivers would lead me to expect pretty flat frequency response across the included angle of the cone (a by product of the EnABL process). The treated, and perhaps untreated, Lowthers, I will check on this, have high frequencies firing at almost right angles to the polar axis of the cones.
The sound field at 90 degree off axis does not have quite the color of the sound within the included angle of the main cone, but it is only a matter of degree, rather than any absence. Slightly drier sound sums it up pretty well. Having the EnABL pattern on the outer frame ring does help to drag the front wave to a mid frame meeting with the back wave. Only a slight perturbation in the perceived sound at 90 degrees, likely caused by some very slight lobing of phase, rather than frequency, indicates that you have crossed from back wave into front wave and immediately after that the front wave just paints itself onto the balloon of sound. Really quite intriguing to experience.
You can be certain I was not expecting this unusual behavior, but do intend to utilize it, because the resulting sound is just wonderfully musical and unstrained in character.
Again, thank you for your help and critique!
Bud
I agree. My experience with conventional cone drivers would lead me to expect pretty flat frequency response across the included angle of the cone (a by product of the EnABL process). The treated, and perhaps untreated, Lowthers, I will check on this, have high frequencies firing at almost right angles to the polar axis of the cones.
The sound field at 90 degree off axis does not have quite the color of the sound within the included angle of the main cone, but it is only a matter of degree, rather than any absence. Slightly drier sound sums it up pretty well. Having the EnABL pattern on the outer frame ring does help to drag the front wave to a mid frame meeting with the back wave. Only a slight perturbation in the perceived sound at 90 degrees, likely caused by some very slight lobing of phase, rather than frequency, indicates that you have crossed from back wave into front wave and immediately after that the front wave just paints itself onto the balloon of sound. Really quite intriguing to experience.
You can be certain I was not expecting this unusual behavior, but do intend to utilize it, because the resulting sound is just wonderfully musical and unstrained in character.
Again, thank you for your help and critique!
Bud
Hi , As A very simple englishman.. at a total loss with maths but quite a sensible approach ( in my view of course..)
i would like to ask some silly questions.. about baffles..
i hope you all don't mind me going off track a little
but before hand..
i roughly understand refraction.. the bending of something.. sound in this context
i understand the wave cancelation in a baffle
i understand that in a baffle, cross overs are not always necessary? with suitable drivers of course
I understand basic baffle constuction and design and have read Brigg's books from the fifties in detail.. and i realise that open baffles are nothing new... just coming back into fashion
I am under the impression that.. generally..high gauss drivers work better due to the higher damping (and better cone control).. as do triode amplifiers..
I have heard a few baffles and built quite a few.. and i am just starting to complete another pair
but always work by the suck it and see method.. and a little guess work..
so my questions..
Has anyone achieved that funny 'sound in the head' effect that possible with quad esl57's for example..?
if so how where/ what where the drivers, how where they mounted and baffle type/ shape.. i'm sure it is possible.. I have been close to it... but not there..
i don't really understand the discussion about edge refraction
i assume the goal is to decrease the way the sound cancels back to front ?
i understand the effects of a rough surface on moving air.. the same as golf balls.. the effect of the dimples = less drag i believe? but why would you want that on a baffle edge? or am i missing something.
and would speaker cloth have the same effect?
thanks
steve
i would like to ask some silly questions.. about baffles..
i hope you all don't mind me going off track a little
but before hand..
i roughly understand refraction.. the bending of something.. sound in this context
i understand the wave cancelation in a baffle
i understand that in a baffle, cross overs are not always necessary? with suitable drivers of course
I understand basic baffle constuction and design and have read Brigg's books from the fifties in detail.. and i realise that open baffles are nothing new... just coming back into fashion
I am under the impression that.. generally..high gauss drivers work better due to the higher damping (and better cone control).. as do triode amplifiers..
I have heard a few baffles and built quite a few.. and i am just starting to complete another pair
but always work by the suck it and see method.. and a little guess work..
so my questions..
Has anyone achieved that funny 'sound in the head' effect that possible with quad esl57's for example..?
if so how where/ what where the drivers, how where they mounted and baffle type/ shape.. i'm sure it is possible.. I have been close to it... but not there..
i don't really understand the discussion about edge refraction
i assume the goal is to decrease the way the sound cancels back to front ?
i understand the effects of a rough surface on moving air.. the same as golf balls.. the effect of the dimples = less drag i believe? but why would you want that on a baffle edge? or am i missing something.
and would speaker cloth have the same effect?
thanks
steve
mige0 said:
Yes, and I am working on that web page I indicated I would put up.
