I recently completed some aperiodically loaded GRS 12" subs and figured I'd post here.
I was previously running GRS 10" sub drivers in 1-ft^3 sealed boxes (heavily stuffed w/ fiberglass) and was happy but felt I was sometimes approaching the excursion limits of the 10" drivers.
The Parts Express page indicated a 1.5 ft^3 box would yield an F3 of 37-Hz for the 12" drivers. I thought that was pretty decent (these are for music only, and there would be room gain) and suggested these as an Xmas gift my wife could wrap and put under the tree (she was freaking-out that I didn't have anything to unwrap).
After placing the order it became apparent that the recommended sealed box would result in a 4.5-db peak at approx. 60-Hz (very near where one of my room modes seems to live). My current (at the time) 10" GRS subwoofers seemed to accommodate smaller overstuffed sealed boxes better (less peaky), at least according to WinISD.
Attempting to play with the "Advanced" parameters in WinISD by setting Ql=3 to model an aperiodic enclosure (according to a post by Jeff Bagby), I was only able to reduce that peak by about 1.5-db, but it shifted a little higher/closer to my room mode.
So I attempted to play with Qa and model an enclosure that was heavily stuffed AND aperiodic. I had no idea whether this made any practical sense, but was able to reduce the peak to a total of about 1.5 or 2db, so I proceeded with the cabinet builds.
The result is I've got 1.6-ft^3 enclosures (two "subs"), about 1.5-pounds of polyester filling in each, and each with an aperiodic port of my own design.
There was little science involved in designing the ports. I tried to keep the area of the opening consistent with what two commercial aperiodic ports would have provided (based on rule-of-thumb recommendations that I'd want two of the commercial plastic ports for a 12" driver).
I winged it when it came to how much stuffing to use in the aperiodic ports, using two layers of batting. I sort of quickly tossed them together so I could give them a listen first, then I'd measure, then adjust. If necessary, rinse/repeat.
I was very careful removing the old 10" subs, thinking there was better than a 50% chance I'd want to put them back because the new subs would be too peaky/awful. I feared I'd be unable to tame the 12" drivers properly with my aperiodic port experiment.
My very initial listening impression was that the new woofers were less peaky than the old. I had previously thought I had a bit of a problem with the 10" models as some tracks like "Hotel California" from "Hell Freezes Over" didn't sound quite right. That initial bass was less resolved than I've heard it before. There is this pitch change going on in that bass and the 10" models weren't doing it justice, while the 12" were doing very nicely.
I went back and looked at my earlier WinISD predictions...
In modeling the 10" model with Ql=100 and Qa=5, WinISD indicates a Qtc of .839 (yeah, I know that is already sort of high).
In modeling the 12" model with Ql=3 and Qa=5, WinISD indicated a Qtc of 1.063 (gasp).
So the 12" model should be even more peaky/boomy than the fairly peaky 10", but that isn't what my ears were telling me.
Next, I got the Woofer Tester out and tested both the old GRS 10" subs, and the new GRS 12" subs in their completed cabinets. I'm relieved to know my perceptions were accurate and I'm not suffering from builder's bias.
The GRS 10" completed subs measured Qts (which Jeff Bagby says = Qtc) is 1.0248 and Fs is 58-Hz. My enclosures are approx. 1-ft^3. My initial WinISD model didn't account for the driver's volume, so if I allow for the driver's approx. volume and specify .85-Ft^3 in WinISD, and change Qa to 10 for a heavily stuffed box, WinISD predicts 1.012. So predicted is very close to actual, it seems.
The GRS 12" completed subs measured Qts (= Qtc) of .6625 and Fs is 40-Hz. My enclosures are approx. 1.6-ft^3. But once again, my models didn't take into account the driver's volume. Using 1.4-ft^3 in WinISD, and changing Qa to 10 for heavily stuffed, and setting Ql to 3 per Jeff Bagby's post, WinISD predicts a Qtc of 1.187. So it seems practice beats theory this time. I think Troels Gravesen says you can't model aperiodic enclosures, maybe he is right.
