Good luck!
What is missed by many is the fact that the TL action is a given BW, the horn action is a seperate higher BW,this hands off to a baffle action as the frequency increases and finally to the driver.
Its a step process that has to be balanced in energy across the entire FR spectrum.
And yes, its about pressure at a given point of space and time. A sound wave is nothing more than an alternating change in pressure from a positive to a negative as measured from ambient.Throw in some 1/4 wave action (borrow it from Martin,sorry my friend) calculate out the increasing partical effect as the pressure drops along the path and its a basic program.
Fight with the programmer.
Then you have to calculate the pressure flow from a given displacement of a FC as the cone displaces the volume thru a given area(throat) to determine the BW of the horn action.
Fight with the programmer.
Next step is to correct the aspect ratio of the mouth so a spherical wave can be launched. Discover that the correction adds more than a spherical wavefront and has a bit of smoothing of the higher TL actions.
Fight with the programmer.
Develope a whole new approach to thermal loss and frequency response.
Fight with the programmer.
End result, hire a new programmer.
ron
What is missed by many is the fact that the TL action is a given BW, the horn action is a seperate higher BW,this hands off to a baffle action as the frequency increases and finally to the driver.
Its a step process that has to be balanced in energy across the entire FR spectrum.
And yes, its about pressure at a given point of space and time. A sound wave is nothing more than an alternating change in pressure from a positive to a negative as measured from ambient.Throw in some 1/4 wave action (borrow it from Martin,sorry my friend) calculate out the increasing partical effect as the pressure drops along the path and its a basic program.
Fight with the programmer.
Then you have to calculate the pressure flow from a given displacement of a FC as the cone displaces the volume thru a given area(throat) to determine the BW of the horn action.
Fight with the programmer.
Next step is to correct the aspect ratio of the mouth so a spherical wave can be launched. Discover that the correction adds more than a spherical wavefront and has a bit of smoothing of the higher TL actions.
Fight with the programmer.
Develope a whole new approach to thermal loss and frequency response.
Fight with the programmer.
End result, hire a new programmer.
ron
Ron,
That is an excellent summary. I agree many don't have that chain of loadings clear in their own minds, hence poor performing back loaded horn designs.
I'll send you a bill.
Modeling the mouth correctly is the next big step in my simulation tools and I am working on it slowly but surely. I think this will help make the predictions even more accurate. Modeling the impact of mouth aspect ratio, shape, and curvature on acoustic impedance is a key. Then room boundary influences on both acoustic impedance and as reflected sources will be the next big step forward. I am very optimisitic that this can be done in my worksheets.
Never!
The programmer is a great guy, almost as smart as me. 
That is an excellent summary. I agree many don't have that chain of loadings clear in their own minds, hence poor performing back loaded horn designs.
I'll send you a bill.
Modeling the mouth correctly is the next big step in my simulation tools and I am working on it slowly but surely. I think this will help make the predictions even more accurate. Modeling the impact of mouth aspect ratio, shape, and curvature on acoustic impedance is a key. Then room boundary influences on both acoustic impedance and as reflected sources will be the next big step forward. I am very optimisitic that this can be done in my worksheets.
Never!
The programmer is a great guy, almost as smart as me. Then room boundary influences on both acoustic impedance and as reflected sources will be the next big step forward.
This is important in BLHs, despite what i have heard in feedback. The actual volume of a container that has a defined volume has an effect on the applied pressure. Sure the effect falls off as the volume increases, but its still a definable curve.
Reflected sources took me many years to define. As a wave encounters a different medium the energy is reflected/attenuated according to the acoustical impedance mismatch and even the temperature of the different mediums. As the properties of the secondary medium becomes closer to the first the amount of energy absorbed is greater and the amount of energy reflected is less. I attack the question by establishing a reflector as a new source of energy with its own different values and orgin.
Despite what has been produced, its still physics, nothing more, nothing less.
I'll send you a bill.
Put it on my tab.
ron
This is important in BLHs, despite what i have heard in feedback. The actual volume of a container that has a defined volume has an effect on the applied pressure. Sure the effect falls off as the volume increases, but its still a definable curve.
Reflected sources took me many years to define. As a wave encounters a different medium the energy is reflected/attenuated according to the acoustical impedance mismatch and even the temperature of the different mediums. As the properties of the secondary medium becomes closer to the first the amount of energy absorbed is greater and the amount of energy reflected is less. I attack the question by establishing a reflector as a new source of energy with its own different values and orgin.
