Remember that a driver operating in its pistonic range is a constant acceleration device (that is, SPL is proportional to acceleration, meaning that flat SPL implies constant acceleration, with respect to frequency). That means that for a flat SPL, we need to hold acceleration constant over bandwidth.gary f said:
Note that implies that increasing acceleration will increase SPL, NOT bandwidth!
We have a short paper that describes the basics of bandwidth, and includes measurements where we go through this is a bit more detail, and include measurements of a driver by itself and then with over twice the moving mass. The measured frequency response - the bandwidth - didn't change.
http://www.adireaudio.com/Files/TechPapers/WooferSpeed.pdf
It all comes down to the constant acceleration nature of loudspeakers. That is what forces the issue (and the fact that risetime is, as a result, a rate of change of acceleration; that is, changing acceleration itself will not affect bandwidth but changing how fast you can change the acceleration will!).
Dan Wiggins
Adire Audio
i find midrange domes fascinating since many seems to like them better then cone mids, i have not yet jumped on the dome wagon but i am tempted, but all dome mids i can find look all worse the a simular priced cone mid regarding bandwidth and freq response. and how about the dome shape structure? some tweeter mfrs goes for ring radiator designs to adress this issue, so why aren't there any ring radiator domes out there?
wow, that is good news!
I have heard that the cone shape is better then the dome, even for tweeters. but the small voice coil in a cone tweeter gives it a to a low power handling for practical use
re:'why did you choose this driver over a cone mid?"
no great tech reason.. - I couldn't make my mind up which 4" SB to buy....
,was hoping for wide dispersion, & the Beymas were cheap....
I'd forgotten Lynn Olsen's 'Nutshell' page where he evaluates cones:
The Art of Speaker Design, Part II
(halfway down the page): "Strengths are: None...."
"Weaknesses are: High distortion, fatiguing sound, high crossover frequency, limited bandwidth, limited power-handling, and misleading frequency response measurements. "
no great tech reason.. - I couldn't make my mind up which 4" SB to buy....
,was hoping for wide dispersion, & the Beymas were cheap....
I'd forgotten Lynn Olsen's 'Nutshell' page where he evaluates cones:
The Art of Speaker Design, Part II
(halfway down the page): "Strengths are: None...."
"Weaknesses are: High distortion, fatiguing sound, high crossover frequency, limited bandwidth, limited power-handling, and misleading frequency response measurements. "
Lynn Olsen's claim is made up bs with no data to support it. Many domes measure well and sound very good. They need to be used right. Just like horns they work in narrower band.
50 ways to make your speakers
50 ways to make your speakers
I would say the 2 best reasons to use a mid dome are...
1- to avoid using a driver ( 4-6 inch cone) that has to deal with controlled breakup modes as it approaches the hand off to the tweeter ( between 2-4 khz typically). The domes have the potential to remain pistonic or at least better diaphragm behavior through this area.
2- less dispersion change as it hands off to the tweeter than a larger mid or mid/bass cone.
In my own experiences ( mostly with 2 inch soft domes). Once you get it crossed at the right places to make the dome happy, they can have close to ribbon and electrostatic like transparency, I suspect mostly because your not taking the larger cone used below it into a freq region where cone breakup modes are starting to be audible.
1- to avoid using a driver ( 4-6 inch cone) that has to deal with controlled breakup modes as it approaches the hand off to the tweeter ( between 2-4 khz typically). The domes have the potential to remain pistonic or at least better diaphragm behavior through this area.
2- less dispersion change as it hands off to the tweeter than a larger mid or mid/bass cone.
In my own experiences ( mostly with 2 inch soft domes). Once you get it crossed at the right places to make the dome happy, they can have close to ribbon and electrostatic like transparency, I suspect mostly because your not taking the larger cone used below it into a freq region where cone breakup modes are starting to be audible.
Dome-inance...
