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Question on Gio's bipole sealed box - will this work?
Question on Gio's bipole sealed box - will this work?
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Old 3rd January 2007, 12:01 AM   #11
pwan is offline pwan  United Kingdom
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I see. I think I will give it a try myself (as learning experience).

Thanks!
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Old 3rd January 2007, 03:22 AM   #12
planet10 is offline planet10  Canada
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Question on Gio's bipole sealed box - will this work?
Quote:
Originally posted by Scottmoose
Castle have the second driver firing vertically upward.
And the Linn Isobarik...

Don't forget that a bipole config like Gio's also allows for push-push operation of the drivers increasing the downward dynamic range, and reduction of driver vibration loading the box because of active force cancelling.

dave
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Old 3rd January 2007, 09:05 AM   #13
Scottmoose is offline Scottmoose  United Kingdom
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How did I forget the Isobarik?

On the whole, I prefer bipole -more advantages to be reaped, but vertical firing is next best, and a little more forgiving if near a wall.
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Old 3rd January 2007, 11:12 AM   #14
pwan is offline pwan  United Kingdom
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Personally I wish to go with bi-pole too but it seems it needs 3-4 feets behind the speaker due to the back firing.

Just wonder what the difference between firing virtically and 45 degree? Will it need slower space behind the speaker?
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Old 3rd January 2007, 02:39 PM   #15
Scottmoose is offline Scottmoose  United Kingdom
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Vertically will reduce speaker - rear wall spacing to a couple of feet or less. Alternatively, damp the rear wall behind the speakers. A nice, patterend rug for example can make an attractive aesthetic, and also damp some of the rear-wave down.
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Old 3rd January 2007, 02:43 PM   #16
planet10 is offline planet10  Canada
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Question on Gio's bipole sealed box - will this work?
Quote:
Originally posted by pwan
Personally I wish to go with bi-pole too but it seems it needs 3-4 feets behind the speaker due to the back firing.

Just wonder what the difference between firing virtically and 45 degree? Will it need slower space behind the speaker?
I have 2 customers with BD-Pipes in their HTs and both use them almost hard-up to a wall.

If you can get them angled with the back wall a bipole can be taken closer to a wall (18-24" in a pinch)

dave
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Old 3rd January 2007, 03:04 PM   #17
Scottmoose is offline Scottmoose  United Kingdom
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Worth knowing, that. Cheers Dave!
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Old 3rd January 2007, 10:17 PM   #18
gmilitano is offline gmilitano  Canada
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Quote:
Originally posted by planet10

I have 2 customers with BD-Pipes in their HTs and both use them almost hard-up to a wall.

If you can get them angled with the back wall a bipole can be taken closer to a wall (18-24" in a pinch)
That is how I have mine set up @ 2 ft.
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Old 5th January 2007, 11:49 AM   #19
bjorno is offline bjorno  Sweden
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Hi,

The following text is just my 2 cents of thoughts and opinions after reading all the posts above.

First a question I think many of you will find quite intriguing or quite objectionable:

Has nobody ‘successfully’ built a pair of speakers with 2 small FR drivers and approved the resulting imaging quality besides from the earlier posted assertions?

I don’t argue there are no vertically appearing combing effects that destroys the off axis dispersion and I don’t urge anyone in the first place to build FR speakers with dual vertically paired close mounted drivers if the C-C distance is more than 3-4 inch and if the drivers is not known as having smooth minimum phase qualities.

These types of speakers is not of my first preferences, however, I don’t reject this concept as impossible either and I don’t exclude this possibility when making speakers even for use in the near field or when very short listening distances is preferred for some reason, like the common use of PC speakers.

Listening to a stereo setup with 2 small drivers/small baffles placed at ear height---- without----- any crossovers and when mounted on top of each other (when C-C equal or less than 10 cm, 4"), is in my opinion much better than what it appears to be due to the very small acoustic path difference that exists caused by normal head movement of the ears at a normal 2-3 m listening distance, especially when listening in small rooms when the speakers are close to the walls and/or partly affected by the reflexes from surrounding obstacles.

The diffraction from the speaker baffle itself causes a much broader and hearable effects on the on axis frequency response than the off axis response does that originates from the dual FR drivers C-C distance.

In my opinion: The combing effect is not noticed worse at all when sweet spot listening to paired consistent drivers and the impression is very different if compared to vertically oriented crossed over drivers that I find are more restricted as often both the sound color and the localization changes more, if moving the head vertically.

Look at the submitted plots, where a real driver dispersion data (not the FE 127E) is plotted with different driver layouts at different frequencies at 10’ or about 3 m and pay attention to the vertical plots.

The first thing to notice is that the horizontal off-axis response is as good as for one driver and the vertical response has, of course, a more narrow dispersion due to the C-C distance.

Off axis comb-filter effects is not worse than the dispersion anomalies from the driver itself, this almost up to about 8 kHz for the Fe127E driver when used as FR, but if crossed over or with one driver tilted up or down, an apparent change to much lower dispersion quality occurs even below 4 kHz, causing the soundstage to appear wider and unnatural.

What dispersion can be expected besides the normal driver dispersion anomalies?

At 305 cm listening distance and 10 cm C-C distance between the drivers, the vertical listening angle corresponds to about 1.88 degrees.

This dispersion angle can be found covering up to more than 11 kHz with little loss; the half angle is about 13 kHz and the SPL drops about 3 dB at 20 kHz. At 57 cm the loss at 20 kHz is worse and close to 6 dB.

The 10-degree angle dispersion/3m is good to 6.3 kHz where level is down about –3 dB compared to a single driver caused by the c-c distance and is also followed with a suck out at 9.9 kHz, about 20 dB deep.

The latter is of course of less importance when listening as default listening height is centered vertically between the drivers.

At the sweet spot, I think this data is not bad at all if superimposed on good FR drivers and not forgetting my own naturally declining high frequency hearing caused by ageing, which is also a factor to include as of great importance.

When comparing to MTM’s** with 8” C-C (4”, 4”, 4”) distance between the M’s and if crossed over at about 3 kHz and at least 2,5 m listening distance, I find it more pleasant and enjoying when listening to 2 good quality 4” FR drivers mounted close together and is in my opinion a favored situation, causing less strain and listening fatigue in the long run.

By the way, I have never seen any supporting research arguments for MTM’s or similar based configurations having sharp vertical or horizontal MMA’s or for this case the more useful concept of CMMA, but rather many indications in various published papers I think are more of supporting the very opposite.

** The M (T) M (ignore the T driver) at 4 kHz has no better dispersion characteristics than the two 4” FR drivers have at 8 kHz.

b

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Old 5th January 2007, 11:52 AM   #20
bjorno is offline bjorno  Sweden
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