The port tuning is actually higher than where the peak lies. I would imagine it is the coupling affect of two drivers in addition to using large cabinets for Electrovoice wrote a paper about such a phenomenon 30 years ago.
Hi,
The port tuning is the lowest point of the impedance between the
two peaks, the upper peak is related to driver Fs and the lower
peak something I can't quite put my finger on in physical terms,
but its nothing to do with driver Fs.
Fbox is always higher than Fs except for TL's where the options
make it complicated, and generalisations don't help much.
rgds, sreten.
The port tuning is the lowest point of the impedance between the
two peaks, the upper peak is related to driver Fs and the lower
peak something I can't quite put my finger on in physical terms,
but its nothing to do with driver Fs.
Fbox is always higher than Fs except for TL's where the options
make it complicated, and generalisations don't help much.
rgds, sreten.
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It is very complicated indeed. Cabinet shape, size, wadding, mass air load in the chamber, in addition to the affects of the port offer too many variability’s at times. I think many assume reflex cabinets are simplistic. What they are is more forgiving for mistakes by new designers than building a horn. This is why I literally measure the cabinet instead of assuming simulation design software results is written in stone.
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Have a look at http://www.diyaudio.com/forums/subw...r-mechanical-parameters-electrical-means.html .
Gave me perfect bass down to 20 Hz with 3 opamps and a couple of components in a 57L ported enclosure with my JBL K140 15" .
Cheers ,
Rens
Is it wise to electrically "change" or mask physical properties of a driver?
To a certain extent propably yes, but I wonder how much distortion you get at high output.
There are many spekers doing that however, Philips MFB, Acebass, etc. Some subwoofers are claimed to sound good and to have less distortion
motional feedback subwoofer - Google-haku
To a certain extent propably yes, but I wonder how much distortion you get at high output.
There are many spekers doing that however, Philips MFB, Acebass, etc. Some subwoofers are claimed to sound good and to have less distortion
motional feedback subwoofer - Google-haku
modifying Daytons
Hi there a: Hope the can of gooope from PE has not arrived yet. Numeous alternatives have been provided that would be better than "spaying till well done" and are not detructive, allowing trying other concepts, if neede. Hope you will post your reults . .....regards, Michael
Hi there a: Hope the can of gooope from PE has not arrived yet. Numeous alternatives have been provided that would be better than "spaying till well done" and are not detructive, allowing trying other concepts, if neede. Hope you will post your reults . .....regards, Michael
You may also consider the Linkwitz Transform circuite. At one time Linkwitz sold
these boards but I don't think they are currently avaliable.
Linkwitz Transform Subwoofer Equaliser
these boards but I don't think they are currently avaliable.
Linkwitz Transform Subwoofer Equaliser
The lower and upper peaks are just the remnants of the Fc peak with the null applied. Move towards true aperiodic and the bandwidth of the tuning increases and eliminates the dual lumps.
Bottom line, the 19hz lump is NOT a lowering of Fs. No standard sealed or vented box lowers Fs.
Attachments
The fs of the loudspeaker in the cabinet usually shifts downwards if the cabinet is optimum sized or larger than the loudspeaker's requirements.
The link below offers the TS Parameters of one of my older Beyma 18-inch drivers.
Beyma Speakers - Beyma 18LX60 speaker - Beyma 18LX60 1200 watt 18" woofer for all bass applications. Beyma 18LX60 and other Beyma 18" speakers here.
This is the measured impedance curve of the loudspeaker in the box.
As you can see, the loudspeaker offers an fs of 27 Hz in free air and, 19.04 Hz in the box. A 3 cubic foot box for a 15-inch pro driver is not going to give you low bass for the limiting factor is the enclosure size.
The issue with this is that when you run a "parameter test" once a speaker is installed in a box, the software doesn't know that the 1st impedance peak is not a raw-driver's Fs (remember, Fs= free-air(!) resonance)----and since it doesn't know, it still goes ahead uses that 1st peak to calculate what it thinks is the driver's free-air resonance, and spits out the results without alerting you that the driver is not really suspended in free-air.
But it is flawed because there is no Fs once a driver is enclosed. There is nothing "free air" about a driver "enclosed"---a kind of oxymoron. The reason for this is that once a driver is enclosed it now forms one driven resonant system with the enclosure and vent, that are now inseparable from each other. This goes back to University Physics 101 with the studies of a driven damped double-mass double-spring harmonic oscillator.
This is why a vented enclosure's primary system is called Fb, not Fs (similarly for a sealed box, the system resonance is Fc). Rest assured, the primary system resonance (Fb, or "port tuning" as it is known) for that enclosure you posted is just slightly below 40Hz, right where the impedance dip is.
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