Damping and Suspension
Wouldn't that be an overdamped alignment or am I confusing this for sealed ?
A system Q of 0.7 gives a "critically damped" 2nd order response in a sealed or IB system and a woofer Q of 0.4 in the proper sized and vented box gives an equivalent "critically damped" 4th order response. Those responses are the equivalent of a Butterworth high pass filter which gives the lowest cutoff (-3dB) frequency with zero ripple (rise) in the passband.
There is still stored energy and delay but all high pass responses have those. If you want to minimize energy storage and delay, you need Q to go to as close to zero as possible but this greatly attenuates the bass response (reducing bass effiency). Those woofers are really useful only in horn loaded designs where the cone size can be transformed into many feet in diameter.
Naturally, most of those woofers have very little excursion capability since the magnet needed becomes cost prohibitive (and heavy/large). Also, there is no market for extremely low Q long excursion woofers except, as I said before, in small boxes for auto sound.
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Wouldn't suspension linearity be key too, especially in an IB where the drivers are operating in free air and hence no air spring ?
Yes, the smaller the box, the less important woofer suspension linearity is. An IB or dipole woofer needs good suspension linearity (and symmetry) since you'll be listening to that suspension's stiffness below resonance.
At and above resonance, the suspension only needs to not "pull up tight" since resonance (by it's nature) smooths out serious distortions and above resonance the response is mass controlled. But below resonance, you're listening to suspension linearity or lack thereof.
All the above summary must be laid on top of motor linearity which can be more a concern (and often is) than suspension linearity because coil overhang costs dearly for the designer/maker of the woofer while a larger spider and/or surround is more easily achieved. I have never seen a woofer with more motor linearity than its suspension capability but plenty of the opposite. For IB and dipole operation, it's best to find a woofer with an excellent balance of suspension non-linearity beginning when motor non-linearity begins. If that is done well in a design, the woofer can perform remarkably well even in its non-linear region.
Wouldn't that be an overdamped alignment or am I confusing this for sealed ?
A system Q of 0.7 gives a "critically damped" 2nd order response in a sealed or IB system and a woofer Q of 0.4 in the proper sized and vented box gives an equivalent "critically damped" 4th order response. Those responses are the equivalent of a Butterworth high pass filter which gives the lowest cutoff (-3dB) frequency with zero ripple (rise) in the passband.
There is still stored energy and delay but all high pass responses have those. If you want to minimize energy storage and delay, you need Q to go to as close to zero as possible but this greatly attenuates the bass response (reducing bass effiency). Those woofers are really useful only in horn loaded designs where the cone size can be transformed into many feet in diameter.
Naturally, most of those woofers have very little excursion capability since the magnet needed becomes cost prohibitive (and heavy/large). Also, there is no market for extremely low Q long excursion woofers except, as I said before, in small boxes for auto sound.
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Wouldn't suspension linearity be key too, especially in an IB where the drivers are operating in free air and hence no air spring ?
Yes, the smaller the box, the less important woofer suspension linearity is. An IB or dipole woofer needs good suspension linearity (and symmetry) since you'll be listening to that suspension's stiffness below resonance.
At and above resonance, the suspension only needs to not "pull up tight" since resonance (by it's nature) smooths out serious distortions and above resonance the response is mass controlled. But below resonance, you're listening to suspension linearity or lack thereof.
All the above summary must be laid on top of motor linearity which can be more a concern (and often is) than suspension linearity because coil overhang costs dearly for the designer/maker of the woofer while a larger spider and/or surround is more easily achieved. I have never seen a woofer with more motor linearity than its suspension capability but plenty of the opposite. For IB and dipole operation, it's best to find a woofer with an excellent balance of suspension non-linearity beginning when motor non-linearity begins. If that is done well in a design, the woofer can perform remarkably well even in its non-linear region.
"A system Q of 0.7 gives a "critically damped" 2nd order response ..."
Qm = .5 is critically damped, .7 gives lowest LF cutoff w/flat response.
"I have never seen a woofer with more motor linearity than its suspension capability but plenty of the opposite. "
One would think, but IIRC from the Dumax curves at Adire's site, this was not the case.
I was very surpri8sed to see that while BL xmax was defined as the point where BL was 70% of its rest value, Xsus was defined as *2X* the rest suspension stiffness.
Qm = .5 is critically damped, .7 gives lowest LF cutoff w/flat response.
