Why do I need a 4 ohm cab ?

[largo]

I know that 4 ohms will give me maximum power output from my amp.
However, I have seen numerous posts on boards and in "For Sale" sections saying they won't buy a cab because it's not 4 ohms.
I used to be one of those people until I got my 8 ohm Barefaced cab. Truth is, I have hardly had to up the volume on my amp and now have the capacity to add a second cab if I want to.
So, I guess my question is this. By having to push more volume through my amp do I increase the chances of it breaking/burning out? Or, is this 4 ohm cab simply a myth that most people make too big a deal of.

[Colledge]

i have the same train of thought as you, i'd much rather have the ability to add an extra cab to the mix if i needed it than get slightly more power into one cab.

[chris_b]

Using the example of a 410, in my experience 2 410 8 ohm cabs will sound much better than 1 410 4 ohm cab not because of the watts but because of the extra speakers. I always buy 8 ohm cabs and use 2 of them.

[Musicman20]

I think it depends on the amp and the volume you want.

If its a fairly big cabinet that can take the power (high end 4x10) then by all means if you dont need anymore speakers, get the 4ohm version. 4 ohm mid sized cabs sell better second hand it seems.

Smaller cabinets? Always go for 8 ohm IMO (eg 2x10). Otherwise, you amp can hit it with a lot of power!

I think its more the modern amps that work much more efficiently and sound 'bigger' into one 4 ohm cabinet than one 8 ohm cabinet, and Im talking 2x12-4x10 upwards. It depends on the amp. My TC RH450 is loud no matter what, and at 8 ohms works perfectly. Markbass amps, apparently, work much stronger at 4 ohms.

Your ears wont be able to tell much difference between a 4 or 8 ohm cabinet in reality, but your amp might sound 'fuller' working at 4 ohms.

[Noisyjon]

I think it's also a lot to do with newer 8 Ohm speaker designs being more efficient and sensitive meaning there's more SPL (sound pressure level) coming out of the speaker with the same amount of Watts as a more un-efficient older speaker.
The goal posts have moved in terms of needing less resistance and more speakers to achieve louder results IMO...

I'm running 2 x Barefaced Compacts off a MarkBass SA450 and it's a staggering amount of power and volume from that setup!

JTB

[chris_b]

[quote name='largo' post='948086' date='Sep 7 2010, 10:56 AM']....So, I guess my question is this. By having to push more volume through my amp do I increase the chances of it breaking/burning out?....[/quote]
I believe amps are designed to work at 4 ohm. At 8 ohm they are reined in so 4 ohm shouldn't stress any amp. Also no amp should break or burn under normal working conditions unless it has a fault, or you've covered over any ventilation grills.

[MythSte]

Mr Fitzmourice will tell you the facts, but im pretty sure that if you are running a 300w amp at 4ohms, with an 8ohm cab, your only losing about 3dB of volume. That amount of loss can be made up by suitable positioning of the cab!

+1 also to Jonthebass, newer speakers are much more efficient than older ones, so squeezing every available watt out of them isn't as necessary

[JTUK]

You either have enough or you don't with your amp/cab but 300-500w HAS to be enough.
I shudder to think what some people put on stage and try to run at as even if they are deaf, then why should we be..?

It seems bass players can now try and keep up with a cowboy and his 4x12, and then it becomes a wall or din of sound in most pub sized venues.
I run 400 tops through 2 mini cabs and I am a light-touch player. That keeps up with a VERY loud drummer, too loud, if I am honest, and gtr and keys. I am sure most of my bass playing mates would be FAR louder than I can be as they attack the bass with a harder action.
If I see a bass stack and a gtr stack...I am pretty much out of there. Not only because the band will not work for me...almost blatantly true, in every instance, but I don't want my ears assaulted by people who don't have any left...and if they are wearing plugs that adds insult to injury..!!!

[PaulWarning]

sorry to hi jack the thread but it is relevent, if using 2 x 4 ohm cabs gives you a 2 ohm load, what would 1 x 4 ohm cab and 1 x 8 ohm cab give you?

[Wil]

[quote name='PaulWarning' post='948367' date='Sep 7 2010, 03:11 PM']sorry to hi jack the thread but it is relevent, if using 2 x 4 ohm cabs gives you a 2 ohm load, what would 1 x 4 ohm cab and 1 x 8 ohm cab give you?[/quote]

The formula is (impedance of cab 1 X impedance of cab 2) / (impedance of cab 1 + impedance of cab 2).

So, 2.667 ohms (roughly).

With cabs that are the same impedance, you'd use the following: impedance of single cab / number of cabs = total impedance

So, for instance if you had 3 x 16 ohm cabs (why on earth you would is another matter) you'd get 5.3 ohms (roughly).

Edited September 7, 2010 by Wil

[51m0n]

The MB LMII & its derivatives (sa450 etc etc, not the SD ones or F1/F500) had the same limiter circuit in , and when runninginto 8ohm loads the would choke a bit early, leaving the amp not as good at delivering into 8ohms as into 4ohms.

Whilst 2 8ohm 4x10s is louder than 1 4ohm 4x10 (by a lot) the ae410 is loud enough on its own, I really dont need another cab, I might like one for the pose, but then I've got to transport it, and set up/pull down is way more agro so I wouldnt recommend that option to anyone playing normal venues.

If you are on a 50ft stage you might want to get an amp that pushes 2ohms and go for it though!

[PaulWarning]

[quote name='Wil' post='948370' date='Sep 7 2010, 03:13 PM']The formula is (impedance of cab 1 X impedance of cab 2) / (impedance of cab 1 + impedance of cab 2).

So, 2.667 ohms (roughly).

With cabs that are the same impedance, you'd use the following: impedance of single cab / number of cabs = total impedance

So, for instance if you had 3 x 16 ohm cabs (why on earth you would is another matter) you'd get 5.3 ohms (roughly).[/quote]

Thanks

[derrenleepoole]

As we all know, not every player has the same requirements for amplification. I'd love a Phil Jones D200 head, but it only gives out 150 watts of power - so with this in mind I'd be very tempted to get a small 4 ohm cab to maximise output for instances where volume is not an issue, or there are strict requirements on stage for space etc. If you play in a small acoustic trio, then such small heads and small 4 ohm cabs make perfect sense. I guess it's a case of knowing what works for you and how to use it. It comes back to knowing that power is nothing unless it can move air! So more speakers equals a great perception of volume regardless of power output.

[Bill Fitzmaurice]

[quote name='largo' post='948086' date='Sep 7 2010, 05:56 AM']Or, is this 4 ohm cab simply a myth that most people make too big a deal of.[/quote]Myth. It arises from the assumption that sound levels and power levels are linear with respect to each other. They are not. Sound levels are logarithmic with respect to power; ie., it takes ten times the power to sound twice as loud. That being the case the roughly 70% power increase seen with a 4 ohm load versus 8 ohm load doesn't make a significant difference.

[Alien]

Using my Hartke as an example, the amp will deliver 350W into 4 Ohms, or 240W into 8 Ohms. The 46% increase in power equates to an increase in SPL of 1.64dB (assuming that the 4 and 8 Ohm cabs have identical outputs at 1W/m).

In reality, any increase of less than 2dB is inaudible with a dynamic signal (ie. music), and in a band situation you'd probably be hard pushed to notice a change of less than 5dB.

[attachment=58348:1dB_diff...ce_250Hz.wav]

This shows how little difference 1dB really makes with a test tone. With music it makes next to no difference.

A

[Mr Rabble]

Ampeg SVT (or Marshall VBA) owners need a 4 ohm cab, because it's not safe to run their head at 8 ohm.