Talking about Xmax, with 18" or bigger, no matter single or multiple, I don't think we'd need very much of it in ordinary household usage.
I've been using the cheapest Eminence 18"ers, now 2 per side in OB. They have 'only' 6mm of Xmax. However I've never used it up.
All the abuses from dinosaur's footsteps to pipe organ have never bothered me or those woofers. The movement of the cone can not be seen most of the time and barely seen only in those exteme materials and extreme level. I can say that is only a fraction of that 6mm Xmax.
And, the 'more than enough' voice coil length is probably a bad thing, isn't it?
I've been using the cheapest Eminence 18"ers, now 2 per side in OB. They have 'only' 6mm of Xmax. However I've never used it up.
All the abuses from dinosaur's footsteps to pipe organ have never bothered me or those woofers. The movement of the cone can not be seen most of the time and barely seen only in those exteme materials and extreme level. I can say that is only a fraction of that 6mm Xmax.
And, the 'more than enough' voice coil length is probably a bad thing, isn't it?
Re: Richard C. Morgans - Horn Optimization
I have no real preference for the LeCleac'h, Tractrix, conical with transitional characteristics, AX2, Oblate Spheroid, or any other profile. What I'm most interested in is spatially consistent, and rapid, time-decay characteristics in the beam that is pointed at the listening area - unfortunately, this is a spec this is not easily found for any horn. The prosound industry almost never publishes time-domain information, much less time-domain at different emission angles.
So it'll have to be done by direct MLS measurement with different horns and waveguides. Since time errors arising from diffraction and reflection don't lend themselves to frequency-domain correction, the horns with narrow-angle problems in the time domain will have to be rejected. I'll be on the lookout for time ripples that have narrow beamwidths of less than 5 degrees, since this can be very disruptive of stereo image perception (due to each ear hearing a different time signature).
I suspect the phase-plug is one of the bad actors here, since the wavefront is not perfectly uniform at the outset, and gets much worse as it passes through the horn.
gedlee said:
I have no real preference for the LeCleac'h, Tractrix, conical with transitional characteristics, AX2, Oblate Spheroid, or any other profile. What I'm most interested in is spatially consistent, and rapid, time-decay characteristics in the beam that is pointed at the listening area - unfortunately, this is a spec this is not easily found for any horn. The prosound industry almost never publishes time-domain information, much less time-domain at different emission angles.
So it'll have to be done by direct MLS measurement with different horns and waveguides. Since time errors arising from diffraction and reflection don't lend themselves to frequency-domain correction, the horns with narrow-angle problems in the time domain will have to be rejected. I'll be on the lookout for time ripples that have narrow beamwidths of less than 5 degrees, since this can be very disruptive of stereo image perception (due to each ear hearing a different time signature).
I suspect the phase-plug is one of the bad actors here, since the wavefront is not perfectly uniform at the outset, and gets much worse as it passes through the horn.
Just for the record, it was Hoerninger who compiled the links about the Morgans articles at the University of Adelaide and elsewhere:
http://www.audiovoice-acoustics.com/forum/showthread.php?t=146
http://www.audiovoice-acoustics.com/forum/showthread.php?t=146
"One of the things I'll be mentioning to Great Plains Audio is applying Aquaplas (now called Antivibe) to the tangential surround of the aluminum compression driver diaphragm. JBL applies Aquaplas/Antivibe to the whole diaphragm when you buy a 435Be, but I feel this is a mistake. The part of the diaphragm with the most chaotic radiation is obviously the surround, and it's an area where mass-damping and outright suppression of radiation is desirable. That is NOT true of the diaphragm dome, where low-as-possible mass and uniform emission into the phase plug assembly are primary goals. Raising the mass of the diaphragm is extremely undesirable, since it depresses efficiency and decreases HF extension."
