Cool, all I could see was what looks like both sides of the vent hole being rounded over and not knowing what diameter you used, wasn't sure if the hole is big enough to slide a large enough tube inside it to fiddle with tuning.
None I'm aware of unless there's something here: Collo's DIY Subwoofer Enclosures
Without test gear, historically, one starts with lining the top, one side and back with 1" acoustic fiberglass insulation or similar, then play whatever music has the lowest bass and/or loudest [mid] bass to find the vent length that makes it sound the tonally smoothest over the widest BW and if the vent's output tends to be distracting in any way ['boomy'/'loose'/'flabby'/'chuffing'], it gets damped somehow either by loosely covering the back of the driver with an acoustic 'blanket' being for extreme situations and stuffing the vent and/or just stretching layers of expanded knit cloth/whatever over the face of it.
Nowadays, it's become popular to just add loose polyfil or similar stuffing ~halfway down the cab [or lower]. I personally don't like the slightly muffled tonal character it can add to wide BW drivers and judging by the number of folks that simmed a smooth response in MathCad only to pull much of it back out, so starting out with minimal damping seems a good plan.
GM
None I'm aware of unless there's something here: Collo's DIY Subwoofer Enclosures
Without test gear, historically, one starts with lining the top, one side and back with 1" acoustic fiberglass insulation or similar, then play whatever music has the lowest bass and/or loudest [mid] bass to find the vent length that makes it sound the tonally smoothest over the widest BW and if the vent's output tends to be distracting in any way ['boomy'/'loose'/'flabby'/'chuffing'], it gets damped somehow either by loosely covering the back of the driver with an acoustic 'blanket' being for extreme situations and stuffing the vent and/or just stretching layers of expanded knit cloth/whatever over the face of it.
Nowadays, it's become popular to just add loose polyfil or similar stuffing ~halfway down the cab [or lower]. I personally don't like the slightly muffled tonal character it can add to wide BW drivers and judging by the number of folks that simmed a smooth response in MathCad only to pull much of it back out, so starting out with minimal damping seems a good plan.
GM
GM,
Using a Parts Express 4" dia. flared port,"the12volt.com" site calls for a 2.55" long 4"dia. port for a 45 cu. ft. cabinet for 45 Hz.
My question for ear tuning is , if you start with longer tube, how do you know when to stop shortening it? I can use a tone CD & a sound meter to adjust. Do I look for the highest output at the port? I suppose I could use various lengths of PVC to determine the desired final length.
Using a Parts Express 4" dia. flared port,"the12volt.com" site calls for a 2.55" long 4"dia. port for a 45 cu. ft. cabinet for 45 Hz.
My question for ear tuning is , if you start with longer tube, how do you know when to stop shortening it? I can use a tone CD & a sound meter to adjust. Do I look for the highest output at the port? I suppose I could use various lengths of PVC to determine the desired final length.
GM,
PS: The existing ports are 4 inch dia. with only the outside edge rounded over 1/8th inch.
I can use a Parts Express port that will fit (no o.s. or i.s. flare) or increase the size of the hole to accept the PS flared o.s. & i.s. port.
What do you consider equal to 1" acoustical fiberglass? Is polystyrene foam board or foam rubber as good or better?
PS: The existing ports are 4 inch dia. with only the outside edge rounded over 1/8th inch.
I can use a Parts Express port that will fit (no o.s. or i.s. flare) or increase the size of the hole to accept the PS flared o.s. & i.s. port.
What do you consider equal to 1" acoustical fiberglass? Is polystyrene foam board or foam rubber as good or better?
Typically, MLTLs damp the vent enough to render simple reflex cab tuning moot except as a starting point, so for a given vent mach the MLTL's vent will have the same or smaller area, but be shorter; conversely, for a given area/length the MLTL will be tuned lower.
45 ft^3 ?! I assume you mean 4.5 ft^3, though not sure what this has to do with the MLTL which is somewhat smaller. Regardless, their math is off quite a bit assuming a typical cubic or acoustic ratio reflex as Fb should be around 35-36 Hz. FWIW, the ~3.7478 ft^3 MLTL should be about the same whereas the simple reflex would be up around ~39 Hz, so has significant vent damping.
