earlier this year, a local friend presented me with two of these things. They're his dad's, and he wants decent cabinets built for them. Of course, that includes decent crossovers. Pretty cool, I'd never seen one before. These are from the mid-late '50's.
In the course of telling another buddy about them, and asking if he'd ever seen that model, he says "Yeah, I think I've got one in my living room." How in the world I've been to his house 100 times and never noticed it, I will never understand (it's not a big room), but sure enough, what he had was a complete, unmolested 606 cabinet from 1953, including the original crossover and driver. This one was originally blonde, but the finish deteriorated many years ago, so I brought it home, scraped the old stuff off, and refinished it with oil and wax. It's gorgeous, very solid, and incredibly well built. The guy with the two others had the woofer reconed, but it was done with the later cone, the one with the accordion surround (8H?), so I'm leaving it alone for now to concentrate on building cabs for his original two.
Anyway, I read all of Markwart's material on the subject, tried a few different crossover designs/values, got the T-S parameters, and I've been mulling over the cab design. I know it's gonna be 3/4" Baltic birch, with a baffle that slants about 10 degrees back, and a 6" flared port. Still not set on an overall volume, but I'm leaning towards 4.5 - 5 cubic feet. Plenty of bracing. I'm going to get the finish as close to piano black as I can. got a few questions.
1) I see where a lot of people have the alnico magnets remagnetized. I'm not sure why; do they really lose that much power over time? Is this a function of age, or use? The drivers test out fine, so I'm not convinced this is a necessity, at least not at this point, and I'm really hesitant to ship these monsters anywhere.
2) feet. The vast majority of my builds have been for guitar/bass amps, and I just stick some round rubber feet on and call it a day. Now I'm looking at those, or those pointy feet, or no feet....heck, I don't know. I can see how no feet would help the cab couple with the floor, but I'm not sure I'd want that, except maybe on concrete, where the floor's not gonna resonate. Anybody got any favorites?
3) Has anybody here actually had much experience with these drivers? They're very strange. That coaxial horn has a way with vocals that I've never heard from any other driver; you'd swear the singer was standing right there. At the same time, getting anything close to a flat response has eluded me so far, even with the 3rd-order Butterworth crossover approach that Markwart settled on. I guess it's a function of the horn, or maybe the overall coaxial geometry, but there's always a solid midrange hump that I really haven't been able to flatten much. It's not necessarily a bad thing (vocals!), I'm just interested in whether I've reached the point of diminishing returns on crossover research.
anyway, any input is appreciated.
In the course of telling another buddy about them, and asking if he'd ever seen that model, he says "Yeah, I think I've got one in my living room." How in the world I've been to his house 100 times and never noticed it, I will never understand (it's not a big room), but sure enough, what he had was a complete, unmolested 606 cabinet from 1953, including the original crossover and driver. This one was originally blonde, but the finish deteriorated many years ago, so I brought it home, scraped the old stuff off, and refinished it with oil and wax. It's gorgeous, very solid, and incredibly well built. The guy with the two others had the woofer reconed, but it was done with the later cone, the one with the accordion surround (8H?), so I'm leaving it alone for now to concentrate on building cabs for his original two.
Anyway, I read all of Markwart's material on the subject, tried a few different crossover designs/values, got the T-S parameters, and I've been mulling over the cab design. I know it's gonna be 3/4" Baltic birch, with a baffle that slants about 10 degrees back, and a 6" flared port. Still not set on an overall volume, but I'm leaning towards 4.5 - 5 cubic feet. Plenty of bracing. I'm going to get the finish as close to piano black as I can. got a few questions.
1) I see where a lot of people have the alnico magnets remagnetized. I'm not sure why; do they really lose that much power over time? Is this a function of age, or use? The drivers test out fine, so I'm not convinced this is a necessity, at least not at this point, and I'm really hesitant to ship these monsters anywhere.
2) feet. The vast majority of my builds have been for guitar/bass amps, and I just stick some round rubber feet on and call it a day. Now I'm looking at those, or those pointy feet, or no feet....heck, I don't know. I can see how no feet would help the cab couple with the floor, but I'm not sure I'd want that, except maybe on concrete, where the floor's not gonna resonate. Anybody got any favorites?
