Any particular reason to pick a 4 ohm cab over an 8 ohm cab

[xgsjx]

After reading a post by ashevans09 with a similar title but for valve amps, I thought I'd ask this Question.

Here's the imaginary set up (some may have it):

Amp is a MB LMII

there is two EBS 2x10 cabs, one is 500 watt & 4 ohm, the other is 500 watt & 8 ohm.

I know the 4 ohm is going to pull the full load from the LMII & the 8 ohm is going to take 350 watts max, but this is my question...

Why choose the 4 over the 8? is there a big difference in how much volume the 4 ohm cab is going to produce or does it give a clearer sound?

[alexclaber]

Although a 4 ohm cab will generally get you another 2dB of output from your amp vs an 8 ohm cab (3dB more voltage sensitivity but the amp will reach its current limitations before you get the full 3dB), unless it is a large cab or has high excursion drivers the cab will not be able to do anything of use with that extra power. Certainly in the case of a 2x10" cab the only 2x10" that would benefit from 500W rather than 300W is an Acme. All other 2x10" cabs will be running into distortion by the time you get 300W of low-end hitting them.

With a high-end 4x10" and a moderately powerful amp then a 4 ohm load will give you a little more output than an 8 ohm load. But with a cheap 4x10" less than 200W could take it to its limits in the bottom.

If you're comparing dissimilar cabs then it's perfectly likely that an 8 ohm cab could be louder than a 4 ohm cab - if the 8 ohm cab is more sensitive then it will be louder with less power, or it might be that the 8 ohm cab can handle full voltage (i.e. power) from your amp whilst the the 4 ohm cab starts distorting with less voltage so the lower impedance doesn't end up equally more power and just more loudness.

Here's the relationship:

Power = volts x amps
Amps = volts / impedance
Power = (voltage squared) / impedance

If you halve the impedance then you double the power. But in doing so you double the current flow (amps) and most amps cannot do this so the voltage drops. But to produce lows you need speakers to move air and that requires plenty of cone area x excursion (fore-aft movement).

Go back fifteen years and we thought 300W was a lot of power and 500W was as much as you could ever need! Many cab makers have hardly moved forwards with their speakers but their amps are far more powerful than then - all that extra power is simply wasted unless you have cabs that can make use of it. And that does not mean you need to look for a cab that is rated at 500W or a 1000W or so on because that only tells you how much heat they can handle - even an expensive 1000W rated neo 4x10" can't handle more than 300W in the lows without distortion.

In summary, don't worry about trying to get maximum power from your head unless it's really low on power (like 200W into its lowest impedance load).

Alex

[bass_ferret]

You probably wont hear a difference in volume between 350 watts and 500 watts. But add another 8 ohm EBS 2x10 and you will definitely hear the difference in volume. So guys chasing full beans from 1 cab would be much better off with 2 cabs if they can transport the buggers.

[alexclaber]

[quote name='bass_ferret' post='394352' date='Jan 29 2009, 09:18 AM']You probably wont hear a difference in volume between 350 watts and 500 watts. But add another 8 ohm EBS 2x10 and you will definitely hear the difference in volume. So guys chasing full beans from 1 cab would be much better off with 2 cabs if they can transport the buggers.[/quote]

Exactly! Dropping to a 4 ohm load from an 8 ohm load may get you 2dB from your amp but your cab probably won't be able to make use of that.

But add a second matching cab and the speakers will couple in the lows and low midrange, increasing the system sensitivity by 3dB, so with the same power input you'll be 3dB louder. Also you'll double the excursion limited power handling, thus giving you 3dB more output potential if you have the power to take the speakers to that point (and generally you will because most speakers have such poor excursion limited power handling). And so the extra 2dB more output from your amp driving a lower impedance might actually be of use!

Alex

[51m0n]

[quote name='alexclaber' post='394349' date='Jan 29 2009, 09:15 AM']Go back fifteen years and we thought 300W was a lot of power and 500W was as much as you could ever need! Many cab makers have hardly moved forwards with their speakers but their amps are far more powerful than then - all that extra power is simply wasted unless you have cabs that can make use of it. And that does not mean you need to look for a cab that is rated at 500W or a 1000W or so on because that only tells you how much heat they can handle - even an expensive 1000W rated neo 4x10" can't handle more than 300W in the lows without distortion.[/quote]

+1 my old rig (circa '94) had 2 410s each rated at a then very respectable 280w, driven at 150w each (also had a couple of 15's rated at 250w a piece, driven at 300w each, if you belived crown's specs). This was considered huge overkill.

I now have an amp rated at 500w and a cab supposedly capable of coping with 800w RMS (god knows what the peaks are like) - I've certainly not given it even close to enough beans to make it stressed.