As I said above my ports are somewhat easily adjustable because I figured there would be some trial and error in getting these setup, but it looks like I'll leave them as-is.
I've included a few pics. One shows one of the subs under an end table (there is another on the other side of the loveseat, under an identical end table). I'm also including pics of the inside and outside rear panel (showing the aperiodic port construction). In a nutshell, I've used compressed poly batting between two pieces of plastic screening, between the hardwood panels recessed into the rear panel.
Also screen shots of the Woofer Tester results of the old and new subs.
I know these aren't everyone's cup of tea, they're inexpensive drivers with stamped frames, etc.
But they sound pretty darn good.
I was previously running GRS 10" sub drivers in 1-ft^3 sealed boxes (heavily stuffed w/ fiberglass) and was happy but felt I was sometimes approaching the excursion limits of the 10" drivers.
The Parts Express page indicated a 1.5 ft^3 box would yield an F3 of 37-Hz for the 12" drivers. I thought that was pretty decent (these are for music only, and there would be room gain) and suggested these as an Xmas gift my wife could wrap and put under the tree (she was freaking-out that I didn't have anything to unwrap).
After placing the order it became apparent that the recommended sealed box would result in a 4.5-db peak at approx. 60-Hz (very near where one of my room modes seems to live). My current (at the time) 10" GRS subwoofers seemed to accommodate smaller overstuffed sealed boxes better (less peaky), at least according to WinISD.
Attempting to play with the "Advanced" parameters in WinISD by setting Ql=3 to model an aperiodic enclosure (according to a post by Jeff Bagby), I was only able to reduce that peak by about 1.5-db, but it shifted a little higher/closer to my room mode.
So I attempted to play with Qa and model an enclosure that was heavily stuffed AND aperiodic. I had no idea whether this made any practical sense, but was able to reduce the peak to a total of about 1.5 or 2db, so I proceeded with the cabinet builds.
The result is I've got 1.6-ft^3 enclosures (two "subs"), about 1.5-pounds of polyester filling in each, and each with an aperiodic port of my own design.
There was little science involved in designing the ports. I tried to keep the area of the opening consistent with what two commercial aperiodic ports would have provided (based on rule-of-thumb recommendations that I'd want two of the commercial plastic ports for a 12" driver).
I winged it when it came to how much stuffing to use in the aperiodic ports, using two layers of batting. I sort of quickly tossed them together so I could give them a listen first, then I'd measure, then adjust. If necessary, rinse/repeat.
I was very careful removing the old 10" subs, thinking there was better than a 50% chance I'd want to put them back because the new subs would be too peaky/awful. I feared I'd be unable to tame the 12" drivers properly with my aperiodic port experiment.
My very initial listening impression was that the new woofers were less peaky than the old. I had previously thought I had a bit of a problem with the 10" models as some tracks like "Hotel California" from "Hell Freezes Over" didn't sound quite right. That initial bass was less resolved than I've heard it before. There is this pitch change going on in that bass and the 10" models weren't doing it justice, while the 12" were doing very nicely.
I went back and looked at my earlier WinISD predictions...
In modeling the 10" model with Ql=100 and Qa=5, WinISD indicates a Qtc of .839 (yeah, I know that is already sort of high).
In modeling the 12" model with Ql=3 and Qa=5, WinISD indicated a Qtc of 1.063 (gasp).
So the 12" model should be even more peaky/boomy than the fairly peaky 10", but that isn't what my ears were telling me.
Next, I got the Woofer Tester out and tested both the old GRS 10" subs, and the new GRS 12" subs in their completed cabinets. I'm relieved to know my perceptions were accurate and I'm not suffering from builder's bias.
The GRS 10" completed subs measured Qts (which Jeff Bagby says = Qtc) is 1.0248 and Fs is 58-Hz. My enclosures are approx. 1-ft^3. My initial WinISD model didn't account for the driver's volume, so if I allow for the driver's approx. volume and specify .85-Ft^3 in WinISD, and change Qa to 10 for a heavily stuffed box, WinISD predicts 1.012. So predicted is very close to actual, it seems.
