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size of cadenzas and calindas

 
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steviolin
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PostPosted: Fri Jul 15, 2011 4:30 pm    Post subject: size of cadenzas and calindas Reply with quote

Hello from a new member. I dabble in building cabinets from scratch, and sometimes use sites like lalena to calculate the size of a cabinet for any drive unit parameters. Both the Cadenza and Calinda are similar speakers. Both have an ABR (based on Kef 139), and both use B200 main drivers (1022 and 1054). The Vas's of these drivers are similar but the Qs of the 2 drivers are very different. .41 and .23. When these are put into a calculation for a reflex cabinet the figures come out as 142 litres for the Cadenza, tuned to 24Hz and 20.36 litres for the Calinda tuned to 56hz. I would be very grateful if any of you can explain how such dissimilar drivers end up in almost identical sized boxes, with the same bass loading. Thank you

Steviolin
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ColinR
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PostPosted: Fri Jul 15, 2011 8:25 pm    Post subject: Reply with quote

One can be considered as a “general driver” the other was designed for a job.

You’ll have to persuade one of the people involved in the design of the SP1022 to “come clean” to get the full picture but my experience indicates that the SP1022 can be regarded as a “round” extended range B139B Shocked, for it can be found in several OEM damped reflex designs (LNB), pure bass boxes (Fried) and reflex configurations (Griffin).

The use by KEF in a particular size of box suggests the heavy hands of marketing and bean counters to fit into a range, I’d love to know what the engineers had in mind and what kind of research beastie existed.

The SP1054 has CAD/CAM roots found in one KEF design to fit in a range, but only used as a midrange in OEMs – works well in my horns too Very Happy .
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speakerguru
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PostPosted: Sun Jul 17, 2011 9:35 am    Post subject: Reply with quote

Normally "hi-fi" drivers are designed so that the compliance of the driver is much larger than that of the trapped air in the box. The net result is that the compliance of the driver has a minor secondary effect on the response of both closed box and reflex designs. (Just as well because it changes drastically with use and age.) You could check this by looking at the analysis in papers by Benson, Thiele and Small. I think that Don Keele also did a paper specifically on this topic while he was at JBL.

The long and short of it is that as long as the moving mass and motor strength (Bl) are the same then the drivers will perform similarly in identical boxes.

I can't remember all the differences between the 1022 and 1054. ! think the 22 had a rubber surround and the 54 a PVC one. The moving mass will not be very different. Motor? The magnet ferrite ring was the same. Was the coil diameter different?
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steviolin
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PostPosted: Mon Jul 18, 2011 12:31 pm    Post subject: size of cadenzas and calindas Reply with quote

speakerguru wrote:
Normally "hi-fi" drivers are designed so that the compliance of the driver is much larger than that of the trapped air in the box. The net result is that the compliance of the driver has a minor secondary effect on the response of both closed box and reflex designs. (Just as well because it changes drastically with use and age.) You could check this by looking at the analysis in papers by Benson, Thiele and Small. I think that Don Keele also did a paper specifically on this topic while he was at JBL.

The long and short of it is that as long as the moving mass and motor strength (Bl) are the same then the drivers will perform similarly in identical boxes.

I can't remember all the differences between the 1022 and 1054. ! think the 22 had a rubber surround and the 54 a PVC one. The moving mass will not be very different. Motor? The magnet ferrite ring was the same. Was the coil diameter different?


Thank you for this response. You seem to be saying that the only factor in determining the size of an enclosure is the compliance (Vas). Thus the Qt of the driver is irrelevant. Have I misunderstood you? All of the literature I have read states very clearly that the Qt of the driver is a fundamental factor (as is the compliance) in the design of a system, and directly influences the bass response.
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audiolabtower
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PostPosted: Mon Jul 18, 2011 12:49 pm    Post subject: Reply with quote

I'm no expert but think the point is the resonance of larger drivers is low compared to the system resonance of most "domestic" size boxes (discounting HUGE crates/transmission lines etc) so in the bass the driver becomes a secondary rather than primary effect?
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speakerguru
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PostPosted: Tue Jul 19, 2011 8:15 am    Post subject: Re: size of cadenzas and calindas Reply with quote

steviolin wrote:
You seem to be saying that the only factor in determining the size of an enclosure is the compliance (Vas).

That's exactly the opposite of what I said. Please read again more carefully.

Vas, which is another way of stating the compliance of the driver suspension, is of secondary importance because it is normally much bigger than the box. It's like putting two capacitors in series. If one is much larger than the other, then the total capacitance will be not much different to the capacitance of the smaller one.

For a closed box system it is the Qt of the driver in the box which determines the system response not the free air Qt of the driver alone. Small gives the various "Qt"s different suffixes to avoid confusion. When you put a driver in a closed box the resonance goes up and all the associated Qs go up as well in direct proportion. That's how the system response is dominated by the driver moving mass, motor strength and box compliance. The driver Vas is swamped by the box.
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steviolin
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PostPosted: Tue Jul 19, 2011 7:26 pm    Post subject: size of cadenzas and calindas Reply with quote

Thank you for this reply. It is interesting that even with the shortcomings of the 1022s many aspects of the Cadenza are highly rated.

