8 ohm/4 ohm = rarely use amp's full potential

[Tommy TGrip]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

 

[Sparky Mark]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

Quite a few cab manufacturers offer 4 ohm versions of their cabs. Hartke even offered cabs that had a switch to select 4 or 8 ohm operation.

 

[Wasnex]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

The following is a copy of: Help me figure out the impedance of a driver I made one slight edit to correct a typo.

Maxing out the amps power may be less beneficial than you think.

Here is the deal. The minimum decibel change we hear clearly is 3dB. In order to get the 3dB, the amp has to double power when the impedance drops from 8ohms to 4ohms, and the sensitivity of the 4-ohm cab must be the same as the 8-ohm cab. Unfortunately, 4ohm drivers are often 1-2db less efficient than their 8-ohm counter parts.

Results: If the amp doubles power, but the 4-ohm cab has a 2dB lower sensitivity rating than the 8-ohm cab, you only gain 1dB which is not enough to hear.

If you have an amp that is 4ohms minimum, the best choice is often a pair of 8-ohm cabs. If your amp doubles power when you add the second cab, you get +6dB over the max SPL one of the cabs will make by itself. If the amp holds the power at the same level when you add the second cab, you get +3dB...this is how tube amps operate. Many solid-state amps will increase the power when a second cab is added, but not double the power. So you get +4dB to +5dB.

Let's assume an amp makes 225W at 8ohms and 380W at 4ohms. This is the actual specs for a GK series I RB700

Our 4-ohm cab has a sensitivity rating of 95dB 1W/1m, and our 8-ohm cabs have a sensitivity rating of 97dB 1w/1m

With one 4 ohm cab the amp makes 380W. The decibel change from 1-380 is ~25.8dB. Let's round this up to 26dB. For the calculated max volume add the decibel change to the sensitivity rating. 95+26.=121dB max

With one 8 ohm cab the amp makes 225W. The decibel change ~23.5. Let's round this up to 24dB. Max SPL is 97+24=121dB. Exactly the same as the 4 ohm cab. The amp made less power, but the 8-ohm speaker is 2dB more efficient.

With two 8 ohm cabs the load is 4 ohms, so the amp makes 380W. The 380W is shared equally by the cabs, so each cab gets 190W. The decibel change is ~22.8, which we will round up to 23dB. The max SPL of one cab 97+23=120dB. If you tight pack the cabs, you get +6dB for frequencies where the driver spacing is within about 1/4 wavelength. I.E. you get more lows. Combined output of both cabs: 120+6=126dB.

Summary of Max SPL
One 4ohm cab = 121dB
One 8ohm cab = 121dB
Two 8ohm cabs = 126db

So in this example you get the same SPL with either a 4-ohm or 8-ohm cab. With two 8-ohm cabs you get +5dB.

 

[squarepeg]

I have a Barefaced Super Twin (4 ohms). Whether I use a 100 watt Traynor Custom Special, a 150 watt GK MB150, a 280 watt GK 400RB, or a Glockenklang Heart Rock (750 watts @ 4 ohms), it's loud enough to be heard in a band with three guitarists who use 100 watt Marshall heads and 4x12 cabinets.

 

[Sparky Mark]

I have a Barefaced Super Twin (4 ohms). Whether I use a 100 watt Traynor Custom Special, a 150 watt GK MB150, a 280 watt GK 400RB, or a Glockenklang Heart Rock (750 watts @ 4 ohms), it's loud enough to be heard in a band with three guitarists who use 100 watt Marshall heads and 4x12 cabinets.
View attachment 4660215
View attachment 4660216

I love your EB3 but I'd have to put the Barefaced on its side when using the Traynor. (Does the BF have feet on the side with the ports nearest?).

 

[squarepeg]

I love your EB3 but I'd have to put the Barefaced on its side when using the Traynor. (Does the BF have feet on the side with the ports nearest?).

No, that's the side with the handle. It does look a bit of a muffin top with the Traynor hanging over both sides of the cabinet.

 

[Sparky Mark]

No, that's the side with the handle. It does look a bit of a muffin top with the Traynor hanging over both sides of the cabinet.

Ah, I can see a handle on the left hand side of the BF, I thought it might have feet on the other side (next to the ports).

 

[squarepeg]

Ah, I can see a handle on the left hand side of the BF, I thought it might have feet on the other side (next to the ports).

No, it has handles on both sides.

 

[squarepeg]

 

[Sparky Mark]

View attachment 4660226

Apologies to the OP for derailing this thread but I've added feet to some cabs without having to drill new holes by using the holes already there for the corner protectors. Sometimes the original screws are still long enough to secure the feet and corner protectors. The feet just need to be taller than the height of the handle. I also understand if you are happy with the overhang.