3) Has anybody here actually had much experience with these drivers? They're very strange. That coaxial horn has a way with vocals that I've never heard from any other driver; you'd swear the singer was standing right there. At the same time, getting anything close to a flat response has eluded me so far, even with the 3rd-order Butterworth crossover approach that Markwart settled on. I guess it's a function of the horn, or maybe the overall coaxial geometry, but there's always a solid midrange hump that I really haven't been able to flatten much. It's not necessarily a bad thing (vocals!), I'm just interested in whether I've reached the point of diminishing returns on crossover research.
anyway, any input is appreciated.
Under normal home usage, and without any major physical shocks(drops) I would guess your Altec 604C has lost about 1db/watt in SPL efficiency over the last 55 years from Alnico magnet aging.
If your two speakers measure similar A=B T/S parameters that are close to the datasheet, I would never risk sending them out for Alnico V magnet recharge.
SOME CABINET THOUGHTS:
a) The 604C horn center sounds best at ~40" height = ear level. No baffle slant is common with a 40 degree vertical horn already located at ear level. The cabinet will be over 50" tall. An MLTL is often recommended for tall single driver cabinet construction. MLTL has proven sonic advantages over even "golden ratio" bass reflex cabinets. Post your T/S measurements and experts here will give you a design.
b) The 16" cone midbass extends to 1,600Hz, so cabinet edge diffraction must be reduced or imaging is severely compromised. 4-6" radius edges, or large angle-cut edges. The cabinet will be ~22-23" wide. 55"H x 23"W x 18"D ---> about 10 cuft internal volume. F3 below 30Hz.
3) Develop a plan for room mode compensation. 1) flexible port tuning. 2) Switched passive components in xover. 3) Active equalization. 4) Move speaker around...and...around...and...around.
4) A very tall cabinet benefits from a very short base... single board plinth... 1.5" high square foot-kick base that also encloses the Xover and rear amp connectors.... four 0.5" high nylon circular slide feet for hard floors.
5) A large radius on the internal and external port terminations is important, and is easier with circular ports and plastic pipes. A clever solution to adjust the port length is important.
CROSSOVER: Read the diyAudio threads on
"Quasi-optimal" crossover for high-efficiency loudspeaker system Jean-Michel Le Cléac'h Xovers, as alternatives to Markwart's well reviewed design.
http://www.diyaudio.com/forums/mult...sover-high-efficiency-loudspeaker-system.html
================
Altec 604C
15" Duplex Speaker
Magnets: Alnico V
Power Rating: 35 watts, 50 peak
Free Air Resonance: 38Hz
Response: 30Hz - 22kHz
Crossover: 1600 Hz
Network: N-1600-A - series filter network
Impedance: 16 ohms nominal
HF horn: 6-section sectoral-style horn with divider vanes - 90° horizontal and 40° vertical
Phase Plug: Circumferential
Cone: all paper cone - half-roll surround
Frame: 15.2" cast frame, rear mount - green hammertone
Weight with network: 40 lb.
comment: first to use extended throat 6-section sectoral-style "egg crate" horn with divider vanes - much closer sounding to the newer models than previous versions...
--------------WEB---------->
There are five primary mechanisms working in concert to demagnetize Alnico magnets - fortunately only a couple of them are likely to affect loudspeakers...
1. Age:
The flux in all magnets diminishes slowly over time, due to thermal fluctuation of the magnetic moment. All grades (3, 5, 5G, 7, & 8) of Alnico suffers from this problem more than ceramic ferrite magnets, and what we call "permanent magnets" are not quite permanent after all. The lower the permanence coefficient of the magnetic circuit, the faster the magnetic domains return to their random equilibrium. In typical Alnico 5 or 5DG magnets, the flux drops very slowly, at 2~3% per decade, for broadband sensitivity loss of only 1dB over 40-years, although losses at high frequencies may be more severe. Sumitomo Special Metals Co, of Osaka, Japan, have documented this phenomenon in considerable technical detail, but the research is not available on-line.
