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Multi-Way Conventional loudspeakers with crossovers

Sealed vs. ported... and what their relationship to BSC is?
Sealed vs. ported... and what their relationship to BSC is?
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Old 30th August 2005, 04:50 PM   #1
fjhuerta is offline fjhuerta  Mexico
diyAudio Member
Join Date: Apr 2005
Location: Mexico City
Default Sealed vs. ported... and what their relationship to BSC is?

Hello all!

I've been playing around with my new speakers for a while (first ones, too!)

The design is mine. It's an MTM with Focal 5N421 woofers and the Neo3 PDR tweeter. The crossover is a standard 3rd order Butterworth at 3KHz, and the woofers are wired in series with impedance EQ. BSC is provided by an inductor wired in parallel with a resistor. I didn't need to use an L-Pad on the tweeter.

The speakers were supposed to have a 4" port, but due to size constraints (and the internal reinforcements), I had to abandon the idea. There was no way I could stick a port that large inside the enclosure. So, what I did was leave a 4" hole (2" MDF thick) and work the crossover into that space. I listened to the speakers with the port unplugged, and tuned the crossover that way.

When I arrived to what I considered was a good sounding speaker, I sealed the port and put the crossover in place. Now the balance was completely wrong! The speakers had zero bass now, and lots of treble. I tried playing around with the BSC resistor, but all I managed was to shift the balance towards dull and warm.

After thinking about it (and using the wonderful Woofer Tester!), I checked out the system Qts. It's close to 0.29. I think that's far too low.

My questions are...

Considering Qts, would you rather use a smaller vent (say, 2"), and go vented again?

If I do, do I need to remove damping (apparently, I need to. I used polyfill and foam on the walls).

Since Qts is so low, should I tune the speakers a bit high to restore some of the lost midbass? I think that when I tested my speakers with the port unblocked, they were tuned at around 70-80 Hz. I'd try tuning them this time around 40 Hz. Does this sound right? I think tuning them lower wouldn't get me enough of a midbass boost.

Last... is there anyway to at least keep some of that wonderful sealed bass sound? Even though they are light on the bass and midbass, I just listened to the Superbass Telarc SACD, and I swear I had never listened to such amazing lows. Taut, defined, very fast... unfortunately, not very balanced.
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