Hi and sorry to jump in but if damping is key then at B&W with the Matrix concept they are quite wrong instead.
They brace extensively the cabinet to get high stiffness on the panels i guess
https://www.youtube.com/watch?v=IOnbkyjfQOI
Regards, gino
They brace extensively the cabinet to get high stiffness on the panels i guess
https://www.youtube.com/watch?v=IOnbkyjfQOI
Regards, gino
Last edited:
Seriously, you need to start studying the details and not keep repeating the same things. You look for comfirmation of your own theory in all designs.
It has been said so many times; Stiffnes is great if you can bring the ressonance well above the pass band of the driver. Which B&W does. They use a seperate midrange cabinet that is floating on the bass cabinet and the midrange driver itself floats against the midrange sphere.
They also describe that the cabinet has high mass and high damping.
Too strong focus on one aspect of a construction will lead to mediocre/bad result.
The simple cost and cost effective solution has been mentione many times. Using a properly braced plywood or MDF cabinet (curved sides will also increase stiffnes) you can get the panel ressonance out of the woofers frequency band. You should be able to raise it to an octave above the woofers XO without using exotic materials.
Above this area you need damping. Most effect and for very little cash will come from decoupling your midrange and tweeter. If you worry about the speaker chassis moving (wich has been pointed out that you should not) fasten the chassis to a mass anchor inside the encosure and decouple this from the box.
For the panels itself, the CLD aproach is probably the most effective. Again this can be done with relatively cheap materials.
Add stuffing to the enclsure to reduce internal standing waves that can trigger the panel ressonances or reflect out through the cone.
Spend the money you saved on alu/panzerholtz + expensive machining/tools on other stuff that will have dramatic effect. DSP crossover to precisely controll the FR and phase of the drivers & room EQ below Schroeder, a low difraction cabinet layout, a custom bass system that suits the room with large surface area etc etc.
Best regards
Last edited:
I have found this thread very interesting. Last year I built some active three way sealed speakers with high quality drivers (scanspeak and SB), high quality active crossovers, and MC2 amps.
I am extremely pleased with the outcome, but am continually dismayed by the 'stethoscope test' on my cabinet walls.
They are made from 18mm MDF with substantial oak and MDF cross-bracing, and 8-12mm of bitumen/aluminum (silent coat) internal damping. Over the bitumen is a 2cm layer of high density wool felt, and finally they are densely stuffed with glass fibre.
I was hoping with a well braced, well damped, well stuffed enclosure I would be safe - but it appears resonance is hard to tame!
I have even tried external application of tiles with 'green glue' type damping adhesive, which didn't seem to achieve much. So I am left with two options:
1. Either start again with the cabinet. ( I would now probably try either 9mm ply with 12-18mm bitumen damping and minimal bracing, or a full complex CLD enclosure with chipboard/plywood.)
2. De-couple the drivers from the current cabinet.
Given the complexity of the first option and cost, I have decided to try decoupling the drivers first - particularly as this has been shown to have a massive effect on panel resonance if done properly.
To decouple the drivers I am using two techniques:
1: I am making new baffles from stabilised hardwood which will be epoxied onto the current MDF baffles - if I understand things correctly this should provide greater damping and stiffness through the use of the two different materials bonded with epoxy - ? form of CLD, as the new hardwood baffle will only be tied to the rest of the cabinet via the epoxy.
2. 3mm sorbothane gaskets for all the drivers (given results shown demonstrate that the mid and tweeter can excite just as much resonance as the woofer) which are held to the new baffle with thin countersunk head screws and rubber O-rings - to prevent the metal screw from touching the speaker frame.
I hope that with these two measures I should get a good degree of decoupling of the drivers from the cabinet.
I will report back on my success - hopefully with photos and measurements in the next few weeks!
I am extremely pleased with the outcome, but am continually dismayed by the 'stethoscope test' on my cabinet walls.
They are made from 18mm MDF with substantial oak and MDF cross-bracing, and 8-12mm of bitumen/aluminum (silent coat) internal damping. Over the bitumen is a 2cm layer of high density wool felt, and finally they are densely stuffed with glass fibre.
I was hoping with a well braced, well damped, well stuffed enclosure I would be safe - but it appears resonance is hard to tame!