Frankly the new rig is significantly louder than the old one too, it just doesnt fill the back of a club as well

Edited January 29, 2009 by 51m0n

[xgsjx]

So for amps that usually get turned up about as far as 1/3 - 1/2 way at most for small - medium gigs, there would be no advantage in a 4 ohm cab over an 8 ohm?
If I wanted extra depth (more volume at lower hz), would adding a 15" 8 ohm cab be the best route?

[bass_ferret]

The position of the volume knob has no bearing on how loud it will go. An amp will only out out its maximum power, and if it has a hot input, tone controls up it will probably max out well before half on the master.

Only you can decide whether a 1x15/2x10 sounds better that 2x2x10's. I would go for the latter for reasons that have been discussed hundreds of times on this forum

[alexclaber]

[quote name='xgsjx' post='395199' date='Jan 30 2009, 09:43 AM']So for amps that usually get turned up about as far as 1/3 - 1/2 way at most for small - medium gigs, there would be no advantage in a 4 ohm cab over an 8 ohm?[/quote]

Most amps reach full power by 50% on the master volume assuming the pregain is turned up to almost clip on loud notes. Generally the cheaper the amp the earlier on the master it hits full power because less experienced players tend to put two amps side by side and then deem the amp which is louder at equal knobs positions to be the more powerful amp! So if you want to sell more amps you skew the volume knob to take the amp to maximum output sooner rather than later. I remember a lot of Trace Elliott amps being particularly ridiculous like this - by 9 o'clock they'd be clipping on loud notes! As Ashdown is a descendant of TE I wouldn't be surprised if they have continued the habit...

[quote name='xgsjx' post='395199' date='Jan 30 2009, 09:43 AM']If I wanted extra depth (more volume at lower hz), would adding a 15" 8 ohm cab be the best route?[/quote]

Depends on the 15". But generally if you have a ten and a fifteen that are similar in specs and price (i.e. two tens cost the same as one fifteen) the fifteen will have more excursion. Combine that with the fifteen having more area than two tens and the fifteen will move more air which equals more bottom. However, two matching 2x10" cabs may couple more effectively than a 2x10" and a better quality 1x15" and it's hard to know without testing. (Coupling is where the efficiency of the system increases because of increased cone area - that's why 8x10" and 2x15" cabs are so damned loud!)

You may have noticed that your tone gets growlier as you turn up, which a lot of bassists like. However when that's happening it also tends to mean that the bottom gets thinner which isn't so good. Both those symptoms tend to be due to the speakers being pushed past their clean excursion limit so if you team up two dissimilar cabs that still couple well you could get growl from one as it pushes past Xmax whilst the other maintains the fat clean bottom by staying within Xmax. Just something that dawned on me recently when pondering why dissimilar speakers sometimes sound better than matched ones.

Alex

[Mr. Foxen]

[quote name='alexclaber' post='395311' date='Jan 30 2009, 12:15 PM']You may have noticed that your tone gets growlier as you turn up, which a lot of bassists like. However when that's happening it also tends to mean that the bottom gets thinner which isn't so good. Both those symptoms tend to be due to the speakers being pushed past their clean excursion limit so if you team up two dissimilar cabs that still couple well you could get growl from one as it pushes past Xmax whilst the other maintains the fat clean bottom by staying within Xmax. Just something that dawned on me recently when pondering why dissimilar speakers sometimes sound better than matched ones.

Alex[/quote]

Did you just suggest mixing drivers could possibly be good?

[chris_b]

[quote name='Mr. Foxen' post='395561' date='Jan 30 2009, 05:07 PM']....Did you just suggest mixing drivers could possibly be good?....[/quote]
At last......!

Mixing drivers is ALWAYS good if it gets you the sound that you want!!

Edited January 30, 2009 by chris_b

[alexclaber]

[quote name='Mr. Foxen' post='395561' date='Jan 30 2009, 05:07 PM']Did you just suggest mixing drivers could possibly be good?[/quote]

I don't believe I've ever insisted that is is always a bad idea.

Alex

[Bill Fitzmaurice]

[quote name='alexclaber' post='395601' date='Jan 30 2009, 01:05 PM']I don't believe I've ever insisted that is is always a bad idea.

Alex[/quote]
+1. It can work reasonably well. The problem with doing so is that the results are totally unpredictable, so if you don't have the opportunity to try before you buy you're taking a big chance on the result. With identical cabs there's no question that they will work together well.

[monquixote]

Weirdly I have almost the set up you describe (LMKII and a 4 Ohm EBS 4x10) and having used the LMKII with a variety of set ups I can confirm running with a 4Ohm cab (especially one with decent speakers like the EBS) is a heck of a lot louder than an 8.

I'm not sure that you actually need that much power as even with a brutally loud rock drummer I never get my amp up to half way!

