Well I finally got the speakers loaded in 2 of my T48's, grabbed the monitor amp off the truck QSC 2450 and crossed them over at 100Hz cut 35Hz.
Hooked up my volt meter to the binding posts ran some low end based music, Black Label Society and with the volt meter reading around 20 volts.
All I can say is Thank You Bill! I had them in a small 12 by 10 shed at first putting the speakers in everything was rattling. Moved them outside and measured out 18 feet pulled out the Radio Shack Db meter 112Db with C weighting both hooked up to one side of the QSC. I read somewhere that 400 watts x 10 ohms would be about 62 volts? My wife came out thinking a kid had one of those ghetto thumpers parked on the street. Priceless more testing on the way once I get my other 2 T48's here.
Thank You Bill!
" Everyone Has a Photographic Memory, Just Not Everyone Has Film In The Camera"
I know what you mean about the 'OMG factor'. This past weekend I had two (3015LF) T48s V-plated in the school gym for an event. They were driven with 1 side of a Crown CE2000 (parallel), and idling at 10 volts (20W).
James R wrote:Well I finally got the speakers loaded in 2 of my T48's, grabbed the monitor amp off the truck QSC 2450 and crossed them over at 100Hz cut 35Hz.
Hooked up my volt meter to the binding posts ran some low end based music, Black Label Society and with the volt meter reading around 20 volts.
All I can say is Thank You Bill! I had them in a small 12 by 10 shed at first putting the speakers in everything was rattling. Moved them outside and measured out 18 feet pulled out the Radio Shack Db meter 112Db with C weighting both hooked up to one side of the QSC. I read somewhere that 400 watts x 10 ohms would be about 62 volts? My wife came out thinking a kid had one of those ghetto thumpers parked on the street. Priceless more testing on the way once I get my other 2 T48's here.
Thank You Bill!
2 on one side of an amp would be 5ohms. But for calcs it's either (V*V)/R=W or sqrt(W*R)=V sqrt(400*10)=63.2 but for Voltage input calcs I usually go conservative and calc as if it were the driver alone. Power compression also kicks in about 300W on those so keeping it about 50V or less will keep it cool and prevent the neo magnet from killing itself with heat. Reports are that neos will loose their magnetism under high heat reducing output and the resulting heat damage is permanent.
gdougherty wrote:Reports are that neos will loose their magnetism under high heat reducing output and the resulting heat damage is permanent.
I've heard that rumor. Would the cabinet or cone ignite at some point before the NIB magnet got warm enough to demagnetize? This could also be BS designed to limit the sales of otherwise superior NEO drivers.
Perhaps someone here has the materials science background to speak to the "how hot before it demagnetizes" question. I don't run my gear very hot, but I would like to know the practical limits.
Has anyone here demagnetized a NEO driver through hard use?
gdougherty wrote:Reports are that neos will loose their magnetism under high heat reducing output and the resulting heat damage is permanent.
I've heard that rumor. Would the cabinet or cone ignite at some point before the NIB magnet got warm enough to demagnetize? This could also be BS designed to limit the sales of otherwise superior NEO drivers.
Perhaps someone here has the materials science background to speak to the "how hot before it demagnetizes" question. I don't run my gear very hot, but I would like to know the practical limits.
Has anyone here demagnetized a NEO driver through hard use?
I'm pretty sure it's more than a rumor. I think it was someone here talking about driver repair work they did. I'd think that as long as you keep it below the RMS value that you'd be okay. For practical purposes the point of significant power compression is the more useful goal as that will keep the magnet and voice coil at a good temp. 300W into a T48 generates a lot of noise. 50V band passed pink noise into a T48 is not anything you want to be near either. Outdoors and in larger venues you'll want more drivers anyway. You can only do so much with a single driver.
"Neodymium magnets are very strong relative to their mass, but are also mechanically fragile. Like other ferromagnetic materials, neodymium magnets lose their magnetism above a temperature known as the Curie point. But the most powerful grades lose their magnetism at a relatively low temperature: 80 degrees Celsius (176 degrees Fahrenheit) and above. High-temperature grades will operate at up to 200 and even 230°C but their strength is only marginally greater than that of a samarium-cobalt magnet."
Wayne from Pi Speakers did some cooling plug temperature measurements of the Lab12 driver. He measured 195F on the pole piece and over 130f at the outside of the magnet. Seems like you could do some permanent damage if driven hard enough. For what it's worth I have driven my 3015lf drivers plenty hard, and they seem to be just fine. I think you would need an extended amount of time at very high power levels to cause heat damage. More likely, you'd encounter physical damage first...just my opinion of course
James R wrote:Well I finally got the speakers loaded in 2 of my T48's, grabbed the monitor amp off the truck QSC 2450 and crossed them over at 100Hz cut 35Hz.
Hooked up my volt meter to the binding posts ran some low end based music, Black Label Society and with the volt meter reading around 20 volts.
All I can say is Thank You Bill! I had them in a small 12 by 10 shed at first putting the speakers in everything was rattling. Moved them outside and measured out 18 feet pulled out the Radio Shack Db meter 112Db with C weighting both hooked up to one side of the QSC. I read somewhere that 400 watts x 10 ohms would be about 62 volts? My wife came out thinking a kid had one of those ghetto thumpers parked on the street. Priceless more testing on the way once I get my other 2 T48's here.
