KEF Q Series-How does the ABR work?

[Pistol Pete1]

It's well documented that I'm keen on these speakers at the moment, and awaiting a chance to demo them.....(Q500, Q200 etc....)

Reading the info leaflet, I notice that even though the Q500 looks like it has 3 bass drivers (very similar in looks to the old Mission 753's), and one midrange/tweeter unit, it actually only has the midrange/tweeter and ONE bass unit!!![:|]

The other two speaker-like cones are in fact non working bass cones called 'front firing auxilary bass radiators' (ABR's)????????[:^)]

Can anyone explain, in plain english, how these work??? Surely when the actual bass cone moves out, the bass radiators move inwards (sealed box type). Surely that means that the ABR's are out of phase with the working bass cone???

Please explain...someone...before my brain explodes......[]

 

[Pistol Pete1]

Also is this a tried and tested way to gain what a port gives to the speaker?

If so, why isn't it used in many speakers?

 

[Anonymous]

have you demoed any other speakers yet pete? rx6's? b&w 683/4's?

 

[Pistol Pete1]

Well I demoed the Q500/Q200/3001 eggs recently, but the dealer didn't have it set up well at all....

In fact the centre speaker was placed on the front with a wash bag type thing under it to angle it up to the listener...

The receiver wasn't set up either......didn't even use HD decoding with a blu ray I took in.....

So obviously they were not shown at their best, but still sounded 'ok' with movies but not good with 2 channel (think 80Hz crossover was still in play!!!)

Not demoed the other's or the KEF's properly yet....hoping to do it at the end of next week, or week after....

 

[Anonymous]

i know nothing about the new kef eggs pete, but they obviously wont be as good as the kef q300/500 and other mentioned brands for music. aren't they more style speakers?

 

[Pistol Pete1]

Yes they are, but I'll be using them as rear speakers only (working with the Q500 and Q200 centre at the front).

Here are the eggs:

http://www.hifix.co.uk/sku2.lasso?item=227de52dd14c992762b86ca6182df60cd63156b82a21233e

The Q100/300 are too big to be positioned at each end of the couch (literally)....

The Q800ds is just too expensive.......

 

[Anonymous]

aha, now things make more sense

 

[Pistol Pete1]

Should work well......

If I prefer the B&W 684's, HTM62 centre, I'll add the M1 satelite's at the rear instead.........

And if I really like the Monitor Audio RX6, RX centre, I'll re-mortgage for the RXFX's, I guess....

or get the smaller Radius 90's instead.......

Anyway, still noone can explain this ABR system????????

 

[Andrew Everard]

OK here goes with the simplified explanation:

Just as a bass reflex port allows some of the air inside the speaker to move in and out of the cabinet, being driven by the air being moved within the box by the rear of the bass drive unit and thus boosting bass, so an ABR - which is basically a speaker cone without any motor driving it - is driven from behind by the movement of the air behind the main drive unit.

The idea is that the sound produced by the ABR(s) is slightly behind that of the main drive unit, but with 180 degree phase reversal, thus reinforcing the main drive unit's output at low frequencies.

In other words, ABRs basically do what the more common reflex ports do, but without the more common problems of air turbulence and 'chuffing' possible with larger ports.

 

[Frank Harvey]

Basically, the extra drivers move more air

(200% more)

 

[Andrew Everard]

They're not actually drivers.

 

[Frank Harvey]

Ok, if we're being pedantic, 'bass cones'. Or, 'non driven bass drivers with no magnet/coil assembly'.

 

[Andrew Everard]

No, not pedantic, just accurate.

 

[Frank Harvey]

I think everyone knew what was being referred to seeing as we were talking about ABR's

 

[Andrew Everard]

Getting very bored with this, David...

 

[Pistol Pete1]

Andrew,

If the sound produced by the ABR's are slightly 'behind' the main drive unit, surely that will muffle the bass, and it'll lose it's 'tightness'?

Surely in a multiple cones set up every cone SHOULD move at exactly the same time to produce deep, tight, punchy bass???

 

[Andrew Everard]

No, they are behind, in that they are 180 degree phase inverted, just like the air in a port tube, so when the powered bass cone moves backwards, the ABR diaphragm moves forwards, and vice versa. That's how they reinforce the bass output of the main bass driver, by using energy which would otherwise be used to compress the air in a sealed box enclosure, and thus be lost as heat, to drive the ABR diaphragms

Of course, they can't produce the same air-shifting 'power' as three conventional drive units: while there may be three times the radiating area, there's still only one motor (as in magnet and coil), so they merely enhance the output of the powered drive unit. They merely make the most of some of what would otherwise be wasted energy.

 

[Pistol Pete1]

Ok, so they do work to a degree then?

And as it's a only an 'enhancement', I assume not many companies use it, as it's a bit, dare I say, 'gimmicky'???

 

[Andrew Everard]

Yes, they do work. More than a few companies at all levels of the market have explored this design over recent years: it tends to be used in some compact subwoofers, for example.

I just wanted to clarify the statement made above that using two ABRs will shift 200% more air: at the very best, assuming there are no losses of energy to the air inside the cabinet, any wadding or damping used within, or indeed the wall of the cabinet itself, even if the ABRs were 100% efficient - which they can't be, due to the mass of the diaphragms and the resistance in their suspensions - each would only move 50% as much as the main drive unit.

In real terms, the amount of energy each ABR puts into the air in the room is likely to be considerably less than this. They merely make a small, but useful, contribution to perceived bass.

 

[Pistol Pete1]

Thanks for your clarification on this......

To me it sounds like it would have been a better design to just add another 'live' cone to the design of the Q series floorstanding speakers....

Saying that, I assume this design is a way to help the bass by 30-40% without the extra cost of adding another fully working cone.

And I imagine this design is a more expensive way than just adding a port in the cabinet.....which helps with potential room positioning problems (sealed box vs rear port), and therefore can be positioned closer to the rear/side walls for improved bass output.....