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 lfmn16 12-21-2013 09:40 AM

Could someone please confirm watts and ohms?

I did use the search function, but I just want to make sure I understand things correctly since I need to upgrade my rig:

Ohms are pretty easy - 2 eight ohm cabinets = 4 ohms, two four ohm cabinets = 2 ohms, a four ohm cabinet and an eight ohm cabinet = about 2.7 ohms. If you have a head that is a minimum of 4 ohms, you can't run the eight and four ohm cabinets together.

I can't find this spelled out, but is there a difference in ohms between running both cabinets directly to the head and running one cabinet to the head and the other cabinet to the cabinet running from the head? I don't get why you would choose one over the other.

Watts - when pairing cabinets, it's best to use 2 of the same cabinets. However, if you don't, you are limited by the power of the weaker cabinet, so if I run a 700 watt 4X10 and a 350 watt 2X10, I shouldn't pair it with a head that puts our more than 350 watts.

Thanks to anyone that wants to confirm or correct.

 B-string 12-21-2013 10:01 AM

Quote:
 Originally Posted by lfmn16 (Post 15275403) I did use the search function, but I just want to make sure I understand things correctly since I need to upgrade my rig: 1Ohms are pretty easy - 2 eight ohm cabinets = 4 ohms, two four ohm cabinets = 2 ohms, a four ohm cabinet and an eight ohm cabinet = about 2.7 ohms. If you have a head that is a minimum of 4 ohms, you can't run the eight and four ohm cabinets together. 2I can't find this spelled out, but is there a difference in ohms between running both cabinets directly to the head and running one cabinet to the head and the other cabinet to the cabinet running from the head? I don't get why you would choose one over the other. 3Watts - when pairing cabinets, it's best to use 2 of the same cabinets. However, if you don't, you are limited by the power of the weaker cabinet, so if I run a 700 watt 4X10 and a 350 watt 2X10, I shouldn't pair it with a head that puts our more than 350 watts. Thanks to anyone that wants to confirm or correct.
1 Correct.
2 There is no difference with many amp heads (SS), tube output amps you may need separate cables to switch output taps or one cable to two cabs to match the load needs.
3 Not quite, you take the lowest rated cab (350 in your example) and multiply by the number of cabs (350 X 2 in your example, amp with no more than 700 watts).

 Rob22315 12-21-2013 10:08 AM

EE 101

In series, Rtot=R1+R2+R3 . . .

In parallel, 1/Rtot=1/R1+1/R2+1/R3+ . . .

Two series 8 ohm cabs=16 ohms

Two parallel 8 ohm cabs=4 ohms (1/(1/8+1/8))

 lfmn16 12-21-2013 10:23 AM

Quote:
 Originally Posted by B-string (Post 15275486) 1 Correct. 2 There is no difference with many amp heads (SS), tube output amps you may need separate cables to switch output taps or one cable to two cabs to match the load needs. 3 Not quite, you take the lowest rated cab (350 in your example) and multiply by the number of cabs (350 X 2 in your example, amp with no more than 700 watts).
Thanks!

 Vince Klortho 12-21-2013 11:54 PM

I would revise the answer to #3 be speaker capacity is 700W but you can power it with practically what ever you want. It is possible to run a system with more power than the speakers can handle without problems (I have for decades.) Just be careful and listen for signs of issues.

Remember that you have a volume knob and it does not have to be set on 10.

Or 11 either. :cool:

 Munjibunga 12-22-2013 12:48 AM

Quote:
 Originally Posted by Vince Klortho (Post 15277840) I would revise the answer to #3 be speaker capacity is 700W but you can power it with practically what ever you want. It is possible to run a system with more power than the speakers can handle without problems (I have for decades.) Just be careful and listen for signs of issues. Remember that you have a volume knob and it does not have to be set on 10. Or 11 either. :cool:
Very true. I run my MB800 or MB Fusion 800 heads into my 8-ohm Bergantino AE210 often. The AE210 is rated at 400 watts and the MB amps are rated at 500 watts into 8 ohms. I also run them into my 4-ohm CN212 which is rated at 700 watts and the amps are rated at 800 watts into 4 ohms. I've never had a problem in either instance. I also know what an overdriven cab sounds like, so I don't go there.

