Regarding the last post, Bl/MMs tells absolutely nothing about a driver's performance. It has nothing to do with acceleration. I can take a DVC driver and double the BL/MMs relationship depending on how I wire the coils, but this does nothing for the sound of the driver.
Nick McKinney wrote a paper called Bl/Mms=Nonsense back in 2000. I'd post the info here but the link shows the images as well.
http://web.archive.org/web/20010810141852/lambdacoustics.com/library/whitepapers/bl_mms.htm
Bl alone also tells nothing about the driver without respect to the DCR of the driver. BL^2/Re is a basic way to compare motor strength.
John
Nick McKinney wrote a paper called Bl/Mms=Nonsense back in 2000. I'd post the info here but the link shows the images as well.
http://web.archive.org/web/20010810141852/lambdacoustics.com/library/whitepapers/bl_mms.htm
Bl alone also tells nothing about the driver without respect to the DCR of the driver. BL^2/Re is a basic way to compare motor strength.
John
soongsc said:
I'm curious as to which drivers you compared. Knowing that would help with a few things. One it would tell if they are identical. Two it would let us know where the shorting ring was placed. Placement of shorting rings has a significant effect too.
As you change the amplitude of the response it will clearly change the impulse response. The shorting ring did not create the ringing. The ringing was there without the shorting ring as well, it was just attenuated due to the inductive rise. In all cases when done right, a shoring ring is going to allow the driver to more accurately reproduce the signal put into it. The other thing is that the inductive rise typically masks other breakups in the impedance curve. The higher the impedance at any given point, the less significant small changes become. As you lower the impedance as inductance comes down, all of those issues become more critical.
What you did was add a moving shorted turn to the driver. This is nowhere near the same as adding a shorting ring. It's going to greatly change the Q of the driver. It also creates all kinds of other issues with flux modulation due to pushing this shorted turn through the gap. Take a solid sleeve of alum and put it in a gap. It will almost hover there and as you push it through a lot of current is created which changes the magnetic field.
Equalization does nothing to keep inductance linear. It does nothing to lower distortion. It does nothing to keep the response of the driver the same at inward and outward strokes. It does nothing to keep flux from moving. It does nothing to pull heat from the coil and keep power compression low.
I can build 2 perfectly identical drivers one with and one without a shorting ring. You can EQ so they are both perfectly identical in response, but they will not sound the same. The impulse response and CSD plot will show that the energy in the driver with EQ and no shorting ring will decay much slower than the one with the shorting ring.
John
soongsc said:
This is because as you remove the inductance, you are now unmasking those other issues that may be significant. Cone breakup issues, spider resonance, resonance in the VC former, etc can all now be more easily noticeable. When you extend the bandwidth of the driver significantly you can expect you're going to have to fix other issues that may not have been audible before.
The scratches on my car aren't that noticeable when it is covered in mud. Does that mean I shouldn't ever wash it though? It looks much better clean and if I really want it to be nice I have to fix the scratches too. I can't ever fix them if I cant' see them though.
John
Lynn Olson said:
Well put, agree 100%
I invite you to have a listen on my high efficient double 6.5" mid on top of two 15" as this is kind of explosive thing on active set up – the music you love for testing Lynn (live, old fashioned or dense recordings), simply performs great.
From calculation it is 1% D-IM at max SPL of roughly 120dB (!) - not at the low 95-100dB as with the 15" / 18" speakers outlined as an example for Earl
Hence I'm so much interested in John's new 6.5" as I consider his designs to be the very best available in terms of VC heat related power compression – in the frame of non ferro fluid cooled speakers (which puts other trade off's I'd like to avoid).
And as John mentioned – there isn't a wide diversity of makes on that segment of specialised mid drivers .
I admit its kind of new territory to enter with this approach as usually economic reasons prevent from splitting the band as low as 300Hz adding to cost and complexity of a speaker.
It simply doesn't make sense considering FR and displacement capabilities of ready available speakers *only* - and I wouldn't have taken that route myself without the eye opening work of John Kreskovsky.
What's to gain at the end of the day - is considerable less IM at a given SPL, no XO break in the voice band and moderate directivity at high XO point simplifying the task of seamlessly blend over to the tweeter IMO .
