EDITED:
I apologize if this is old news, but 18 sound has a couple of 1.4" horns now..
here's the elliptical mouth one- 12" x 15" !!
http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=177
This 1.4" driver has an aluminum diaphram and PEN suspension:
http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=253
I apologize if this is old news, but 18 sound has a couple of 1.4" horns now..
here's the elliptical mouth one- 12" x 15" !!
http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=177
This 1.4" driver has an aluminum diaphram and PEN suspension:
http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=253
Re: Interesting Paper from 18Sound
To me its interesting that shortening rings affect distortion differently.
While at low frequencies there is a reduction in 3rd order distortion (even better as the AIC approach) whereas at higher frequencies (around 1kHz) there is a noticeable increase in 3rd order distortion peaking.(Fig 30 32 33)
Sadly there are no plots for a saturated magnet structure (Type 600) shown to compare there.
-------
The thermal load due to AIC seems to increase roughly by 10% (Fig. 57).
I guess for thermal modulation effects a similar paper could be written as was for the minimising of inductance modulation (Fig. 8 and 10 show some over compensation of AIC - if I interpret right).
The VC has low thermal capacity combined with high thermal resistance - a bad combination - even more so as no small part of the VC cooling usually is provided by membrane (dust cap) excursion, pumping air through the gap.
This makes rise / decay of power compression due to VC heating / cooling even a more complex subject.
Any papers on that? No better materials than aluminium or copper available for VC's?
Greetings
Michael
Lynn Olson said:
To me its interesting that shortening rings affect distortion differently.
While at low frequencies there is a reduction in 3rd order distortion (even better as the AIC approach) whereas at higher frequencies (around 1kHz) there is a noticeable increase in 3rd order distortion peaking.(Fig 30 32 33)
Sadly there are no plots for a saturated magnet structure (Type 600) shown to compare there.
-------
The thermal load due to AIC seems to increase roughly by 10% (Fig. 57).
I guess for thermal modulation effects a similar paper could be written as was for the minimising of inductance modulation (Fig. 8 and 10 show some over compensation of AIC - if I interpret right).
The VC has low thermal capacity combined with high thermal resistance - a bad combination - even more so as no small part of the VC cooling usually is provided by membrane (dust cap) excursion, pumping air through the gap.
This makes rise / decay of power compression due to VC heating / cooling even a more complex subject.
Any papers on that? No better materials than aluminium or copper available for VC's?
Greetings
Michael
Variac said:
Sharp eyes, Variac. I already have a pair of XT1464's sitting in the basement, awaiting the selection of a 1.4" compression driver. These will be the quick-n-dirty horns that will be compared to some new LeCleac'h horns that are in progress.
The candidates for the 1.4" compression driver are various versions of vintage Altec 288's, Great Plains Audio 399's fitted with the optional #23834 16-ohm aluminum diaphragm (not the standard Pascalite), Radian 745P, and as you guessed, the 18Sound 1460A - although the Euro/dollar ratio makes the 18Sound rather pricey right now. I like the sound and technology of the Hendricksen/Tangerine phase plug, so I'll most likely get the GPA 399's with the #23834 diaphragm. The 18Sound has an offbeat phase plug that is a hybrid of traditional circumferential and radial - they say it measures better, who knows.
On a purely subjective basis, I'm not really a fan of JBL compression drivers, but this comes down to personal taste - each of these things has their own sound. I am sure that some people would come down in favor of the costly beryllium TAD and JBL drivers, but I remain on the fence about beryllium - it measures better, but sonically - the ones I've heard don't do that much for me. When a driver costs that much, I expect to be jumping up and down at how fantastic it sounds, like an ionic tweeter or something. Now those things sound really different, and have truly spectacular measurements.
As mentioned in previous posts, the compression driver is intended for mid and upper-mid reproduction, while the extended highs are carried by a supertweeter. Since there is no requirement for response extending to 20 kHz, the additional power-handling of large-format compression drivers offers lower distortion and greater headroom in the critical 1 to 3 kHz region.
Well played Mr. Olson!
This is very encouraging- Quick and dirty is what is now needed, and I think that will separate the wheat from the chaff rather quickly. Finding a good horn seems to be harder than finding a decent driver...
