GK Backline 600

[Lowbassist]

Not sure if this is where I should ask the question or not but I have a Backline 600 and it has two speaker connections on the back and it say min 4 ohms. I have a 410 cabinet that is 8 ohms and a 115 cabinet that is 4 ohms. Is it safe to connect both cabinets? One to one connection and the other to the other connection? I understand that the two cabs in parallel is 2.66 ohms but I don’t know if these two connections are parallel internally? Or does it mean that you shouldn’t connect any cabinet less than 4 ohms?

 

[Al Kraft]

Your instinct to ask before connecting was right on target! Do not use those two cabs together with that head, it will indeed result in a 2.67 Ohm load (as you recognized) which your head will not handle.

You may connect any cabinet with a 4 Ohm or greater impedance or any combination of cabs that present a combined 4 Ohm or greater impedance load to the amp. The total load impedance for multiple cabs doesn't change if you connect both to an output on the head or if you connect one cab to the other.

 

[Lowbassist]

Thanks Al for confirming that.
So my next question is, how to I increase the 4 ohm 15” speaker to 8 ohms so then I can use them together? I’m assuming some sort of resistor in series with the speaker coil? I can solder so if this is an option, I’d try it.

 

[basscooker]

Another 8 ohm 410 would work better

You can't change the cab impedance like that to positive results. You COULD see if you can source the 8 ohm equivalent driver from the maker.

Then there could be other factors in play with the 410/115 acoustically, as well as power distribution.

 

[B-string]

Thanks Al for confirming that.
So my next question is, how to I increase the 4 ohm 15” speaker to 8 ohms so then I can use them together? I’m assuming some sort of resistor in series with the speaker coil? I can solder so if this is an option, I’d try it.

No. Your only options are install an 8ohm driver (speaker) or have your existing driver re-coned with an 8ohm coil cone. If you add a resistor in series it has to handle half power as the speaker does 200-400watts which is a huge expensive resistor, it will also rob half that amp power as just heat (so your cab will be quieter in the end).

 

[Al Kraft]

The resistor deal is not a good idea. I'd first try each cab with the head and see what you think.

If you want to use them together (and FWIW I'm generally not a fan of the 115/410 combo) contact the 115 cab manufacturer and see if there is an 8 Ohm replacement speaker. You want to be sure the speaker characteristics are matched to how the cab and speaker are tuned to work together. Don't just drop in any 15" 8 Ohm driver.

You may be better off trading in or selling your 115 and buying an 8 Ohm cab that works well with your 410.

 

[Lowbassist]

Great advice from all. Thanks!
I just might Frankenstein this cab and drop a 8ohm in it and see how that sounds.
Will update when completed.

 

[Al Kraft]

Great advice from all. Thanks!
I just might Frankenstein this cab and drop a 8ohm in it and see how that sounds.
Will update when completed.

If you check with the company that manufactured the cab or with the speaker manufacturer or a local speaker tech they can probably direct you to a specific 8 ohm 15" speaker that matches the T/S parameters of the 4 Ohm speaker (or at least something that's close).

No reason to gamble with your money and just filling the hole with a speaker of the right diameter is about 1% of the overall replacement equation and probably less than 0.1% of "the performance in that cab/enclosure" equation. Your cab was tuned for a speaker with certain T/S values and getting a close or exact match will give you a much better end result IME. It's worth the extra time IMO.

 

[S-Bigbottom]

WELCOME TO TALKBASS!!!

Sell off the mismatched 15 cab and just use the 4x10, it may be enough.
Or take the money from the 15 cab sale and use it to get the match of your current 8ohm 4x10 that will play well together with no guessing.

 

[newfuture]

All good advice here.

One question you had- the speaker outputs at the head are indeed parallel.

One way you can use both cabs is to wire them in series for 12ohms. You'll get less than the 8ohm rated power, and it's clumsy, so, uh, I guess don't do that, but it's possible.

In your shoes, I'd either keep both cabs and plan on using one at a time, sell the 115 for another 410, maybe even sell the 115 for a 210 for a more modular setup.