Michael
Custom drivers not openly available. Sorry about that. But the shorting ring was on the whole pole piece. Current in a shorting ring will not only effect the magnetic field in the gap, but also the VC current itself.John_E_Janowitz said:
What I have seen is that shorting ring will change CSD at the lower frequencies below 1KHz, but not above. If you have wide range drivers that show better CSD than the Jordan JX53 or the JX92S, then we will be talking approximately in the same magnitude of CSD performance. If they are not as good, then I'm sure there are lots of things that will not be heard. If you can be more specific in the frequency ranges you are talking about regarding flux modulation, it would be much appreciated.
Many things can change the Q of a driver, but not shorting the VC former loop per my tests. Others have experienced change in Q when using shorting ring at the bottom of a pole piece.
Listmania Part II
The revised comparison table is too hard to type here, I attached a file instead.
By John's advice, I put in Re and Le, and setup 250Hz and 2.5kHz with 10V input to "simulate" the current flow through the voice coil. Then, again, add the Mms and Sd into the picture for a rough estimation of acousitic output. Finally I generate a number as "Hi / MB ratio" to indicate the power flatness -- ability to maintain wide bandwidth (instead of breakup).
So, the numbers of 250Hz might be a hint of the midbass acoustic power at specific voltage input. While the ones of 2.5kHz indicate the midhigh capability.
Looking at the midbass alone, the followings are very good:
18Sound - 10NDA610
Audax - PR 170 Z0 (what a surprise!)
B&C - 12PE32
Beyma - 102Nd, 122Nd
PAS - ER-1508C
TAD - TM-1201
Now take the midhigh into acount. Except for those widerangers, most of them fall down. Only the followings stand out:
18Sound - 10NDA610
AE - TD15M, TD15M custom
10NDA610 is fully equipped: strong motor, light cone, extremely low inductance. So powerful in such a wide range!
TD15M (and custom) somewhat lack in motor strength, but still very good overall.
This comparison table is made only for my own interest and share here for your reference. Many other factors are not considered of course, like cone materials and profiles, design concepts and target applications... etc. So it's not a performance comparison as a whole. Any comments are welcome. (OK, I know, there's still a catch about Le. The numbers in the table are all Le @ 1kHz, not 250Hz and 2.5kHz respectively. But you got the idea)
ps. In this regard, the Lowther DX4 is indeed very good in this comparison. If someone afford to chop the whizer and make it a midrange, it should be an excellent performer. And the 2 Fostex are also very decent, just lack a bit of output.
The revised comparison table is too hard to type here, I attached a file instead.
By John's advice, I put in Re and Le, and setup 250Hz and 2.5kHz with 10V input to "simulate" the current flow through the voice coil. Then, again, add the Mms and Sd into the picture for a rough estimation of acousitic output. Finally I generate a number as "Hi / MB ratio" to indicate the power flatness -- ability to maintain wide bandwidth (instead of breakup).
So, the numbers of 250Hz might be a hint of the midbass acoustic power at specific voltage input. While the ones of 2.5kHz indicate the midhigh capability.
Looking at the midbass alone, the followings are very good:
18Sound - 10NDA610
Audax - PR 170 Z0 (what a surprise!)
B&C - 12PE32
Beyma - 102Nd, 122Nd
PAS - ER-1508C
TAD - TM-1201
Now take the midhigh into acount. Except for those widerangers, most of them fall down. Only the followings stand out:
18Sound - 10NDA610
AE - TD15M, TD15M custom
10NDA610 is fully equipped: strong motor, light cone, extremely low inductance. So powerful in such a wide range!
TD15M (and custom) somewhat lack in motor strength, but still very good overall.
This comparison table is made only for my own interest and share here for your reference. Many other factors are not considered of course, like cone materials and profiles, design concepts and target applications... etc. So it's not a performance comparison as a whole. Any comments are welcome. (OK, I know, there's still a catch about Le. The numbers in the table are all Le @ 1kHz, not 250Hz and 2.5kHz respectively. But you got the idea)
ps. In this regard, the Lowther DX4 is indeed very good in this comparison. If someone afford to chop the whizer and make it a midrange, it should be an excellent performer. And the 2 Fostex are also very decent, just lack a bit of output.
Cone is the major cause of CSD in wide range drivers. Once the cone in is well damped, one can expect some 12 db improvement. How much improvement can reduced inductance improve CSD? In other threads (for example EnABL thread) I have posted data on this issue, would appreciate if you can show some data as well.John_E_Janowitz said:
OSWG BEM simulation
Hi Earl, all,
It took some time, but I finally got around to run the BEM simulation of the OSWG with driver internal flare and mouth radius.
