Double Check: Mixing a 4 ohm output amp with an 8 ohm speaker

[Phoenix1]

I've just read the sticky post on ohms and I think I have this right, but just checking. I am planning to run a bass amp with a 4 ohm output (TC BH250) into a single 8 ohm speaker cab. I play small outdoor gigs but don't push my amp. I understand the following to be true:

1. Although it is not a match, it will be safe for both amp and speaker.
2. I may not get quite as much volume out of the speaker than I would if the cab were 4 ohms.
3. I can safely add a second 8 ohm cab in parallel, but I may or may not notice an increased volume.
4. I may get a fuller sound with two 8 ohm cabs because I'm moving more air, but not louder.

My questions are aimed at helping me decide whether to purchase (and lug around) a second cab.

Please let me know if I am correct.

Thanks.

 

[agedhorse]

Yes, it's fine.

With a solid state amp, the rated minimum load (4 ohms in this case) is the MINIMUM that the amp can safely drive... it can easily drive a higher inpedance load like 8 ohms, the power delivered will decrease to about 1/2 of the 4 ohm rating.

It will be both more full on the low end and louder when you add a second 8 ohm cabinet.

 

[ColonelZulu]

Why would you think not be louder if you're moving more air? I'm assuming the amp is set at the same output. A 4ohm load would have less resistance than an 8 ohm load so more current flow. Doesn't that make your amp more "efficient"?

 

[S-Bigbottom]

2. I may not get quite as much volume out of the speaker than I would if the cab were 4 ohms.
3. I can safely add a second 8 ohm cab in parallel, but I may or may not notice an increased volume.
4. I may get a fuller sound with two 8 ohm cabs because I'm moving more air, but not louder.

Of the same make and model, the 8 Ohm version of a single speaker cab will usually be more loud. (in most situations)
More speakers will make more fuller and loud than more power. Unless we are talking about a 40 watt and a 500 watt amp.
Think of three people talking in a room and twenty five people talking in the same room. More voices or speakers, more volume.

Here is your cheat sheet for hooking up with a 4 Ohm Minimum solid state amp.
Use one 8 Ohm cab, it is happy and you should be also.

Use two 8 Ohm cabs and it is more happy as are you with more sound. This is a 4 Ohm load to the amp, its minimum.

Use one 4 Ohm cab and it is good, you can not hook up any more. A multi speaker cab is best at 4 Ohms than a single speaker in 4 Ohms.

Use three 8 Ohm cabs and it can damage the amp as that makes a 2.67 Ohm load.

Use one 8 Ohm cab and a 4 Ohm cab and that is also 2.67 Ohms, damage.

Use two 4 Ohm cabs and that is a 2 Ohm load, also bad.

 

[el murdoque]

When you look at the rear of your amp, you will see that the load specified is a "4 Ohm minimum load". 8 Ohm is bigger than 4, so it fulfills the requirement.

1. Although it is not a match, it will be safe for both amp and speaker.
2. I may not get quite as much volume out of the speaker than I would if the cab were 4 ohms.
3. I can safely add a second 8 ohm cab in parallel, but I may or may not notice an increased volume.
4. I may get a fuller sound with two 8 ohm cabs because I'm moving more air, but not louder.

1. Yes quite so - the output of the amp will be roughly halved and as long as your speaker can take about 125 Watts, you'll be fine.
2. That is correct, as the output is, as I said, roughly halved.
3. You can, with the same rules as stated in 1. You will most likely perceive a higher volume.
4. If you hook up a second, identical cabinet, you can expect a fuller, bigger sound. You can also expect a +6dB volume increase.

 

[Grahams Groove]

Bottom line is that you won't hurt anything running the single 8-ohm cab you currently have. Try it out and consider more/different cabs if you determine you need more volume.

 

[Nuisance]

For a while. But I boiled this:

Down to this. It's smaller, lighter and sounds better.

 

[HolmeBass]

Terminology matters - your amp doesn't have a "four ohm output". It has an "output that supports a minimum load of four ohms". Since fewer ohms is a bigger load, the speaker you connect must be a minimum of 4 ohms. 8 or higher is fine, since that is above the minimum.

 

[Phoenix1]

Bottom line is that you won't hurt anything running the single 8-ohm cab you currently have. Try it out and consider more/different cabs if you determine you need more volume.

Thanks, everyone for really helpful replies. I think I have the personal choice of whether to improve the sound of my rig (I use it mostly outdoors) by adding one more thing I have to lug around. I am leaning toward an Ampeg SVT-210AV to complement my Fender Rumble 12" cab.

 

[lug]

I'd recommend a 2nd Rumble 12" cab if you like your current sound. You know they will mix well since they will have the same parameters and you will definitly notice it being louder/fuller.

 

[Grahams Groove]

Thanks, everyone for really helpful replies. I think I have the personal choice of whether to improve the sound of my rig (I use it mostly outdoors) by adding one more thing I have to lug around. I am leaning toward an Ampeg SVT-210AV to complement my Fender Rumble 12" cab.

