That's probably why loose sand is so effective - there's the 'viscous' element in how it behaves: it resists motion but has no "spring back", the energy is converted to heat. Think of pushing your hand firmly through fine sand on the bench, this requires energy on your part to make happen - but the sand doesn't "bounce" ...
Pooh,
Are you talking about a low density foam that you are adding the sand to? It seems like that would be difficult to do with a single component foam as they react relatively fast. I'm not sure what a random addition of mass would do to help the foam become more lossy. I have designed and built many audio parts with high density self skinning rigid foam and the damping of the material I would rate as very good. For JBL we used a medium density self skinning flexible foam to damp the wooden substructure that they supplied to us. We over molded the wood with the urethane and then they went so far as to put a layer of neoprene around the tweeter area so they actually had a three layer face with progressively more density. They were called the XPL speakers and were their top of the line product at the time and were sold mainly in Japan.
Are you talking about a low density foam that you are adding the sand to? It seems like that would be difficult to do with a single component foam as they react relatively fast. I'm not sure what a random addition of mass would do to help the foam become more lossy. I have designed and built many audio parts with high density self skinning rigid foam and the damping of the material I would rate as very good. For JBL we used a medium density self skinning flexible foam to damp the wooden substructure that they supplied to us. We over molded the wood with the urethane and then they went so far as to put a layer of neoprene around the tweeter area so they actually had a three layer face with progressively more density. They were called the XPL speakers and were their top of the line product at the time and were sold mainly in Japan.
Anyone with experience of using glass-fibre reinforced gypsum for making horns? Looks like it might have many advantages over resin based fibreglass.
GFRG - Glass Fiber Reinforced Gypsum. Lightweight architectural gypsum
GFRG - Glass Fiber Reinforced Gypsum. Lightweight architectural gypsum
I've tried a number of combinations over the years, and one of the better one's is a sandwich of wood (ply or mdf) - butyl rubber (available as a sticky rope commonly used for car windshield gaskets - and aluminum. Probably overkill but it worked great on a set of subwoofers. Of course they are heavy but not something I move around much after dialing in the room placement. I've also used lead sheet painted on the touch surface side with black industrial enamel as top panels. And if anyone remembers them the Microsonic panel dampeners work like gangbusters. Not sure if they are in business anymore which is too bad they had a truly great product. Also went crazy on a set of monitor stands once fabricated from .25 inch steel plate and 2 inch steel tubing each filled with 90 lbs of lead shot and welded sealed and tight. Those have to be one of the deadest sets of stands on the planet. Anyway I think as everyone here demonstrates there are several approaches to solving the cabinet dampening issue. I've never played with the urethane panel material the Earl Geddes likes but it does sound really promising. By the way a good piece of styrofoam between two pieces of sheet metal makes a damn good foundation for amp, turntable, etc.
Most homes are built upon several layers of material from course aggregate at the base to the top level which is sand. Under pinning the foundation holds these layers in place and becomes a solid dampened mass. The only restraint to this is building earth quake, mud or rock slope or coastal/water saturated earth where we have problems. If we're discussing flat be it horizontal or vertical these course sands pack down tight with the use of an gas powered vibration compactor and it is a prerequisite for a foundation construction code, outside of that Florida "self leveling" sand
This sand is not the typical soft type that's found at the beach, finely ground and rounded, but rather (heat) fractured so that is has sharp irregular shape that locks into place.
When we examine this the same is true in an enclosure wall. The outer surfaces act as the under pinning and the natural vibrations compact the material. The additional constrained layers only adds to the efficacy.
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Which brings me around to things (junk) I've discovered in my storage unit. Outside of finding those pesky caps that were hiding for the last year dot 5 (YEAH), I'd found a vinyl (?) 1/8" foam mat that was picked up some 12 years ago for dampening the side panels of my full tower computer cases... large undampened metal panels combined with 150cfm air flow, dual PS, 7200rpmHD's and additional water cooling, I was disparate for some noise reduction and this helped alot. Simply cut to shape and glued on with Super77 worked a peach. Am on the hunt for more if it's still available. Used as a drawer liner, it didn't have any "acoustical" terms attached to it so that spelled "CHEAP" <$5 ~48"x 16"@ HD if memory serves me correct.
Also this extra sheet I have is like new, hasn't hardened up one bit so it's quite stable in the long term. Testament to that is the storage of this piece, in my storage closet which would typically hit >130f in the summer. Once had a can of low expanding (THANK HEAVENS) latex foam, rupture. What a mess
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It appears to me that the "vivid tone colors" are a result GPA 416 having high nonlinear distortion, while JBL 2226 has lower nonlinear distortion. Do you think so ?
Have you measured distortion of the GPA driver ?
I try to find information of GPA but the data at their page is sparse, even suspiciously so. No freq response etc.
