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Passive cardioid speakers with rear woofer and rear tweeter (might addd lateral vents for midrange)

Peas

Member
Joined
May 13, 2020
Messages
55
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Location
Germany
Hi folks, being an owner of a surround setup with fixed speaker placement, I have always searched for perfection in stereo music and accurate bass as well.

Bass is in fact better as a surround setup is more flexible and controllable. I had ripole subwoofers for a long time, which were the best I had. Clean and precise, yet quite down low even for home theater use. A simple miniDSP 2x4 was sufficient to linearize. Just a notch filter for the chamber resonance of the ripole and flattening the longitudinal modes did the trick.

But stereo was less than perfect in that not-so-well treated room with speakers placed close to the front wall. Sometimes, I placed other DIY speakers of mine freely standing into the room to enjoy my favourite music. But this is less than comfortable, so I decided to redesign my front speakers. The process started a couple of years ago, with minor changes during the years. Initially, it was a mere closed box design, now it's bass reflex and filters have been optimized.

The basics are quite simple: Two front firing 8" woofers with a reflex port at the back side, coupled with a single bandpassed and inverted 8" rear woofer in CB, 6.5" midrange (0.3 to 2.3 kHz) and a bigger air motion tweeter that is again paired with a smaller rear AMT at the backside.

For the rear woofers, I need an addititional power amp. They could easily be controlled by the miniDSP, but it is also possible passively, which I did. While the front woofers are filtered third order, the rear woofer is filtered second order, but lower, keeping in mind the upcoming baffle step that increases directivity. As there is boundary coupling due to the wall, the SPL for the rear woofer must be lower to achieve the intended cardioid effect. So, 6.8 ohms in line are reducing the level of that driver. With the resistor, no additional notch will be needed for the bass resonance after filtering (other than at the front).

The effect is just amazing regarding the fact that the soundstage gets almost as "sorted" and wide as with free-standing speakers. The phantom center is more precise and imaging / localisation clearly improved.

I wouldn't say it's as good or even better compared to free-standing speakers and a treated room, but it comes close. So it's more a problem solver than an improvement or milestone, as they say in marketing.

The rear tweeter is explained quite simply: Again, it's filtered second order instead of third order. And it gives some extra ambience. Nice to have, nothing more.
 

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Beautiful cabinet!
2-way MTM?

The cardioid speaker design is interesting.
 
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