BillFitzmaurice.info

How does one accomplish a nominal impedance calculation, when multiple cabs are in use?

Why I ask: I have 6 TTLS in my truck, loaded with 4 Ohm drivers.

The horn "adds" about 2 Ohms of impedance... but is that added before the electrical impedance is calculated, or after?

Are my 6 cabs presenting a nominal 2.7 Ohm load? (Full parallel at 4 Ohms each, with 2 Ohms added on top)

Or are they presenting a 1 Ohm load (6 Ohms each, full parallel)?

It will really help me out on my next amplifier purchase, to know what to look for.

Thanks!

Each cab is nominally 6 ohms. Wired parallel six cabs would be 1 ohm. I would not size an amp with the intent of using it at its minimum load rating, that's pretty much asking for trouble. Always give yourself some wiggle room.

Bill Fitzmaurice wrote:Each cab is nominally 6 ohms. Wired parallel six cabs would be 1 ohm. I would not size an amp with the intent of using it at its minimum load rating, that's pretty much asking for trouble. Always give yourself some wiggle room.

Thanks!

I plan to get a 1 Ohm stable amp that has been successfully stress-tested at a lower impedance.

Some car audio amps that are 2 Ohm stable get tested at 1 Ohm, and work fine, as long as the electrical system of the vehicle can keep up good supply.

For something like this I'd go with a series-parallel configuration. Lightens the load, and you should be able to get an amplifier with plenty of power to do that easily.

Here are some 0.5 ohm stable arc welders, oops , i mean car amps:

http://www.sonicelectronix.com/cat_f47- ... fiers.html

CoronaOperator wrote:Here are some 0.5 ohm stable arc welders, oops , i mean car amps:

[url]ttp://www.sonicelectronix.com/cat_f47-485_i23 ... fiers.html[/url]

missing the "haych" on the front of the link..

Corrected link.... http://www.sonicelectronix.com/cat_f47- ... fiers.html

Tom Smit wrote:missing the "haych" on the front of the link..

corrected

Hey Ryan,
Yep it's what we often do, work things out with nominal impedance.

Ages and ages back someone pointed out looking at impedance charts for the driver as well though.
The reason being that some frequencies are running well below nominal impedance, and that can be even more of a problem when paralleling cabs when it comes to amp loads.

If it turns out that by paralleling you have impedance at some frequencies below your amps specs (vs nominal impedance), you may well have to consider series/parallel...

Grant Bunter wrote:Hey Ryan,
Yep it's what we often do, work things out with nominal impedance.

Ages and ages back someone pointed out looking at impedance charts for the driver as well though.
The reason being that some frequencies are running well below nominal impedance, and that can be even more of a problem when paralleling cabs when it comes to amp loads.

If it turns out that by paralleling you have impedance at some frequencies below your amps specs (vs nominal impedance), you may well have to consider series/parallel...

Oh, I'm well aware. That's why I make the point to say "nominal" a lot.

But it seems to me that some car audio amplifier manufacturers take that into account, and make "1 Ohm stable" amps that can handle dropping down to .3 Ohms for a single note's duration without complaining too much.

It's one of those amps I'll be getting. Something that the car audio community has verified can handle periodic dips to "unsafe" territory without letting out the magic smoke.

I'm seriously considering this amplifier: http://www.caraudiobargain.com/new-cab- ... amplifier/

My audio team president bought one, and ran it at .25 Ohms (nominal!) full-tilt for about 4 hours. It did end up dying a horrible death, but he's getting it replaced.

I really don't want to continue to run series-parallel, only because an amp rated for 1.2kw at 4 Ohms is gonna be very expensive, and the current amp I'm running is only capable of 550w at 4 Ohms... so each cab is only getting about 90w. Half of power handling. And that 3dB could be the difference between a first-place trophy, and a 4th place ribbon.

Edit: btw, thanks, everyone, for your contributions. I realize I'm kinda doing something that's off the reservation, so to speak, and I appreciate all the viewpoints you guys provide. I really like this community, and all the awesome help and ideas.

you can wire lower then the minimum impedance with car audio because of box/impedance rise. basically with car audio if you wire to 1ohm your amp will read around 2ohm, maybe even 3ohm.

truitt wrote:you can wire lower then the minimum impedance with car audio because of box/impedance rise. basically with car audio if you wire to 1ohm your amp will read around 2ohm, maybe even 3ohm.

In this case, we are taking the "box rise" into account at the onset; that is why 6 6-Ohm cabs go down to 1-Ohm nominal. They're loaded with 4-Ohm drivers, but that extra 2-Ohms is the "box rise".

Good looking out, though. Not everyone knows about impedance rise.