Lowering Fs.

[OMNIFEX]

Originally Posted by tinitus

I suppose it shows a very low tuned vented box, and what we see is port tuning ?

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.

[audiomagnate]

Originally Posted by OMNIFEX

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.

Now I'm even more confused. What are the "two drivers"?

[sreten]

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.

[OMNIFEX]

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.

[doctordata]

Originally Posted by audiomagnate

I have a pair of discontinued Dayton 15" PA woofers I would like to use in a pair of home subwoofers: Dayton Audio PF385-8 15" Cast Frame Driver 4" VC 295-080

Opinions, ideas, comments?

Have a look at STAHL - 'Acebass' Synthesis of Loudspeaker Mechanical Parameters by Electrical Means .
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

[Juhazi]

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

[audiomagnate]

Originally Posted by doctordata

Have a look at STAHL - 'Acebass' Synthesis of Loudspeaker Mechanical Parameters by Electrical Means .
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

How does this differ from conventional servos?

[j.michael droke]

Originally Posted by audiomagnate

Thanks again streten. The boxes are currently tuned to 35 Hz and I don't like the sound. It's great for rock but other music makes it sound thumpy and resonant. I'll pick up a can of undercoating and give it a shot. My scale is not accurate at those weights so I'll just keep spraying until I get to my desired Fs.

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

[woody]

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

[badman]

Originally Posted by sreten

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 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.