Unfortunately, the number of compression driver candidates in the world is almost limitless!! there are so many pro driver makers and they each make a few models.. so there is no way for a mortal with limited funds to try even a significant portion of them
For example I know that you know that BMS makes these 1.4" monster Coax drivers:
http://www.bmspro.info/photos/bmspro_info/4594.pdf
It would be amusing if you ended up with coaxials, but a different type than you expected!! The specs aren't fantastic for the high frequency driver, but we know from experience that while co-ax's might measure a bit ragged, they can sound pretty great. Rumor has it that the drivers cost $1500 ea.
Still, they cover a lot of ground..and the mid driver looks pretty good, . and they say a lot of the right things in their cut sheet...Maybe someone that has a pair will speak up.
Where did you get the horn and how much?
This is very encouraging- Quick and dirty is what is now needed, and I think that will separate the wheat from the chaff rather quickly. Finding a good horn seems to be harder than finding a decent driver...
Unfortunately, the number of compression driver candidates in the world is almost limitless!! there are so many pro driver makers and they each make a few models.. so there is no way for a mortal with limited funds to try even a significant portion of them
For example I know that you know that BMS makes these 1.4" monster Coax drivers:
http://www.bmspro.info/photos/bmspro_info/4594.pdf
It would be amusing if you ended up with coaxials, but a different type than you expected!! The specs aren't fantastic for the high frequency driver, but we know from experience that while co-ax's might measure a bit ragged, they can sound pretty great. Rumor has it that the drivers cost $1500 ea.
Still, they cover a lot of ground..and the mid driver looks pretty good, . and they say a lot of the right things in their cut sheet...Maybe someone that has a pair will speak up.Where did you get the horn and how much?
I can now reveal that there will be a new AH-425 Azurahorn, commissioned for this project.
Specifications are: 425 Hz cutoff, T = 0.7071, throat size = 35.4mm (actual measured size of an Altec 288), internal flare rate of matching compression driver = 8 degrees, overall diameter = 418mm, length from front of horn to back of mounting plate = 262mm, diameter as measured from the portion that is at 90 degrees with respect to the central axis (the footprint if it is laid face-down on the floor) = 364mm.
Pricing and availability to be determined, although it'll probably fit midway in size and cost between the AH-340 and the AH-550. Unlike the AH-340, it can be shipped economically from Australia through Auspost, instead of FedEx or UPS. This is not a minor concern: Auspost is five times cheaper than FedEx or UPS!
Here's some PR info I sent to Martin Seddon of Azurahorn for his Website, if he'd like to use it:
------------
The AH-425 is designed to match the emissive area of a single 15" midbass driver, such as the Altec/Great Plains Audio 416 & 515, JBL 1500AL & 2235, 18Sound 15NMB420, AE Speakers Lambda TD15M, or one or two 12" midbass drivers, such as the Altec/GPA 414, JBL 1200FE, 18Sound 12NDA520, and other high-quality, high-efficiency professional studio-monitor drivers. All of these drivers are well-suited for a crossover in the 800 Hz to 1 kHz range. The combination of a large-format compression driver, primarily resistive diaphragm loading down to 550 Hz, and low diffraction assures relaxed and effortless midrange with very high headroom (125 dB SPL at one meter).
The tradition of combining a 15" midbass driver with a matching-area horn & compression driver goes all the way back to the Lansing Iconic of 1937, one of the most influential loudspeakers of all time, and the progenitor of all large-format studio monitors. Note the mouth area of the Lansing multicell horn was similar to the emissive area of the 15" midbass driver, and the system measured +/- 2dB from 40 Hz to 10 kHz, in an era when the only program sources were AM radio, optical soundtracks, and shellac 78 rpm records. (FM radio broadcasting, magnetic tape recording, microgroove LP records, and stereophonic sound were still several years in the future.)
http://audioheritage.org/html/profiles/lmco/iconic.htm
http://www.lansingheritage.org/images/lmco/advertizements/1937-electronics.jpg
http://www.lansingheritage.org/images/lmco/advertizements/1939cat-1.jpg
http://www.lansingheritage.org/images/lmco/advertizements/1939cat-2.jpg
The AH-425 can also work well with AH-204 and AH-50 midbass and bass horns combined with Lowther and AER drivers, and a suggested crossover around 1 kHz. This retains the articulation and upper-bass resolution of the Lowther family (while avoiding the mechanical crossover from the cone to the whizzer) and combining Lowther bass, midbass, and upper-bass with the dynamic high frequencies of large-format compression drivers. For best transient response, it is suggested the diaphragms of the Lowther and the compression driver are aligned, not the horn-mouths, and the crossover adjusted accordingly.