Back before computer simming programs and driven with a high output impedance, I typically tuned it to Fs and if it sounded too bass heavy, I damped the vent. Later, with low output impedance [< 0.5 ohm], I started at Fs and went up [shorter and/or larger vent] or down [longer vent] till it sounded tonally balanced. Unfortunately, many [most?] folks are somewhat tone deaf, so I guess it boils down to what sounds pleasing to them and/or their significant other if a factor.
Right, start with just the baffle depth vent I simmed and try one or more longer vents, just slide them in partway and use Blu-Tack or similar to seal around it as any air leak, even a pinhole, can not just negate the longer length, but tune it even higher than the baffle thickness vent.
Nothing I’ve ever used, though the late, lamented Miraflex R-25 worked well for stuffing apps. Never tried any foam-based insulation except as cab material for super high Qt drivers. No clue about foam rubber.
GM
45 ft^3 ?! I assume you mean 4.5 ft^3, though not sure what this has to do with the MLTL which is somewhat smaller. Regardless, their math is off quite a bit assuming a typical cubic or acoustic ratio reflex as Fb should be around 35-36 Hz. FWIW, the ~3.7478 ft^3 MLTL should be about the same whereas the simple reflex would be up around ~39 Hz, so has significant vent damping.
Back before computer simming programs and driven with a high output impedance, I typically tuned it to Fs and if it sounded too bass heavy, I damped the vent. Later, with low output impedance [< 0.5 ohm], I started at Fs and went up [shorter and/or larger vent] or down [longer vent] till it sounded tonally balanced. Unfortunately, many [most?] folks are somewhat tone deaf, so I guess it boils down to what sounds pleasing to them and/or their significant other if a factor.
Right, start with just the baffle depth vent I simmed and try one or more longer vents, just slide them in partway and use Blu-Tack or similar to seal around it as any air leak, even a pinhole, can not just negate the longer length, but tune it even higher than the baffle thickness vent.
Nothing I’ve ever used, though the late, lamented Miraflex R-25 worked well for stuffing apps. Never tried any foam-based insulation except as cab material for super high Qt drivers. No clue about foam rubber.
GM
GM,
Thank you for your patience with my mistake. My error was in converting from ft^3 to liters with 144 instead of 1728 !
Yes, the MLTL is your design of 3.7478 ft^3.
Unless I misunderstand, you have me perplexed about a trial port length. I was under the impression that a port tube length mattered whether it was inside or outside the enclosure & that only tubes cut to length would work.
I'll be using your recommended 1" audio fiberglass lining (top, back & one side) without the usual dacron stuffing to start.
Please give me your opinion of PSP-inc.com flared ports.
Thank you for your patience with my mistake. My error was in converting from ft^3 to liters with 144 instead of 1728 !
Yes, the MLTL is your design of 3.7478 ft^3.
Unless I misunderstand, you have me perplexed about a trial port length. I was under the impression that a port tube length mattered whether it was inside or outside the enclosure & that only tubes cut to length would work.
I'll be using your recommended 1" audio fiberglass lining (top, back & one side) without the usual dacron stuffing to start.
Please give me your opinion of PSP-inc.com flared ports.
Happy Holidazes and all that jive!
You’re welcome!
Yeah, I’m pretty much lost without the little CONVERT freeware program and all the conversion tables I’ve generated in Excel from it: Convert for Windows - joshmadison.com
True, and a hole in a baffle is a ‘tube’ vent. For high aspect ratio cabs, whether it’s baffle or bottom firing can matter also, i.e. where in the cab is the vent opening referenced to its long dimension and driver location; but my comment had to do with ease of vent tube removal, temporary sealing. If you use a flanged vent, then of course it’s not an issue.
Never used any store bought flared vents nor seen any measured comparisons, so my only opinion is that longer ones probably need to be supported at the internal end to keep from potentially ringing and the flare probably isn’t large enough to do much damping except at very low vent excursions, i.e. low SPL.
