that's why I assumed we were talking about compression drivers in horns? I'm kind of confused was the discussion is about now.
noah katz said:
Perhaps. But there will be a lot of frequencies going through that cone (some better attenuated, some much less) , and I'm not entirely convinced they don't matter.
I am not going to enter into this argument because you guys are talking about things that do exist, but are not major concerns. I worry about those things that matter, not those that don't. Some sound does come through the cone - so what? - its way down from the direct sound and not a significant factor.
My test involved a rear wall that was made as refelctive as possible, and then damped as much as possible. By knowing the distance to the rear wall I could find the impulse from that wall in the system impulse response at the known increase in travel time. It was insignificant to unobservable.
My test involved a rear wall that was made as refelctive as possible, and then damped as much as possible. By knowing the distance to the rear wall I could find the impulse from that wall in the system impulse response at the known increase in travel time. It was insignificant to unobservable.
In his Pluto Speaker, Mr Linkwitz found the rear wall reflection to be a real and audible problem:
http://linkwitzlab.com/Pluto/construction.htm
So it looks like the answer to "does it really matter?" were "it depends!"
- Klaus
http://linkwitzlab.com/Pluto/construction.htm
So it looks like the answer to "does it really matter?" were "it depends!"
- Klaus
SL´s findings cleary support Earls view IMHO:
He measured the reflection coming through from the end of an unstuffed pipe to be 29 dB below the original signal. With appropriate stuffing the reflection was >40 dB down and SL states: "The earlier sound coloration is no longer noticeable".
He measured the reflection coming through from the end of an unstuffed pipe to be 29 dB below the original signal. With appropriate stuffing the reflection was >40 dB down and SL states: "The earlier sound coloration is no longer noticeable".
gedlee said:
Don't misunderstand, I am talking about the rear wall of the speaker enclosure, not the rear wall of the room.
gedlee said:
Hi Earl:
The challenge is that some of us are unconvinced that the threshold for these is low enough to be arbitrary. I'd think that your work with HOMs would apply to internal box resonances as well, due to the complex internal environment of a typical enclosure there are some high order resonances guaranteed to be set-up (cone-basket, for example). Sure there's SOME attenuation from a cone, but I'd expect the amount has high variability by cone material, size, profile, frequency, drive level, surround type, and other factors. Add to this that as soon as a cone is in breakup mode, it's going to have less damping of specific frequencies acting to excite it, and I think it's fairly clear that there IS a role played by the internal reflections.
Of course, acoustically transparent was an overstatement, as there's significant attenuation possible with a driver, but it's so variable that perhaps best practice would dictate a lot of care be applied to having appropriate absorption and enclosure design near the driver. Certainly since it's a real artifact, there's no harm in attempting to design it out.
gedlee said:
That´s what we (and Mr. Linkwitz) were talking about too. 🙂
Your explanation was easy to understand - even for Germans. 😀
Rudolf
badman said:
I don't disagree here. Doing an enclosure design that is "reasonable" is always the best approach, its going overboard that I disagree with because it doesn't make a significant difference.
All of my systems use a CLD baffle. The baffle is the critical mounting for the drivers and this approach works well to minimize the transference of energy from the drivers into the box. But the air in the box couples very poorly to the physical structure and so with a decent amount of damping this source of excitation can be minimized to the point of insignificance.
There is a small glitch in the systems that I produce that I took about a year to track down. I thought that it was one of those aspects that you mentioned - reflection trough the cone, box vibration, etc. It wasn't. It was simply the spider resonating. But no one making speakers seems to care because every driver that I have tested has this same problem. And its correctable! They just aren't interested.
So when I tested for sound coming back through the cone, it was using the high quality B&C speakers that I use. I can't speak to other less robust devices, but then I don't use those.
gedlee said:
Surely you see the problem with this approach- your driver selection isn't the only valid option. Something like the excellent fostex FF85k is a much thinner cone operating at much higher frequencies. It's still a fantastic driver, just optimized differently. So to dismiss these effects as universaly irrelevant because they weren't problematic with your test, and your driver(s) is not wise.
badman said:
I can't speak to all the wrong ways to do things, its always possible to do a design where almost anything is a problem. But its also just as reasonable to do a design where these issues are not relavent. I choose to do the later and thats the point of view from which I speak.
gedlee, you mentioned that spider resonance is correctable.
do you have any suggestions/ideas what a better spider would be? thanks.
do you have any suggestions/ideas what a better spider would be? thanks.
MisterTwister said:
There are ways to design a spider such that the most agregiuos modes are surpressed, but the exact details of that are proprietary.
badman said:
But thats not at all what I said. IF sound coming through the cone is a problem then it is easily resolved - thats what I said. Its only a problem if you let it be a problem.
Rudolf said:
Pluto is a rather special case, where 1st reflective surface is many, many woofer's diameters away and very small area. Most 'boxes' have rear wall within one or two driver's diameters, which subtends pretty big.
Besides, I'm not sure even 40dB down is enough to be labeled 'insignificant'.
gedlee said:
easily resolved.... only by going to your selected driver or a similar one, for which it's not an issue- if that's even the case. If one likes the use of a specific driver that isn't a B&C driver or other similar construction, that's not a solution. Maybe I LIKE a copper sleeve through the pole for other reasons- this automatically precludes all pro drivers I know of unless you include lambda. And they are wider bandwidth transducers with lighter cones and smaller voicecoils, just like the fostex unit I referenced.
So, again, you're pigeonholing people into your specific designs. They're not perfect, none are, so there's no reason that people should consider your so-called solution as any more valid than the empirically substantiated results of people taking care treating the areas around the inside of the driver mounting, frame, etc, for minimized reflections.
"Don't misunderstand, I am talking about the rear wall of the speaker enclosure, not the rear wall of the room."
I did misunderstand, thanks for clarifying.
"easily resolved.... only by going to your selected driver or a similar one, for which it's not an issue- if that's even the case."
Pro drivers are high efficiency w/light cones, so it seems to me more run-of-the-mill drivers would be less transparent.
"So, again, you're pigeonholing people into your specific designs..."
When did it become Dr. Geddes' task to solve everyone else's problems?
I did misunderstand, thanks for clarifying.
"easily resolved.... only by going to your selected driver or a similar one, for which it's not an issue- if that's even the case."
Pro drivers are high efficiency w/light cones, so it seems to me more run-of-the-mill drivers would be less transparent.
"So, again, you're pigeonholing people into your specific designs..."
When did it become Dr. Geddes' task to solve everyone else's problems?
badman, Bratislav, you guys just raise questions without accepting answers from the Doc. Why not search the available literature for yourselves? Everybody here would be thankful for a short scientific review. Or do you even have your own data to show?
Markus
Markus
markus76 said:
If you're a fan of following blindly go to it. When my results disagree with the doc, I like to have open discourse. This is a discussion forum, it does not require literature review the way a professional paper does, but I'm not aware of any research on audibility of early inside-cab reflections, save "the Docs" extremely vague description of his own testing.