Hi Lynn, I read your comments about handling the back wave in an open baffle. I have been thinking of something like the Auditorim Solovox 23 which has curved wooden guides behind a shallow U frame. I presume to deflect the sound. My thought was that if the curved solid panels were replaced with expanded steel mesh or plastic mesh and rolled fibre maybe 8" - 10" dia was placed on the inner side, tied to the mesh and a third roll placed on the outer side at the centre this should maybe achieve what you and I want with reguards to the rear wave. Do you have any comment on such a layout? Thanks for any time you give this suggestion, jamikl
I think there is considerable misunderstanding about the back wave of a dipole, particularly with regards to the midrange and the impulse. In the figure below I show three traces for amplitude, phase and impulse response. The red trace is what the on axis, unequalized dipole response of an 18 cm midrange driver might look like when mounted on an appropriate baffle. The green traces show what the response would be when this drive is equalized to a bandpass response. The blue trace is the response of a minimum phase band pass filter having the same amplitude response at the equalized dipole midrange. When looking at the red trace, the raw dipole impulse clearly shows the negative pulse form the back wave. But when the response is equalized to the desired bandpass the impulse differs form the ideal only due to the slight deviation form the ideal roll offs. The difference in the phase at low frequency is because the dipole eq is not applied to DC and ultimately the dipole mid rolls off at a rate 6dB greater than the ideal (below 20 Hz).
The point here is that the dipole has a minimum phase response and when equalized to the desired acoustic target using MP EQ the response will be identical to the MP target. Damping the rear wave will only alter the raw dipole response thus requiring different eq. Damping the rear wave will also be a factor in determining how the room reflections from the back wave will build in the reverberant sound field. Such damping can also add coloration to the sound since there will be reflection between the driver back side and the damping material, and there will be a change in the loading of the driver.
An externally hosted image should be here but it was not working when we last tested it.
The point here is that the dipole has a minimum phase response and when equalized to the desired acoustic target using MP EQ the response will be identical to the MP target. Damping the rear wave will only alter the raw dipole response thus requiring different eq. Damping the rear wave will also be a factor in determining how the room reflections from the back wave will build in the reverberant sound field. Such damping can also add coloration to the sound since there will be reflection between the driver back side and the damping material, and there will be a change in the loading of the driver.
Lynn Olson said:
Have you heard a speaker that has constant directivity, at least in the HF range (where that was not accomplished with blatant use of diffraction, which we know is bad)? If not, I would suggest that your assessment of the Quad's is only in comparison to everything else which has this same changing directivity with frequency characteristic. Also, from a quick browse through the net, good directivity characteristics where actually one of the claims for the Quad (although I'm by no means an expert on this).
I'm not saying that CD is necessarily required. I'm saying that smooth directivity is. I'm also not saying this should be pursued at the expense of the other traits you list above. I'm just saying that it will make the end result better, so why not design with that in mind? That's what separates the great designs that do everything well from the pretty good ones that do some things well but not others.
soongsc said:
Yes, exactly. Cabinet heavily dominats driver.
The dimensions / frequencies were chosen to be in a range where more or less ever driver is close to ideal.
These plots were taken when I did some investigation into the behaviour of enclosures.
Tall enclosers - open and closed - enclosures with internal Helmholz resonators – enclosures in the B&W Nautilus stile and some others that were pretty advanced ones.
The aim was to investigate what different styles of chambers by itself add to the sound – meaning - they were without any damping material.
This gives you the most clear idea of what you burden to your dampening measures.
Its pretty revealing to take a closer look at such results – and in the end it lead me to OB
I don't want to repeat what Lynn has pointed out several times – I'm in 100% agreement with his judgements about sound coloring due to dampening materials.
What hasn't been mentioned quite often though – the energy that is stored and released over a relative long time at resonance frequencies has to come from somewhere (thus the hip term "stored energy" for resonancies).
The easy conclusion here is that its not enough for a cure to absorb the "stored energy" when it's released.
There is a deficiency created even more early – at the time of storage - and that deficiency, I claim, is as important to the coloration of the sound as the resonances we observe in CSD.
This is somehow in contrary to JohnK's point of view
At least for the part of the cabinet created resonances.
