What can I use for an "external speaker" in this setup?

[tbassist4]

Hey everyone,
I've had a Crate BT220 combo amp (220 watts and 1x15" speaker) for about four or five years now. There's a jack on the back that says "external speaker," which I assume means a cab or something smaller. The manual says the jack is in series with the main speaker and recommends 4 ohms.

What size cab can I drive from that jack being that the head is only 220 watts and its already driving a 15" speaker? I tried to look this up online and in the stickies here, but no luck. My hope is that I can power another 15" cab with it, but I'm assuming that's unlikely. A man can dream through, right?

[wave rider]

Seems like you could power an efficient 15"er no sweat. 4 ohm might limit your choices, maybe a Peavey?

I wonder why series instead of parallel. Seems like that would add impedance and draw less power from the amp?

=wr=

[a01020201]

i have the same amp, and am running a Ampeg 4x10he off of it, this was not why i bought the cab, but my Ampeg B2RE is in the shop and i said what the hell why not try it, the 4x10 is wired for 8 ohm, but it sounds good. My neighbors probably think it sounds good inside there house lol

[tbassist4]

Originally Posted by wave rider

Seems like you could power an efficient 15"er no sweat. 4 ohm might limit your choices, maybe a Peavey?

I wonder why series instead of parallel. Seems like that would add impedance and draw less power from the amp?

=wr=

Thanks for the reply. I'm noticing what you said about limited choices as I'm looking around. Would a 4x10" cab also work as long as its rated at 4 Ohms, or does this take more power?

Also, I'm noticing that all of these cabs have watt ratings of anywhere from 600-1200 watts. Should I be concerned with this number? I've heard about underpowering and I don't want to mess anything up...

[tbassist4]

Originally Posted by a01020201

i have the same amp, and am running a Ampeg 4x10he off of it, this was not why i bought the cab, but my Ampeg B2RE is in the shop and i said what the hell why not try it, the 4x10 is wired for 8 ohm, but it sounds good. My neighbors probably think it sounds good inside there house lol

That's at 8 Ohms? Hmm, and you've had no problems so far? How long have you been running it? If I can run bigger cabs then that will make my decision easier in the end.

I'm just a little paranoid - this is my only amp. My whole idea in getting a cab is that I can use it to transition to a big boy amp (head).

[bongomania]

Underpowering is a myth, plain and simple. Read about it in the FAQ to learn how and why. Speaker cabs can be run safely with one watt of power. The wattage ratings on cabs are just a general indication of how much power they can take without burning up--they do not need anywhere near those amounts to operate properly.

[HEADLE]

I have to assume that it can't support a two ohm load. You can add a 4 ohm 15" speaker and get more surface area but that is a wacky setup and will cut your power output. You could always get an 8 ohm speaker for the amp and a 8 ohm 15" cabinet and rewire it to be parallel. Then you could have full power and more surface area. That would be the best.

H

[tbassist4]

Originally Posted by bongomania

Underpowering is a myth, plain and simple. Read about it in the FAQ to learn how and why. Speaker cabs can be run safely with one watt of power. The wattage ratings on cabs are just a general indication of how much power they can take without burning up--they do not need anywhere near those amounts to operate properly.

Awesome, thanks so much. So I can safely drop some money on a nice cab, even if its not running optimally? What would be the disadvantage of me running an 8 Ohm cab off this versus a 4 Ohm cab? The idea is that I want to get something that will help my sound now, but also allow me to transition into a nicer setup later.

[a01020201]

my cab is only 200 watts, but because the power is ran at 4 ohm instead of 8 ohm it is really not getting as much power as it could handle, i think it sounds good, but it is not my perminent setup. from my understanding it would not hurt the cab.

[tbassist4]

Originally Posted by a01020201

my cab is only 200 watts, but because the power is ran at 4 ohm instead of 8 ohm it is really not getting as much power as it could handle, i think it sounds good, but it is not my perminent setup. from my understanding it would not hurt the cab.

Nice, nice. I like how this is sounding. I've also heard some stuff about clipping, am I in any danger of that? If a 220 watt amp clipped, what peak wattage would it release? I know it's more than 220, but I have no idea how much more.

[bongomania]

Originally Posted by HEADLE

I have to assume that it can't support a two ohm load. You can add a 4 ohm 15" speaker and get more surface area but that is a wacky setup and will cut your power output. You could always get an 8 ohm speaker for the amp and a 8 ohm 15" cabinet and rewire it to be parallel. Then you could have full power and more surface area. That would be the best.

+1, he's right. Since the external speaker jack is in series with the internal speaker, and since it recommends a 4 ohm cab, that means the internal speaker is 4 ohms, and the combination of it with an external 4-ohm cab would result in an 8 ohm total load on the amp. This effectively cuts the wattage output by somewhere between a third and a half. So that's a weird setup.