Despite what has been produced, its still physics, nothing more, nothing less.
I'll send you a bill.
Put it on my tab.
ron
I am feeling wordy(is that a term?)
My studies into thermal dissapation linked with acoustics. The defined transfer of energy from a singular partical packet to another as a heat transfer i defined. The loss in energy over a given distance with a given frequency is clearly definable. Loss in energy for a given frequency is a calculated curve thats definable for a given distance and mass/temperature/Y modlus of a defined medium.
There is a great deal more to design of an electromechanical transducer or even the enclosure than most would think.
As an electromechanical transducer operates there is a transference of mechanical motion to heat (its deeper than that)
as the unit heats it looses efficency. As the VC heats there is added resistance, as the added resistance increases there is a change in Qes which changes the total Qts. As the loading increases there is a change in the Qms which again has to be a calculated factor.
The whole point is to calculate the final effect after the unit has come up to operation parameters and disregard the stated values.
ron
My studies into thermal dissapation linked with acoustics. The defined transfer of energy from a singular partical packet to another as a heat transfer i defined. The loss in energy over a given distance with a given frequency is clearly definable. Loss in energy for a given frequency is a calculated curve thats definable for a given distance and mass/temperature/Y modlus of a defined medium.
There is a great deal more to design of an electromechanical transducer or even the enclosure than most would think.
As an electromechanical transducer operates there is a transference of mechanical motion to heat (its deeper than that)
as the unit heats it looses efficency. As the VC heats there is added resistance, as the added resistance increases there is a change in Qes which changes the total Qts. As the loading increases there is a change in the Qms which again has to be a calculated factor.
The whole point is to calculate the final effect after the unit has come up to operation parameters and disregard the stated values.
ron
MJK said:
I did not intend to use a Lowther driver in an enclosure designed around Fostex drivers. I was only saying I can fail miserably and learn from my experiences with Fostex drivers and still dream about a Lowther driver. Once I will be more comfortable with the BLH designs, I will probably try a design with the Lowther drivers.
ronc said:
I think I will need this one explained in more details.
I agree that there is a lot more to designing BLHs. The chosen design, the drivers, the materials, the way it is assembled, the damping material ... they all have an important factor in the final presentation. Oh and lets not forget the listening room and enclosure placement.
If I cannot get the BLH designs working properly, I will probably join a forum about room acoustics and modify the room around the BLHs
I'll move the walls or something 
and yes, with my head 
Which makes me think of studies I have read about the resonance of different resistors and capacitors in tube amp circuits. I can't remember the source of the info, but it was said that you can have two components, for example resistors, with the same measured value, but the sound produced will be very different. I firmly believe that the choice of materials can make significant difference in the sound reproduction.
Great musical instuments were born from careful selection of woods and varnishs (Stradivarii).
Aha! I wondered if Ron would pop up as well! Good to see you back again Ron -hope work is getting a bit less hectic? Did you get my email re that info. on the steel we were discussing? Hotmail's forced me over to this Windoze Live thing & it's been playing up. I'll have to shift all my things to my frugal-horn email so at least I know it works.
Anyway, I make no pretense at being an expert, but re the TL & horn action question, the basics are roughly like this:
Most domestic horn designs are actually hybrids between horns and QWRs (or TLs if you prefer). If we follow pure horn math for a horn that's good down to, say, 40Hz, you'll end up with a cabinet with a mouth large enough to drive a small car though. See how far you'd get trying to shoe-horn a couple of cabinets that size into your living-room. This can be reduced depending on the radiation-space it's firing into. 1/2 space you can reduce by a factor of 2, 1/4 space by a factor of 4, 1/8 space by a factor of 8. But even using the room reflection-boundary conditions, which allow us to reduce the mouth size, it's usually still too large for most people, so basically, the mouth size is compromised, i.e. reduced in comparison to the ~optimal for the length and flare-rate. The cabinet then basically operates like an expanding QWR at the lowest frequencies, and as the impedence match (remember, that's basically what a horn is) improves, as frequency increases & the mouth size optimises for that frequency, TL action hands over to horn loading.
