Hi all,
Simple discussion, we often model with the published specs but what if the specs are different? I was measuring a driver today that I was working with and for the S&G's I did the free air parameters measurements after calibrating and I did it both wired as a single voice coil and dual voice coil in series to see if it changes anything significantly. I didn't think much of it. But then I looked at the published TS parameters and they're different. Not wildly different. But maybe different enough that I should model an enclosure for this particular driver based on my measured value or is this too getting into minutia and published values are fine?
The driver is a Dayton MX15-22.
Here's their published TS parameters:
And here's the DATS information I got from my particular copy of this driver (single and dual voice coil in series measured):
I noticed right away the impedance curves are different from the published. Instead of peaking on 20hz, it's right-shifted to 25~26hz or so? The Fs measured at 25.47~25.7hz instead of 21.7hz per the publication. And of course some values are different depending on using one voice coil at 2ohm vs two voice coils in series at 4ohm. I assume I should model using the two voice coils in series' values?
Do I need to input the Vas and do the measured mass here, my understanding is that won't effect the TS parameters already listed with measured value.
Very best,
Simple discussion, we often model with the published specs but what if the specs are different? I was measuring a driver today that I was working with and for the S&G's I did the free air parameters measurements after calibrating and I did it both wired as a single voice coil and dual voice coil in series to see if it changes anything significantly. I didn't think much of it. But then I looked at the published TS parameters and they're different. Not wildly different. But maybe different enough that I should model an enclosure for this particular driver based on my measured value or is this too getting into minutia and published values are fine?
The driver is a Dayton MX15-22.
Here's their published TS parameters:
And here's the DATS information I got from my particular copy of this driver (single and dual voice coil in series measured):
I noticed right away the impedance curves are different from the published. Instead of peaking on 20hz, it's right-shifted to 25~26hz or so? The Fs measured at 25.47~25.7hz instead of 21.7hz per the publication. And of course some values are different depending on using one voice coil at 2ohm vs two voice coils in series at 4ohm. I assume I should model using the two voice coils in series' values?
Do I need to input the Vas and do the measured mass here, my understanding is that won't effect the TS parameters already listed with measured value.
Very best,
Thanks,
Updated with Vas. Here's two different drivers of the same type with their differing specs:
Fs and Qts are fairly different, 16% & 7% difference from published spec on Fs, 26% and 13% difference from published spec on Qts.
Very best,
Updated with Vas. Here's two different drivers of the same type with their differing specs:
Fs and Qts are fairly different, 16% & 7% difference from published spec on Fs, 26% and 13% difference from published spec on Qts.
Very best,
Published specs are an average and production values are usually plus or minus 10%.
Sometimes with fast runs and cheap drivers like the Dayton might be +/- 20 or even 30%
Plug each set of paramters into a box program with the same box volume and tuning and see what the resulting graph might tell you. The end products may be similar id not exactly the same
Sometimes with fast runs and cheap drivers like the Dayton might be +/- 20 or even 30%
Plug each set of paramters into a box program with the same box volume and tuning and see what the resulting graph might tell you. The end products may be similar id not exactly the same
Yet SPL w/m are ~identical, ergo so is eff.:
n0 = (9.7822 * 10-10 * Vas * Fs3) / Qes
SPL @ 1W/1m = 112.2 + 10 * log(n0)
driver #1 = 86.334 , #2 = 86.583, so a matched set and as Fs drops, these will go up closer to spec, so personally would just use the published specs unless shrinking box size was a priority, then recommend designing with either averaging each spec or whichever is the smaller of Fs*Vas*Qts.
n0 = (9.7822 * 10-10 * Vas * Fs3) / Qes
SPL @ 1W/1m = 112.2 + 10 * log(n0)
driver #1 = 86.334 , #2 = 86.583, so a matched set and as Fs drops, these will go up closer to spec, so personally would just use the published specs unless shrinking box size was a priority, then recommend designing with either averaging each spec or whichever is the smaller of Fs*Vas*Qts.
Thanks; this is the practical type thing I needed to hear. I figured it was minutia but was curious. I only recently started measuring drivers for fun. I picked up the DATS as a longer term goal to measure drivers in enclosures to build crossovers eventually (not there yet by a country mile).