Edited January 30, 2009 by monquixote

[alexclaber]

[quote name='monquixote' post='395716' date='Jan 30 2009, 08:45 PM']Weirdly I have almost the set up you describe (LMKII and a 4 Ohm EBS 4x10) and having used the LMKII with a variety of set ups I can confirm running with a 4Ohm cab (especially one with decent speakers like the EBS) is a heck of a lot louder than an 8.[/quote]

I'd be very interested to know which 4 ohm and which 8 ohm cabs you've compared. I keep hearing anecdotes about this but no-one ever goes into much detail! Is the LMII just a weird case where the 4 ohm performance is much better than the 8 ohm performance?

[quote name='monquixote' post='395716' date='Jan 30 2009, 08:45 PM']I'm not sure that you actually need that much power as even with a brutally loud rock drummer I never get my amp up to half way![/quote]

In that case either you are not using full power so there is no advantage to the amount of extra output from a lower impedance load, or (as with the gain staging of most typical amps) you are reaching full power on louder notes with the master volume only halfway.

Here's an interesting question for y'all to consider - what impedance is the cab whose impedance curve is shown below?

Alex

[bass_ferret]

[quote name='alexclaber' post='395601' date='Jan 30 2009, 06:05 PM']I don't believe I've ever insisted that is is always a bad idea.

Alex[/quote]

[quote name='Bill Fitzmaurice' post='395610' date='Jan 30 2009, 06:17 PM']+1. It can work reasonably well. The problem with doing so is that the results are totally unpredictable, so if you don't have the opportunity to try before you buy you're taking a big chance on the result. With identical cabs there's no question that they will work together well.[/quote]
+2. It can and often does work. But it most often comes up here in the context of guys wanting to buy gear that are not going to have the opportunity to try at gigging volumes, and in the context of confident posts that you get more bottom from 15's and more punch from 10's etc.

I have had mixed cab rigs that I thought sounded great and some that sounded f***ing awful IMO. Somebody would have liked it.

Went to see a band a thin string mate is depping for a couple of weeks ago. He warned me the bass overplayed and boy oh boy he was not kidding. I didn't think it was possible to overplay Pinball Wizard but I know now. Funny thing he did not play the 2 most important notes. Anyway he was using a JE Sig Buzzard, MB TA503, 151HF and 104HF and I thought it sounded sh*t (and so did my thin string mate). The low notes were drowning out the rest of the band and demolishing light fittings - one of which only just missed my beer, but all his twiddling at the dusty end was lost. It might not have been the mixed cabs, could have been poor playing dynamics or inproper use of the tone controls. He obviously either loved the sound he was getting or could not hear how bad it was the other side of the lights.

There is no right or wrong. There is, however, more likelyhood of randomly mixed cabs sounding crap.

Edited January 30, 2009 by bass_ferret

[EBS_freak]

[quote name='monquixote' post='395716' date='Jan 30 2009, 08:45 PM']Weirdly I have almost the set up you describe (LMKII and a 4 Ohm EBS 4x10) and having used the LMKII with a variety of set ups I can confirm running with a 4Ohm cab (especially one with decent speakers like the EBS) is a heck of a lot louder than an 8.

I'm not sure that you actually need that much power as even with a brutally loud rock drummer I never get my amp up to half way![/quote]

I've compared EBS 2x10 8 ohms with EBS 2x10 4 ohms. 4 ohm appears considerably louder.

[Bill Fitzmaurice]

[quote name='alexclaber' post='395732' date='Jan 30 2009, 03:57 PM']Here's an interesting question for y'all to consider - what impedance is the cab whose impedance curve is shown below?

Alex[/quote]
6 ohms. Nominal impedance is generally considered to be within the range of 1.2 to 1.5 x DCR. DCR usually shows up as the lowest reading on a chart, in this case 4 ohms. The minimum impedance below 100 Hz, which is cabinet derived, makes it look more like an 8 ohm cab, but what the amp cares about is that minimum load area above 100 Hz, and in this case to be safe I'd call it 6 ohms.

Of course, Alex's point here is that impedance is neither constant nor obvious.

[quote]I've compared EBS 2x10 8 ohms with EBS 2x10 4 ohms. 4 ohm appears considerably louder.[/quote] With otherwise identical drivers the most difference that could exist is 3dB, and then only if the amp used was particularly anemic. If the difference is more than 3dB that would indicate the drivers are different in more than just impedance.

Edited January 31, 2009 by Bill Fitzmaurice

[bass_ferret]

[quote name='EBS_freak' post='395881' date='Jan 31 2009, 12:35 AM']I've compared EBS 2x10 8 ohms with EBS 2x10 4 ohms. 4 ohm appears considerably louder.[/quote]
Thats interesting. Some amps, and my EBS HD350 was one, have some fancy power stages that change the delivery so you dont have to run them at minimum load to get the most out of them. My HD350 was 300 watts into 4 ohms and 350 into 2 ohms. IIRC the Genz Benz GB750 is the same. But I suspect that 2 EBS 2X10'S at 8 ohms each would have been even more considerably louder.

