High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread

[agedhorse]

Apparently, it seems that more often than not, those with the understanding of "the engineering and math behind these effects" seem to be unable to produce a product that I am comfortable playing through.

Then I suggest that you design and build what you are comfortable with... which presumably you already have.

 

[Al Kraft]

Given that speakers (even the most efficient ones) convert most of the power you send them to heat and that standard grade Neo magnets (not those with alloys that extend their capability in higher temperature operation) tend to experience a loss of field stength greater than say an ALNICO magnet with heat, I wonder if some designs simply have insufficient/minimally adequate thermal margins. I'm no expert in this area, but I understand that especially with Neo magnets the material as well as geometry have an impact on expected temperature related field strength degradation in a given application.

Could it be that some people are actually able to perceive/hear some normal change (even in what we might call a perfect design) as temperatures rise over extended use, especfially with lots of low bass (e.g. 5 string players)? I would not expect this to be noticeable in quiet jazz trio situations, but I can imagine rock and roll with lots of low end signal warming things up a bit. Maybe higher temperature rated Neo magnets are routinely used in speaker motor applications and temperature rise in the applciation is insignificant. In any case I would expect a HPF to be useful.

Anyway, that's just a wild guess based on a limited undertstanding of the material science, but without any meaningful knowledge or experience in speaker design.

 

[Mike Arnopol]

a point I was making---on a jazz gig with upright and a piezo--piezos put out MUCH more subsonics. I could take videos to illustrate this. Even at a low-to-medium volume you can see crazy excursion with the piezos. With electric bass--even at medium volumes--you can see big excursion due to subsonics. But with piezos---it's pretty crazy. When using a good HPF--you see very little cone movement.

 

[agedhorse]

The Neo alloys used in commercial speakers are virtually unaffected by the operating temperatures in speakers.

 

[Mike Arnopol]

That's interesting because the chief designer at Eminence told me that the neo woofers were much more susceptible to thermal compression as opposed to the ferrite woofers. But then again, what does he know? He's only the guy that designed them. (The neo and ferrite woofers at Eminence). The question is not if the neo alloys are affected by heat----the question is do they dissipate heat as well as ferrite?

 

[agedhorse]

I give up Mike, you win (again).

 

[Clemouze]

That's interesting because the chief designer at Eminence told me that the neo woofers were much more susceptible to thermal compression as opposed to the ferrite woofers. But then again, what does he know? He's only the guy that designed them. (The neo and ferrite woofers at Eminence). The question is not if the neo alloys are affected by heat----the question is do they dissipate heat as well as ferrite?

Can't you just speak normally and don't be agressive.
I'd like to hear argument and answers for this subject, I m interested

 

[Clemouze]

I give up Mike, you win (again).

So why the Eminence designer guy told that ?
Maybe a specific Neo magnet different than the ones you speak about ?

 

[agedhorse]

So why the Eminence designer guy told that ?
Maybe a specific Neo magnet different than the ones you speak about ?

I have no idea why.

That statement flies in the face of the undisputed fact that the highest power, highest performing speakers (especially in the pro audio subwoofer market) use Neo magnet based motors. This is a market that is 100% performance based, and higher cost is not a big issue.

Now there is SOME possibility the terminology is part of the challenge, but only when you dissect the meanings to a semi-molecular level...

1. There's a difference between thermal conductivity and the resistance to thermal compression. Thermal conductivity is the ability of heat (or thermal energy) to conduct through the material. Resistance to thermal compression is the magnetic material's change in field strength versus temperature. Different materials, and different "alloys" of materials behave differently in this regard, and are generally defined by the Curie temperature of the material.

2. The thermal resistance of magnetic materials are based on the material itself and how it's processed.

ALNICO has the lowest resistance (highest conductivity) to thermal energy, and also has the highest working Curie temperature (~500-600 deg C). Unfortunately, it's fairly heavy, expensive and has a lower magnetic strength per unit weight. It also has the unfortunate challenge of permanent loss of of magnetic strength with self-demagnetization as well as from mechanical shock.

