# Ideas for active 3-way bookshelf speakers



## gordoste (Aug 2, 2020)

Hi all, I'm a DIY speaker newbie and am looking at ideas for my first project. I have a young family so I don't want big floor-standing speakers that can get damaged, although I suspect that if my DIY efforts turn out well, a bigger system would be on the cards in a few years. I don't want to spend a fortune but I am also not looking for a budget system. I am OK with basic woodwork but nothing too fancy. I also enjoy electronics and am comfortable soldering and the like. I am drawn to the idea of active crossovers due to the upgradability and various other factors discussed in numerous long threads. I've also seen a number of small form-factor TPA3116 power amps that could be built into the speakers, however I haven't come across many projects doing that.
I am considering building an active crossover version of the Troels Gravesen Bookshelf-3WC speakers - identical drivers (they are in my pricerange), but fed from some kind of active crossover system (most likely miniDSP). The enclosure seems fairly simple to make. The passive crossover would be replaced by a 2x50W TPA3116 such as this for mid&tweeter and a 1x100W TPA3116 such as this for the woofer (power would be external).
Would I also need to include speaker protection circuit(s)?

I just thought I'd post my ideas here to get some feedback. Many thanks in advance!
Stephen


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## Da Wiz (May 8, 2019)

The only speakers safe around young kids are either big heavy ones they can't tip over and are usually pretty expensive OR are mounted in or on a wall so they can't be reached by kids OR are suspended from the ceiling. Smaller speakers on stands are more dangerous than a tall but not-heavy speaker because not only can the speaker hurt a small kid if knocked off the stand, if the stand is knocked-over, the STAND could also hurt a kid and may have sharper corners than the speaker that cause more serious damage to a kid if it falls over. At any rate, the bigger/wider the base of the speaker or stand, the less likely it is that a kid could knock it over, and weight down low in the speaker can also help stabilize it. I know a guy who attached 3/8 inch clear plastic about 3-feet square to the bottom of small tower speakers using a non-permanent flexible adhesive called Blu-tac or Fun-tac or something like that. Find it at OfficeMax, Staples, sometimes Home Depot, etc. Often it is in office supplies near glues and such. It is flexible putty-like adhesive that comes right off later when you don't want the items stuck together any longer. The flexible adhesive comes in different colors... Blu-tac is light blue, another brand was brick red, and a third brand I have seen is yellow. Looks like a blister pack with a rubber eraser inside. But the "eraser" is a mildly sticky putty that doesn't mar surfaces and with the right combination of mating surfaces, it can hold quite well enough for a kid to not be able to push over a speaker. This person then covered the exposed plywood with matching carpet. When you are done with the adhesive, you can remove and re-use it to stick something else or throw it away. And the adhesive is cheap... $2-ish for a package. The clear plastic can be the trickiest item to find, but some hardware stores that sell glass for replacing broken windows also sell plexiglass replacement windows that are popular for homes along golf courses. There are also some stores in larger urban areas that specialize in sheet plastics and other types of plastics where you can probably get pieces cut to size and even with tints and such that can change the appearance of the base quite a bit.


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## gordoste (Aug 2, 2020)

Thanks for the reply! This is a good solution for the problem you describe, but I'm planning on putting my speakers on a wide TV cabinet, or possibly wall-mounted. The speaker design is specifically created for half-space (i.e. sitting against the wall).
I am going to use a Raspberry Pi with 6-output external USB soundcard (ESI U46DJ) to do the active crossover and EQ, and a 2nd-hand 7.1 AV receiver in direct mode for 6 channels of amplification. A future project might be to replace the amplifier with a DIY one, perhaps built into the speaker housing (once I figure out power requirements).


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