Are the SB17NBAC35-8 T/S specs way off?

[DaveFred]

The German magazine Hobby Hifi measured this woofer one year ago.

Inhalt HOBBY HiFi 06/18

The results:

Re= 5,6 Ohm
Le= 0,17 mH
Fs = 29 Hz
Qms = 5,6
Qes = 0,44
Qts = 0,41
Sd = 127 qcm
VAS = 45 liters
MMS = 0,5 kg/s

Enclosure:

45 ltr. Bassreflex
Port ø 70mm, 270 mm long
- 3dB: 24 Hz

17 ltr. sealed
**** 560 mF capacitor (GHP) ****
- 3 dB: 36 Hz.

Best regards

Ludger

Was that a series capacitor?

Can this article be read online or can I order a PDF that I can translate?

Thank you,

David.

 

[YSDR]

Was that a series capacitor?

That magazine usually recommends a big value series capacitor to the woofer, to shape the low-end roll-off.
But this creates another problems as any other passive filtering around the resonances. But of course they forget to mention it. However, the negative effect is usually not negligible.

 

[celef]

I think magico is also using this trick, to stretch the low end a bit, but then the speaker loses the gentle roll off that is so nice with a sealed enclosure

 

[Jonasz]

www.audioexcite.com >> SB Acoustics SB17NBAC35-8

 

[celef]

www.audioexcite.com >> SB Acoustics SB17NBAC35-8

Same problem, he must also be using dats?

 

[spendormania]

That magazine usually recommends a big value series capacitor to the woofer, to shape the low-end roll-off.
But this creates another problems as any other passive filtering around the resonances. But of course they forget to mention it. However, the negative effect is usually not negligible.

Yes. You'll get a little more group delay but if the box has a proper design, it's not a problem at all.

@ David: There are no additonal informations about the GHP-principle in the article.

Here's a post that might help you. Just put it in the deepl translator.

GHP was ist das wie funktioniert das

 

[YSDR]

Same problem, he must also be using dats?

It's hard to believe that Qes=0.5+ goes down to the advertised 0.38 at any measurement level.

 

[celef]

just try it for your self, compare impedance curves measured with different stimuli at different levels on drivers with a high and narrow resonance peak

 

[Jonasz]

It's the same phenomenon as a lot of Scan-Speak Revelators, way higher Qts than published. I don't mind I like closed boxes. 🙂

 

[celef]

yes, scan-speak and seas seems to have the worst official numbers

i like closed boxes too but i am still concerned about the numbers, even small errors will push me away from my target response

 

[YSDR]

just try it for your self, compare impedance curves measured with different stimuli at different levels on drivers with a high and narrow resonance peak

Do you know the main reason why the resonance peak is narrow? The same reason as to why the Qes is high. The motor is weak (relative to lower Qes drivers).

 

[Jonasz]

The magnets are probably weaker in the production units than the pre production ones? 🙄

 

[YSDR]

The magnets are probably weaker in the production units than the pre production ones? 🙄

That's possible. Or the air gap is not so tight.

 

[celef]

Do you know the main reason why the resonance peak is narrow? The same reason as to why the Qes is high. The motor is weak (relative to lower Qes drivers).

you will get a different shape depending on test stimuli and level

 

[celef]

i did a series of quick tests for one sb17nac 4 ohm

sine -10dbfs

qts: 0.3406
qms: 6.431
qes: 0.3597
fs: 33.33 hz

***

sine -1dbfs

qts: 0.3362
qms: 6.732
qes: 0.3538
fs: 32.78

***

pink noise -12dbfs

qts: 0.3939
qms: 9.6199
qes:0.4107
fs: 38.27

***

mls 0dbfs

qts: 0.3806
qms: 7.5005
qes: 0.4009
fs: 36.29