There might be a border line where the pure speaker model of JohnK is valid and where our speakers loose control over resonating effects that occure later on from reflections (walls inside cabinets, at horn mouth, at OB diffraction edges). I'm not enough of a math type to figure it out myself.
The CSD plots of different XO's form JohnK are very revealing each time I look at them – showing clearly that its not the driver itself but the filter tranfer function that creates decay.
Very hard for me to integrate this into my picture of things - but don't doubt a second.
Michael
John Sheerin said:
Well, I've spent time listening to the Gedlee Summa, which has one of the most tightly-controlled directivity patterns of any loudspeaker, as well as listening to a number of top-line products from Revel and Harmon International, so I'd say, yes, I've auditioned a number of modern controlled-directivity loudspeakers. And of course anyone that goes to a THX movie theatre is listening to modern controlled-directivity JBL theater speakers - Altec multicells are long gone from the scene.
I regret that I don't know of any loudspeakers that "do everything well", at any price point. I'm not trying to be cute or engaging in hyperbole; loudspeakers perform so poorly in so many domains that tradeoffs are inevitable.
Time-decay response is a particularly bad area, and it has taken decades of materials research science to approach the measured performance of late-Fifties electrostats. Distortion performance is nothing to brag about either, being several orders of magnitude worse than amplifiers. In terms of subjective colorations, we are a long long way from zero-coloration loudspeakers - very few speakers ever made can fool you that a real instrument is playing in the room.
How many speakers sound like a concert grand piano, for example, much less a full orchestra? A simple A/B test of a speaker compared to the voice of somebody you know shows how far from reality most speakers are. There's only been a few times in my life where the reproduction approached the real thing - one of them at BBC Research Labs in the mid-Seventies, listening to a quadraphonic test recording made at the Last Night at the Proms.
Reducing subjective coloration on the human voice - surely something that must have been solved a long time ago - is still a very difficult task. You'd think the 300 Hz to 5 kHz voice range would be easy; it isn't, at least in my experience. And this is the comparatively easy part; surmounting the challenges of 20 kHz, 20 Hz, gaining more headroom, and spatial realism is harder still.
If you believe that "speakers that do everything well" exist, I admire your optimism. I've never heard one yet, and I've heard everything from the JBL Ranger-Paragon, to Klipschorns, to the Plasmatronics, to electrostats from Quad ESL57 to ESL63 to Infinity Servo-Static to Beveridge to Sound Labs, various models of exotic drivers from MBL, Manger, Lowther, AER, Feastrex, horns and waveguides from Altec A5 and A7 to eXemplar to Blue Thunder to Summa to JBL to OMA to Classic Audio Reproduction T1's to some of the most strange home-made confections imaginable. All had colorations. All of them were better at some things than others. All of them sounded like loudspeakers.
My personal favorite all-rounders have been BBC monitors, but they have obvious tradeoffs compared to horn systems. And I'd be reluctant to give BBC monitors the title of "doing everything well" - plainly, they don't. Sub-bass - nope, not there. The stunning spatial qualities of true omnis like MBL - nope, not there. The startling HF realism of the Plasmatronics - nope, not there. The gratifying cohesion and all-of-one-piece quality of the Feastrex - nope, not there. The stupendous dynamics of the OMA or the latest CAR T-1 with field-coil magnets - nope, not there.
That's why I think designers are compelled to choose what to optimize, whether they acknowledge it or not. Aiming for this or that parameter forces a tradeoff elsewhere. One thing we have going for us is better materials science and better modeling and measurement techniques - the problem now is what to optimize. If CD is on your list, great! At least we can see what's going on more clearly than in years past, rather than guessing and hoping for the best.
Sorry if the previous post sounded a little cranky - really, that wasn't the intent. But I don't see much reason for complacency, considering the immense distance loudspeaker development still has to cover. I feel we're still at the primitive stage of the art (unlike optics), where very difficult tradeoffs must still be made.
I acknowledge there is a wide spectrum of belief in the audio community - some believe that most, or nearly all, of the major problems have been solved, while others believe we are still in the early stages. I'm in the latter camp, based on the very slow rate of progress in loudspeaker design over the last fifty years. Looking back from the perspective of 1959 (which I remember as a ten-year-old), I thought we'd have gee-whiz technology fifty years later, like no more fossil fuels, diseases worldwide on the decline, cancer finally abolished like smallpox and polio, and fully automated factories cranking out so much abundance the workweek in the advanced nations would be 20 hours or less. Comparing 1909 to 1959, that seemed like a perfectly reasonable straight-line extrapolation, given the rapid technical and social advances of the previous half-century.
