Omnifex is right: 15 Hz or lower

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Omnifex recently asked this forum to identify drivers with resonance below 15 Hz. What followed was mostly derision, seen all too often in this forum (and from the usual guys). But I think an examination of his question and the responses can be very informative for clarifying the "fault lines" in discussions here.

The main division is between people with an intellectual curiosity about R&D in creating better sound methods versus those who just want to saw MDF into boxes to get the best results feasible within their constraints.

To begin with, Omnifex is absolutely right that the linear portion of driver behaviour is north of their resonance. Duh*. That is true even when a sim says you can mask the resonant bump with a counter-resonance.

After reading the criticisms, Omnifex concluded you need to build your own. He's right about that but I sure don't know why. Some of the posters seemed certain that if Nature had wanted humankind to have drivers with low resonance, Nature would have made them.

The AR1 speaker of 1954 had a driver with a 12 Hz resonance in free air. Why is it not possible, Nature's will notwithstanding, for humankind to make such drivers today? Too much starch in the spiders? Certainly no need to make 2-lb cone assemblies to achieve that. Certainly no need to win the car-audio wars by winding the VC with 14-gauge wire.

Instead of dumping on a fair question, where are the creative forum members who want to suggest ways to get driver resonance down? Or ways to address rear radiation without doing more harm than good?

Let's see some posts from creative people!

Ben
*well, the motion is linear but speaker output is an artful mishmash of various factors varying with driver diameter
 
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just a guy

Member
2006-05-12 6:59 pm
To begin with, Omnifex is absolutely right that the linear portion of driver behaviour is north of their resonance. Duh*. That is true even when a sim says you can mask the resonant bump with a counter-resonance.

First, he did not say that. He gave no clues as to why he wanted a low fs driver.

Second, linear in what way? Using a driver on both ends of it's resonance is not a problem. Not in frequency response or in any other way.

Third, the resonance at fs does not have to (and usually doesn't) create a resonant bump. The only time this happens is when qts is very high. This has been pointed out to you before.

After reading the criticisms, Omnifex concluded you need to build your own. He's right about that but I sure don't know why. Some of the posters seemed certain that if Nature had wanted humankind to have drivers with low resonance, Nature would have made them.

You don't have to build your own. There are plenty of companies that will build anything you want to your spec.

If there were a need to have a 15 hz or lower fs driver there would already be a market for it. The reasons an fs that low is a bad idea were stated clearly in that thread. It requires either a sloppy (loose) suspension or a very high moving mass or both. It's not a good idea.

The AR1 speaker of 1954 had a driver with a 12 Hz resonance in free air. Why is it not possible, Nature's will notwithstanding, for humankind to make such drivers today? Too much starch in the spiders? Certainly no need to make 2-lb cone assemblies to achieve that. Certainly no need to win the car-audio wars by winding the VC with 14-gauge wire.

The AR1 (from my limited knowledge of that model) is an acoustic suspension woofer. That means that it has a necessarily very weak suspension and relies on the air spring of the box for it's restorative force.

While this was a novel idea back in 1954 it's not such a good idea now. Drivers have improved greatly and it's now possible to have low(ish) fs AND low Vas so there's no need for acoustic suspension anymore.

Instead of dumping on a fair question, where are the creative forum members who want to suggest ways to get driver resonance down? Or ways to address rear radiation without doing more harm than good?

The ways to get fs down were stated very clearly and very early on. It's moving mass and suspension. You adjust those two variables until you have the fs you want. There's literally nothing else you can do.

Your entire post is a criticism of a discussion in which you invite new and innovative ideas but offer none yourself. If you think there's a way to accomplish these goals other than what was already stated, let's hear them. If not you are just stirring the pot with your own added ingredients consisting of your desire to not use drivers at their resonance frequency.
 
Hi,

Your just pontificating. No practical application was described.

What was the sealed Fbox of the AR1 ? Did 12Hz Fs help or hinder ?
My supposition for the AR1 and its actual Fbox is that that Vbox
was very much lower than driver Vas, and we all know that for
a speaker with Vbox << Vas, intrinsic driver Fs hardly matters.

Being creative is using the real facts well, not making them up.

It is easy to make a very low Fs driver, that they don't exist is a
clue that doing that creates problems without any real benefits.

You lose control of the suspension, and what that allows.

rgds, sreten.
 
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While I think that the tone in the original thread (now closed) was a bit negative, I think that people were trying to ferret out whether using a driver with such a low Fs was really warranted. It's the way that this was done that was a little off-putting.

I almost joined in the scrum. I wanted to ask Omnifex if he knew the "penalty" for a very low Fs, high mass, high-compliance driver and to ask him if he felt that his needs really be served by that? This is a little different than the "tell us what your application is and then we will tell you what you need to know" kind of responses that I saw posted.

