Latest speaker group test

[Big Chris]

FrankHarveyHiFi:dino560b:Placing that many bass drivers in a small (ish) box is never a good recipe. It generally means there is too much piston area for the available cabinet volume. The results tends to be an emphasis for to much mid-bass energy and can be deemed to be 'muddy' or 'thick' in the bass. I could imagine these work OK in a typical US style room which is generally larger and built from wood. But in a U.K room with solid construction, I doubt they are a good match. This is why KEF didn't make the other two drivers active - the designer has stated that making them active would actually give no more bass than having a single active one - the use of the ABR's allowed the benefits of a port in a sealed cabinet.

What does ABR stand for?

I thought they were called BMRs.

 

[Frank Harvey]

Auxilliary Bass Radiator.

 

[Anonymous]

OK, so it's an ABR design - so lets look at that:

ABR has been used for many years. Imagine this. A driver moves in an out at say 50 times per second (50Hz). It then has to push a sprung mass. In a sealed cabinet, that is just an air spring which compresses. Typically the best kind of transient response.

A ported design uses the tuned hemholz to enhance the low frequency. In this case the driver has to push an air load which is coupled to the air outside the box. The transient response is affected.

An ABR design used a moving mass to to generate a similar type of response to a ported design. But in this case, the mass is usually in the form of a driver without a motor assembly or voice coil. Ie/ a cone, suspension and added mass. The mass is usually larger and so the bass driver has to push the ABR in an out at say 50-100 times per second. This tends to affect the transient response so much that the bass can sound slow.

ABR's we popular in the 1970's but as hi-fi became more 'audiophile', they dissapeared with manufacturers favouring sealed or ported designs. For me a sealed box (if you have to have a box at all), is the best choice between accuracy and practicality.

Hope that helps!

 

[plastic penguin]

Perhaps the mag should be the order of the day. Read and decide for yourselves, and then should you have any further questions...err, maybe you could start another thread about additional questions that're being questioned...

 

[AEJim]

dino560b:
OK, so it's an ABR design - so lets look at that:

ABR has been used for many years. Imagine this. A driver moves in an out at say 50 times per second (50Hz). It then has to push a sprung mass. In a sealed cabinet, that is just an air spring which compresses. Typically the best kind of transient response.

A ported design uses the tuned hemholz to enhance the low frequency. In this case the driver has to push an air load which is coupled to the air outside the box. The transient response is affected.

An ABR design used a moving mass to to generate a similar type of response to a ported design. But in this case, the mass is usually in the form of a driver without a motor assembly or voice coil. Ie/ a cone, suspension and added mass. The mass is usually larger and so the bass driver has to push the ABR in an out at say 50-100 times per second. This tends to affect the transient response so much that the bass can sound slow.

ABR's we popular in the 1970's but as hi-fi became more 'audiophile', they dissapeared with manufacturers favouring sealed or ported designs. For me a sealed box (if you have to have a box at all), is the best choice between accuracy and practicality.

Hope that helps!

Don't forget that a sealed-box design also has it's own trade-offs! Sensitivity, Bass extension and Power handling being limited in comparison to similar-sized ported/ABR designs. In testing we've found timing on a good ABR design to be subjectively better than a ported one - sealed box still being the best option but more useful in a large cab/small driver arrangement.

 

[jiggyjoe]

I just wonder why Kef over the years has tried so many different bass loading principles. Coupled-cavity, ported bass reflex and now ABR reflex?

You don't see many other manufacturers doing this.

surely it would be easier for them to master one????

 

[Frank Harvey]

Coupled cavity isn't something that could be incorporated in budget speakers. Well, it could, but the cost of the extra needed has to come from somewhere, so everything else would be compromised. As an example, comparing a £500 standmount to a £500 floorstander, more of the budget for the floorstander ahs to be set aside for the extra cabinetry, and any extra drivers (usually an extra bass driver). If the unit is a three way, a more complex crossover is needed, costing money - notice you don't see many three way speakers under £1k?

I'd love to see the comeback of coupled cavity, but I guess over the years KEF have decided, under testing, that the more conventional type of design is a better use of budget, and possibly 'faster' as far as bass is concerned.

I'm sure KEF could fill you in on the exact answers.

 

[Anonymous]

I wonder, as I mentioned in my comments on the Totem Arro review, which picked as a weakness something I'd always thought their strength, whether amplifier matching doesn't have something to do with it.

Unless I'm reading it incorrectly, the main audio review room uses an upmarket Naim CD player with Bryston amplification, which would suit some speakers well but not others. Perhaps it would be an idea to have a range of amplifiers from different price points and with different sound balance to test speakers with. After all, I'm pretty sure most people with a Naim/Bryston system like that aren't going to hang budget speakers on the end of them.

