If your measurements are at the same distance they won`t show much difference.
But go back like 2m or 3 or more then you might notice the spl is much higher far away compared to the enclosure with no flares at all.
This is due to improved air coupling.
Maybe there is a misunderstanding somewhere.
I am talking about something like this:
Now why would they complicate the design unnecessarily?
Maybe because it works.
I'd really like to see the theory that supports something like that. AFAIK the only way that I know to affect the change in SPL when measuring at difference distances from a source is if the effective size of the source is changed.
I am talking about something like this:
Now why would they complicate the design unnecessarily?
Maybe because it works.
That's not a waveguide. That's a flared vent, and yes they will make a difference at higher SPL levels as particle velocity and therefore turbulence are reduced at the end of the vent. At lower SPL levels the difference will be less noticeable (and measurable).
The "waveguides" I'm referring to are the 45 degree angled sections that some builders install along and inside the vent.
And BTW, some builders do "complicate their design unnecessarily". I'm a crappy box-builder, so I try not to do that
. I don't incorporate anything in my designs unless they suit an audible and measurable purpose.
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Bob Brines also did the same measures and found no difference. I nly put them in when i need the bracing.
dave
Scott uses them all the time in his designs... the latest a horn-loaded vent on a DBR for the Cube Magus 8.
dave
Well, it is a 48 Hz (slightly lossy) MLTL, so it was going to be short any way you look at it
. When I did the vented box comparison, the output at the low end was similar (the MLTL's response was slightly better, if I remember correctly). The offset MLTL sim approach however allowed me to make sure that the 100 Hz ~ 200 Hz region was as smooth as possible, extending the usable passband of the build. A vented box with a vent this size and length will likely feature response aberrations in this region, the location and effect of these aberrations being somewhat unpredictable unless the sim program does a good job of matching the build's actual topology. And of course that extra internal panel does brace and reinforce the box somewhat
. All in all, for the cost of an extra panel in the box, I think it's a better approach.
I'm pretty active on Steve Meade's forum.
The way most T-lines are designed in the car audio SPL world just about kills me. "make the t-line area equal to Sd, make the length equal to the 1/4 wavelength of the driver's Fs. Put the driver at the closed end". That's all they do. I've tried to help people by simulating stuff for them in HornResp. I rarely get much traction.
Interesting.
I know a lot of people don't want to learn Hornresp.
One thing that I've found works fairly consistently, is to tune a transmission line to the same frequency as a vented box with the same driver, and make it the same volume.
IE, if you're vented box calculator says you need a two cubic foot box that's tuned to 30hz, you can use the same criteria for a tline and wind up with a response curve that's almost identical. This is because of Hoffman's Iron Law, of course.
I know a lot of people don't want to learn Hornresp.
One thing that I've found works fairly consistently, is to tune a transmission line to the same frequency as a vented box with the same driver, and make it the same volume.
IE, if you're vented box calculator says you need a two cubic foot box that's tuned to 30hz, you can use the same criteria for a tline and wind up with a response curve that's almost identical. This is because of Hoffman's Iron Law, of course.
Yup, and no matter how much you manipulate the taper, when you adjust to get a flat response, the total box volume tends to be that of a vented alignment using the same driver.
The main advantage of a using a TL for subwoofer duty is not just getting a slightly lower F3 (the large vent does help in getting this, particularly at higher SPL levels as there is less vent compression). It also provides a means of manipulating the impact of vent resonances to extend the passband of a box that has such a large vent. And advantage that's basically given away if you use the "classical" approach of locating the driver right at the start of the line.
That design can result in a fairly large peak at the lower end of the passband. Perhaps the car audio crowd likes this
.
That design can result in a fairly large peak at the lower end of the passband. Perhaps the car audio crowd likes this
I suspect you are correct in regards to the peak.
It also often greatly reduces the mechanical power handling of the sub, but most of these folks don't seem very concerned about that.
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