I dont think i'm driving it that hard. It barely moves even 1mm around port tuning of 34hz. and it still gets hot.
but it doesnt even heat up at all when its flexing good like 19hz or 20hz barely even warm or above 40hz. coil doesnt even burn my finger when its in the box playing 19hz all day. just feels warm not searing hot. i can reach my finger in through the pole piece venting and feel the back of the coil on the inside because the pole piece venting is wide enough and doesnt go too deep inside the sub. its very tapered and smooth. good for SQ.
I can see right inside the venting and the coil is well centered in the gap. does not leave the gap very far either in my free air testing.
but it doesnt even heat up at all when its flexing good like 19hz or 20hz barely even warm or above 40hz. coil doesnt even burn my finger when its in the box playing 19hz all day. just feels warm not searing hot. i can reach my finger in through the pole piece venting and feel the back of the coil on the inside because the pole piece venting is wide enough and doesnt go too deep inside the sub. its very tapered and smooth. good for SQ.
I can see right inside the venting and the coil is well centered in the gap. does not leave the gap very far either in my free air testing.
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First, some facts:
1. The woofer in question (DS18 SLC12S) has 2" coil, DC resistance Re=3.6 ohms, resonant frequency Fs=40 Hz and declared power handling P=220W (RMS).
2. Vented box has tuning frequency Fb=34 HZ.
3. OP wonders why woofer gets hot at 20 Hz in free air and not in 30-40 Hz range, but it gets hot at 30-40 Hz range when mounted in a vented box tuned to 34 Hz.
Answer is very simple: woofer in free air has the highest impedance (much, much higher than Re=3.6 ohms) exactly at the Fs=40 Hz, so dissipated power is the lowest possible. High excursion at that frequency (because there is no box) also helps in cooling the coil. At 20 Hz woofer impedance is very low, approaching Re=3.6 ohms (slightly higher, actually), so it gets hot because the input signal is the same voltage as before, but the impedance is much lower.
When in box, impedance is about the lowest (approaching R=3.6 ohms, but higher than that) at the tuning frequency Fb=34 Hz, so dissipated power (and temperature) is the highest. At that frequency woofer motion is at minimum, restricting the coil cooling. The result is hot coil.
Simple, but often neglected Ohm's law in action. Which in turn begs for question: Why on Earth someone wants to abuse that poor woofer with high power sinusoidal signal?
Edit: Oh, and that declared 220 W RMS power handling actually is 220 W according to AES, so NO 220 W sinusoidal signal, please!
1. The woofer in question (DS18 SLC12S) has 2" coil, DC resistance Re=3.6 ohms, resonant frequency Fs=40 Hz and declared power handling P=220W (RMS).
2. Vented box has tuning frequency Fb=34 HZ.
3. OP wonders why woofer gets hot at 20 Hz in free air and not in 30-40 Hz range, but it gets hot at 30-40 Hz range when mounted in a vented box tuned to 34 Hz.
Answer is very simple: woofer in free air has the highest impedance (much, much higher than Re=3.6 ohms) exactly at the Fs=40 Hz, so dissipated power is the lowest possible. High excursion at that frequency (because there is no box) also helps in cooling the coil. At 20 Hz woofer impedance is very low, approaching Re=3.6 ohms (slightly higher, actually), so it gets hot because the input signal is the same voltage as before, but the impedance is much lower.
When in box, impedance is about the lowest (approaching R=3.6 ohms, but higher than that) at the tuning frequency Fb=34 Hz, so dissipated power (and temperature) is the highest. At that frequency woofer motion is at minimum, restricting the coil cooling. The result is hot coil.
Simple, but often neglected Ohm's law in action. Which in turn begs for question: Why on Earth someone wants to abuse that poor woofer with high power sinusoidal signal?
Edit: Oh, and that declared 220 W RMS power handling actually is 220 W according to AES, so NO 220 W sinusoidal signal, please!
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so at 19 and 20hz the impedance rises again since the subwoofer is moving a lot and resonates more from being in the box. it moves more in the box at 20hz than it does free air at 20hz.
thats why it handles it fine at 20hz in the box but not in free air? since it resonates and moves more and impedance rises higher when in the box at 19hz and 20hz?
you must be reading the wrong thing because mine is 250W RMS not 220W RMS and the specs on mine says 41hz FS but i think its actually lower than that from how much ive been playing it.
thats why it handles it fine at 20hz in the box but not in free air? since it resonates and moves more and impedance rises higher when in the box at 19hz and 20hz?
you must be reading the wrong thing because mine is 250W RMS not 220W RMS and the specs on mine says 41hz FS but i think its actually lower than that from how much ive been playing it.
