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Multi-Way Conventional loudspeakers with crossovers

Bass reflex not so good
Bass reflex not so good
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Old 3rd July 2020, 08:50 PM   #31
ScottG is offline ScottG  United States
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..and yet it works well in this capacity.

It does not have to be *braced, a very basic "tie-down" (like 4 corners) suspending the "sheet" (..more of a panel really) does the job well. I should note that I've done this sort of suspension before with a very open-weave thin fiber poly net (..cheap fish net).

It will generate turbulence, but that turbulence interferes very little with the driver's motion because it's not well coupled to the driver (..not being on-wall).

It does need to be off of the walls though, or you start into mechanical motion losses of the driver. (..in this respect the sheet should be about 4" less than the interior of the rear panel on all sides: in total 8" less horizontally and 8" less vertically at a minimum.)

4 inch rockwool has decent absorption down to below 200 Hz (almost 150 Hz).

*moreover, frame or "window-pane" bracing common to supporting a rockwool panel creates turbulence that does interfere with the motion of the driver.
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Last edited by ScottG; 3rd July 2020 at 09:04 PM.
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Old 3rd July 2020, 10:36 PM   #32
francesco81rs is offline francesco81rs  Italy
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I would tend to exclude the problem about the mechanical solidity between the front panel and the woofer, or the sealing between the woofer and the panel.
The woofer seat is obtained with a CNC machine and is "perfectly" planar.
Each bolt is inserted into the wood with a kind of "spider" that couples the bolt to the wood itself.
I attach a photo hoping it will be a little clearer.
ScottG wrote that it could be the woofer itself that manifested that peak around 250hz, I tried to take a measurement of its impedance (free air) but I don't see peaks around that frequency.
Ah I also tried to take an impedance measurement with the two woofers in series, but the trend of the curve does not seem very different (clearly they are now 16 ohms nominal).
Attached are the graphics of the woofer and the curves of the woofers in the cabinet connected in series.
I don't know if I'm wrong but I'm more and more convinced that it's an internal resonance problem.
Do you think it would be a good idea to try to fix some pyramid-shaped wooden blocks on the bottom of the case (opposite side of the front panel) to try to break the wave front?
The idea of ​​the panel suspended diagonally to me seems good to try!
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File Type: png impedence-416-8b-log.png (66.9 KB, 42 views)
File Type: png bass-series-no-fill-lin.png (77.7 KB, 41 views)
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Old 3rd July 2020, 11:22 PM   #33
ScottG is offline ScottG  United States
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1st driver is really clean, 2nd has a very minor "bump" around 130 Hz.

The 414 (which is why I thought it would have been the driver's):

https://5e8772ee-a-62cb3a1a-s-sites....attredirects=0
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Old 3rd July 2020, 11:35 PM   #34
ScottG is offline ScottG  United States
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Quote:
Originally Posted by francesco81rs View Post

I don't know if I'm wrong but I'm more and more convinced that it's an internal resonance problem.

Do you think it would be a good idea to try to fix some pyramid-shaped wooden blocks on the bottom of the case (opposite side of the front panel) to try to break the wave front?

The idea of ​​the panel suspended diagonally to me seems good to try!

I think you are correct. You might try calculating your interior cabinet dimensions with this app:

Internal Standing Wave Calculator for Loudspeaker Enclosures and Rooms


Other than the double-sheet of 4" rockwool solution, you could put in blocks of honeycomb ceramic (break-up standing waves).

Another idea would be bag's of perlite. Blocks (or panels) of perlite should also work.

In all instance though, make sure the bags or blocks are off of the interior cabinet surfaces as much as possible. (..again, 4" minimum.)

The more stiff the fill, the lower the reduction in reflections though. ..and you could always do a combination of that rear interior panel + bag/blog to alter the standing wave AND reduce reflections.
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Last edited by ScottG; 3rd July 2020 at 11:41 PM.
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Old 3rd July 2020, 11:46 PM   #35
ScottG is offline ScottG  United States
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Quote:
Originally Posted by francesco81rs View Post
I would tend to exclude the problem about the mechanical solidity between the front panel and the woofer, or the sealing between the woofer and the panel.
The woofer seat is obtained with a CNC machine and is "perfectly" planar.
Each bolt is inserted into the wood with a kind of "spider" that couples the bolt to the wood itself.
I attach a photo hoping it will be a little clearer.

Yeah, it looks good. I'd make sure that I caulked a seal around it for final installation though.

Note though that it COULD be the baffle itself.

That panel is large and there is a lot of stress/vibration put on it with the two drivers (..and the ports).
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