Robh3606,
You could try a supplier such as McMaster-Carr. I imagine they may have the neoprene in the correct thickness. One of the problems as you said with the entire finished product was the neoprene as it had a tendency to pull back from the edge where it was inserted and customers weren't to happy about that. Funny thing was that if we even had a pinhole in the bottom of the baffle where you would never see it they would reject the part. But they screwed things up so many times you wouldn't believe it. They could barely cut two pieces of wood the same in there own cnc wood shop. This was all done in the old Balboa Street facility that was their premiere plant for the pro audio and high end lines produced for Harman.
You could try a supplier such as McMaster-Carr. I imagine they may have the neoprene in the correct thickness. One of the problems as you said with the entire finished product was the neoprene as it had a tendency to pull back from the edge where it was inserted and customers weren't to happy about that. Funny thing was that if we even had a pinhole in the bottom of the baffle where you would never see it they would reject the part. But they screwed things up so many times you wouldn't believe it. They could barely cut two pieces of wood the same in there own cnc wood shop. This was all done in the old Balboa Street facility that was their premiere plant for the pro audio and high end lines produced for Harman.
I don't where the idea got started that a slather of 2nd-harmonic distortion makes everything sound nicer ... it seems like an especially popular idea over in solid-state land.
In my experience, high-distortion drivers (and amplifiers) sound worse, not better. 2nd-harmonic distortion can impart a false warmth, but since IM distortion also goes up, complex music quickly becomes congested-sounding. 3rd-harmonic, in isolation, lends an hard edge to the music, and is not generally welcome. The correct ratio of 2nd and 3rd (about 4:1) restores a sense of proportion, but IM distortion is then substantially worse, with noticeable degradation of spatial qualities, and coloration added to voice.
I've played with amplifier distortion spectra and my general philosophy is reduce high-order terms and IM distortion as much as possible. In practical terms, that means getting rid of Class AB switching artifacts from the signal chain.
If a bass driver makes a concert grand piano sound the same as a generic electric piano, I don't consider that "accurate". There's something wrong with the driver.
Conversely, I don't know of added distortion spectra that will magically make a bad recording sound more realistic ... the mythical "don't suck" switch that every sound engineer would like to have.
Sorry about the annoyed tone, but I'm getting very tired of the "euphonic distortion" myth that is endlessly put out by manufacturers of bad-sounding transistor amplifiers as an excuse. Real acoustic music, without electronic "help", does not sound like an audiophile recording. It does not sound "accurate". It sounds real and vivid, which is completely different.
If tone colors are flattened and dulled, that is not "accuracy". It's a design or manufacturing defect. When designing electronics, if this happens, I look for low-level IM distortion, power-supply hash, or RFI getting into the audio signal. If a bass driver is tonally flat and dull, I am not sure what the distortion mechanism is, but it has to be there. As in electronics, the first place I would look are low-level IM distortion mechanisms.
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Elias said:
Lynn,
So in light of your non-answer to Elias and my questions regarding whether you have measured the GPA 416 or JBL 2226 in your "Beyond the Ariel" design, can we take it that the answer is you have not measured either driver's response?
Art
I've done nearfield measurements of both, and there's nothing exceptional there. They both have the typical broad rise around 1.5 kHz that most 15" drivers have, and the dropoff above that is a little rougher in the JBL, while the GPA is somewhat smoother. The published curves of the JBL 2226 were somewhat smoother than what I measured; the region above 2 kHz wasn't that pretty. Then again, it's a high-power 15" prosound driver, so no surprise. It's not a full-ranger.
The broad rise at 1.5 kHz is steeply attenuated by the 3rd-order lowpass filter; whether it's worthwhile to add an additional notch filter is yet to be determined. Initial tests indicated audibility of the notch filter was low, and did not change the basic character of the driver.
As expected, both drivers are completely flat below 700 Hz, since they are in the piston band, with the LF rolloff controlled by T/S parameters.
The broad rise at 1.5 kHz is steeply attenuated by the 3rd-order lowpass filter; whether it's worthwhile to add an additional notch filter is yet to be determined. Initial tests indicated audibility of the notch filter was low, and did not change the basic character of the driver.
As expected, both drivers are completely flat below 700 Hz, since they are in the piston band, with the LF rolloff controlled by T/S parameters.
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I cannot see how this could explain the "vivid tone color" differences betwen JBL and GPA drivers, as you mentioned they both were low passed with 3rd order at 700Hz. The cone breakup resonanses etc are most likely not the cause.I strongly suspect there is exessive nonlinear distortion going on in GPA driver, and I was hoping someone could show measurements ?
One area to look at between these two drivers would be the coil length and gap depth differences that could have a profound effect on the usable linear motion of the drivers. These older high efficiency drivers often have a very limited linear excursion limit. Another thing to look at is the actual FR after the low pass filter is applied. Though we tend to think that a 3rd order filter will rapidly attenuate the out of band frequencies the peaks such as the 1.5khz peak and other lessor peaks can still be audible even with attenuation. I would also look carefully at a waterfall response to see if there are any areas that have a slow decay time that can change the coloration of any driver.