------------
I'd like to thank Bjorn Kolbrek and Martin Seddon for the extensive technical assistance on this project, as well Jean-Michel Le Cléac'h for the latest spreadsheet updates, detailed information about the effect of the T-profile on group-delay characteristics, and general encouragement for all of us.
P.S. People might ask why I didn't go with another horn builder. Well, cost does matter, which includes shipping cost to Colorado. The wood horns are many times the price of the fiberglass horns, the Music Concrete horns from France were certainly in the running as well, particularly since they make a 400 Hz horn, but since I am still a little uncertain of the outcome of the horn midrange, I was reluctant to get into this too deeply before I knew how the project was going to turn out.
I'm way over my head when it comes to horns (as many people keep thoughtfully reminding me) so I'm going to take it step-by-step, evaluating each piece of the system, and deferring the fancy audiophile fine-tuning for the end of the project.
Specifications are: 425 Hz cutoff, T = 0.7071, throat size = 35.4mm (actual measured size of an Altec 288), internal flare rate of matching compression driver = 8 degrees, overall diameter = 418mm, length from front of horn to back of mounting plate = 262mm, diameter as measured from the portion that is at 90 degrees with respect to the central axis (the footprint if it is laid face-down on the floor) = 364mm.
Pricing and availability to be determined, although it'll probably fit midway in size and cost between the AH-340 and the AH-550. Unlike the AH-340, it can be shipped economically from Australia through Auspost, instead of FedEx or UPS. This is not a minor concern: Auspost is five times cheaper than FedEx or UPS!
Here's some PR info I sent to Martin Seddon of Azurahorn for his Website, if he'd like to use it:
------------
The AH-425 is designed to match the emissive area of a single 15" midbass driver, such as the Altec/Great Plains Audio 416 & 515, JBL 1500AL & 2235, 18Sound 15NMB420, AE Speakers Lambda TD15M, or one or two 12" midbass drivers, such as the Altec/GPA 414, JBL 1200FE, 18Sound 12NDA520, and other high-quality, high-efficiency professional studio-monitor drivers. All of these drivers are well-suited for a crossover in the 800 Hz to 1 kHz range. The combination of a large-format compression driver, primarily resistive diaphragm loading down to 550 Hz, and low diffraction assures relaxed and effortless midrange with very high headroom (125 dB SPL at one meter).
The tradition of combining a 15" midbass driver with a matching-area horn & compression driver goes all the way back to the Lansing Iconic of 1937, one of the most influential loudspeakers of all time, and the progenitor of all large-format studio monitors. Note the mouth area of the Lansing multicell horn was similar to the emissive area of the 15" midbass driver, and the system measured +/- 2dB from 40 Hz to 10 kHz, in an era when the only program sources were AM radio, optical soundtracks, and shellac 78 rpm records. (FM radio broadcasting, magnetic tape recording, microgroove LP records, and stereophonic sound were still several years in the future.)
http://audioheritage.org/html/profiles/lmco/iconic.htm
http://www.lansingheritage.org/images/lmco/advertizements/1937-electronics.jpg
http://www.lansingheritage.org/images/lmco/advertizements/1939cat-1.jpg
http://www.lansingheritage.org/images/lmco/advertizements/1939cat-2.jpg
The AH-425 can also work well with AH-204 and AH-50 midbass and bass horns combined with Lowther and AER drivers, and a suggested crossover around 1 kHz. This retains the articulation and upper-bass resolution of the Lowther family (while avoiding the mechanical crossover from the cone to the whizzer) and combining Lowther bass, midbass, and upper-bass with the dynamic high frequencies of large-format compression drivers. For best transient response, it is suggested the diaphragms of the Lowther and the compression driver are aligned, not the horn-mouths, and the crossover adjusted accordingly.
