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Old 28th June 2008, 08:53 PM   #921
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Quote:
Originally posted by salas

I would like to get a full test sheet with serial number against a reference driver if buying a $4K unit. Especially with the versions and tunings going on, I would like to know the spec and match of a given pair.
Point well taken, and that is actually something that the folks at Feastrex indicated to me was one thing they intended to do. Since the pairs are in fact well matched, providing such a printout with each pair is definitely a good idea.

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Old 28th June 2008, 09:04 PM   #922
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Quote:
Originally posted by Poindexter

The part about putting a pair of nickels on (and off) the rice paper cone of a four thousand dollar driver might still make me a little nervous, though.
Yeah, I'd be nervous about a "rice paper" driver, period. Fortunately they're made with "tough as nails" mulberry paper . . .

What makes Clark nervous are the references he has seen mentioning the affixing of modeling clay to the cone. That is a great idea -- but only if you are testing a subwoofer with a cone that bears more similarity to a motorcycle helmet than to a tiny paper whizzer cone fullrange driver.

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Old 28th June 2008, 09:08 PM   #923
MJK is offline MJK  United States
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Originally posted by cdwitmer
The weights that I used had a happy proprensity to wedge themselves between the main cone and subcone, and the small signals input by WT2 would not easily dislodge them. (A pair of tweezers came in handy.)
That exact same thing happens with my Lowthers, the nickels are easy to remove with a pair of tweezers. It really works well and the quailty of the measurements is good. Very quick, very easy, and accurate.
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Old 28th June 2008, 09:43 PM   #924
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Something tells me that I'm going to have to invest in WT3 before very long... it's on offer at Partsexpress for $99 at the moment. I'll still get the nerve pills in though. I look at the paper cones of high price FR drivers & come out in a cold sweat.
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Old 29th June 2008, 01:08 AM   #925
mluckow is offline mluckow  United States
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Quote:
Originally posted by cdwitmer

Fortunately they're made with "tough as nails" mulberry paper . . .
I was Mr. Teramoto's interpreter when he was trained by Keith Larson (of Smith & Larson, the makers of Woofer Tester) in how to use Woofer Tester Pro, and Keith used a single coin (I think it was a penny, but it might have been a nickel) when he was doing measurements of a D5nf driver. Mr. Teramoto didn't have a problem with that at all.

Also, Mr. Teramoto brought along several pieces of the cone paper left over from making cones (which he sometimes wads up and uses as damping material in enclosures), and that stuff is amazingly tough--it's even difficult to tear it when you're deliberately trying. So, there's no way a coin or two on the cone is going to do any damage. Chris is right, this mulberry paper is tough as nails. They call it "paper," and it does look like paper, but it's unlike any other paper I've ever seen.

Mike
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Old 29th June 2008, 01:37 AM   #926
GM is offline GM  United States
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Default Re: well, along that route...

Quote:
Originally posted by blumenco

So it seems that run in is important, but that also there is some "cooling" which must happen after "burn in." Huh?

We have resources to do closed box measurements instead. How should these go? Are the Feastrex drivers, using a phase plug going to leak too much for a closed box measurement?

.........Feastrex drivers are indeed "special" and might require some special measurements in addition to the traditional measurements to see what is actually going on with them.

Seeing that these drivers are at the leading edge of cone driver technology (and especially magnetic circuit quality and raw evenly distributed power at VC gap) the proper way of measuring them might not have even been invented yet.

I have absolutely no idea what those special processes might be, but I do understand that it is generally held belief that a powerful magnetic circuit mated to a lightweight paper cone yields a lack of bass response. These drivers are simply impossible according to that traditional logic.
First, if you want a good measurements reference book, get a copy of D'Appolito's TESTING LOUDSPEAKERS.

Right, once broken in a bit, For standard small signal T/S you want to measure them at room temp with a tiny signal since any VC heating will raise Qes, Qts. Better is to measure them at a higher signal level that more realistically represents its in-use parameters.

WRT measuring Vas, if you're going to use the added mass method, I recommend you have someone make you a ring with a little grab handle for each type of driver to ~evenly distribute the weight and so you don't have to dink with stuff moving around/whatever.

WRT any phase plug/whatever leaks, for this reason I recommend using the closed box method outlined in D'Appolito's book since it more accurately represents how Vas will affect cab design/tuning. Obviously, this is the way to do higher power measurement. If you want to be anal about it, do both added mass and closed box, which will also allow you to accurately calc Sd.

