Hi,
I have been running a big driver for 3days (@250mV) to run in the surround ready for testing.
I set it to free air resonant frequency of 43Hz and came back to it today. Fs is now 69Hz.
But, the workshop temperature has dropped to 14degC from the 20degC it was at the start.
Could the temperature have affected the Fs or is the change more to do with running in?
Tried searching but could not find anything similar.
I have been running a big driver for 3days (@250mV) to run in the surround ready for testing.
I set it to free air resonant frequency of 43Hz and came back to it today. Fs is now 69Hz.
But, the workshop temperature has dropped to 14degC from the 20degC it was at the start.
Could the temperature have affected the Fs or is the change more to do with running in?
Tried searching but could not find anything similar.
It would mean that Cms has changed by a factor of (43/69)²=0.39. That's a huge change...
Sure there is some sensitivity to temperature, and I would guess that the suspension would get stiffer with sinking temperature, but not that much for that small a change. Breaking a driver in would typically lower the resonance.
Are you sure about those measurements? How were they done?
Sure there is some sensitivity to temperature, and I would guess that the suspension would get stiffer with sinking temperature, but not that much for that small a change. Breaking a driver in would typically lower the resonance.
Are you sure about those measurements? How were they done?
That's a Huge change in Fs in my experience. I have a set of Vifa PL18 whose Fs rose by about 4 Hz over 5 years of sitting in my basement, even after flopping them on a function generator for a couple days.
FS should go up as temperature goes down, but that seems like a small temperature change and a large Fs change.
Sheldon
FS should go up as temperature goes down, but that seems like a small temperature change and a large Fs change.
Sheldon
Newb opinion here but I just started measuring T/S with SE a few weeks ago and I noticed a large difference in FS if the drivers were cold. By cold I mean middle 30 degree F. It's winter here in Denver and my measurement rig is out in the garage. I had to make all my measurements with drivers warm and sitting inside the house. Also the Re was about .1 or .2 ohms lower in the cold drivers.
When I was was messing with T/S measurement a couple of years ago I found the Q of the resonance dropped substantially if the driver was simply held or suspended in mid-air. If the back of the magnet was held against a large (non-magnetic) mass so as to prevent the mass of the frame moving the opposite direction to mass of the cone, then much higher and more consistent Q measurements were had. I can't see it affecting Fs but it's worth keeping in mind. Just don't block off any vent at the back of the centre pole piece!
Hi,
this first driver was tested in my normal way. Suspended in a vertical position, but very near a wall.
Oscillator into series resistor and then to speaker. DVM across the driver test leads.
This speaker is secondhand but a lightly used small venue PA bass unit. I had not expected any change due to running in but maybe it stffens up when left idle for a while so that's why I decided to try long term running.
I checked Fs some weeks ago and last week's Fs was near identical. Left it for three days (too busy with other jobs) and in the meantime winter arrived properly. I measured Q=0.255 when Fs=43Hz. But I see little point measuring it at that low temperature (it will never be used like that).
I noted that the voltage on the DMM was low.
Odd, that's not the way I left it.
Sure enough as I raised the frequency, the driver voltage came up and Fs turned out at the higher figure.
I have it's partner to measure & I'll repeat the initial check and after some days running in.
this first driver was tested in my normal way. Suspended in a vertical position, but very near a wall.
Oscillator into series resistor and then to speaker. DVM across the driver test leads.
This speaker is secondhand but a lightly used small venue PA bass unit. I had not expected any change due to running in but maybe it stffens up when left idle for a while so that's why I decided to try long term running.
I checked Fs some weeks ago and last week's Fs was near identical. Left it for three days (too busy with other jobs) and in the meantime winter arrived properly. I measured Q=0.255 when Fs=43Hz. But I see little point measuring it at that low temperature (it will never be used like that).
I noted that the voltage on the DMM was low.
Odd, that's not the way I left it.
Sure enough as I raised the frequency, the driver voltage came up and Fs turned out at the higher figure.
I have it's partner to measure & I'll repeat the initial check and after some days running in.
Hi,
Zaph has done some testing on a driver in different temperatures.
http://www.zaphaudio.com/temp.html
He tested with large temp differences but the fs change is substantial.
Could it also be that your instruments and amp got affected by the temperature change?
Zaph has done some testing on a driver in different temperatures.
http://www.zaphaudio.com/temp.html
He tested with large temp differences but the fs change is substantial.
Could it also be that your instruments and amp got affected by the temperature change?
Hi,
I don't think the instrumentation was wrong or had changed.
No amplifier, oscillator drives 220r+driver directly.
Setting on the oscillator matched the frequency readings from the DVM.
Thanks for that link, he used a much wider temperature range but is confirming BIG changes in these two parameters.
I don't think the instrumentation was wrong or had changed.
No amplifier, oscillator drives 220r+driver directly.
Setting on the oscillator matched the frequency readings from the DVM.
Thanks for that link, he used a much wider temperature range but is confirming BIG changes in these two parameters.
Hi,
the surround is pleated fabric with some shiny black goo that is very slightly tacky. They appear very stiff when I try to push the cone in towards the magnet. But I think that's fairly normal for a PA type driver aimed at high efficiency. The pair are claimed at 103db/2.8V (8//8ohm) in the cabinet.
the surround is pleated fabric with some shiny black goo that is very slightly tacky. They appear very stiff when I try to push the cone in towards the magnet. But I think that's fairly normal for a PA type driver aimed at high efficiency. The pair are claimed at 103db/2.8V (8//8ohm) in the cabinet.
