Purifi-based monitor - options

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IslandPink
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#106 Re: Purifi-based monitor - options

Post by IslandPink »

Thanks Scott. I got there in the end, but with a bit of help from Nick.

I've done a few odds in last couple of weeks -
Compared my TDA chip amp to an old Sony amp that Jon loaned me - for testing.
Despite its low power, the chip amp is better, at the levels I'm using for listening, the Sony sounds fuzzy and lacking dynamics - probably a case of drying-out caps.
Jon is soon to order a new Denon amp ( with the 'single high-current output pair' ... ) which he'll loan me for the final stages.

I made up a parallel ( components in series ) notch and tried that out. It was centred on 3.5kHz. From this, it does seem fruitful to attack the 3.5kHz peak of the Purifi output ; though it also knocks down 5kHz, it's not especially narrow.
There was a reduction in the slight edginess on certain vocals. 'The Dry-Cleaner from Des Moines' proved to be a usefully discriminating track for this, and sitting on-axis to the drivers.

So, tonight I'm going to solder-up the alternative series ( components in parallel ) notch to do the same job.
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#107 Re: Purifi-based monitor - options

Post by Toppsy »

Mark,
Unless I have missed something, I'm a little confused here why you are building and testing a notch filter for the Purifi driver centred on 3.5kHz as you say to attack the 3.5kHz peak of the Purifi output when, as I understood things last we spoke, you were crossing over to the Beryllium dome tweeter around 1kHz -1.5Khz?
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#108 Re: Purifi-based monitor - options

Post by Nick »

You need to either go back on this thread or just accept it does make sense.
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#109 Re: Purifi-based monitor - options

Post by Toppsy »

Nick wrote: Sat Aug 27, 2022 7:21 pm You need to either go back on this thread or just accept it does make sense.
fair enough. Strike my inappropriate post.
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#110 Re: Purifi-based monitor - options

Post by Nick »

No worries it took me a few goes before I got a handle on what was going on.

Question for Scott is the idea of damping overtones not even more relevant with tweeters?
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#111 Re: Purifi-based monitor - options

Post by IslandPink »

There isn't a similar situation with the tweeter, especially with this one which isn't breaking up until probably above 15kHz.

Colin, the low-pass on the Purifi is not a brick-wall thing, hence the 3.5kHz is still in the mix.
Current model has the Purifi down 3dB by around 1.5kHz.
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#112 Re: Purifi-based monitor - options

Post by IslandPink »

Just working with this LPass circuit, now.
The 2.0R might be a bit low, I was looking for something i the 2.2 to 2.5R range but I don't have it in the planar ones. Might go to 3.3R after listening just now ( more dip ) . Generally it's the best I've had though, vocal tone is very nice, and it sounds more dynamic than the last option with the parallel notch ; however the two options weren't really close enough on their dB profile to be an exact comparison, so I won't claim to know for sure.
However I will say there's no loss of HF transparency, from the extra component or two in series with the driver.
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#113 Re: Purifi-based monitor - options

Post by IslandPink »

ps. CD player now on the blink - oh joy !
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#114 Re: Purifi-based monitor - options

Post by pre65 »

IslandPink wrote: Sat Aug 27, 2022 10:28 pm ps. CD player now on the blink - oh joy !
Again ?
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#115 Re: Purifi-based monitor - options

Post by IslandPink »

Last time it was filament supply fault on output valve. Might be the laser this time, it's affecting even the optical out signal.
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#116 Re: Purifi-based monitor - options

Post by Nick »

IslandPink wrote: Sat Aug 27, 2022 9:20 pm There isn't a similar situation with the tweeter, especially with this one which isn't breaking up until probably above 15kHz.

Colin, the low-pass on the Purifi is not a brick-wall thing, hence the 3.5kHz is still in the mix.
Current model has the Purifi down 3dB by around 1.5kHz.
Yep, but unless I misunderstand, the xover doesn't matter. If there is a resonance at 3.5kHzm it can be excited by at tone at 1.16k which will get through the xover.
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#117 Re: Purifi-based monitor - options

Post by Toppsy »

IslandPink wrote: Sat Aug 27, 2022 10:27 pm However I will say there's no loss of HF transparency, from the extra component or two in series with the driver.
That sweeping statement is likely to fly in the face of your single driver no XO purists. However is good news Mark, bearing in mind the intended use of the speakers and is something I have found over the years working with Scott (and also with young Chris) that a well designed and implemented XO actually enhances the sound of a speaker.

Good to see you are progressing this build.
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#118 Re: Purifi-based monitor - options

Post by IslandPink »

That's not a sweeping statement, Colin, it was rather specific.
To be even more specific, I was concerned that I might hear a loss of microdetail or loss of tonal colour in the upper harmonics of female vocals, by using the alternative notch filter.
In a more general view, I've heard overall improvements from applying a crossover, but also disadvantages, either general or in specific areas.
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#119 Re: Purifi-based monitor - options

Post by Toppsy »

Aye Mark, XO design is definitely a black art and can either make or break a speaker. That's why I leave it to someone more knowledgeable on the subject then me. I applaud your efforts.
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#120 Re: Purifi-based monitor - options

Post by chris661 »

Nick wrote: Mon Aug 08, 2022 11:07 pm This to me seems to be putting the cart at least three steps in front of the horse, and what I don't understand is what of any effect it will have on the generation of the harmonic by the actual resonance of the cone itself.

But I guess if we are saying this is at the point where the cone behaves like a piston then there is no harmonics generated in the cone.

But given its being referred to as a bell resonance, it seems to me that the tone of an actual bell is far from single frequency and that involved zero coil or magnet or current.

Nick,

We're on similar trains-of-thought here, but after reading your post again, my train has just switched tracks in a way that might be relevant:

- Cones do not "generate" harmonics. All they can do is convert mechanical force (voice coil) into sound (by pushing air).
- Cones might, by their own resonances, be more efficient at converting force into sound at some frequencies, but the force can still only come from the voice coil.
- Bells still require mechanical stimulus. Striking them = broad-band stimulus. As a result, there's two parts to the sound of a bell: the initial "clang" and the resonant decay.

Chris
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