Purifi-based monitor - options

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#61 Re: Purifi-based monitor - options

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Sorry please see my edit, just added, I had missed your post from not refreshing. Will read your post ..soon...
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#62 Re: Purifi-based monitor - options

Post by IslandPink »

I think I'll look at a 3-component series notch. I don't need super attenuation, nor the aggressive phase shifts that occur either side with the bottomless notch, not in this area. I'm just playing around with it on Spice.
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#63 Re: Purifi-based monitor - options

Post by IslandPink »

This looks tasty, will get the bits together and give it a try tomorrow. This has the driver parameters on the right, and the crossover coils have the expected DCR.
PurifiLP_notch_ii.JPG
PurifiLP_notch_ii.JPG (158.25 KiB) Viewed 1910 times
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#64 Re: Purifi-based monitor - options

Post by IslandPink »

I wonder if it's possible to get rid of the Zobel, if you play around more with the values on the notch ?
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#65 Re: Purifi-based monitor - options

Post by Scottmoose »

IslandPink wrote: Mon Aug 01, 2022 6:06 pm Thanks yes, had a look at his measurements now, see what you mean.
I need to do more listening once i've got the treble down another dB ( just about to do some soldering )

I was wondering myself about the slot port. Maybe that's an advantage ? Not sure how you'd simulate it, but main plan is just to listen. Will be able to compare the Mk.1 and Mk.2 cabinets side by side fairly soon.
Most software has the ability to adjust Ql[v] i.e. the vent losses. I can't recall off-hand (I'm on my laptop) if Hornresp uses that or a slightly different term, but I know David will have included it. Alternatively, a regular vented box modeller will do OK; Jeff's, WinISD, Unibox, BassBoxPro (some minor reservations about the latter's vent dimensions, although its alignment modelling is usually fairly accurate for conventional boxes), AJHorn etc. all have variations that work in more or less the same way. Just something to keep an eye on -this is how Dave's Fonkens etc. work. Having some vent resistance and damping can often be quite effective; it can also help 'resist' changes in alignment under dynamic load conditions (as you know, T/S values vary to some extent with drive level).
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#66 Re: Purifi-based monitor - options

Post by Scottmoose »

Remember with your zero pole / bottomless notches, they are, (in this case, as Chris alludes to ;) ) well in the stopband, so the phase-wrap is broadly immaterial by that point. You're just using it to kill distortion born in the motor, and the amplified sub-harmonic modes.

Edit -minor point. For full effect, the notch is often better done as a parallel type in series with the driver, rather than a series filter shunted across it. That can depend on the nature of the baseline filter though, but potentially worth looking at.
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#67 Re: Purifi-based monitor - options

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I'd better update my version of Hornresp in case anything important to vents has been added.
Scottmoose wrote: Tue Aug 02, 2022 11:43 pm 1. Remember with your zero pole / bottomless notches, they are, (in this case, as Chris alludes to ;) ) well in the stopband, so the phase-wrap is broadly immaterial by that point. You're just using it to kill distortion born in the motor, and the amplified sub-harmonic modes.

2. Edit -minor point. For full effect, the notch is often better done as a parallel type in series with the driver, rather than a series filter shunted across it. That can depend on the nature of the baseline filter though, but potentially worth looking at.
1. Not in my case, it was Chris's example. Mine being close on the downslope I will use a 'soft' notch for this.

2. When you say 'for full effect' do you think the parallel notch sounds better ?
This was how I've previously done these , for instance joining the FE208Ez to the G3 ribbon - and it worked really well.
However my interest in the series notch ( as above ) was that it takes out effectively one component from the signal path when you're away from the notch, might be better under critical listening ?
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#68 Re: Purifi-based monitor - options

Post by Scottmoose »

Assuming the objective is suppressing subharmonics, then it needs to be a parallel notch in series with the driver because the way this works is basically by kicking up the impedance. There's nothing wrong with series notches shunted across the driver for FR shaping, impedance flattening etc., but they don't really help to suppress the distortion.

Purifi have a short pdf about this on their site, although slightly confusingly, they refer to series notches as parallel (presumably because they're shunted across the driver) and visa versa. https://purifi-audio.com/wp-content/upl ... filter.pdf
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#69 Re: Purifi-based monitor - options

Post by IslandPink »

Very interesting stuff, thanks.
I need to read through again in more detail tomorrow though !
I will say that he doesn't exactly compare like for like, since none of his 'parallel' notches have three components.
However...

At this point I'm not really sure what I'm trying to correct, but it looks like trying both types of notch is a good idea.
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#70 Re: Purifi-based monitor - options

Post by Scottmoose »

They do, it's just buried in the values. Remember series and shunt LC[R] circuits have the inverse effect on impedance so the relative levels of resistance differ. The R in those shunt LCs is provided by the inductor DCR. The more resistance you add to a shunt LC, the less attenuation you will have at its tuning frequency; the values are specified to provide approximately the same levels of attentuation between the series and shunt notch options so you can then compare the distortion amplification. Not quite perfect, but ~'good enough for purpose'.
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#71 Re: Purifi-based monitor - options

Post by IslandPink »

Well yes, I understand all that, I was entering DCR numbers for the inductor myself on Spice. However we know that a value like 0.3R is not the same as a proper resistor like 4R7, so I still it's not a like for like comparison.
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#72 Re: Purifi-based monitor - options

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IslandPink wrote: Thu Aug 04, 2022 10:58 am Well yes, I understand all that, I was entering DCR numbers for the inductor myself on Spice. However we know that a value like 0.3R is not the same as a proper resistor like 4R7, so I still it's not a like for like comparison.
Not sure I understand this, it may not be the same as a 4R7 "proper" resistor, but it is identical to a R3 proper resistor.
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#73 Re: Purifi-based monitor - options

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You're comparing a soft notch to a nearly bottomless notch.
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#74 Re: Purifi-based monitor - options

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You may be missing what I meant, From what you posted it seems as if you were suggesting the DCR of the inductor is not the same in its effect electrically as a 0 ohm DCR inductor with an actual resistor of the same value as the previous DCR added in series. It was the use of the word "proper" that I was questioning.
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#75 Re: Purifi-based monitor - options

Post by Scottmoose »

There is no such thing in the pdf file I linked to as a 'soft touch' to a 'nearly bottomless notch'. Since series and parallel notches have the reverse effect to each other on impedance, they inherently have opposing requirements for the amount of resistance required to achieve a given amount of attenuation at the target tuning frequency. To put it another way: to increase the Q of a parallel notch in series with the driver, you increase (not decrease) the level of resistance in circuit. The converse is true of a series notch in shunt with a driver. The comparison in the pdf is like-for-like because both the series and the parallel notches have the requisite resistance values for the desired attenuation at the notch tuning frequency. That is the comparative baseline. Changing the amount of resistance present would alter the level of attenuation (reduce it, actually, in the case of the series notch shunted across the driver) which would invalidate the comparison.

Both a parallel notch in series with the drive unit, or a series notch in shunt with the drive unit, can be used to attenuate a cone mode. However, only the former will prevent the distortion amplification the cone mode causes lower down. While the latter attenuates the cone mode itself, the distortion it causes at sub-multiples of its frequency remains more-or-less unaffected. As I say, there's uses aplenty for series LCR circuits shunted across drivers, but clobbering HD amplification isn't one of them.
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