Hey, folks...
I created very small mid-bass enclosures (for 6.5" woofers) in the bottom of my doors (0.07 ft^3). I know that's tiny, but (without getting into ALL the parameters of the system), I didn't need them to play lower than ~120 Hz, so I thought I could "get away with it."
The overall system sounds good, but I couldn't help but wonder whether giving those drivers a little extra "breathing room" might make it sound even better. So, I entertained the idea of making these small, cylindrical enclosures into aperiodic membranes by adding a "vent" to the back of each. There are some good write-ups online for constructing them, so I felt confident.
Before diving in and cutting up what I had, I created a "test enclosure" --a small box with the same volume as the enclosures in my doors. Before creating my first vent, I drilled a small hole (0.5" diameter) into the center of the box, directly center behind the woofer's magnet (just to see what might happen). I stuffed the enclosure full of polyfil and remounted the 6.5" woofer.
TL;DR:
I pressed on the cone, and it (predictably) allowed more excursion, with a gentle puff of air released from the hole. Curious as to how it would sound, I hooked it up and my objective seemed to have been achieved! It boosted output between 90-110 Hz by at least 6dB. And I didn't do any REW measurements (yet), but it sounded nice with music, too! And there was no chuffing from the hole (that was my initial concern).
On a first blush, this "small hole solution" seems to WORK... but am I missing something??
Is it because the enclosure is so small? Because of the frequency band (~90-300 Hz)? Because of the polyfil? Did I just get lucky??
I couldn't find any record anywhere of anyone having done this successfully, so I full expect that I AM missing something!
If anyone has any thoughts about this (specifically, whether the hole can be used in lieu of an aperiodic membrane in certain cases--rather than WHY I would do that instead of a million other 'better' things), I would love to hear from you!
Thanks!!
I created very small mid-bass enclosures (for 6.5" woofers) in the bottom of my doors (0.07 ft^3). I know that's tiny, but (without getting into ALL the parameters of the system), I didn't need them to play lower than ~120 Hz, so I thought I could "get away with it."
The overall system sounds good, but I couldn't help but wonder whether giving those drivers a little extra "breathing room" might make it sound even better. So, I entertained the idea of making these small, cylindrical enclosures into aperiodic membranes by adding a "vent" to the back of each. There are some good write-ups online for constructing them, so I felt confident.
Before diving in and cutting up what I had, I created a "test enclosure" --a small box with the same volume as the enclosures in my doors. Before creating my first vent, I drilled a small hole (0.5" diameter) into the center of the box, directly center behind the woofer's magnet (just to see what might happen). I stuffed the enclosure full of polyfil and remounted the 6.5" woofer.
TL;DR:
I pressed on the cone, and it (predictably) allowed more excursion, with a gentle puff of air released from the hole. Curious as to how it would sound, I hooked it up and my objective seemed to have been achieved! It boosted output between 90-110 Hz by at least 6dB. And I didn't do any REW measurements (yet), but it sounded nice with music, too! And there was no chuffing from the hole (that was my initial concern).
On a first blush, this "small hole solution" seems to WORK... but am I missing something??
Is it because the enclosure is so small? Because of the frequency band (~90-300 Hz)? Because of the polyfil? Did I just get lucky??
I couldn't find any record anywhere of anyone having done this successfully, so I full expect that I AM missing something!
If anyone has any thoughts about this (specifically, whether the hole can be used in lieu of an aperiodic membrane in certain cases--rather than WHY I would do that instead of a million other 'better' things), I would love to hear from you!
Thanks!!
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Hey, Dave... I think you've tapped into the crux of what I'm curious about.
If you added up the surface area of all the small holes in that diffuse array and instead drilled a single, centrally-located 'large' hole of that same surface area, would it 'behave' in the same manner?
My gut would be to do it your way... but I don't know enough about these things to give a GOOD explanation of why.
Thanks for your thoughts!
If you added up the surface area of all the small holes in that diffuse array and instead drilled a single, centrally-located 'large' hole of that same surface area, would it 'behave' in the same manner?
My gut would be to do it your way... but I don't know enough about these things to give a GOOD explanation of why.
Thanks for your thoughts!
Ah... yes... the surface area of the walls... that makes sense!
Yeah, that restrictive membrane was my plan. Maybe I had 'dumb luck' with my single hole?
I always appreciate your insights, Dave. Thanks for posting!
Yeah, that restrictive membrane was my plan. Maybe I had 'dumb luck' with my single hole?
I always appreciate your insights, Dave. Thanks for posting!
A single hole "works", sort of, as mentioned above, but by itself does not provide enough friction so not enough damping.
Besides that, it will certainly whistle at some frequencies.
As mentioned above, you need way more friction, either by a lot of tiny holes or by making air flow between some damping material fibers, which are even narrower paths.
Besides that, it will certainly whistle at some frequencies.
As mentioned above, you need way more friction, either by a lot of tiny holes or by making air flow between some damping material fibers, which are even narrower paths.
David Weems suggests the area of the resistive vent should be around 10 square inches per cubic foot of enclosure volume.
For your 0.07 cubic foot enclosure that would indicate a vent of area 0.7 square inches, i.e., a hole of diameter 0.944 inches - stuffed with damping material.
For your 0.07 cubic foot enclosure that would indicate a vent of area 0.7 square inches, i.e., a hole of diameter 0.944 inches - stuffed with damping material.
Gershman Grande Avant Garde interesting resistive build on the bass platform
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It also depends on the Q of the driver, those holes might not do anything.
Typical car speakers are meant for more of an IB alignment.
When I tried using the small apertures w/resistive fiber in some boxes, the results weren’t any different than if the entire back of the cabinets were open. These were some decent, JBL 4” drivers, and I did have a 1” panel of foam behind them. I just sealed the cabinets and added more of the foam to lower the peaks I saw at 100-120hz. They took more power that way also, and breakup was much more gradual.
What I have done in my car doors behind my 6.5” drivers, is to reinforce the thin sheet metal with a 3/8” thick sheet of polyethylene (cutting board), all around the speaker. Secured using some wafer head screws every couple inches or so.
Then use a piece of acoustic duct (closed cell) foam directly behind the driver. Also have a few loosely rolled bundles of regular bubble wrap in the corners where the window mechanisms won’t get tangled up in them, or block the water drains.
Another method is to wrap fiberglass batting in thin drop cloth plastic and secure with tape. I haven’t done that before.
This has killed a good bit of the back wave and made it possible to eq the rest into sounding more like what you would expect.
Typical car speakers are meant for more of an IB alignment.
When I tried using the small apertures w/resistive fiber in some boxes, the results weren’t any different than if the entire back of the cabinets were open. These were some decent, JBL 4” drivers, and I did have a 1” panel of foam behind them. I just sealed the cabinets and added more of the foam to lower the peaks I saw at 100-120hz. They took more power that way also, and breakup was much more gradual.
What I have done in my car doors behind my 6.5” drivers, is to reinforce the thin sheet metal with a 3/8” thick sheet of polyethylene (cutting board), all around the speaker. Secured using some wafer head screws every couple inches or so.
Then use a piece of acoustic duct (closed cell) foam directly behind the driver. Also have a few loosely rolled bundles of regular bubble wrap in the corners where the window mechanisms won’t get tangled up in them, or block the water drains.
Another method is to wrap fiberglass batting in thin drop cloth plastic and secure with tape. I haven’t done that before.
This has killed a good bit of the back wave and made it possible to eq the rest into sounding more like what you would expect.