Hi all, i have an OEM 15" driver.....so no T/S parameters.....and am in the process of learning how to measure T/S.
I want to try the driver in sealed and ported boxes....for sub duty up to say no higher than 120-150Hz...and of course as low in freq as possible.
Once i measure T/S, I'll take it to Hornresp....
In the meantime, i've done an impedance sweep...free air, pointing up, sitting on the floor.
I've never seen such flattish impedance curve on a low end driver; have always seen a much sharper peak at fs.
Can someone tell me just from impedance, what to expect from this driver? How probably to best use it?
thx Mark
I want to try the driver in sealed and ported boxes....for sub duty up to say no higher than 120-150Hz...and of course as low in freq as possible.
Once i measure T/S, I'll take it to Hornresp....
In the meantime, i've done an impedance sweep...free air, pointing up, sitting on the floor.
I've never seen such flattish impedance curve on a low end driver; have always seen a much sharper peak at fs.
Can someone tell me just from impedance, what to expect from this driver? How probably to best use it?
thx Mark
If your impedance plot is correct, the free-air resonance is around 100 Hz, which means the driver is not suitable for subwoofer use.
Do you have any drivers around with known specs that you can compare your measurements to? That should help you figure out if your measurements are reasonably accurate.
If you have other test equipment around, you could also do a quick manual impedance measurement to confirm. You'll need a signal generator, multimeter, and some resistors to do that (and maybe a potentiometer depending on the chosen method). The average multimeter is only accurate up to a few hundred hertz, but for woofer basics you should be OK.
Do you have any drivers around with known specs that you can compare your measurements to? That should help you figure out if your measurements are reasonably accurate.
If you have other test equipment around, you could also do a quick manual impedance measurement to confirm. You'll need a signal generator, multimeter, and some resistors to do that (and maybe a potentiometer depending on the chosen method). The average multimeter is only accurate up to a few hundred hertz, but for woofer basics you should be OK.
Just from the impedance curve I’d say you have a real POS. Either that or measurement error.
100 Hz fs? And a very low ratio of Qms to Qes, and a high voice coil inductance. If the measurements are right (or even close) the best use might be cheap entertainment if you’re bored some Saturday afternoon. Don’t try to do anything serious with it.
Testing a driver sitting on the ground will corrupt the measurement, but never anything THIS serious. It needs to be suspended several feet away from obstacles. I use a piece of plywood with a hole in it, up on saw horses (Or two chairs).
100 Hz fs? And a very low ratio of Qms to Qes, and a high voice coil inductance. If the measurements are right (or even close) the best use might be cheap entertainment if you’re bored some Saturday afternoon. Don’t try to do anything serious with it.
Testing a driver sitting on the ground will corrupt the measurement, but never anything THIS serious. It needs to be suspended several feet away from obstacles. I use a piece of plywood with a hole in it, up on saw horses (Or two chairs).
I would have expected at least some 40-50 Ohm at resonance, not apparent 12-14 ohm.
Suspect measurement error, probably something as simple as poorly chosen series resistance.
Or speaker is sitting on a huge cotton ball, a sheep´s back, a few mattresses or something similarly resistive that murders Q .
Or it´s on he floor, face down, on a thick carpet.
None of those affects high frequency rising impedance, so that part of the curve can be trusted.
What´s the amp/source feeding it?
Can you show a couple pictures?
One showing general setup, cone close up (mainly to check its edge), if possible a sideways one looking at the spider between frame spokes a sideways or back one showing magnet.
Suspect measurement error, probably something as simple as poorly chosen series resistance.
Or speaker is sitting on a huge cotton ball, a sheep´s back, a few mattresses or something similarly resistive that murders Q .
Or it´s on he floor, face down, on a thick carpet.
None of those affects high frequency rising impedance, so that part of the curve can be trusted.
What´s the amp/source feeding it?
Can you show a couple pictures?
One showing general setup, cone close up (mainly to check its edge), if possible a sideways one looking at the spider between frame spokes a sideways or back one showing magnet.
that may be a reason for the strange impedance plot.
try measuring again, firmly holding the magnet against a rigid object (table or similar) pointing horizontally, for best possible air circulation.
there can be all sorts of problems, such as the speaker vibrating against the floor (carpet??), air not circulating freely...
i measured completely different impedance plots for a driver just held in my hand and the same driver pressed firmly agains the desk edge.
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My bet would be blocking any vents on the back of the magnet has messed things up.
Chris
Chris
Hi folks, first thanks to everyone for the replies.
I can see i should have given more info from the start. Pls accept my apology for not having done so.
The DATS data is good, other than being on the floor maybe throwing if off some.
The impedance curve changes very little whether I measure with the driver laying flat on the floor, or standing propped upright.
The first thing i did was DATS check other drivers like a 12pr320, then my 18n862 subs. DATS is fine.