Well-documented examples of the unique properties/advantages of employing a good (and preferably) compact-format dome mid:
Home build:
SP44
...It uses the 2" Accuton C50; its successor, the C51 CELL, is a beast in its optimum application range of 800-5K with 93+ sensitivity and 120W powerhandling... no cone can even come close to its clean pistonic operation, micro-resolution, output capacity and wide off-axis dispersion on the upper end, which allows for both flawless dispersion matching to a tweeter - which can now operate very comfortably with far less distortion and considerably higher powerhandling - as well as an XO point above the most critically sensitive range... a very nice tweeter option to hand off to would be the Raven Point Source (replace waveguided faceplate with flat variant, though)
Near-field studio monitor:
http://www.stoll-speakers.com/Neue_Dateien/Q-2b.pdf
... Uses something that's reminiscent of a Morel MDM55; allows for a minimum-width/"baffle-less" mid/tweet module which along with the perpendicularly positioned woofer module allows for (quasi-) omni dispersion - essentially, a 3-way (considerable) step-up of the Linkwitz Pluto (and even the LX Mini) concept...
(Obscenely expensive) "high-end" extravaganza:
Western Electric - WE SELECT - Gauder Akustik - Berlina RC 11 Loudspeaker
... Employs the (ridiculously priced) diamond variation of the aforementioned C51, the BD51, from 1-6K... word on the street is that the "humble" C51 is 99% as good resolution-wise, and actually a bit more dynamic despite of it lacking the bling-bling aura of its exotic sibling...
Mr. Dickie's very fine creations:
Drive units
... Behold the D50... just "good old" alu diaphragm, but proper/innovative engineering ... no breakups until 20K... nuff said...
(Relatively compromised) but considerably less complicated/expensive alternative to deploying upper mid domes (which preferably necessitate a 4-way design):
Waveguide a Bliesma (preferably the BE variant) and mate to a well-behaved 8" at 1K (according to Bliesma's maker - former Accuton production manager - , you can even ditch the waveguide if you cross steep and don't require excessive SPLs)
FWIW, during a conversation several years ago with the maker of (the late) Transducer Lab (about the potentially ATC-obsoleting 3" graphite wide-range ueber-dome mid he was developing at the time, but unfortunately had to put on ice as the company's principal apparently felt they needed to limit themselves to producing 31 flavors of hard-dome tweeters... what a shame), he talked about the considerable inherent flaws of cone drivers in general (regardless of their design particulars) and cited the example that, strictly speaking, even a 5" starts losing clean pistonic operation as low as 800 Hz... one would imagine that he possesses the credentials to know what he's talking about, no?
Enjoy!
Well-documented examples of the unique properties/advantages of employing a good (and preferably) compact-format dome mid:
Home build:
SP44
...It uses the 2" Accuton C50; its successor, the C51 CELL, is a beast in its optimum application range of 800-5K with 93+ sensitivity and 120W powerhandling... no cone can even come close to its clean pistonic operation, micro-resolution, output capacity and wide off-axis dispersion on the upper end, which allows for both flawless dispersion matching to a tweeter - which can now operate very comfortably with far less distortion and considerably higher powerhandling - as well as an XO point above the most critically sensitive range... a very nice tweeter option to hand off to would be the Raven Point Source (replace waveguided faceplate with flat variant, though)
Near-field studio monitor:
http://www.stoll-speakers.com/Neue_Dateien/Q-2b.pdf
... Uses something that's reminiscent of a Morel MDM55; allows for a minimum-width/"baffle-less" mid/tweet module which along with the perpendicularly positioned woofer module allows for (quasi-) omni dispersion - essentially, a 3-way (considerable) step-up of the Linkwitz Pluto (and even the LX Mini) concept...
(Obscenely expensive) "high-end" extravaganza:
Western Electric - WE SELECT - Gauder Akustik - Berlina RC 11 Loudspeaker
... Employs the (ridiculously priced) diamond variation of the aforementioned C51, the BD51, from 1-6K... word on the street is that the "humble" C51 is 99% as good resolution-wise, and actually a bit more dynamic despite of it lacking the bling-bling aura of its exotic sibling...
