Mirror Image speakers

[hjames]

I recently got a set of 4312A speakers to replace my old L36 Decade pair.
I've seen pictures and noticed that some Studio Monitor speakers came in Mirror image configs. Mine have identical mid and high speaker placement. I haven't measured the pattern for the mid and high mounting screws, but they do look to be in the same square pattern.
I don't want to seem like a novice or a butcher, but could I swap the mid and high drivers (and internal wires, of course) on one speaker to make them a mirror image pair - or is there internal bracing and baffling related to the mid high locations?
Is it even worth doing?
Thanks for your info!

[Don C]

There is a separate sub enclosure for the midrange driver. It would be pretty hard to break the glue and move it to the other side without ruining it.

[mike]

I've seen quite a few mismatched 4312A's and 120Ti's on Ebay over the last few years. I think the dealers must of mixed them up, giving the customer either two left speakers or two right speakers.

Mike

[speakerdave]

The benefits of mirror imaging are debateable. In my opinion, for predominantly direct path identical sides are preferred. I think mirror imaging may help the situation where there is a lot of signal bouncing off the side walls, and it also helps center and also spread the image when small three-way monitors like 4312A's and my LSR32's are used horizontally in a small space. I wouldn't worry a whole lot about it.

David

[Robh3606]

Mirror imaging does make a difference but depends on how the drivers are laid out. Any doubt look at the polar responses. When you have 2 rights or 2 lefts the sound fields are not symetrical. Your pans won't be right and the sweet spots for placement won't be the same plane so you can only optimize for one side. You can't be in two places at once. Take a look at the 4411 and 4412 which use the same cluster type driver patern. They have lefts and rights. Look what happens in the Horizontal Off Axis Response 20 and 40 degree windows if you are on the wrong side of the monitor. You end up with notches on the LF side at the crossover frequency 1k between the woofer and the mid with this cluster configuration. Take a look at the vertical. You have the same kind of issues again at the crossover frequency 4K betwen the mid and tweeter. These systems are sensitive to placement in both axis.


http://www.jblpro.com/pub/obsolete/4411.pdf

http://www.jblpro.com/pub/obsolete/4412.pdf

Check out a 4410 which uses a vertical driver alignment to enhance imaging. The polars are symetrical in the horizontal axis but because on the finite driver spacing have the same issue in the vertical axis. Looking at the graphs the prefered position is on axis or above.

http://www.jblpro.com/pub/obsolete/4410.pdf


If I were you I would leave them be. I would not chop them up.



Rob:)

[Zilch]

See D'Appolito Figure 5.35c. Even vertically aligned drivers on offset centerlines produce asymmetric polar responses.

"A pair of these speakers must be built in mirror image," he concludes. (P. 83.)

[speakerdave]

Dammit! Now I have to move an 077! :banghead:

[hjames]

Thanks for all the info everyone!
Sounds like there are internal sub-boxes,
so I guess I better just leave 'em alone ...

[speakerdave]

Mirror imaging does make a difference but depends on how the drivers are laid out.

I moved the 2405 in one of my 4333A's over to the other side so that they are now mirror imaged. I have to say you were right. Imaging is clearer, instrument placement is more precise, soundstage is deeper, the cat has stopped barfing on the rug, my rash has cleared up, and the kids are doing better in school. All-in-all it's a better life. Thanks.

David

[hjames]

Thanks for the update.
I gave up on the 4312As - sold 'em a few weeks ago via eBay - they just didn't seem to have the sizzle of my ancient L36s.
But thats ok - maybe its the mythical Alnico reality distortion field - I did just get an old set of 4320 Control Monitors - just brought them home yesterday.
Massive things but the price was nice, and I've got to admit there is something about a pair of 15 woofers.
I've got some 2405s on the way and I hope to rebuild/replace my crossover networks to make these puppies act like nice 3 ways ...
then stick them up on top of the shelf where my venerable L36s live now (bought them new in 1976!).