Also for practically all solid-state heads there is no difference between running a cab to each output and daisy chaining cabs. Do one or the other based on convenience. Some amps have only one output jack, so you have to daisy chain to do more than one cab.

 OOZMAN 12-22-2013 01:01 AM

Doesn't daisy chaining cabs put them in series? So if you have two 4 ohm cabs and daisy chain them, you will end up with an 8 ohm load to the head. That's what my speakers did anyway. Not sure if my speakers are just oddball though.

 Vince Klortho 12-22-2013 01:15 AM

Usually daisy chaining places speakers in parallel. If yours are connected in series then yes, I think they are oddballs.

 Munjibunga 12-22-2013 01:36 AM

Quote:
 Originally Posted by OOZMAN (Post 15277893) Doesn't daisy chaining cabs put them in series? So if you have two 4 ohm cabs and daisy chain them, you will end up with an 8 ohm load to the head. That's what my speakers did anyway. Not sure if my speakers are just oddball though.
No. Daisy chaining them puts them in parallel, and two 4-ohm cabs will present a 2-ohm load to your amp. How do you know that your cabs were in series and presented an 8-ohm load to your amp? What kind of cabs are they? If you connected them with standard speaker cables, I can't think of any way the cabs could have ended up in series.

 dincz 12-22-2013 01:38 AM

Apologies if I'm stating the obvious, but the comments about #3 are valid only if the two cabs have the same impedance.

 96tbird 12-22-2013 07:17 AM

Could someone please confirm watts and ohms?

The standard for instrument cabs is that jacks are wired parallel.

The same for jacks on integrated amps.

If someone had altered a cab's jacks to series and sell it on the used market, you would hope they would let you know :eek:

It's easy to check though.

 Rich McCoy 12-22-2013 07:33 AM

If your amp puts out 250 watts at 8 ohms, and 400 watts at 4 ohms you could use one cab rated at greater than 250 watts or two cabs rated at 200 watts each.

 RickenBoogie 12-22-2013 08:12 AM

Wattage ratings on cabs are misleading. The basic rule is, use common sense, and listen for any signs the spkrs are being stressed. Otherwise, use what you like, but don't expect more than any particular cab is capable of delivering.

 oboylebass 12-22-2013 08:15 AM

Yeah but you don't refer to it as "ohms". It's called impedance. i.e. The impedance of this cabinet is 4 ohms. Or... What's the impedance of two 8 ohm cabinets?

 B-string 12-22-2013 09:27 AM

Ohms is the measurement of AC impedance or DC resistance, the same "yardstick" is used for either.So I'm not quite sure what distinction you are attempting?

 Rob22315 12-22-2013 09:33 AM

Quote:
 Originally Posted by B-string (Post 15278736) Ohms is the measurement of AC impedance or DC resistance, the same "yardstick" is used for either.So I'm not quite sure what distinction you are attempting?
Yes, this is 'more correct'. Impedance has both a DC component - reisitance; and an AC component - reactance. Speaker impedance in specs is the DC component or resistance. The unit of measure is ohms for all of this but absent a representation of the AC component, it's resistance. The DC component is a number, the AC component can be very complex depending on the number of reactive components and the circuit design.

 DogBone 12-22-2013 11:28 AM

I always take wattage limitations with a grain of salt.

Chances are a driver will reach it's mechanical limitations far sooner than it will reach its wattage (thermal) limitation.

In other words, a speaker will fart out before it will melt. ;)

User your ears, and you'll be fine.

 dincz 12-22-2013 12:46 PM

Quote:
 Originally Posted by Rob22315 (Post 15278758) Speaker impedance in specs is the DC component or resistance.
It varies wildly across the frequency range but the specs show nominal impedance. If it was resistance, the specs would list resistance not impedance.

The DC resistance isn't of much interest but it's typically around 3/4 of the nominal impedance.

 lfmn16 12-22-2013 02:20 PM

Thanks to everyone for their input!

 Munjibunga 12-23-2013 06:33 PM

Quote:
 Originally Posted by oboylebass (Post 15278494) Yeah but you don't refer to it as "ohms". It's called impedance. i.e. The impedance of this cabinet is 4 ohms. Or... What's the impedance of two 8 ohm cabinets?
All this time I thought it was "ohmage." LOL.

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