fibreglass damping
- Thread starter Professor smith
- Start date
Yes Fibreglass can be ejected out of the port - not really ideal for domestic use.
Although the air flow is 2 way, the air as it flows into the port tends to flow from all directions, while the air leaving the port is thrown forward in one direction, so there is a displacement of air. I noticed this with a small computer sized sub. Turning up the sub so that a gust of air can be felt from the port I held a small paper windmill in the flow, You need to leave a distance for the return air flow, too close and the impeller stops. The windmill always turns one way.
Using fiberglass or rockwool in a vented cabinet is not a good idea. Manufacturers have been banned from using it in vented cabinets for some time (decades) that's why you see so much foam in use today. In a sealed cabinet there should not be an issue (if the driver has a solid dust cap) and unless the driver uses Ferro fluid in the voice coil gap and there is any way for the fiberglass fragments to enter the motor assembly such as a vented pole piece. Kapoc is a very good damping material made from short fiber cotton I believe. Pure natural wool is also excellent and can be uesd as a loose fill or in a vented cabinet used in the form of felt to line the cabinet walls. Perlite is excellent but is more difficult to use as it must be contained in a thin film bag to position it and to prevent dust and particles entering either the driver or the air in your room. There are some long fiber nylon damping materials that are said to be very good (close to wool) but they are not commonly available.
There have been studies in the HVAC industry showing that small quantities of fiberglass entering your home (from insulated walls and ceiling) can be an irritant and so they have developed methods to seal around electrical fixtures and such.
An American medical researcher by the name of Hulda Clark who worked for the Canadian Government for over 20 years researching tissue biopsies said that she always found fiberglass fragments in lung tumors. There are safer options than fiberglass.
There have been studies in the HVAC industry showing that small quantities of fiberglass entering your home (from insulated walls and ceiling) can be an irritant and so they have developed methods to seal around electrical fixtures and such.
An American medical researcher by the name of Hulda Clark who worked for the Canadian Government for over 20 years researching tissue biopsies said that she always found fiberglass fragments in lung tumors. There are safer options than fiberglass.
Will this be sufficient to prevent emission of fibreglass particles in a ported speaker?
Vance Dickason, in his Loudspeaker Cookbook, found that polyesters were not very effective at increasing the apparent volume of an enclosure nor damping the sound.
Fiberglass was noticeably better.
So sealed fiberglass batts are probably the handy way to go. I wouldn't do open fiberglass with a ported enclosure, because it is true that ports can rectify and "eject" air.
There are foams and such, but you'll have to get the book and see his extensive tests of different brands and see what's available today.
Fiberglass was noticeably better.
So sealed fiberglass batts are probably the handy way to go. I wouldn't do open fiberglass with a ported enclosure, because it is true that ports can rectify and "eject" air.
There are foams and such, but you'll have to get the book and see his extensive tests of different brands and see what's available today.
Bagging fiberglass in a pillowcase would be adequate to prevent quantities of glass fibers being ejected from the port.
Using string stapled in a zig-zag pattern over the fiberglass also works.
Fiberglass is effective for keeping upper reflections (above 400 Hz or so) from being heard through the ports.
That said, this is the Subwoofer forum, fiberglass damping in ported subs used below 125 Hz or so generally reduces output and does little else, as fiberglass is fairly transparent to low frequencies.
If fiberglass is fairly transparent to low frequencies, why would fiberglass stuffing reduce sub output?
from:Volume filling a reflex box
" Volume filling of a reflex enclosure can present a potential problem because the filling acts to decrease the effective port Q and reduce its output by increasing the loss resistance [3]. As an example using the boxnotes download [4], the resonances inside a 10 litre 167 x 267 x 200mm box are ..."
Sorry, I didn't realize subwoofer drivers didn't produce any frequencies above 80Hz.
Anyway, my point (and a nitpicky one at that) was that you can't have "negligible effect" together with "significant effect".
One point that just occcured to me was that a speaker driver manufacturing guy I know, once told me that he had found various voice coils that had been damaged by the ingress of fibreglass. Maybe not surprising, given the abrasive nature of the material, and the amount of air that a vented speaker can move!