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Multi-Way Conventional loudspeakers with crossovers

Thick or thin, braced or mass loaded?
Thick or thin, braced or mass loaded?
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Old 28th January 2018, 08:28 PM   #1
stephenmarklay is offline stephenmarklay  United States
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Default Thick or thin, braced or mass loaded?

At some point I was interested enough to read the BBC papers and in particular the construction of the LS3/5a monitors.

In a nutshell, if you have not cared to read that stuff, they found that thin walls with extra mass (bitumen paper) was better at taming wall resonance than thicker plywood or MDF. Harbeth et al. still uses this.

I recently read the Kef LS50 white paper, where they talk about the LS3/5a as well. They found that the major issue was the baffle mounting (or driver) created a lot of mechanical vibration (as opposed to air pressure which was low) that contributed to box coloration.

They also found an more interesting, but not surprising perhaps, is that adding braces did not fix this at all. It was not until the did not attach the brace to the walls but some damping material instead that the energy was allowed to dissipate to an inaudible level.

I am curious what technique that you guys are using.

This is not a “my [insert your thing] is better than yours.” I am curious what you guys prefer, if you have measured it etc.

Thanks so much
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Old 28th January 2018, 10:59 PM   #2
planet10 is offline planet10  Canada
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Thick or thin, braced or mass loaded?
I just posted this in another thread that is relevant.

Strangest Box Material You used or Have Seen?

dave
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Old 28th January 2018, 11:09 PM   #3
nigelwright7557 is offline nigelwright7557  United Kingdom
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I tend to stick to 18mm plywood.
My cabinets can be just screwed for sealed cabinets or glued for W bins.
I don't seem to get much vibration from either.

If the panel material is stiff (>18mm) then I would expect sound waves to just bounce back off them rather than rattle the panel. unless you are seriously pumping out hundreds of watts.

I ran a mobile disco with two 18mm dual driver cabinets for many years and it was very loud and sounded great.
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Old 29th January 2018, 02:02 AM   #4
stephenmarklay is offline stephenmarklay  United States
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Quote:
Originally Posted by nigelwright7557 View Post
I tend to stick to 18mm plywood.
My cabinets can be just screwed for sealed cabinets or glued for W bins.
I don't seem to get much vibration from either.

If the panel material is stiff (>18mm) then I would expect sound waves to just bounce back off them rather than rattle the panel. unless you are seriously pumping out hundreds of watts.

I ran a mobile disco with two 18mm dual driver cabinets for many years and it was very loud and sounded great.

Thanks nigelwright. Yeah from what I have seen the actual sound waves (air pressure) does cause some vibration but not typically at high amplitude.

On the other hand the vibration from the driver(s) does transit to the rest of the enclosure and can be at a similar level to the actual speaker driver itself!
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Old 18th February 2018, 11:27 AM   #5
Jollygreenaudiophile is offline Jollygreenaudiophile  United States
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Thick or thin, braced or mass loaded?
I just finished a set of mid-bass/mid-range cabinets using 6-8" woofers. 5 foot tall 16 x 16". Since I love this range of frequencies and usually have them turned up a bit I figured I would try and for once follow all my instincts to their logical conclusions wherever that went. It went "expensive"! to "cut" the sound waves I found 1" Maple dowels I cut just short enough to get into the cab. Pre-drilled on one end with a anchor and stud I opened them until hand tight. I also added "springs" over the studs. When trying to dissipate ANY form of energy you either "Transfer" or "Transduce" it. Moving it away or into another form. If you just move it . Then you should be guiding it to a transducer. Your cabinet acts as a transducer changing the sound into vibration. The best way to get rid of vibration is to destroy it. Transduce that form of energy into heat. Then let it dissipate through air convection or even transfer it "Heatsink" to an area condusive to cooling. Some materials will transduce vibration into heat like "Sorbothane". But you must first mechanically give the Sorvothane a static load. This changes the material;s form from solid to liquid. In liquid form It will transduce the vibration into heat and the liquid itself moves the heat in a convection pattern until equalized "Gone". Also "Sound Diodes work well as they mechanically only let the energy travel in one direction. Trapping it "effectively" to then be transduced by other means. Vibration follows random patterns always seeking the easiest path. A tensioned spring will transduce vibration into heat as well. But it usually just a random occurrence that the vibration "finds" the spring. Isolation spike DO work as a guide for vibration. But you need something at the pointy end to transduce it. Like a rubber pad/spring/sorbothane ect. A quartz tip on a spike set in the middle of three ball bearings will "I'm told" transduce vibration as well. Those cabinets I was working on? They weighed roughly 58lbs empty. Add 40lbs. for transducers, "speakers" so 98lbs. After I added all of the above i could think of? 305lbs. Mass loading works too!
The results after completion were amazing. I went to adjust something behind one the first time I fired them up. As I passed the plane of the front baffle the "almost" silence was deafening. And the most articulate mid-bass I ever hear was coming from the front o0f the cabinet. Nothing from within could i distinguish. Vibration is a very insidious thing. Which is maybe why we call them "Parasitic Modes of Vibration"
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Old 18th February 2018, 12:04 PM   #6
eduard is offline eduard  Netherlands
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Hello,
Some decades ago the French did a lot of test with cabinet materials. In one of the test they made a small monitor with several cabinets. The one working the best was a sand damped double cabinet. In order to make the sand work they made the innner 8mm and outer cabinet5 mm thickness. There are some small blocks of wood placed between inner and outer cabinet. The sand is15 mm thick.Which seems rather thin but using thicker material the vibration would kind of stay inside the wood. If the wood would vibrate it will be damped by the sand. If the cabinet would be to sturdy the sand will just add weight.
If you search online you will find the French l'audiophile magazine.The number is 36 published in 1985.
Greetings, Eduard
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Old 18th February 2018, 07:20 PM   #7
midrange is offline midrange  United Kingdom
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Thick or thin, braced or mass loaded?
This low tech experiment agrees with the BBC method for midrange, but found thick and solid better for bass.

Cabinet walls and Loudspeaker Energy Preservation - [English]
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