DIY Open Baffle Martin Design Question

peet_pete

Well-Known Member
http://www.quarter-wave.com/Project09/Project09.html

On this project he states he has an active crossover. Is there a project with similar drivers that uses a passive crossover that could be used with this design? Or how do I find one that would work? I was looking for an OB project with off the shelf parts if possible and I mean all the parts as I've never built a speaker, so everything needed. I just want to get an idea of how these sound.

I just don't want to need 2 amps or bi-amp plus more electronics. As I don't see a crossover on the speaker back I'm assuming it's somewhere else.
 
One option would be to wire the two speakers in series with a low pass filter on the woofer and a high pass filter on the full range. For example only, say 3000hz low pass witch will filter out anything above and a 1000hz high pass filter which will filter out anything below that. Filters such as these can be found on eBay etc. for very little money allowing you to experiment. The reason you can't see the active crossover is that it is usually placed between the preamp and the power amp if that is the setup, or directly behind the integrated amps otherwise.
This link will show you diagrams on how to wire speakers in series and parallel.
http://www.hometoys.com/content.php?url=/htinews/jun05/articles/nigelb/speakers.htm
 
You're overlooking a fundamental feature of the referenced project: "Not having to worry about the relative [driver] sensitivity and applying boost or cut to the full range driver to balance the SPL frequency response is a very powerful design tool." I understand the initial reluctance to add a second amplifier and electronic crossover, but the benefits are legendary and cost is probably a lot less than imagined. For one thing, the tweeter amp can be quite small. One or two watts is plenty for efficient tweeters. Behringer's very capable CX2310 electronic crossover can be had for only $80 new (at amazon.com). You can build your own electronic crossover with skills not far beyond what's necessary for speaker building. Another option that a lot of folks don't consider is line-level passive crossovers, which can be assembled at very low cost and have many of the same advantages as active electronic crossovers.
 
You're overlooking a fundamental feature of the referenced project: "Not having to worry about the relative [driver] sensitivity and applying boost or cut to the full range driver to balance the SPL frequency response is a very powerful design tool." I understand the initial reluctance to add a second amplifier and electronic crossover, but the benefits are legendary and cost is probably a lot less than imagined. For one thing, the tweeter amp can be quite small. One or two watts is plenty for efficient tweeters. Behringer's very capable CX2310 electronic crossover can be had for only $80 new (at amazon.com). You can build your own electronic crossover with skills not far beyond what's necessary for speaker building. Another option that a lot of folks don't consider is line-level passive crossovers, which can be assembled at very low cost and have many of the same advantages as active electronic crossovers.
Parts express sells line level high and low pass filters with rca jacks.
 
I couldn't find those filter modules at Parts Express, but I did recall an old article on R/C filter design that could be quite useful in this context. The title is RC Filter Design for High-Impedance Crossover Networks by Charles W Harrison Jr. The scan I have is missing the magazine name and publication date, but I believe it appeared somewhere in the Audio Anthology from Audio Amateur Publications. Here are the relevant drawings:

12dB.png 18dB.png

I believe there's enough information there to make your own 12dB/oct and 18dB/oct high-pass and low-pass filters. If you know the desired crossover frequency and your amplifiers have gain controls, then Bob's your uncle. If you're not too sure about crossover frequency, then it's best to start with an electronic xovr that's fully variable.
 
Designing a passive crossover can be a daunting task. A simpler and no more expensive option ( good crossover parts are not cheap ) would be to use you amp to power the full range drivers ( running them full range ) while powering the Alpha 15A woofers with this $85 plate amp from Parts Express.

The Yung SD100 has it's own low pass filter and if you don't have a preamp you can connect your source to it and then line out to your amp.

http://www.parts-express.com/yung-s...-amplifier-module-with-6-db-at-45-hz--301-502

If you happened to have an extra amp or AVR collecting dust you could use it to power the woofers using this low pass to filter out the highs while running the full rangers with your main amp.

http://www.parts-express.com/parts-express-80-hz-low-pass-8-ohm-crossover--266-442

An even better option are these "active" FMods which are placed upstream of the amp and change the woofer's frequency before it's amplified.

http://www.parts-express.com/harrison-labs-fmod-inline-crossover-pair-70-hz-low-pass-rca--266-252

Others may not agree but to me it makes sense to run full range drivers full range sans filters and allow the woofers to fill in the bass that the full range drivers can't reproduce.
 
Thanks for the responses. I guess active crossover is desired for fine-tuning and room adjustment and passives require a bit more knowledge of amplifier gear and how it will impact output sound-wise? And I guess this project was created more for testing and flexibility rather than plug in play. I'll need to do some more research to decide what would be a good first OB project.
 
The easiest OB project is this: Single drivers with no crossover that a 12 year old could build in an afternoon. They were my first OB's and they're good enough to live with. If more bass is needed a sub can be added.

I had a friend on another forum who after building the Betsy's sold his expensive Omega's.

http://www.wildburroaudio.com
 
http://www.quarter-wave.com/Project09/Project09.html

On this project he states he has an active crossover. Is there a project with similar drivers that uses a passive crossover that could be used with this design? Or how do I find one that would work? I was looking for an OB project with off the shelf parts if possible and I mean all the parts as I've never built a speaker, so everything needed. I just want to get an idea of how these sound.

I just don't want to need 2 amps or bi-amp plus more electronics. As I don't see a crossover on the speaker back I'm assuming it's somewhere else.

Did you look here on the Quarter-Wave site?
http://www.quarter-wave.com/OBs/OB_Theory.html
I built a small passive OB based on Martin's original article some years ago & like it VERY much! The updated article gives data for currently available drivers.
 
If you buy the same drivers that Martin used, the price of an inexpensive active crossover and a chip amp to drive the tweeters is not going to add significant cost to the total project. You'll also end up with the active crossover that is an excellent tool to design passive networks or build multi-driver speakers in the future. For reference, the FE108 Sigma is selling for around $150/piece and the Eminence Alpha 15 is around $60/piece.

FWIW, I have a FE108 Sigma in small BR boxes that I built in an afternoon. I had these earmarked for another location but they sound so nice that they became my shop speakers. It is no bass killer but that is not what I was after. These have no crossover network, not even a capacitor. They are fed signal directly from the receiver I use in the shop.
 
My folding wing $100 Betsy's ( + materials ) requires a single amp which can be wired straight to the drivers. The foam rolled top and bottom is pipe insulation. Quarter round is used to hide the door hinges. Black duct tape on the back seals the gaps.

HPIM3961.jpg
 
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