"I have never seen a woofer with more motor linearity than its suspension capability but plenty of the opposite. "
One would think, but IIRC from the Dumax curves at Adire's site, this was not the case.
I was very surpri8sed to see that while BL xmax was defined as the point where BL was 70% of its rest value, Xsus was defined as *2X* the rest suspension stiffness.
Our Tumults have a BL limited Xmax of 43mm one way; the suspension and basket only allow for ~35mm one way.
Likewise, our Extremis has a BL limited Xmax of 13mm one way; the suspension usually limits out just before that, around 12 to 12.5mm one way.
Dan Wiggins
Adire Audio®
Likewise, our Extremis has a BL limited Xmax of 13mm one way; the suspension usually limits out just before that, around 12 to 12.5mm one way.
Dan Wiggins
Adire Audio®
Isn't there problem with increasingly larger surround for large x-max woofers?
I have the impression that inner half of the width of suspension should be calculated as cone area. Now we have a large effective radiating area that is soft and very loose coupled to cone.
I have the impression that inner half of the width of suspension should be calculated as cone area. Now we have a large effective radiating area that is soft and very loose coupled to cone.
Other than corrugated surrounds (those on guitar speakers), surrounds operate very predictably in the piston range of the woofer. I've never seen a roll surround cause distortion and their operation has been examined with strobes and scanning lasers. What extremely large roll surrounds do when used on small pistons is cause asymmetrical air volume displacement because their effective diameter decreases with outward displacement and increases with inward displacement. But on 12" or larger woofers, this is not much of a concern.
Hi Misterears,
Which camp are you in?
I have read reports of a few roll surrounds turning into reverse roll due to pressure changes front to rear. This volume displacement error is evident as distortion.
Very "soft" surrounds will not support the cone edge well and could give rise to the early onset of breakup (more distortion).
but
is a very effective description of distortion.
Which camp are you in?
I have read reports of a few roll surrounds turning into reverse roll due to pressure changes front to rear. This volume displacement error is evident as distortion.
Very "soft" surrounds will not support the cone edge well and could give rise to the early onset of breakup (more distortion).
Summer Camp?
I didn't know there were "camps" but feel free to put me in any "camp" you choose to...maybe I'll have more friends than I have now🙂
By distortion I meant to say physical distortion. I've never seen collapsing on a half roll surround on a commercially made system but no doubt some might exist somewhere and surely there must be home built systems with that problem (due to the builder using too small of an enclosure for the transducer's design...maybe a small sealed sub with EQ to lift the low end).
I do recall Audax having some super soft (almost latex like) woofer surrounds that were shallower than a half circle and were quite wide and were used in commercial vented boxes (all from Europe), but that was back in the 70s. I don't remember them physically distorting but they allowed very easy and premature bottoming of the coil below the box tuning frequency.
As far as early breakup due to soft surrounds, yes, but the most common thing I've seen was what is often call "cone cry" where the cone goes into a "pocket book" mode and literally cries over a narrow frequency range at high drive. I recall the Audax mentioned above had this problem.
That condition is often solved by using a "flat attach" where the cone body goes horizontal where the surround attaches (which supplies hoop strength for the cone) or as you said, a heavier/stiffer surround which can inhibit and dampen the cone's pocket book mode. This issue does not occur in the subwoofer frequency range though. It's typically ~800Hz for a 10", ~650Hz for a 12", ~500Hz for a 15" and ~400Hz for an 18".
Thanks for pointing out my distoted "distortion" statement. I suspect I was moving too fast.
I didn't know there were "camps" but feel free to put me in any "camp" you choose to...maybe I'll have more friends than I have now🙂
By distortion I meant to say physical distortion. I've never seen collapsing on a half roll surround on a commercially made system but no doubt some might exist somewhere and surely there must be home built systems with that problem (due to the builder using too small of an enclosure for the transducer's design...maybe a small sealed sub with EQ to lift the low end).
I do recall Audax having some super soft (almost latex like) woofer surrounds that were shallower than a half circle and were quite wide and were used in commercial vented boxes (all from Europe), but that was back in the 70s. I don't remember them physically distorting but they allowed very easy and premature bottoming of the coil below the box tuning frequency.
As far as early breakup due to soft surrounds, yes, but the most common thing I've seen was what is often call "cone cry" where the cone goes into a "pocket book" mode and literally cries over a narrow frequency range at high drive. I recall the Audax mentioned above had this problem.