While I agree that altering the combo amp to have an 8 ohm internal speaker and a parallel external jack would be a good solution, IMO there's a better one. Since you plan to upgrade the amp anyway, get the biggest, nicest, beefiest 4-ohm cab you can afford. That way you can use it with your combo in the short term, without altering the combo; and when you upgrade the amp, you'll already have a nice big 4-ohm cab, which will be enough for most gigs.

Don't worry about whether it's "silly" or "non optimal" to power a massive cab with a tiny amp. That's really a non-issue for most typical cases and purposes.

[bongomania]

Originally Posted by tbassist4

If a 220 watt amp clipped, what peak wattage would it release? I know it's more than 220, but I have no idea how much more.

Absolute worst-case scenario, it could be almost double. However, the wattage will be divided equally between the internal and external speakers, so even in that absolute worst-case scenario the external cab would not ever see more than 220W. So just make sure whatever cab you buy is rated for greater than 220 watts, and you'll be perfectly safe.

[tbassist4]

Originally Posted by bongomania

+1, he's right. Since the external speaker jack is in series with the internal speaker, and since it recommends a 4 ohm cab, that means the internal speaker is 4 ohms, and the combination of it with an external 4-ohm cab would result in an 8 ohm total load on the amp. This effectively cuts the wattage output by somewhere between a third and a half. So that's a weird setup.

While I agree that altering the combo amp to have an 8 ohm internal speaker and a parallel external jack would be a good solution, IMO there's a better one. Since you plan to upgrade the amp anyway, get the biggest, nicest, beefiest 4-ohm cab you can afford. That way you can use it with your combo in the short term, without altering the combo; and when you upgrade the amp, you'll already have a nice big 4-ohm cab, which will be enough for most gigs.

Don't worry about whether it's "silly" or "non optimal" to power a massive cab with a tiny amp. That's really a non-issue for most typical cases and purposes.

Dang, you guys have been really helpful, thanks so much! I just have one last (multi-part) question:

Say I was to lug this setup to a gig. Obviously I'd need more volume, so if I cranked the amp, would I have to worry about clipping, or should I just use the Crate alone for gigs until I get proper equipment? Does the wattage split between the speakers (each would get 110 in a perfect world) when they are wired in series, or does one amp bear more than the other? What would my peak wattage be during a huge clip using this setup (220 watts over 2x15" speakers wired in series)?

Thanks so much for your help guys, I really appreciate it.

Tyler

[Bmorefoozler]

That 220w is almost certianly peak already... It's probably a 100 w RMS combo...

Bongo is probably most right here, get your future 4 ohm cab, and then sell the combo and get a mini head.

[tbassist4]

Originally Posted by bongomania

Absolute worst-case scenario, it could be almost double. However, the wattage will be divided equally between the internal and external speakers, so even in that absolute worst-case scenario the external cab would not ever see more than 220W. So just make sure whatever cab you buy is rated for greater than 220 watts, and you'll be perfectly safe.

Awesome, thanks so much for taking the time to help me out! That gives me a lot of options; now I can start trying out cabs.

[Stumbo]

From the manual:

Output Power Rating 220W RMS 2% THD, 4Ω, 120 VAC
Gain Distortion Channel 103dB
Clean Channel 61dB
CD Inputs 33dB
Tone Range Low 20dB @ 50Hz
Lo Mid 24dB @ 150Hz
Hi Mid 18dB @ 1kHz
High 32dB @ 10kHz
Signal to Noise Ratio 65dB below full power, tones flat, gain and level @ “10”
Input Impedance 220k ohms
Maximum Input Signal Level Accepted 15 volts peak-to-peak
Balanced Line Out Jack 2 volts peak-to-peak @ full rated power w/600 ohm load

Internal Speaker Size 15”
Type Crate Custom Cast Frame
Magnet 66 oz.
Voice Coil 2.5”
RMS Rating 250 watts
Impedance 4 ohms
Input Power Requirements 120 VAC, 60Hz, 250VA
100/115VAC, 50/60Hz, 250VA
230VAC, 50/60Hz, 250VA
Size 24-1/2” H* x 24-1/2” W x 16-1/2” D
Weight 87 lbs
*without casters
BT220 Technical Specifications:
www.crateamps.com

+1 on the 100w RMS (at a low distortion rating, like 1%)

You can add any 4ohm cab you like (2x15, 4x10, etc).

YOu could also replace the combo's 15 with an 8ohm, buy another 1x15 8ohm and run them together to get 4 ohms and the full power from the combo, if you were planning on keeping the combo. RUn the combo for smaller gigs, both for larger gigs.