# impedance

Discussion in 'Amps and Cabs [BG]' started by mclaud, Nov 8, 2001.

1. ### mclaudGuest

Oct 25, 2000
portugal, lisbon
hi!

this may seem stupid, but here comes.

what are the diferences between a 4 ohms cab and a 8 ohms cab with the same power.

if i have a 4 ohms amp with 600 watts (mono), what would be the best choice, 2 cabs at 8 ohms or 2 cabs at 4 ohms and what would be the the impedance in both cases and why?

one more thing, if you want to plat loud what would be best, a good power handling or a good sensitivity. for example, between a cab with 400 watts rms with 100 dB/1 W/1 m and a cad with 350 watts rms with 105 db/1 W/1 m what would play loud and why.

tanks!

2. ### downstairs

May 13, 2001
if you have 2 cabs of 8 ohms, it makes 4 ohms, if you have 2 4 ohm cabinets it makes 2 ohms, get the 2 8 ohm cabs just so you don't fry out your amp.

3. ### Mudbass

...a cab with 400 watts rms with 100 dB/1 W/1 m and a cad with 350 watts rms with 105 db/1 W/1

The second cab is a better choice. The cab with 350 watts and 105db @ 1w has a five db advantage that the other cab can't match even with it's 50 extra watts of power handling capacity.

4. ### Steven Green

Jul 25, 2001
Pacific NW
If I'm not mistaken, if you have a cab that have +5 dB more than the other, it will be nearly 4X as loud (I think+3 dB doubles volume).

So, if you are giving specific examples that apply to you, go for the cab with the better sensitivity rating and only (1) 4-ohm, or (2) 8-ohm cabs giving you a total 4-ohm load, which would match the 4-ohm head in your example.

5. ### JMXVorsprung durch Technik

Sep 4, 2000
Cologne, Germany
No!

+10dB is double volume

To get a boost of +3dB you need twice the power, people confuse that often.

6. ### Joris

One more nit to pick: +10 dB is perceived as double volume.

In fact it's ten times the sound pressure and power, but we perceive it as approximately twice as loud. Damn human hearing

7. ### JMXVorsprung durch Technik

Sep 4, 2000
Cologne, Germany
Thanks master Joris

8. ### MikeyD

Sep 9, 2000
Human hearing is actually pretty amazing. Probably this same phenomenon is why this particular "instrument" has a dynamic range of around 10^12 (one trillion) in pressure-squared (measured logarithmically with SPL, in decibels). That is a huge range - I can't think of many devices that have that kind of operating range.
- Mike

9. ### Joris

Yeah, the human hearing has yet to be equalled by equipment those humans build.

Sep 9, 2000
Puny humans!
- Mike

11. ### Joris

Aren't we but dust?

Oh well as long as I can play bass with my inferior equipment