After looking at the PWT response of Beyma CP380M, I modified the parameters of the DE250 a little. The parameters used in the simulation are:
Sd: 15cm2,
BL: 7.5Tm,
Cms: 2.0 E-5 m/N
Rms: 1.0 Ns/m
Mmd: 1.2g
Le: 0.025mH (measured inductive part of impedance of CP380M at 15kHz)
Re: 6.3 ohms.
Front chamber: 0.75cm3.
The internal flare starts at 1.5cm2 (10:1 compression ratio, fairly typical), and is conical with a wall angle of 6 degrees to a 1 inch exit, giving a length of 5.51cm. This is perhaps a little long, the compression ratio may be lower.
The OSWG has a throat angle of 6 degrees, flaring to 45 degrees, and is 5.7 inches long. It is followed by a radiused mouth, 4 inch radius, ends at 90 degrees.
BEM frequency sweep 300Hz to 15kHz, 150 points.
The waveguide is placed in an infinite baffle, for simplicity. Field points are at 3m distance. Driving voltage is 2.83V.
Attached is the frequency response with driver at different angles. Does this resemble your measurements, Earl?
It would in any case be interesting to see a frequency response measurement of your waveguide with driver, without the crossover. Also the electrical impedance would be interesting to see.
Bjørn
Hi Earl, all,
It took some time, but I finally got around to run the BEM simulation of the OSWG with driver internal flare and mouth radius.
After looking at the PWT response of Beyma CP380M, I modified the parameters of the DE250 a little. The parameters used in the simulation are:
Sd: 15cm2,
BL: 7.5Tm,
Cms: 2.0 E-5 m/N
Rms: 1.0 Ns/m
Mmd: 1.2g
Le: 0.025mH (measured inductive part of impedance of CP380M at 15kHz)
Re: 6.3 ohms.
Front chamber: 0.75cm3.
The internal flare starts at 1.5cm2 (10:1 compression ratio, fairly typical), and is conical with a wall angle of 6 degrees to a 1 inch exit, giving a length of 5.51cm. This is perhaps a little long, the compression ratio may be lower.
The OSWG has a throat angle of 6 degrees, flaring to 45 degrees, and is 5.7 inches long. It is followed by a radiused mouth, 4 inch radius, ends at 90 degrees.
BEM frequency sweep 300Hz to 15kHz, 150 points.
The waveguide is placed in an infinite baffle, for simplicity. Field points are at 3m distance. Driving voltage is 2.83V.
Attached is the frequency response with driver at different angles. Does this resemble your measurements, Earl?
It would in any case be interesting to see a frequency response measurement of your waveguide with driver, without the crossover. Also the electrical impedance would be interesting to see.
Bjørn
Attachments
Paul W said:Bjørn,
As if you haven't received enough requests...
It would also be interesting to see simulations for the JBL 243X "throatless" style driver Lynn is also considering.
Paul
Seems like I have to release my BEM SW...
I would need the parameters of the driver if I should do this. But honestly, I can't keep running simulations for everyone for free. Sorry. This is a spare time project, and I can't afford using too much time on running time consuming simulations for everyone.
I will continue to run simulations I find interesting personally. The sims I did for Lynn was of this kind, as I was involved in the considerations that led to the desing of the AH-425.
There are also problems with running simulations for others. BEM is not well suited for iterative design. If I do a 20-hour BEM simulation, and the person I do it for finds an error, or that he has given me the wrong parameters, I have to do another 20-hour simulation. And this ties up my time and my computer power quite a bit. I will rather spend that time working on the SW, and eventually make it available to the public later. I hope you understand.
Bjørn
Kolbrek said:
Seems like I have to release my BEM SW...
....
I will rather spend that time working on the SW, and eventually make it available to the public later. I hope you understand.
Bjørn
Soon as you take preorders, Bjørn - please drop me a PM.
-------------
Have put my work and some personal findings about BDMD (and the extra ordinary event of this very day
) into a paper available through the link below in order to give a more compact picture about the topic and some of the conclusions having evolved from this thread . Michael
Re: OSWG BEM simulation
Bjorn
Thank you very much for this. From your data I am assuming that the mouth of this waveguide would be 10", my smallest. I have data for this device and I will post it as a comparison, but I should also say that this waveguide is the worst of the bunch being just too small. The 12" and 15" devices are much better. But at any rate I'd have to say that you have achieved all of the pertinent features that I find. First the constant directivity, and the -6 dB / oct HF loss is typical. The lowest resonance peak is "tamed" by the HP filter and the next one, which I don't typically see this strong (but I use foam remember) needs a second tank circuit to control. The hole on axis is now quit accurate.
