Let me preface this discussion by stating that I occasionally skate with well-sealed (foam tip) planar IEMs which sound positively wonderful. I’m perfectly happy with that as my solo rig. I do not expect to achieve anything close to that level of audio quality with anything I can screw, clamp or strap to a board. But, I want to come as close as I possibly can, with a 10lb max weight budget, so that I can enjoy tunes while still hearing traffic, (and maybe entertaining others on a group ride.)
While tunes on a board is silly/dangerous/rude/impractical on many levels, I know it can be done, and want to have some fun fooling around with the project.
Primarily as an exercise for someone else with a Lacroix Lonestar, I tried to engineer a decent system with some bass within that weight budget. I have a few ideas I’d like to bounce off anybody here with something to add.
- Instead of wasting energy, bulk, $ on a DC-DC buck converter to power 12V-24V audio gear, I finally found a well-regarded chip amp board happy with a single-ended DC supply up to 50V.
(It was only $65, and is available for around that elsewhere now.)
The board is only rated to 50V, but the amp chip is happy with 53V, so I’ll have to replace 4x 50V electrolytic caps with 63V versions, then be able to run safely with 12S (50.4Vbat max.) It has 4 separate balanced channels, each of which can provide 150/260W into 8/4ohms at 1% distortion, at least 100/200W of clean power into same = more than enough. It weighs about 9oz. I will use it as a 2.2 amp.
- As impractical as they are, since the input impedance of this amp is very high (100k ohms,) this may be a great place to use a PLLXO = passive line-level crossover for bi-amping. The smallest decent crossover I have (Audiocontrol 2xs) is larger and heavier than the amplifier, has unbalanced connections. I’m going to try a 2nd order (12db/oct) balanced PLLXO with 1k, 10k resistors for R1, R2, and 1uF, 0.1uf (100nF) for C1, C2 for a crossover point around 150hz.
Alternatively, if I can push the crossover point to around 1khz, I’d simply use a 2nd order speaker level crossover with air core coils, MKP caps. The woofer I chose below may or may not sound nice at 200-1000hz.
Alternatively, I can use the new saltine-sized DSP board from partsexpress to make a 2-way active crossover, but I hate to go back to the digital domain after such a nice DAC/PRE (Earstudio ES100.) It comes pre-configured as a 2-way crossover, with adjustable xo point and levels via the onboard pots, but it’s not balanced. (I really want to stick with balanced signal cabling as the board produces a LOT of interference, and I don’t want to waste bulk/weight with metal shielding.)
- BASS is hard to come by on a weight/size budget, but I’ve got gobs of power to play with. I tried one of these in an Apache 2600 case boom box, is fine for stationary listening, but need more to cut through the noise when skating. (I tried skating with it.) Tang Band W6-2253S 6-1/2" Low Profile Subwoofer
I’d like to use a pair of these. I’m thinking of making a wedge shaped enclosure the width of the deck, with one facing up/forward, the other up/back, (triangular sides,) with the amplifier stashed in the bottom. I usually prefer the sound of a sealed enclosure (or open baffle) but these could use a bit of help on the bottom, would benefit from a tuned enclosure. If the enclosure is spaced up from the surface of the deck a tad on rubber feet, I’d have room for a single 8-10in passive radiator underneath or a pair of 5.25-6.5in passive radiators on the triangular end caps.
Alternatively, I have a pair of Tang Band W6-1139si, which might sound better, but weighs more than 2x as much! Likewise, I’ve got a W8-1363SB to try too, but one of 'em weighs more than 8lbs.
The first (shallow) subwoofer I mention, used in the boombox, want to use 2x here, is the lightest weight 6.5in woofer I found by a country mile. It’s around 2lbs. The next lightest contender was around 3.5lbs, and I’d need a pair of either.
On a cabinet-size / weight / size budget, these 3 Tang Band subwoofers are about the only game in town. They make smaller ones (5-1/4, 3in, 2in) but they are too small to make any sense here… I’d need too many of 'em and they would cost considerably more in the quantity needed to equal a pair of either of the 6.5in.
In lieu of proper bass, it might be “enough” to use a pair of bass shakers secured to either end of the deck… I’ve never tried them in a home theater, might be fun. In this case, I’d run the “tops” full-range.
I’m on the fence about what to use for the “tops”, leaning toward 3.5in neo magnet “full-range” cone speakers. I had great results pushing 50W/side into 3in FR speakers on a recent boombox build, want a bit more powah. The pair will weigh about a pound.
There are 2 very interesting new-ish choices for tops: There are now knock-offs of Bohlender & Graebner planar tweeters & mids, for 1/3 the price, some of which can be crossed at only ~500-700hz. There are also now high power 1in and 1.25in Corundum (synthetic sapphire) tweeters for $50-$60 that are good down to 800-1000hz. Either one would get the XO point “out of the way”, vastly improve dispersion (in at least 1 axis) vs the dinky cones.
GRS PT6816-8 8" Planar Slim Tweeter 8 Ohm
Peerless DA32TX00-08 1-1/4" Corundum Dome Tweeter
Speaker attachment to the board??? I propose a prism shape enclosure for the woofers (and amp) above that will sit top center on the deck. For the highs, I’d like to share the truck top plate bores to mount a simple small pear shaped baffle front and rear. When I stand on the board as I would ride (goofy), torso at about a 45deg angle, looking forward, the front speaker is ahead of and to the right of my right shoulder, rear speaker to the left of and behind my left shoulder… both aimed up at my noggin.
Source / input: I absolutely love the Earstudio ES100 bluetooth receiver, which has a 4V p-p balanced output. It’s the size of a matchbox, battery lasts 12hrs+. There are now better receivers with a somewhat hotter signal, DSD support, DSP EQ for $20-$30 more, but no point in upgrading for this project unless the speakers are proven to sound good.
Anyone have any thoughts on this planned audio rig? I plan to deploy it on my already heavy-as-hell Lacroix Nazare. Looking at some long-distance skates this Summer, serious tunes would be quite nice.