Acoustically, my ‘adventures’ in horn design experimentation convinced me that short of a round over large enough to support the desired fundamental that there will be mouth turbulence and that empirically finding the right density of damping material to line its perimeter will work just as well even for a sharp transition such as a driver mounted on a flat baffle without rebating it.
GM
You’re welcome!
Yeah, I’m pretty much lost without the little CONVERT freeware program and all the conversion tables I’ve generated in Excel from it: Convert for Windows - joshmadison.com
True, and a hole in a baffle is a ‘tube’ vent. For high aspect ratio cabs, whether it’s baffle or bottom firing can matter also, i.e. where in the cab is the vent opening referenced to its long dimension and driver location; but my comment had to do with ease of vent tube removal, temporary sealing. If you use a flanged vent, then of course it’s not an issue.
Never used any store bought flared vents nor seen any measured comparisons, so my only opinion is that longer ones probably need to be supported at the internal end to keep from potentially ringing and the flare probably isn’t large enough to do much damping except at very low vent excursions, i.e. low SPL.
Acoustically, my ‘adventures’ in horn design experimentation convinced me that short of a round over large enough to support the desired fundamental that there will be mouth turbulence and that empirically finding the right density of damping material to line its perimeter will work just as well even for a sharp transition such as a driver mounted on a flat baffle without rebating it.
GM
GM,
It may be a nit-picking question but, I'm unable to find 1" thick fiberglass. All I've found is 3/4" & 2" thick.
Should I resort to attempt the slicing of the 2" down to 1" or use either the 2" or 3/4" ?
It may be a nit-picking question but, I'm unable to find 1" thick fiberglass. All I've found is 3/4" & 2" thick.
Should I resort to attempt the slicing of the 2" down to 1" or use either the 2" or 3/4" ?
Greets!
Slicing long ways? Hmm, that sounds like an exercise in futility. Here's what you're looking for and some hardware/big box stores will sell by the sheet. I typically get mine from a local heating/AC contractor and usually can buy his scraps even cheaper and sometimes get it for free.
If you still can't find it or it's too expensive, go with the 3/4" and if you feel the need for more damping just cut smaller panels to add at specific points, like beside or to the rear of the driver, though adding thickness to the top plate is often enough. I hold it in place with a cardboard washer and roofing nail sunk just enough to hold it in place. Some folks use the big plastic washer roofing nails, but I have plenty of already paid for cardboard. 😉 If you can shoot long staples, then that's fine too.
GM
Slicing long ways? Hmm, that sounds like an exercise in futility. Here's what you're looking for and some hardware/big box stores will sell by the sheet. I typically get mine from a local heating/AC contractor and usually can buy his scraps even cheaper and sometimes get it for free.
If you still can't find it or it's too expensive, go with the 3/4" and if you feel the need for more damping just cut smaller panels to add at specific points, like beside or to the rear of the driver, though adding thickness to the top plate is often enough. I hold it in place with a cardboard washer and roofing nail sunk just enough to hold it in place. Some folks use the big plastic washer roofing nails, but I have plenty of already paid for cardboard. 😉 If you can shoot long staples, then that's fine too.
GM
Yikes! I never paid more than a $1 for a 2x4 ft x 1" sheet, though based on most recent pricing in the link I just posted, $2 seems reasonable.
GM
The link was just to show what I get from local HTG/AC contractors for cheap, not that a casual DIYer would have to buy in bulk to get it. Home Depot near me use to sell it in rolls, but I couldn't even find it on the O-C website recently.
GM
GM
GM & Bob,
I thought I had answered before but I didn't check.
Anyone that would sell less than 6 had a higher final cost than the 6 from ATS so that's what I ordered.
The 12volt site's port calculator shows the 4" port at 3/4" length works out to be 49.5 Hz. What frequency should I tune the port for ? I gather that tuning it to a lower frequency than the speaker's 40 Hz would extend the bottom at the expense of the mid bass volume. Is 33 HZ too low to tune to?
