Speakers that can be placed close to the back wall

Vapor1 A question: Do any of your speakers use the EXtended Bass Shelf? I thought that technique only used front ported designs? Could you explain more in detail? Thanks!

Hey Chuck, yes we use the EBS alignment on some of our designs and it definately helps make boomy bass a non-issue. Front ported or rear ported, makes no difference ... it's the length of the port and size of the cabinet that determines tuning.

One of the major reasons why most manufacturers don't use EBS tunings is because they typically require about twice the cabinet volume. However, that's one of the benefits to using AudioTechnology woofers, Per Skaaning will build them custom to our specs - so we're able to get a woofer that can tune to an EBS alignment in a .75cu/ft cabinet. Normally that's impossible with a 7" woofer.

To show you a bit more about what an EBS alignment actually is, look at this image that I found quickly using google

http://www.hometheatershack.com/forums/attachments/ported-subwoofer-build-projects/32772d1316499344-sonosub-design-titanic.jpg

That's not a 'real' EBS, but close enough for illustration. The green line would be your standard QB3 alignment, grey would be an EBS-3, and red and EBS-6. The -3 and -6 mean just that, down 3db and 6db from flat. We use EBS-3 alignments because -6 is too much 'shelving down' in our opinion.

You can see how in a real room where bass is boosted, if the tuning is flat, you will end up with a bump. However if you start with the grey line, that bump will be much more benign and overall in-room response will be closer to flat. You can also see how EBS alignments actually give more bottom end extension.

The downside to an EBS alignment is you give up a bit of power handling.

Vapor1. Interesting that you're focusing below 100 Hz instead of more typical diffraction loss or BSC below 500 Hz with, say, a 9 inch wide baffle. Something to do with the speaker depth?

Front ported or sealed

Typical boundary reinforcement from placement close to the wall would be roughly +3 dB per octave. So I like to aim for roughly -3 dB per octave rolloff across the lower part of the bass region when the speakers are going close to the wall. I call this "room gain complementary" - or RGC - tuning. It's not quite the same thing as extended bass shelf - or EBS- tuning, but they are variations on the same theme. RGC tuning usually calls for a bit smaller box than EBS tuning. And as has been mentioned, port location doesn't really matter, though I personally think the argument can be made that rear porting offers a couple of potential small advantages when tuned properly.

Here's a more lengthy look at room gain complementary tuning, if anybody's interested:

http://www.audiocircle.com/index.php?topic=61810.msg890800#msg890800

Having a wall right behind the speaker will affect any midrange energy that wraps around the baffle and then bounces off the wall, introducing peaks and dips in the frequency response as the wall bounce energy goes in and out of phase, depending on the distance and wavelength. This can be minimized by blending the speaker into the wall as much as possible (perhaps via a very shallow enclosure), or by using drivers that are inherently strongly directional and/or using a wide baffle so that relatively little midrange energy wraps around the baffle and bounces off the wall.

Imo, ime, ymmv, etc.

Duke
dealer/manufacturer