Also had a 2nd one of the 15"s, still sealed in its box. Found it has the same impedance curve.
The driver is a Meyer ST-815. Stout SOB...maybe the stiffest cone I've encountered, away from Lab12 drivers.
It is/was used in a number of Meyer self-powered models, where the specs said it goes down to 40Hz...(i.m thinking that's f-6.)
I have the pair as replacements if needed, for MTS4a's, a 4 -way design that uses an 18" underneath this 15"
Anyway, I just finished repurposing a box that was used for a sealed 18", by adding an adapter plate to mount the 15".
Here's the raw trace in green, and a super quick FIR tuning in blue. Ungated, indoor, taken at dustcap, 1/48th.
Purpose was to see what the heck is this driver about ????,
and how much boost it would take to get to 40Hz....
It took a tad less than 10dB boost at 47Hz to produce the blue curve. That's too much for me to stomach, so next step is to do like Meyer and port it.
I can see i should have given more info from the start. Pls accept my apology for not having done so.
The DATS data is good, other than being on the floor maybe throwing if off some.
The impedance curve changes very little whether I measure with the driver laying flat on the floor, or standing propped upright.
The first thing i did was DATS check other drivers like a 12pr320, then my 18n862 subs. DATS is fine.
Also had a 2nd one of the 15"s, still sealed in its box. Found it has the same impedance curve.
The driver is a Meyer ST-815. Stout SOB...maybe the stiffest cone I've encountered, away from Lab12 drivers.
It is/was used in a number of Meyer self-powered models, where the specs said it goes down to 40Hz...(i.m thinking that's f-6.)
I have the pair as replacements if needed, for MTS4a's, a 4 -way design that uses an 18" underneath this 15"
Anyway, I just finished repurposing a box that was used for a sealed 18", by adding an adapter plate to mount the 15".
Here's the raw trace in green, and a super quick FIR tuning in blue. Ungated, indoor, taken at dustcap, 1/48th.
Purpose was to see what the heck is this driver about ????,
and how much boost it would take to get to 40Hz....
It took a tad less than 10dB boost at 47Hz to produce the blue curve. That's too much for me to stomach, so next step is to do like Meyer and port it.
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Going by the MTS4a manual, I'd say it's about being able to take 600 watts continuous in a 140 dB @ 1 meter pro sound application. In that realm, typically durability, power handling, and output take precedence over low frequency extension (and lots of other things).
Yep, that's what i figured too, before seeing if i could use it for a sub.
Since last post, I've been able to switch the driver to a repurposed 18" vented box. It was easy to do because both type boxes were made for same 18" driver, so the adapter fit both.
Heck yeah, ports !!!!
Here's raw in orange; processed in green.
That's some EQ boost I can live with, and it got to a lower frequency than I hoped for. Yay!
Oh here's impedance in the vented box. I'm still very puzzled by how different the curve looks from any sub driver i've measured.
Meyer has always touted a gradual smooth phase rotation....maybe the impedance is a key to it ????
Looks to me like the vents are completely unloading (might as well not be there, the tuning is so far off). The fundamental peak doesn’t move at all, and the two peaks on either side of tuning minimum aren’t even close to symmetrical. And you’ve got another little blip a bit higher up indicating internal reflections.
It’s a MID range driver with relatively high mechanical damping (low Qms, to get smooth response when the cone starts to break up). That damped impedance peak is BAD for bass drivers, good for a midrange.
It’s a MID range driver with relatively high mechanical damping (low Qms, to get smooth response when the cone starts to break up). That damped impedance peak is BAD for bass drivers, good for a midrange.
Well, like i say...i'm puzzled as heck.
BUT, I'm also questioning the conventional wisdom about how impedance should look (for both a sealed and ported version of this box.)
I've used the two peak method to tune several ported boxes with greatt success..so am aware how "normal" looks.
The thing is, the impedance trace is what it is. And i see Meyer used this driver 40-100Hz in the MTS4, 40-900Hz in the CQ-1, and most telling of all 40-120Hz in PSW-2 sub. So it does work as a sub driver, impedance so be it, does it not?
I don't see how it can be a MID range driver.....
The vented box i simply threw the driver in may be miles wrong. It was designed for the 18n862. But heck, other than the funky impedance trace, it sure tuned up easily. I'm going to try to measure excursion tomorrow..
Yeah, re the blip indicating internal reflections. The dampening foam is out of the boxes...and to tell the truth I don't care and won't bother to put it back.
I low pass steep...by 250Hz i'm over 60 dB down.
Good lab practice is to substitute resistors of known values for the driver and see how they trace. That confirms the test set-up end to end.
In fact, I never bother with calibration - instead, just plot the resistors' curves bracketing the driver impedance curve.
B.
In fact, I never bother with calibration - instead, just plot the resistors' curves bracketing the driver impedance curve.