A friend of mine has both Cadenzas and Calindas and rates the quality of the Calindas, particularly the bass, as superior.

Can the details of your horns with the 1054s be found anywhere- they sound fascinating.

quote Colin R.One can be considered as a “general driver” the other was designed for a job.

You’ll have to persuade one of the people involved in the design of the SP1022 to “come clean” to get the full picture but my experience indicates that the SP1022 can be regarded as a “round” extended range B139B Shocked, for it can be found in several OEM damped reflex designs (LNB), pure bass boxes (Fried) and reflex configurations (Griffin).

The use by KEF in a particular size of box suggests the heavy hands of marketing and bean counters to fit into a range, I’d love to know what the engineers had in mind and what kind of research beastie existed.

The SP1054 has CAD/CAM roots found in one KEF design to fit in a range, but only used as a midrange in OEMs – works well in my horns too Very Happy .[/quote]
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steviolin
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PostPosted: Tue Jul 19, 2011 8:06 pm    Post subject: Re: size of cadenzas and calindas Reply with quote

speakerguru wrote:
steviolin wrote:
You seem to be saying that the only factor in determining the size of an enclosure is the compliance (Vas).

That's exactly the opposite of what I said. Please read again more carefully.

For a closed box system it is the Qt of the driver in the box which determines the system response not the free air Qt of the driver alone. Small gives the various "Qt"s different suffixes to avoid confusion. When you put a driver in a closed box the resonance goes up and all the associated Qs go up as well in direct proportion. That's how the system response is dominated by the driver moving mass, motor strength and box compliance. The driver Vas is swamped by the box.
Quote:



Hmm. I agree with all that you say, but I feel that my original question has not been addressed.

To continue with the theme of a closed box, the "swamping" of the Vas of the driver by the box is not the full story. The ratio of the Volume of the box to the Vas of the speaker determines the ratio of the Q of the speaker in the box to the free air Qt of the driver. This is according to the formula

Vas/Volume of box=[Q of speaker in box/ Qt driver] squared -1

Example if Vas/Volume of box =3 then the total Q of the speaker in the box will be twice the Qt of the speaker (and the resonant frequency will be double the free air resonance)

My original question asked why 2 drivers with virtually identical compliance but with 2 very different Q's have been utilised in almost the same box, when the formula above would suggest different sizes should be used.

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speakerguru
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PostPosted: Wed Jul 20, 2011 7:00 am    Post subject: Reply with quote

OK back to your original question. The OP says "When these are put into a calculation for a reflex cabinet the figures come out as 142 litres for the Cadenza, tuned to 24Hz and 20.36 litres for the Calinda tuned to 56hz." What it doesn't say is what response the calculation was producing.

The box tuning frequencies give a slight clue. They are about an octave apart. If the resulting system cut off frequencies are in the same proportion then no wonder the box volumes requested are so different. To go an octave lower requires an 8x increase in box volume (with an appropriate adjustment of motor strength) I seem to recall.
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steviolin
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PostPosted: Thu Jul 21, 2011 11:21 am    Post subject: size of cadenzas and calindas Reply with quote

Thank you for all your input Loudspeakerguru, it is much appreciated. I have checked up on the specs of the 1022 and 1054 and there are differences, but I do not know enough to ascertain if they completely account for the very different Qt's of the drivers. No units I'm afraid and the tabled figures come out a bit scrunched together

SP1022 SP1054

Vas 134.5 130

Mech. Resist. .43 .7

Susp. Comp 1.78 2.2

Magnet 1.25T 1.35T

Sensitivity 8.5V 6.4V

Qt .41 .23

Moving mass 24g 21.3g

The calculations for the box volumes as I said in my original posting give very different figures for these 2 drivers. They are for optimally flat frequency response. As you rightly point out the actual bass response of these two [speaker+box] results are very different.


To offer a guess to my own question, I feel that the Calinda is slightly overdamped (total Q of speaker in box <0.7) which would extend but lower the bass, but since the ABR is adjacent to the floor this might be intentional, otherwise it might boom. The Cadenza is quite notably underdamped, but if it is on stands this might be ok. Even so it does seem compromised. As the response from Colin R said, the Cadenza cabinet might have been chosen for reasons other than purely acoustic.
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speakerguru
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PostPosted: Fri Jul 22, 2011 9:12 am    Post subject: Reply with quote

I've remembered a bit more. The 1022 was a 1014 with a bigger magnet. Same moving parts but with a bigger magnet ring, top and bottom plates. Thus KEF had two 8" units; one with a small magnet for closed box designs and one with a larger magnet/lower Q for reflex designs. The 1022 turned out to be a very wasteful design as the 1" pole piece was saturated by the bigger magnet and did not result in much increase of gap flux. Thus when the Cadenza replacement was designed the bass unit was improved by using a 1.25" coil to reduce saturation and also incorporate the new velbex surround of the SP1039 Model 104 unit which provided better damping than the rubber one.

Re LF alignment, I suspect this was done by listening, trial and error and modicum of measurment. KEF LF measurement techniques were not fully developed then and I remember being given the job of running analogue simulations of the Model 104, to find out what was happening at LF, after the Model had already been on the market for some time.
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