The reason many domestic horn designs have a somewhat rough response is this compromising of the horn mouth area. We can get the extension desired using TL action, but there are consequences. Due to the impedence mis-match at the mouth in the lower frequencies, you get a supersonic shockwave (standing wave) that's reflected back from the mouth along the horn path. Hence the ripple in the response of most domestic hybrid horns. There are ways of minimising this, & blending the TL action into horn action, & careful design should help reduce it to managable levels. That's where the knowledge of wider physics & of aspects of horn design not covered by the formulas or most textbooks (which don't really account for the compromising of mouth area & the consequences of this) come in. Luckily, you've got Martin, Ron & Greg assisting, & they'll guide you in the right direction. The combined knowledge / expertise there is downright astonishing.
Oh yeah -one quick suggestion from me if I may -I'd advise you avoid the tractrix profile for a bass horn. Tractrix has it's advantages, but IMO it's not at it's best performing LF duties. I'd go for a hypex, or, as the length is probably going to be limited, good old exponential if possible.
Hope that helps a bit
Scott
Anyway, I make no pretense at being an expert, but re the TL & horn action question, the basics are roughly like this:
Most domestic horn designs are actually hybrids between horns and QWRs (or TLs if you prefer). If we follow pure horn math for a horn that's good down to, say, 40Hz, you'll end up with a cabinet with a mouth large enough to drive a small car though. See how far you'd get trying to shoe-horn a couple of cabinets that size into your living-room. This can be reduced depending on the radiation-space it's firing into. 1/2 space you can reduce by a factor of 2, 1/4 space by a factor of 4, 1/8 space by a factor of 8. But even using the room reflection-boundary conditions, which allow us to reduce the mouth size, it's usually still too large for most people, so basically, the mouth size is compromised, i.e. reduced in comparison to the ~optimal for the length and flare-rate. The cabinet then basically operates like an expanding QWR at the lowest frequencies, and as the impedence match (remember, that's basically what a horn is) improves, as frequency increases & the mouth size optimises for that frequency, TL action hands over to horn loading.
The reason many domestic horn designs have a somewhat rough response is this compromising of the horn mouth area. We can get the extension desired using TL action, but there are consequences. Due to the impedence mis-match at the mouth in the lower frequencies, you get a supersonic shockwave (standing wave) that's reflected back from the mouth along the horn path. Hence the ripple in the response of most domestic hybrid horns. There are ways of minimising this, & blending the TL action into horn action, & careful design should help reduce it to managable levels. That's where the knowledge of wider physics & of aspects of horn design not covered by the formulas or most textbooks (which don't really account for the compromising of mouth area & the consequences of this) come in. Luckily, you've got Martin, Ron & Greg assisting, & they'll guide you in the right direction. The combined knowledge / expertise there is downright astonishing.
Oh yeah -one quick suggestion from me if I may -I'd advise you avoid the tractrix profile for a bass horn. Tractrix has it's advantages, but IMO it's not at it's best performing LF duties. I'd go for a hypex, or, as the length is probably going to be limited, good old exponential if possible.
Hope that helps a bit
Scott
Scottmoose said:
Actually, it's great for bass-horns with the caveat that it has to be ~2x larger than an expo for a given Fc due to having to be able to load to a ~a half octave lower. Factor in the Tractrix's huge end correction mouth flare and a whole wall can turn into just a mono unit if it goes fairly low.
FWIW, all the theoretically ideal BLHs I've calc'd are around/at M(T) = 0.5 (hyperbolic), so < ideal will morph to a faster expansion with increasing cut-off for a given throat (St).
Sounds like a reincarnation of me a couple months ago. I finally got tired of cutting wood. It is fun to experiment but I found out wood is not like a erector set. I think I got it kindof right this time around. I get half wave around 55Hz which is where my horn action kicks in and TL action takes care of getting me to mid 30's. The only thing I really didn't pay alot of attention to was the baffle. But it seemed that Martin's analysis worksheet accounted for this.
Thanks Scottmoose for taking the time to expand on the concept. Can the BLH can be viewed as a simple low-pass filter ?
I am glad to see there are many of you that feel there is something interesting to learn by just playing with the driver and raw material (plywood, MDF, cement, glues, damping material, etc ...)
I read lots of material from all types of sources, and it is sometimes frustrating not to know what is true, false or how it fits in the big picture. It's when I'm stuck in this situation that I take my tools and try to put the pieces together.
I admit there are a lot of projects that I started and never finished because I followed the wrong path and got discouraged.