2. Thermal losses:
There are two distinct forms of temperature related flux loss: reversible, where the flux recovers to its original level as the temperature returns to normal; and irreversible, where the flux never recovers. Good thermal design in the magnetic structure minimizes reversible losses, and (mercifully) the temperatures that endanger alnico alloys, the Curie point, are far higher than those observed in loudspeakers, at 520 degrees Celcius. In loudspeakers, thermal losses in magnetic energy can be neglected.
3. Pulse loss:
Alnico speakers are intrinsically susceptible to modulation of the flux by the AC field from the voice coil. When operating normally, this momentary (AC) flux is superimposed over the permanent (DC) magnetic field. During normal listening, there the magnetic flux is dynamically modulated, causing third harmonic distortion. This non-linearity is a major contributor to the 'Alnico Sound', and is often welcomed by musicians and Alnico speaker lovers. Unfortunately, as the input power rises, the strength of the modulating field may exceed the intrinsic coercivity of the Alnico, partially degaussing the magnet. A single high power 'pop' can reduce sensititivity by 2dB, and repeated pulses, such as loud cracks from a faulty connection will cause additional (smaller) losses. Alnico drivers become noticeably quieter, especially at the top of their range. A speakers' sensitivity to discharge is proportional to the aspect ratio of the Alnico slug, the length of voice coil winding, and amount of available amplifier power. Virtually all Alnico woofers that have been enjoyed loudly show some flux loss, and those with short slugs and long coils suffer most. Most such designs date from the 1950s and 60s, when 35-watts was considered high-power, and amplifiers lacked the ability to endanger magnets. The problem effects virtually all Alnico drivers that have been used with modern, high power amplifiers.
For example: Low frequency drivers with 4-inch voice coils (JBL D120, D130, D140, LE15, 2205, 2215, 2231, Gauss, or TAD drivers) can lose 2~3dB, becoming 'dull' or 'slow' sounding, unless they have been grossly abused, in which case they more and sound dreadful. Drivers with short Alnico slugs and 3-inch voice coils, (JBL 2213, 123A, etc) are effected more severely, so typically show 3dB sensitivity loss, while small alnico woofers (JBL 116A, 125A, 127A etc) are commonly 4dB down after quite modest use. Conversely, speakers with higher coercivity ( taller Alnico slugs) and short voice coils, such as Tannoy dual concentrics, Altec and EV woofers, rarely suffer unless they have been badly abused. Users report that Altec 416, 515, and 604 drivers become 'mushy' after heavy use, but most of their loss of definition is due to fatigued cones. Remagnetization can restore the magnet, but cannot address cone fatigue.
Most Alnico compression drivers (JBL LE85, LE175, 375, 2410, 2420, 2440, 2441, Altec 288, 290, 802, 804, 806, 808, Emilar EA-175, TAD 2001, 4001, Goto Unit, etc) have tall magnets, short voice coils, and modest power inputs, so do not suffer degaussing. Those compression drivers with low aspect ratio magnets, especially if used <500Hz (Vitavox S2, University ID series, Klipsch K-55-V, Electrovoice 1823M etc) can suffer flux loss, and will benefit from remagnetization.
4. Shock:
Knocking or hammering on an Alnico magnet causes a sudden, dramatic reduction in magnetic energy as the shockwave knocks the closely aligned magnetic domains from their parallel pattern into a more random pattern. Shocks during shipping (from accidental drops) can cause a reduction in sensitivity. Mercifully, beating expensive loudspeaker magnets with hammers is not a common pastime. The solution is remagnetization, and, providing nothing else was broken, original performance is restored.
5. Disassembly:
If an Alnico magnet structure is opened, such as to re-centre a shifted pole-piece, repair a broken throat, or remove a bug-screen, the magnetic field collapses instantly. While this type of damage is not common, ill-advised repairs create very unwelcome problems. If a compression driver is dropped, aside from the possible 'shock' loss (see above) the magnet may shift inside the structure, breaking the throat molding. In these circumstances, the output may drop 20dB, as the magnet is seriously discharged. If there are other issues such as shifted pole, broken throat, corrosion, or loose internal parts, we can discharge the magnet, repair the problem, then remagnetize the driver, back to factory spec.