------------
I'd like to thank Bjorn Kolbrek and Martin Seddon for the extensive technical assistance on this project, as well Jean-Michel Le Cléac'h for the latest spreadsheet updates, detailed information about the effect of the T-profile on group-delay characteristics, and general encouragement for all of us.
P.S. People might ask why I didn't go with another horn builder. Well, cost does matter, which includes shipping cost to Colorado. The wood horns are many times the price of the fiberglass horns, the Music Concrete horns from France were certainly in the running as well, particularly since they make a 400 Hz horn, but since I am still a little uncertain of the outcome of the horn midrange, I was reluctant to get into this too deeply before I knew how the project was going to turn out.
I'm way over my head when it comes to horns (as many people keep thoughtfully reminding me) so I'm going to take it step-by-step, evaluating each piece of the system, and deferring the fancy audiophile fine-tuning for the end of the project.
XT1464 pricing info at www.Speakerstore.nl.
Pretty inexpensive - 43 euros each. Note the more scary price of the 1460 at 331 euros each - although that's nothing compared to the US$1300 (and up) prices I've seen for Beryllium anything.
Hint to US builders: buy your overseas-made product now. The dollar is still continuing to fall. Note the latest prices of gold and oil (which track each other quite closely). Peak Oil is not just a rumor anymore - Deutsche Welle television devoted a 15-minute segment to it just a few nights ago.
Pretty inexpensive - 43 euros each. Note the more scary price of the 1460 at 331 euros each - although that's nothing compared to the US$1300 (and up) prices I've seen for Beryllium anything.
Hint to US builders: buy your overseas-made product now. The dollar is still continuing to fall. Note the latest prices of gold and oil (which track each other quite closely). Peak Oil is not just a rumor anymore - Deutsche Welle television devoted a 15-minute segment to it just a few nights ago.
Re: Re: Interesting Paper from 18Sound
Its possible the output at 1Khz is increased because of the lowered inductance? (I didn't look at the paper)
Its not the VC material, its getting the heat from the VC to the magnet structure that is the problem. This is one place I found aluminum formers work better as long as you don't get too much heat into the glue bond for the spider and the cone. Kapton is like a heat dam in comparision. Long copper tubes make the best heat conductors when combined with aluminum formers. The original ScanSpeak and Skanning drivers used this format. The long copper tube also shorts the inductance the best. For keeping the magnetic flex field from moving it works about the same as thick aluminum rings above and below the gap (McIntosh patent)
Aluminum and/or copper surrounding the magnetic gap as close as possible is your best friend for many reasons.
mige0 said:
Its possible the output at 1Khz is increased because of the lowered inductance? (I didn't look at the paper)
Its not the VC material, its getting the heat from the VC to the magnet structure that is the problem. This is one place I found aluminum formers work better as long as you don't get too much heat into the glue bond for the spider and the cone. Kapton is like a heat dam in comparision. Long copper tubes make the best heat conductors when combined with aluminum formers. The original ScanSpeak and Skanning drivers used this format. The long copper tube also shorts the inductance the best. For keeping the magnetic flex field from moving it works about the same as thick aluminum rings above and below the gap (McIntosh patent)
Aluminum and/or copper surrounding the magnetic gap as close as possible is your best friend for many reasons.
Re: Re: Re: Interesting Paper from 18Sound
From a reliability stand point I agree – not when modulation is concerned.
Actually ANY modulation whatsoever = distortion.
--------
Lets do a quick calculation.
Lets assume the voice coil wire is made of 10m / 0,2mm Copper
Then the resulting resistance at 20° is around 5,5 Ohm
Lets assume that the same voice coil has got 120°C warm
Then the resulting resistance at 120° is around 7,5 Ohm
Obvious the resulting current for the same input is dropping at around 35% - SPL will drop by 35% consequently.
This is a 35% !! DISTORTION - nothing in the range of (or far below) 1% as for THD or IM like we are familiar with.
120°C is nothing THAT unusual.