The GRS 12" completed subs measured Qts (= Qtc) of .6625 and Fs is 40-Hz. My enclosures are approx. 1.6-ft^3. But once again, my models didn't take into account the driver's volume. Using 1.4-ft^3 in WinISD, and changing Qa to 10 for heavily stuffed, and setting Ql to 3 per Jeff Bagby's post, WinISD predicts a Qtc of 1.187. So it seems practice beats theory this time. I think Troels Gravesen says you can't model aperiodic enclosures, maybe he is right.
As I said above my ports are somewhat easily adjustable because I figured there would be some trial and error in getting these setup, but it looks like I'll leave them as-is.
I've included a few pics. One shows one of the subs under an end table (there is another on the other side of the loveseat, under an identical end table). I'm also including pics of the inside and outside rear panel (showing the aperiodic port construction). In a nutshell, I've used compressed poly batting between two pieces of plastic screening, between the hardwood panels recessed into the rear panel.
Also screen shots of the Woofer Tester results of the old and new subs.
I know these aren't everyone's cup of tea, they're inexpensive drivers with stamped frames, etc.
But they sound pretty darn good.
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Sorry for the delay, hadn't noticed the question.
The ports are made from 1/8" tempered hardboard (the stuff that is smooth both sides). They're 6.5" x 6.5".
There are two, ones is glued/screwed to the inside of the cabinet, and the second is screwed into weld nuts that are glued to the inside unit.
Hope that helps.
Yep, that is exactly what it is, two layers.
So think of it was a sandwich. The two pieces of hardboard (each with the four large holes) are the bread.
Then there are two pieces of plastic gutter screen (purchased at Menards).
And between those is two layers of the 3/4" bonded Dacron (purchased at Walmart).
I added the gutter screen because I figure the Dacron would need support to prevent from blowing out the hole, and yes, I was correct, there can be quite a bit of air movement there.
Could you just "walk us through" those screen shots? What are we looking at and what does it tell us?
The speaker measurements are what we need to see, more than detailed invocations of the sims to three decimal places. Or how the near-field or open-field measurements compare to the sims.
Thanks.
B.
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There are five pics...
The first one (1) is just a shot of one of the completed new subs living under one of the end tables.
Second (2) shows the inside of the back panel, with the inside piece of the aperiodic panel glued and screwed in. You can see some extra holes, that is where my weld-nuts get glued in (I just hadn't done it yet). Weld nuts are like tee-nuts, but don't have prongs. I hot-glue them into the holes, and the screws that hold the outside aperiodic panel in place thread into those weld-nuts.
(3) Shows the rear of the completed sub with the aperiodic port assembled. The eight screws you see are inserted through holes in the rear panel and thread into the weld nuts I refer to in #2 above. So the screws pull the entire assembly together.
(4) The Woofer Tester result for the old (10" sealed) subwoofer. You can see a Qts (which is = to Qtc) of 1.0248 and Fs (which is = Fc) = 58.5177-Hz.
(5) The Woofer Tester result for the new (12" aperiodic) subwoofer. You can see a Qts (again = Qtc) of 40.8985, and Fs (= Fc) of 40-Hz.
Hope that helps, let me know if you have any questions.
Oh, the weld nuts I use, I get them from McMaster. The part # for these is 90594A111. They are narrow base. I apply hot melt glue to them, and push them into the holes. The hot melt glue squeezes out and makes a little sort of mortise for the nut, so it won't spin.
This is the same method I use for mounting drivers, they won't budge from the hole, removing them requires heat, or you'll damage the baffle. I've posted about this method at techtalk.parts-express.com a few times over the years but I don't think anyone has copied it yet.
You can also use tee-nuts, just break the prongs off. You just want something that ideally isn't perfectly round.
Hope that helps, let me know if you have other Q's.
Thanks. I gather that's a set-up for measuring T/S values? Do you have measurements of the sound output?
B.
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