B.
Trying to make sense of the impedance curve; only idea so far is maybe the driver is in extreme need of some break in.
Ok, before i figure out how to run a long loud break in, without loosing my GF, i decided to make some smell-test sensitivity measurements.
Idea being to see what the true nominal impedance is, in the vented box.
I always make sensitivity measurements of a passband with all processing in place.
here's the sub's processed output that was measured.
I use pink noise, and compare the time averaged SPL (Leq) to the time averaged Vrms,
both taken over the same time interval (half minute or longer, until averages read stable).
A little math takes whatever voltage, SPL, and distance to common specs...ie 2.83v @ 1m, etc.
Voltage sensitivity for 2.83v at 1m turned out to be 90.7dB. I consider this the average voltage sensitivity across the entire passband...a real-world, measured spec, imho.
That's not a good 1 watt power sensitivity for a sub imo, but i wasn't yet disappointed because its measured impedance curve is nearly always above 8 ohms.
So I measured average current over the same interval/conditions, and got the processed passband has a 11.7 ohm nominal impedance.
Which raises 1w @ 1m power sens to 92.6 dB.
Ok, not great, but not bad at all given a f-3 @29Hz. (and the fact I always gauge subs in terms of 18" drivers)
Real question then to me, is 'how much boost is going on, to get that extension to 29Hz'?
here's the EQ curve being applied to the raw response, to get the processed curve shown above.
No problem as far as boost. Heck, it even has cut below 37Hz ! Oversized, wrong size box Lol.
So now i wanna do the break in, remeasure impedance, learn how to make T/S measurements, and check out max excursion in Hornresp.
And then finally do some large-signal testing.
Must say, so far it appears to be an interesting and unusual driver. maybe break in changes the unusual part.....who knows ??
Idea being to see what the true nominal impedance is, in the vented box.
I always make sensitivity measurements of a passband with all processing in place.
here's the sub's processed output that was measured.
I use pink noise, and compare the time averaged SPL (Leq) to the time averaged Vrms,
both taken over the same time interval (half minute or longer, until averages read stable).
A little math takes whatever voltage, SPL, and distance to common specs...ie 2.83v @ 1m, etc.
Voltage sensitivity for 2.83v at 1m turned out to be 90.7dB. I consider this the average voltage sensitivity across the entire passband...a real-world, measured spec, imho.
That's not a good 1 watt power sensitivity for a sub imo, but i wasn't yet disappointed because its measured impedance curve is nearly always above 8 ohms.
So I measured average current over the same interval/conditions, and got the processed passband has a 11.7 ohm nominal impedance.
Which raises 1w @ 1m power sens to 92.6 dB.
Ok, not great, but not bad at all given a f-3 @29Hz. (and the fact I always gauge subs in terms of 18" drivers)
Real question then to me, is 'how much boost is going on, to get that extension to 29Hz'?
here's the EQ curve being applied to the raw response, to get the processed curve shown above.
No problem as far as boost. Heck, it even has cut below 37Hz ! Oversized, wrong size box Lol.
So now i wanna do the break in, remeasure impedance, learn how to make T/S measurements, and check out max excursion in Hornresp.
And then finally do some large-signal testing.
Must say, so far it appears to be an interesting and unusual driver. maybe break in changes the unusual part.....who knows ??
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If you have a signal generator, put about a 10 Hz sine wave into it, and you'll get excursion with almost no sound.
Not sure why you keep calling it a subwoofer when its a midrange driver. I see no reason for putting a midrange into this subwoofer cabinet. You will tear it apart.
If it's been sitting around for ages, it's going to take some real excursion to loosen up and read in the normal range.
Does the ST-815 use ferrofluid?
Does the surround look level, or has the cone sagged forward or backwards?
Have you tried pushing the driver by hand to the extent of the accordion pleat surround?
Break-in in actually softens every flexing component in the speaker (edge and suspension) and one of its consequences is that resonance peak lowers and broadens, it loses Q .
Here I see resonance peak already too low and wide, and actually looks like it has had a long work life.
Yep, thx. Solves how to break-in without being annoying
I guess i call it a sub driver, because so does Meyer 😉
I realize the impedance curve would say otherwise and lead you to comment so, but i think we all knew something is wrong with the curve.
Plus, as said in #12, the driver is what's in the PSW-2 sub ..........
Yep, been on the shelf for 10 years.
I don't have any experience with ferrofuild in a driver. Pretty sure the ST-815 doesn't have it, but how do you tell?
Everything seems to be falling in place as the driver is breaking in...
here's the impedance curve in the vented box as it stands now, (which can be compared to the curve in #10 when first measured)
The driver has never been used...note it was on a shelf for 10 years...
The main peak, currently around 60Hz, has been getting sharper, as its freq continues to drop.
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