Ferrite magnets do not demagnitize with time or drive. They are affected by temperature but that is reversible. They will return to normal when they return to room temperature. Ferrite is basically a lousy magnet material for speakers but it is cheap and readily available. JBL has done a ton of things within the magnetic circuit to make the material behave in a more stable manner. At 100 degrees F, a Ferrite motor will be down about 1.5 dB in level which means the midband of the woofer will be lower by that much and there will be increased output around the system resonance. The TS parameters will be completely different - as though the BL was reduced by about 18%.
Alnico magnets, by their nature are easy to demagnitize with drive. They will not change with time and their dependence on temperature is really small - maybe 1% at 100 deg.F. Alnico stability and resistance to back EMF is really good. This is why they make the best sounding magnetic structures. Unfortunatelly, given a big enough pulse of magnetic energy, they will demagnitize by up to 3 dB. The sensitivity to demagging is dependent on the specifics of the magnetic circuit and the length of the coil providing the field. Underhung woofers (LE15 and such) midranges, tweeters and compression drivers do not have sufficient back EMF fields to push the operating point of the structure below the knee. They are essentially stable regardless of input signal. The short gap-long coil speakers are the ones that have a problem. A 2235 can take a hit of up to 3 dB if a big enough hit of current takes place. 1.5 dB to 2 dB is more common. The effect does not get better or worse with time, it solely depends on how much current is driven through the coil. The more current, the more field. Once the field is bigger than a certain number, some amount of demagnitizing occurs. It is perminent (until externally recharged) and will only increase if a larger sustained current hit occurs.
If your two speakers measure similar A=B T/S parameters that are close to the datasheet, I would never risk sending them out for Alnico V magnet recharge.
SOME CABINET THOUGHTS:
a) The 604C horn center sounds best at ~40" height = ear level. No baffle slant is common with a 40 degree vertical horn already located at ear level. The cabinet will be over 50" tall. An MLTL is often recommended for tall single driver cabinet construction. MLTL has proven sonic advantages over even "golden ratio" bass reflex cabinets. Post your T/S measurements and experts here will give you a design.
b) The 16" cone midbass extends to 1,600Hz, so cabinet edge diffraction must be reduced or imaging is severely compromised. 4-6" radius edges, or large angle-cut edges. The cabinet will be ~22-23" wide. 55"H x 23"W x 18"D ---> about 10 cuft internal volume. F3 below 30Hz.
3) Develop a plan for room mode compensation. 1) flexible port tuning. 2) Switched passive components in xover. 3) Active equalization. 4) Move speaker around...and...around...and...around.
4) A very tall cabinet benefits from a very short base... single board plinth... 1.5" high square foot-kick base that also encloses the Xover and rear amp connectors.... four 0.5" high nylon circular slide feet for hard floors.
5) A large radius on the internal and external port terminations is important, and is easier with circular ports and plastic pipes. A clever solution to adjust the port length is important.
CROSSOVER: Read the diyAudio threads on
"Quasi-optimal" crossover for high-efficiency loudspeaker system Jean-Michel Le Cléac'h Xovers, as alternatives to Markwart's well reviewed design.
http://www.diyaudio.com/forums/mult...sover-high-efficiency-loudspeaker-system.html
================
Altec 604C
15" Duplex Speaker
Magnets: Alnico V
Power Rating: 35 watts, 50 peak
Free Air Resonance: 38Hz
Response: 30Hz - 22kHz
Crossover: 1600 Hz
Network: N-1600-A - series filter network
Impedance: 16 ohms nominal
HF horn: 6-section sectoral-style horn with divider vanes - 90° horizontal and 40° vertical
Phase Plug: Circumferential
Cone: all paper cone - half-roll surround
Frame: 15.2" cast frame, rear mount - green hammertone
Weight with network: 40 lb.
comment: first to use extended throat 6-section sectoral-style "egg crate" horn with divider vanes - much closer sounding to the newer models than previous versions...
--------------WEB---------->
There are five primary mechanisms working in concert to demagnetize Alnico magnets - fortunately only a couple of them are likely to affect loudspeakers...