I'd recommend a 2nd Rumble 12" cab if you like your current sound. You know they will mix well since they will have the same parameters and you will definitly notice it being louder/fuller.

I generally agree with lug here. If you need to move more air and want things to sound fuller, adding more of the same is a safer bet. I will also say that I personally disliked the SVT-210AV cab. I thought the voicing was very boxy and muddy sounding, and I was wrestling to EQ around it until I finally sold the cab. I've generally been able to get what I want out of the rumble combos I've played when they were backlined.

 

[Phoenix1]

Problem is I can't seem to find a Rumble 12 cab, and I'm not sure they even made one. The 15 is way too heavy. In fact, the 12 I have used to be a Rumble 100 combo, but the amp died. So I'm about to just use the speaker. My dilemma is whether to add a second cab.

 

[Grahams Groove]

Problem is I can't seem to find a Rumble 12 cab, and I'm not sure they even made one. The 15 is way too heavy. In fact, the 12 I have used to be a Rumble 100 combo, but the amp died. So I'm about to just use the speaker. My dilemma is whether to add a second cab.

Then your nextbest options are:

• Take the plunge on a used extension/second cab and just see how it sounds with the current setup.
• Flip the rumble cab and buy 2 similar/same cabs to maintain a modular setup.
• Flip the rumble cab and get a 2x12 if that's what you're going for.

 

[ender6000]

I've just read the sticky post on ohms and I think I have this right, but just checking. I am planning to run a bass amp with a 4 ohm output (TC BH250) into a single 8 ohm speaker cab. I play small outdoor gigs but don't push my amp. I understand the following to be true:

1. Although it is not a match, it will be safe for both amp and speaker.
2. I may not get quite as much volume out of the speaker than I would if the cab were 4 ohms.
3. I can safely add a second 8 ohm cab in parallel, but I may or may not notice an increased volume.
4. I may get a fuller sound with two 8 ohm cabs because I'm moving more air, but not louder.

My questions are aimed at helping me decide whether to purchase (and lug around) a second cab.

Please let me know if I am correct.

Thanks.

you probably would be louder as well because the lower ohmage , if you have a solid state amp , would result in your amp putting out more wattage. and I was always under the impression that you're ok as long as your speakers ohmage is equal to or less that your amp.

 

[agedhorse]

you probably would be louder as well because the lower ohmage , if you have a solid state amp , would result in your amp putting out more wattage. and I was always under the impression that you're ok as long as your speakers ohmage is equal to or less that your amp.

Ohmage isn't a word...

Going form a single 8 ohm cabinet to two 8 ohm cabinets will be louder because of increased power AND because of mutual coupling between the speakers. Equal contribution form both mechanisms.

 

[ender6000]

Ohmage isn't a word...

Going form a single 8 ohm cabinet to two 8 ohm cabinets will be louder because of increased power AND because of mutual coupling between the speakers. Equal contribution form both mechanisms.

ain't ain't a word except it is constantly used ,,,,, as a word. you criticize my use of the term "ohmage" which by the way is used all the time and then you go on to say

Going form a single 8 ohm cabinet ??? which makes ,,,,,,, no sense !!! to say exactly what I just said.

 

[Richard Lindsey]

I was always under the impression that you're ok as long as your speakers ohmage is equal to or less that your amp.

No, that's exactly wrong, at least for solid-state amps (the situation can be different for tube amps). You want the impedance of your speaker cab to be equal to or GREATER THAN the minimum rating for the amp. IOW, if the amp is rated for a 4 ohm minimum, the load posed by the speaker should be 4 ohms or greater.

 

[gln1955]

you probably would be louder as well because the lower ohmage , if you have a solid state amp , would result in your amp putting out more wattage. and I was always under the impression that you're ok as long as your speakers ohmage is equal to or less that your amp.

Please, you have a lot to learn before you give advice or argue with those that know more than you do.

 

[Grahams Groove]

ain't ain't a word except it is constantly used ,,,,, as a word. you criticize my use of the term "ohmage" which by the way is used all the time and then you go on to say

Going form a single 8 ohm cabinet ??? which makes ,,,,,,, no sense !!! to say exactly what I just said.

You're comparing a typo from a person who is an expert in this field to using incorrect terminology and giving incorrect advice. Those things are not the same.

 

[agedhorse]

ain't ain't a word except it is constantly used ,,,,, as a word. you criticize my use of the term "ohmage" which by the way is used all the time and then you go on to say

Going form a single 8 ohm cabinet ??? which makes ,,,,,,, no sense !!! to say exactly what I just said.

Yes, auto-correct incorrectly corrected my (obvious) typo, but that's different than providing incorrect info.

1. "ohmage" isn't a word and ohmage isn't used all the time except by the under-educated or under-knowledgeable. On this forum, most members would like to learn correct information and terminology, so out of respect to most members I will note where incorrect terminology is being used.

and I was always under the impression that you're ok as long as your speakers ohmage is equal to or less that your amp.

2. This is factually incorrect and potentially dangerous to an amp. The speaker impedance needs to be GREATER or equal to the minimum rated load that the amp can safely drive.