100W 4 Ohm Combo into 200W 8 Ohm Extension Cab Questions

The Sophomancer

The Sophomancer

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Nov 9, 2016
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#1
Hey everyone,

I apologize in advance if this topic has already been talked about to death, or if there is a specific thread regarding these questions; I did some research on the subject before posting this, but since this topic has to do with hooking up extension cabs which can potentially damage your equipment if you're not careful, I just want to be 100% certain before I try anything with my gear :P

Anyway, here's by dilemma - I'm a noobie at the bass, and my first amp was an Acoustic B100 1x15 Combo, which I've been fairly satisfied with; I'm not a bass expert (or super wealthy), so I can't (and don't particularly feel the need to) upgrade my equipment just yet. But what I DO want is just a little bit more balance and presence in the mix when I'm jamming, so I am currently planning on picking up a cheap Acoustic 1x15 cab, using it as an extension off of the 1x15 amp, and having a nice pair of glorious 15's.

What I'm a bit confused about is this: my Combo 1x15 amp is supposedly 4 Ohms (from what I can tell by the Acoustic website and manual - if this is incorrect, it would be appreciated if you could tell me otherwise), and the 1x15 cab is 8 Ohms. Would it be safe for me to use the 1x15 as an extension cabinet, or would it go under the safe Ohm level, and potentially fry my equipment? It doesn't seem to make sense to use a 4 Ohm cab as an extension though, because wouldn't the impedance be 2 Ohms then...? (As I mentioned, I'm a total beginner when it comes to some of this stuff.) If I had a stand-alone 4 Ohm amp head, I think it would be easier to understand, but since it's a combo amp with its own speaker, I'm not 100% sure how the impedance works in this situation. If I can't use the 8 Ohm extension cab, what would my alternate options be?

My other question has to do with the wattage: as I mentioned, the amp combo is 100 watts, and I'll probably pick up the bass cab model with 200 watts (as long as the bass cabinet has a higher wattage rating than the amp it's all good, right?) If/when I hook up the extension bass cabinet, each speaker will be receiving 50 watts, correct? If this is the case, do you all think that 50 watts per speaker is enough to be heard in a moderately-loud rock band, or in a doom metal band? I know that "loudness" and how much an instrument punches through the mix is a subjective matter, but based upon all of your guys' general experience, is 100 watts split between two speakers truly enough to be heard at small gigs and venues, or should I just trade in the 100W combo now, and upgrade to slightly higher wattage amps/cabs?

Thank you all very much in advance for taking the time to read this and to respond with your insight - I bet some of you have already answered this question a butt-load of times and want to scream when you hear it being asked again, but I'm extremely paranoid about damaging equipment, so I just want to be positively, absolutely, undeniably, unquestionably 100%-ly CERTAIN that it's all good before doing so. ;)
 
#2
Yes, according to the website and manual, you can connect an extension cab to that combo. No, I don't think it will provide you with enough power/volume for a heavy rock or metal band, while still maintaining clean tone and headroom. My absolute minimum for clean volume in metal and rock bands was 250 watts into at least 2 speakers, ie: 210s, 212s, 215s....
 
#3
As long as the internal speaker in the combo has its resistance rated at 8 ohms (and of course theres an output jack that allows for adding an extension speaker) yes, you can add another 8 ohm cab to that amp. Treat the internal speaker as its own cab, you seem to have grasped the concept of impedance/resistance generally.

As far as the combo + ext cab giving you enough for loud rock/doom? Ehhhh maybe? Might not be pretty, might get the acoustic amp to some ss overdrive. Some people will have you believe this abjectly horrific, but some types of ss overdrive can either sound real nice or be appropriate to the music giving a real effed up sound. How you eq can help you maintain cleaner headroom longer. Cut the lowest freqs and your amp will work a little less hard as it approaches its max limit of clean volume.
 
#5
According to the manual your amp runs the extension cab jack in series with the internal 4 ohm speaker. So a 4 ohm external cab will actually give the amp an 8 ohm load (4 + 4 in series), it'll more than likely then make considerably less than 100 watts, and the 200 watt power handling rating of your prospective cab is moot, since 50 watts or less is all it'll see anyway. I'd guess that around 30 watts per speaker is more likely, and the whole exercise seems pretty unlikely to work all that well for the types of music you would like to use it for.
 
#7
Thank you all for the great information and words of advice!

I've been pretty happy with my Acoustic B100 for practicing, and I've used it a couple of times for some small gigs in the past, but I think after reading some of your guys' comments, maybe I need to rethink my situation, and consider upgrading my equipment after all... :\ For the styles of music that I'm interested in, 100 watts just doesn't seem like it's going to cut it in the long run, and it seems like running an external cab from it won't really resolve my situation or benefit my sound very much.

I'm also aware that Acoustic equipment (aside from the vintage stuff, perhaps) isn't exactly top-tier in terms of quality, and is often regarded by many musicians as over-sized paperweights, so perhaps I'll rethink my strategy and go in search of a used amp head and 2x15 cab by somewhat-more-reputable companies instead.

Once again, thanks a ton for your guys' assistance! It's fairly daunting when you're trying to figure out all of the details and variables that go into music equipment and whatnot, so it's great to talk to people who have experience in the matter. ^-^
 
#8
For doom on a budget you can't go wrong with an old, heavy Peavey head and a 2x15 cab, especially if it has the Black Widow speakers... often louder than its ratings comparative to more modern gear. Sometimes Ampeg fridges show up cheap used depending on where you are. Killer doom (really any loud music) machine which will sound good under just about any amp. Good luck!
 
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