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Sonce is absolutely right about one thing: It would never occur to me to torture any
speaker with a continuous sinewave. They are built and designed to reproduce music.
The power content of music is continuously changing and practically never continous at a constant high level. Unless overdriven , of course. This latter going for and/or the speaker plus the amplifier.
speaker with a continuous sinewave. They are built and designed to reproduce music.
The power content of music is continuously changing and practically never continous at a constant high level. Unless overdriven , of course. This latter going for and/or the speaker plus the amplifier.
At low frequencies impedance of the woofer in a vented box has two peaks and a dip between them. Dip is at the box tuning frequency (34 Hz here). Below that impedance is rising, so there is less power dissipated around 20 Hz.
Oops, I was reading specification of the smaller, 10" model. But nothing important changes, difference between 40 Hz and 41 Hz is negligible, also between 220 W and 250 W.
One more thought. Below box tuning frequency, the woofer goes "unloaded", and may move a lot, but produces very little sound, because the woofer is out of phase with the port.
stuff in my room still vibrates at 20hz though and low frequencies are good for breaking in speakers without making too much noise
I just got the new subwoofer arrived put it in the box and its slamming hard now.
I just got the new subwoofer arrived put it in the box and its slamming hard now.
such things as this should be done gradually and with "feeling" not abrupt and brutally. Same like breaking in of a car engine.
So you don't care about your ears...it sounds like you are driving them too hard too! I have a lifelong friend who played lead/rhythm guitar in several local and regionally known Hard Rock bands for many years...he really hates having to wear his hearing aids now...just sayin'.
Mike
I dont have any hearing problems and im not driving them that hard! I dont listen to my music that loud.
Yup, correct.
At the port frequency the membrane also got the lowest excursion. Besides the the lower impedance (= a lot more current), the driver does not get much cooling by the airflow, that only works at higher excursions. So it's both, the low excursion and the high current.
As a real world example. I worked on 15" acoustic suspension subwoofer that was powered by a 400 WRMS amp. The woofer had a 3" voice coil on a kapton former. The pole piece was T-shaped. At 20Hz it could run for several minutes at full power, no problem. At 100Hz, at full power, it could run for 10 seconds before the VC melted the kapton. Under normal use, with music or movies, these subs almost never failed.
Glad to see test numbers presented coherently (a rarity in this thread). Seems right that a kapton former VC would destruct in 10 seconds at 100 Hz.
But are you saying that you measured 400 WRMS into the driver terminals at 20 Hz (sine wave) and it ran for several minutes? BTW, that (and the 100 Hz test) would as loud as a "jet" airliner.
B.
Despite marketing claims, it is not 250 W RMS continuous sinusoidal signal, but 250 W AES clipped noise signal which energy is far below 250 W RMS.
Realflow, Sonce is correct.
This is not to say your speakers are rubbish - it is just how speakers are tested / rated and really reflects what they will experience in real life.
As the earlier heated discussion on power with LMFahey noted, continuous powers are not really seen in music.
I have seen mixed comments on "coloured formers" - remember they live in a very tight space with not a lot of places for the heat to go other than the pole piece or air.
Do some reading on some of the professional high power subs - you will note a couple of things:
- The manufacturers jump through hoops on cooling and airflow design
- The voice coils are generally 4" and on some of the crazier ones 6"
- They generally use the AES rating - which has a significant crest factor.
Oh - and stop worrying - just use the things. They will be OK on music unless you really try to kill them, or use them on a church organ bass pedal.
I have some subs with 2.5" coils, and even though I don't care if I blow them up, would be very judicious about how long I hit them with a continuous sinewave for. I am quite confident that they would start making "toasty smells".
This is not to say your speakers are rubbish - it is just how speakers are tested / rated and really reflects what they will experience in real life.
As the earlier heated discussion on power with LMFahey noted, continuous powers are not really seen in music.
I have seen mixed comments on "coloured formers" - remember they live in a very tight space with not a lot of places for the heat to go other than the pole piece or air.
Do some reading on some of the professional high power subs - you will note a couple of things:
- The manufacturers jump through hoops on cooling and airflow design
- The voice coils are generally 4" and on some of the crazier ones 6"
- They generally use the AES rating - which has a significant crest factor.
Oh - and stop worrying - just use the things. They will be OK on music unless you really try to kill them, or use them on a church organ bass pedal.
I have some subs with 2.5" coils, and even though I don't care if I blow them up, would be very judicious about how long I hit them with a continuous sinewave for. I am quite confident that they would start making "toasty smells".
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