WHAT'S THE IMPEDANCE OF MY BASS CAB?

[ThisBass]

Originally Posted by megafiddle

However, the rated nominal impedance is a minimun value.

That means all drivers out there referring to the AES recommendation are wrong.
Ähm, and probably a lot of others out there as well with rated specs referring to a Znominal and Zmin.

[ThisBass]

Originally Posted by megafiddle

Amp manufacturers need to be aware of this. When rating an amp to handle an 8 ohm cabinet, the amp
needs to be able to actually handle 6 ohms, as the actual impedance could be that low.

so what do you suggest for a valve amp impedance output select.

1) EQ flat all the way: ?
2) EQ +12dB bass boost: ?
3) EQ +6dB LowMid boost: ?


2) I'd suggest to select 8 Ohm OT output for a 4 Ohm vented cab.

[megafiddle]

I need to correct that, it should be:
"However, the rated nominal impedance is based on the minimun value."

Nominal and minimum are not the same. Sorry about that.

[megafiddle]

Originally Posted by ThisBass

so what do you suggest for a valve amp impedance output select.

1) EQ flat all the way: ?
2) EQ +12dB bass boost: ?
3) EQ +6dB LowMid boost: ?


2) I'd suggest to select 8 Ohm OT output for a 4 Ohm vented cab.

You certainly have a good point. If you can restrict your signal to a certain part of the spectrum,
you should be able to safely operate the cabinet as a higher impedance cab (which it is under those
conditions).
And you can gain additional power from better matching with a tube amp.

But amp and speaker manufactures have to assume worst case conditions.

[ThisBass]

Originally Posted by megafiddle

But amp and speaker manufactures have to assume worst case conditions.

That's the deal

[fernandobicho2]

Very good!
Thank you all!

In other thread here, from 2004, How is this 4 ohms ?
fellow david_l_perry


says:

Just had confirmation from PAS

>The BG-1080C-8 is an 8 ohm speaker rated at 200 watts.
>
> Allan Sohl
>
> PAS Engineer


So, I must assume the drivers in my cab are 8 0hm, because they're BG-1080C-8
http://imageshack.us/a/img842/7154/d...oliath4x10.jpg

[Arjank]

Originally Posted by Bassmec

I can measure it accurately, I have the all tube old school former Celestion lab technology to do so right here:

but you are over there somewhere, so I will have to factor in a very long lead length which will introduce unacceptable errors.
So why not just take an ancient loudspeaker test engineers word for it EH! 8 Ohms nominal son!.

Great setup!

[Arjank]

Originally Posted by ThisBass

Sometimes a spectrum has most amount of energy/power at the lows. (The bass guitar for example)
Whereas sometimes a spectrum has more amount of power at low mids.
Depending on signal nature and eq settings the individual users spectrum differ significant

Depending on impedance curve the amplifier sees different impedance values depending on the signal spectrum.
The Impedance curve by itself does not change.

Yes, true, it's the same as I told you but then with different words

[Arjank]

Originally Posted by fernandobicho2

Just had confirmation from PAS

>The BG-1080C-8 is an 8 ohm speaker rated at 200 watts.
>
> Allan Sohl
>
> PAS Engineer


So, I must assume the drivers in my cab are 8 0hm, because they're BG-1080C-8
http://imageshack.us/a/img842/7154/d...oliath4x10.jpg

If the PAS engineer says so....

PAS has another driver with a low Re value, the LX-2800.
See pdf files here http://www.pas-toc.com/pdf/drivers/

The Re of the LX-2800 is 4.6 ohms(even a bit higher then your BG-1080C-8) and if you look at the impedance CURVE, you'll see that between 80 and 200hz it's approx 6ohms. Thats why I say that such a driver would fall in the 6ohm category and not 8.

Maybe some manufacturers would put it in either 4 or 8ohms, I would put it in the 6ohms category so people would know that the impedance can drop to 3ohms in a pretty broad frequency range when you wire them parallel and thus putting extra strain on the amp.

According to DIN a small dip to 3.2ohms will keep a loudspeaker in the 4ohm category (20% deviation), below that it wil be rated 3ohms. Same for 8 ohm loudspeakers, they may drop to 6.4ohms to still be rated 8ohms. Maybe, I say maybe, the impedance curve of the BG-1080C-8 doesn't drop below 6.4ohms, but I do not think so given the Re of 4.4ohms. But since we don't have a graph of the impedance we don't know...

Another eaxmple, the Visaton B200 is rated 6ohms, it has an Re of 5ohms. In the graph you see it just slightly drops below 6ohms.

Edit: the 20% drop is not only according to DIN but also IEC (also for the DC value )

The IEC standard (IEC60268-3) allows any "increase" above the rated value, but limits the
"decrease". The standard does not allow the impedance to fall below the 80 % of the nominal value
at any frequency, including DC.

Case closed.
Maybe put this thread in the AMP FAQ.

[fernandobicho2]

THANK YOU ALL, FELLOWS. YOU'RE GREAT!

[lethargytartare]

Originally Posted by fernandobicho2

Very good!
Thank you all!

In other thread here, from 2004, How is this 4 ohms ?
fellow david_l_perry


says:

Just had confirmation from PAS

>The BG-1080C-8 is an 8 ohm speaker rated at 200 watts.
>
> Allan Sohl
>
> PAS Engineer


So, I must assume the drivers in my cab are 8 0hm, because they're BG-1080C-8
http://imageshack.us/a/img842/7154/d...oliath4x10.jpg

Not even "must assume" -- you can confidently KNOW :-)

Did you ever try contacting SWR with the serial number to ask?

Cheers!
ltt

[BassmanPaul]

Originally Posted by Bassmec

So why not just take an ancient loudspeaker test engineers word for it EH!

Bassmec I have to take exception to this post!

EH is reserved for we Canadians eh! It's part of our national identity!!!

Even we immigrants have to swear at our citizenship ceremony thus: I swear allegiance to the Her Majesty The Queen eh!

[MuthaFunk]

Originally Posted by BassmanPaul

Bassmec I have to take exception to this post!

EH is reserved for we Canadians eh! It's part of our national identity!!!

Even we immigrants have to swear at our citizenship ceremony thus: I swear allegiance to the Her Majesty The Queen eh!

LOL! Well said! Hear Hear!

They just don't get it like us eh!

[fernandobicho2]

My friend Gaspar, sended me two pictures of his Goliath III 8 Ohm... any doubt? eh eh eh (we portuguese usually have 3 "eh" together, or just only a "LOL").

and yes, I've sended my doubd to SWR, but they didn't find any information by my cab's serial.

I hope this thread it's usefull for someone in the future. Thank you. You helped a lot


[IMG]

[fernandobicho2]

Now, the recent answer of Fender.

" If these were originally wired in series/parallel then this would have to be an 8 ohm cabinet total.
Typically the static ohm reading on these speakers will be much lower than what they are.
Best regards, Michael Roberts
Consumer Relations Representative
Fender Musical Instruments Corp."

Thank you

[Arjank]

Originally Posted by fernandobicho2

Now, the recent answer of Fender.

" If these were originally wired in series/parallel then this would have to be an 8 ohm cabinet total.
Typically the static ohm reading on these speakers will be much lower than what they are.
Best regards, Michael Roberts
Consumer Relations Representative
Fender Musical Instruments Corp."

Thank you

Thats what they tell you....
I explained in post #69 how it actually works.