Well, it didn't happen.
Loudspeakers have advanced, but very slowly, and the underlying Rice & Kellogg drivers and Wente & Thuras compression drivers are still with us, 80 years later, just like the four, six, and eight-cylinder internal-combustion engines and the gasoline and diesel fossil fuels that propel them. Will there be a sudden "phase change" that will replace all of it, making it go the way of the wind-up Victrola and the coal-fired steam locomotive? I'm sure of it - but I don't know when it will happen.
I acknowledge there is a wide spectrum of belief in the audio community - some believe that most, or nearly all, of the major problems have been solved, while others believe we are still in the early stages. I'm in the latter camp, based on the very slow rate of progress in loudspeaker design over the last fifty years. Looking back from the perspective of 1959 (which I remember as a ten-year-old), I thought we'd have gee-whiz technology fifty years later, like no more fossil fuels, diseases worldwide on the decline, cancer finally abolished like smallpox and polio, and fully automated factories cranking out so much abundance the workweek in the advanced nations would be 20 hours or less. Comparing 1909 to 1959, that seemed like a perfectly reasonable straight-line extrapolation, given the rapid technical and social advances of the previous half-century.
Well, it didn't happen.
Loudspeakers have advanced, but very slowly, and the underlying Rice & Kellogg drivers and Wente & Thuras compression drivers are still with us, 80 years later, just like the four, six, and eight-cylinder internal-combustion engines and the gasoline and diesel fossil fuels that propel them. Will there be a sudden "phase change" that will replace all of it, making it go the way of the wind-up Victrola and the coal-fired steam locomotive? I'm sure of it - but I don't know when it will happen.
Lynn Olson said:
I only occasionally read posts in this thread, but after 200 pages and over 2 years time, is there a design on the horizon? Each time I'm drawn back in when I see posts made by certain participants, the discussion still seems to drift in the direction that drove me away the previous times, seeming to focus on philosophy rather than design. The first post pointed out that the Ariel was about 12 years old. It's now about 14 years old.
Dave
SLR said:
Yes Dave,
I kind of feel the same way. Check in once in a while. See things that are inconsistent or speculation, reversal of direction, or meandering philosophy. The design considerations seem ad hoc, a reversion to the good 'ld days at best; i.e. following the path of the 60's and 70's. It seems more like a nostalgia thread. Sort of like GM vs Tesla. I love the GM muscle cars from that era, but today I'd rather have a Tesla S than a 2010 GM Camaro throw back.
john k... said:
Wasn't that stated as a premise of the thread when it started? I feel Lynn was very clear that this was a project where a lot of ideas would be considered, and that they could be rejected to move in a different direction. That is one of things I like about this thread.
Lynn has stated his creteria and now is trying things to see what will work for him. I like many of the seakers he likes and enjoy following his thought/discovery process.
I am learning a lot from this thread.
If Lynn is in a wheelchair, I wouldn't expect anything soon. But I do like the nice discussion. There is lots of respect for different ideas here without saying which is best, but lots of people express their preferences very clearly. Hope this keeps up.
BTW, seems like Lynn's stock drop prediction was quite in line with what happened.
There is lots of respect for different ideas here without saying which is best, but lots of people express their preferences very clearly. Hope this keeps up.BTW, seems like Lynn's stock drop prediction was quite in line with what happened.
A two or three year design stage, especially given the enormous amount of input from multitudes of others of varying opinions, seems quite reasonable to me.
I expect at least another year of build/test/listen/modify. Course, I don't design speakers, given my limited knowledge. That's why I read, learn, and wait for people like Lynn (or Zaph, Geddes, North Creek, etc) to be kind enough to allow us to reap the end results of their contributions.
Maybe I'm alone, but I suspect Lynn has other things to do in life besides just design a non-profit speaker........
Thanks, Lynn.