I have even tried external application of tiles with 'green glue' type damping adhesive, which didn't seem to achieve much. So I am left with two options:
1. Either start again with the cabinet. ( I would now probably try either 9mm ply with 12-18mm bitumen damping and minimal bracing, or a full complex CLD enclosure with chipboard/plywood.)
2. De-couple the drivers from the current cabinet.
Given the complexity of the first option and cost, I have decided to try decoupling the drivers first - particularly as this has been shown to have a massive effect on panel resonance if done properly.
To decouple the drivers I am using two techniques:
1: I am making new baffles from stabilised hardwood which will be epoxied onto the current MDF baffles - if I understand things correctly this should provide greater damping and stiffness through the use of the two different materials bonded with epoxy - ? form of CLD, as the new hardwood baffle will only be tied to the rest of the cabinet via the epoxy.
2. 3mm sorbothane gaskets for all the drivers (given results shown demonstrate that the mid and tweeter can excite just as much resonance as the woofer) which are held to the new baffle with thin countersunk head screws and rubber O-rings - to prevent the metal screw from touching the speaker frame.
I hope that with these two measures I should get a good degree of decoupling of the drivers from the cabinet.
I will report back on my success - hopefully with photos and measurements in the next few weeks!
Been trying to do the same for a 1.5 litre full range driver and two opposing passive radiators, tried lots of wall treatments.. the answer is driver decoupling (see some of speakerdave posts) sorbothane only works if you don't tighten up too much,
PS All cabinets "sing' at a certain frequency
PS All cabinets "sing' at a certain frequency
Last edited:
Just a quick thought that could be way off base... If I was to saw through a cross brace thereby leaving a 1-2mm gap, then apply a flexible gap filling adhesive into the gap (silicone sealant for instance), wouldn't this lower stiffness and increase damping??
If so, I could also try this...... Crazy idea? ��
If so, I could also try this...... Crazy idea? ��
Composite marble is made using a polymer resin binder. Resins can have damping factors of 0.2 and greater. Confirm the damping factor for the actual composite from the manufacturer.
Damping factor Q = 1/(damping factor)
0.1 Good
0.2 Better, good minimum criteria for new design
0.4 Very good
0.6 Excellent
Natural stone products, including marble and soapstone, are not well damped.
Damping factor can be calculated from the Q if it's given, as Q = 1/(damping factor).
Last edited:
The damping material would best be put in shear, not tension in this case. So you could overlap the cross braces as much as possible so they effectively slide against each other when vibrating, with the damping material in between. As the brace is already installed, you could cut through the brace, then connect the two on the flat sides with a third panel, using only the damping adhesive for attachment. This again would be putting the flexible adhesive in shear.
As you originally proposed, damping with tension and compression of compliant materials can be effective. Compliance and preload is important in these cases.
Last edited:
Cross bracing can be used for damping. There is a patent for the idea. Silicon would not be the best damping adhesive. Green Glue or other adhesive made for constrained layer damping applications.
https://www.google.com/patents/US7270215
Last edited:
I realize silicone sealant looks good as a dampening material but it isn't, get a cured plug of silicone and drop it on a concrete floor,, what does it do ? bounce .. yes! no good as dampening material, what you need is something that has no "bounce".. something that absorbs the kinetic energy .
OK green glue, or suitable appropriate acoustic treatment alternative...
It remains an interesting option! It would require very little cost/work to modify the existing braces, and potentially dramatically improve damping of the cabinet walls. Trouble is, once I have sawn through the oak braces, there is no going back....
It remains an interesting option! It would require very little cost/work to modify the existing braces, and potentially dramatically improve damping of the cabinet walls. Trouble is, once I have sawn through the oak braces, there is no going back....
"It remains an interesting option! It would require very little cost/work to modify the existing braces, and potentially dramatically improve damping of the cabinet walls. Trouble is, once I have sawn through the oak braces, there is no going back...."
Depending on the configuration of the brace, could you rejoin if necessary with additional plates using two part epoxy put in shear?
"Don't cut the braces, they are dampening opposing vibrations"
Hopefully the brace is stiffening the cabinet, reducing displacement/vibration of the opposing side. That's a viable concern. Is their any test data available to help make the best decision?
Depending on the configuration of the brace, could you rejoin if necessary with additional plates using two part epoxy put in shear?
"Don't cut the braces, they are dampening opposing vibrations"
Hopefully the brace is stiffening the cabinet, reducing displacement/vibration of the opposing side. That's a viable concern. Is their any test data available to help make the best decision?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.