Another Triska Sub

[Jim Shearer]

I wanted to build a small sub to match my FE108eSigma Metronomes. Not a big, thumping HT sub, just a nice, musical sub. The Mets go down to 40 Hz, which is OK for some types of music, but they can’t quite put the kick in a kick drum.

I remembered seeing the Triska sub in a Parts Express catalogue and thought that would be just about right. I decided to change the design slightly, as I don’t like to build with MDF (I’m solidly on the plywood camp,) and the perfectly square, painted design wouldn’t look very good next to the nice birch Mets. Also, the design didn’t seem to have any internal bracing, so I enlarged the vertical dimension to allow for the volume added by a vertical driver brace and several additional pieces. The first photo shows the finished box w/o the driver, passive radiators or plate amp. The birch veneered top and bottom ‘over hang’ the box and should look nice w/ the (yet to be built) grills which will cover the driver and PRs. You can see some of the brace work through the diver cut-out.

The second photo shows the sub all buttoned up (but w/o the grills) in place w/ the Mets. The shiny chrome screws will be replaced w/ black oxide screws, but I didn’t want to wait for them to arrive before beginning listening tests. I haven’t finished tweeking the mass added to the PRs, but the initial tests w/ 48.6 gr. (washers plus screw) are promising. (Yes, I do know the mass to tenths of a gram; the balance near to hand happened to be a 5 place Metler.) Output is good to the mid 30’s (Hz) and still useful at 30 Hz.

When doing the initial frequency tests, I was surprised to hear the door on my equipment cabinet rattling. The volume that this sub can generate may not satisfy a hardcore rocker, but its quite sufficient for music as I play it. The kick drums indeed have ‘kick’ and the low frequencies on Temple Caves from Mickey Hart’s Planet Drum CD are there--things that are missing when the Mets are used w/o sub.

Unfortunately, at this point I haven’t gotten the smooth integration of this sub w/ the Mets that I have w/ my Polk and vintage Visonic (w/ added PE plate amp) subs. My room has an 80 Hz resonance, and the way the plate amp on this new sub has its filters, even set down at its lowest, I get a ‘bump’ in the low 60 Hz range. The control on the plate amp says minimum is 40 Hz, but the specs in the data sheet and on the PE website say 60 Hz. Based on my tests, I’m thinking that the data sheet is right: the lowest setting is 60 Hz, so the sub is coming in at a point where the Mets are still going strong. The data sheet for the plate amp doesn’t say what, if any, filter may be applied to the speaker level inputs (which I use.) On my other subs, the speaker level inputs are ‘shaped’ by a 6 dB 120 Hz filter. I’m certain that this greatly facilitates integration of the subs w/ the main speakers.

I do like this little sub, but I don’t think I’ll be using it w/ the Mets. I probably will change my plans for my next speaker build. I had intended to build a pair of FE126e bipole Mets. Now I’m thinking that a pair of FE127e Fonkens will be a better choice. This sub should nicely compliment the Fonkens, which have a low end limit around 100 Hz. Then the question will be: do I want to make another Triska to have stereo subs?

[Jim Shearer]

second photo: sub w/ FE108e Sigma Metronomes
(maybe someday I'll figure out how to get more than one photo in a post.)

[gychang]

Originally posted by Jim Shearer
Also, the design didn’t seem to have any internal bracing, so I enlarged the vertical dimension to allow for the volume added by a vertical driver brace and several additional pieces. The first photo shows the finished box w/o the driver, passive radiators or plate amp.

This sub should nicely compliment the Fonkens, which have a low end limit around 100 Hz.

is there any more detail on the sub demension used?, did u ever team it with the Fonkens?

gychang

[Jim Shearer]

The only change in box dimensions was an increase of the internal height to 12.75". This accommodates the internal bracing I added: vertical driver brace w/ 40% holes and triangular braces on the sides. The box is VERY solid!

The filters in the plate amp used in this project (as specified in the PE parts list) are such that it doesn't seem to do well w/ the Mets. The tests I did on the Triska sub indicate that the plate amp may say it's capable of XO at 40 Hz, but I measure something closer to 80 Hz when the control is set at minimum (40 Hz.)

This caused a change of plans for my summer speaker build. I had intended to build a pair of bipole FE126 Mets. Instead, I'm working a pair or FE127 Fonkens. I built speaker stands for them, and now I'm in the middle of the Fonken build. Based on my rate of work, I expect to have them finished late this month (mid-September at the latest.) I hold out hope that the Triska will be just what the Fonkens need. If not, then I'll have to upgrade to a better plate amp. (On another sub I am using a Dayton 240 watt plate amp which appears to actually deliver the 40 Hz XO that it claims; that one works very well w/ the Mets and two other sets of speaker I have tried pairing it with.)

Yes, I am SLOW! What some can do in a weekend takes me more like two months.

So I should be able to tell you how the Triska works w/ the Fonkens by mid to late September.

Cheers, Jim