Mr. Dickie's very fine creations:
Drive units
... Behold the D50... just "good old" alu diaphragm, but proper/innovative engineering ... no breakups until 20K... nuff said...
(Relatively compromised) but considerably less complicated/expensive alternative to deploying upper mid domes (which preferably necessitate a 4-way design):
Waveguide a Bliesma (preferably the BE variant) and mate to a well-behaved 8" at 1K (according to Bliesma's maker - former Accuton production manager - , you can even ditch the waveguide if you cross steep and don't require excessive SPLs)
FWIW, during a conversation several years ago with the maker of (the late) Transducer Lab (about the potentially ATC-obsoleting 3" graphite wide-range ueber-dome mid he was developing at the time, but unfortunately had to put on ice as the company's principal apparently felt they needed to limit themselves to producing 31 flavors of hard-dome tweeters... what a shame), he talked about the considerable inherent flaws of cone drivers in general (regardless of their design particulars) and cited the example that, strictly speaking, even a 5" starts losing clean pistonic operation as low as 800 Hz... one would imagine that he possesses the credentials to know what he's talking about, no?
Enjoy!
In SP44, there is 105mm C-C distance between mid and tweeter and xo is 5200Hz acoustic LR4. This means quite sharp bunny-ear lobing off-axis vertically.
Tolvan Data
You must choose your poison!
Tolvan Data
You must choose your poison!
"even a 5" starts losing clean pistonic operation as low as 800 Hz.."
Everything flexes and the word "pistonic" is really not tru in loudspeakers. Everything is flexing some amount even at very low frequency's.
The question is how much, and how is it "controlled". With metal the idea is that we have a linear spring action to the flexure, so only amplitude distortion to deal with although a lot of it. With everything else to a greater or lesser extent we have some hysteresis to dampen the action. If I understand it right this means theres a time lag between stress and strain and with many materials or combinations this gives a damping of the resonances BUT apparently some studies show that our ear doesnt like the types of distortion from this effect if its too pronounced.
And thats just the tip of the iceberg. I dont think u can say that a dome is "always" going to be better above say 1khz than a small cone, BUT for a number of reasons it certainly has the potential to easily be better behaved through the upper freqs due to its structure shape, mass, large VC etc.
In the end however I suspect is you start with a small cone say around 5 inch that is very well refined AND use a tweeter capable of a very low crossover point say 1-1.5 khz, then you can approach the clarity through the mids without resorting to the often difficult to implement mid dome. You still have to get the crossover right here and with such wide dispersion's baffle distraction issues, but with a capable tweeter its easyer for the average DIY guy to get that mid realism this way.
Everything flexes and the word "pistonic" is really not tru in loudspeakers. Everything is flexing some amount even at very low frequency's.
The question is how much, and how is it "controlled". With metal the idea is that we have a linear spring action to the flexure, so only amplitude distortion to deal with although a lot of it. With everything else to a greater or lesser extent we have some hysteresis to dampen the action. If I understand it right this means theres a time lag between stress and strain and with many materials or combinations this gives a damping of the resonances BUT apparently some studies show that our ear doesnt like the types of distortion from this effect if its too pronounced.
And thats just the tip of the iceberg. I dont think u can say that a dome is "always" going to be better above say 1khz than a small cone, BUT for a number of reasons it certainly has the potential to easily be better behaved through the upper freqs due to its structure shape, mass, large VC etc.
In the end however I suspect is you start with a small cone say around 5 inch that is very well refined AND use a tweeter capable of a very low crossover point say 1-1.5 khz, then you can approach the clarity through the mids without resorting to the often difficult to implement mid dome. You still have to get the crossover right here and with such wide dispersion's baffle distraction issues, but with a capable tweeter its easyer for the average DIY guy to get that mid realism this way.
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