what cab for a GK RB-400?

[Dan894]

Hi-
I have questions about head/cab pairing. I’ve tried reading up on this - but it’s not penetrating my thick skull. Thanks for your patience and I appreciate any resources you can point me to.

I have a GK RB-400, SN-74451, 1-89. Years ago I paired it with a huge cab, I don't remember the specs and I sold that cab when I moved. Now I'm looking for something smaller to pair with, mostly for home use. On the GK site, there is a link for a manual for 400 RB, however the manual itself says it is for a 400RB-IV. So I'm not sure if the specs in that manual apply to my head. The manual says the RB-400 delivers 280W/180W into 4 Ohms.
What are the parameters I need to follow for pairing with my GK RB-400, SN-74451, 1-89?
Can it pair with:
-Genz Benz 2x10, 250w, 8 Ohm?
-Peavey 210 Tvx Bass Cab (175 watts (rms) continuous at 4 ohms)?
-Crate 15", 300w 8 ohm?
-kustom brand cabinet, with a Altec Lansing 421A speaker, 15", 100w, 8 Ohm?

Thanks!

 

[Aloe]

hi and welcome to TalkBass!

for a home use max power doesn't matter that much, you likely won't crank it at home anyways. if it's strictly for home and you don't plan to lug it, you can have a great deal on an old heavy cab.

I won't bother with Peavey (it's both underpowered and 4 ohms) or Kustom with a non-stock speaker (a huge red flag), but other two seem a sane choice, since your amp is 180W at 8 ohms. I'm totally not sure, which Crate is it, as Google gives me no bass cabinet with those parameters. so, out of those, I'd pick the Genz.

pretty much any bass cab will work, 4ohms or more. you might prefer 1x12, 1x15 or 2x10, it's your preference. you might prefer to have tweeter or not, it's up to you. a 8 ohm cab rated at 300-400W would be my best bet not to be afraid to turn the amp up. slightly lower is okay, but it likely won't sound good if you dime the amp.

now to the interesting part, different cabs sound differently, there's a popular opinion that they color the sound more than the amp. so, if you can try some cabs with your head and bass, that could give you a much better match than just ordering a cab, looking at specs.

 

[Dan894]

Thank you for all the helpful info! I'm going now to check out the Crate, I will try it with my head and see how it sounds. The Crate has a new eminance speaker.

 

[JMacBass65]

That's a great head, I own one myself. Pair it with whatever sounds best, provided you don't end up going below 4 ohms. For example, two 4 ohm cabs chained together will drop you down to 2 ohms......don't do that. Now, two 8 ohm cabs chained together will net you 4 ohms, that's fine. And any one of your cabs alone will be fine.

 

[Aloe]

The Crate has a new eminance speaker.

please note that bass cabs are designed around a speaker, swapping the speaker for a different model is generally harmful. in other words, I advice to buy a working cab with a stock or proper replacement speaker, not the one, somebody "upgraded" with a different speaker

 

[JMacBass65]

By the way, the Genz Benz is the highest quality cab of the bunch here. In my view (I own one of their amps, and one of their cabs), that's the only one to choose.

 

[abarson]

Hi-
The manual says the RB-400 delivers 280W into 4 ohms/180W into 8 Ohms.
What are the parameters I need to follow for pairing with my GK RB-400, SN-74451, 1-89?
Can it pair with:
-Genz Benz 2x10, 250w, 8 Ohm? Yes
-Peavey 210 Tvx Bass Cab (175 watts (rms) continuous at 4 ohms)? Yes
-Crate 15", 300w 8 ohm? Yes
-kustom brand cabinet, with a Altec Lansing 421A speaker, 15", 100w, 8 Ohm? Not really.

Thanks!

Corrected the output statement.
All of the cabinets listed will work, and I'm assuming the reason you are looking at them is that they are used and inexpensive ie old. The way they stand is also what I'd say is their preference. The Kustom is usable if you are very careful how hard you drive it, as it is very limited in its power handling.

Using one 8-ohms cabinet at first allows you the option of adding another 8-ohms cabinet in the future. Good luck!

 

[Dan894]

Thank you everyone!

 

[Dan894]

GK just sent me this manual for the old RB400.

 

[Wasnex]

For home use, use whatever cab you think sounds good, unless you really like to crank it.

If you plan to gig the amp, then you need to consider how much volume you need. The 400RB is not the most powerful amp, so if you require significant volume, you need an really efficient cab, or two.

To estimate how loud a rig can play, you need the power the amp can make at the expected load, the sensitivity rating of the cab (expressed at 1W/1m), and the power handling of the cab. The original 400RB is rated 200W at 4 ohms and 125W at 2 ohms. Compare the amps rated power and the speakers RMS power rating. Usable power is the lower of the two numbers

Here is the formula:

Calculated SPL = [Log(Usable Power) x 10] + Sensitivity Rating

The section of the equation that is in the brackets calculates the decibel change you get from raising the power from 1W to the Usable Power.

Most modern cabs will easily handle 200W. So lets calculate the decibel change for 125W and 200W

Decibel Change of 1-125W = [Log(125) x 10] = ~21dB
Decibel Change of 1-200W = [Log(200) x 10] = ~23dB

So if you get an 8 ohm cab, the amp can add 21dB to the sensitivity rating. If you get a 4 ohm cab the amp can add 23dB to the sensitivity rating.

