Did I read that right? Using 25 hz (lower) and (a realistic) ~48hz (upper) the LARGER chamber and it's port(s) "tune" the closure's lower frequency; the smaller chamber, etc tunes the UPPER?! Well, finally I feel like I got my head around how this alignment functions.
For years I've pondered which does what? Only then I could begin w"the correct" box/vent relationship for my chosen driver that gives max frequency extension and power handling for the bottom octave (mid-low 20s). Then "juggle" the other port dimensions (slightly) to "EQ" the 2d&3rd octaves for flat, flat response to about 90hz, letting my HT processor handle the rest.
Every sub review I've read over the last 10-15 years claims flat to... only to see almost an octave above the F3 the graph slowly taper down illustrating the F3 5-6 dB below 45-60hz output.
I have more to post. Hafta leave RIGHT now. Thanks for reading this far
Tony
Tony
Yep, that's what it is in a nutshell.
The larger chamber is basically a bass reflex. It is tuned for your desired F3.
When the cone moves backwards, some of the air is fired into a smaller chamber internally through a port as well. Since the smaller chamber is also tuned to the outside, we now get another bass boost. This FREE bass is in the form of a bandpass (due to the two ports) and it is approx double the F3. So, if you design F3 for 50Hz, you will get an extra kick at about 100Hz, where your mid-bass is.
Yep, that's what it is in a nutshell.
The larger chamber is basically a bass reflex. It is tuned for your desired F3.
When the cone moves backwards, some of the air is fired into a smaller chamber internally through a port as well. Since the smaller chamber is also tuned to the outside, we now get another bass boost. This FREE bass is in the form of a bandpass (due to the two ports) and it is approx double the F3. So, if you design F3 for 50Hz, you will get an extra kick at about 100Hz, where your mid-bass is.
I don't think so. I think I read your response correctly. When I built the 3CR-Ti project I measured the tunings as well as listened; and the one behind the driver is the highest tuning.
Think of it this way- the lower you get, the longer the port has to be. The lowest tuning in a DCR has 2 port lengths to go through. Longer vent = lower Fb.
In fact it's more of a resonance chamber. It does induce an additional phase rotation in the impedance for every additional chamber- just like when you add a port to a sealed box. The port firing into the lower chamber lowpasses the sound, as that is the function of a port. You can configure it to yield boost, and the classic alignment likely does this a tad, but it's more meant to smooth the bass range in the response and limit the excursion of the driver.
Later,
Wolf
Here are vent measurements from a DCR I've built for a 4" Tang Band fullrange. There is no adjustment for vent area, so don't look at the relative levels.
Blue: near-cone
Red: vent1 (larger chamber - where the driver is located)
Green: vent2 (smaller chamber)
Blue: near-cone
Red: vent1 (larger chamber - where the driver is located)
Green: vent2 (smaller chamber)
An externally hosted image should be here but it was not working when we last tested it.
That was the original object, AFAIK. At low frequencies the driver effectively 'sees' the total volume of both chambers, Fb being set by this & the total dimensions of the two ports venting into the room. The upper chamber has its own Fb and tuning ~an octave higher, so following the usual reflex deflection behaviour, you get reduced driver excursion over a wider BW -can be useful when you consider that the majority of LF energy in rock & some other genres is in the 70Hz - 120Hz region. I quite like DCRs. They don't usually have a massive edge (if any) over a standard BR, but they're valid enough.
The Fostex-style DBR probably gets even less attention than DCR. I've yet to build one, but from simulations in Hornresp, it seems like it will produce a somewhat better-damped bass response (keepoint) than the equivalent-size straight-BR. If one wants to slightly oversize a BR to get a bit deeper bass, this might be worth considering. The mid-upper bass notch produced by the DBR seems to be of slightly greater magnitude than DCR though, but probably on a narrow enough bandwidth so as not to be night&day difference - see my blue trace two post back. I forget how the two schemes compare excursion-wise, but the hard limit is still down low and likely set by overall Vb/Fb, so maybe it's moot. Might depend on driver used and resulting tunings (4" FR versus 15" woofer for example) and application.
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It has been awhile since I built mine, so I might be recalling incorrectly.😱
For posterity, here's the 3CR near with and without filter (black/red), and the nearfield responses of the ports. However- I cannot tell you which is which as it's been too long ago.
Later,
Wolf
what would you change to get less on your violet plot/output thereby attenuating the upper compared to the green plot? I realize that is a simple question with, in this case, a complex answer. BTW this is for an LFE-only Home Theater application.
I’m grateful for your time and consideration. Tony
what would you change to get less on your violet plot/output thereby attenuating the upper compared to the green plot? I realize that is a simple question with, in this case, a complex answer. BTW this is for an LFE-only Home Theater application.
I’m grateful for your time and consideration. Tony
Hi gp4Jesus
I don't really know. Maybe you can try stuffing the port.
I'm curious as to why you're using a DCR for the LFE output.
Wouldn't a subwoofer be better?
Regards
Mike
I don't really know. Maybe you can try stuffing the port.
I'm curious as to why you're using a DCR for the LFE output.
Wouldn't a subwoofer be better?
Regards
Mike
Stuff the port venting the large chamber to the room?
I did a REALLY bad job of explaining the what and why. OTOH I read the your post again that I quoted. That said, the DCR is not the best choice, possibly the worst choice for an LFE* as it* demands a wider, flat FR. I thought the “Weems DCR” produced more output w/less power & driver movement.
I’m sorry I have yet to buy the materials to build said “sub.” For the last 10+ years I’ve researched this (to death) in attempt to build what I want, first try w/the fewest miscues or mistakes. Most certainly a subwoofer will get an LFE done.
I’m still gonna experiment but w/less enthusiasm expecting to settle w/single chamber ported. I’m grateful for your patience. Tony
have you succeeded w/this calculator?
I messed w/this for HOURS years ago - couldn’t figure it out to save my life. I see “Help” info I’ve never seen before for which I’m VERY grateful. I’ll give it a whirl in due course - working on taxes.
Thanks for your patience. Tony.