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Alpair internal cabinet reflections
Alpair internal cabinet reflections
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Old 24th June 2020, 01:44 PM   #1
Wiggle8 is offline Wiggle8  Canada
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Default Alpair internal cabinet reflections

What frequency range tends to be most affected by internal cabinet reflections in a shallow enclosure for the Alpair metal line?

I am hoping cross over at 4th order HP @ 300Hz on an Alpair 5.2 and I am wondering if I am avoiding some of the trouble area or if the frequencies into the lower mid-range and above are most affected?

I am aiming for 5" internal depth in a wall-mount cabinet. There will be an LDW7 in the same cabinet but it will be in an isolated compartment.
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Old 26th June 2020, 01:04 PM   #2
Wiggle8 is offline Wiggle8  Canada
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Essentially I am thinking I will isolate the Alpair 5 in a 4" PVC cylinder that travels to the back of the inner enclosure and stuffed pretty tightly. Asking for trouble?

I have flexibility on the crossover side, the LDW7 could easily play at a somewhat higher frequency.

Last edited by Wiggle8; 26th June 2020 at 01:09 PM.
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Old 26th June 2020, 01:41 PM   #3
xrk971 is offline xrk971  United States
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Alpair internal cabinet reflections
Use a sports cone or Dagger (tall 3 or 5 sided pyramid). Stuff with fiberglass or polyfill progressively denser at vertex leave about 1in of space behind driver. Line 3in of wall adjacent to driver with felt or melamine foam. This construction method has very little back reflections or resonances. Behaves almost like no rear chamber except that it provides an acoustic suspension.

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Old 26th June 2020, 05:44 PM   #4
planet10 is offline planet10  Canada
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Alpair internal cabinet reflections
Any reflection from a surface closer than a wave length could cause issues.

A heavily tapered lime, as X’s dagger is, is to my mind a better solution than a straight line. I personally prefer quarter-wave lines (open terminus), but in a thin loudpeaker this means out the side, or folded back on itself and out the front (or top).

In this thin gspeaker the midTL stretches from one side all the way to the other across the enture top of the box. Partitions to make the exit end longer than the closed and and to add a bit of taper. Stuffed light behind the driver to heavier near the terminus.

Click the image to open in full size.

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Old 26th June 2020, 09:31 PM   #5
norman bates is offline norman bates  United States
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yea, stagger parallel walls, or a cone.
Although didn't a parts express use pvc stuffed ?

I had a pile of 4's in 6" cubes, good size peak past 1khz, leaned my lesson on that one.
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Old 27th June 2020, 07:57 AM   #6
Scottmoose is offline Scottmoose  United Kingdom
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Yes, I think so. Even for non-TL type rear-chambers for midrange / HF units, avoiding parallel walls is a good idea. With the Viotti One a few years back, I specified a chamber for the mid-tweet based on a parabolic profile that reduced damping requirements somewhat. We were a mite constrained for space with V1 being a boat-hull standmount, so it wasn't as long as I would have preferred, but it worked, and loaded the Sota 5 nicely. I'm still very proud of that speaker as-is, even though I wish I'd had the freedom to take the filter an octave lower. Still worked though; there's a lot more going on in it than might be expected.
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Old 27th June 2020, 11:24 AM   #7
ewollowe is offline ewollowe  Australia
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1.9khz crossover? That seems unusual for a wide range unit like that?
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Old 27th June 2020, 01:59 PM   #8
Scottmoose is offline Scottmoose  United Kingdom
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It was actually more like 2.25KHz; the 1.9KHz was a text error that never got corrected. Mark wanted it to be around there; I was responsible designer, but within broad company instructions of which that was one.

Yes, it's unusual; on the other hand, while most small wideband units are crossed very low, it's not the only way of using them. In this case, the midbass is also a wideband, using a scaled version of the same cone profile so for practical purposes their polar behaviour through (& for a reasonable way above) the transition band was very similar. The extra cone area was felt to improve distortion performance in the midband, and also allow a variation on the BBC midband EQ to be applied without extra filter components. Had to be more than normal; less actually sounded in blind trials like there was too much energy present, and perhaps there was given the polar characteristics of the drivers. As noted, personally I would have liked the filter about an octave lower as a matter of personal taste, but as-is, I still liked it. One of my own pairs was modified that way, the others are standard.
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Old 27th June 2020, 02:31 PM   #9
ewollowe is offline ewollowe  Australia
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Thanks for that Scottmoose.

A lovely looking speaker and well reviewed from what I can see.

I certainly wouldn't say no.
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