Question on Gio's bipole sealed box - will this work?

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Hi,

I am new to speaker building and look for floor-standing sealed speaker for a 15 sq.m room (3.5 x 4m so too small to bipole I think) for both music and AV. I wonder if the box plan below will work fine in case:

http://diyaudioprojects.com/Speakers/FE127E_SB/FE127E_SB.htm

Case 1: Use dual FE127e per ch but both drivers are on the front panel.

Case 2: Use only one FE127e (i.e. completely ignore the back one).


Many thanks!
 
Don't try putting two FR drivers on the front baffle or horrible things will happen to the response due to severe comb-filter effects. A single driver is perfectly feasable though. Use 0.5lbs ft^3 of damping material uniform. Don't expect much LF performance though!

If you want compact, personally I'd do this: http://www.planet10-hifi.com/tom-zHorn.html I know it's more complicated, but trust me, if I can build a pair of double horns in my leaking garage, with a 30 year old hand saw and very little else, you should be able to manage it.
 
The driver on the rear compensates for the baffle step. As Scott mentioned, two drivers on the front will be problematic.

One driver will work, but you will likely find that you will need to compensate for the baffle step.

You will want to couple a sealed design with a subwoofer or two.

Also, look at this thread for a number of designs with the FE127E:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=46934
 
That's the only effective way to do it.

Sadly, you can't get around the laws of physics. When you put two identical drivers, run full-range on the same baffle, nasty things happen. For it to work, the centre-to-centre spacing needs to be less than 1wavelength of the highest frequency to be reproduced apart. If they're further apart, the end result is a massive increase in ripple in the high frequencies (comb-filter effect), while the response additionally rapidly drops away.
 
Hi!
Maybe a dumb question but is it not possible to put the second driver at back of the top, aimed upward at 45 degree's . It will be a higher sound stage in this way. Is it Castle speakers that use this configuration? Can't remember which model.
I imagine one could have speakers closer to walls by this solution.

Just a guess....

Cheers/Peter
 
pwan said:
Thanks Scottmoose.

I guess I can imagin what the "comb-filter effect" is now. Per the picture, the distance between centers is around 10 cm, what frequency will it be?

About 4Khz, give or take.

Peter -no, it's not a dumb question: the BD pipe has exactly that. http://www.t-linespeakers.org/FALL/bd-pipes.html

Castle have the second driver firing vertically upward. It's a good layout -one I like anyway. Harlech S2 and Howard S3 are the two models which have this configuration.
 
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pwan said:
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
 
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.

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