Acoustic (brand) amp question

Rocks · #1 09-28-2010, 12:07 PM

I just picked up an acoustic B100 combo. I was reading the owners manual and it says it is full power as a combo, the internal speaker is 4 ohms. Looking at the MF site they recommend the B115 and B410 cabs as options to add a second cab but both of them are rated at 8 ohms. They also say the external speaker out is 4 ohms in the owners manual. So why are the only speaker cabs Acoustic makes 8 ohms? I have an 8 ohm cab that I'd like to use with it but it would only get half the power as the internal 4 ohm speaker. Can someone give me some insight as to why they have an external speaker out that is only 4 ohms and only sell 8 ohm extension cabs? From what I read the external speaker is in series with the internal so even adding a 4 ohm cab would raise the ohms to 8 ohms, it just doesn't make sense that it was designed this way.

JimmyM · #2 09-28-2010, 12:43 PM

it's because of two things...controlling the weight of the head, and being cheap. they sell the cabs thinking most people aren't going to add a second cab to a cheap combo, but they will want to add them to a separate head.

Rocks · #3 09-28-2010, 12:56 PM

I emailed Acoustic about this, waiting for a reply. I only got this amp because someone was willing to trade it straight up for a BBE sonic maximizer I had and couldn't sell. I figured I'd rather have the amp than the BBE. I already checked and it looks like I can slide my Trace Elliot head in place of the acoustics, its a tight fit but it will go in there. I'll probably yank the acoustic head and turn it into a Trace head with the Acoustic cab/speaker. The Trace is an AH130 so it should be fine with the speaker in the Acoustic as long as I don't get too crazy with the volume and listen for speaker breakup. Then I can use it as a combo or stack it on top of my Trace 15" cab.

EDIT: crap, was just thinking I can't stack it on the Trace cab since it is 8 ohms and 8 ohms mixed with 4 ohms in parallel would probably be bad for my Trace head, oh well.....

Bassdirty · #4 09-28-2010, 01:05 PM

I could be wrong,
But I was under the impression, that you could run an 8ohm cab with it and use both -the combos 15, as well as the external cab.

I thought it was wired to maximize the use of the wattage for the 15 thats there, and still allow an additional cab, and split the wattage.

I actually read this here on talkbass so I know theres a thread somewhere about it.

And, I read it here on talkbass, so it must be true too.

But seriously, I did read something about this topic.

I got a B200, so I was curious too...but I just use it for practice, so I'll prolly never need an additional cab.

Rocks · #5 09-28-2010, 01:12 PM

Basdirty.

I looked at the owners manual and it shows that the external speaker is wired in series with the internal speaker. SO if I am thinking correctly, 8 ohms with 4 ohms in series would be 12 ohms. That tells me I'd be losing wattage and making the amp push against more impedance than it was designed to handle. I could be wrong, it's happened before.

JimmyM · #6 09-28-2010, 03:30 PM

Quote:

Originally Posted by Rocks

Basdirty.

I looked at the owners manual and it shows that the external speaker is wired in series with the internal speaker. SO if I am thinking correctly, 8 ohms with 4 ohms in series would be 12 ohms. That tells me I'd be losing wattage and making the amp push against more impedance than it was designed to handle. I could be wrong, it's happened before.

you don't need to worry about a 12 ohm load. you only need to worry about a load that's too low, like below 4 ohms. however, the 12 ohm load will have very little available power so not recommended. i'm afraid you're just not going to get the answer you're looking for.

Rocks · #7 09-28-2010, 03:37 PM

at least I dumped the BBE

RickenBoogie · #8 09-28-2010, 05:17 PM

Yeah, Acoustic combo's are not bad for the money, but there are some real issues with them, series spkr jack for one. Adding another cab drops the wattage. I suppose adding a 4 ohm ext cab would be best, since it would only then make an 8 ohm load, and on a 100 watt combo, you'd probably get 65 watts divided between the 2 cabs. Not optimal.

LegionHWP · #9 10-11-2011, 03:07 AM

According to another post here on TB the acoustic B100 runs it's extension cab in Parallel NOT in series. How does this affect the safety (ie: is there any danger to the amp or cab) if you hook up an 8ohm extension cab?

Can someone confirm for certain if the b100 runs in series or parallel when you hook up an extension cab to it?

rdwil191 · #10 10-12-2011, 02:55 PM

Quote:

Originally Posted by LegionHWP

According to another post here on TB the acoustic B100 runs it's extension cab in Parallel NOT in series. How does this affect the safety (ie: is there any danger to the amp or cab) if you hook up an 8ohm extension cab?

Can someone confirm for certain if the b100 runs in series or parallel when you hook up an extension cab to it?

it is a series jack, the internal driver is a 4ohm 15", 4ohm min head, 4ohm series jack. if it was parallel, when I hook up my 8ohm B210Neo to it, the load on the head would be 2.67 & bye bye B100

. since it's series 4 + 8= 12ohms. it sacrifices alot of horsepower, but it is louder & well..."fuller sounding", however, you lose what little headroom you have to begin with. I've just been experimenting with this set-up, no real-world usage as the B100 by itself is all I need at the moment.