GK 400RB-iii 1x15 Combo Port

[fretbuzz2003]

Hey all. I recently picked up a GK 400RB-iii 1x15 Combo for a good price. However the speaker port is missing. I was wondering if anyone with one of these amps could measure the port for me so I could find a replacement?

I tried contacting GK but they said they do not have any cabinet specifications for an amp that old. Otherwise I tried sizing a port for a 45 Hz frequency and came up with a 4" diameter x 2.5" long port. I am not an acoustical engineer so I'm not sure if that is reasonable or not. Thanks.

 

[fretbuzz2003]

Not that anyone is following, but the port I found was 4" dia x 4.375" long. It fits the cutout and by my calculations that should tune the cab to 40Hz. Not sure if that is good or not for the speaker but it sounds pretty decent.

 

[fretbuzz2003]

Can anyone please recommend an fb to tune the cabinet too?

 

[agedhorse]

A good choice for Fb depends on the driver… if you don’t know the TS parameters of the driver, any suggestions are just a guess.

 

[fretbuzz2003]

Unfortunately I do not have any information on the speaker, so I will have to guess.

 

[agedhorse]

Unfortunately I do not have any information on the speaker, so I will have to guess.

Then you have your answer.

 

[fretbuzz2003]

Then you have your answer.

I hoping someone more experienced could offer a more educated guess, but forget that I asked.

 

[agedhorse]

I hoping someone more experienced could offer a more educated guess, but forget that I asked.

Those who are experienced would give you EXACTLY the same answer that I gave you... there is no way to know without either the original port length OR knowing the TS parameters of the speaker.

Sorry you don't like the answer, but that's the answer the more experienced folks SHOULD give you. I just might have a little experience in this subject myself...

 

[CochinoBass]

Unfortunately I do not have any information on the speaker, so I will have to guess.

I have a 400RB IV 115 combo, I am pretty sure the cabinet and speaker are the same, only the head is different. I am assuming you need the length of the tube that goes inside the port hole. If so I can measure mine and let you know tomorrow.

 

[agedhorse]

I have a 400RB IV 115 combo, I am pretty sure the cabinet and speaker are the same, only the head is different. I am assuming you need the length of the tube that goes inside the port hole. If so I can measure mine and let you know tomorrow.

Check the diameter, the speakers may not be the same as GK changed at some point around then.

 

[CochinoBass]

OK, I'll get diameter and length of the tube.

 

[agedhorse]

OK, I'll get diameter and length of the tube.

If the diameter is different, that pretty much means that the driver is different. That means the length measurement won’t matter as it won’t be correct either.

 

[fretbuzz2003]

OK, I'll get diameter and length of the tube.

Awesome, thanks!

I found the speaker label. It is a 0820010-B. I requested the speaker specs from GK but have not heard back.

In the meantime I tuned the cabinet to 40 Hz. It sounds good, a bit boomy maybe. Or that could just be me being used to guitar amps (this is my first bass amp).

 

[agedhorse]

If you tune too low, mechanical power handling suffers and it can become easier to damage the speaker.

This isn’t a guitar cabinet.

 

[CochinoBass]

I'll see if I can find a part number on my speaker also.

 

[CochinoBass]

My speaker has the same part number, 82-0010-B. The port is 4" in diameter and the tube is 4 1/2 inches deep.

 

[agedhorse]

View attachment 7416910My speaker has the same part number, 82-0010-B. The port is 4" in diameter and the tube is 4 1/2 inches deep.

Then 4-1/2” deep port is a reasonable assumption.

 

[fretbuzz2003]

View attachment 7416910My speaker has the same part number, 82-0010-B. The port is 4" in diameter and the tube is 4 1/2 inches deep.

Thank you so much! Is the port flared at the outside or both ends?

I cut my port to 3-1/2" to tune it to 40 Hz. So I should be safe as far as excursion goes.

 

[agedhorse]

Thank you so much! Is the port flared at the outside or both ends?

I cut my port to 3-1/2" to tune it to 40 Hz. So I should be safe as far as excursion goes.

Sure, but that may be why it’s boomy too

 

[fretbuzz2003]

Sure, but that may be why it’s boomy too

Thanks for that, I will order another 4-1/2" long port.