Hello Lynn
Do you have any personal experience with Aguaplased compression drivers?? Have you ever listened to the differences before and after coating a titanium diaphram?? Have you ever listened to a 2435 vs a 435be?? If the answer is no to all of the above you really should have a listen. The amount of mass added and the subsequent loss in HF extension or sensitivity can be compensated in the network.
The surrounds in a 2435/435Be are Kapton not metal like a Tangential diaphram.
Rob
Hello Lynn
Do you have any personal experience with Aguaplased compression drivers?? Have you ever listened to the differences before and after coating a titanium diaphram?? Have you ever listened to a 2435 vs a 435be?? If the answer is no to all of the above you really should have a listen. The amount of mass added and the subsequent loss in HF extension or sensitivity can be compensated in the network.
The surrounds in a 2435/435Be are Kapton not metal like a Tangential diaphram.
Rob
Attachments
Mr. Timbers, Chief Enginee at JBL, stated in the Lansing Heritage Forum
... we have hard measurements in addition to much subjective listening that shows that the application of Aquaplas to the metal diaphragm of our compression drivers improves the sound."
The whole answer can be read here
http://www.audioheritage.org/vbulletin/showpost.php?p=213900&postcount=3
... we have hard measurements in addition to much subjective listening that shows that the application of Aquaplas to the metal diaphragm of our compression drivers improves the sound."
The whole answer can be read here
http://www.audioheritage.org/vbulletin/showpost.php?p=213900&postcount=3
Well, to be honest, I think there's a lot of mysticism about WECO, Altec, JBL, and TAD. True, they made great, classic loudspeakers, but physics still applies to them, and there are areas of design that were overlooked or ignored.
It hardly seems controversial to treat the surround and spider differently than the diaphragm - this has been standard practice for direct-radiators for 80 years. The task of the surround and spider is to assure pistonic motion, prevent side-to-side rocking motions, minimize nonlinear distortion, and minimize spurious emission. Rice & Kellogg were aware of all these requirements.
The aluminum tangential surround was originally chosen to provide maximum excursion linearity for a near-full-range WECO theater driver. Due to the limited HF content of movie soundtracks, spurious emission above 8 kHz was not a concern, but power-handling was very important, with only one speaker system behind the screen, and very large theaters.
Adding mass to a diaphragm always lowers efficiency, lowers the mass rolloff point, and lowers the maximum HF extension of a driver. In direct-radiator tweeters, the amount of damping goo to apply to a silk-dome tweeter is a judgement call between leaving in resonances and too much depressing of efficiency and HF extension. Similarly, the reason the Bextrene drivers of the Seventies were so woefully low in efficiency (85 dB/metre typically) wasn't the Bextrene cone itself, but the very generous application of damping goo to quiet down the 1.5 kHz and higher modes - raw Bextrene is actually very resonant. The BBC developed the inherently lossy polypropylene cone specifically so they wouldn't have to mess with applying damping goo to the cone.
Now that optical soundtracks are no longer in use, and compression drivers are expected to cover the 8~20 kHz range, it exposes problems with diaphragm breakup and surround spurious emission - the same problems seen in direct-radiators for the last 80 years. The problem with compression drivers is that they are much bigger than the equivalent direct-radiator tweeter, so these HF problems creep in at lower frequencies.
Spurious emission from the surround is a problem for direct-radiator tweeters, and as shown by the 1979 Murray paper, is a problem for compression drivers as well. I guess the reason I have a slight problem with applying Aquaplas to a beryllium diaphragm is that after decades of PR about how wonderful beryllium is, now it has to be treated with the same kind of damping goo as other, less awesome drivers using titanium or aluminum diaphragms. The plain fact is that large-format compression drivers just aren't at their best above 8 kHz - the HF cutoff of old optical soundtracks, which is what the WECO and Altec compression drivers were originally designed for.
I've listened to the big TAD speakers (with my favorite recordings) over several months, and liked them, but wasn't bowled over by them. HF and extreme HF were good but not great. So I'm not really in the beryllium camp, despite the obviously superior measurements. I'm looking forward to auditioning a K2, but I'm not expecting extreme HF better than anything I've heard before.
