Because I hate Excel.
MathCad is a much more powerful program which handles any unit of measure and has many more math functions already available. Programming in MathCad is extremely flexible and I can reconfigure a worksheet to simulate an entirely new geometry arrangement in a matter of minutes.
I have Excel. I use it for simple math and making tables. I have purchased every version of MathCad since number 4 out of my own pocket. No academic versions, all licensed and registered. That has cost me a significant amount of my own hard earned dollars. That is how much I believe in MathCad. Excel is not an option.
MathCad is a much more powerful program which handles any unit of measure and has many more math functions already available. Programming in MathCad is extremely flexible and I can reconfigure a worksheet to simulate an entirely new geometry arrangement in a matter of minutes.
I have Excel. I use it for simple math and making tables. I have purchased every version of MathCad since number 4 out of my own pocket. No academic versions, all licensed and registered. That has cost me a significant amount of my own hard earned dollars. That is how much I believe in MathCad. Excel is not an option.
planet10 said:
AHhh come on man
i thought i had this licked. Now you mean to tell me that Sd has nothing to do with the cross sec area ?Say that a driver has 127 Sd . my box has inside dimensions of 10 wide 30 height and 36 depth. So i install the driver and start making a constant cross area line. I wouldnt set my divider at 12.7 approx ? That would be 10 x 12.7 which is close to the Sd of the driver. All things being equal, the volume in the box would stay constant with a few basket derivations if i swapped out drivers of the same approx diameter. So small Vas drivers and large Vas drivers would actually retune inside this constant line length Volume box? I actually stewed on this yesterday reading MJK's site and made an assumption, I thought that swapping drivers would only change the electrical characteristics of the motor itself.
Vancouver needs a snow storm.
I almost get a headache...so many calculations(for me..Im a kid..)
-btw,whats the diffirence between TQWT and TL.Both are pipes
-I should build "S0=SL aligment" to avoid problems,but in general people build "S0>SL aligment"
I wil stay at: l=(c/f*1/4) -(c/f*1/4)*0.35 <---second part means lenght to decrase if it is heavily stuffed
l=(c/f*1/4)*(1-1*0.35)
l=(c/f*1/4)*0.65
MJK:its familiar to your tables
-btw,whats the diffirence between TQWT and TL.Both are pipes
-I should build "S0=SL aligment" to avoid problems,but in general people build "S0>SL aligment"
I wil stay at: l=(c/f*1/4) -(c/f*1/4)*0.35 <---second part means lenght to decrase if it is heavily stuffed
l=(c/f*1/4)*(1-1*0.35)
l=(c/f*1/4)*0.65
MJK:its familiar to your tables
Attachments
Interesting... I don't see how SD doesn't affect SL. In a perfect world, SD would be a point source and SL would also be infinitessimally small. But since we are causing air particles to move over SD>0, that same motion must travel in a SL>0.
My favourite rule of thumb is that SL>=SD, thus preventing an instantaneous pressure increase at the point where the driver is mounted to the line. Basic fluids says that changes in pressure or velocity results in energy loss, a situation that is usually avoided (except by the tube guys, wink wink) Fortunately, this must be normally be true since the driver frame makes the mounting area larger than the actual SD and that alone often forces SL to be greater.
At the other end, it makes no sense to put make SL>>>SD as that puts a very large air mass inside the line that has to be excited by the driver. We are limited by motor strength and we get another large pressure change (decrease) causing losses.
In the end, SD may not actually go into the calculation of SL but it puts constraints on the range of practical dimensions of the line. It must be factored into the overall volume.
ensen.
My favourite rule of thumb is that SL>=SD, thus preventing an instantaneous pressure increase at the point where the driver is mounted to the line. Basic fluids says that changes in pressure or velocity results in energy loss, a situation that is usually avoided (except by the tube guys, wink wink) Fortunately, this must be normally be true since the driver frame makes the mounting area larger than the actual SD and that alone often forces SL to be greater.
At the other end, it makes no sense to put make SL>>>SD as that puts a very large air mass inside the line that has to be excited by the driver. We are limited by motor strength and we get another large pressure change (decrease) causing losses.
In the end, SD may not actually go into the calculation of SL but it puts constraints on the range of practical dimensions of the line. It must be factored into the overall volume.
ensen.I'll be real honest, I have no idea what the three posts above are trying to express. There are statements in each that make absolutely no sense, they are formed as statements and not as questions. I can only offer a couple of suggestions.
1. Sd = area of the driver cone. I use Sd as a convenient way of expressing the cross-sectional area of a transmission line as a ratio with driver size. I could just as easily use in^2 or m^2. Please don't place any significance on Sd, it is only used as a convenience so I can normalize and compare TL geometries for different sized drivers.
2. The length equations above are just wrong, I have no idea where you got these equations. Put them back wherever you found them. I suggest you look at Table 1 in my alignment table article to get a handle on the length as a function of area ratio.