I find that "pile-on" threads undermine the tone here at DIYaudio. Maybe people should try to employ a more patient "ask and then wait and see" attitude about things. If you don't like the thread, just move on. The OP shouldn't have to answer people's questions - he posed his own. Answering a question with an question is rather rude in face-to-face conversation, no?

Let's try to rise about the "comment section" level of humanity here, people.
 

just a guy

Member
2006-05-12 6:59 pm
He got everything he asked for and more. He got a derivation of fs (how it relates to Sd, Vas (or Cms) and Mmd (or Mms). He was told there's only two ways to affect fs - moving mass and or suspension. He was given several options to obtain a driver with any fs he desired - add weight or have one custom made from any number of companies that do one off designs to spec. He was told that there are downsides to a very low fs - low sensitivity and/or inadequate suspension. This information was all given freely and while we did question him on the details, that was something he promised so it's not inconceivable to expect him to honor his word.

In return he refused to answer what the actual goal was after promising to do that if he was given information. He mentioned VERY early on (like in his first response) that he would trade details of his goals for information. I find that a lot more troubling than anything that came after.

The goal is EVERYTHING - it determines whether he actually needs an fs below 15 hz or not. Blindly giving people what they ask for without knowing the goal is not necessarily helping them. If the goal is misguided and you help to further a misguided goal you really have not helped anyone, in fact you've wasted everyone's time and wasted the OP's money.

The comments that you seem to object to come from a place of understanding the tradeoffs and sincerely questioning whether the OP understood what he was asking for. I don't see any harm at all in that, in fact a bit of confrontation is often a lot more conducive to learning than handing a loaded gun (in the form of incomplete answers to ill conceived questions) to someone that doesn't know what to do with it.

YMMV and we will all have different opinions on how these things should be handled. I don't think anyone overstepped any boundaries except the OP by refusing to keep his word and providing details.
 
CharlieLaub - many thanks for a deep post that said things so perceptively.

As a person who is careful in his professional writing to avoid words like "very low 45%" or "normally....", I'd like to ask about "very low Fs", "high mass", etc.

Although those descriptions are commonplace in our crowd, it is only historical accident that 15 Hz would be consider "very low". I wonder how Rice and Kellogg came to their modal values. I bet they started with a coil and former and a cardboard cone and then created a spider that kept all the pieces together. (If anybody knows the real history, please post it.)

What if spiders where twice the typical diameter and therefore a whole lot more compliant, even keeping the moving assembly the same? I bet if Rice and Kellogg worked with ceramic magnets (large and flat), instead of, I suppose, electromagnets, we'd have bigger spiders??? Being forebears at Bell Labs, ahem, ahem, they probably thought their driver was well below the passband anybody needed back then. Then the passband grew... as disaster movie soundtracks grew.

From time to time people start threads about making their own drivers. Often in the more fun-loving and experimental Planar and ESL forum. I wish there were more experimentation in this section. Motional feedback, the final frontier, gets massive interest here're, but seems hard to make it work*.

Ben
*I've been using MF on and off for nearly 50 years
 
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just a guy

Member
2006-05-12 6:59 pm
Do you have any concept at all of how much money the larger companies (like Harmon for example) invest in R&D and testing? If there was any benefit in changing things (like larger spiders or fs under 15 hz) these companies would be doing it. Even if it was a bad idea but there was a market for it they'd be doing it. But since it's a bad idea AND there's no market for it you don't see it.

Calling the choices made in current state of the art drivers made by these large companies "historical accident" is obtuse at best. Suggesting that these companies as a whole don't really know what they are doing and are stumbling along making bad design choices that only a select few people on diyaudio (like yourself) can improve is hubris beyond control.

Your premise is that drivers should not be used at fs. If you start with a flawed premise everything that follows is nonsense.

The diy crowd (a guy building a conventional moving coil driver in his basement) is not going to come up with something exceeding the performance of the world's largest companies.

What you are advocating is clearly a move back to acoustic suspension drivers - everything you've said leads to that - a very low fs, a very compliant suspension, a very high Vas and a small(ish) sealed box. This technology had it's place in 1954 due to the state of driver tech at that time but we are well past that. Doing the same thing they did 70 years ago is not innovation, regardless of what you want to label it.
 
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Mooly

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Paid Member
2007-09-15 8:14 am
:cop:

Thread closed. Attempting to restart discussions from a closed thread is a violation of forum rules.

Extract from rules.

Some threads become repetitive or conflict prone. The moderation team will, at its discretion, close these threads. Starting a new thread to discuss the same topic is prohibited.
 
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