My Swansong speaker build

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Daniel Quinn
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#46 Re: My Swansong speaker build

Post by Daniel Quinn »

Presumably they were designed with a specific crossover in mind .

Speaking personally doping is instead of the passive xover.
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#47 Re: My Swansong speaker build

Post by Nick »

Yep, but the question still stands.

In my very limited experience the biggest problem was the loss of efficiency and the restriction on power handling it imparts on the driver.
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#48 Re: My Swansong speaker build

Post by Daniel Quinn »

I’ve never noticed this loss of efficiency

Listening I just turn the volume up a little

I was more concerned with a loss of low level detail.

I don’t think a 6.5 inch driver shows the Benefits of doping but I think you should have compared the original driver , that may well have had power handling issues

In case it’s not obvious , I’m fully aware you were not able to compare the drivers and this wasn’t your doing .
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#49 Re: My Swansong speaker build

Post by Scottmoose »

Nick wrote: Tue Aug 02, 2022 2:55 pm Yep, but the question still stands.
In my very limited experience the biggest problem was the loss of efficiency and the restriction on power handling it imparts on the driver.
I wish there was a single answer to this. ;)

As far as marketing goes, depends on the company, so varies from one to another by the usual rules of market, scale, business philosophy & inclination. Some don't do any traditional marketing at all for e.g., others do, still others do a variation where they're advertising in specialist press not aimed at consumers but businesses.

For the rest -it depends on the driver, the type of additions made etc. Adding a coating of any kind will always change the behaviour of a drive unit in some way, but the word there is 'change', which is not an synonym for 'improvement'. It might be, it might not.

Basic law of moving-coil driver engineering (well-known since the 1930s): increase moving mass of a given drive unit by 3, and you will halve acoustical output (as in you will have a 3dB loss). It will lower the resonant frequency, albeit at the price of distortion, since efficiency has dropped and the suspension wasn't designed to cope with that sort of mass, and to an extent suppress many, though usually not all, of the TL modes.

This is of relevance to large mass additions; when you get to smaller additions / light coatings / specifically positioned modifications, it starts getting more complex, because they aren't used for (and don't have a significant effect on) that, but usually to damp / break some kind of uncontrolled resonance at higher frequencies, where some drivers employ TL modes through the cone to extend the upper bandwidth through (more or less) controlled flex or resonance.

Since that's never perfect, you often get some excesses at specific frequencies, hence coatings & other physical modifications e.g. variable cone thicknesses, major changes to the substrate (slits, rings, other additions or alterations from a uniform). Which, if any, will be of help varies with the driver design. Coatings of different types can be a good solution in some cases, but they aren't always viable. To give one example, if an issue is very specific, a conformal coating usually isn't going to be the best solution, since it's a very blunt instrument. It may help a little with the problem, but it will also affect other areas you may not want to change. In those cases, a more specifically targeted modification, either with mass or some other cone tweak, will be more effective, but that usually means an increase in production costs. For low-volume / high margin units you can get away with it; for high-volume / lower margin it isn't always possible, since you'd have to build custom jigs and machines to apply specific amounts of a given material to a given location or set of locations on a complete or partly assembled drive unit. As well as the time, space, cost of the jigs & machines etc., that tends to push up the production QC failure rate. That's just one example, there are others, but it's one of the reasons manufacturers don't necessarily always go to the ends of the earth in additions etc. By motoring analogy, if you're building what's meant to be an entry-level 3-series, you don't throw all the M range (or whatever) gubbins at it.
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#50 Re: My Swansong speaker build

Post by Daniel Quinn »

What’s the figures on dope v passive crossover .me bets there not a million miles apart
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#51 Re: My Swansong speaker build

Post by pre65 »

Daniel Quinn wrote: Tue Aug 02, 2022 8:06 pm What’s the figures on dope v passive crossover .me bets there not a million miles apart
With crossovers one is dealing with known units of resistance, capacitance and inductance. Any of those components can be varied to aid final tuning and there is usually software to get a starting point on values.

Doping, on the other hand, would seem to be a minefield with regard to coating type and thickness. And if one puts on too thick a coating what happens then ?
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#52 Re: My Swansong speaker build

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That’s not the point it’s obfuscation
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#53 Re: My Swansong speaker build

Post by pre65 »

Daniel Quinn wrote: Tue Aug 02, 2022 8:38 pm That’s not the point it’s obfuscation
It is the point to me, how you view it is your affair.
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#54 Re: My Swansong speaker build

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Doping, on the other hand, would seem to be a minefield with regard to coating type and thickness.
I think the point with regards to the original question (though not Colin's speakers) was if the doping was done by the driver manufacturer then all that uncertainty would be removed.
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#55 Re: My Swansong speaker build

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Daniel Quinn wrote: Tue Aug 02, 2022 8:06 pm What’s the figures on dope v passive crossover .me bets there not a million miles apart
I would have expected increasing the moving mass of the drive unit with dope while retaining the same motor would mean that the excursion for a particular excitation (I assume that driving current is proportional to force on the cone of mass m. For a given force f, acceleration a = f / m. If m is increased then acceleration is decreased. If acceleration is decreased then the displacement in the time period of the signal frequency will be decreased, so the volume of sound will be reduced). For a electrical xover below the cut off frequency for a low pass filter the attenuation of the signal will be close to 0 (assuming low DCR inductors are used).

