Tardis Loading

[simon dart]

I came across this bass loading technique in some rather esoteric subs for the ARS Acoustica System Max.

It would appear to work by using a driver on the front with to two further drivers phase lagged with respect to the first: one on the front and one on the back. I think it fools the drivers into behaving like the box is much bigger than it really is. The cabinets looked to be around 40 litres but went really deep with impressive control fom SEAS 8" drivers I think.

Has anyone any further information on this? I've not seen it anywhere else.

[GM]

Greets!

I agree, it appears to be an elaborate variation of Harry Olson's original Isobarik alignment.

GM

[Moondog55]

I think I know what the BIG capacitor bank is for, I have used large uF as a passive bass boost in sealed boxes, it gives an octave or so of bass extension and while it is supposed to have a really steep 18dB rolloff or greater with the box i built I couldn't hear the rolloff.
I read a page about it in Vance Dickasons "Speaker Recipes" and had a go, well worth it if the cost of the capacitors does not worry you.
It was only my second sub box so while I was pleased at the time it took up to much room ( 15 inch 4R car sub in a 130 litre filled box)so this "isobaric " setup may work for me, I do not understand the diagram how-ever aren't all 3 drivers in parallel here??

[simon dart]

Yup, all three drivers are in parallel. two one the front and one on the rear.

I hadn't thought of the passive bass "boost" aspect.

Observing the sub under heavy drive it was obvious that the two drivers fed via the capacitor array were phase lagged at low frequencies, which would also be true if passive bass augmentation was how it works. Perhaps there's a bit of both going on.

I really should knock up a box and see what goes on rather than guessing. So many speakers... so little time...

[kelticwizard]

With the greatest of respect, I see a wiring diagram, I don't see how these are actually mounted in a cabinet.

Any chance we can have a quick, crude MSPaint sketch of how these are supposed to be arranged in a cabinet?

[kelticwizard]

Is this what you mean?

[kelticwizard]

Originally posted by Moondog55
I think I know what the BIG capacitor bank is for, I have used large uF as a passive bass boost in sealed boxes, it gives an octave or so of bass extension and while it is supposed to have a really steep 18dB rolloff or greater with the box i built I couldn't hear the rolloff.

I am a little unfamiliar with that technique. Could you elaborate a little? What size caps, which drivers and what exactly was the effect? Is the cap hooked up in parallel to the driver?

Did it affect phase at all? Did it affect sensitivity at all?

[richie00boy]

The scheme was developed by KEF Pete. I can scan you the pages out of the LDC if you want to have a look.

The cap is in series with the drive unit, and the box is sized to have a specific Q which is then used in conjunction with the cap to achieve a lower F3 than would normally be achieved, at the expense of the system response being 3rd order and the attendant side effects of increasing system order.

[kelticwizard]

Well, I've got the Loudspeaker Design Cookbook though I have not read it yet.

Unfortunately, my scanner is kaput. Actually it is just fine but my old Windows 98SE computer is kaput and my new computer has Windows XP, which requires a Windows XP scanner driver. This item is not available for my trusty old scanner, I have looked extensively on the web.

Summary: I need a new scanner.

So I'll be looking at my Loudspeaker Design Cookbook, but if you want to scan the pages anyway for the benefit of other readers, that would be great. I'd do it myself but..........

[Moondog55]

Yes it worked well, the 18dB roll-off was below 20hz so worth the effort.
From Vance Dickason's "Cookbook"
Use a driver with high Qms ( Kapton voice-coil) set box size to give a Qtc of 1.1 then calculate the series capacitor as

C = 0.234/Re X Fc

From memory the cap bank for the Kicker 15 inch was 1470uF
Just thinking about it this approach will probably work well with ELF subwoofers