Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Mac Kerr]

this would be with active crossover only and nothing but the speaker interconnect wire between the amp and speaker.

So the choice should be based on what the amp loading will be in the configuration you want to use them in.

Mac

[Chris Van Duker]

Out of curiosity, I went to the manufacturer's spec sheets for the 4 ohm and 8 ohm models.

4 ohm here: http://www.faitalpro.com/products/files/18XL1600/4/18XL1600_datasheet_4.pdf
8 ohm here: http://www.faitalpro.com/products/files/18XL1600/8/18XL1600_datasheet_8.pdf

Both show the same winding depth, at 31mm. The 8ohm driver has a lower moving mass, by 12.5 grams, and a slightly lower efficiency rating at 1.61% vs. 1.73%. Also interesting is that there isn't a 2x difference between the DC resistance ratings: 3 vs. 5.4 ohms -- that is, the 8 ohm driver is a "heavier" load for its rating than the 4 ohm driver.

-C

[John Roberts {JR}]

Out of curiosity, I went to the manufacturer's spec sheets for the 4 ohm and 8 ohm models.

4 ohm here: http://www.faitalpro.com/products/files/18XL1600/4/18XL1600_datasheet_4.pdf
8 ohm here: http://www.faitalpro.com/products/files/18XL1600/8/18XL1600_datasheet_8.pdf

Both show the same winding depth, at 31mm. The 8ohm driver has a lower moving mass, by 12.5 grams, and a slightly lower efficiency rating at 1.61% vs. 1.73%. Also interesting is that there isn't a 2x difference between the DC resistance ratings: 3 vs. 5.4 ohms -- that is, the 8 ohm driver is a "heavier" load for its rating than the 4 ohm driver.

-C

For this discussion the AC impedance is what matters. The small efficiency difference and DCR would be some of those small differences one would expect.

JR

[Douglas R. Allen]

Stop thinking about windings and wire gauge and reread what JR wrote. We are discussing 2 speakers that have the same output for the same Watts input, so at 1600W the acoustic power out is the same, the electrical power in is the same, the difference between the two is the heat power out.

The number of windings, and wire gauge and the magnetic flux all have an impact on the impedance of the speaker. We don't know any of those things here, and they don't really matter, because we do know that they have the same output for the same input, so the heat must be the same.

Since in real life the impedances are unlikely to actually be 4Ω and 8Ω, and power numbers can vary wildly at high levels with small changes in perceived volume it is sort of academic. The more important drivers in the decision about what driver to use in a speaker would probably be how does the impedance work with the crossover and how will it load the amps in the configuration you want to use. In the case of subs that are on their own amp, the crossover issue does not apply.

Mac

Mac;

The OP wanted to know which voice coil would get hotter.

"""if both speakers are powered to their max aes power rating will the voice coil of the 4ohm woofer get hotter than the vc in the 8ohm woofer"""

Voice coils wick heat just as a heat sink does to some extent. I'm saying that the coil with less windings regardless of imp. will not wick or handle current the same as one with more windings and get hotter but the OP is talking about more or less the same driver with different coils.

I realize the heat generated should be the same but how much overall surface area of the coil should come into play as well. Like how much surface area a heat sink has determines how much heat it can handle.
Are you saying that it doesn't?

I guess the only way to know for sure would be to take a 4 ohm and a 8 ohm version of these speakers and apply the same "wattage" as the op wanted to know, not voltage, to them and see which one gets hotter.

Douglas R. Allen

[Jeff Harrell]

Mac;

The OP wanted to know which voice coil would get hotter.

"""if both speakers are powered to their max aes power rating will the voice coil of the 4ohm woofer get hotter than the vc in the 8ohm woofer"""

Voice coils wick heat just as a heat sink does to some extent. I'm saying that the coil with less windings regardless of imp. will not wick or handle current the same as one with more windings and get hotter but the OP is talking about more or less the same driver with different coils.

I realize the heat generated should be the same but how much overall surface area of the coil should come into play as well. Like how much surface area a heat sink has determines how much heat it can handle.
Are you saying that it doesn't?

I guess the only way to know for sure would be to take a 4 ohm and a 8 ohm version of these speakers and apply the same "wattage" as the op wanted to know, not voltage, to them and see which one gets hotter.

Douglas R. Allen

you got it Mr. Allen. a friend has a temperature reading gun. i have the 4ohm version. i can borrow an amp rated 2000 watts at 8ohms. my amps are rated 1700 watts bridged at 4ohms. a friend has a test benck watt meter that he uses to measure amp power with which will be used make sure both speaker are tested at the same power level. i have a frequency/tone generator. i have a test box for the 18" woofer. all i need is to find a 8ohm 18xl1600 woofer to borrow. at $599.00 each i'm not going to buy one. i though someone here might know for sure the answer to my question. thanks for your help , Jeff
btw as i posted earlier these woofer dont have anything but speaker wire between them and the amp. the crossover is an active Ashly xr4001.

[Ivan Beaver]

you got it Mr. Allen. a friend has a temperature reading gun. i have the 4ohm version. i can borrow an amp rated 2000 watts at 8ohms. my amps are rated 1700 watts bridged at 4ohms. a friend has a test benck watt meter that he uses to measure amp power with which will be used make sure both speaker are tested at the same power level. i have a frequency/tone generator. i have a test box for the 18" woofer. all i need is to find a 8ohm 18xl1600 woofer to borrow. at $599.00 each i'm not going to buy one. i though someone here might know for sure the answer to my question. thanks for your help , Jeff
btw as i posted earlier these woofer dont have anything but speaker wire between them and the amp. the crossover is an active Ashly xr4001.

And just how do you plan on getting the temp gun on the voice coil?