1. Age:
The flux in all magnets diminishes slowly over time, due to thermal fluctuation of the magnetic moment. All grades (3, 5, 5G, 7, & 8) of Alnico suffers from this problem more than ceramic ferrite magnets, and what we call "permanent magnets" are not quite permanent after all. The lower the permanence coefficient of the magnetic circuit, the faster the magnetic domains return to their random equilibrium. In typical Alnico 5 or 5DG magnets, the flux drops very slowly, at 2~3% per decade, for broadband sensitivity loss of only 1dB over 40-years, although losses at high frequencies may be more severe. Sumitomo Special Metals Co, of Osaka, Japan, have documented this phenomenon in considerable technical detail, but the research is not available on-line.
2. Thermal losses:
There are two distinct forms of temperature related flux loss: reversible, where the flux recovers to its original level as the temperature returns to normal; and irreversible, where the flux never recovers. Good thermal design in the magnetic structure minimizes reversible losses, and (mercifully) the temperatures that endanger alnico alloys, the Curie point, are far higher than those observed in loudspeakers, at 520 degrees Celcius. In loudspeakers, thermal losses in magnetic energy can be neglected.
3. Pulse loss:
Alnico speakers are intrinsically susceptible to modulation of the flux by the AC field from the voice coil. When operating normally, this momentary (AC) flux is superimposed over the permanent (DC) magnetic field. During normal listening, there the magnetic flux is dynamically modulated, causing third harmonic distortion. This non-linearity is a major contributor to the 'Alnico Sound', and is often welcomed by musicians and Alnico speaker lovers. Unfortunately, as the input power rises, the strength of the modulating field may exceed the intrinsic coercivity of the Alnico, partially degaussing the magnet. A single high power 'pop' can reduce sensititivity by 2dB, and repeated pulses, such as loud cracks from a faulty connection will cause additional (smaller) losses. Alnico drivers become noticeably quieter, especially at the top of their range. A speakers' sensitivity to discharge is proportional to the aspect ratio of the Alnico slug, the length of voice coil winding, and amount of available amplifier power. Virtually all Alnico woofers that have been enjoyed loudly show some flux loss, and those with short slugs and long coils suffer most. Most such designs date from the 1950s and 60s, when 35-watts was considered high-power, and amplifiers lacked the ability to endanger magnets. The problem effects virtually all Alnico drivers that have been used with modern, high power amplifiers.
For example: Low frequency drivers with 4-inch voice coils (JBL D120, D130, D140, LE15, 2205, 2215, 2231, Gauss, or TAD drivers) can lose 2~3dB, becoming 'dull' or 'slow' sounding, unless they have been grossly abused, in which case they more and sound dreadful. Drivers with short Alnico slugs and 3-inch voice coils, (JBL 2213, 123A, etc) are effected more severely, so typically show 3dB sensitivity loss, while small alnico woofers (JBL 116A, 125A, 127A etc) are commonly 4dB down after quite modest use. Conversely, speakers with higher coercivity ( taller Alnico slugs) and short voice coils, such as Tannoy dual concentrics, Altec and EV woofers, rarely suffer unless they have been badly abused. Users report that Altec 416, 515, and 604 drivers become 'mushy' after heavy use, but most of their loss of definition is due to fatigued cones. Remagnetization can restore the magnet, but cannot address cone fatigue.
Most Alnico compression drivers (JBL LE85, LE175, 375, 2410, 2420, 2440, 2441, Altec 288, 290, 802, 804, 806, 808, Emilar EA-175, TAD 2001, 4001, Goto Unit, etc) have tall magnets, short voice coils, and modest power inputs, so do not suffer degaussing. Those compression drivers with low aspect ratio magnets, especially if used <500Hz (Vitavox S2, University ID series, Klipsch K-55-V, Electrovoice 1823M etc) can suffer flux loss, and will benefit from remagnetization.
4. Shock:
Knocking or hammering on an Alnico magnet causes a sudden, dramatic reduction in magnetic energy as the shockwave knocks the closely aligned magnetic domains from their parallel pattern into a more random pattern. Shocks during shipping (from accidental drops) can cause a reduction in sensitivity. Mercifully, beating expensive loudspeaker magnets with hammers is not a common pastime. The solution is remagnetization, and, providing nothing else was broken, original performance is restored.