Let say you get an 8 ohm cab with a 97dB sensitivity rating. Calculated SPL = 21 + 97 = 118dB.

Lets say you get a 4 ohm cab with a 95dB sensitivity rating. Calculated SPL = 23 + 95 = 118dB.

The key idea I am trying to show you is the sensitivity of the cab is very important. The amp makes 75W more at 4 ohms than 8 ohms, but the SPL is the same with both cabs. The amp makes about 2dB more power at 4 ohms, but the 8 ohm cab is 2dB more efficient.

In my experience, a rig rated for 118db will work in low volume situations, but it will probably run out of headroom in most cover band situations. My personal goal is a rig capable of 124dB minimum.

We can rearrange the formula to figure out how high of a sensitivity rating we need given the decibel change our amp can produce. First, rename "Calculated SPL" to "Target SPL" and start with this formula:

Target SPL = Decibel Change + Sensitivity Rating

The solve for Sensitivity we rearrange the formula.

Sensitivity Rating = Target SPL - Decibel Change

So if our Target SPL is 124dB and our Decibel change is 21dB (for 125W at 8 ohms) or 23dB (for 200W at 4 ohms) we get

Sensitivity rating for 8 ohms = 124 - 21 = 103dB 1W/1m
In other words the cab needs a 103dB 1W/1m sensitivity rating to produce 124dB with 125W.

Proof: Calculated SPL = [Log(125) x 10] + 103 = ~124dB​

Sensitivity rating for 4 ohms = 124 - 23 = 101dB 1W/1m
In other words the cab needs a 101dB 1W/1m sensitivity rating to produce 124dB with 200W.

Proof: Calculated SPL = [Log(200) x 10] + 101 = ~124dB​

Another bit of helpful info:
If you add a matching cab, the combined sensitivity is approximately 3dB higher than one cab. So if you have a pair of 8 ohm cabs rated for 103dB 1W/1m, when you add the second cab the combined Sensitivity rating is ~106dB 1W/1m. Also, the combined power handling doubles and, with the typical parallel connection, the combined impedance is 1/2. So in this case the load drops to 4 ohms where the amp is rated for 200W.

Calculated SPL for 200W into a pair of cabs that are each rated 103dB 1W/1m.

Calculated SPL = [Log(200) x 10] + 106 = 129dB.

 

[Standalone]

I have several 400RB amps. And I’ve had a Peavey TVX come through — I think that 175 is rated conservatively and you’d do just fine with it if you know how to not crank low bass at it and can listen for when a cab is pushed too hard. I’d say that applies to the Genz and the Crate.

The TVX has a deep dubby bassy character if you’re looking for that. It’s heavy though.

I’m a fan of single fifteens and have a very old crate 215 that is lightweight and sounds great. Probably has eminences in it.

The all time best cab with that GK 400 though is a Pair of Bag End fifteens. For the reasons @Wasnex discussed — they are sensitive cabs, and a paired stack is excellent.

The Crate will take you in that direction…

 

[Stylee Mousse]

I’m a bit perverse and would give the Kustom /altec 421 a try (assuming it is an olde kustom (I had a kustom single 15 with an EV SRO in it).
I used my 400rb with various 15s including JBL D-140s which are pretty much 50 watt speakers and the did fine.

 

[Ostie]

please note that bass cabs are designed around a speaker, swapping the speaker for a different model is generally harmful. in other words, I advice to buy a working cab with a stock or proper replacement speaker, not the one, somebody "upgraded" with a different speaker

I wouldn’t say “harmful”, in that it will blow up. That depends on the specs of the driver. It may or may not perform well, odds are against it. It’s hit or miss. I would pass on that cab, and look at the Genz.

 

[Gervais Cote]

I had this amp head in the past and if I was still using it, I would pair it with 15" speakers. To me, this amp was kind of bright and detailed so the "booming" effect of a larger driver will balance the tone IMO. Mine also had a lot of hiss so better have a tweeter attenuator or no tweeter at all if yours is the same.

 

[cataract]

I’ve been running my 400RB through 2 Mesa Subway 112 cabinets with uhh really great results. Crushing Mids City huzzah

 

[Standalone]

I’ve been running my 400RB through 2 Mesa Subway 112 cabinets with uhh really great results. Crushing Mids City huzzah
View attachment 5319148

Nice. A post described this as a bright amp but I’d describe it as rich in the mids. Even with the contour on.

 

[Stylee Mousse]

I felt it to be balanced and has nice definition and pretty smooth highs. Not dull at all. I ran mine through paper only. No horns

 

[Ken R]

1986 G-K 400rb into a Genz-Benz neo 2x12 is a killer combo, a Peavey 2x15D does a smoking job too!View attachment 5320042 View attachment 5320044

 

[basscooker]

Rb heads sound great through aluminum cone Hartke cabs. Actually way back when, I was probably provided as many 800RB + Hartke 410/ 810 backlines as I was SVT + 410/ 810

 

[Bill Whitehurst]

Those old RBs are famous for 'punching way above their weight class'.
The reason is that the power rating is at the point where it is still clean.
While clean is a good thing, when pushed they get a nice grind and put out more than their rated power.
If you combine that with sensitive speakers, you'll find the old 400RB can more than handle most gigs.
I find that they like EVs,
A pair of TL606s will make you smile.
They also seem to like Fridges and those can be had at a reasonable price if you find someone that is just done with moving one.