AMT sub - using dynamic woofer

[djk]

[mige0]

DFD / Deep Frame Dipole sub-woofer



Summing on the effects of DFD / „Deep Frame Dipole“ sub-woofers there are obviously several mechanisms to observe.

Being a dipole loudspeaker, first to look at naturally is the typical dipole FR which basically is related to the separation distance.

In the context of aiming after high SPL output, the separation distance – in our case the depth of the „Deep Frame Dipole“ woofer - can and should be optimized with respect to the bandwidth of desire.
Meaning – for a given XO - we should put the first dipole peak slightly (½ to 1/1 octave possibly) above XO frequency, as this directly affects the attenuation at the lower end of the bandwidth related to the well known comb filter effect seen in the green traces.
Comparing the Ripole speakers – stacking side by side versus stacking one behind the other – shows most clearly what to gain.

Another effect entering the picture with DFD woofers is that we basically create sort of pipe / transmission line / quarter wave speaker as well.
Here a cute little trick comes in handy to upshift pipe-peaking.
Comparing the N-frame and the Ripol (depth-stacking) shows most clearly that with conical pipe we get the nasty peak out of bandwidth.
This is a nice benefit in balancing bandwidth restrictions due to dipole behaviour and due to pipe behaviour.

The last effect that is easy to observe is kind of suck out + some loading occurring with the Ripols.
Mainly the sensitivity at middle frequencies is lowered, giving a more flattish FR in this area, and also the low and lowest department is pushed a few dB.
Sadly this comes at the expense of heavy peaking. Unfortunately, my first guess that distributed arrangement of speakers in the pipe will prevent the pipe from peaking, did not hold


All in all - with respect to SPL maximization / volume minimization - we possibly can say that its best to make “Deep Frame Dipole” sub-woofer as deep as possible, keep the pipe in conical shape and stuff it with speakers.



Michael

[mige0]

Originally Posted by sendler

Excellent work! One pretty picture equals a thousand words including the sketchup shots. They make the layout instantly understandable. Which of the graphs, red or blue, will be more representative of the anechoic far field response?

Thanx.
The blue trace is what you are looking for *if* you are interested in anechoic far field response – but – as said in the intro posting – both FR are kind of academic, considering a typical in room listening scenario.

Originally Posted by sendler

How much does the dual ripol shake? Is the dipole distance "d" the same for a three port, vibration canceling dual ripol of the same footprint as the four port dual ripol?

These speakers were built first hand to get an impression of the effects that can be optimized.
As for shaking - you know I'm a fan of swinging speakers – I don't think its becoming a problem.

Originally Posted by sendler

Is the dipole distance "d" the same for a three port, vibration canceling dual ripol of the same footprint as the four port dual ripol?

?? there is no three port speaker ??
The dipole distance is seen in the green traces and is also equivalent to the depth of the speakers.

All speakers have roughly 80cm separation, with the only exception of the ripole stacked side by side which is half of that: 40cm.


Michael

[mige0]

Originally Posted by Zero Cool

The Tymphany LAT subs work in a similar fashion to a AMT

https://www.madisound.com/store/prod...oducts_id=8311

The LAT is of the same idea but SPL capability is certainly not in the same league, I think


Michael

[mige0]

Originally Posted by DQ828

I'm amazed your Dipole Peak is so so high when I calculate the peak for a 80cm H frame it is 160Hz yours appears to be over 200hz?

David

Well possibly I'm wrong - I calculated with 340m/s which gives 2.35ms time of flight for 0.8m which I dialed in and which equals roughly 210Hz ?

Anyway, the good thing on doing "comparative research" is that some 10-20% off do not affect validity of trends and conclusions to draw from.


Michael

[Mike Mount]

Thanks for posting this... solidifying several ideas
that I have held a long time. great images...

[Rudolf]

Originally Posted by mige0

I calculated with 340m/s which gives 2.35ms time of flight for 0.8m which I dialed in and which equals roughly 210Hz ?

Michael,
as with BR pipes, the geometric length of a H or U frame needs to be corrected by an end factor resulting in the effective length. MJK assumes the effective length to be = geometric length + 0.6 x reffective. reffective would be the radius of a circle with the same opening area as the H or U frame.
U and H Frames page 3

Rudolf

[mige0]

Originally Posted by Rudolf

Michael,
as with BR pipes, the geometric length of a H or U frame needs to be corrected by an end factor resulting in the effective length. MJK assumes the effective length to be = geometric length + 0.6 x reffective. reffective would be the radius of a circle with the same opening area as the H or U frame.
U and H Frames page 3

Rudolf

Thanx - and what would you calculate from that ?

Got confused for a moment ...

The green trace is the overlay of "inverse EQing" - this is not affected by any "opening factors" IMO (except I may add half of the mouth "diameter" to the path length probably).

Might be, far field is not "exactly" what the blue traces tell (its a work around after all) - but on the other hand - how *exact* do we need it finally in circumstances we never listen to ?

Might be - when temperatures are more friendly, I'll try to do a outdoor check, just to get a feeling ...


Michael

[sendler]

Originally Posted by mige0

All in all - with respect to SPL maximization / volume minimization - we possibly can say that its best to make “Deep Frame Dipole” sub-woofer as deep as possible, keep the pipe in conical shape and stuff it with speakers.

Any ideas on the cause of the dip/peak at 160Hz of the N frame? Aside from the bump at 90Hz, the deep RiPol looks better up to 150Hz as the big peak at 280 could be easily notched with digital EQ. Would you expect increasing the dimensions slightly to allow a golden ratio of 80*50*31 for each side of the deep ripol to smooth the wiggles 85-210Hz? And maybe a slight taper, somewhere in between straight and full conical which in this N frame is currently about 1:2. Taper at 1:5? Magnets at the throat or the mouth? As you can see I am very interested in a RiPol layout for two AE IB15s per side to be used under a swinging Eminence Kappalite 3012 mid with DCX and/ or lin phase pc cross.

[sendler]

Originally Posted by Rudolf

Michael,
as with BR pipes, the geometric length of a H or U frame needs to be corrected by an end factor resulting in the effective length. MJK assumes the effective length to be = geometric length + 0.6 x reffective. reffective would be the radius of a circle with the same opening area as the H or U frame.
U and H Frames page 3

Rudolf

So this is good news. The in room bass extension may be even lower than the current blue traces show.