Still I think there needs to be some clarification between dipoles and OB speakers. The ture dipole would use the driver response only up to about the first dipole peak with the response eq'ed flat below it. The typical OB speaker tends to push the useful range of the driver/baffle combination much higher in frequency where there is concern over the smoothness of the response.
By the way Bud, I looked at you jet fighter baffle. The one thing I noticed was that the mic position was at like 100 M. I think you need to look at the response at a reasonable listening distance. (in case some one else hasn't mentioned it).
John K and Michael,
Yup, moving that microphone around does make the pretty picture much more bleak. Yet, I do not see anything that surprises me. Sure the 100 meters out was nice, but the response curves here, with all three drivers and also just one at the top, are still smooth, compared to what I expect to see from a closed box anyway. That they have a hump shape works for me around the two lower drivers, as they will be rolled off somewhere around 160 Hz... or maybe a bit higher for the OB Beta 8. Music will tell all here.
When I narrow the neck for the top driver, even more than originally shown, that just smooths the baffle response to that driver, which will be the Lowther, just sitting out in open air.
It will all likely sound like crap when finished, but that is not a draw back, as it will teach me many things in the process and the next experiment will be weirder still. This has always been my path, even when I try to fall off of it and use accepted practices.... sigh. You should hear my output transformers that should not work as well as they do, or the silly electron pools....
Thanks guys, very nice help.
Bud
Yup, moving that microphone around does make the pretty picture much more bleak. Yet, I do not see anything that surprises me. Sure the 100 meters out was nice, but the response curves here, with all three drivers and also just one at the top, are still smooth, compared to what I expect to see from a closed box anyway. That they have a hump shape works for me around the two lower drivers, as they will be rolled off somewhere around 160 Hz... or maybe a bit higher for the OB Beta 8. Music will tell all here.
When I narrow the neck for the top driver, even more than originally shown, that just smooths the baffle response to that driver, which will be the Lowther, just sitting out in open air.
It will all likely sound like crap when finished, but that is not a draw back, as it will teach me many things in the process and the next experiment will be weirder still. This has always been my path, even when I try to fall off of it and use accepted practices.... sigh. You should hear my output transformers that should not work as well as they do, or the silly electron pools....
Thanks guys, very nice help.
Bud
mige0 said:
It's my thread, I figure I can abuse it every now and then, just to keep things interesting.
I certainly grant that intel "services" are necessary, if nothing else to offset the Russian KGB/FSB, Brit MI5/MI6, French Intel, the Israeli Mossad, Saudi overseas operatives, the Pakistani ISI, and many, many others. All of them with dirty hands, and long histories - the Brit secret police go back to the reign of Queen Elizabeth the First!
The real hazard is what happened with the Roman Praetorian guards - who started out guarding the Emperor, had extraordinary extra-legal powers of assassination, imprisonment, and secret operations, and after a few decades started deciding for themselves who was going to be the Emperor. "Who Watches The Watchers?"
The imperial trend I see developing are the kind of tactics that used to be reserved for the Third World - assassinations, mysterious small-plane crashes, rent-a-crowds, rent-a-thugs, media control, and collaboration with narco-mafiosi, neofascist elements of the police and military, local war lords, and the most extreme and violent religious crazies - are now moving to the First World.
I direct your attention to NATO's Secret Army - Operation Gladio, a meticulously researched book that grew from the doctoral thesis of a student at Zurich's renowned ETH University (Einstein's alma mater). As a result of a number of trials in Italy in the Nineties, it was revealed the period of Italy's "Strategy of Tension" - a wave of bombings and assassinations, including Aldo Moro, the Italian Prime Minister, were not carried out by Maoist fringe groups, but neofascist elements of the police and military- and these groups were funded and controlled by NATO as a bulwark against the Italian Communist Party.
More trials in Germany, Holland and other European countries revealed that NATO was operating secret "stay-behind" cells in nearly every European country, had been doing so since the Fifties, and were responsible for decades of seemingly random terrorist attacks - indeed, this was a major reason why DeGaulle expelled NATO from France, when the French secret service realized who was funding the assassination attempts against him.
The techniques described above are common enough in the Third World, but seeing the same methods used in Europe over a thirty-year time span is a different story. Now, I am seeing the same kind of "coincidences" happening in the USA - lone gunman assassinations, former-military snipers carrying out waves of terrorism (just before a critical election), unexpected small-plane crashes in reasonably good weather, revelations of CIA assets at strategic locations in the US media infrastructure, and hidden sponsorship of extreme religious movements.
