Back to the old electronic brain

What if the cabinet is just a bit on the small side? Don't get me wrong I'm not too well versed on the kappalites, but a cabinet can get boomy if it's too small and tuned too high. Unfortunately that's the least convenient option, so maybe modelling how the same box with a lower tuning would respond and taking that lower power handling compromise if it's not too much of a dip. Some like having a bit of a bump in the mid-high bass/low mids, having an absolutely flat Butterworth type of curve isn't always desired, but at the same time too much of a bump won't please too many either. Bass cabs are all about managing compromises to get the best low end and power handling for your needs while being in a weight and form factor that you can manage.

But you probably know all of these things already. Error is all part of the trial process. Unfortunately my battlestation is in storage while I undergo a course, so I'm exclusively posting on my phone, so no winisd or hornresp from me :/

 

Have you measured the actual FB? WinISD is famous for giving wonky results with shelf ports. Most of my DIY cabs with them have required about a 30% reduction in modeled shelf length.

 

I know many don't, but have you measured?
Are the curves as measured matching the ones from the software?
There's a tendency to tweak the size of box and the graph shows what appears a small change, but a hump in the graph appears that seems acceptable. It may not be in real life both hearing and measuring. Without even building the box you can take flat headphones and eq them to the curve of the software to hear what the hump sounds like.

Prototypes in MDF are a good idea, you don't need to crank protos to measure them.

And of course, read the threads on driver burn-in. It may have some effect.

 

2.6 per driver is little small
50hz is little high

That driver is happy around 3.2 per driver
And 40/45 hz and that is still small

I'd have to look at the model. I'd assume the blooming is from the first impedance peak. Which is related to box size.

Lowering tuning might help a little. But I'd assume the response peak is from box size.

When you put a speaker into a box resonant frequency will rise. Even if a reflex model shows decent F3 values.

Usually it's from the continued misunderstanding of high tuning.

Rather sealed or reflex that first resonance impedance peak doesn't change. Even though ported model shows more bass. That first impedance peak is the end of the road.
And small boxes will raise that frequency rather high.

 

If you placed single 3015 in a sealed box at 2.6 cubic feet
I'll assume with the large Vas of a typical 15" speaker you'd be close to .9 or 1 rippple response. And system Q would be way way up around 75 to 85 hz. F3 be horrible and be rather boomy.

Reflex model might not show as much in response chart. But it's misleading
Cause the first big impedance spike is still the end of the road. And yes be rather boomy if you just doubled a 40 hz driver to 80hz. Reflex models can hide the fact that the box raises resonance. Made worse cause people assume high tuning makes more bass. Since high tuning can yield lower F3 in the model. But in real performance doesn't with actual complicated waveforms or source material.

Model your dual drivers in that airspace. In sealed box. Whatever resonant frequency it shows. Is your problem frequency. Using a EQ to cut that frequency I'll assume 75 to 85hz will help reduce the boom

Only reason you'd high tune a 15" to 50+ hz would be for pa use for program material. Or as a midbass application assuming it would be high passed at 80hz
Essentially leaving the reflex point as secondary protection for the woofer and expecting the port to never operated much with 80hz crossover. Basically a thermal vent.

Standard tuning for bass application is 40hz. Specially with a 15" driver that has Fs of 40hz. First impedance curve peak from the box will actually raise that to 60 to 65hz. Then Tune at 40hz which yeilds pretty well known 50hz f3 for 15" driver

 

Bearing in mind the popularity or at least fashionability ( is that a word - it is now) of HPFs and a bit of reading and experience with home built cabs, I'm beginning to wonder if a flat response below about 60 or 80 Hz is actually what most of us want. I'm wondering if for many of us we should be aiming our designs at a controlled roll off, the fly in the ointment being what to target for. I suppose seeing response curves for known good sounding kit would be a start.
I'm thinking that maybe I've been naive in assuming my ideal would be flat response down to fundamental and nothing below, and actually it's more complicated than that.