Acoustic Amp as 'Guitar Head' for Larger Monitor Speaker

[vibrolucky]

I have two decent Acoustic Amps (Fishman Loudbox Artist & Roland AC-60)
and 75% of the gigs I play can get by just fine using these.

I recently acquired a top quality 15" passive monitor speaker with horn, and a thought occurred to me...

Wire one (or both) with an external 'speaker out' jack and (assuming the ohms are the same value), use the Acoustic Amp as a 'Guitar head' to power the Monitor. Obviously it wont be louder, but maybe a 'bigger' sound? 15" speaker has to have a bigger sound than an 8" speaker.

Before you say 'just buy a powered speaker', I have one already and already doing this using the line out with great results...so its more of a hypothetical. Just curious if anyone has ever tried doing this?

The goal being getting a bigger sound without spending any more money on a powered mixer, etc.for using the passive speaker for something.

[MikeBmusic]

"assuming the ohms are the same value" - do you have electronics background? Putting two speakers in series the 'ohms' will add, so neither speaker will be seeing as much voltage across it and the amp will be seeing a higher load on it (less volume overall). Putting them in parallel, will essentially halve the 'ohms' the amp sees (unless you add some resistors into the circuit), which could damage the amp.

[pf400]

I don't understand. Can I just run a cable from "line-out" to a speaker cab, or monitor? Where do I look to check for compatibility? And any recommendations? I have a keyboard amp Roland KC110 and an electric Cube 80XL that I might want to extend.

[MikeBmusic]

Originally Posted by pf400

I don't understand. Can I just run a cable from "line-out" to a speaker cab, or monitor? Where do I look to check for compatibility? And any recommendations? I have a keyboard amp Roland KC110 and an electric Cube 80XL that I might want to extend.

'Line Out' is not an amplified signal - it's what you'd run to a powered speaker or another amp.

[B. Adams]

It might work OK, might not.

As has been stated, you'll have to watch out for impedance mismatches, plugging a 4 ohm load into an amp that is designed for and 8 ohm load will strain the amplifier, and could cause failure. I'd be very hesitant to run both speakers at the same time. If the new speaker is 4 ohms, I'd be hesitant to run it at all. That's unlikely though, as monitor speakers are typically 8 ohms.

Also, efficiency is important as well. If your new speaker has 90dB/1m efficiency and your amps speaker is 100dB/1m, your new speaker will be a lot quieter.

The tuning of the larger cabinet will be very different from your amp, so your guitar will likely need a very different EQ setting, and the amps controls might not be enough to make it work.

The best way to do it, at least as a test, would be to run from the line out of your amp into a power amp, intended for PA usage, and see how it sounds. Someone in your area might have one you can borrow if you don't have easy access to one. If it works OK, it might be worth it to you to put the work into modifying your amp. Just be careful and try not to blow anything up.

[vibrolucky]

Originally Posted by MikeBmusic

"assuming the ohms are the same value" - do you have electronics background? Putting two speakers in series the 'ohms' will add, so neither speaker will be seeing as much voltage across it and the amp will be seeing a higher load on it (less volume overall). Putting them in parallel, will essentially halve the 'ohms' the amp sees (unless you add some resistors into the circuit), which could damage the amp.

Perhaps I didn't make myself clear. This is to install an external jack that will completely bypass the internal speaker of the acoustic amp. Acoustic amp uses an 8 ohm speaker, and the Monitor is 8 ohms...so in essence they are the same.

As stated before by a previous person, the traditional 'line out' won't power a passive monitor.

[nickv6]

Just talking about the speaker size.....those 15inchers give a fantastic sound. Check out those old pedal steel amps which turn up on auctions for almost nothing....clean, clear sound. Heaavy though late at night when the set is over......

[varmonter]

What drives your small amp speakers may
not be able to drive the big 15 inch.
You know when the guitar player says
my 15 is 200 watts? it takes power to drive
them efficiently . yes they are both 8 ohms.
That's resistance. Not power ..my fear is that
you will wire your amp but not be happy with
the weak sound the 15 puts out. If you like
the 15 get a bigger powered speaker.
or buy a DSP amp and install it in the passive
speaker. you will save damage to your small guitar amp.

[denmalley]

I would not mess with this. Whoever designed those amps built a power section to drive an 8" speaker. You don't wanna fry that trying to push a 15 incher with horn.

[Murphy Slaw]

I mic my J-45 with an SM57 and play through an old XR600 Peavey powered mixer into 2; SP-2's (15 and horn) all the time in my music room. Sounds fantastic.

I'd hate to lug it around but it makes a killer acoustic rig !

[lschwart]

This seems like more trouble than it's worth. If you really want to be able to use that passive speaker as an extension speaker for larger gigs, consider trading-in your Artist and AC-60 for an acoustic amp designed to do this. For example, both the older Genz Benz Shenandoah acoustic amps (easy to find used and great amps) and the new Genzler Acoustic Array Pro have actual speaker outs designed to be used in tandem or in place of the internal speaker. I used to hook a 15" Yorkville speaker (YX15) to the speaker out of my ProLT, and it sounded fantastic, that power amp had no trouble driving both speakers.

But, all that said, the best way to use a PA speaker to expand the reach of a small acoustic amp is going to be powered speaker from the DI out. That will give you separate control over the levels of the two speakers in case you want to use the amp as a monitor, and you'll know you have exactly what the speaker needs to be driven properly and sound its best.

Louis