[alexclaber]

[quote name='EBS_freak' post='395881' date='Jan 31 2009, 12:35 AM']I've compared EBS 2x10 8 ohms with EBS 2x10 4 ohms. 4 ohm appears considerably louder.[/quote]

But what amp were you using? I can guarantee that an EBS 2x10" 4 ohm would be no louder than an 8 ohm one when powered by one side of my PLX 3002 because of the amp having enough power at 8 ohms to take the cab to its limits.

Alex

[monquixote]

[quote name='alexclaber' post='395732' date='Jan 30 2009, 08:57 PM']I'd be very interested to know which 4 ohm and which 8 ohm cabs you've compared. I keep hearing anecdotes about this but no-one ever goes into much detail! Is the LMII just a weird case where the 4 ohm performance is much better than the 8 ohm performance?[/quote]

I don't know if it is something that is more apparent with class D amps like the Mark Bass. A 3 dB lift should only be perceived as 25% louder (I think) and I would anecdotally suggest it seemed to make more of a difference than that.

I've used my LMKII with one or two 8 ohm Behringer, Warkwick, Markbass and Ashdown cabs and my own 4ohm EBS cab and I would agree that using a cab with decent sensitivity speakers like an EBS makes as much or more difference as dropping the impedance.

[quote name='alexclaber' post='395732' date='Jan 30 2009, 08:57 PM']In that case either you are not using full power so there is no advantage to the amount of extra output from a lower impedance load, or (as with the gain staging of most typical amps) you are reaching full power on louder notes with the master volume only halfway.[/quote]

I've still got stacks of power on hand with the LMKII. I usually have it set so the gain is well back from the clip level with the master on about 40% to play with a loud drummer and I've had it up to 3/4 out of interest which still sounded undistorted, but had everyone running for the exit with bleeding ears!

I don't really need the power, but it's good to know it's there.

Edited January 31, 2009 by monquixote

[Mr. Foxen]

Could it be the sweep of the volume pot changes at different loads? I don't really know how they work. Would its be % of total power as it goes arounf (although 100% might not be at the end) or would the greater max output be further round the dial?

[EBS_freak]

[quote name='alexclaber' post='395996' date='Jan 31 2009, 10:30 AM']But what amp were you using? I can guarantee that an EBS 2x10" 4 ohm would be no louder than an 8 ohm one when powered by one side of my PLX 3002 because of the amp having enough power at 8 ohms to take the cab to its limits.

Alex[/quote]

We're talking about two different things here. First up - TD650 amp. You can get both amps to sound the same in volume, but you have to run the amp harder to get there. Both cabs will give up when the speakers reach their limits - but it's how much juice you have to put in for them to reach their limits.

Ferret - yeah - 2x 2x10 at 8 ohm each vs 1x 2x10 at 4 ohms are considerably louder - presumably due to the extra volume of air that is being shifted. 4x 2x10s at 8ohms... now that's loud.

[EBS_freak]

[quote name='Bill Fitzmaurice' post='395931' date='Jan 31 2009, 03:54 AM']With otherwise identical drivers the most difference that could exist is 3dB, and then only if the amp used was particularly anemic. If the difference is more than 3dB that would indicate the drivers are different in more than just impedance.[/quote]

The speakers are identical apart from the impedance - unless Eminence are BSing us.

[Protium]

[quote name='alexclaber' post='395311' date='Jan 30 2009, 12:15 PM']Most amps reach full power by 50% on the master volume assuming the pregain is turned up to almost clip on loud notes. Generally the cheaper the amp the earlier on the master it hits full power because less experienced players tend to put two amps side by side and then deem the amp which is louder at equal knobs positions to be the more powerful amp! So if you want to sell more amps you skew the volume knob to take the amp to maximum output sooner rather than later. I remember a lot of Trace Elliott amps being particularly ridiculous like this - by 9 o'clock they'd be clipping on loud notes![b] As Ashdown is a descendant of TE I wouldn't be surprised if they have continued the habit...[/quote][/b]

Christ, more speculative ammo for the anti-Ashdown crew to use...

FWIW this is definitely not the case with my ABM

[Bill Fitzmaurice]

[quote name='EBS_freak' post='396071' date='Jan 31 2009, 07:15 AM']The speakers are identical apart from the impedance -[/quote]
In that case the difference at small signal will be precisely 3dB, and the difference at full output, assuming the amp is able to drive both to full output, will be precisely 0dB. Again, the only advantage to the 4 ohm is if the amp has the ability to drive the 4 ohm cab to full output and not the 8 ohm, and if your amp can't driver an 8 ohm 2x10 to full output you really need a larger amp, because you've got no dynamic headroom.