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Cabinet bracing revisited…..
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Since he has two boxes he can easily do an A/B comparison. Initially he can just screw in the baffle to back braces that I suggested, so they're easily removed. But if left permanently they should be glued as well, as screws have a tendency to loosen over time.
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If you decide to experiment with added bracing, I would suggest adding something that can be easily removed. It is quite possible that you will like the sound of the unbraced cabinets better.
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Originally posted by lasse View PostYes, as a naval architect I fully understand the complexity of vibration control in structures.
My professor always told us in structural design to "think in deformations" and that was why the external bracing was natural to me (like a ship webframe stucture)
To stick with the ship analogy the motion of the ship w.r.t. to the sea will induce large low frequency distributed forces on the structure that cause large deflections but this non-resonant movement doesn't result in much sound. This is what happens with the forces from the internal pressure in speaker cabinet which only become large enough to be significant in the stiffness controlled region below the resonances. If you look at the measurements of the sound from the cabinets in the low frequency stiffness controlled region in the BBC publication linked above it is so low it has disappeared off the bottom of the plot. The speaker measured by the BBC is likely to be both sealed and with unbraced panels although probably not using a woofer with a floppy suspension. So reasonably representative of your speaker. In addition an acoustic suspension speaker isn't going to be bothered at low frequencies whether sound comes from the driver or from the cabinet because it is effectively all moving together +/- 180 degrees when the wavelength of sound is so large compared to the size of the cabinet. The engineers that designed your speaker will have been more aware of this than we are because it is basic engineering knowledge.
Sticking with the ship analogy the majority of the sound heard comes from the engines driving the ship structure into various resonant motions. This is also what happens with speaker cabinets with the loudest sound coming from resonances that are primarily forced by the drivers vibrating the structure directly and not the forces from the internal air pressure which are relatively weak at these higher frequencies. In addition to this the ear is more sensitive to resonances at higher frequencies as shown in the cited figure which the BBC exploited in their design approach. Note the cabinet resonances are quite close to the threshold of audibility and are not particularly intrusive. Poor cabinet design w.r.t. resonance control doesn't usually create in-your-face audible deficiencies.
Originally posted by lasse View Post
I beleive one could see the LST as "a AR3a on stereoids" as they share the same drivers and XO apart frpm the transformer that enables the user to modify the energy distribution in different ways.
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Yes, as a naval architect I fully understand the complexity of vibration control in structures.
My professor always told us in structural design to "think in deformations" and that was why the external bracing was natural to me (like a ship webframe stucture)
I beleive one could see the LST as "a AR3a on stereoids" as they share the same drivers and XO apart frpm the transformer that enables the user to modify the energy distribution in different ways.
Regards//lasse
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Whether connected by braces or not the baffle and rear panel move in opposite directions, which is outward when the cone moves inward, inward when the cone moves outward, in response to the air within the enclosure being alternately compressed and decompressed. Tying them together with braces reduces how much they move. The baffle being of smaller area would have less movement than the back if the internal air pressure changes were the only force applied to it, but it's not. Thanks to Newton's Third Law the force that pushes the cone and voice coil in one direction also pushes the driver frame, and the baffle along with it, in the opposite direction. BTW, you've been claiming to be working on your opus magnum for at least five years. Tolstoy only need six years to write 'War and Peace'.
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Originally posted by lasse View PostBracing is obviously something not totally aggreed upon.
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Having looked up the AR-LST it appears to be the side wall speakers for a 5.1 system with AR-3As as LCR speakers. Perhaps it was for one of the quadraphonic systems of the time?
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Hi,
I thank you for your feedback.
Bracing is obviously something not totally aggreed upon.
I realize that there is a third option for me and that is to do nothing at all.
Regards//lasse
Stockholm, Sweden
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Of course they move together if you add a couple of braces. What else are they going to do? To make matters worse the vibration of the driver is going to force this back to front mode efficiently. Side to side and top to bottom braces introduce similar kinds of modes but they don't get forced by the driver in the same way because of symmetry.
Tempted though I am to reply to your claim that you know how braces work it wouldn't be constructive. However I am currently developing, simulating and writing at some length on the engineering of speaker cabinets and will make a note to include a section on the pros and cons of the type of bracing you support. That should be a bit more constructive.
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They don't move together. They move in opposite directions. I'm more than a bit familiar with how braces work. It's what enables my pro-touring sound speakers to be built with nothing heavier than 1/2" plywood. My personal electric bass cabs are made of 1/8" and 1/4" plywood. They don't have panel vibrations, or panel sourced coloration.
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Originally posted by billfitzmaurice View PostRemove the woofer, glue two 30x30mm braces between the back and baffle. On the baffle place them at the driver screw holes at the 10:00 and 2:00 positions. This will stiffen both the back and baffle, while providing more secure fastening of the woofer. The effect on the back will be equivalent to doubling its thickness. Don't bother with spline braces, they're ineffective.
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Remove the woofer, glue two 30x30mm braces between the back and baffle. On the baffle place them at the driver screw holes at the 10:00 and 2:00 positions. This will stiffen both the back and baffle, while providing more secure fastening of the woofer. The effect on the back will be equivalent to doubling its thickness. Don't bother with spline braces, they're ineffective.
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Originally posted by lasse View Post
Please, give me your thoughts on this. Am I basically wrong in this? If not, which â€bracing-principle†do you recommend?
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