That condition is often solved by using a "flat attach" where the cone body goes horizontal where the surround attaches (which supplies hoop strength for the cone) or as you said, a heavier/stiffer surround which can inhibit and dampen the cone's pocket book mode. This issue does not occur in the subwoofer frequency range though. It's typically ~800Hz for a 10", ~650Hz for a 12", ~500Hz for a 15" and ~400Hz for an 18".
Thanks for pointing out my distoted "distortion" statement. I suspect I was moving too fast.
Peavey Low Rider
Hi all,
this might fit in this thread... Looking for large drivers for dipole bass I found the Peavey Low Rider at Parts Express. This is an 18" driver, lightweight at 26 lbs, shallow 7" mounting depth, and with a high 9.6 mm Xmax (for a pro driver). Kevlar impregnated cone. Mms is very low at some 160 g, comparable to a 12" Peerless XLS. Fs in the 28 range, Qts 0.34 (0.5 at 20 Hz would be nicer but there's always LT). Eff. 97 dB/W. All for <190 USD a piece. And it looks good, wide open basket. Pretty much the only thing not to like about it is the monstrous shipping charges to my place
(more than the price of one driver, to ship a pair). The data sheet does not recommend infinite baffle, but I suppose this is because of low Q, not because of some other problem with it.
My dipole cabinet is designed to take two 10" or two 12" drivers. Right now I have double 10" Vifas in it which at some point will be up for replacement, if only out of curiosity what I'd get with something else, they work fine actually.
Now, a single Low rider equates pretty much exactly two 12" XLS's in volume displacement, at half the weight, half the cost, and half the moving mass (!) - and presumably lower airspeed through half the number of basket braces. And it would be used at a fraction of the power it was designed for (800 W RMS).
Now for the negatives - I can't find any except maybe earlier cone breakup than 10" or 12" drivers / nasty Kevlar style (they don't show frequency response in the data sheet). Hardly a problem for a sub-100 Hz range I suppose. Energy storage should be OK with a stiff cone and at that frequency range. Any opinions? What did I miss?
Cheers,
Hi all,
this might fit in this thread... Looking for large drivers for dipole bass I found the Peavey Low Rider at Parts Express. This is an 18" driver, lightweight at 26 lbs, shallow 7" mounting depth, and with a high 9.6 mm Xmax (for a pro driver). Kevlar impregnated cone. Mms is very low at some 160 g, comparable to a 12" Peerless XLS. Fs in the 28 range, Qts 0.34 (0.5 at 20 Hz would be nicer but there's always LT). Eff. 97 dB/W. All for <190 USD a piece. And it looks good, wide open basket. Pretty much the only thing not to like about it is the monstrous shipping charges to my place
(more than the price of one driver, to ship a pair). The data sheet does not recommend infinite baffle, but I suppose this is because of low Q, not because of some other problem with it.My dipole cabinet is designed to take two 10" or two 12" drivers. Right now I have double 10" Vifas in it which at some point will be up for replacement, if only out of curiosity what I'd get with something else, they work fine actually.
Now, a single Low rider equates pretty much exactly two 12" XLS's in volume displacement, at half the weight, half the cost, and half the moving mass (!) - and presumably lower airspeed through half the number of basket braces. And it would be used at a fraction of the power it was designed for (800 W RMS).
Now for the negatives - I can't find any except maybe earlier cone breakup than 10" or 12" drivers / nasty Kevlar style (they don't show frequency response in the data sheet). Hardly a problem for a sub-100 Hz range I suppose. Energy storage should be OK with a stiff cone and at that frequency range. Any opinions? What did I miss?
Cheers,
Hi,
is Kevlar stiffer than paper?
I wonder whether it does give a stiff cone compared to paper.
is Kevlar stiffer than paper?
I wonder whether it does give a stiff cone compared to paper.
"there must be home built systems with that problem (due to the builder using too small of an enclosure for the transducer's design...maybe a small sealed sub with EQ to lift the low end). "
Maximum enclosure pressure at a driver's thermal limit will be achieved with a vented box at Fb.
Maximum enclosure pressure at a driver's thermal limit will be achieved with a vented box at Fb.
You've Got Me Under Pressure
Yes, if constant voltage input is used as the criteria. 😉 I was referring to the fairly common practice in vehicles (I did it recently in a 240SX sub) of using a very small sealed box (giving a highish system resonance) and then 12dB/oct boosting below that to flatten response.