I'll dig up my data and post it.
Kolbrek said:
Bjorn
Thank you very much for this. From your data I am assuming that the mouth of this waveguide would be 10", my smallest. I have data for this device and I will post it as a comparison, but I should also say that this waveguide is the worst of the bunch being just too small. The 12" and 15" devices are much better. But at any rate I'd have to say that you have achieved all of the pertinent features that I find. First the constant directivity, and the -6 dB / oct HF loss is typical. The lowest resonance peak is "tamed" by the HP filter and the next one, which I don't typically see this strong (but I use foam remember) needs a second tank circuit to control. The hole on axis is now quit accurate.
I'll dig up my data and post it.
Member
Joined 2003
Here is my data for the Nathan 10" waveguide with a DE250. We mostly agree, but the bump at LFs is not in your data. This is likely due to the throat and the gap in front of the diaphragm not being correct.
There is clearly more damping of the resonanaces in my device, this could be the foam, but, in general, I don't find the foam having that much of an effect. Perhaps the driver has more Bl than you have used. I'll dig up an impedance curve and post it too.
An externally hosted image should be here but it was not working when we last tested it.
There is clearly more damping of the resonanaces in my device, this could be the foam, but, in general, I don't find the foam having that much of an effect. Perhaps the driver has more Bl than you have used. I'll dig up an impedance curve and post it too.
Sorry for interrupting again.
Well, maybe the tweeter is already chosen - I haven't read the whole (very interesting indeed!) thread, but still:
Has anyone read something about new Alcons Audio pro-ribbons? The RBN1801 and smaller RBN601, particularly?
Some states on RBN1801:
108dB/m sensitivity
210W continious power handling / 3kW peak handling
1kHz - to over 20 kHz responce.
RBN601 is similar, but smaller and less powerful. But even that is very enough. If only we could have 130dB SPL in the whole band..
Well, maybe the tweeter is already chosen - I haven't read the whole (very interesting indeed!) thread, but still:
Has anyone read something about new Alcons Audio pro-ribbons? The RBN1801 and smaller RBN601, particularly?
Some states on RBN1801:
108dB/m sensitivity
210W continious power handling / 3kW peak handling
1kHz - to over 20 kHz responce.
RBN601 is similar, but smaller and less powerful. But even that is very enough. If only we could have 130dB SPL in the whole band..
Re: Listmania Part II
Although to be fair the manufacturer measurements are taken in full space in a 30L box. This is in comparison to other manufacturer graphs some of which are taken with infinite baffle.
It has a rising response with little midbass; which can mean its range is actually not very wide. This is unless you use a wide baffle which can make it usable from around 300hz. Although the cone at first impressions from the graph is good and minimal breakup. Its 10 inch size is very deceptive. Take note its Xmax by the simplest definition is 0; the manufacturer uses a diff formula.
Although to be fair the manufacturer measurements are taken in full space in a 30L box. This is in comparison to other manufacturer graphs some of which are taken with infinite baffle.
Thanks for attention. I've noticed its rising response, too.
And also, I'm still confused by such "evaluation". The results are quite different from what I've experienced (subjectively). So it'd probably be something wrong (or lackings) with the table
By the way, 250Hz was picked because of many smaller drivers are affected by their low end resonant peak of impedance at slightly lower frenquency than this. Say, some drivers actually ride on the half way towards their peak at around 150Hz. So I can not take that frequency (or lower) to calculate their actual impedance by the Re and Le. Around and below this region, driver's behavior is dominated by other things instead of inductance.
So in the end, this seems all in vain. Or I need many more other factors to make it right.
And also, I'm still confused by such "evaluation". The results are quite different from what I've experienced (subjectively). So it'd probably be something wrong (or lackings) with the table
By the way, 250Hz was picked because of many smaller drivers are affected by their low end resonant peak of impedance at slightly lower frenquency than this. Say, some drivers actually ride on the half way towards their peak at around 150Hz. So I can not take that frequency (or lower) to calculate their actual impedance by the Re and Le. Around and below this region, driver's behavior is dominated by other things instead of inductance.
So in the end, this seems all in vain. Or I need many more other factors to make it right.