Having a range of amps, as well as the reference ones, more suited to the budget/midrange market to which WHSAV appeals, means that different tastes also could be taken into account. If I have a criticism of the WHFSAV testing, it is that, liking punch but not fatigue, a decent midrange but not forward treble, the speakers that seems to do well in tests are ones I tend not to like. Perhaps a rating, which I've seen used in some Finnish/German magazines, which indicates overall sound balance might be a good idea.

This isn't meant as a beef, by the way, just random thoughts. In the end, as the magazine stresses, it's your ears that should be the arbiter.

 

[Frank Harvey]

Which amplifier was used in this demo? Can this be clarified?

 

[Clare Newsome]

First and foremost the same reference set-up - in the same room; with the same team of testers - we used when the KEF Q300 both got five stars in its First Test then went on to win the Group Test.

 

[Frank Harvey]

Ta

 

[jiggyjoe]

I agree coupled cavity may be too expensive for budget speakers, but I don't see how ABR loading can be that cheap either not compared to ported reflex.

You still have to pay for the ABR drivers

A friend of mine had kef reference 107 (coupled cavity) and they were amazing! As good in the bass as any sub these days.

[EDITED BY MODS - DISTASTEFUL COMMENT; SUBSEQUENT POSTS REFERRING TO THIS COMMENT HAVE ALSO BEEN DELETED]

 

[Anonymous]

Coupled cavity was a doubled edged sword. First used in the 104/2 I believe (if memory serves) and was very effective. It was however rather expensive to manufactur, and being INSIDE the box, people could not 'see' the value for money.
On the subject of ABR cones used in place of ports, take a look at the New Q video, here on the WHF sound and vision website for more explanation from one of our UK engineers.

 

[Anonymous]

Still doesn't get round the fact that ABR's are generally linked with slooooooow bass

 

[Anonymous]

Generalising is dangerous.

 

[chebby]

Alex, was there any truth that ABRs and other 'passive' radiator devices (KEF 104, Celestion Ditton 15 etc.) were used in the late 1960s as a means for reducing the cost - to the consumer - of speakers due to (pre VAT) Purchase Tax not being applicable to professional loudspeakers? (I think 'professional' was defined as any speaker with more than two drivers per cabinet at that time.)

It's just they did seem to proliferate for a while then went out of 'fashion' again.

 

[Anonymous]

Chebby - interesting point about definition of pro and non pro years ago with tax advantages- no idea actually - will try to find out.

 

[chebby]

I have found that speakers with drivers of 12" or more in diameter were deemed - at the time - to be 'professional' and therefore exempt from Purchase tax.

Bang & Olusfen developed the Beovox 3800 speakers (with 12" Goodmans bass drivers) to make use of this exemption.

 

[Anonymous]

Ever been to a live concert? I think you may find that often bass sounds "sloooooow" and woolly

-particularly at a large classical concert.

But I digress - cannot agree with your assumption about ABRs -

Anyway, why are so many "audiophiles" obessed with "speed" as opposed to tonal accuracy and bandwidth? (Pls don't answer - it'll cause a furore?)

 

[Anonymous]

wow - did not know that at all - thanks for info

 

[Anonymous]

This is my personal view. Can't see why this would be deemed 'dangerous'. I have listened to the speakers in question at a dealer last week. And they are not for me. At the side of some other speakers I auditioned, they sound SLOW and I have to agree with the review, they do sound muddled in the bass.

Come on these are £1000 boxes. Not cheap and there are better speakers out there (not just my view). Sorry Mr KEF!

Alex Foxon:Generalising is dangerous.

 

[Frank Harvey]

Dino - out of interest, which amplifier did you hear them with?

 

[Anonymous]

Cyrus 8XP

FrankHarveyHiFi:Dino - out of interest, which amplifier did you hear them with?

 

[Anonymous]

They are no assumptions. They are based on technical information I found on the net- Impulse plots etc.....

Very bad analogy BTW, errrrrm. Got me thinking there, I have to imagine it was just a joke.

nahojgrooc:

Ever been to a live concert? I think you may find that often bass sounds "sloooooow" and woolly

-particularly at a large classical concert.

But I digress - cannot agree with your assumption about ABRs -

Anyway, why are so many "audiophiles" obessed with "speed" as opposed to tonal accuracy and bandwidth? (Pls don't answer - it'll cause a furore?)

 

[chebby]

Okay.

I wanted to find something of an 'official' nature regarding the Purchase Tax definitions of 'professional' equipment (exempt) regarding loudspeakers.

I found it in a 1952 House of Common debate on "Radio Relay Apparatus (Tax)" ...

http://hansard.millbanksystems.com/commons/1952/oct/28/radio-relay-apparatus-tax#column_1881

The key quote is...
"It provides that in respect of what is technically called the cone type of loud speaker, that is to say the ordinary common or garden radio loud speaker, the line of demarcation shall be a diameter of 12 inches. A
loud speaker of a diameter of less than 12 inches shall be treated as a domestic set and shall be liable to tax. That of a diameter larger than 12 inches shall be treated as a public address system and so be immune."