Taming a supertweeter

This may seem a trivial question to real DIYers, but this seemed the best place to ask it.

I'm running Quad ESL 63s which are notoriously a little dull at the top end. Recently I had a chance to acquire some JAS Supertweeters. Despite the two technologues (ESL dipole and Ribbon monopole) with the JAS set to come in at 16Khz, the effect on some recordings is wonderful- on others it is not. My overall impresion is that the supertweeters are too loud and I'd like to turn them down a little. (Doing a little checking, the Quads are said to be 85 dB/W/M and and JASs 96 dB/W/M, so my impression may have some basis in measurement- although I realise the measurements can only be a guide given the different radiation patterns)

Unfortunately the supertweeters do not have a volume control, hence my questions:

1) Would it be OK simply to put a resistor in series with the supertweeter- or do I risk screwing something up?

2) The JASs are said to be an 8ohm design. Does that mean an 8ohm resistor in series would cut the output level by about half? (I can never remember whether that is -3dB or -6dB). In practice I expect to find the right level on a "suck-it-and-see" basis, but it woudl be nice to be in the righr ball park.

3) What power rating would I need for the resistor? I think the crow-bars on the Quads cut-in at around 8.5V, so I could take this as a sensible upper limit.

The JASs are in parallel to the Quads. Does this mean that at this volume setting and with no resistor in line the JAS would be drawing around 1 amp? Or with an 8ohm in series it would be passing around 0.5 amp?

This would seem to imply a resistor rated for around 4-8 watts which seems a higher rating than most at Maplin! (I ended up with rectangular lumps of what looks like marble- and is presumably ceramic- with a wire sticking out each end!) Perhaps my maths or my assumptions are at fault somewhere. I've simply been using V=IR and Power =VI (It's been a long time since I was at school. I realise AC is not the same as DC, but not what to do about it!)

I'd be grateful for the advice of any speaker builders out there.

Many thanks in advance

 

look up "L pad"
or I am sure one of the guys on here will have a suitable design.

 

SPot-on , a L-pad is what you want.

In the very high treble there's very little power available, regular 0.6W metal film resistors will be just fine for trials until you decide the values you need, after which you can swap them for 2/3W metal film parts

 

"with the JAS set to come in at 16Khz,"

At my advanced years Im not sure that I can actually much above 16Khz which probably explains why I enjoy the top end of my ESL 63s. For the first time since I moved on from valve radios in the 60's I have a top end without tizz. It took some getting used to tho' but now I am delighted with the clarity and imaging of the ESL 63s and especially the mid - top end.

Good luck with tweeters but if you add a resistance to circuit with capacitance and impedance you will have created a tuned circuit that might colour the sound etc

 

Well, I'm getting on a bit myself and have noticed a that my ability to hear higher frequencies is diminishing. Nevertheless I can hear these on that setting (I don't know how sharp the cross-over is).

At the risk of starting another contentious debate, with my current set up SACD (especially when recorded in DSD) is clearly superior to CD (although some CDs sound very good) and it feels that a lot of the difference is in these highest frequencies.

The Quads have very nice sound and I was extremely sceptical about the supertweeter, but it does make the sound more airy. To use adapt Peter Walker's description, its like moving forward in the auditorium.

However on some recordings the effect is too much it can be pleasant, but unrealistic or it can be unpleasant with just a little too much emphasis on the higher frequencies.

On reflection I think the "unpleasant" recordings have all been with CD rather than my, much more limited, collection of SACDs. Perhaps I should experiment with the CD players filter settings before trying to reduce the level of the super-tweeter

Many thanks to all who made suggestions about reducing the output of these speakers. It's now time to experiment.