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Old 16th August 2010, 11:20 AM   #1
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Default Using one full range in front and one in back

I've seen design where people use one full range speaker mounted in front and one facing the back. What is the purpose for the extra full range on the back. Is it there to increase the efficiency or for a more fuller sound. Thnx.
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Old 16th August 2010, 11:34 AM   #2
gaust is offline gaust  United Kingdom
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I'm not claiming to be an expert, but I believe the reason is to negate the need for Baffle-Step Compensation (BSC). BSC is required because while higher frequencies are directional and project mostly forward from the speaker box, lower frequencies are omni-directional and project both forward and back (start to wrap around the box), meaning that a listener sitting in front of the speakers only hears a proportion of the lower frequencies.

In order to counteract this a baffle-step correction network is used to decrease the high frequencies so that they match up with the low frequencies.

Using a second driver on the back of the speaker box means that as the sound from the front driver decreases in frequency and begins to wrap more around the speaker box, the same is happening from the back driver meaning that they compensate for each other and mean that the overall level of the lower frequencies matches with the upper frequencies.

I am prefectly happy to be corrected if this is badly describes, ill-informed or just plain wrong!!
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Old 16th August 2010, 02:20 PM   #3
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Sounds about right, though I never considered that to be the primary intention.

I always thought that is was to created a more omni-directional sound, by reflecting sound to the listener, too (many instruments are fairly omni). With treble that beams a little, having extra treble being reflected would give a more spacious sound.
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Old 16th August 2010, 02:21 PM   #4
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Edit, Chris beat me to it.

Partly; it also provides a different polar response / dispersion that some people favour, similar to an omni in some ways. Less precise imaging, apparantly larger soundstage due to increasing the degree of reflected to direct radiation.
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Old 16th August 2010, 04:24 PM   #5
chrisb is offline chrisb  Canada
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another option that eliminates some of the placement issues that a bipole (or dipole for that matter) can create (i.e. relative to rear wall / boundary) is to place second driver on top or side of enclosures

there are numerous examples of commercial and DIY designs with such feature - having build a few of the latter as well as more conventional bipoles, there are many advantages to not having to worry about rear-facing wide-bandwidth drivers.
"Perception is a highly non-linear function" - Earl Geddes
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Old 16th August 2010, 04:29 PM   #6
hm is offline hm  Europe
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Default double horns

Hello ,
i do it with my double horns:

explained in the middle at:
about what

i did a few constructions all more or less
physically the same:
look at my HP, with measurements, feedback, plans

Click the image to open in full size.
Click the image to open in full size.

Cornet and RDH20 one of my best constructions.
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Old 17th August 2010, 12:22 AM   #7
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Cool! Thanks everyone for your inputs. I now understand why. May have to try it soon. Thanks again.
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Old 17th August 2010, 01:58 AM   #8
2litre is offline 2litre  United States
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I think these questions are pretty much on topic.

Whenever I see a bipolar speaker build one point that is often mentioned is that they sound best when pulled out a bit into the room.

Well I have a very small primary listening room. It's my computer room and all speakers end up there eventually, always in a less than optimal configuration, because of WMA files and internet radio.

I've thought of doubling up my sealed HiVi B3's in a front / top set up so that I can keep them closer to the wall while gaining +3db in volume (driven by an SI T-amp).

If I was to do that, should I .5 one of the drivers?
If so, which one?

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Old 17th August 2010, 03:14 AM   #9
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Originally Posted by 2litre View Post
If I was to do that, should I .5 one of the drivers?
If so, which one?
Be pretty easy to find out what works best once you make them. On ours (that Chris' wife has) they work well with no filters

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Old 17th August 2010, 12:50 PM   #10
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Quick question...

People seem to always use the same driver for bipoles, thus increasing the cost significantly if one was to use expensive drivers. Double CHR 70s or EL 70s in the Lotus 2 or Metronomes respectively for example.

My question was that if one was to make a speaker with for example an Alpair 10, would it be reasonable to add a upward or rearward firing cheaper driver for ambience such as the aforementioned CHR 70 or EL 70?

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