Overdamped vs. classic vented alignments

[sreten]

I've stated in several posts I like overdamped vented alignments
so I thought I try and illustrate why with a typical Vifa 165mm driver.

One version of overdamped is detuning the port by root 2.

Classic vs. overdamped.

C is flat to 60hz, O droops by 3db at 60hz.
C is -3dB at 44Hz, O is -3dB at 60Hz, nearly half an octave.
They are both -6dB at 38Hz.

Of particular interest is the dB loss between 30 and 40Hz,
for the classic it is 8dB, whilst for overdamped just over 3dB.
this makes a big difference in IMO.

The white line on the graph shows a 6dB/octave slope.

What should be obvious is that the classic alignment is rolling
off at 12dB/octave at F3 and will sound like it, i.e. the bass
cutoff will appear to be around 44Hz.

The overdamped alignment does not begin to approach 12/dB
per octave until 26Hz, the apparent bass cut-off being much
less linked to a particular frequency, I'd say just under 30Hz.

Transient response of the O vs. C is by definition much better.

When you factor in room gain and placement IMO a clear
winner emerges, the overdamped alignment is much more
flexible, the classic alignment must be mounted in free space.

sreten.

edit : picture deleted

[sreten]

oops, wrong picture, sreten.

[sreten]

Correction : paragraph 7 should read :

What should be obvious is that the classic alignment is rolling
off at at near 24 dB/octave at F3 and will sound like it, i.e.
the bass cutoff will appear to be around 44Hz.
Any room gain below 44Hz cannot be gainfully used.

Correction : paragraph 8 should read :

The overdamped alignment does not begin to approach 24/dB
per octave until 26Hz, and has a whole region near 6dB/octave
the apparent bass cut-off being much less linked to a particular
frequency, I'd say just under 30Hz.
This allows room gain to be used effectively.
F3 is 30Hz with 6dB of room gain at 30Hz, F6 becomes ~ 26Hz.

sreten.

[mikee12345]

I agree.

did you see my jbl alignment? i will EQ it slightly if i feel the midbass is lacking

I modeled it up to see how it would work before i bought it.

[roddyama]

Seconded.

If my TAD 1601a's were tuned for flat FR (in 125l box), it would be 3db @ 42Hz and roll off at 24db/oct below that. This alignment has an fb of ~40Hz. I've lowered the fb to ~30Hz, which is how I run it, and the f3 raises to >47Hz, but the f6 goes from 38Hz to 32Hz. I also have a boost circuit that can be used depending on the room gain/source material/mood. The boost will bring the total FR back to flat with f3 = ~28Hz and a brick wall roll off below that.

[mikelm]

Thirded

I have found that whether it is in a crossover cct or LS tuning or anywhere else, avoiding the classic 0.7 amplification factor or 'Q' in favour of a more gentle,more damped roll off creates a clearer and more coherent sound

Butterworth is history

long live Bessel !

( IMHO )

[mikee12345]

my basshorn tend to sound rather nice

expo 30hz being built hopefuly this month still-have more work to do on the CAD work of it...changing to 18mm MDF with bracing rather than 25mm MDF

Cheers!

[BAM]

Isn't an overdamped reflex box the basis for daline theory, where it looks like an overdamped ported box is ported using an antiresonant line?

[thoriated]

I do something similar with 3 paralleled 2226J's in my basement blasters, where the box is tuned to 26 hz but I have a series C, shunt L circuit (1320 uF from 4 330uF Solen polypropylenes in parallel & 30 mH) in front of them that resonates at around the same frequency providing 4 db boost between 30 hz and 40 hz passively with the boost tapering off until about 70 hz, plus giving a little boost below 26 hz by partly 'transforming' the bass reflex impedance peaks into amplitude gain. An advantage of this approach as compared to active boost, IMO, is that a voltage amplitude at the speaker terminals in the boost range that considerably exceeds that of the amplifier output capability is achievable without clipping, plus at least the upper load impedance magnitude peak is minimized. Cone excursion at a constant input voltage is maximum at around 40 hz with this setup that also blocks most energy below about 20 hz.

[mikelm]

Originally posted by thoriated
I do something similar with 3 paralleled 2226J's in my basement blasters, where the box is tuned to 26 hz but I have a series C, shunt L circuit (1320 uF from 4 330uF Solen polypropylenes in parallel & 30 mH) in front of them that resonates at around the same frequency providing 4 db boost between 30 hz and 40 hz passively with the boost tapering off until about 70 hz, plus giving a little boost below 26 hz by partly 'transforming' the bass reflex impedance peaks into amplitude gain. An advantage of this approach as compared to active boost, IMO, is that a voltage amplitude at the speaker terminals in the boost range that considerably exceeds that of the amplifier output capability is achievable without clipping, plus at least the upper load impedance magnitude peak is minimized. Cone excursion at a constant input voltage is maximum at around 40 hz with this setup that also blocks most energy below about 20 hz.

It sounds as if you are using resonance to amplify the bass. If this is the case I would say - in the nicest possible way - that this is the opposite of the original idea.

or did I miss something ?