Hopefully, I am wiser now. I think I can prove it ... My original idea was to build a tube amp, buy a source and mod it, build the speakers and all cables. It took me about a month of research to realize I was about to start 5 projects and not complete one.
The new version is:
I purchased a Decware Taboo, a basic Oppo DV-980H player, and will build the BLH and cables. That's probably more reasonable and I think I will be able to deliver. For now, I have my old Sima PW-3000 amp driving the Fostex FE207E drivers attached to large Rubbermaid storage bins. It's quite funny to have a pair of Fostex drivers looking at you every day and asking for a real place to live
I just can't wait to get it all working together
It's great to know there a lot of generous people in this community willing to help each other. I really appreciate all the feedback I am getting and the great pool of information in this forum.
Once I have details and pictures, I will share them with you all. I can probably start with the Rubbermaid bins
Daze, I will contact you shortly. I am sure you will have interesting stories to tell
I am glad to see there are many of you that feel there is something interesting to learn by just playing with the driver and raw material (plywood, MDF, cement, glues, damping material, etc ...)
I read lots of material from all types of sources, and it is sometimes frustrating not to know what is true, false or how it fits in the big picture. It's when I'm stuck in this situation that I take my tools and try to put the pieces together.
I admit there are a lot of projects that I started and never finished because I followed the wrong path and got discouraged.
Hopefully, I am wiser now. I think I can prove it ... My original idea was to build a tube amp, buy a source and mod it, build the speakers and all cables. It took me about a month of research to realize I was about to start 5 projects and not complete one. The new version is:
I purchased a Decware Taboo, a basic Oppo DV-980H player, and will build the BLH and cables. That's probably more reasonable and I think I will be able to deliver. For now, I have my old Sima PW-3000 amp driving the Fostex FE207E drivers attached to large Rubbermaid storage bins. It's quite funny to have a pair of Fostex drivers looking at you every day and asking for a real place to live
I just can't wait to get it all working together
It's great to know there a lot of generous people in this community willing to help each other. I really appreciate all the feedback I am getting and the great pool of information in this forum.
Once I have details and pictures, I will share them with you all. I can probably start with the Rubbermaid bins
Daze, I will contact you shortly. I am sure you will have interesting stories to tell
Just to add an interesting note...
I was having a discussion about audio in general with a tech at Simaudio, I think about a month ago, and I shared with him my intention to build a BLH.
He replied:
"don't forget to put cotton pads around the wizzer cone to soften the mids, and the amp will love a zobel network with your drivers."
We continued the discussion and he said he could not understand why there was so many people going back to building tube amps and horns.
My answer was:
"People probably feel the newer technologies are not easily accessible to the common man and find comfort in going back to the sources, something they can experiment with, using simple tools."
I doubt that nowadays somebody can build a cell phone in their basement and master all the technologies involved.
With my BLH project, I feel I have a chance to create something new, learn the basic principles that drove the technology, and maybe have a chance to make it better.
I was having a discussion about audio in general with a tech at Simaudio, I think about a month ago, and I shared with him my intention to build a BLH.
He replied:
"don't forget to put cotton pads around the wizzer cone to soften the mids, and the amp will love a zobel network with your drivers."
We continued the discussion and he said he could not understand why there was so many people going back to building tube amps and horns.
My answer was:
"People probably feel the newer technologies are not easily accessible to the common man and find comfort in going back to the sources, something they can experiment with, using simple tools."
I doubt that nowadays somebody can build a cell phone in their basement and master all the technologies involved.
With my BLH project, I feel I have a chance to create something new, learn the basic principles that drove the technology, and maybe have a chance to make it better.
lowtherdream said:
Guess it is time to do a page which revisits the Marc Wauters 98 cent whizzer trick so people can start experimenting from the original instead of from the "don't have the specified material so i'll fake it" variation.
The Zobel is to help out the amps that aren't best suited. A series resistance to increase the SimAudio's output impedance would likely work even better (but not as well as just starting with an amp that naturally has a higher output impedance).
dave
planet10 said:
Greets!
Absolutely! Lowthers were/are designed for high output impedance (low DF) amps or at least 2.5 ohms series R if SS driven, so the horn's Fh3 should be designed based on whatever this higher effective Qts winds up being.