I expect at least another year of build/test/listen/modify. Course, I don't design speakers, given my limited knowledge. That's why I read, learn, and wait for people like Lynn (or Zaph, Geddes, North Creek, etc) to be kind enough to allow us to reap the end results of their contributions.
Maybe I'm alone, but I suspect Lynn has other things to do in life besides just design a non-profit speaker........
Thanks, Lynn.
zigzagflux said:
Well, that's certainly true. My primary focus has been the various stages of physical and mental rehabilitation (who knew there would be so many!) and steering our retirement assets through the rough waters of the world economy. The capital-gains tax situation became very complex when I had to make fast market moves last summer and fall. I am still trying to determine if the markets are close to bottom or whether more surprises await. See dshort.com for one of my weather stations.
The completion of the AH425 mated to the GPA Alnico/Tangerine 288 has marked a major milestone in the project, since I was most concerned about the critical and coloration-prone midrange. Measurement data is now coming in from two different builders and looks promising.
The next phase is determining if the hybrid structure between open-baffle and the Gary Pimm quasi-cardioid is feasible, and if it meets the goals of minimization of stored energy. If so, the 414's and 12NDA520's will tried there.
Sorry if anyone was expecting a cookbook project or a series of design tutorials ... plenty of other threads to choose from, so you shouldn't go hungry.
Well I just glad I make my own market decisions. Looking for a bottom is sure to burn you. Look for relative value on the basis of when you need the money. The S&P at 675 is cheap if you have 10 years. Doesn't matter if it goes down another 10% or 20% or even 50%. If the S&P doesn't hit 1500 or more over the next 10 years we all have bigger problems than the market. If you are waiting to figure out if a bottom is in you are sure to miss it.
From now on, I promise that if I post to this thread I will stay on target and only discuss the market.
I apologize for getting off target occasionally and discussing matters related to speakers.
Seriously, I just like to see some progress without all the idle BS.
From now on, I promise that if I post to this thread I will stay on target and only discuss the market.
I apologize for getting off target occasionally and discussing matters related to speakers. Seriously, I just like to see some progress without all the idle BS.
Support for Lynn & this thread
Hi Lynn and friends,
First of all on behalf of the silent masses who read this thread with great interest I would like to thank Lynn for his generosity & patience. He gives us all the benefit of his vast experience and considerable IQ, we then "peer review" his ideas (sometimes amusing always interesting...!) against a wide range of old & new ideas, materials & technology. This is good sound R&D practice, spreading the work load and utilising many brains to help solve our common acoustic problems.
I note with interest that those who like to criticise this approach usually have a commercial interest and are a bit…. insecure! Or are solo DIY enthusiasts who have simply failed in their own attempts to build that elusive beast the perfect loudspeaker.
I share Lynn's view that we are very far away from creating a loudspeaker which when we turn our back on it (or them) convince us that a concert grand piano, drum kit or singer is performing live. But we will make progress.
Who is to say that Lynn or any individual is right or wrong, some or all of the time, we all benefit from openly sharing our ideas good & bad.
I have learned a lot from this thread and one day, time permitting, I hope to be able to contribute some helpful information.
Thanks again to all of you guys and keep the faith… its good fun too!
Derek Wilson
Retired (early!!) speaker designer.
Hi Lynn and friends,
First of all on behalf of the silent masses who read this thread with great interest I would like to thank Lynn for his generosity & patience. He gives us all the benefit of his vast experience and considerable IQ, we then "peer review" his ideas (sometimes amusing always interesting...!) against a wide range of old & new ideas, materials & technology. This is good sound R&D practice, spreading the work load and utilising many brains to help solve our common acoustic problems.
I note with interest that those who like to criticise this approach usually have a commercial interest and are a bit…. insecure! Or are solo DIY enthusiasts who have simply failed in their own attempts to build that elusive beast the perfect loudspeaker.
I share Lynn's view that we are very far away from creating a loudspeaker which when we turn our back on it (or them) convince us that a concert grand piano, drum kit or singer is performing live. But we will make progress.
Who is to say that Lynn or any individual is right or wrong, some or all of the time, we all benefit from openly sharing our ideas good & bad.
I have learned a lot from this thread and one day, time permitting, I hope to be able to contribute some helpful information.
Thanks again to all of you guys and keep the faith… its good fun too!
Derek Wilson
Retired (early!!) speaker designer.