Neodymium material has the next lowest thermal resistance (higher conductivity) to thermal energy, and has a working curie temperature of ~300 deg C (with the "alloys" used in speaker motors), it also has MUCH higher magnetic field strength per unit weight than any other material. The challenge with Neo is in the cost of processing. Here's a good article about what goes into the refining and manufacturing of Neo magnet materials: How Are Neodymium Magnets Made - Ideal Magnet Solutions

Ferrite magnet material has the highest thermal resistance (lowest conductivity), and has a working Curie temperature of ~350 deg C (for the common "alloys" used in speakers), and has a low magnetic strength per unit weight. the advantage is that the material is generally quite cheap (though there are some extended grades that improve this aspect somewhat, at a higher price)

Now let's look at these temperatures compared with the temperature of the insulation on the voice coil winding itself. The Polyamide insulation most often used has a working temperature of a little over 200 deg C, which is the highest grade material available for common production. The bonding adhesives temperature limits are about the same.

Therefore, it's virtually impossible to create enough thermal energy transfer from the 200 deg C voice coil across an air gap that has air moving within the gap removing heat) to the magnetic material which is continuously conducting the heat to the other huger mass metal structures (return structure) to raise the temperature of the magnet to anywhere near its Curie temperature.

The difference between the locations of the magnetic material requires that the calculations be done differently (Neo and ALNICO are typically slug magnets in the pole circuit and Ferrite is typically a ring magnet between the pole and return circuits), but in all cases, there is simply not enough thermal energy present to heat the magnet up high enough without the voice coil failing well before.

This is why speakers perform the way they do. It's been demonstrated again and again, based on science, engineering and math as well as real world confirmation. If it didn't work, and if there were speakers suffering from this phenomenon, then there would be a good argument against this, but in the pro audio world, Neo speakers are subject to brutal conditions night after night for years without problems.

There are all kinds of electro-dynamic compression effects, plus design workarounds to limit their practical impacts, but these are unrelated to thermal issues.

 

[fdeck]

Here's a thought experiment. Run an impedance curve before and after driving a speaker hard for a while. Or, run the curve at a performance power level. This will tell you a lot about what's happening under the hood. For instance, changes in coil resistance and magnetic field would both have their own signatures in such a test.

I haven't quite gotten around to setting myself up for impedance curve measurement yet, so my neighbors will be spared of this, at least temporarily.

 

[agedhorse]

Here's a thought experiment. Run an impedance curve before and after driving a speaker hard for a while. Or, run the curve at a performance power level. This will tell you a lot about what's happening under the hood. For instance, changes in coil resistance and magnetic field would both have their own signatures in such a test.

I haven't quite gotten around to setting myself up for impedance curve measurement yet, so my neighbors will be spared of this, at least temporarily.

This is good information, I agree.

This is also the basis for the technology behind IASYS analysis by Audio Control. It looks at lower temperature pulse based analysis to determine electro-dynamic linearity of loudspeakers. This splits the thermal compression apart from the electro-dynamic compression mechanism in order to develop limiting algorithms. It's used a lot in loudspeaker crossover/processors to quantify what's happening non-destructively. I used one for years when developing such products (including powered speakers). I think it should be clear that this is not my first rodeo regarding speaker technology, I back my comments up with 40 years of engineering based commercial loudspeaker design.

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[fdeck]

This is good information, I agree.

This is also the basis for the technology behind IASYS analysis by Audio Control. It looks at lower temperature pulse based analysis to determine electro-dynamic linearity of loudspeakers. This splits the thermal compression apart from the electro-dynamic compression mechanism in order to develop limiting algorithms. It's used a lot in loudspeaker crossover/processors to quantify what's happening non-destructively. I used one for years when developing such products (including powered speakers). I think it should be clear that this is not my first rodeo regarding speaker technology, I back my comments up with 40 years of engineering based commercial loudspeaker design.

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Wow, that looks like a cool box. Naturally I'm limited to much more primitive gear. One can learn a lot using a regular PC sound card, the drawback is verifying that it's actually measuring what you think it is. Fortunately, creating measurement gear is my day job.

Don't know if you remember the Nicolet brand of signal analysis equipment and oscilloscopes, but that's where I work. They were one of the first, if not the first, makers of a practical Fourier Transform analyzer.

 

[agedhorse]

I do remember Nicolet, though I never owned any.

 

[Downunderwonder]

Need to compare actual heat transfer of the magnet structures not just the material properties. If I am reading it right the neo magnet being thinner and better at transferring heat should naturally result in a cooler coil every time, everything else equal.

