Foam Core Board Speaker Enclosures?

[iko]

There aren't any real measurements that I know of. There's a simulation a few pages back.

[adason]

...why I am asking is that I would like to see the proof that the spiral inside is actually doing something
that whole box is quite big itself for small fullrange driver, maybe it would sound the same in the box of the same size
if someone could measure fr response of the spiral horn, and compare it to the fr response of closed box of thesame size, that would make me believe (and even embark on making it, but not before)

[xrk971]

Originally Posted by adason

I have not gone thrue 60 pages of this thread...are there and frequency response measurements in this thread?

(I mean no desrespect, I just want to see facts)

That would be great if someone performs a measurement of their Cornucopya after they build it. I don't have the equipment to do so, and most others are still in construction stages - except for Cal. (Cal - do you have means to do a measurement?)

Bring on your microphones and tone generators! It would be great if we can confirm Don Hills' model - which shows some serious dips and peaks. But to my untrained ears, my 20 inch spiral horns sound great with the TC9FD drivers mounted about 7 feet apart on the short wall at 4 ft height. The room dimensions are about 18 ft x 30 ft x 8 ft tall. I think any simulation needs to account for the room walls and ceiling/floors as the reflected sounds from the edges of the spiral are critical to the character of this cabinet.

[iko]

My prediction is that the measurement will not look like the simulation, with all due respect for Don's skills. I think the simulation might be oversimplified.

[xrk971]

Originally Posted by adason

...why I am asking is that I would like to see the proof that the spiral inside is actually doing something
that whole box is quite big itself for small fullrange driver, maybe it would sound the same in the box of the same size
if someone could measure fr response of the spiral horn, and compare it to the fr response of closed box of thesame size, that would make me believe (and even embark on making it, but not before)

Adason,

The spiral definitely has a PROFOUND effect on the sound. My initial pre-conceived notion was that it would not work because the box is so small, flat, and open - it is all channels and open air to the outside with no real containment except for front and back. Furthermore, after I made the box out of foamcore, well, it resembled a pizza box literally in feel (weight) and dimensions, further prejudicing me to thinking it would not work. However, like I said, I was blown away by the sound quality when I turned it on for the first time. I have Cal to back me up at this point, but I believe several others are close to finishing theirs.

When I place my ears next to the output horns on the edges, I can definitely hear the low and mid bass coming through. There is also some passive output from the front panel as a radiator. The edge outputs when reflected off the ceiling, floor, walls, integrate with the direct radiation from the drivers combine to reach your ears in a way that is different from any other cabinet I have ever heard.

I think you are right for asking for facts to back things up, but an SPL vs freq measurement will not give you the sense of the ambiance that the Cornucopyas provide when you listen to them in person. I don't think the Cornu's are known for faithfully reproducing music without coloration - they don't claim to be monitors by any stretch - and if you read the detailed 6 Moons review, it confirms this. What they do have is an almost ethereal presence and spacious sound stage with a very wide sweet spot.

If you have a few days time, some cheap foam core boards, a razor, and hot glue... give it a try.

In response to your proposal of comparing with sealed box of similar size: I may just do this - a 20 x 20 x 2.38 in Cornucopya is the same as a 5 in wide x 16 in tall x 12 in deep box which is simple enough to make. I can tell you right away that without at least a BR port, the regular box is already handicapped. I don't have measurement tools but can record with a high quality mic to mp3.

[adason]

thanks for the response xrk971, one easy thing you could do is to measure your spiral horn first, than close the side openings and remeasure again the same box (it does no matter what inside is the box is closed)

[badman]

Originally Posted by adason

(it does no matter what inside is the box is closed)

Actually, it does. The long pathlength will make a significant contribution even in a closed box but not in the same way. Quarterwave vs half wave vs. horn...

it gets funky in a hurry, but a sealed labyrinth enclosure still makes a difference vs. a "normal" sealed box.

[xrk971]

I was thinking the same thing, and in fact, have a BLH box that I built that is about same dimensions as dummy box (5 x 15 x 10) but of course, it has channels and horn internally even if I were to seal it. However, if Adason is satisfied with simply covering output ports on Cornucopya, I can easily do that and record some sounds. I expect it will sound terrible...

[adason]

yeah, I agree, it does matter what's inside the box for sure, that statement was oversimplification

I got bunch of really good sounding 4" fullrange speakers, do not know the maker, maybe over the holidays break I can try something

[xrk971]

Adason,
But isn't your question really aimed at how much of a difference in sound comes from the spiral horn rather than whether or not a sealed box enclosure of same size sounds better or worse? The internal channels will have some effect but that has to be re-radiated back out the driver. Granted, there is some sound come from vibrations on the flat front baffle. The covering up the horn mouths is much easier than building a foam box which really would not have further use.
Regards,
Xrk971