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| Re: 4Pi - alternate compression driver mounting? [message #94481 is a reply to message #94480] |
Wed, 22 September 2021 14:53   |
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Wayne Parham
Messages: 18795
Registered: January 2001
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Illuminati (33rd Degree) |
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I don't think there are any build threads from people that used that approach. But I've seen a lot of photos of loudspeakers made this way, so you might search again. Hard to search for photos, I guess, just gotta scan the internet for them.
Some people put the waveguide in a box and mount it traditionally, setting the tweeter box on top of the woofer cabinet. Others have the waveguide sitting on top, bare. Many people paint the waveguide.
When sitting the waveguide bare on top, the biggest challenge is what to do with the waveguide mounting holes. I would suggest using a filler material - like is commonly used in auto body repair shops - to fill the holes. Then lightly sand the front face so the filler blends and to remove any mold lines. Paint the waveguides with enamel and set 'em on a cradle. I use the cradle approach when I mount wood horns, and I think it looks really nice. See one of my tweeter cradles, below:
Tweeter Cradle
One last thing - I mentioned above that the woofer/tweeter geometry should be the same but you can center the tweeter. I assumed you knew that but wasn't sure, so I thought it best to clarify. It's just important that the waveguide face be flush with the midwoofer face and that the two are as close together as possible. That's why most people turn the cabinet upside-down - to make it closer to the tweeter.
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| Re: 4Pi - alternate compression driver mounting? [message #94770 is a reply to message #94769] |
Wed, 10 November 2021 16:25 |
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Wayne Parham
Messages: 18795
Registered: January 2001
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Illuminati (33rd Degree) |
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There's the rub.
When flipping the box over, the waveguide and midwoofer are placed closer together than they would be if the woofer remained low in the box with the waveguide perched on top. So flipping the box over brings 'em closer together, pretty much the same distance apart as they are in the stock design.
I say "pretty much the same distance apart" but they're not exactly the same distance. Not that we need to split hairs about tenths of an inch or anything like that, but the difference is more than that - they're about an inch further apart.
That's not horrible, but it will draw the vertical nulls closer together making the forward lobe smaller. It's not what we want.
On the other hand, the forward lobe is pretty large and the nulls are spaced far enough apart we don't have to push it. That's why the stock design has a gap between the midwoofer and tweeter. If we needed, we could brings them closer together to get more distance between vertical nulls. But we really don't need that - the nulls are widely spaced.
Then we also have to consider the internal standing waves. If we move the midwoofer or the port, the standing waves will align differently inside the cabinet. So we cannot know for sure if modifications will create midrange anomalies without measuring the cabinet.
I moved stuff around for testing way back when I originally designed this cabinet, and I tried a lot of configurations both with mathematical models and then ultimately with measurements of physical loudspeakers. But that was a long time ago and I cannot remember what movements were OK and what weren't. I know this particular configuration measured well.
So for the person considering this mod, those are things to consider.
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). But, sorry in advance if this is is a totally non-sensical question...
