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Re: 4pi: Cabinetmaker's build [message #99565 is a reply to message #99564]

Tue, 07 July 2026 20:13

Wayne Parham
Messages: 19066
Registered: January 2001

Illuminati (33rd Degree)

That chart shows the overall tonal balance, but it can't show the sharp dips we would expect to see from a crossover null.

If the polarity is right, you'll see nulls at approximately +-20 degrees above and below the speaker. If it's wrong, you'll see a null on-axis.

Watch this video to understand what I'm expecting to see:

Vertical Nulls

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Re: 4pi: Cabinetmaker's build [message #99568 is a reply to message #99291]

Wed, 08 July 2026 08:10

dustboy
Messages: 15
Registered: March 2026

Chancellor

What is the test signal you are using there?

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Re: 4pi: Cabinetmaker's build [message #99569 is a reply to message #99568]

Wed, 08 July 2026 11:36

Wayne Parham
Messages: 19066
Registered: January 2001

Illuminati (33rd Degree)

That was a gated (fast) log sine sweep, often called a "chirp" signal.

My main focus was the crossover region, because I was looking for nulls. You can see them on the computer screen in the foreground when I move the microphone above and below the speaker. Watch for the notches to grow as I get close to the location of the vertical nulls, and shrink back when I get past them.

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Re: 4pi: Cabinetmaker's build [message #99579 is a reply to message #99291]

Sun, 12 July 2026 21:01

dustboy
Messages: 15
Registered: March 2026

Chancellor

Got it. Yes, I am seeing a null show up at about 20 degrees above and below, around 1450 Hz. Looks fairly flat on-axis.

I hear a tiny bit of resonance with male vocals and acoustic strings in the middle range, how do I find the source of that? Not sure whether it's a standing wave in the cabinet or the 3DP ports ringing or what.

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Re: 4pi: Cabinetmaker's build [message #99580 is a reply to message #99579]

Sun, 12 July 2026 21:45

Wayne Parham
Messages: 19066
Registered: January 2001

Illuminati (33rd Degree)

Excellent. OK, then, that tells us that the drivers are hooked up properly. Crossover is doing exactly what it is supposed to do.

As for the throatiness or resonance, I suggest a couple things:

1. Check your damping material. Make sure you added the sheet that spans the cross-section in addition to the ones that lines the walls. That cross-section sheet is extremely important because it traps the lower midrange better than the ones that line the walls. It should span front-to-back and side-to-side completely, essentially splitting the cabinet into two areas, one exposed to the woofer and the other exposed to the tweeter and port. Bass will pass right through but midrange and treble will not.

2. Explore the flanking-sub approach. The self-reflection from the front wall often manifests as a throatiness. It definitely causes a defect in the lower midrange if the speakers are anywhere near the wall.

You can also take the speakers outside temporarily or in the middle of a very large room to see if that's the problem.

If the problem is a bell mode in the port, you might try damping it with putty.

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Re: 4pi: Cabinetmaker's build [message #99623 is a reply to message #99291]

Sun, 26 July 2026 15:17

dustboy
Messages: 15
Registered: March 2026

Chancellor

It seems to be the placement. I pushed them all the way back to the wall and the 'throatiness' went away, perhaps at the cost of soundstage. They are best about 30-36" into the room but I don't have the space for that. Need to put some casters on them, these babies are HEAVY!

I assume the best left/right orientation for the horns is on the inside, away from the walls, is this correct?

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Re: 4pi: Cabinetmaker's build [message #99624 is a reply to message #99623]

Sun, 26 July 2026 18:17

Wayne Parham
Messages: 19066
Registered: January 2001

Illuminati (33rd Degree)

Excellent observations, and an excellent question. I'm glad you asked it.

The "mirror image" I've always used is purely for aesthetics. There's no significant difference whichever side each speaker is placed.

That said, I've always placed the ports outside, except for the four Pi model. I place the tweeters outside on that model.

The reason is trivial, but I'll tell you why. It's because of the vertical nulls we discussed earlier. They are perfectly above and below the speaker if the midwoofer and tweeter are both centered. But with the tweeter slightly offset, the nulls are too. Or perhaps I should say the maxima above and below are slightly offset. They track a line drawn between the driver centers.

So the upper null is a little bit towards the tweeter side and the lower null is a little bit away from the tweeter side. Just a smidge. Insignificant. Still, that's why I always set 'em up with the tweeters outboard.

Back to your speaker placement. That's a great observation too. I've noticed that as well, and it's exactly what the flanking sub configuration mitigates. Try that setup sometime - I'll bet you'll hear the improvement right away, especially since you could hear the SBIR from the wall behind the speakers. Flanking subs are specifically designed to counteract SBIR from nearby boundaries, e.g. the wall behind the speakers.

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