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Cabinet design help needed

groovaholic

groovaholic

Protect your hearing. Protect your hands.
Supporting Member
Sep 19, 2004
5,346
9,906
Mount Prospect, IL
#1
9E67DA1E-5F04-44BB-A9F6-B4618B66BECA.jpeg
I have a pair of these drivers (wired in series for an 8-ohm load) in a cabinet that I built in my garage.

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Given the total investment of approximately $90, it sounds really good.
But it seems to bottom out on the low notes when I feed it more power.

My guess is that my guesswork cabinet dimensions and porting are not ideal for these drivers -- their XMax isn't really impressive.

I've plugged the T/S parameters into WinISD, but I really don't know what I'm looking at...yet. I hope to learn a lot more about this topic.

The cabinet that I've built is heavy for it's size, and I found out that the base plate on my circular saw was bent, so some of the cuts aren't as square as they should be.

So I'm looking to build a new cabinet for the same drivers, but I'd like to apply a little more of a scientific approach this time.

Essentially, I'd just need to know ideal volume and porting.

But the philosophy behind what makes "ideal" would be great to know too.
 
#2
I think you'll find there is no such thing as an ideal set of dimensions. It just isn't that simple. Even worse, we aren't, like the hi fi boys, aiming for the most accurate reproduction. We're aiming for the most musical, which may not be the same thing.

Before you go deep into new boxes, have you played about with internal damping, and can you change port size? It might also be worth doing some measurements: an impedance curve isn't very difficult and will give you some clues about how well the box is working with the speakers. And although you are planning a new box, you'll probably find that a few experiments at this stage will help too.

Most of all try different amounts of internal damping. Quilt wadding from the local craft shop will do fine. I was astonished by how much it changes the sound, I bet you will be too...
 
#3
Those drivers work best in a big cab, 3.5 cubic feet per driver, tuned to 60 Hz. Even then F3 is only 70 Hz, and F10 is 48 Hz. Worse, maximum power at 80 Hz is only 40 watts each, because of that small xmax. So even if you make a new cab in the ideal size for those drivers it's not going to work as well as a much smaller cab loaded with better drivers.
 
#4
The usual trade-off is a larger box can potentially have lower extension. But power handling is lower.

Smaller box will increase power handling.

You can view this in winisd in the cone excursion window. For instance build 2 seperate models of the same driver. Make one box 3 cubic feet and the other 2 cubic feet. Apply 50 watts to each model and you'll see the effects of box size.

Sensitivity is very high on these drivers that's a good thing. Be interesting to see overall Q in the pretty standard 1.6 to 2.2 cubic per driver.

Fs is high on these. So high tuning to 60hz will cause lower bass notes to unload below tuning.

Your current enclosure just has holes cut for ports. So I'm assuming it's very high tuned to about 80hz. Which will cause it to fart out in the low-end pretty quick.

You could try a shelf response with these drivers if possible. The cabinet volume is made smaller on purpose and good for power handling. Then is tuned below Fs of the driver.

What is the suggested volume by winisd for a Qb3 alignment?

What is the suggested volume for a -3dB or -6dB extended bass shelf? Or EBS
 
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#5
What matters to the OP is maximum low end output, not maximum power handling, so looking at the excursion window doesn't tell him what he wants to know. The Maximum SPL window factors in thermal and mechanical power handling and SPL, so that's the window where he should compare different box sizes. In this case one driver tuned at 60 Hz has maximum SPL at 60 Hz of 108 dB from 1 cu ft, 115 dB from 2 cu ft, 118dB from 3.5 cu ft.
 
#6
I’ve actually altered the porting since that pic; installed a mid in the upper port and installed a port tube in the lower opening.

I’m looking for a better blend of power handling and LF extension.

BUT right now the cab has more LF than I need, and less power handling.

So maybe shrinking the box size is viable for what I need out of it.
(That need is, primarily, at-home use. The cab might occasionally be brought out as a second rig for outdoor shows)

I’ll post an updated pic (and dimensions) ASAP
 
#9
groovaholic said:
BUT right now the cab has more LF than I need, and less power handling.
Click to expand...
Is that what your modeling says? Or just a guess? Forget about power handling, look at the Maximum SPL chart to see what you really have and what changing the tuning will accomplish. Not that it matters, but your port is grossly undersized too. To prevent chuffing you need at least a 4 inch diameter port per driver.
 
#10
Modeling? No, it's an observation based on playing through the cabinet.

The tonal balance is shifted more toward the lows than I need it to be, and I heard what sounded like over-excursion on the low end when I played low notes with the volume up.
 
#11
What I’m seeing in WinISD is that lengthening my port will make the low end drop off more gradually, and will push the point of over-excursion to a lower frequency.

If I make that frequency lower than my normal lowest note, the driver should be protected, right?
 
#12
groovaholic said:
The tonal balance is shifted more toward the lows than I need it to be
Click to expand...
Or it's shifted toward the midbass. Your ears are not reliable frequency measuring tools. It's common to think that what you're hearing is an octave or more lower than what you're really hearing. You may be right, you may not. You have the right tool with WinISD, why not use it?
If I make that frequency lower than my normal lowest note, the driver should be protected, right?
Click to expand...
Probably not. Most of the power of the lower notes is in the second and third harmonics, not the fundamental, so if you tune the cab to the lowest fundamental frequency excursion won't be as well controlled an octave or more higher where you need that control. That's why most bass cabs are tuned to between 50 and 60 Hz, walking a fine line between low frequency response and excursion control.
 
#14
True, sealed cabs can be stuffed, but ported should only be lined. Over damping will change the port tuning, in extreme cases causing the cab to behave like it's sealed. The effect can be seen in WinISD in the box window advanced tab by changing the Qa value from the default, 100, to 50 for a lined, 10 for stuffed, 5 for stuffed and compressed, 1 for heavily compressed. At 1 the upper impedance peak can completely disappear.
 
#16
Your tone isn't low heavy, it barely has any lows at all. Fb is around 30 Hz, half what it should be. F3 is around 115 Hz, F10 is around 70 Hz. Raising Fb would help, but with that size box nothing is going to give an F3 lower than 100 Hz with those drivers. I bet those drivers were used by Community in a 2 way PA box on a stick, probably similar to this one, so they weren't intended to deliver much below 100 Hz.
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#17
Interesting -- it must be a hump in the midbass that is giving the impression of weight in the low end.

It sounds like whatever I do, these drivers will tend to bottom-out at band-level volumes.

Sounds like I should leave well enough alone and leave it as an at-home cabinet, and it probably wouldn't be worth my time to modify the cabinet with improved performance in mind.

Here's the response graph I'm getting out of WinISD:
upload_2018-10-18_8-26-5.png
 
#18
That graph is better than what I get, but I've been using WinISD for more than ten years. A good design would have the flat section on the right extend to at least 100 Hz before response starts to roll off, crossing the -3dB line no higher than 60 Hz.
 
#19
Rick James said:
That graph is better than what I get, but I've been using WinISD for more than ten years. A good design would have the flat section on the right extend to at least 100 Hz before response starts to roll off, crossing the -3dB line no higher than 60 Hz.
Click to expand...
I’d trust your graph, then.

I’m a total WinISD newbie.
 

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