[rabbits]

When I was young we were told that you should not mix ported and acoustic suspension speakers. I never understood why. My system has ported SAE MK X main speakers. My center channel, sub woofer and sides are all ported Polks. I'm thinking about making a man an offer on a pair of ADS l910s to replace my SAE MK Xs as mains. Any thoughts or advice? Thanks.

[richidoo]

Hey rabbit! The problem is that the phase response of the low frequencies will not match between the sealed and ported. The port is a mechanical amplifier, it reacts to the woofer movement and pressure wave inside the box before it starts making noise and this has a delay. Ported speaker's low frequencies will be time delayed and out of sync with the sealed woofer's LF. Depending on placement relative to listener, The two bass sounds could cancel or augment each other in places in the room, making peaks and dips caused by the speaker differences. Also, the bass will sound muddier and less detailed the lower it goes and the more the phase error increases. Many people say this doesn't matter because our hearing sensitivity at LF is not acute. I disagree.

For small woofers like 6-8" then ported benefits usually outweigh the drawbacks. But with larger woofers, 12"+ the scale starts to favor sealed for audiophile quality music. For thumpin dance music and home theater LFE, ported is usually preferred sound wise. Most good designers try to put it somewhere in the middle to make punchy but natural sounding bass compromise.

If the ported center's woofer is small and the mains woofers are large, then the delayed center's port will blur the upper bass of the mains. I think maybe juststuffing a sock into that center speaker's port, and then using your receiver to boost up it's bass a little might be an option for you. Just don't boost it too much, it's not meant to handle low bass. Ask Polk if it's OK to plug the port as it might be needed for cooling. Usually it's not a problem.  Polks usually try to swing above their size, so they lean heavy on the porting, it is probably wide open standard alignment, so the phase error will be max and the loudness of the error will be max. But if you block the port the bass of the small woofer will roll off higher than the port did, so you will need to boost it to restore some of the oomph. This is important on a center channel to avoid male voices sounding wimpy.

The side speakers won't matter as much. I would just keep those ported as you have.

If your receiver has no bass boost for center channel, you could use a linkwitz transform to boost it externally, but this is a bit extreme solution.

[rabbits]

Thank you for the good explanation. I suppose I'll just stick with my ported SAE MK Xs for a while. My sub, sides and center are all ported Polks. It makes me a little sad. I've always wanted l810 or l910 A/D/S. When I was young I sold them and became convinced of their superior sound. I can't justify replacing everything else to indulge my nostalgia for an old speaker that I haven't even heard in almost four decades. There's something inelegant about the sock solution for the center and then where would I be with my ported sub? Alas. One of my big problems is that I never hear other speakers. There's not much opportunity around here to listen to (or even know about) other speakers. What I've got sounds pretty good to me. I mostly listen to "classical" music these days. Thanks again.

[richidoo]

OT: Check out WCPE fm radio. The tower is in Wake Forest, NC, but it is 100kW so you might get it. They use very high quality FM processing and exceed 50-15k FR. It is compressed as expected for radio, but otherwise vg SQ. It is all classical music, no commercials, no news. On Sunday night they have a new releases show that gets a little more exciting than rest of the week, but it's all good.