Audax HM130C0; WinISD says 10ohms not 8

[Kev06]

I've been putting the parameters for this audax mid range driver (e.g. here) into WinISD pro/alpha; I've tried it several times in a couple of different orders, however WinISD is auto-calculating the nominal impedance (Z) as 10 ohms, whereas the datasheets all say it should be 8 ohms.

Does anyone know why there is this discrepancy, or is 'nominal' so vague as for it to be unimportant?

Thanks
Kev

 

[JonSnell Electronic]

The spec shows Re as 6.2 Ohms so I would check your meter and test leads for stray resistance however you are measuring the DC resistance and not the impedance. That may be your discrepancy.

 

[Kev06]

Thanks Jon. Unfortunately I don't have the driver yet though, so I can't check if Audax has measured their DC resistance correctly or not.

Cheers
Kev

 

[kelticwizard]

The rule of thumb is that nominal impedance is about 25% higher than DC resistance.

Most speakers rated 8 ohm nominal have a DC resistance between 5 and 6 ohms, though slightly over 6 is not unusual.

I don't know why WinISD is rating this speaker at 10 ohms.

 

[Kev06]

Thanks, thats good to know. It seems at least a reasonable Re then.

Strange; WinISD pro calculates various parameters to make them marry up, so there can be slight differences from the spec sheets but its unusual (in my limited experience with it) for it to get the impedance so different. Although thinking about that, it also seems odd that the calculated values are normally so completely bang on 8 or 4 ohms; perhaps it has some nominal thresholds and these audax parameters have pushed over into the next one up?

Cheers
Kev

 

[Greebster]

a little more info on that driver http://www.diyaudio.com/forums/multi-way/109411-audax-hm130c0-information.html

 

[Kev06]

Thanks! Andrew's parameters in that thread seem to tally with the ones I've been using which is reassuring. I also did a search around and found a more complete PDF (attached). I can't see anything wrong with how I'm using the data, so I guess either Audax's figures don't add up to their Z-nominal, or WinISD isn't using them correctly (or a bit of both).

As an aside, its interesting to see what the last post in that thread says; a big peak at 700-800Hz needing a notch filter. There does seem to be a peak in the audax response curve around there, which may go against my intention to keep it simple.

Cheers
Kev

 

[Greebster]

That pdf seriously helps 🙂

 

[Kev06]

Hopefully, though looking at the impedance curve axis, it does seem to have two 10ohm lines instead of a (presumably) 5 and a 10 🙂

Cheers
kev

 

[dumptruck]

WinISD guesses from the parameters and you are supposed to change it to what you see on the graph if needed, or just ignore it, as it doesn't really matter for the bass sim unless you're trying to get an accurate estimate of max spl and power required from WinISD.

 

[Kev06]

Ah, thanks very much. My experience with other calculated values has been that changing them stops WinISD validating when saving the profile, but you're right; I can change the Z value and it still accepts it 🙂

Cheers
Kev

 

[vacuphile]

Have you punched in the right number for Le?

 

[Kev06]

Yes, I had Le in there correctly, though thanks for the suggestion. It didn't seem to change Znom with or even completely without it, unfortunately.

Though I'm not sure if WinISD alpha/pro may also have some sort of issue with Le; if its there the high end with many drivers seems to roll-off far sooner than the response charts suggest they should - though its equally possible that I'm missing something. I'm pretty sure I've not been messing up the milli/micro (etc) though so there doesn't seem much else for me to get wrong

Cheers
Kev