In those cases, the box's equivalent air stiffness can be as much as 10 times the woofer's stiffness plus the EQ lift forces extreme pressures (to regain the lost output in the box's air stiffness controlled region).
This can be done in vented boxes too (Carver's) but PRs need to be used since the low tuning in a small box forces that and a rather large PR (or PRs) are needed with enormous excursion capabilities....often not feasible for a home builder.
Yes, if constant voltage input is used as the criteria. 😉 I was referring to the fairly common practice in vehicles (I did it recently in a 240SX sub) of using a very small sealed box (giving a highish system resonance) and then 12dB/oct boosting below that to flatten response.
In those cases, the box's equivalent air stiffness can be as much as 10 times the woofer's stiffness plus the EQ lift forces extreme pressures (to regain the lost output in the box's air stiffness controlled region).
This can be done in vented boxes too (Carver's) but PRs need to be used since the low tuning in a small box forces that and a rather large PR (or PRs) are needed with enormous excursion capabilities....often not feasible for a home builder.
Kevlar
The problem of adding most fibers to cellulous paper is that cellulous paper uses no binders of any type to hold it together and therefore, to hold the added fibers. Typical paper cones use the inherant fibrous nature of the individual fibers to generate a Velcro-like interlocking structure so no adhesive or binder is needed (hence their low density 😎 ).
So, most often the added fibers simply slip and slide (micro-motions) and do not help to reduce the mending tendencies within the paper. Therefore, the cone is no stiffer. What Kevlar in the cellulous paper can do is toughen the cone so as to both limit extreme flexing and help the cone endure repeated flexing which we know can fatigue and permanently alter the performance of a cellulous cone. They act as do "bump stops" on a car's suspension system. 
In Pro speakers and especially in nearly unlimited input power systems, this can be a life saver. So, Kevlar is most often an endurance additive rather than achieving an immediate sonic benefit. Even an all Kevlar cone can have more of a stability benefit than an immediate performance advantage (since it has a much lower stiffness-to-density ratio than cellulous paper 🙁 ). In fact, in some applications, a transducer designer might trade off immediate performance to have a much longer lived transducer in the field (I know those are fighting words to an audiophile
).
The problem of adding most fibers to cellulous paper is that cellulous paper uses no binders of any type to hold it together and therefore, to hold the added fibers. Typical paper cones use the inherant fibrous nature of the individual fibers to generate a Velcro-like interlocking structure so no adhesive or binder is needed (hence their low density 😎 ).
So, most often the added fibers simply slip and slide (micro-motions) and do not help to reduce the mending tendencies within the paper.
Therefore, the cone is no stiffer. What Kevlar in the cellulous paper can do is toughen the cone so as to both limit extreme flexing and help the cone endure repeated flexing which we know can fatigue and permanently alter the performance of a cellulous cone. They act as do "bump stops" on a car's suspension system. In Pro speakers and especially in nearly unlimited input power systems, this can be a life saver. So, Kevlar is most often an endurance additive rather than achieving an immediate sonic benefit. Even an all Kevlar cone can have more of a stability benefit than an immediate performance advantage (since it has a much lower stiffness-to-density ratio than cellulous paper 🙁 ). In fact, in some applications, a transducer designer might trade off immediate performance to have a much longer lived transducer in the field (I know those are fighting words to an audiophile
)."Yes, if constant voltage input is used as the criteria."
Fine; at a constant voltage the veneted box wilol develop even higher pressure than constant power because of the impedance minimum at Fb.
"In those cases, the box's equivalent air stiffness can be as much as 10 times the woofer's stiffness plus the EQ lift forces extreme pressures (to regain the lost output in the box's air stiffness controlled region)."
What I said holds regardless of box volume. A vented box always have higher ouptut for the same input because its augmented by resonance, and this is reflected in higher box pressure.
My point was to counter the common misconception (not sure that you hold it) that venetd boxes develop lower pressure because they have a hole in them.
Thanks for the interesting info on cone materials.
Does paper really fatigue? The vast majority of pro drivers have paper cones, and I've never heard of a cone wearing out, though I've had little exposure to the pro audio world.
From what I can tell exotic cone materials sell more on marketing appeal than any technical superiority.
Fine; at a constant voltage the veneted box wilol develop even higher pressure than constant power because of the impedance minimum at Fb.