It hardly seems controversial to treat the surround and spider differently than the diaphragm - this has been standard practice for direct-radiators for 80 years. The task of the surround and spider is to assure pistonic motion, prevent side-to-side rocking motions, minimize nonlinear distortion, and minimize spurious emission. Rice & Kellogg were aware of all these requirements.
The aluminum tangential surround was originally chosen to provide maximum excursion linearity for a near-full-range WECO theater driver. Due to the limited HF content of movie soundtracks, spurious emission above 8 kHz was not a concern, but power-handling was very important, with only one speaker system behind the screen, and very large theaters.
Adding mass to a diaphragm always lowers efficiency, lowers the mass rolloff point, and lowers the maximum HF extension of a driver. In direct-radiator tweeters, the amount of damping goo to apply to a silk-dome tweeter is a judgement call between leaving in resonances and too much depressing of efficiency and HF extension. Similarly, the reason the Bextrene drivers of the Seventies were so woefully low in efficiency (85 dB/metre typically) wasn't the Bextrene cone itself, but the very generous application of damping goo to quiet down the 1.5 kHz and higher modes - raw Bextrene is actually very resonant. The BBC developed the inherently lossy polypropylene cone specifically so they wouldn't have to mess with applying damping goo to the cone.
Now that optical soundtracks are no longer in use, and compression drivers are expected to cover the 8~20 kHz range, it exposes problems with diaphragm breakup and surround spurious emission - the same problems seen in direct-radiators for the last 80 years. The problem with compression drivers is that they are much bigger than the equivalent direct-radiator tweeter, so these HF problems creep in at lower frequencies.
Spurious emission from the surround is a problem for direct-radiator tweeters, and as shown by the 1979 Murray paper, is a problem for compression drivers as well. I guess the reason I have a slight problem with applying Aquaplas to a beryllium diaphragm is that after decades of PR about how wonderful beryllium is, now it has to be treated with the same kind of damping goo as other, less awesome drivers using titanium or aluminum diaphragms. The plain fact is that large-format compression drivers just aren't at their best above 8 kHz - the HF cutoff of old optical soundtracks, which is what the WECO and Altec compression drivers were originally designed for.
I've listened to the big TAD speakers (with my favorite recordings) over several months, and liked them, but wasn't bowled over by them. HF and extreme HF were good but not great. So I'm not really in the beryllium camp, despite the obviously superior measurements. I'm looking forward to auditioning a K2, but I'm not expecting extreme HF better than anything I've heard before.
Hi Lynn,
I sent you an email a few weeks back, but I guess it got caught in your spam filter.
....anyway I have a pair of Altec Constant Directivity horns (MR-94) and throats that you're most welcome to borrow for a while if you wanted to experiment/compare them to your Azura horns.
Details are in the email and I'm close to downtown Denver.
Cheers
Steve
I sent you an email a few weeks back, but I guess it got caught in your spam filter.
....anyway I have a pair of Altec Constant Directivity horns (MR-94) and throats that you're most welcome to borrow for a while if you wanted to experiment/compare them to your Azura horns.
Details are in the email and I'm close to downtown Denver.
Cheers
Steve
"Well, to be honest, I think there's a lot of mysticism about WECO, Altec, JBL, and TAD. True, they made great, classic loudspeakers, but physics still applies to them, and there are areas of design that were overlooked or ignored."
Hello Lynn
Like dampening the diaphram as an example? So I take it you have never heard an Aquaplased Compression driver?? Since you have never heard one I think you should reserve judgement on the effects of how it was applied until you actually get a pair and hear for yourself. It's real easy to sit back and pick nits.
'Adding mass to a diaphragm always lowers efficiency, lowers the mass rolloff point, and lowers the maximum HF extension of a driver."
Like all drivers a balance of trade offs. What matters is the end product not just one part of the puzzle.