--------
Lets do another quick calculation on how much energy is needed to heat up that same wire by 100°C
The weight of that VC wire is slightly below 3g
To heat up this <3g of copper we need around 1 Watt for 1 sec for each Kelvin increase (no cooling assumed here)
From this we only need 10 sec of 10W input to get our 100°C increase – or 1 sec of 100W input.
In other words – if you want to enjoy the fortissimo at 115dB SPL and have a 95dB sensitive speaker - well after 1 (!) sec you have reached 35% of distortion - having a 105dB sensitive speaker you can enjoy your 115db SPL fortissimo a fantastic 10 sec until you end up at 35% distortion.
Quite revealing – no?
Of course there is heat leakage due to cooling in real world speakers, but don't expect them to cool down a 100Ws input immediately.
Heating up the VC is an immediate process – cooling down isn't.
-----
Lets do last quick calculation.
Lets assume a 50mm = 2" VC with a height of around 13mm (one layer wound to be optimistic )
This will provide a heat radiating area of around 40cm2 from front AND back.
If we – optimistically – assume to keep the magnet structure at 20°C while the VC is at 120° the heat leakage due to radiation is somewhere at around 3W
This means the decay from our 35% distortion fortissimo would last around 30 sec
Unfortunately – if the VC is cooled down to 70°C (half way down) then there is only about 1W cooling through radiation left (still optimistically assuming the magnet structure to be at 20°C), further stretching the time of distortion decay.
In fact decay would be rather asymptotic / exponential than linear of course.
Sure it might not really be 35% of distortion.
Sure there is also convection as cooling mechanism but if pianissimo follows fortissimo you only have the additional cooling during fortissimo.
But anyway - a decay time in the minute range to come down to reasonable distortion levels should be a very good argument for developing better working materials for VC wires – no?
Anybody ever considered temperature decay matching of drivers?
The AIC paper draws a slightly different picture as I already have pointed to.
Greetings
Michael
PPUUhh – hope I haven't mixed all that formulas and constants
nickmckinney said:
From a reliability stand point I agree – not when modulation is concerned.
Actually ANY modulation whatsoever = distortion.
--------
Lets do a quick calculation.
Lets assume the voice coil wire is made of 10m / 0,2mm Copper
Then the resulting resistance at 20° is around 5,5 Ohm
Lets assume that the same voice coil has got 120°C warm
Then the resulting resistance at 120° is around 7,5 Ohm
Obvious the resulting current for the same input is dropping at around 35% - SPL will drop by 35% consequently.
This is a 35% !! DISTORTION - nothing in the range of (or far below) 1% as for THD or IM like we are familiar with.
120°C is nothing THAT unusual.
--------
Lets do another quick calculation on how much energy is needed to heat up that same wire by 100°C
The weight of that VC wire is slightly below 3g
To heat up this <3g of copper we need around 1 Watt for 1 sec for each Kelvin increase (no cooling assumed here)
From this we only need 10 sec of 10W input to get our 100°C increase – or 1 sec of 100W input.
In other words – if you want to enjoy the fortissimo at 115dB SPL and have a 95dB sensitive speaker - well after 1 (!) sec you have reached 35% of distortion - having a 105dB sensitive speaker you can enjoy your 115db SPL fortissimo a fantastic 10 sec until you end up at 35% distortion.
Quite revealing – no?
Of course there is heat leakage due to cooling in real world speakers, but don't expect them to cool down a 100Ws input immediately.
Heating up the VC is an immediate process – cooling down isn't.
-----
Lets do last quick calculation.
Lets assume a 50mm = 2" VC with a height of around 13mm (one layer wound to be optimistic
)This will provide a heat radiating area of around 40cm2 from front AND back.
If we – optimistically – assume to keep the magnet structure at 20°C while the VC is at 120° the heat leakage due to radiation is somewhere at around 3W
This means the decay from our 35% distortion fortissimo would last around 30 sec
Unfortunately – if the VC is cooled down to 70°C (half way down) then there is only about 1W cooling through radiation left (still optimistically assuming the magnet structure to be at 20°C), further stretching the time of distortion decay.
In fact decay would be rather asymptotic / exponential than linear of course.