5. Disassembly:
If an Alnico magnet structure is opened, such as to re-centre a shifted pole-piece, repair a broken throat, or remove a bug-screen, the magnetic field collapses instantly. While this type of damage is not common, ill-advised repairs create very unwelcome problems. If a compression driver is dropped, aside from the possible 'shock' loss (see above) the magnet may shift inside the structure, breaking the throat molding. In these circumstances, the output may drop 20dB, as the magnet is seriously discharged. If there are other issues such as shifted pole, broken throat, corrosion, or loose internal parts, we can discharge the magnet, repair the problem, then remagnetize the driver, back to factory spec.
Ferrite magnets do not demagnitize with time or drive. They are affected by temperature but that is reversible. They will return to normal when they return to room temperature. Ferrite is basically a lousy magnet material for speakers but it is cheap and readily available. JBL has done a ton of things within the magnetic circuit to make the material behave in a more stable manner. At 100 degrees F, a Ferrite motor will be down about 1.5 dB in level which means the midband of the woofer will be lower by that much and there will be increased output around the system resonance. The TS parameters will be completely different - as though the BL was reduced by about 18%.
Alnico magnets, by their nature are easy to demagnitize with drive. They will not change with time and their dependence on temperature is really small - maybe 1% at 100 deg.F. Alnico stability and resistance to back EMF is really good. This is why they make the best sounding magnetic structures. Unfortunatelly, given a big enough pulse of magnetic energy, they will demagnitize by up to 3 dB. The sensitivity to demagging is dependent on the specifics of the magnetic circuit and the length of the coil providing the field. Underhung woofers (LE15 and such) midranges, tweeters and compression drivers do not have sufficient back EMF fields to push the operating point of the structure below the knee. They are essentially stable regardless of input signal. The short gap-long coil speakers are the ones that have a problem. A 2235 can take a hit of up to 3 dB if a big enough hit of current takes place. 1.5 dB to 2 dB is more common. The effect does not get better or worse with time, it solely depends on how much current is driven through the coil. The more current, the more field. Once the field is bigger than a certain number, some amount of demagnitizing occurs. It is perminent (until externally recharged) and will only increase if a larger sustained current hit occurs.
cool. they're staying here, then.
I'll be doing good to create a decent "golden ratio" box; not sure I wanna go for the MLTL thing just yet.
Fs = 48 Hz
Qms = 2.74
Vas = 160 liters
Cms = 0.12 mm/N
Mms = 92.5 g
Rms = 10.13 kg/s
Piston diameter = 13.5 inches
Sd = 143.5 square inches
Qes = 0.397
Re = 10 ohms
Le = 2.34 mH
Qts = 0.303
ok, I was thinking I'd just use a 3/4" roundover on the cut-out.
the 606 cab is easily 8 cubic feet, and already sounds woofy. Is that because the port's not the right size/shape?
prolly leave that up to the owner. He's not that picky, and these might get moved quite a bit.
cool.
is the Precision Port stuff any good? they look real nice.
thanks!
I just sold my 604 C's after spending 2 years trying to get a decent sound out of them. I was close many times. I would not send them out to get remagged as mine didn't sound any better after having it done. They are a great sounding speaker but will need a sub for theater type work. They don't play real deep. the Fs of mine was 52. If you get them reconed with the accordion surround then you won't need a sub as they will play nice and deep as my 604 E did. You could give one of my crossover designs a try if you'd like. I thought they sounded best with them but It's up to you. Heres a link to them. I spent like $300 on the GPA crossovers and they sounded like ***.
ToddsAltec604Ccrossover2 | Flickr - Photo Sharing!
or this one.
604wiring | Flickr - Photo Sharing!
I wish you good luck with them. and yes definitely rubber feet or something that will isolate them from the floor.
ToddsAltec604Ccrossover2 | Flickr - Photo Sharing!
or this one.
604wiring | Flickr - Photo Sharing!
I wish you good luck with them. and yes definitely rubber feet or something that will isolate them from the floor.
Last edited:
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