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Cab redo...need some porting advice...

Sundogue

Sundogue

Apr 26, 2001
8,795
481
65
Wausau, WI
#1
I have a 410 cab that blew a couple of speakers. I also have a 210 cab that has great tone, but lacks a little in the volume department...partly because it was ported for different speakers than what is in there now, so I don't turn it up too much.

So...I have these two Eminence BP102's (10") speakers. What I am going to do is load them into my 410. Using some plywood, I'll block the other two speakers holes and the rectagular tuning port at the bottom (as this port won't work for these speakers anyway). It's not permanent...it can always be reversed when I get the blown speakers replaced).

In the plywood (right in the middle of where the speaker holes are covered), I'm going to mount two 3" ports (that are currently 4.5" long).

According to WinISD, this 410 is actually a better fit volume-wise than my 210 for my two BP102's.

The volume of my 410 cab is 8793.5 cu. in. (accounting for internal bracing and other displacement). The BP102's like 2.26 cubic feet per speaker (or 4.52 cubic feet for both), so this cab at 5.09 cubic feet cab actually gives them more space than my 210.

According to WinISD, using two 3" ports, I could tune it to 39Hz with a port length of 2.6 inches. This would keep the SPL up around 94 db with my low E (I only play a 4 string)...and it it is pretty flat all across the spectrum at 94 db.

With the ports left at 4.5" long, I can tune it down to 33 Hz (which is unnecessary using a 4 string bass)...plus with it tuned to 33 Hz, the SPL drops to 91 db on the low E...and it really starts taking the plunge in decibels at 50 Hz. Across the rest of the spectrum it only hits a max of 94 db, starting at 100 Hz.

My question is, should I try to tune it to 39 Hz? That seems to be the sweet spot for tuning and giving me the max db's. Also, how accurate is WinISD and it's port calculations? I've found it to be a bit off with my last two cab builds (of course, being relatively new to cab building...I'm sure I was a little "off" as well :hmm: ). Just curious what others feel about WinISD's port calculations.

Obviously, I'll start with longer ports and cut them down as I test them.

Anyone else have any opinions on porting this 410 (made into a temporary 210)? Remember these are the 8 ohm BP102's, and there will be two of them wired as a 4 ohm cab (and it will have a tweeter). I know it's a large 210 cab, but it's of a temporary nature.
 
#4
I made the new "baffle board" piece to cover the two open speaker holes last night. I have the cutout in it for the 3" ports.

I'm still not sure what frequency I should tune the cab to.

If I tune it to 39Hz, WinISD shows it's pretty flat across the spectrum at 94db all the way down to 45Hz, with only a drop of -1.6db at the low E. That seems to be a good spot and it's a +3db gain over the SPL of the speakers themselves.

If I tune it to 43Hz, I get a bump in db from about 44Hz all the way to 160Hz (only a gain of +1db or so though)...but a drop of 2.13db at the low E.

At 45Hz, I can get a 2.25db boost at around 57Hz, and a bump from 45Hz all the way to 200Hz, but also a drop of almost -3db at the low E.

At 50Hz, I get a 3.66db boost at 60Hz, but a huge drop-off of -5db at the low E.

I could play around all day long trying to figure out which way to go on this.

So, if anyone...bgavin, billfitzmaurice, etc. have any suggestions, I'd appreciate it.
 
#6
Yeah, that's what I'm thinking too.

It's not that I'm not going to do whatever I want in the end anyway, but I like to hear opinions on it...because someone might come up with something I haven't considered.

I'm going to build Bill's Omni 10 and I want to take my time with it, so for the time being I want to maximize my current 210 options. I just want to get the most out of what I have until the Omni 10 is built, and given my time contraints lately...that could be a while.
 
#7
One more point to add.

The port "baffle board" that covers the speakers and blocks the old square porting does cover the bottom two speakers holes in this 410. It's the only way I could cover the speaker holes and the old port with one board.

However, I'm going to put casters on the bottom of the cabinet and when in use, the cab will be turned on it's side so the two BP102's will be vertically aligned...NOT horizontal.

I also know that the BP102's are better for low end, so I will be using my tweeter in this. I may still lose some high mids because I don't think the BP102's and the tweeter's frequency coverage overlap. I'm not sure what the specs are on the Peavey 410TXF's tweeter.
 
#10
Well, yes I will be doing it by ear...and by sight. But I'd like to know if anyone see an advantage to tuning it slightly higher to get a little more oomph out of it, the way companies like Eden do. They don't go as low cleanly, but the low mids pump out more.

But I also don't want to risk overexcursion. However, the BP102's have a huge xmax.

I would think the speakers themselves must fall within the T/S specs...or why even have T/S specs?
 
#11
Sundogue said:
Well, yes I will be doing it by ear...and by sight. But I'd like to know if anyone see an advantage to tuning it slightly higher to get a little more oomph out of it, the way companies like Eden do. They don't go as low cleanly, but the low mids pump out more.
Click to expand...

I typically tune for the cleanest possible sound on my low E if it's a dedicated bass cab. I only play 4 stringers. I usually end up tuning a little lower than expected, that's just what sounds best to me. I may be leaving ultimate SPL on the table, but I don't care. YMMV. For that matter, maybe I need to check the calibration on my signal generator.:cool:

Anyhow, I've tried tuning a bit of bump into the curve, and it did work pretty well for my coax single 12 cab for EUB purposes. I've since retuned maximally flat since I now use the cab for vocals. The driver in question didn't really cut it for bass except for practice volumes, so...

I would think the speakers themselves must fall within the T/S specs...or why even have T/S specs?

AFAIK they're nominal (think average) specs, and a certain amount of deviation is to be expected I think. I think Bill F mentioned testing drivers individually to determine T-S parameters himself? Hopefully someone with more insight will jump into this thread.
 
#12
Well, I tried tuning the cab last night...and a bit this morning.

I put the ports in and left them at 4.5"...which according to WinISD, tunes my cab at 33 Hz.

It sounded very deep and full. I liked the tone and it sounded fairly loud, but starting at the A on down my speakers wanted to jump out of the cab! What the?

I cut the port tubes down to 3" and according to WinISD my cab tuning should be around 37.5. My speakers didn't jump around as much on any notes, so maybe I'm getting closer to what I need, but it didn't sound quite as deep or full.

I'll try the ports at 2.5" tonight (which WinISD shows my cab should be at 39.5 Hz).

What would the ideal tuning be to prevent overexcursion?
 
#14
Sundogue said:
What would the ideal tuning be to prevent overexcursion?
Click to expand...
Don't tune too high and you shouldn't have excursion probems. You've been slowly raising the tuning freq and you're getting close to the 40Hz mark now, which is all good. If you keep tuning higher and get into the 50's, the -3dB point gets lower but excursion will get worse.

I'm not sure why you had such excursion problems when the cab was tuned to 33 Hz. I don't know a lot about the speakers you used but I have a vauge memory of them having a rather largex x-max? If so, then maybe you over-reacted. Perhaps they're designed to move that far. I'm only guessing at this stage. I don't have the speaker data in front of me and I don't have time right now to look them up, but it's something for you to consider.
 

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