Speaker Asylum

Posted by moray james (M) on September 27, 2009 at 12:24:46

Speaker stand mass loading alternative

I was fortunate enough to be visiting Noel Nolan of Skylan stands several weeks ago and he was working on some alternate ideas for damping both speaker and rack columns. Noel has had numerous requests from customers looking for possible alternatives for sand and kitty litter used in mass loading/damping. We listened to a series of speaker stands the columns damped with a number of different weight high density open cell foam blocks. The blocks of foam are cut oversized and run the length of the Polymer column. Noel had devised a clever insertion device which wrapped the foam plug compressing it thus permitting the entire block of foam to be totally inserted into the column and the jig removed. This insured that the oversized foam block makes perfect smooth contact with the column walls. I actually tried to insert one of the large blocks of foam into a column by hand after suggesting that the jig was probably not necessary. Well after skinning my hand badly and not being able to get the foam placed even half way down the column I had to admit that Noel's clever jig was exactly what was required.
We auditioned the foam damped speaker stands against a reference set of Noel's stands and were both surprised as to the impact of the open cell foam. No the foam is not up to reference standard but when compared to the same stand with empty columns there was a noticeable improvement. Next we moved on to the foam inserted into noels MDF rack columns. Here was a big surprise because the improvement was more apparent than we had found with the Polymer columns. This turned out to be as a result to the stiffness of the MDF compared to the Polymer column material. After a few hours of listening we began to discuss possible alternates to sand and kitty litter for customers who have a difficult time locating either of these products. After a pint of Guinness the idea of Rice as a mass loading material came up. Off we went to the food store and bought a 20 Kg bag of discount rice. Turns out that the 20 Kg bag was perfect to fill all eight columns of the stands holding up Noel's Harbeth HL5's. The result was vastly superior to the foam damped stands and surprisingly good compared to the reference sand damped stands which include specially damped tops and bases.
While the rice filled stands are not quite as efficient in terms of damping as is sand fill Noel was aware that many Harbeth owners find that full column sand damping makes for just a bit too much bass energy. Half filling is a pain to do and this is exactly what prompted Noel to recommend filling the stands with kitty litter. After some time though many found that even filling half way with kitty litter there was still a bit too much bass energy. So it was we next compared a set of four post stands, one set half filled with kitty litter and the other entirely filled with rice. This was an interesting comparison as the rice filled stands sounded clearer and cleaner with more controlled and articulate bass than that obtained with the half filled kitty liter stands. The rice stands actually weighed more than the kitty litter stands. While the rice is not as effective in damping due to particle friction (compared to either kitty litter or sand) the added volume results in increased mass which worked out to be an almost perfect combination. The especially nice part of all this is that the rice (we uses long grain just incase you were wondering) is inexpensive and easy to obtain all over the world at any food store. Combine the fact that you don't have to pre measure anything as with half filling with sand or kitty litter you just buy a 20 Kg bag of rice and fill all four columns up to the top and you are done. The rice is especially easy and clean to work with and there is no surface scratches as can happen with sand plus any spillage is picked up a jiffy.

Stand / Speaker interface experiments...
Fast forward to today, after allowing the rice in the test stands to fully settle into place for a few weeks we decided to experiment with speaker / stand interfaces. The Skylan stand comes fitted with Polyurethane tabs (four small disks, one at each corner of the stand top plate). The magnetic disks are about a centimeter in diameter and approximately 3 mm thick, just high enough to clear the Polyurethane pads. We listened to a selection of tracks of various kinds of music with the speakers seated upon the stock Polyurethane tabs. This was our reference sound. Next we placed the loudspeakers (Noel's Harbeth HL5's) up on three small ceramic disk magnets. The choice of material here was for several reasons, the small ceramic disk magnets are easy to find (most folks need only look on the fridge door) and also because they are very hard, being a sintered ceramic material. We placed a layer of electricians PVC tape on each side of the magnet disks to provide a small compression interface between the cabinet and the stand surface (Scotch tape would likely do as well). The three disks were positioned with two at the front corners of the stand top plate and the third disk in the centre of the rear of the stand top plate. This results in a tripod configuration and is very stable but more importantly results in a significant increase in the mass per disk that would otherwise be obtained using four disks. The result was an immediate improvement in bass weight and control along with improved focus of sound stage. Voices and instruments now had a clearer place within the sound stage. We next moved the two front magnet disks to the top of the metal threaded inserts (the ones the column rods screw into) on the top plate and left the central disk at the rear of the top plate as before. The idea here was to increase the hard coupling of the speaker to the stand (top plate, coupling rod, base plate, spikes and floor). Placing the magnetic disks onto the column rod inserts couples more energy to the stand via the threaded rod. This also couples more energy into the column damping material. This position resulted in further improvements in bass articulation as well as dynamics. Spatial cues were clearer and the sound stage opened up even further than was noticed with the previous disk position. As with all things your personal taste, likes and dislikes will come into play. I think that you may find experimenting with these ideas could result in enhancing the level of your listening enjoyment. I hope that this posting has been of interest and use. Best regards Moray James.
moray james