Help with impedance and cabs/heads

[doctormoose87]

Hi all.

I know it's probably somewhere on the site anyway but; I've no idea about Ohms and wattages for cabs and heads.

I've got a hartke HA3500A head and the VX410 cab. Now the head has 2 outputs on the back to the cabs rated at 8ohms. The head is 240w @ 8ohms or 350w @ 4ohms. The VX410 is rated at 8ohms. So far I've kinda figured that the head is safe to use with the cab, but I'm thinking of adding either a 1x15 or a 2x10 for a bit of extra grunt. So do I need to find a cab with a 4ohm rating or a 8ohm??? I don't understand about the whole ohm to watt thing so if anyone could shed some light on this it would great.

(Really I should have learnt this years ago but never thought it important d'oh)

Many thanks

Andy

[bongomania]

Add an 8 ohm cab, and read about "why" in the FAQ at the top of the Amps forum.

[doctormoose87]

Thank you. I have done and understood about 1/2 of it lol. So I'm ok with a cab rated at 8 ohms as long as I don't run it at 2ohms or above the wattage rating of the cab?????

[bongomania]

Those are good starting points. The "bigger reality" gets a little fuzzy because there are amps that can go down to 2 ohms, and circumstances when it can work to use an amp rated higher than the cab--but it's better to save those cases for when you've got more of the technical knowledge under your belt.

[doctormoose87]

Cool. Thank you. I guess now I have some maths to think of when I'm drooling over amps

[Pollinator95]

For the moment, all you need to know is:
- Two (2) 8 Ohm cabs total a 4 Ohm load, and two 4 Ohm ones total 2 Ohms.
- When you have two or more cabs with equal impendance (Ohms) connected, the wattage is spread evenly between them.
- Hooking a 300W amp to a 300W cab might sound bad at high volume, despite the ratings.
- Behringer Watts aren´t quite the same as regular Watts .

You´ll find more out as you go on.

[doctormoose87]

Sweet so I can get that ashdown I've been drooling over as an extra cab as it's the same as the VX410. That with the nice weather in the 'shire in the UK has made my day