3. Purplepeople, you have lost me completely with the fluids analogy. The air perticles in a TL are oscillating back and forth about an average position. I look at this as a vibration problem and not as a fluid flow problem. I can not make any sense of your rules of thumb for sizing TL geometry.
1. Sd = area of the driver cone. I use Sd as a convenient way of expressing the cross-sectional area of a transmission line as a ratio with driver size. I could just as easily use in^2 or m^2. Please don't place any significance on Sd, it is only used as a convenience so I can normalize and compare TL geometries for different sized drivers.
2. The length equations above are just wrong, I have no idea where you got these equations. Put them back wherever you found them. I suggest you look at Table 1 in my alignment table article to get a handle on the length as a function of area ratio.
3. Purplepeople, you have lost me completely with the fluids analogy. The air perticles in a TL are oscillating back and forth about an average position. I look at this as a vibration problem and not as a fluid flow problem. I can not make any sense of your rules of thumb for sizing TL geometry.
Don't even get me started on Excel... it is really a 3rd rate program. It is a shame it dominates the industry, because unless you are very good, and very patient to put up with it, the stuff that comes out in Excel is 3rd rate.
I use a much better spreadsheet most of the time. It was last revised in 1988. On my 10 year old 100 MHz 68040 box it still runs circles around Excel on my dual 867 G4. And it does lots of thengs that Excel doesn't hope to do. A general rule of thumb i use is that things that take an afternoon to do in Trapeze take a week to do in Excel (if doable).
BTW: Trapeze could never do what Martin does in MathCad so Excel would be toast in the 1st 10 minutes.
dave
It only has an approximate relation to line Xsection purely due to the general trend that larger drivers typically have larger Vas.
If you have a 3" driver with the same Vas (and Qt, Fs, et al) as a 10" driver (a totally unlikely scenerio, but for illustrative purposes...) then they would use the same line.
dave
ooooooooooooo!!!
MJK said:
If Sd is just an expression of Cross sectional area then i DID understand. I panicked Dave said it wasnt. But i get the Vas. analogy as well. Interdependent. Anyway this is a dead subject for me. I am using what i understand and building the box. Tapered line- 66 inches heavy stuffing -2 turns -front exit with a 1/2 So. From that ill just play with stuffing.
Okay, a chance to get less wordy.
Drivers have a physical size. For example a 3" driver might have an SD of 5 sq in. But you cannot mount this on a baffle that is only 2" wide... the enclosure must be at least 3" wide. SD affects SL but only it's form, not necessarily its dimensions.
MJK: I'm no longer mathematically equipped to debate the whether the excitation of air particles in a transmission line can be described by one model or another. However, my belief is that while wave theory can be used, at low frequencies and high amplitude, the air moves far enough for some fluid dynamics to be in play. Putting a sweaty hand in front a bass driver is enough to show that the air is actually being moved. Once we get into fluids flow, then we can start looking at the relationship between pressure and velocity.
ensen.
Drivers have a physical size. For example a 3" driver might have an SD of 5 sq in. But you cannot mount this on a baffle that is only 2" wide... the enclosure must be at least 3" wide. SD affects SL but only it's form, not necessarily its dimensions.
MJK: I'm no longer mathematically equipped to debate the whether the excitation of air particles in a transmission line can be described by one model or another. However, my belief is that while wave theory can be used, at low frequencies and high amplitude, the air moves far enough for some fluid dynamics to be in play. Putting a sweaty hand in front a bass driver is enough to show that the air is actually being moved. Once we get into fluids flow, then we can start looking at the relationship between pressure and velocity.
ensen.
Oh,dear
MJK has done table aligments for pipe lenght depend on freq and S0 and Sd.Thats cool,pipe lenght is not problem if I chose S0:Sl=1:1.If I chose smaller Sl,pipe lenght becomes shorter,but S0 becomes huge(If S0=Sl).
-MJK and other smart heads:How can I determine Sd of pipe(S0:Sl=1:1),If I know the Vas (upper posts said,that Sd as no connection v pipe`s SL-->rule of thumb)
MJK has done table aligments for pipe lenght depend on freq and S0 and Sd.Thats cool,pipe lenght is not problem if I chose S0:Sl=1:1.If I chose smaller Sl,pipe lenght becomes shorter,but S0 becomes huge(If S0=Sl).
-MJK and other smart heads:How can I determine Sd of pipe(S0:Sl=1:1),If I know the Vas (upper posts said,that Sd as no connection v pipe`s SL-->rule of thumb)
Grandma´s_SUB said:Oh,dear
-MJK and other smart heads:How can I determine Sd of pipe(S0:Sl=1:1),If I know the Vas (upper posts said,that Sd as no connection v pipe`s SL-->rule of thumb)
Greets!
I use a standard T/S vented box calculator to determine my pipe design's net volume (Vb), which BTW proves Sd isn't a factor in speaker cab design per se since all that's required is Fs, Vas, Qts.
GM
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