" I guess the reason I have a slight problem with applying Aquaplas to a beryllium diaphragm is that after decades of PR about how wonderful beryllium is, now it has to be treated with the same kind of damping goo as other, less awesome drivers using titanium or aluminum diaphragms."
Well that's too bad becasue you are missing the point. It works on Titanium and Aluminum as well. It's not about using it on Berylllium the point is using it. If it improves the performance why not use it. You have said yourself you were not bowled over by Beryllium undamped. May be you will like it better coated???
"I'm looking forward to auditioning a K2, but I'm not expecting extreme HF better than anything I've heard before."
The K2 is a 3 way using a 1" Be compression tweeter. Same size as a typical tweeter. No large diaphram issues there.
http://www.audioheritage.org/html/projectmay/technology/045be.htm
Rob
Hello Lynn
Like dampening the diaphram as an example? So I take it you have never heard an Aquaplased Compression driver?? Since you have never heard one I think you should reserve judgement on the effects of how it was applied until you actually get a pair and hear for yourself. It's real easy to sit back and pick nits.
'Adding mass to a diaphragm always lowers efficiency, lowers the mass rolloff point, and lowers the maximum HF extension of a driver."
Like all drivers a balance of trade offs. What matters is the end product not just one part of the puzzle.
" I guess the reason I have a slight problem with applying Aquaplas to a beryllium diaphragm is that after decades of PR about how wonderful beryllium is, now it has to be treated with the same kind of damping goo as other, less awesome drivers using titanium or aluminum diaphragms."
Well that's too bad becasue you are missing the point. It works on Titanium and Aluminum as well. It's not about using it on Berylllium the point is using it. If it improves the performance why not use it. You have said yourself you were not bowled over by Beryllium undamped. May be you will like it better coated???
"I'm looking forward to auditioning a K2, but I'm not expecting extreme HF better than anything I've heard before."
The K2 is a 3 way using a 1" Be compression tweeter. Same size as a typical tweeter. No large diaphram issues there.
http://www.audioheritage.org/html/projectmay/technology/045be.htm
Rob
Hi Lynn, is it worth leaving the phase plug out altogether then? If the "extended high frequency response" is neither needed nor desired, then would the reduction in breakup SPL as a result of pathlength cancellation be an asset rather than a liability?
JBL tech note on cone compression drivers
Some intersting discussion between Tom Danley and Earl Geddes on what happens at the driver/horn (or waveguide) interface here
Cheers,
Mike
Hi Lynn,
You have made multiple posts noting your preference for the sound of Alnico magnets. Here is a post from Greg Timbers of JBL on the topic of Alnico magnets from the Lansing Heritage forum:
http://www.audioheritage.org/vbulletin/showthread.php?p=110522#post110522
I've had the pleasure of spending some time with Greg talking shop, and he is the real deal. He's been at JBL for nearly 30 years and knows whereof he speaks.
Cheers!
You have made multiple posts noting your preference for the sound of Alnico magnets. Here is a post from Greg Timbers of JBL on the topic of Alnico magnets from the Lansing Heritage forum:
http://www.audioheritage.org/vbulletin/showthread.php?p=110522#post110522
I've had the pleasure of spending some time with Greg talking shop, and he is the real deal. He's been at JBL for nearly 30 years and knows whereof he speaks.
Cheers!
Just saw the Greg Timbers post over at the Lansing Heritage forums.
I stand corrected - a 10 dB reduction in hash in the time domain decay characteristic is damned impressive, and especially noteworthy for metal-diaphragm compression drivers. If Aquaplas/Antivibe can do that, by golly, I'm a convert. 10 dB is a huge reduction and should be immediately audible within the first moments of listening. (By comparison, playing around with felt in strategic areas is typically only good for 3-5 dB of hash/reflection reduction, and is not as immediately audible.)
The reason I bring this up is that the time domain is the one area where compression drivers and horns are traditionally at their weakest, with significant amounts of delayed energy compared to the best direct-radiators. Of course, in terms of headroom and dynamic range, compression drivers and horn/waveguides have it all over direct-radiators.