Sure it might not really be 35% of distortion.
Sure there is also convection as cooling mechanism but if pianissimo follows fortissimo you only have the additional cooling during fortissimo.
But anyway - a decay time in the minute range to come down to reasonable distortion levels should be a very good argument for developing better working materials for VC wires – no?
Anybody ever considered temperature decay matching of drivers?
nickmckinney said:
The AIC paper draws a slightly different picture as I already have pointed to.
Greetings
Michael
PPUUhh – hope I haven't mixed all that formulas and constants
Compression driver alternative
Earlier in the thread the Beyma TPL-150 was mentioned and considered....
Beyma will be releasing a horn for this Heil variant soon, which looks to improve a few areas.
http://profesional.beyma.com/newsletterMarzo2008/TDTPL preliminary.pdf
I tried to attach the pdf, but even after shrinking it it was still to big.
C
Earlier in the thread the Beyma TPL-150 was mentioned and considered....
Beyma will be releasing a horn for this Heil variant soon, which looks to improve a few areas.
http://profesional.beyma.com/newsletterMarzo2008/TDTPL preliminary.pdf
I tried to attach the pdf, but even after shrinking it it was still to big.
C
Re: Re: Re: Re: Interesting Paper from 18Sound
I appied for a patent on a VC wire material that had about 10% of the variation of Re with temp. A few % nickel added to copper does the trick, but it raises the resistivity of the wire. However at some temperature the two slopes cross so the NI-CU wire works better for drivers that tend to be warm and the CU works better for cooler situations.
mige0 said:
I appied for a patent on a VC wire material that had about 10% of the variation of Re with temp. A few % nickel added to copper does the trick, but it raises the resistivity of the wire. However at some temperature the two slopes cross so the NI-CU wire works better for drivers that tend to be warm and the CU works better for cooler situations.
Re: Re: Re: Re: Interesting Paper from 18Sound
Hi Micheal, I snipped the last half or so.
Let me explain what happens internally with my TD and Apollo drivers:
1 - My magnetic gap is tall, 18mm of steel plate on the outside compared to the 6-13mm of regular drivers.
2 - My solid copper pole is tall, about 100mm give or take of height
3 - My solid copper pole is thick, about twice as thick as I have seen done on other drivers
4 - My steel pole is ~100mm tall and solid.
5 - The clearance between the voice coil and the above "heatsinks" is about 50% less than most other drivers.
6 - The VC former is made of both Aluminum and Kapton, the Aluminum runs the entire height of the former which is roughly 60mm give or take.
Steel is a poor conductor of transient heat, but you can sink a lot of heat into it. Copper is the opposite and in this case the copper sleeve is pressed tight onto the steel pole. Then this is in very close tolerance to a tall heat conductive voice coil former. This conducts the heat into the steel pole better than most any other solution I have seen.
Then -
We install a solid chunk of aluminum onto the top of the pole to act as a phaseplug/heatsink. The 15" drivers have one around 100mm tall and 50mm thick. You are welcome to drive one as hard as you want and touch the phase plug with your bare hands.........
And that is a standard TD motor, now lets look at the Apollo:
Add another solid aluminum ring about 150mm in diameter and 18mm thick at the thickest point, 7mm at the thinnest, and spaced as close to the voice coil as the steel plate.
Add yet another solid aluminum ring below the magnetic gap on the outside of the voice coil, almost the height of the magnet stack, and as close to the voice coil former as a regular speaker would have its clearance.
Now I am not saying these drivers don't have power compression, but lets just say I will put them up against any other design with no worries, especially when it comes to covering the 20Hz-1Khz range at the same time.
The above is talking only about heatsinking BTW, the copper sleeve and aluminum rings also work to help keep the magnetic flux field stationary, which is a source of distortion in ceramic magnet speakers.
mige0 said:
Hi Micheal, I snipped the last half or so.
Let me explain what happens internally with my TD and Apollo drivers:
1 - My magnetic gap is tall, 18mm of steel plate on the outside compared to the 6-13mm of regular drivers.
