Marten and Avalon can both be placed close to rear walls. That is due to their down-firing ports and crossover tuning. Marten actually advertise the fact their speakers have been designed to be placed close to rear walls. Avalon perhaps a bit less so because of their cabinet design and dipole-like sound characteristics, though the Avalons would still be more room friendly than true dipoles or speakers with rear-firing ports.
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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 |
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. |
The most important factor in choosing a speaker that's going to live close to walls is how the bass is tuned. Walls/boundaries will boost bass, possibly by a large amount. If you have a typical QB3/flat bass tuning and put that speaker close to a wall, you'll end up with 6db or more bump in the bottom couple octaves ... end result is a thick, muddy sound. The ideal tuning for near wall placement is an Extended Bass Shelf. Even sealed boxes aren't always ideal for near wall, and can suffer the same effect as I said above, because there's no way to replicate an EBS curve with a sealed enclosure. Unfortuantely most manufacturers don't tell you what type of tuning they employ. Instead you have to rely on anecdotal evidence like "I have brand x close to a wall and it sounds great", or the manufacturer marketing speak without any explination of why. |
REGA RS7/R7 see R7 review in STEREOTIMES #25 in http://www.stereotimes.com/speak022306.shtml pertinent extracts: " ...Like many speakers built for UK and European listening rooms, the R7s can be placed near a rear wall without exaggerating the bass response..." " ... 34-years experience in the audio world have taught me that the most common system building error is mismatching the speaker to the room. Place a mini-monitor in too large a room and you get the bass-shy squawk box syndrome. Far more common in the US is buying a speaker whose bass response is more than the room can handle, resulting in various manifestations of boom, thud, and rhinocerine mud-wallowing. Its more than a simple matter of room dimensions and overall volume: wall and floor construction also play a crucial role. Its been my general experience that if you can get clear and tight response down to 40 Hz in-room, stop and count your blessings. And think very hard about pursuing response into the bottom octave. One is more likely to screw up everything achieved in the musically useful range of 40 Hz and above. While my own reference speaker, the Sound Lab Dynastat, is flat to 20 Hz in my large basement listening room, the number of times Ive absolutely needed that bottom octave for musical reasons in the last two years is zero. While the lowest range of the organ might be majestic in a large cathedral, mismatched bass-heavy speakers that literally shake the house on its foundations are more likely to induce vertigo and viscera displacement than aesthetic satisfaction. So how do you walk the line between bass-shy mini-monitors and elephantine bass heaviness in the normal room? Enter the new Rega R7 loudspeaker...." |
