Tuning KLS9 - page 2

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Tuning KLS9
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1) Short Port 
This comprised an 8cm diameter hole in the cabinet wall (19mm thick). 
With no cabinet damping it gave massive bass but there was a bit too much of it we felt and control was lacking in the lower registers. However, some people might well like the massive impact this gave drums and bass lines. 
Our analysis shows forward radiation from the HM21OZO reached down to 60Hz before diving downward rapidly. Port output forms a fairly high Q peak centred at 50Hz and its output extends down to 30Hz or so (-6dB).
2) Ideal Port 
This comprised a 6.6cm diameter port, 6cms long, the size given by various equations. Audax also suggest it is the right size. So what did we get? 
Bass again seemed a little too prominent and it was more resonant and less apparently controlled than the other options. However, just a small amount of wool in the port drastically damped down bass level and cured its boomy quality. Putting wool in the cabinet had a similar effect and gave a slightly cleaner overall sound. 
Measurement showed this port gives a rounded peak centred at 38Hz, extending port output down to 20Hz (-6dB), a very low value. Forward radiation from the HM21 OZO rolled off less steeply, allowing the unit to reach down to 50Hz.
3) Long Por
This comprised a 6.6cm diameter port 19cms long. Some authorities, like Vance Dickason, recommend using long ports. 
This gave the best results in our situation. We were looking for bass of a sensible level that had good definition and control. Adding wool to the 
bottom 20cms or so of the cabinet usefully reduced internal standing waves at 180Hz and 480Hz, attributable to the cabinet's height and depth dimensions respectively. This made the 'speaker sound just a fraction cleaner. Putting more wool in gave an unpleasantly boofy quality to the bass though. 
A small amount of wool in the port also helped control bass level and tightness and it was like this that we achieved the best general balance for KLS9. 
Measurement showed forward radiation reached down to 45Hz, so there was little change here from the 'Ideal' port. That was surprising considering port output changed a lot, the centre moving down to about 34Hz, the -6dB point measuring an amazingly low 12Hz! Our room reaches down to around 25Hz (-6dB) so such downward extension is a bit lost. I notice many readers have 20-24ft long rooms, 12ft wide. In a room like this KLS9 would have no trouble reproducing 16Hz organ notes at their correct level. 
The position of the tags changes on the tweeters; some are 180degrees apart, some 30degrees. This is why we left out clearance holes in the original cut-out diagram. Drill 'em when you've got the tweeters! 
Audax tell us, by the way, that they check tweeter phase with a 9V battery as they do with bass units. The convention is that when the cone/dome moves forward, the battery's positive terminal is connected to the driver's positive (red) terminal. 

As standard, KLS9 gives a flat frequency response with a little bass lift. Treble can be rolled off smoothly, if desired, to give a warmer sound by connecting a 1.5µF capacitor across the tweeter. This will drop output at 20kHz by -I dB or so; not a lot but quite audible all the same. 
The most striking feature of this loudspeaker is the sheer depth of its bass and the ease with which it reproduces low frequencies. There's little to touch it at present in this area. I can almost guarantee that it will astonish you in this respect but please bear in mind you will only get to hear and feel this in a room at least 15ft long. 
The High Definition Aerogel HM210Z0 bass/midrange driver offers superb midband clarity and good detailing. A smooth response and, absence of crossover suckout gives this 'speaker a very even tonal balance, which is also quite obvious subjectively. 
Like all our kit loudspeakers, KLS9 is a very easy load so it will work well with any amplifier. Most of the time I drive it from our K588 I Mkll valve amplifier, which delivers 20watts per channel. It was run from an Audiolab 8000S during development and for testing but we also used a Roksan Caspian. A 20watt NAD 310 solid-state amplifier was tried as 
well and I was pleased to find that it worked perfectly well with KLS9, making the NAD sound like a real power house. That's how it should be. At just £230 KLS9 is a lot 'of loudspeaker; I'm sure you'll enjoy it. 



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