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Old 6th September 2008, 04:58 AM   #1
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Default SB Acoustics 6" Params

Just wanted to post this up, there's obviously big differences between the data Zaph got for the SB Acoustics 6" driver and the published data sheet. I have a couple pair here that I just got from Madisound, and was modeling up a box tonight. The data below is with a totally fresh driver, no break-in at all. I used a WT2 and Delta Mass method for Vas testing.

Here's what I got, that's more like it! I gotta wonder if the unit Zaph had was defective, the 1.17 Le makes me wonder. I could post a pic of the Inductance curve from the WT2, but it's damn near ruler flat out to 20khz ... even lower than Scan Revelators I've tested.

No FR or distortion data to post yet, but there was a prominent phase wiggle at 1500hz, so there likely is a cone/surround resonance there as shown on Zaphs data at the factory spec sheet.

Re = 5.5880 ohms
Fs = 39.3941 Hz
Zmax = 50.9692 ohms
Qes = 0.5213
Qms = 4.2336
Qts = 0.4641
Le = 0.1740 mH (at 1 kHz)
Diam = 122.5734 mm ( 4.8257 in )
Sd =11800.0004 mm^2( 18.2900 in^2)
Vas = 23.1003 L ( 0.8158 ft^3)
BL = 6.0895 N/A
Mms = 13.9762 g
Cms = 1167.8557 uM/N
Kms = 856.2701 N/M
Rms = 0.8171 R mechanical
Efficiency = 0.2546 %
Sensitivity= 86.0757 dB @1W/1m
Sensitivity= 87.6340 dB @2.83Vrms/1m
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Old 6th September 2008, 10:56 AM   #2
breez is offline breez  Finland
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I have a broken in pair and got 0.96mH inductance, but I'm not sure if it is correct. I'm using LIMP for measurements and I remember getting two conflicting values for Le. The value changes if I copy the T/S data to clipboard (using the button in the program's window).

It just so happens to be that I'm now building a small box to help with impedance measurements. I will take new results later today and post the results.
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Old 7th September 2008, 02:52 PM   #3
breez is offline breez  Finland
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Hi

Using delta mass (16.8 grams worth of coins) the following parameters were estimated with LIMP (part of ARTA software package):

Woofer #1:

Fs = 31.49 Hz
Re = 5.40 ohms[dc]
Le = 976.38 uH
L2 = 501.94 uH
R2 = 1.98 ohms
Qt = 0.40
Qes = 0.42
Qms = 6.78
Mms = 13.44 grams
Rms = 0.392489 kg/s
Cms = 0.001900 m/N
Vas = 36.46 liters
Sd= 116.90 cm^2
Bl = 5.816173 Tm
ETA = 0.26 %
Lp(2.83V/1m) = 87.93 dB

Woofer #2:

Fs = 31.83 Hz
Re = 5.40 ohms[dc]
Le = 1116.50 uH
L2 = 493.30 uH
R2 = 2.05 ohms
Qt = 0.41
Qes = 0.43
Qms = 7.34
Mms = 15.36 grams
Rms = 0.418130 kg/s
Cms = 0.001628 m/N
Vas = 31.25 liters
Sd= 116.90 cm^2
Bl = 6.175771 Tm
ETA = 0.22 %
Lp(2.83V/1m) = 87.29 dB

The woofers have been broken in using high excursion sine for 50h+. No guarantees about accuracy!
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Old 30th September 2008, 03:39 AM   #4
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TurboFC3S, have you listened to these sb acoustics woofers?
how do you like them? they look extremely well built.
do you have any pictures from the back view?
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Old 30th September 2008, 04:56 AM   #5
peter_m is offline peter_m  Canada
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I'm surpised no one posted a design for them by now.

Peter
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Old 30th September 2008, 06:21 AM   #6
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Looking at Zaph's results in his 6.5" group there is really not a lot of diiference with your results Turbo. Am I missing something?

He's showing .45 mh for Le opposed to your .17 mh, but those values come from different methods. Yours is at 1khz while Zaph's is done using curve fitting over a range frequencies. Both can have their inaccuracies (especially with full copper sleeves on pole pieces), so looking at the actual impedance gives a better idea of what is going on.

Too bad they have such a good motor on a cone/surround with that breakup problem...Have you used this yet Turbo?
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Old 30th September 2008, 06:28 AM   #7
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Zaph has called into question the accuracy of the delta-mass method before, I believe.
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Old 30th September 2008, 02:07 PM   #8
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actually this woofer has smaller sd area then the others in the group. maybe that's why it has slightly weaker bass performance.
and at this price I would not be afraid to install phase plug and modify cone/surround to smooth out breakup.
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Old 2nd October 2008, 11:38 AM   #9
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Hi,

I have ordered some of the 5" and doing a projekt. Right now im waitting for the enclosures to be finished.

the enclosure drawing can be seen here.
http://www.hifi4all.dk/forum/forum_posts.asp?TID=67715

later, ill add it to my website.
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Old 2nd October 2008, 02:09 PM   #10
USXX is offline USXX  Denmark
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A coil sitting in an air gap surrounded by iron does not behave like a true inductor - far from. As a consequence of eddy-current losses, it behaves more like a semi-inductor. Therefore you CANNOT use an LCR-meter to measure loudspeaker voice coil inductance - an certainly not if the coil has been removed from the air gap. In the case of the SB driver, there is a copper cap on the pole piece, which also conducts eddy-currents and significantly reduces the (apparent) inductance.

Loudspeaker voice coil inductance (in Henry) is calculated by an empiric equation:

Le = ((Re*20000/(2*pi*f3))+0.5)/20000

, where f3 is the frequency at which the impedance (i.e. modulus) is 3 dB (i.e. a factor sqrt 2 ) higher than Zmin (the minimum impedance above resonance).

This is considered to be the best single inductor approximation/representation, though it is a poor model, which I never use myself.

The hump on the impedance curve is always to be expected when using a low damping surround. Look at the Scan-Speak 18W/8531 for instance. You can easily get rid of the hump by using a high damping surround (material) - that is if you can live with the loss of dynamics and transparency (I can't).
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