2 - My solid copper pole is tall, about 100mm give or take of height
3 - My solid copper pole is thick, about twice as thick as I have seen done on other drivers
4 - My steel pole is ~100mm tall and solid.
5 - The clearance between the voice coil and the above "heatsinks" is about 50% less than most other drivers.
6 - The VC former is made of both Aluminum and Kapton, the Aluminum runs the entire height of the former which is roughly 60mm give or take.
Steel is a poor conductor of transient heat, but you can sink a lot of heat into it. Copper is the opposite and in this case the copper sleeve is pressed tight onto the steel pole. Then this is in very close tolerance to a tall heat conductive voice coil former. This conducts the heat into the steel pole better than most any other solution I have seen.
Then -
We install a solid chunk of aluminum onto the top of the pole to act as a phaseplug/heatsink. The 15" drivers have one around 100mm tall and 50mm thick. You are welcome to drive one as hard as you want and touch the phase plug with your bare hands.........
And that is a standard TD motor, now lets look at the Apollo:
Add another solid aluminum ring about 150mm in diameter and 18mm thick at the thickest point, 7mm at the thinnest, and spaced as close to the voice coil as the steel plate.
Add yet another solid aluminum ring below the magnetic gap on the outside of the voice coil, almost the height of the magnet stack, and as close to the voice coil former as a regular speaker would have its clearance.
Now I am not saying these drivers don't have power compression, but lets just say I will put them up against any other design with no worries, especially when it comes to covering the 20Hz-1Khz range at the same time.
The above is talking only about heatsinking BTW, the copper sleeve and aluminum rings also work to help keep the magnetic flux field stationary, which is a source of distortion in ceramic magnet speakers.
Re: Re: Re: Re: Re: Interesting Paper from 18Sound
The problem with this is not only that nickel raises resistivity, but that nickel is also magnetic. Using any kind of magnetic material in the coil or form introduces a force factor that resists movement of the coil, acting like there is a parking brake on and constantly attempting to pull the coil back to center. It will also cause the coil to be pulled laterally towards whatever edge is closest and can rub much easier. Even a small percentage of nickel causes a significant effect. If this wasn't the case, you would be able to use ceramic coated 27% nickel clad copper wire (kulgrid 28) with ceramic adhesives. It would virtually be a burn-up proof coil. The wire is good for continuous operation up to 1000degrees F and the adhesive is good to even higher temperature. Unfortunately the Nickel required for the ceramic to be put on the wire doesn't allow this to work.
John
gedlee said:
The problem with this is not only that nickel raises resistivity, but that nickel is also magnetic. Using any kind of magnetic material in the coil or form introduces a force factor that resists movement of the coil, acting like there is a parking brake on and constantly attempting to pull the coil back to center. It will also cause the coil to be pulled laterally towards whatever edge is closest and can rub much easier. Even a small percentage of nickel causes a significant effect. If this wasn't the case, you would be able to use ceramic coated 27% nickel clad copper wire (kulgrid 28) with ceramic adhesives. It would virtually be a burn-up proof coil. The wire is good for continuous operation up to 1000degrees F and the adhesive is good to even higher temperature. Unfortunately the Nickel required for the ceramic to be put on the wire doesn't allow this to work.
John
Another clever trick used by the prosound drivers is winding the voice coil on both the inside and outside of the VC former, so each side can radiate infrared directly onto the pole-piece and top plate. The VC's of audiophile speakers don't usually use a double-wound VC, which is an indirect comment on their peak headroom.
Magnetar and Variac, I dunno which horn will sound better. The LeCleac'h, with its trademark rollover, has a lot softer edge termination to the circular mouth than the sharp-edged and rectangular-mouth XT1464. To the XT1464's credit, there is thankfully no diffraction "pinch" in the throat region. I've suspected for a long time the reason the Altec 811 and 511 sectoral horns sound so dreadful is the diffraction "pinch" in the throat region - take a good look at one some time, they have a really weird profile that you can't see until you look at the back portion.
Build quality of the black molded-plastic XT1464 is pretty good as well - but users of old-style 3-bolt Altec 288's will have to drill their own set of holes in the mounting flange, which only has the modern 4-bolt pattern. I suspect clever users of the XT1464 could always fill the thing with open-cell foam and see what effect that has on the time-domain response.