I thought I had answered before but I didn't check.
Anyone that would sell less than 6 had a higher final cost than the 6 from ATS so that's what I ordered.
The 12volt site's port calculator shows the 4" port at 3/4" length works out to be 49.5 Hz. What frequency should I tune the port for ? I gather that tuning it to a lower frequency than the speaker's 40 Hz would extend the bottom at the expense of the mid bass volume. Is 33 HZ too low to tune to?
Bummer, guess I've just been lucky. Yesterday I got so many free scrap ~2x2 ft pieces that I could barely pack them into a pair of taped up king size waterbed sheets, so I could move them around/store in bulk for now. Had the devil of a time getting them up into the attic. Apparently, they had been cut too small for an access cover plate on some sort of undisclosed large machine project.
Typical port calculators are for reflex where the cab's air mass condition is one of ~ uniform particle density, so doesn't take a high aspect ratio's TL loading impact on vent size into account, which for a given net Vb will lower tuning. Best I can tell in a MathCad sim, it would tune it to ~41 Hz. Basically, for a given alignment you’re trading the longer vent required to tune a simple square or modestly rectangular cab for a long cab with a shorter vent and more importantly, getting a better damped response.
Anyway, as I mentioned back in post #55: http://www.diyaudio.com/forums/full-range/190224-enclosures-hemptone-fr8-2.html#post2599911, tuning is room, personal preference dependent, so experimenting with up to a 5" long vent [ ~30 Hz] is what I'd do if the simple reflex vent hole sounds too high tuned. I’m guessing it will be fine for most music unless the cabs are near/at a wall and/or corner.
Note that if driven with a high output impedance [SET or matching impedance] amp, tuning it to its actual Fs is usually best overall, so would require a somewhat larger diameter vent [5” dia./~45 Hz for reference].
GM
Typical port calculators are for reflex where the cab's air mass condition is one of ~ uniform particle density, so doesn't take a high aspect ratio's TL loading impact on vent size into account, which for a given net Vb will lower tuning. Best I can tell in a MathCad sim, it would tune it to ~41 Hz. Basically, for a given alignment you’re trading the longer vent required to tune a simple square or modestly rectangular cab for a long cab with a shorter vent and more importantly, getting a better damped response.
Anyway, as I mentioned back in post #55: http://www.diyaudio.com/forums/full-range/190224-enclosures-hemptone-fr8-2.html#post2599911, tuning is room, personal preference dependent, so experimenting with up to a 5" long vent [ ~30 Hz] is what I'd do if the simple reflex vent hole sounds too high tuned. I’m guessing it will be fine for most music unless the cabs are near/at a wall and/or corner.
Note that if driven with a high output impedance [SET or matching impedance] amp, tuning it to its actual Fs is usually best overall, so would require a somewhat larger diameter vent [5” dia./~45 Hz for reference].
GM
GM,
They're up & running. I'm impressed, not only with the stereo separation but with the delicate sound that seems to float away from the cabinets. I've never been one to attempt to describe 'wines', so I hope my description is understandable. There isn't any prominent bass. The initial installation of flared 4" ports with 5" straights sounds pleasant. I haven't tried any SPL/frequency tests with my tone CD & sound level meter, but my ears are satisfied so far. I presently have the enclosures in my loft next to the wide open living area downstairs.
Thanks for all of the help, gentlemen.
Lady Holiday never sounded so good.
Frank
PS: This turned out so well I'm ready to tackle whatever you can recommend for my Wharfedale Super 12 CS/AL speakers. They're presently in small OB's on top of cheap passive 15" subs. I had tried them in various enclosures but could never find any that didn't sound 'boxy'.
They're up & running. I'm impressed, not only with the stereo separation but with the delicate sound that seems to float away from the cabinets. I've never been one to attempt to describe 'wines', so I hope my description is understandable. There isn't any prominent bass. The initial installation of flared 4" ports with 5" straights sounds pleasant. I haven't tried any SPL/frequency tests with my tone CD & sound level meter, but my ears are satisfied so far. I presently have the enclosures in my loft next to the wide open living area downstairs.