WRT "Seeing that these drivers are at the leading edge of cone driver technology (and especially magnetic circuit quality and raw evenly distributed power at VC gap) the proper way of measuring them might not have even been invented yet.", if its impedance can be measured, so can its T/S specs. Alan Babb tried to convince us that his drivers (now 'DC Gold' branded) were 'special' in this way, which was eventually proven to be pure BS, so you're going to have a tough 'row to hoe' if you let your current ignorance of driver design/measurement hold sway over the physics of the situation.

WRT the ".......generally held belief that a powerful magnetic circuit mated to a lightweight paper cone yields a lack of bass response. These drivers are simply impossible according to that traditional logic.", what really matters here is that Qes tells us what the driver's relative motor strength is, so regardless of how powerful or lightweight its components may be, the fact of the matter is that if it has a medium Qes of ~0.43 as the D9NF apparently does, then all else being equal one could argue that the only thing 'special' about its powerful motor/low mass diaphragm design is that it's not a well designed system by traditional standards, instead being geared more for car audio apps than ultra wide BW HIFI and why it has more bass response.

Sorry if I busted any 'bubbles', but there's no defying the electro-mechanical resonant laws of physics, no 'magic', no 'special'/whatever involved in its basic design, just a balancing of design trade-offs, i.e. the standard of trading efficiency for BW, which when coupled to a high output impedance amp as I imagine most will, yields a ~maximally flat half space response to well below the driver's Fs if the cab is big enough and tuned low enough.

WRT any 'special' Feastrex measurements, these will need to be done with a TEF or similar system to measure its various acoustic properties in its mass controlled and breakup modes BW since this is where any 'magic' may be, i.e. 'God' is in the finer details of motor, diaphragm, suspension, etc. design, construction, so if it does have some new, special VC/gap and/or cone design that has an audible effect, then here's where it should show up, not down in its pistonic BW around Fs where T/S specs reside.

GM
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Old 29th June 2008, 02:21 AM   #927
SunRa is offline SunRa  Romania
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Quote:
WRT any 'special' Feastrex measurements, these will need to be done with a TEF or similar system to measure its various acoustic properties in its mass controlled and breakup modes BW since this is where any 'magic' may be, i.e. 'God' is in the finer details of motor, diaphragm, suspension, etc. design, construction, so if it does have some new, special VC/gap and/or cone design that has an audible effect, then here's where it should show up, not down in its pistonic BW around Fs where T/S specs reside.

I tend to agree, most of our instruments and our understanding of loudspeaker theory resides from a pistonic model of how loudspeakers work. I guess these instruments tends to give up on us when confronting with devices that work out of their pistonic modes... like fullranges. Probably most of our subjective evaluations of sound could have an answer in this non-pistonic puzzle..
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Old 29th June 2008, 05:15 AM   #928
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Default Gm,

Points well taken. I will be the first to admit my ignorance of driver measurement, and of the long established science behind it, and of my ignorance of anything really. Idiots call themselves experts.

My whole point is that "god" or whatever IS in the finer details, just as you say. Looking at the history of science, it is usually observations of the deeper down details that were not being measured before or were being conveniently ignored that eventually unravels the grander "framework" of previous "established" knowledge.

My dad is a bio-statistician, actually. I grew up around his anecdotal stories about the history of science. Contemporary stories of pharmaceutical companies trying all sorts of ways to BS their way to cancer drug approval by the FDA by presenting their data in a statistically dishonest (or underinformed) fashion. In the face of commercial motivation, he always preached honesty and undying skepticism regarding the presentation of a product.

And trust me, I am hardly "bringing" that attitude to Feastrex. Considering Dr. Akiyama's scientific background, and Mr. Teramoto's own scientific/aesthetic development of the drivers by a mind boggling trial and error process. Incredible honesty, a "battling with oneself" has been there all along. I am just joining a team of life long researchers. If this apprenticeship works long term, I feel that it is our shared notions of being painfully honest with ourselves which is our greatest trait in common. Language barrier? Ha!

We do not claim to be "above the laws of physics." Or as "special." Hardly. I brought up these notions because it had been used in other posts. I realize now that I was not specific enough in my qualifications. I was meaning to express a scientific curiosity. NOT as a claim to having found the land of milk and honey.