FWIW, I used an 18 under a 410, and a 15 under a 410 for years and always liked the pairing.

 

[DJ Bebop]

FWIW, I used an 18 under a 410, and a 15 under a 410 for years and always liked the pairing.

I think more of the liking comes from the 410 being on top of the 15 closer to your ears and the two running the amp at a 4-ohm load than any sound coming from the 15. A 410 is going to be louder than a 15, more so if the 410 is on top. The 18 might give a little more, in the midrange to poke through than a 15. If one is to do that, a better pairing would be two 15s or 18s with one 410.

I’ve been here before…

 

[FatBoutedGirls]

I’m not a fan of square 4x10 cabs either, but making it an 8x10 is greater than the sum of it’s parts.

 

[Drop1]

They covered it. To put it plainly, trying to change the cabs load without changing the drivers only throws away power and creates heat.

Also, a capable 4 ohm cab is just as loud as 2 8 ohm cabs on the same power. The only time adding a second cab is a benefit output wise is if you have more power available than 1 single cab can handle.
Otherwise it's just wasted resources.
Maybe you do have enough power to drive 2 cabs enough to be worth it. Idk.
If I dont have at least a 100w excess power, I don't worry about a second cab at all. No point.
There is a benefit in running 2 cabs though. Less distortion. The cabs don't need to be run as hard to achieve the same volume. Also more drivers can add a bit of perceived volume due to the way they move air. It's not really louder , but it can seem like it is.

Personally, packing around a second cab is not something I enjoy. 1 good cab with the right resistance is my preference.

Double the power with double the drivers will get you roughly 6 db gain. 10db is double the sound. You can decide if it's worth it to change drivers or cabs.

I was a bit distracted typing that. Someone please corrected if needed.

 

[DJ Bebop]

They covered it. To put it plainly, trying to change the cabs load without changing the drivers only throws away power and creates heat.

Also, a capable 4 ohm cab is just as loud as 2 8 ohm cabs on the same power. The only time adding a second cab is a benefit output wise is if you have more power available than 1 single cab can handle.
Otherwise it's just wasted resources.
Maybe you do have enough power to drive 2 cabs enough to be worth it. Idk.
If I dont have at least a 100w excess power, I don't worry about a second cab at all. No point.
There is a benefit in running 2 cabs though. Less distortion. The cabs don't need to be run as hard to achieve the same volume. Also more drivers can add a bit of perceived volume due to the way they move air. It's not really louder , but it can seem like it is.

Personally, packing around a second cab is not something I enjoy. 1 good cab with the right resistance is my preference.

Double the power with double the drivers will get you roughly 6 db gain. 10db is double the sound. You can decide if it's worth it to change drivers or cabs.

I was a bit distracted typing that. Someone please corrected if needed.

More surface area (speakers) means more volume. Two 8-ohm 15 speakers will be louder than one 4-ohm 15 speaker.

 

[Rip Van Dan]

Not sure if this is where I should ask the question or not but I have a Backline 600 and it has two speaker connections on the back and it say min 4 ohms. I have a 410 cabinet that is 8 ohms and a 115 cabinet that is 4 ohms. Is it safe to connect both cabinets? One to one connection and the other to the other connection? I understand that the two cabs in parallel is 2.66 ohms but I don’t know if these two connections are parallel internally? Or does it mean that you shouldn’t connect any cabinet less than 4 ohms?

Yes the connections are parallel connections and no you can't use both of your cabs at once on your amp. If your 115 was an 8Ω cab, you'd be fine but running that low 2.67Ω load on your 4ohm minimum load amp is a recipe for disaster.

The connections are not marked parallel although the manual should say that, because that is the industry standard connection for speaker outputs. Unless it is marked otherwise, presume it is a parallel connection. I have an old 4Ω Sunn 212 cab that has three connections on it. One is the input to the cab from the amp and then it has both a parallel output and a series output. They are very clearly marked. I used that cab back in about 2006 when I had bought the Backline 250 with its corresponding GK115bpx cab, only to find out it was a 125-watt rms amp, not 250-watts amp and it had an 8Ω minimum load. That series connection allowed me to add an 8Ω cab to the 4Ω cab because series connections add ohms together instead of reducing them like parallel connections do. So I ran a 12Ω load (8Ω+4Ω in series connection = 12Ω). That dropped the power to about 85-watts but adding the two 12" speakers to the one 15" one made up the difference and then some.