"In those cases, the box's equivalent air stiffness can be as much as 10 times the woofer's stiffness plus the EQ lift forces extreme pressures (to regain the lost output in the box's air stiffness controlled region)."
What I said holds regardless of box volume. A vented box always have higher ouptut for the same input because its augmented by resonance, and this is reflected in higher box pressure.
My point was to counter the common misconception (not sure that you hold it) that venetd boxes develop lower pressure because they have a hole in them.
Thanks for the interesting info on cone materials.
Does paper really fatigue? The vast majority of pro drivers have paper cones, and I've never heard of a cone wearing out, though I've had little exposure to the pro audio world.
From what I can tell exotic cone materials sell more on marketing appeal than any technical superiority.
Vented boxes develop a pressure peak around the tuning frequency and much lower pressure below that.
Sealed boxes also have its pressure peak around its resonance frequency, but constant pressure below that.
Sealed boxes also have its pressure peak around its resonance frequency, but constant pressure below that.
Misterears,
interesting points on the point of Kevlar...
Any conclusions about the likely (SQ and othwerwise) trade offs of one Low Rider vs two XLS12 for dipole use?
interesting points on the point of Kevlar...
Any conclusions about the likely (SQ and othwerwise) trade offs of one Low Rider vs two XLS12 for dipole use?
Big Is Better
I'd go with the 18" with the only caveat being I'd like to hear the driver swept free air at and beyond Xmax at and below resonance since some suspensions (spider usually) are very non-linear, or at least not matched well for the motor's linearity, when used in free air. 😡
I don't know how you could manage to do that but I wouldn't buy it and have to keep it unless it could swing maybe 50% beyond Xmax at resonance and still sound extremely clean. By clean I mean some 2nd and 3rd HD but no bizarre higher order suspension non-linearities...or God forbid "hard" bottoming.
I still remember an otherwise nice 10" Phillips woofer I swept once....nice Xmax and super clean but had a killer CRACK when overdriven (with no spider "pull up" before that....way too easy to over drive it with that unbearable overload sound).
But that's my view about all dipole drivers: I'd listen to them when driven hard around resonance before I'd buy. It's a bit like a new car that squeaks over every bump in the road and crashes hard when the speced suspension travel is reached. You don't want to risk hearing or fearing that everytime you show off your awesome 18" woofer's capabilty 😉
I'd go with the 18" with the only caveat being I'd like to hear the driver swept free air at and beyond Xmax at and below resonance since some suspensions (spider usually) are very non-linear, or at least not matched well for the motor's linearity, when used in free air. 😡
I don't know how you could manage to do that but I wouldn't buy it and have to keep it unless it could swing maybe 50% beyond Xmax at resonance and still sound extremely clean. By clean I mean some 2nd and 3rd HD but no bizarre higher order suspension non-linearities...or God forbid "hard" bottoming.
I still remember an otherwise nice 10" Phillips woofer I swept once....nice Xmax and super clean but had a killer CRACK when overdriven (with no spider "pull up" before that....way too easy to over drive it with that unbearable overload sound).
But that's my view about all dipole drivers: I'd listen to them when driven hard around resonance before I'd buy. It's a bit like a new car that squeaks over every bump in the road and crashes hard when the speced suspension travel is reached. You don't want to risk hearing or fearing that everytime you show off your awesome 18" woofer's capabilty 😉
btw. i got one 😉
the littel one is a SLS 8"
An externally hosted image should be here but it was not working when we last tested it.
the littel one is a SLS 8"
This explanation could only come from a man that listens to a fullrange speaker with dots painted on it
"more efficient - power wise that is . . . " No it isn't. What does "power wise" mean? It takes more energy into the V8 to get the same power out as the 4 cylinder.
"If you put both of those engines in two identical cars with everything the same except of the motor (obviously), . . ." The V8 is heavier, so it has to be put in a lighter car for both cars to weigh the same.
"Torque (muscle) is what gets the V8 down the road quicker . . ." Torque, a force, influences acceleration. Power is the rate at which work is being done. But of course it's better to have more torque if you plan on accelerating and you have enough grip.
Also the gear ratios are not going to be the same for a car with the same amount of power and 50% higher RPM range. You will actually have more torque (and way more HP) at the rear wheels with an engine that revs higher, as some one already pointed out, even though it wasn't the "right engine." The concept still holds true.
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