 

[ArtechnikA]

Quite a few cab manufacturers offer 4 ohm versions of their cabs. Hartke even offered cabs that had a switch to select 4 or 8 ohm operation.

This right here. Hartke 1x12 Neo.
I liked it so much I bought a second.
Lots of versatility.
It can get loud with my 150W backup amp at 4 Ohms; if I'm using the 500/300W small amp, I switch to 8 Ohms to throttle back the amp to the 300W cab rating.
For intermediate settings, both at 8 Ohms presents a total 4-Ohm load to the amp and everybody stays safe.
2 stacked 12's looks good, has good dispersion, and is still packable.

 

[ctmullins]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

Forget about watts. Watts don’t make noise. Your ear has never heard a watt.

Your ear hears decibels. Decibels are produced by drivers in a box. If you want more decibels, get more drivers, or more efficient drivers, or both.

If you want one cabinet that makes lots of noise, get a 4 x 10 or a 4 x 12 at 8 ohms. Preferably vertical, so it forms a column array.

 

[jnewmark]

I have a Shuttlemax 12.2, which allows me to use two, 4 ohm cabs. Works for me.

 

[Jonny Reese]

Way too much time is spent thinking about this. Practically speaking it doesn't make any perceptible difference. I rehearsed with a loud group last night and my markbass F1 (500W at 4 ohms, 300W at 8 ohms) was pounding out delicious bass bombs through an 8 ohm 410. Master volume was just at 10:00 and I wanted for nothing.

 

[Gustopher]

I’ll never need all the power in my Hartke LH1000 but it’s nice to have headroom. I use two 212 8ohm cabs most of the time because I like how 2 sound, but I can usually never turn my amp up past 2-3.

 

[Jaco who?]

As usual, the OP posts once with not nearly enough info, but I'm guessing if your amp is 300 watts @ 4Ω, you're probably not ready to spend a whole lot. My rule is no 4Ω cabs unless they provide enough speaker area/displacement to be loud enough on there own - which rules out 112 and 210 cabs. A used GenzBenz Neox212T or maybe a 410 Peavey might work for you.

 

[brianrost]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

This topic keeps coming up here at TB. No, it's not a waste. In combo amps that have no extension speaker option, the amp is mated precisely to the speaker for 100% of the promised wattage. It's when adding more cabinets that variable impedance comes into play. Tube amps use transformers and can put out the exact same wattage into any load that the amp supports (typically, 8 , 4 or 2 ohms). Some early solid state amps had transformer based outputs and did have impedance selectors. I haven't seen one built like that since the 1970s.

A 2:1 power ratio is the ideal and many solid state amps do NOT double wattage as impedance halves. For years Peavey sold a wide range of amps that were 130w @8 ohms, 210W @4 ohms and 300W @2 ohms. They marketed those as 300 watt amps. My SWR Baby Blue combo was rated at 120W @8, 160 W @4, 180W @2. I found that running an extension cabinet yielded very little extra volume (plus made the amp run very hot). My A.M.P. heads are much closer to the ideal...BH-260 is 160 @8, 260 @4 and the BH420 is 220 @8 and 400 @4.

Assuming the 4 ohm cabinet is of the same efficiency as the 8 ohm cabinet, doubling the wattage only adds 3dB of headroom, noticeable but not a lot. Personally I prefer at least 4x the wattage to get a useful volume increase (6dB).

The main reason for the 4 ohm output is for running two 8 ohm cabs in parallel. I've done this for years, one cab for small jobs, two cabs for bigger ones. I get 3dB more output from the increased wattage and the acoustic coupling of the cabs gives me another 3 dB...so I get the same 6dB of extra headroom as using one cab with an amp of 4x the wattage.

 

[InhumanResource]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

You’re not wasting anything. If you are talking about efficiency, double cabs gets you more volume way faster than double watts.

 

[ThisBass]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

There are tons of single cabs available that are loaded with two 10"s or two 12"s
Most amount of these available cabs provide a nominal load that equals 4 Ohm.

 

[MarkA]

Pretty much all amps are twice as much watts at 4 ohms, but in reality most bass players are only going to use a single cab. Seems like a waste to me. I'm in the market for a cabinet. My amp is 150 watts at 8ohm and 300 watts at 4 ohms. But I only want one cabinet

A 4 Ohm cab could make sense for you. Depends on the cab and the context in which you'll play it. Look at it in terms of "loudness per schlep" (and relative to your volume needs) rather than simply power, make sure the cab will readily handle the amp's power, and check the sensitivity spec between the 8 and 4 Ohm versions, if available.

If you want more specific feedback, knowing your amp, the cabs you're looking at, and what you want to be able to do (Jazz trio? Loud bar band without PA support?) would help.

Sometimes a bigger, 4 Ohm cab makes sense. It might in your case. Depends on the specifics of the situation.