T-S parameters are off...what am I doing wrong?
Thread Starter
50 Watt CAFz'r
Joined: Jun 2004
Posts: 67
Hi,
I measured a speaker using the process described on this page:
http://www.bcae1.com/spboxad3.htm
The speaker is a RF midbass from the Fanatic Q series, model FNQ2406.
Here are the published specs:
Nom. Impedance: 4 ohm
Fs: 45 Hz
Qes: .299
Qms: 2.576
Qts: .338
Vas: .75 ft3
Here are my measured values for the fields 1-9 in the above page:
Speaker resistance: 4.0 ohm
Resistor resistance: 4.3 ohm
Test Voltage: 3.02 V
Free air fs: 49 Hz
Voltage at Resonance: .527 V
F High: 78
F Low: 28.6
In Enclosure fs: 100
Internal Volume of enclosure: 0.179 ft3
And here is the Data Output:
3dB Down Voltage = 0.908 V
Impedance At Resonance = 20.341 ohm
Calculated fs = 47.231 Hz
Qts = 0.336
Qes = 0.418
Qms = 1.709
Vas = 0.567 Ft3
So the fs and the Qts are reasonably close, but the Qes, Qms and Vas are way out of whack. I realize there could be measuring error, but even if I adjust the values a little I still get approx. the same results. In fact, I couldn't even enter by guessing the measurements that would give me Qms of 2.576.
Any ideas on what's wrong with the setup?
Thanks,
molo
I measured a speaker using the process described on this page:
http://www.bcae1.com/spboxad3.htm
The speaker is a RF midbass from the Fanatic Q series, model FNQ2406.
Here are the published specs:
Nom. Impedance: 4 ohm
Fs: 45 Hz
Qes: .299
Qms: 2.576
Qts: .338
Vas: .75 ft3
Here are my measured values for the fields 1-9 in the above page:
Speaker resistance: 4.0 ohm
Resistor resistance: 4.3 ohm
Test Voltage: 3.02 V
Free air fs: 49 Hz
Voltage at Resonance: .527 V
F High: 78
F Low: 28.6
In Enclosure fs: 100
Internal Volume of enclosure: 0.179 ft3
And here is the Data Output:
3dB Down Voltage = 0.908 V
Impedance At Resonance = 20.341 ohm
Calculated fs = 47.231 Hz
Qts = 0.336
Qes = 0.418
Qms = 1.709
Vas = 0.567 Ft3
So the fs and the Qts are reasonably close, but the Qes, Qms and Vas are way out of whack. I realize there could be measuring error, but even if I adjust the values a little I still get approx. the same results. In fact, I couldn't even enter by guessing the measurements that would give me Qms of 2.576.
Any ideas on what's wrong with the setup?
Thanks,
molo
Thread Starter
50 Watt CAFz'r
Joined: Jun 2004
Posts: 67
OK... well I don't know what is "within spec" for something like this, but some of them just seemed too far off.
Are you saying that Qms of 1.709 vs. 2.576 could just be a variance between one speaker to another?
Thanks,
molo
Are you saying that Qms of 1.709 vs. 2.576 could just be a variance between one speaker to another?
Thanks,
molo
Yankee
Joined: Oct 2003
Posts: 3,599
Every day manufacturers equipment is tested and much of it is found to be "lies and damn lies". Usually they find amplifiers not measuring up to specs. Why not speakers too? In fairness, if your sine wave generator, your resistor, your measuring electronics, or the speaker box volume are off then the measured result could be a little off too.
I also note the web site is geared to subwoofers and that may be a variance too?
I also note the web site is geared to subwoofers and that may be a variance too?
Guest
Posts: n/a
Vas varies a great deal, and is very difficult to measure. The delta Volume method is even harder to get accurate numbers from, since the volumes need to be stunning precise.
I calculate using the Delta Mass method.
if you want, send me the speakers and I can measure the T/S's for you for $15 each plus return shipping.
I calculate using the Delta Mass method.
if you want, send me the speakers and I can measure the T/S's for you for $15 each plus return shipping.
Guest
Posts: n/a
I use a delta mass calculation - I measure the added mass down to a tenth of a gram.
It's much harder to get to a small percentage error with volume since you have to compensate for the shape of the cone in terms of volume, reflections from internal surfaces, basket volumes, etc..
Delta Volume works great - if you can get the volume smack dab perfect.
It's much harder to get to a small percentage error with volume since you have to compensate for the shape of the cone in terms of volume, reflections from internal surfaces, basket volumes, etc..
Delta Volume works great - if you can get the volume smack dab perfect.
Guest
Posts: n/a
I did measure the difference between a fresh woofer and one that was broken in. The 'required' enclosure volume dropped significantly - breaking speakers in is mandatory before measurement or initial listening.
As for thermal compression - it does happen, but I haven't had time to measure that phenomenon - usually when I heat a woofer up, it doesn't work when I am done...
As for thermal compression - it does happen, but I haven't had time to measure that phenomenon - usually when I heat a woofer up, it doesn't work when I am done...