Thanks for all of the help, gentlemen.
Lady Holiday never sounded so good.
Frank
PS: This turned out so well I'm ready to tackle whatever you can recommend for my Wharfedale Super 12 CS/AL speakers. They're presently in small OB's on top of cheap passive 15" subs. I had tried them in various enclosures but could never find any that didn't sound 'boxy'.
Greets!
Not really, unless you mean they don't have a typical reflex's 'boxy' sound. Regardless, glad you like them enough to want to make others!
My dim memory and a few factory cab references implies up to a ~10.4 ft^3 net cab tuned to 30 Hz depending on room location.
What have you tried besides the OBs?
GM
Not really, unless you mean they don't have a typical reflex's 'boxy' sound. Regardless, glad you like them enough to want to make others!
My dim memory and a few factory cab references implies up to a ~10.4 ft^3 net cab tuned to 30 Hz depending on room location.
What have you tried besides the OBs?
GM
GM,
Curses! I spoke too soon. The right speaker turned out to be intermittent due to a broken connection from the voice coil to the braided lead in. My attempted repair failed. It's on it's way to simplyspeakers.com.
I bought them off of ebay.
Frank
Curses! I spoke too soon. The right speaker turned out to be intermittent due to a broken connection from the voice coil to the braided lead in. My attempted repair failed. It's on it's way to simplyspeakers.com.
I bought them off of ebay.
Frank
GM,
I bought my first Wharfedale Super 12 CS/AL from my Dr. back in the late 50's. It was a new model in !956 & my Dr. had it installed in a Karlson enclosure. Later, when I tried stereo with an additional speaker, I tried a Hartley 'Boffle' that was a cube with a dozen curtains with diminishing holes from front to a solid curtain in the back. They were thick reinforced wool underlayment used at the time for carpeting.
I then tried the sand filled Open Baffle for the Super 12. It was designed by Briggs & intended for a 12" woofer & a paralleled 10", The Super Three tweeter had a capacitor & was the only crossover component. It almost caused a divorce when my wife found I had dried sand in her oven! The latest venture was a 16.5"x18"x28" OD sealed enclosure designed just for the 12 CS/AL in some long forgotten article. It was very well reinforced & lined with fiberglass.
I now have these speakers in small OB's With Fostex tweeters. The bass is handled with subs but I have tried tall OB's with dual parallel wired 12 CS/ALs & alternately a 12 CS/AL on top with a Wharfedale 12" woofer below having an inductance for a 100Hz crossover.
If I could be guided through the math necessary I'd entertain a very tall Sonotube or a square cross section MLTL enclosure. The subs should not be necessary & their elimination would help with wife acceptance.
Frank
I bought my first Wharfedale Super 12 CS/AL from my Dr. back in the late 50's. It was a new model in !956 & my Dr. had it installed in a Karlson enclosure. Later, when I tried stereo with an additional speaker, I tried a Hartley 'Boffle' that was a cube with a dozen curtains with diminishing holes from front to a solid curtain in the back. They were thick reinforced wool underlayment used at the time for carpeting.
I then tried the sand filled Open Baffle for the Super 12. It was designed by Briggs & intended for a 12" woofer & a paralleled 10", The Super Three tweeter had a capacitor & was the only crossover component. It almost caused a divorce when my wife found I had dried sand in her oven! The latest venture was a 16.5"x18"x28" OD sealed enclosure designed just for the 12 CS/AL in some long forgotten article. It was very well reinforced & lined with fiberglass.
I now have these speakers in small OB's With Fostex tweeters. The bass is handled with subs but I have tried tall OB's with dual parallel wired 12 CS/ALs & alternately a 12 CS/AL on top with a Wharfedale 12" woofer below having an inductance for a 100Hz crossover.
If I could be guided through the math necessary I'd entertain a very tall Sonotube or a square cross section MLTL enclosure. The subs should not be necessary & their elimination would help with wife acceptance.
Frank
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