Presumably because if it isn't held firmly, it would end up on the bottom of the enclosure. 😉 In those cases, or at least the ones I've seen, the driver isn't usually physically fixed to the baffle by anything other than the pressure of the rear structure, so the clamping needs to be reasonable, though not excessive. I disassembled a pair of compact Monitor Audio HT speakers a few weeks ago that were built in that way.
Another thread on the subject Mechanical isolation of driver from cabinet
Lots of different opinions from experts, precious little evidence either way, what are we mere mortals supposed to deduce from it all?
Lots of different opinions from experts, precious little evidence either way, what are we mere mortals supposed to deduce from it all?
That you do the best research you can, and make a sensible judgement call which will vary depending on where your own priorities lie.
I'm only interested in the physical facts of the matter. Decoupling reduces cabinet vibration at the cost of a small decrease in output is my conclusion at the moment.
Have you any evidence of this? All I can find is calculations based on the relative moving masses of the cone and everything else. For example
Issues in speaker design - 2
The section on Driver Mounting Resonances seems particularly relevant to the topic under discussion.
Attachments
Andrew Jones showed that panel resonances in the cabinet are largely due to the transfer of motion from the driver frame to the cabinet via the mounting point. If you can totally decouple the driver frame from the cabinet, you significantly reduce the cabinet panel resonances. The is little to no excitation from the internal air pressure.
I use drivers without any baffle (AKA "nude" mounting) in open baffle systems. You are correct in that the reaction force from the cone movement will cause an equal movement of the driver (frame and motor), but because the mass ratio is relatively high (like 50:1) the frame movement, and thus the loss of SPL, is essentially zero or very close to it. It's a non-issue.
The problem is how to effectively decouple the driver, since mounting it by screws is very effective at holding it in place, and this is lost. One idea I have (DIY only) is to suspend the driver inside the cabinet using wires. You can do this by hanging the driver at its balance point. If that is not possible, you can hang it using a suspension behind the frame, plus one around the magnet. Getting it hung level and balanced takes a bit of fiddling. I just use monofilament nylon, 50lbs, which is marketed as an invisible picture hanging wire.
Once the driver can be hung freely, then it is just a matter of finding some compliant way to seal up the gap between the frame and the cabinet - the hole being thru-cut to a slightly larger OD than the drivers' frame. You could use, for example, a "flat attachment" style aftermarket surround that has just the right diameter and glue it to the frame and cabinet faces to span the gap. For example:
https://www.amazon.com/Grade-Speaker-Surround-Repair-Attachment/dp/B07CQ5RP6F
https://www.amazon.com/Pioneer-Flat-attach-Speaker-Surround-Repair/dp/B00CXXOFAI
This would be very compliant. It's way too soft to support the driver by itself, but with the driver weight hanging by the wires you can use as flimsy a material as you wish.
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And puts it all into the driver. The little bit of output lost are the tiny little details that give life & blood to the voices, instruments, and space the performance seems to take place in.
Choose your compromises. I have consistently found that given a decent cabinet, the downsides of decoupling the driver far outweigh the upside.
I started playing with this when we short circuited the gaskets in the, then new, KEF 105 midranges to make large gains in midrange DDR.
dave
Sorry Dave, if I take what you say at face value it makes no physical sense. I may be misunderstanding what you are saying, can you be more explicit about what you are saying happens to the small signal please?
Obviously you are not understanding.
Lets say a driver weighs 2kg and the cone mass is 15g. That is a 0.015/2 = 0.0075.
Lets say a driver & box weighs 20kg and the cone mass is 15g. That is a 0.015/20 = 0.00075.
Numbers PFA.
I can hear that difference. And i have often seen anecdotal reports of others hearing the same. All the details need to be right.
dave
Lets say a driver weighs 2kg and the cone mass is 15g. That is a 0.015/2 = 0.0075.
Lets say a driver & box weighs 20kg and the cone mass is 15g. That is a 0.015/20 = 0.00075.
Numbers PFA.
I can hear that difference. And i have often seen anecdotal reports of others hearing the same. All the details need to be right.
dave
That doesn't explain what is happening to the small signal. It doesn't disappear, what will happen is that it will suffer a miniscule amount of doppler and/or phase shift, is that what you are trying to say?
Not the right interpretation. The greater driver movement creates noise which that signal is now buried in and lost.
dave
dave