That said, due to the increasingly out of phase issue with increasing frequency between the driver's and horn's output, you want the effective Qts high enough that this acoustic XO occurs below our acute hearing BW, which varies from ~200 - 400 Hz depending on who you ask/read, so even 2.5 ohms isn't enough to fall within this BW using MJK's DX4 T/S measurements.
GM
Just come across a fascinating discussion between Thomas Dunker and Jean-michel Le Cleac'h on the High Efficiency Speaker Asylum ( sorry, don't know how to post the link, but its dated: June 08, 2004 ).
Here's a quote from Thomas I found interesting: "It is suggested by Higara and many others, and it is becoming very clear to me, that the theory of horns can never be "complete", since all existing models make some fundamental assumptions."
Cilla
Here's a quote from Thomas I found interesting: "It is suggested by Higara and many others, and it is becoming very clear to me, that the theory of horns can never be "complete", since all existing models make some fundamental assumptions."
Cilla
No theory or model is ever perfect, but is it good enough? I had a manager who used to say better is the enemy of good enough. Every theory and model is a compromise, this can be viewed as a negative or a positive attribute.
Personally, I find models and theories a tremendous help in the design/understanding of horns and believe that they can be good enough to produce excellent results. Others can always find fault and then turn around and claim they are not accurate enough to produce excellent results. To each his own.
Personally, I find models and theories a tremendous help in the design/understanding of horns and believe that they can be good enough to produce excellent results. Others can always find fault and then turn around and claim they are not accurate enough to produce excellent results. To each his own.
Agreed. Good enough is good enough. Perfect is a pain in the proverbial, and usually isn't worth the extra time, effort & cost in order to achieve it, assuming it can be achieved anyway.
Fantastic analogy if you'll indulge me. Back in the early 1960s, Stanley Hooker (one of the greatest engineers of the 20th century IMHO) was in charge of designing the Bristol Siddley Olympus turbojet, for the stillborn TSR2 bomber. One of the requirements foisted on him was for a 1000 nautical mile range ('perfection' -actually less than 900 would have been more than enough). Hooker's comment to the Vice-Chief of Air Staff: 'Why 1,000 miles? Do you realise the extra, unnecessary, 100 miles demanded are going to cost an extra £1million per-mile for engineering development?' (and that was an understatement).
Horn design & theory probably peaked in the 1930s - 1940s. We haven't really progressed since then at all. Those guys at Bell, RCA, Altec et al knew what they were doing. Probably Leach's paper was the single most significant step forward since then, and even that is basically a means to rapidly optimise a horn to a driver, or visa versa.
But that's for horns. Not hybrid domestic horns, given that most of us can't fit a pair of the monsters you'd need to maintain full horn loading down to 40Hz in the living room (IIRC, you'd need a mouth of 67in x 67in for 1/2 space loading). When you start to bring TL / QW action into play, things get 'interesting', because a lot are designed using pure horn theory, have the mouths compromised, and little thought is often given to the TL action & how to try & blend the handover from one mode of operation to the other, or smooth the response out. That's where the software, especially Martin's, comes in very useful indeed.
Fantastic analogy if you'll indulge me. Back in the early 1960s, Stanley Hooker (one of the greatest engineers of the 20th century IMHO) was in charge of designing the Bristol Siddley Olympus turbojet, for the stillborn TSR2 bomber. One of the requirements foisted on him was for a 1000 nautical mile range ('perfection' -actually less than 900 would have been more than enough). Hooker's comment to the Vice-Chief of Air Staff: 'Why 1,000 miles? Do you realise the extra, unnecessary, 100 miles demanded are going to cost an extra £1million per-mile for engineering development?' (and that was an understatement).
Horn design & theory probably peaked in the 1930s - 1940s. We haven't really progressed since then at all. Those guys at Bell, RCA, Altec et al knew what they were doing. Probably Leach's paper was the single most significant step forward since then, and even that is basically a means to rapidly optimise a horn to a driver, or visa versa.
But that's for horns. Not hybrid domestic horns, given that most of us can't fit a pair of the monsters you'd need to maintain full horn loading down to 40Hz in the living room (IIRC, you'd need a mouth of 67in x 67in for 1/2 space loading). When you start to bring TL / QW action into play, things get 'interesting', because a lot are designed using pure horn theory, have the mouths compromised, and little thought is often given to the TL action & how to try & blend the handover from one mode of operation to the other, or smooth the response out. That's where the software, especially Martin's, comes in very useful indeed.
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