Until very recently, that was always the hard choice - good time-domain performance with rapid decay characteristics, or outstanding dynamic range. Choose one or the other. Ribbons, electrostats, or ionic speakers in the first group, and compression drivers in the second.
It now looks like low-diffraction horns and waveguides, combined with appropriately damped compression drivers, will start to compete in the time domain with direct radiators - which is really good news for the entire audio industry. Something to look forward to.
P.S. If you think I'm emphasizing the time-domain decay characteristics, you're right. I'm with Newell and Holland on this one - the speakers with the most rapid, and resonance-free, decay characteristics are usually the best.
I stand corrected - a 10 dB reduction in hash in the time domain decay characteristic is damned impressive, and especially noteworthy for metal-diaphragm compression drivers. If Aquaplas/Antivibe can do that, by golly, I'm a convert. 10 dB is a huge reduction and should be immediately audible within the first moments of listening. (By comparison, playing around with felt in strategic areas is typically only good for 3-5 dB of hash/reflection reduction, and is not as immediately audible.)
The reason I bring this up is that the time domain is the one area where compression drivers and horns are traditionally at their weakest, with significant amounts of delayed energy compared to the best direct-radiators. Of course, in terms of headroom and dynamic range, compression drivers and horn/waveguides have it all over direct-radiators.
Until very recently, that was always the hard choice - good time-domain performance with rapid decay characteristics, or outstanding dynamic range. Choose one or the other. Ribbons, electrostats, or ionic speakers in the first group, and compression drivers in the second.
It now looks like low-diffraction horns and waveguides, combined with appropriately damped compression drivers, will start to compete in the time domain with direct radiators - which is really good news for the entire audio industry. Something to look forward to.
P.S. If you think I'm emphasizing the time-domain decay characteristics, you're right. I'm with Newell and Holland on this one - the speakers with the most rapid, and resonance-free, decay characteristics are usually the best.
Thanks to Magnetar for nailing down the T/S measurements of the Pyle PDW21250 21" woofer. The averaged measurements of four samples are:
FS - 31.61
RE - 5.59
RES- 59.81
QMS- 4.03
QES- 0.38
QTS- 0.34
L1- 1.88
VAS - 274.29 liters
SPL - 95.4
Mo' data, mo' betta. Thanks again, Magnetar, and congratulations on your new "Stargate" speaker!
FS - 31.61
RE - 5.59
RES- 59.81
QMS- 4.03
QES- 0.38
QTS- 0.34
L1- 1.88
VAS - 274.29 liters
SPL - 95.4
Mo' data, mo' betta. Thanks again, Magnetar, and congratulations on your new "Stargate" speaker!
Charles Hansen said:
Most interesting point made on underhung speakers not being able to demagnetize Alnico - something I didn't know. So it's overhung speakers (big bad woofers that play loud) that have issues with Alnico demagnetization when a strong pulse is sent through the system. By inference, the deluxe choice for this class of drivers is neodymium, or field-coils for the real extremists. Thanks, Charles, for the link!
Level Limiting via AlNiCo demagnetization
Funny thing is, these big, bad woofers of yesteryear as in his post (123A, 2213) are spec'd at a 50W input level. Sure, if you have high SPL at 200Hz you might have an issue, but these drivers are sub-style woofers. You're going to typically run into excursion limits way before power input is exceeded. These woofers (and I've got a pair of either, which are equivalents AFAIK) are about .48 Qts and 25Hz Fs.
So, with normal 'full range' material, in properly sized (not undersized, these aren't high-power mids!) bass cabs, you're hitting Xmax long before you have any issues with demagnetizing them.
It only takes a little juice to get a woofer like these pumping some serious LF energy. None of the 4 I have have any loss of energy. Will be interesting to see whether their bigger-motored brother the 122A has lost any of it's juice, or the uber-motored mid LE-5-2. (edit: wrong name)
Will post this historical oddity soon when I run the sweeps on these.
