Pallet Carousel for heavy speakers?

[DonStauffer]

Any opinions on using one of these pallet carousels to construct a turntable for heavy/large speakers? Does anyone know how smoothly they turn?

https://vestil.motionsavers.com/products/carousel-pallet-turn/hca-40-2/

 

[1audiohack]

I have considered these too. So I am curious to hear of any experience with them.

Barry.

 

[DonStauffer]

Northern Tools carries them as an internet only item. Slightly more money, but I trust the company. The one review I saw said it's really easy to spin a pallet on them. I was encouraged. And you can get really big diameters, and they're steel. Lots of lazy susan bearings I found under $500 had aluminum races, which I didn't feel comfortable with for heavy loads with possible torsion. And actually very few of them were even as large in diameter as 24", which was what I decided my minimum was.

The more I think about it, the more I think this would be just fine. I could imagine it not turning smoothly, but I doubt it. And even if it was a little rough, it would still work, I think. Maybe route a circular groove in a piece of wood to set on top of it.

 

[DonStauffer]

I ordered one. It might take a week. I'll try to remember to follow up on this thread when I have some impressions of how it works. I feel pretty good about it.

 

[1audiohack]

Cool thanks!!

Barry.

 

[DonStauffer]

Now I'm thinking about a platform, markings for different angles & axes, and maybe some kind of stops or detents, maybe every 10 degrees, and possibly a locking mechanism. Still formulating it in my head.

 

[weltersys]

And even if it was a little rough, it would still work, I think. Maybe route a circular groove in a piece of wood to set on top of it.

Don,

It is quite easy to route a circular groove in Baltic Birch with a round nose bit using a jig, then fill the "Lazy Susan" with ball bearings or marbles of the same diameter. Also quite easy to spin a 400 pound speaker on such, in fact a light breeze can cause the speaker to spin off axis..

The difficulty is not achieving an easy spin, but in elevating the speaker/turntable from boundaries to achieve valid polar response measurements not contaminated by reflections, and rotating the speaker from it's acoustic origin point, while not having the turntable itself cause reflections.

Art

 

[DonStauffer]

Thanks for your observations on the difficulties and goals. I hadn't thought of routing wood into a de facto raceway for bearings.

I already have a 40" high, heavy-duty platform made of 2x4, designed to be stable but not contribute reflections, so I think I'll be OK if I just put that on the turntable. The speakers are heavy but in 3 parts so I can get them on top of the platform.

 

[weltersys]

I already have a 40" high, heavy-duty platform made of 2x4, designed to be stable but not contribute reflections, so I think I'll be OK if I just put that on the turntable. The speakers are heavy but in 3 parts so I can get them on top of the platform.

Although the platform won't contribute much reflections, the floor bounce from the individual sections at 40" + will.
This site has a calculator that shows where the problems will occur.
Speaker Boundary Interference Response (SBIR)
SBIR calculator

For your full range measurements to be valid, they should be done in the "far field". Pat Brown wrote:
"A working “rule-of-thumb” for determining the boundary between near-field and far-field is to make the minimum measurement distance the longest dimension of the loudspeaker multiplied by 3.
He then writes:

"It is often thought that a remote measurement position is necessary for low frequencies since their wavelengths are long. Actually the opposite is true. It is more difficult to get into the far-field of a device at high frequencies, since the shorter wavelengths make the criteria in Item 4 more difficult to satisfy.

Item 4:
4. The distance from the source where the path length difference for wave arrivals from points on the device on the surface plane perpendicular to the point of observation are within one-quarter wavelength at the highest frequency of interest ."

This is an important distinction between high frequency and low frequency measurement, criteria #4 can be satisfied at 95 Hz for a subwoofer of one square meter measured at one meter (ground plane), but a large system like you plan to measure will require a longer measurement distance, which unless elevated sufficiently will be affected by Boundary Interference.

Art

 

[DonStauffer]

For on-axis measurements I just gate out the floor reflection and merge in near-field measurements to fill in below the cutoff frequency. 40" is high enough for substantial overlap for a good merge. Hopefully real off-axis data won't be needed below the gating cutoff.

 

[DonStauffer]

Spkr Turntable.mp4 - Google Drive

 

[DonStauffer]

Progress update:

CAD design finished.

The base will be made of 2x4s, arranged so the carousel will be supported at almost all points.I'll use 3 half-sheets of 5/8" plywood: One for the centering ring and disk for the carousel, and two to make the 48" top surface double-thick for rigidity. De-sta-co makes a "straight line action" clamp that seems perfect for a "brake" to lock the platform at a particular angle. I have yet to design something like "detents" or a pin & hole arrangement to easily choose angles in 10 degree increments, but I have worked out the geometry.

The carousel delivery was delayed; I expect it tomorrow. The clamp may arrive by the weekend.

 

[DonStauffer]

Carousel arrived. It's well made. It does have about 1/16" of horizontal play, which wouldn't matter for its intended function, but I'm considering ways to reduce that a lot. The clamp (lock) also arrived, and looks perfect for the job. I still think this is going to be good.