Again, if it's not marked as a series connection, presume it is a parallel connection.

 

[Drop1]

More surface area (speakers) means more volume. Two 8-ohm 15 speakers will be louder than one 4-ohm 15 speaker.

It really doesn't. Adding a second cab on the same power removes 3db from each cab.
Say you have 400w and 2 cabs able to take 400w each.

Say 1 cab does 120db at 400w.

You add a second cab , it still would only do 120db with each cab seeing 200w each unless you add more power. More cone alone does not equal more sound.

 

[agedhorse]

One way you can use both cabs is to wire them in series for 12ohms. You'll get less than the 8ohm rated power, and it's clumsy, so, uh, I guess don't do that, but it's possible.

Terrible advice. Not only is the power reduced to about 1/3 of what the amp can provide into the single 410, the series impedances of each cabinet will interact and really impact the performance.

The higher impedance cabinet in a series connection will receive more power than the lower impedance cabinet, so power sharing is also compromised.

It really doesn't. Adding a second cab on the same power removes 3db from each cab.

This is incorrect. As an example, adding a second identical 8 ohm cabinet to his existing 8 ohm cabinet results in the amp delivering almost double the power into the now 4 ohm combined load.

The increase in SPL is ~3dB from the ~doubling of the power and ~3dB from the acoustic coupling of the two driver for a net increase of ~6dB.

For somebody who has all that trick car audio test equipment and the bragging rights that go along with it, I would expect this most basic concept and calculation would be a no brainer.

 

[Drop1]

Terrible advice. Not only is the power reduced to about 1/3 of what the amp can provide into the single 410, the series impedances of each cabinet will interact and really impact the performance.

The higher impedance cabinet in a series connection will receive more power than the lower impedance cabinet, so power sharing is also compromised.



This is incorrect. As an example, adding a second identical 8 ohm cabinet to his existing 8 ohm cabinet results in the amp delivering almost double the power into the now 4 ohm combined load.

The increase in SPL is ~3dB from the ~doubling of the power and ~3dB from the acoustic coupling of the two driver for a net increase of ~6dB.

For somebody who has all that trick car audio test equipment and the bragging rights that go along with it, I would expect this most basic concept and calculation would be a no brainer.

That's not what I was saying. I was explaining using 2 cabs "on the same power" is kinda pointless. Double cone area but half power to each cab.
If you're gonna follow me around trying to insult me, at least read everything in context.

I dont even know what amp he has but using 2 8ohm cabs on 4 ohm capable amp of course gives you more power (if the amp is designed that way, on some amps. there new Amps out there that deliver equal power across multiple loads, but you know that).
Don't take cheap shots lol. You can do better.

 

[agedhorse]

That's not what I was saying. I was explaining using 2 cabs "on the same power" is kinda pointless. Double cone area but half power to each cab.
If you're gonna follow me around trying to insult me, at least read everything in context.

I dont even know what amp he has but using 2 8ohm cabs on 4 ohm capable amp of course gives you more power (if the amp is designed that way, on some amps. there new Amps out there that deliver equal power across multiple loads, but you know that).
Don't take cheap shots lol. You can do better.

The amp is in the title of the thread. It almost doubles rated power when the load is reduced from 8 ohms to 4 ohms.

 

[Drop1]

The amp is in the title of the thread. It almost doubles rated power when the load is reduced from 8 ohms to 4 ohms.

I didn't say anything about that. At all. Don't be so selective in your reading please. I don't care if you take shots. You can't upset me. It's all rather fun in fact. I think someone of your caliber can do better with the digs though. You have a bad habit of using selective quotes and not looking at the whole thing.
I was giving op some general info. Nothing more and certainly nothing about his specifc amp.