Hi Andrew,
Bitumen paint does go "harder" in colder conditions, and when left idle for a length in time.
I have found when treating surrounds to run them pretty hard before taking measurements. Even while the bitumen is thickening.
But I have not seen that much of a difference. Have you any idea of what they should be? Try running a couple of volts at resonance. The Fs may go down.
Geoff.
Bitumen paint does go "harder" in colder conditions, and when left idle for a length in time.
I have found when treating surrounds to run them pretty hard before taking measurements. Even while the bitumen is thickening.
But I have not seen that much of a difference. Have you any idea of what they should be? Try running a couple of volts at resonance. The Fs may go down.
Geoff.
Hey Andrew its not uncommon to see temperature induced changes such as those you witnessed.
I ordered some Peerless XLS10's late last year and literally the first thing I did when they arrived was test the parameters on one of them. They'd been out in the cold for a day or two on the delivery van so the whole of the driver was pretty cold the touch. Peerless stated an Fs of 19hz and I was getting 32hz, which even accounting for run-in is still way off the mark and especially considering Vik tested the XLS10 and found the measured Fs was virtually identical to the published figure.
I redid measurements after a few hours of running in and them found much more acceptable, this also happened to be after they'd acclimatised.
I ordered some Peerless XLS10's late last year and literally the first thing I did when they arrived was test the parameters on one of them. They'd been out in the cold for a day or two on the delivery van so the whole of the driver was pretty cold the touch. Peerless stated an Fs of 19hz and I was getting 32hz, which even accounting for run-in is still way off the mark and especially considering Vik tested the XLS10 and found the measured Fs was virtually identical to the published figure.
I redid measurements after a few hours of running in and them found much more acceptable, this also happened to be after they'd acclimatised.
Yeah, silly me. The link was down when I first looked. Later, looking for something else, saw the test, and thought of Andrew.
I hope all the widerangers I've been tweaking don't freeze up come winter. I might have to embed some nichrome wire into the surrounds.
New meaning for ring radiator!
The Fr is probably not that critical at low level, though sensitivity is possibly down. Could be a headache in the living room, but less likely a problem in sound reinforcement.
Can't help but wonder how Cal and Dave in Canada get on in winter.
Geoff.
I hope all the widerangers I've been tweaking don't freeze up come winter. I might have to embed some nichrome wire into the surrounds.
New meaning for ring radiator!
The Fr is probably not that critical at low level, though sensitivity is possibly down. Could be a headache in the living room, but less likely a problem in sound reinforcement.
Can't help but wonder how Cal and Dave in Canada get on in winter.
Geoff.
Brrrr! It was a mere 13 degrees and sunny yesterday. Took my shirt off at noon. 
As you know, I'm not a technical guy but my measuring devices tell me that it takes a while for a cold driver to "warm up" especially woofers. This is a noticeable difference. Takes the big woofers as much as 2 hours for things to come around. I start out Eqing heavily on the low end and bump it down till it stabilizes. I think that might be why I had so much trouble with the notch filters on the A7's.
Saying that does not address the same factors on the amp but I'm way too dumb to understand or explain that.
As you know, I'm not a technical guy but my measuring devices tell me that it takes a while for a cold driver to "warm up" especially woofers. This is a noticeable difference. Takes the big woofers as much as 2 hours for things to come around. I start out Eqing heavily on the low end and bump it down till it stabilizes. I think that might be why I had so much trouble with the notch filters on the A7's.
Saying that does not address the same factors on the amp but I'm way too dumb to understand or explain that.
Hi,
I have warmed up the driver a bit, probably not quite as warm as it's final operating environment, and the Fs has dropped back to 44.9Hz.
I tried 800mV (up from the 250mV) and the reading, within experimental error, is the same at 44.8Hz. I will need to hook up an amp into my test arrangement and see if that makes a significant change.
It appears that the coated fabric surround is pretty sensitive to temperature changes.
Re-designing my box and tuning is going to be a bit of "guess and try", it seems!
I have warmed up the driver a bit, probably not quite as warm as it's final operating environment, and the Fs has dropped back to 44.9Hz.
I tried 800mV (up from the 250mV) and the reading, within experimental error, is the same at 44.8Hz. I will need to hook up an amp into my test arrangement and see if that makes a significant change.
It appears that the coated fabric surround is pretty sensitive to temperature changes.
Re-designing my box and tuning is going to be a bit of "guess and try", it seems!
Hi Richie,
thanks for trying to put some sense into the numbers.
A stiff surround = low VAS.
A stiff surround = high Fs.
Do the two factors nearly cancel when designing the box and it's tuning?
Using my model (Barry Porter 1984),
a change of -36% in Vas requires just +14% in Fs to keep the port length in tune (maybe that's the wrong way to look at it)
That -36% =0.64*(Vas)=0.8^2*(Vas)
+14% is not Fs/0.8, it's more like +25%
At least the numbers move in the same direction so there is partial cancellation in my model.
What happens with other software models?
thanks for trying to put some sense into the numbers.
A stiff surround = low VAS.
A stiff surround = high Fs.
Do the two factors nearly cancel when designing the box and it's tuning?
Using my model (Barry Porter 1984),
a change of -36% in Vas requires just +14% in Fs to keep the port length in tune (maybe that's the wrong way to look at it)
That -36% =0.64*(Vas)=0.8^2*(Vas)
+14% is not Fs/0.8, it's more like +25%
At least the numbers move in the same direction so there is partial cancellation in my model.
What happens with other software models?
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