And what source do you plan on using at the stimulus? Sine wave-noise-music?  There may be some very slight differences in the impedance curve (due to different L/C values that would affect the amount of current flowing at THAT freq.  Other freq would be different.

Also remember that the overall temp will change over time-even with a steady source-due to the heat of the surrounding areas-magnet etc.

[Jeff Harrell]

And just how do you plan on getting the temp gun on the voice coil?

And what source do you plan on using at the stimulus? Sine wave-noise-music?  There may be some very slight differences in the impedance curve (due to different L/C values that would affect the amount of current flowing at THAT freq.  Other freq would be different.

Also remember that the overall temp will change over time-even with a steady source-due to the heat of the surrounding areas-magnet etc.

i have a small test box without a back. so holding the temp sensor at the vented pole piece was the idea. i have a tone generator that can be set to any freq between 20&20k. i figured "IF" i could find an 8ohm driver to borrow i would send a 100hz steady tone for 30 minutes with the level adjusted to show 1600 watts rms and hold the temp gun to the vented pole piece and see what the temp is. hook the other speaker up to the same amp adjust to 1600 watts and repeat above. the temp gauge is a Fluke 63. i would take a reading of the pole piece before and after. i dont know if doing it this way will work but ti would be neat to try. anyone have a faitalpro 18xl1600 8ohm you ant to lend me ?

[John Roberts {JR}]

The OP is asking if the X Watt 4 ohm driver gets hotter than the X Watt 8 ohm driver. I will ASSume he meant a significant temperature difference.

Logic suggests similar amounts of heat energy being pushed into the VC., so now the difference, if any centers on how fast that heat gets out.

The relationship to calculate the temperature rise of a heat source above the surrounding environment's temperature is the "thermal resistance" of that heat source to ambient in degrees per watt. Temp rise is simply multiplying the power dissipated times this thermal resistance (heat is like current in this thermal Ohm's law). 

caveat: I am not a loudspeaker driver designer.

Heat gets transferred from a hot body to the cooler ambient around it by several mechanisms. Radiation, conduction, and convection. I expect the total thermal resistance between VC and air, is complex with several components contributing. The VC wire will be wrapped on a former, and that will serve to conduct heat away. Some drivers are designed to encourage forced air flow cooling from VC motion. I expect direct radiation from the wires to be modest, but secondary radiation of conducted heat probably happens.

This is all part of the work that the design engineer did when making the drivers handle the same power rating. One may be slightly hotter than the other but not enough for the mfr to derate the power handling.

This inspection is looking for a difference that the driver designer no doubt worked to avoid.  I would be surprised if they were exactly the same, or different enough to matter for typical applications. 

JR   

[Ivan Beaver]

i have a small test box without a back. so holding the temp sensor at the vented pole piece was the idea. i have a tone generator that can be set to any freq between 20&20k. i figured "IF" i could find an 8ohm driver to borrow i would send a 100hz steady tone for 30 minutes with the level adjusted to show 1600 watts rms and hold the temp gun to the vented pole piece and see what the temp is. hook the other speaker up to the same amp adjust to 1600 watts and repeat above. the temp gauge is a Fluke 63. i would take a reading of the pole piece before and after. i dont know if doing it this way will work but ti would be neat to try. anyone have a faitalpro 18xl1600 8ohm you ant to lend me ?

Depending on what the impedance is at 100Hz (it could be 8 ohms or 30 ohms or something else), you will probably kill the driver with a sine wave pretty quickly (if it is close to 8 ohms).

This is why you can take some drivers and plug them directly into and AC outlet  and they don't blow up (due to an impedance rise at 60Hz, while others will "melt down" pretty quickly-due to an impedance low at that freq.

I doubt anybody will "loan you" a driver to be that destructive with.  But some people like that kind of thing-just look at the you tube videos of people destroying speakers.

I have done that myself-sometimes on purpose.

[Art Welter]

i have a small test box without a back. so holding the temp sensor at the vented pole piece was the idea. i have a tone generator that can be set to any freq between 20&20k. i figured "IF" i could find an 8ohm driver to borrow i would send a 100hz steady tone for 30 minutes with the level adjusted to show 1600 watts rms and hold the temp gun to the vented pole piece and see what the temp is. hook the other speaker up to the same amp adjust to 1600 watts and repeat above. the temp gauge is a Fluke 63. i would take a reading of the pole piece before and after. i dont know if doing it this way will work but ti would be neat to try. anyone have a faitalpro 18xl1600 8ohm you ant to lend me ?

Jeff,

To expand on what Ivan just wrote,   the AES power rating uses compressed pink noise with a 6 dB crest factor.
Sine waves only have a three dB crest factor, twice the average power of an AES test signal.

If you set the voltage with a sine wave for 1600 watts, about 80 volts for 4 ohms, 112 volts for 8 ohms, the voice coil will likely burn before 1/2 hour is up, unless you happen to find a frequency corresponding to a high impedance peak.

I have done "full power" (sine wave at the AES rating) testing of various woofers, but have taken care to keep the tests very short, only a few seconds per frequency.
When slow to type in test descriptions, I have noticed the distinctive adhesive burning smell that signals the voice coil is close to burning.

In addition, since the sine wave is at a single frequency, it is not indicative of the average impedance-   for instance, the speaker would draw far more power at Fb than other frequencies, and because the voice coil hardly moves at Fb air cooling would be less than frequencies just above Fb.

A more meaningful test would be to apply pink noise (or the compressed AES pink noise) to both speakers, continue upping the input level 3 dB at 10 minute intervals and see which speaker tracks with less power compression.

Power compression won't show much difference between variants of the same type of speaker, but can be quite a lot between different types of speakers.

Art