Re: Helium - a true micromonitor
It's like early Christmas around here.
For the past few days I've been listening to the Helium tuning and crossovers in the ND91-4 boombox project that I started last year. It has very similar dimensions for the flat pack enclosure, but is slightly bigger- about 0.055 cu ft. HWD in inches it's 5.5x3.5x5, and a strip of 3/4x1/2x5.5 inch fir along one edge. Crossover is external, so it doesn't eat into the enclosure volume at all.
First off, props to Scott for the work to figure this one out and post it here. Very nice results, and well documented.
Adding the NF16 tweeter to my project made a huge improvement. After almost a year listening to just the ND91-4, I'm excited again about this project, not disappointed like before. Plus the port tuning change removed the muddiness I was hearing.
BTW, tf you see recommendations on the web for the ND91-4 in a 0.035 cu ft. (1 litre) enclosure and a 1 x 4 inch port, I'd approach that as optimistic. You should probably count on the port length being much longer, and the box a little bigger for practical reasons.
+1 on the 40ohm resistor across the tweeter terminals that Scott suggested. I might make that switchable, but I enjoyed to balance on vocals a lot more with the resistor in place.
Port tuning I did by subjective listening and fiddling with a tone generator. Best port dimension, using 3/4" PVC is: 4-1/4" for the long straight section, then an elbow, then a short, 1-1/4" section. Pipe ends were flared. So total length ended up as about 7 inches, depending on how one accounts for the flare and elbow. I made adjustments in 1-inch increments.
My woofer coil was the Jantzen 20g 1mH from PE; caps were Metal Poly from PE also. Not that they needed to be- this isn't a wispy nuance application so more budget components will go into the next build.
Overall impressions are very good. It's a warm balance on vocals- not husky, just nicely warm, then a smooth, even bass response. No one will be pounded by the raw bass output of this boombox, but the impression is of a full sound. I've heard larger speakers that didn't do this well. Midrange is sweet and the top end smooth. Sounds like a cliche at this point, but the voicing works really well. It's no smiley face sound, just robust, enjoyable performance. My guess is that it would work well for home theatre, so long as you have more modest listening levels in mind.
I'm thinking of making a set of these for the living room.
Thanks again, Scott. And Happy Holidays to you and yours.
It's like early Christmas around here.
For the past few days I've been listening to the Helium tuning and crossovers in the ND91-4 boombox project that I started last year. It has very similar dimensions for the flat pack enclosure, but is slightly bigger- about 0.055 cu ft. HWD in inches it's 5.5x3.5x5, and a strip of 3/4x1/2x5.5 inch fir along one edge. Crossover is external, so it doesn't eat into the enclosure volume at all.
First off, props to Scott for the work to figure this one out and post it here. Very nice results, and well documented.
Adding the NF16 tweeter to my project made a huge improvement. After almost a year listening to just the ND91-4, I'm excited again about this project, not disappointed like before. Plus the port tuning change removed the muddiness I was hearing.
BTW, tf you see recommendations on the web for the ND91-4 in a 0.035 cu ft. (1 litre) enclosure and a 1 x 4 inch port, I'd approach that as optimistic. You should probably count on the port length being much longer, and the box a little bigger for practical reasons.
+1 on the 40ohm resistor across the tweeter terminals that Scott suggested. I might make that switchable, but I enjoyed to balance on vocals a lot more with the resistor in place.
Port tuning I did by subjective listening and fiddling with a tone generator. Best port dimension, using 3/4" PVC is: 4-1/4" for the long straight section, then an elbow, then a short, 1-1/4" section. Pipe ends were flared. So total length ended up as about 7 inches, depending on how one accounts for the flare and elbow. I made adjustments in 1-inch increments.
My woofer coil was the Jantzen 20g 1mH from PE; caps were Metal Poly from PE also. Not that they needed to be- this isn't a wispy nuance application so more budget components will go into the next build.
Overall impressions are very good. It's a warm balance on vocals- not husky, just nicely warm, then a smooth, even bass response. No one will be pounded by the raw bass output of this boombox, but the impression is of a full sound. I've heard larger speakers that didn't do this well. Midrange is sweet and the top end smooth. Sounds like a cliche at this point, but the voicing works really well. It's no smiley face sound, just robust, enjoyable performance. My guess is that it would work well for home theatre, so long as you have more modest listening levels in mind.
I'm thinking of making a set of these for the living room.
Thanks again, Scott. And Happy Holidays to you and yours.
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