 

[Mike Arnopol]

All I know is that Jerry McNutt, the chief engineer and I were developing a custom 8 driver for me. I was lamenting that there wasn't a Neo basket capable of having a gap long enough for the Xmax I wanted
He told me that while the ferrite basket woofer would obviously weigh more that due to the greater mass of the magnet that there would be better heat dissipation and that there would be less thermal compression than the same parameter woofer with a neo magnet. I am certain that I am less knowledgeable than many here as far as a technical understanding of this, but I am certain that the designer of the drivers is likely more knowledgeable than anyone here. I have used 6 different custom drivers from Eminence in my cabs and have gone through about 30 prototypes. My limited knowledge is directly from the designer. I'm sorry that I may have been overly pissy about stuff but I do get a bit fatigued from Andy's condescension. While not as knowledgeable, every prior prototype and production driver that I use have been extensively auditioned in real world gig situations. I have played bass at some of the highest level gigs for 45 years. I I'm only saying this because I consider direct professional experience the most important in assessing gear.

I don't need a non-bassist telling me that my experience and judgement are "psychological"

 

[SoulReflection]

All I know is that Jerry McNutt, the chief engineer and I were developing a custom 8 driver for me. I was lamenting that there wasn't a Neo basket capable of having a gap long enough for the Xmax I wanted
He told me that while the ferrite basket woofer would obviously weigh more that due to the greater mass of the magnet that there would be better heat dissipation and that there would be less thermal compression than the same parameter woofer with a neo magnet. I am certain that I am less knowledgeable than many here as far as a technical understanding of this, but I am certain that the designer of the drivers is likely more knowledgeable than anyone here. I have used 6 different custom drivers from Eminence in my cabs and have gone through about 30 prototypes. My limited knowledge is directly from the designer. I'm sorry that I may have been overly pissy about stuff but I do get a bit fatigued from Andy's condescension. While not as knowledgeable, every prior prototype and production driver that I use have been extensively auditioned in real world gig situations. I have played bass at some of the highest level gigs for 45 years. I I'm only saying this because I consider direct professional experience the most important in assessing gear.

I don't need a non-bassist telling me that my experience and judgement are "psychological"

Before getting "pissy" you should recognize "fatigue" and take a rest....your potential clients are reading this.

 

[agedhorse]

Condescending Mike? This is the basis of my education AND much of what I do for a living. I am doing my best not to stray far from the facts, and trying hard to deliver this information in a "gentle" way.

Is it possible that you misunderstood what Jerry was saying? Is it possible that for your application, the steel slug pole piece that's used in the ferrite motor was better thermally for the VC diameter and winding height that your driver used? This is one argument for not using a T-yoke or undercut pole piece in spite of the different magnetic field shaping opportunities. The pole piece and to a smaller extent the return plate help remove heat from t he voice coil, but this has little to do with the temperature of the magnet or the operating conditions of the material.

The location of the magnetic material is different between the two drivers, the magnet on a ferrite driver is nowhere near the voice coil so the magnet itself factors very little in thermal performance. IF it made sense to place the Neo material in the ring location rather than within the pole piece itself, there would be no difference in the operating temperatures of the two magnets. In fact, there are some Neo drivers that use (a series of small) ring magnets in place of or in addition to the pole piece slug, but the benefits in general of the pole location far outweighs any potential issues.

Just consider that perhaps you are missing some bit of critical information here.

 

[/\/\3phist0]

Before getting "pissy" you should recognize "fatigue" and take a rest....your potential clients are reading this.

Or clients that will now never be, advice, and engineering knowledge freely given, is to be used, or not as you see fit. What I've seen attitudinally from Mike on more than one occasion has made my opinion of him and his product as a thing to be avoided.
Pissing matches in public rarely have a positive outcome.
Sad, never will I own or entertain MA products. In addition I would councel any who ask against the choice.

Another consideration is that I feel as though Eminence works with Andy also and perhaps even the very engineer that you name. You drop people's names, claim to align with their expertise. Yet you discount and rail against another well pedigreed and WIDELY known and respected engineer in the industry?
Hurting yourself more than you recognize. @Mike Arnopol

 

[beans-on-toast]

At the end of the design process, it helps to bring someone in with golden ears to evaluate the woffers.

Nope, not there yet.

 

[Al Kraft]

Just consider that perhaps you are missing some bit of critical information here.

IME in 42 years as an engineer I've found that most techncial discussions where there isn't unanimous agreement pretty much come down to "some critical bit of critical information" that is emabrassingly obvious after it is suddenly provides clarifying context,...and the underpinning science and math are rarely at odds when that context re-centers the discussion.