KLH2 3-Way Loudspeakers

[DeZZar]

So I had a set of these pretty cool speakers from the 80's show up. A guy I met a while ago wanted me to take a look at them for him so I obliged.



They come with this active analogue bass computer which seams to monitor the speakers for signs of duress whilst boosting the source signal to bolster bass output. Basically an early example of the technique now built into your bose, bang, sonos active systems today - crank the bass at low volume, back it off as the signal goes up = customer wow factor.

Thought you guys might be curious to see how these perform so I am making my evaluation report available here as well:

KLH2 Loudspeaker Report - Public.pdf

[DeZZar]

Few more pics...

[Steve Lee]

Is that a raised foam panel surrounding the tweeter and midrange, DeZZar?
(I'm fairly sure it serves an acoustic purpose if so).

[DeZZar]

Yeah it is. And I'm sure that's what the engineers probably thought as well - but its not doing a great job lol

[djg]

In 50 years they'll be laughing at today's DIY efforts.

[fpitas]

Or everyone will have speakers the size of an acorn that make Bose cubes seem good.

[ugly woofer]

The foam most likely fills in the space between the drivers and grill, so that you listen with the grills on.

[LOUT]

Is there a pair of inductors right next to eachother in the bottom/left of that picture..in (if I'm remembering right) the worst adjacent configuration (or am I rembering wrong and that's the best configuration....aside from the close-ness)?
And is one of those inductors broken?
Does the loose winding rattle?

[Wolf]

They are orthogonally mounted, so they are fine. It'd be better if they were air-core in that position, but I've done it too with little to no effects using solid core coils.

Later.
Wolf

[DeZZar]

...aside from the close-ness)?
And is one of those inductors broken?
Does the loose winding rattle?

here's another shot of the crossover out of the box. The two air core inductors look like they were probably hand made in the factory with the speakers. Wiring is a little loose but it doesn't move around.

The placement isn't ideal but I can't say if they are affecting each other or not.

[DeZZar]

I've subsequently measured with the bass computer supplied with these - here's what its doing. It has a "Position" switch which seems to just adjust the level of the bass post - but here is the bass performance passive against the two positions available for active



This is what allows them to use a pretty small box for these (somewhere around 20L) and still get bass down to 35 Hz. I also notice it acts as a high pass likely set around 30 Hz to roll off the sub-sonic stuff which I'm sure helps significantly with the power handling. Pretty cool for 40 years ago.

[LOUT]

That response kind of looks like it's from a sealed box, like it's not seeing the port's contribution. Is that because it's a nearfield measurement that doesn't include a blended in nearfield from the port or is that just how it works with that port?
Any idea what the port/box tuning is?

[DeZZar]

it's all covered in the report I wrote for them...attached in my first post. It's just an undersized box for the woofer basically. Check out my report though...

[DeZZar]

Just wrapping up an upgrade on these speakers for a customer and thought I would share the results.

When they showed up this was the factory response for these. The pink line is how they were and the green is with the tweeter inverted.


After some tweaking I manage to smooth the integration between the midrange and tweeter with the final result not being bad at all especially for a 40 year old speaker with original drivers. I tamed the top end of the tweeter a little as well.


Here's the before and after:

[DeZZar]

Some nice new foam front panels, new terminals, new wiring throughout (they literally had dental floss!!)


And the upgraded crossover. The size comparison is just hilarious!
Updated all capacitors to get rid of the electrolytic, replaced all resistors with audio grade versions and tweaked a couple of values here and there. I didn't update the iron core inductor even though its tiny. Mains reasons were that its on the bass driver, its a fairly costly upgrade and realistically if I change the DCR on it I introduce the need to potentially tweak the entire crossover which was out of scope for this job.



Some nice new wiring on the Analogue Bass computer that comes with these. These wires are taps into the speaker cables.


And a nice new set of custom speaker cables with the bass computer taps built in as plugs at the amplifier end.




And yes, the whole lot in sum total results in a materially better sounding speaker! They actually sound pretty darn good!

[fpitas]

I'm not sure I've seen a 3 way with such a small woofer. Probably helps Doppler distortion when the woofer cone is going crazy.

[DeZZar]

I think the design principal here was a small speaker with some wow factor in the bass performance. The box is undersized for the woofer and the whole lot is compensated for in the active bass management computer thing. The woofer plays up to around 250hz and after the active EQ is working pretty hard compared to a larger woofer for the same output.

[fpitas]

Yes, I can imagine they'll be huffing and puffing to produce any quantity of 35Hz.