Very best,
Depends on who you ask. 😉 I use to joke about Lowthers and similar needing 250+ hrs to break in; this to me isn't broke in, just plain broke from a purely mechanical POV.
Today, drivers are much more complex material wise to the point where I've no clue other than recommend asking the manufacturer for a baseline knowing that it will be very conservative and ramp it up power wise over a short time at ~1.56x measured Fs with pink noise till Fs dropped to its limit, though personally did/would start with the power that drove it to barely audible distortion. The main thing is not so much power the VC bounces off the back plate (a clicking sound/Xmech).
Today, drivers are much more complex material wise to the point where I've no clue other than recommend asking the manufacturer for a baseline knowing that it will be very conservative and ramp it up power wise over a short time at ~1.56x measured Fs with pink noise till Fs dropped to its limit, though personally did/would start with the power that drove it to barely audible distortion. The main thing is not so much power the VC bounces off the back plate (a clicking sound/Xmech).
I simply play music, usually the Best of the Shadows and do that for a couple of hours or other music with strong bass lines. But to be honest I don't actually hear much difference in how the speakers as a whole sound. What I can hear is a difference between a cold speaker and one that has been working for a while
Curious, How did you position the driver for your measurements - horizantal on a bench, vertical clamped in a vise, vertical hanging, etc? I'm testing some drivers and finding the TS parameters such as FS, Qts and VAS vary at least 20% if not more depending on the driver's position. I'm using REW software.
Hmmm? Interesting point; I've been using mine with the drivers magnet down on the bench as that is how they picture them in the adds.
How much difference would there be when compared to measuring a driver on an AIS baffle in the vertical plane?
How much difference would there be when compared to measuring a driver on an AIS baffle in the vertical plane?
I've found that suspending the driver in air, in a vertical orientation gives me TS numbers closest to the published specs. I use the added mass technique if that matters.
I've also found that Fs will drop roughtly 10% when going from a 100mV drive voltage to 1V. From what I've read, 1V would be the max drive voltage to insure staying in the small signal range of the driver, most tests use 100 mV. I need to see if the TS parameters vary with a 1V drive voltage.
On a side note, there is a Seas technical page http://www.seas.no/index.php?option...omments-to-the-datasheets&catid=65&Itemid=281 that indicates they use a 2V (rms) drive voltage to measure Fs. They don't indicate what drive voltage they use for TS parameters.
I've also found that Fs will drop roughtly 10% when going from a 100mV drive voltage to 1V. From what I've read, 1V would be the max drive voltage to insure staying in the small signal range of the driver, most tests use 100 mV. I need to see if the TS parameters vary with a 1V drive voltage.
On a side note, there is a Seas technical page http://www.seas.no/index.php?option...omments-to-the-datasheets&catid=65&Itemid=281 that indicates they use a 2V (rms) drive voltage to measure Fs. They don't indicate what drive voltage they use for TS parameters.
The small "hump" in the impedance curve a bit higher up in frequency than the expected peak suggests that the measurement is being impacted by an external factor and therefore might not be correct. This could be caused by the driver moving on the bricks due to some resonance at that frequency, for example.
I suggest using the "driver suspended in air" method, as suggested by 4R5.
If the differnece is 10-15 % I would not worry in most cases. Say that the suspension is stiffer than specified so that Fr is higher than specified.
This will increase both Fr and Qt of the driver but these two parameters will work in opposite direction in tuning a bass reflex box.
In other cases the difference might be huge, then it is a problem. Or if electrical parameters are really of and not compensated by mechanical parameters
So plug in measured and published paramters and test how much it really affect your application. A sixth order vented box is more sensitive than a second order closed box to errors, so it all fades out to that fuzzy answer "it depends".
This will increase both Fr and Qt of the driver but these two parameters will work in opposite direction in tuning a bass reflex box.
In other cases the difference might be huge, then it is a problem. Or if electrical parameters are really of and not compensated by mechanical parameters
So plug in measured and published paramters and test how much it really affect your application. A sixth order vented box is more sensitive than a second order closed box to errors, so it all fades out to that fuzzy answer "it depends".