One for the Isobarik Experts

[david ellwood]

The reason for the minimum cable length on naim amps is to ensure stability, otherwise the amp turns into an oscillator and self distructs.

Seems to have been a spate of this kind of thing lately. (though not on naim amps)

 

[Richard Lines]

A 250 driving only tweeters shouldnt be getting hot at all. Its a tiny load even with a pair in parralel.
You only have to look at the amount of mass being moved and how far its being moved to imagine the amount of energy being imparted.

1.7r for a pair suggests 3.4r each which also seems a little on the low side, which tweeter is it and what does the spec sheet say?

David,

As below.

Regards

Richard

 

[Richard Lines]

Good Afternoon All (again),

That's a second pair of IMF 128/ 20 woofers just bought.......

Just the one pair of TDL's to go now.......

Regards

Richard

 

[david ellwood]

So it’s correct according to the spec sheet but why use tweeter with such a low impedance?

you’re going to be dropping a fair bit of signal across the cable and connectors not to mention limiting the damping factor.

Seems a strange choice.

Not to mention having to rebalance the naxo as the tweeters will be giving twice the output for the same voltage.

Are the mid units 4r too?

 

[david ellwood]

So with a tweeter impedance of less than 2r and a nap250 has an output impedance of about .25r I’m beginning to see why your amps were getting hot.

 

[Richard Lines]

Good Evening David,

Details for the midrange as follows;

Might need to get on with acquiring some more amplifiers or changing the tweeters......

Regards

Richard

 

[david ellwood]

Did you notice the excess of treble when you changed the drive units? The mid units appear to be 8r which is the same as the original B110 though I’d imagine they would be more sensitive.

you could try the tweeters in series or separate them but then you’d need another amp.

Even in series you’d have enough voltage to drive them to full power if needed

 

[david ellwood]

Surprised that the old B110 manages 86db where the scans are 83db sensitive so levels will definitely need some adjusting

 

[Richard Lines]

Did you notice the excess of treble when you changed the drive units?

David - the most obvious sonic change appeared to be in the midrange which I have dialled down on the SNAXO. The tweeters don't appear to dominate but there is whole lot more definition of things like cymbals/ triangles etc.

Trying the tweeters in series isn't too difficult a wiring job. I could also look at dialling them down in the SNAXO as well.

Regards

Richard

 

[david ellwood]

I can see REW might be a good investment

https://www.minidsp.com/products/acoustic-measurement/umik-1

 

[Richard Lines]

David,

That was the thinking in having Neil Hallworth come up.............. I assume he would need to do that as a part of making up dedicated Exact filters?

Regards

Richard

 

[david ellwood]

If you’re definitely going exakt then it would be the way to go.

For the sake of £100 I think you’d gain much from some measurement.

learning how your speakers inter react with your room and getting them crossing over smooth.

Impulse response testing with waterfall to see what frequencies are hanging around.

So much fun to be had!

 

[Richard Lines]

If you’re definitely going exakt then it would be the way to go.

David,

In order to get a fair demonstration of what Exact can do for me I kind of have to go through the motions anyway???

I'm kind of hamstrung financially at the moment with only 8 days work in the last 4 months so now isn't the time to be spending large amounts of money.

Regards

Richard

 

[david ellwood]

For the price of a measurement mic and installation of REW you can get your crossover set up so its flat.

Its hard to achieve this by ear (not impossible) but so much faster and less confusing to have a measurement tool.

Also youll be able to account for slight differences in the driver responses and crossover pot tolerences.

 

[Richard Lines]

Good Morning All,

With Kate's kind assistance the Briks came down off the stands again yesterday evening and I've just modified the tweeter wiring so they are in series.

The UMIK-1 arrived this morning so guess what I'll be wrestling with next........ me thinks I'll need to find a 3.5mm stereo jack to 5 pin DIN to get the sound in to the NAC52?

Regards

Richard

 

[Richard Lines]

Good Evening All,

With Kate's assistance the speakers are now back on their stands.

My chair has been set aside and been replaced by a stand c/w microphone.

I managed to get my first set of readings through REW and now need to work out how to use them......

Regards

Richard

 

[Colin L]

Damn, you sit close to those Barik’s. Monitor close. That’s surprising.

 

[Richard Lines]

Damn, you sit close to those Barik’s. Monitor close. That’s surprising.

Obviously I haven't stated why I sit here in this thread. This position is as advised by GIK i.e. 38% from the front wall or 1.78mtrs.

After spending sometime with the REW app last night I 'found' the smoothing function so the above graph looks like below after some, psychoacoustic, smoothing applied.

This would seem to suggest that the midrange wasn't too bright and that the upper frequencies need a wee boost. This doesn't tell me how things are when SO is applied.

Regards

Richard

 

[cctaylor]

Damn, you sit close to those Barik’s. Monitor close. That’s surprising.

I have a similar setup, my Isobariks are crammed into a room 12ft 6in wide room. I sit about 6ft from the speakers. Works fine for me.

 

[david ellwood]

Is this after the series tweeter modification?

And if so did you notice a taming of the treble subsequently?