Thank You Bill!
2 on one side of an amp would be 5ohms. But for calcs it's either (V*V)/R=W or sqrt(W*R)=V sqrt(400*10)=63.2 but for Voltage input calcs I usually go conservative and calc as if it were the driver alone. Power compression also kicks in about 300W on those so keeping it about 50V or less will keep it cool and prevent the neo magnet from killing itself with heat. Reports are that neos will loose their magnetism under high heat reducing output and the resulting heat damage is permanent.
gdougherty could you elberate a little more on the math end for me, I'd really like to know how much was actually being fed to these.
Thanks,
Jim
" Everyone Has a Photographic Memory, Just Not Everyone Has Film In The Camera"
James R wrote:
gdougherty could you elberate a little more on the math end for me, I'd really like to know how much was actually being fed to these.
Thanks,
Jim
The 10ohm is a realistic load for one cab to use for the calcs so for example if 20V was measured it'd be (20V*20V)/10ohms = 40W. If it were two cabs the resistance is halved and wattage doubles to 80W. You can reverse the calc to find useable voltage figures for a given power rating. 300W @ 8ohm comes out to about 49V.
Ok I get that part, thanks. Here's where it gets fuzzy for me If I'm running 2 cabinets at 5 ohms would I double the speaker rating from 1 @ 450 to 2 @ 900 total that would figure out to 67 volts right? so each cab would receive 450w
Thanks,
Jim
" Everyone Has a Photographic Memory, Just Not Everyone Has Film In The Camera"
Voltage is always a constant measure assuming the amp can supply sufficient voltage into the load. Therefore, if voltage squared will be constant and you half the impedance/resistance, you double the wattage. impedance is halved when you double the driver count in parallel and doubled if you double the count in series. I started from RMS wattage and driver spec'd resistance to get the RMS voltage specified by Eminence. From there you can convert to 10ohms or whatever you need.
Keep in mind power compression and xmax both occur below the RMS spec. RMS is just the 8 hours with no damage rating. Anything above xmax increases distortion and anything above power compression is rapidly diminishing returns. Note that from the 300W power compression figure you're probably getting 1db at best additional output bumping things to 450W. 1db is the average threshold for volume changes to be perceived. Exceptionally sensitive ears may notice .5db.
Doubling the cab count doubles power handling and gets an additional 3db of output plus 3db of sensitivity without risk to the driver. Theoretically the single driver would have to take 1200W without power compression (physically impossible) to get the same gain.
By your example
sqrt(450*8) = 60Volts (RMS voltage from actual driver specs)
sqrt(300*8) = 49Volts (power compression onset)
(60^2)/10 = 360W
(60^2)/5 = 720W (2 cab)
(60^2)/2.5 = 1440W (4 cab)
I'm glad that George mentioned the bit about thermal compression. Reality is, it starts shortly after the voice coil wire ( 32 - 40 gauge ) starts heating with as little as 1/10 power capacity, to get worse with more power, until ( as stated ) at 1/2 power, a large portion is waste heat.
The formulas given are for DC circuits. Audio is AC.
The assumption is that the impedance is constant over a speaker's bandpass. It is not, the impedance and phase vary with frequency.
Most will pick the lowest ( worst case ) impedance value, or a nominal value to base calcs.
So AC voltage is multiplied by the cosine of the electric phase angle (φ) Practically speaking using the DC calcs, will probably be sufficient, especially with horn speakers that have a good impedance/phase relationship.
However if you use the same calcs on non-horn speakers ( say 18's in a bass reflex ), I would be more conservative because of the more reactive load that BR design present ( if for no other reason to go easy on the amp )
Based on the test results of Leland's T48s I'm inclined to think that well engineered neo drivers suffer less thermal power compression. That's because small neo magnets don't store as much heat as large ferrite magnets, while the heat sinking employed to keep the neo from overheating would also keep voice coil temperatures lower.
I am not sure about the physics of heat on neo magnets, but we know for a fact that several folks have blown the 3015LF's. It would make sense that if sensitivity goes down as the temp goes up, you try to get a bit more output to compensate and pass the point of no return.
IIRC, someone posted pics of a burnt voice coil. This would indicate heat damage. Whether the heat causes permanent damage to the magnet would affect the decision to recone. How could this be tested?
I have run the Deltalite II 2510's with an amp rated 500w RMS @8 ohm, one per channel, and pushed them pretty hard with no ill effects. I imagine that neos in subs are stressed more.
Whether the heat causes permanent damage to the magnet would affect the decision to recone. How could this be tested?
I not sure about the best way to test a speaker magnet strength PRIOR to recone, except perhaps a flux meter ( expensive ).
Any woofer with a working voice coil can have the BL measured.
The LDC outlines a method to calculate magnet strength by placing a carefully weighted mass on a cone and determining the amount of voltage it takes to "lift" the weight, and return the cone to the "rest' point.
Also: If the magnet is gone - the some of the T/S values will reflect that as well.
everything was rattling. Moved them outside and measured out 18 feet pulled out the Radio Shack Db meter 112Db with C weighting both hooked up to one side of the QSC. I read somewhere that 400 watts x 10 ohms would be about 62 volts? My wife came out thinking a kid had one of those ghetto thumpers parked on the street. Priceless more testing on the way once I get my other 2 T48's here.