If anything, what distinguishes the designs of Feastrex is not their extremities of aspects of spec'ed performance, but as an incredible balancing act of all these resources. A cohesiveness and singularity of single driver design. It all ends up behaving more like a formula one car (paradoxally having the same ride comfort of a Bently) and less like a "hot rod."


Considering the fact that there is the rampant practice of medical research companies trying to get a return on their investment by rushing a "promising" treatment to market without even considering that their treatment might actually HURT people, the notion of speaker companies gussying up specs a bit to sell drivers follows an even less infuriating line of logic. So hence my hesitancy with a fairly commercially motivated "science," historically speaking. At my level of ignorance in the field, I find it hard to separate out all the marketing BS while reading most companies' "driver specs." or of figuring out ways to properly and honestly measure them. This is incredibly annoying to me, and to many customers trying to do legitimate product comparison within the speaker industry, car audio, headphone industry. You name it.

It is the underlying paradox: companies make drivers. Just like companies make drugs. But what regulatory commission is in place to make sure that drivers are spec'ed honestly and free in that sense from purely commercial motivation? Who do you trust?

YOU. (plural) I trust you. Hence why I am posting here. So many here have (from what little I understand) dealt with the wobbly wheel of common practice measurable data within the speaker industry and turned it into a legitimately useful tool for speaker design on a wide scale. The virtues of this pursuit are undeniable. In the midst of all that, it is Feastrex's desire to provide as honest of a picture of their product as possible given current readily available (hence repeatable) measurement technology.

For now, it is my motivation to simply get some measurements (that are very accurate) by widely used techniques as it seems that this will actually help people know the Thiele-Small piece of the larger picture of what they are getting as customers (which they have every right to), and also for the many talented designers out there to be better able to design enclosures. Simple simple simple.

Again, it is not my intention to "curse" the Thiele-Small paradigm any more than it already has been. Just to throw that little plug in there for street cred, ya dig? It is a fight for aesthetics our old friend Terry Cain used to fight. Had to carry the torch a bit.

Regarding the "TEF testing," it seems like an interesting place to go eventually, and thanks for the tip, GM. I know nothing about it, but it seems to be a good start into discovering the finer performance details of these drivers, which are no doubt where alot of their ultimate performance (and distinction from other drivers) comes into play.

Ok, now on to my issue with the delta mass testing. I tried the nickels, I tried many different weights (on the FE87). Everything came out whacked each time. So some are telling me that the added weight is OK, others are saying that the closed box method is good. Use both?

Calculating the area of the drivers is super easy given the cad drawings. Or we could just try water immersion in a graduated cylinder. Any takers?

But why was the mass test on the FE87 failing every time? Perhaps that is a better question for customer service.

Thanks so much everyone for all the info.

And yes, washi paper is CRAZY stuff. Rice paper is edible. Mulberry paper is VERY different. It is super strong. When ripped, (which is difficult even for someone with a strong grip), it expands in volume by roughly 15 times and turns into this cottony fluff which floats in the air for several minutes before finally falling to the floor. And this stuff regularly lasts for 500 years? Only in Japan...

-Clark
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Old 29th June 2008, 08:17 AM   #929
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To echo part of what Clark was saying above, and add one further thought of my own, I am convinced that Feastrex would definitely not be where it is now -- it simply would not be, period -- if not for the Internet and the various people who have come together through forums like this one to discuss, praise and criticize Feastrex speakers, and occasionally complain, give a needed kick in the seat of the pants, and provide reality checks. This community is an essential ingredient in Feastrex's success. As good as Feastrex speakers are now, I think they will continue to improve quite a bit more over time through this community's sharing of opinions and knowledge, and unflagging encouragement. Feastrex has already accumulated tremendous knowledge and experience, as evidenced by the good quality of the products themselves, but there are also still significant gaps in their expertise and know-how, and the market's patience -- generously "cutting them slack" regarding their somewhat idiosyncratic approach to speaker building -- is something for which Feastrex should be very grateful. I know you've made Mr. Teramoto one happy fellow, as he is able to continue doing what makes him happiest of all -- building fullrange drivers.

-- Chris
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Old 29th June 2008, 11:47 AM   #930
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Clark,

Just so I know exactly what role everybody has in this discussion, are you employed by Feastrix?
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