This is the same kind of thing the CIA has done for decades overseas, going back to OSS "Wild Bill" Donovan freeing a key Mafia figure from Federal Prison and parachuting him into Sicily during WWII, thus disrupting Mussolini's Italy - and also re-establishing the Mafia in Southern Italy, where it remains to this day. More recently, the Pakistani ISI, Saudi intel, and CIA joint sponsorship of the religious-extremist Mujahadeen "Freedom Fighters" in Afghanistan is no secret, nor is it any secret that the opium crop of Afghanistan increased many times after the involvement of the ISI, Saudis, and CIA in the region.
It was Peter Dale Scott who came up with the description of "Deep Politics", a method of looking at the complete political and economic system, one that includes criminal elements as well as the "above-ground" economy. A lot of seemingly random and inexplicable events make more sense when the criminal economic system is included - intelligence services have always worked with the criminal world, so much so that they are indistinguishable from it. It should also be remembered that both the Nazi and Soviet empires would have fallen in months if criminal economic flows had been excluded - the systems were criminal more than they were socialist, communist, or fascist.
The real question is the scale of the criminal economy, and to what extent it lubricates world financial markets with untraceable readily-available cash. I've seen figures that indicate the world trade in illegal drugs is one-quarter of the total world economy - I don't know if the true figure is 1/4, 1/10, or less, but in any case it is a huge figure, and covert intelligence operations are right in the middle of it, as they have been for decades - going right back to Wild Bill Donovan in WWII, and before that, the Opium Wars in China before the turn of the century.
I've personally met more than one US serviceman who's flown an Air America (CIA) airplane that they knew was loaded with heroin from the isolated hill country to supply bases in Saigon during the Vietnam War. I've also met an 18-wheel truck driver who told me that an entire dock in Miami in the mid-Eighties was used for nothing more than cocaine shipments from Latin American to the USA - the police knew about it, the FBI knew about it, the DEA knew about it, and nothing was done. One of the few researchers looking into the alliance-of-convenience between intel, drug-smugglers, and "terrorists" is Daniel Hopsicker. Of all the people in the 9/11 Truth Movement (which is a chaotic mess, by and large), his research looks the most solid.
Hi
Lynn, you don't necessarily have to cut the baffle through out to smear the diffraction effects over time.
You know how silencers for cars or ventilation systems are built ( one way to do it at least ) ?
Basically you expand from a small aperture - the pipe – into a volume with larger diameter and repeat that several times.
There is some not too very complicated math describing the attenuation per stage ( Of course standing waves resonance and others is also involved that makes it more complex in reality ).
Same effect you have in every day life experience, when listening through a door ( = small aperture ) from outside your room ( = bigger width than door ).
If you like to explore that approach WITHOUT lowering the lower frequency augmentation through the baffle, you may try to cut or stamp patterns all over the surface – very much like BudP does it with acrylic paint at the boundaries but maybe more chaotic – but NOT go through to the back side.
You will most likely end up with sort of corrugated plate.
Every time the sound wave reaches a gap a new " second source " is created.
There even might be patterns you would like to make a patent for IF you succeed .
There are loudspeakers with baffles looking a little bit like these golf balls for the very same reason ( from Linn or Naim - I don't remember, would have to search )
Instead you can glue obstacles on the baffle which basically should have the same effect.
Greetings
Michael
Lynn, you don't necessarily have to cut the baffle through out to smear the diffraction effects over time.
You know how silencers for cars or ventilation systems are built ( one way to do it at least ) ?
Basically you expand from a small aperture - the pipe – into a volume with larger diameter and repeat that several times.
There is some not too very complicated math describing the attenuation per stage ( Of course standing waves resonance and others is also involved that makes it more complex in reality ).
Same effect you have in every day life experience, when listening through a door ( = small aperture ) from outside your room ( = bigger width than door ).
If you like to explore that approach WITHOUT lowering the lower frequency augmentation through the baffle, you may try to cut or stamp patterns all over the surface – very much like BudP does it with acrylic paint at the boundaries but maybe more chaotic – but NOT go through to the back side.
You will most likely end up with sort of corrugated plate.
Every time the sound wave reaches a gap a new " second source " is created.
There even might be patterns you would like to make a patent for IF you succeed .
There are loudspeakers with baffles looking a little bit like these golf balls for the very same reason ( from Linn or Naim - I don't remember, would have to search )
Instead you can glue obstacles on the baffle which basically should have the same effect.
Greetings
Michael
Well, I must admit the primary reason I suggested a starburst pattern of slots radiating out from the driver is that it's really easy to cut on a table saw, and would have an interesting appearance. Some asymmetry in the radial spacing of the slots would not only look nice, it would probably slightly improve the sound, as well.