And of worthwhile note- IS a loss in magnet strength on the order of 1-3dB that bad a thing? We're constantly looking for higher Qts woofers for open baffles like lynn is planning (and I'm using), and so a loss in motor strength from alnico, with its (otherwise) improved operational stability over ferrite, might be desirable. A tradeoff of nominal efficiency for a higher Qes and accordingly Qts.
Funny thing is, these big, bad woofers of yesteryear as in his post (123A, 2213) are spec'd at a 50W input level. Sure, if you have high SPL at 200Hz you might have an issue, but these drivers are sub-style woofers. You're going to typically run into excursion limits way before power input is exceeded. These woofers (and I've got a pair of either, which are equivalents AFAIK) are about .48 Qts and 25Hz Fs.
So, with normal 'full range' material, in properly sized (not undersized, these aren't high-power mids!) bass cabs, you're hitting Xmax long before you have any issues with demagnetizing them.
It only takes a little juice to get a woofer like these pumping some serious LF energy. None of the 4 I have have any loss of energy. Will be interesting to see whether their bigger-motored brother the 122A has lost any of it's juice, or the uber-motored mid LE-5-2. (edit: wrong name)
Will post this historical oddity soon when I run the sweeps on these.
And of worthwhile note- IS a loss in magnet strength on the order of 1-3dB that bad a thing? We're constantly looking for higher Qts woofers for open baffles like lynn is planning (and I'm using), and so a loss in motor strength from alnico, with its (otherwise) improved operational stability over ferrite, might be desirable. A tradeoff of nominal efficiency for a higher Qes and accordingly Qts.
Congratulations Magnetar - your new toys look truly great!
Hi Magnetar!
Your new speakers look absolutely great!
While many of us use most of time considering the next project, you actually manage to let your ideas materialize - which is very inspiring! Thanks for sharing and please keep up the good work
Kind regards
Peter
Hi Magnetar!
Your new speakers look absolutely great!
While many of us use most of time considering the next project, you actually manage to let your ideas materialize - which is very inspiring! Thanks for sharing and please keep up the good work
Kind regards
Peter
"Funny thing is, these big, bad woofers of yesteryear as in his post (123A, 2213) are spec'd at a 50W input level. Sure, if you have high SPL at 200Hz you might have an issue, but these drivers are sub-style woofers. You're going to typically run into excursion limits way before power input is exceeded."
Hello Badman
Those are the white coned 4311/4312/L100 woofers. They actualy have decent x max number, about 16mm peak to peak especially considering how old the designs are. Back in the day I used to drop the full power of a Dynaco ST-400 into a pair of L100's that were EQ's to remove the midrange and bass humps and used bass shelving to boost below 40hz to bring up the low end. They never once bottomed even with the low end network.
They were also run fullrange in those applications so they would get what ever the amplifier had to give with no network to roll things off.
Your right they are excursion limited by todays standards for a sub but not before you are dumping some serious power into them. The peaks are what you have to worry about not the steady state.
Rob
Hello Badman
Those are the white coned 4311/4312/L100 woofers. They actualy have decent x max number, about 16mm peak to peak especially considering how old the designs are. Back in the day I used to drop the full power of a Dynaco ST-400 into a pair of L100's that were EQ's to remove the midrange and bass humps and used bass shelving to boost below 40hz to bring up the low end. They never once bottomed even with the low end network.
They were also run fullrange in those applications so they would get what ever the amplifier had to give with no network to roll things off.
Your right they are excursion limited by todays standards for a sub but not before you are dumping some serious power into them. The peaks are what you have to worry about not the steady state.
Rob
I ran 4 123a's on a large open baffle in my living room. They are impressive, and I never ran into mechanical limits. I would venture to say that they are one of the better deals in audio....~$125-150 per pair on eBay for 12" Alnico woofers that actually sound good. $60 doesn't buy a lot in a new 12" these days.
Chris
Chris