If you think the Azurahorns are expensive at about $600/pair (shipping is around $90 the pair), you should see the prices of other custom-made horns. The Music Concretes are about half again to twice that (they are heavy to ship), and US-made wood horns seem to be about twice that again. That gets into boutique beryllium-driver territory - OK for the hardcore horn fanatics who already know what they want, but too much for prototyping and just fooling around with various set-ups and measurements.
Magnetar and Variac, I dunno which horn will sound better. The LeCleac'h, with its trademark rollover, has a lot softer edge termination to the circular mouth than the sharp-edged and rectangular-mouth XT1464. To the XT1464's credit, there is thankfully no diffraction "pinch" in the throat region. I've suspected for a long time the reason the Altec 811 and 511 sectoral horns sound so dreadful is the diffraction "pinch" in the throat region - take a good look at one some time, they have a really weird profile that you can't see until you look at the back portion.
Build quality of the black molded-plastic XT1464 is pretty good as well - but users of old-style 3-bolt Altec 288's will have to drill their own set of holes in the mounting flange, which only has the modern 4-bolt pattern. I suspect clever users of the XT1464 could always fill the thing with open-cell foam and see what effect that has on the time-domain response.
If you think the Azurahorns are expensive at about $600/pair (shipping is around $90 the pair), you should see the prices of other custom-made horns. The Music Concretes are about half again to twice that (they are heavy to ship), and US-made wood horns seem to be about twice that again. That gets into boutique beryllium-driver territory - OK for the hardcore horn fanatics who already know what they want, but too much for prototyping and just fooling around with various set-ups and measurements.
Power compression
Hi Nick, yes lots of effort to transmit heat.
Nevertheless you wont get rid of the thermal transients this way – just reducing it by maybe a factor of three or four (my rough guess only) to common designs.
Not bad at all – but by no means comparable for what could be realised with better wire composits.
Good thing is, your speakers do not relay on the dust-cap-air-pump-cooling-effect that is heavily program dependant.
The core part is the VC - anything else is just to keep down the temperatures of the VC ambience to allow for good heat transport.
You may have noticed that I assumed in my example a constant 20°C for the VC ambience.
NO real world speaker will EVER provide that (at usual room temperatures) - yours wont as well.
Sure the aluminium part of your VC helps to enlarge the radiating area of the coil itself – but the aluminium material usually is too thin to allow for massive heat transport (I leave that quick calculation to someone else )
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Earl, yes looking at Konstatan (?) I had the same idea with Nickel , but....
JohnE_J already has shown the weak point...
Maybe there is a workaround?
--------------
Lynn, yes – this I already assumed in my quick example
Greetings
Michael
nickmckinney said:
Hi Nick, yes lots of effort to transmit heat.
Nevertheless you wont get rid of the thermal transients this way – just reducing it by maybe a factor of three or four (my rough guess only) to common designs.
Not bad at all – but by no means comparable for what could be realised with better wire composits.
Good thing is, your speakers do not relay on the dust-cap-air-pump-cooling-effect that is heavily program dependant.
The core part is the VC - anything else is just to keep down the temperatures of the VC ambience to allow for good heat transport.
You may have noticed that I assumed in my example a constant 20°C for the VC ambience.
NO real world speaker will EVER provide that (at usual room temperatures) - yours wont as well.
Sure the aluminium part of your VC helps to enlarge the radiating area of the coil itself – but the aluminium material usually is too thin to allow for massive heat transport (I leave that quick calculation to someone else
)--------------
Earl, yes looking at Konstatan (?) I had the same idea with Nickel , but....
JohnE_J already has shown the weak point...
Maybe there is a workaround?
--------------
Lynn Olson said:
Lynn, yes – this I already assumed in my quick example
Greetings
Michael
Lynn Olson said:
I have to be honest in that I have reconed a few thousand speakers and never saw a driver that did that. I imagine it would be a pita to keep the dimensional tolerances correct and to shim the gap correctly when assembling. We do ours with a layer of Nomex between the windings and the former to lower the outgassing problem that comes with extreme high power. IMHO someone would have to teach me why this is a better way.