So I would take you up on that bet, assuming we could agree on measurements units that were not millions of miles.
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#56 Re: My Swansong speaker build

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The nominal acceleration factor for a drive unit can be calculated as Γ= (B*L)/Mms. Assuming SI units, this gives you the motor accleration factor (note caveat) in meters per second per second per ampere. There are a couple of points associated with that however which can get overlooked:

1/ It only applies under pistonic conditions; as soon as the driver exits the nominal piston bandwidth (which is defined by the cone size), by definition it no longer applies. Above that point, the driver, if it has usable output, generates it via TL modes and resonance: in other words the mass is no longer fixed but varies with frequency, as does the effective cone dimensions. That's (partly) how wideband drive units work. And

2/ If a drive unit can move quickly enough to reproduce, say, a 10KHz signal, by definition it can move quickly enough to reproduce all longer / slower wavelengths. It is physically impossible for it to be otherwise.

Acceleration factor is basically just another way of describing efficiency. Efficiency is good, providing you don't sacrifice too much on its alter, which usually isn't the case. Oddly enough, even though technically it doesn't apply, it can be a good indication of how effective a wideband driver may be at reproducing higher frequencies. All other things being equal, getting mass out of the powertrain tends to promote an efficient top end. Although in most cases, that tends to be handled by direct-coupled sub-cones or dustcaps (i.e. extremely low mass).

On a slightly different note, which is specific to this speaker, a few further points.

a/ Colin has in fact damped the cones of the CHN50s. That's what the black paint does. It's done for aesthetics, but it adds mass, and thereby damping. That's the cause of the modified drivers having the slightly softer top end response that he mentions.

b/ The idea of adding significant mass to cones can get casually bandied about without being properly thought through. Ignoring everything else for a moment: adding significant mass to a midbass or woofer with heavy-duty cones and suspension is one thing. The CHN-50 is a 3in wideband drive unit with an aluminium-magnesium alloy cone only a few microns thick (literal statement: I was involved with its design). Its total moving mass, minus the air load, is just 2g. For those who don't know, that doesn't mean the cone weighs just 2g. It's the total moving mass of the cone, the dustcap, the voice coil, the surround and the spider. Now think about what adding even a couple of grams of mass to that will do. Yes: it will (if it doesn't warp or fracture the cone) push it and the coil way out of alignment, and overload the suspension. A light blow-over with a rattle-can, or the final (final) version of EnABL is one thing. Chucking lots of mass at it is something else entirely.

c/ Could somebody please explain to me in which universe adding mass to a drive unit will create an acoustic high pass mechanism? Assuming no physical damage is caused (just assuming), it will help create an acoustic low pass but there is no functional mechanism in this physical reality that I am aware of by which it can raise the acoustic high pass frequency. Adding mass lowers, not raises, a drive unit's resonant frequency (and efficiency), and since this is a midrange drive unit in a 3-way loudspeaker, not a woofer, it requires both a low pass and a high pass, not just the former.
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#57 Re: My Swansong speaker build

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I was assuming spherical cows :-). And should #2 have a for the same amplitude attached I expect you are assuming that will be taken as read.
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#58 Re: My Swansong speaker build

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I like spherical cows (my standard state) ;)

Absolutely though; we're on the same page. As you say, if you clobber efficiency by kicking up moving mass, all other things being equal you'll need greater excursions for a given SPL. Assuming piston conditions, raising moving mass will ultimately limit the top end output of a drive unit -it's why we call a portion of the range above the mass-corner frequency the mass-controlled bandwidth. Above that, where relevant, is the TL band -which also gets clobbered as mass increases. Exactly where it gets limited and how it does so is another question of course, as the rolloff is rarely absolutely linear.
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#59 Re: My Swansong speaker build

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Scottmoose wrote: Wed Aug 03, 2022 8:49 am Assuming piston conditions, raising moving mass will ultimately limit the top end output of a drive unit -it's why we call a portion of the range above the mass-corner frequency the mass-controlled bandwidth. Above that, where relevant, is the TL band -which also gets clobbered as mass increases.
Well yes, but that is one of the aims of the kind of doping which Daniel describes.
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#60 Re: My Swansong speaker build

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I know, that's what I said. ;) The potential issue I was raising with adding large amounts of mass for that purpose though (notwithstanding reduced efficiency, higher non-linear distortion etc. etc.) was in the sentence after that:
Exactly where it gets limited and how it does so is another question of course, as the rolloff is rarely absolutely linear.
Assuming it's possible with a given driver, you never really know what it will do unless you measure it, other than it will low-pass it in some unspecified way. The frequency at which it occurs, the rate and linearity are unknowns. The latter is where it can get interesting as most methods of adding significant mass don't do so in a uniform fashion over the entire cone, so you can actually start getting some resonances in that rolloff slope as you've no control over anything other than the mass; it isn't always monotonic and that may (or may not) be an issue.

Bit of a moot point of course with midrange units, since as noted, while it can add a low-pass, you still need a high pass; you can add mass to a driver cone until the cows come home but it won't give you that, beyond what the driver (since they're all bandpass devices) inherently has -which will be too low for purpose in the majority of cases, especially since adding mass has the effect of lowering Fs into the bargain. I'm not knocking the idea as a broad concept, it's used in driver design all the time -just noting it's not a panacea, nor do DIY methods of doing so give you a great deal of control, which in many cases is necessary.
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