Advantages of angled woofers in MTM configuration

[RussianBlue]

Hello,

I would appreciate your help in determining whether it is worth the effort to angle the two mid/woofers in an MTM configuration to alleviate timing issues.
The MTM containing two AUDAX PR 17M0 and possibly a MOREL MDT 33 will sit on top of a bass reflex box with a JBL 2235H. Crossover for now will be three-way active through a Behringer DCX unit.
Listening distance will be about 6ft from the speakers, therefore the angle of each woofer should be about 6 degrees, perhaps not worth the hassle?
Thank you for your kind help.

Cheers

BG

[sreten]

Triumph of marketing hype over sensible engineering.

Utterly pointless hassle.

(And if we are talking timing issues the voice coil positions need
to be aligned, you''ll find this is a lot more than 6 degrees).

sreten.

[RussianBlue]

Thank you Sreten,
just what I needed to hear.

Cheers

[Svante]

Assuming that crossover frequency is ~3kHz here:

Looking at the datasheet for this element it appears as if the response has dropped by ~4 dB at 3kHz (it is a bit unclear but I think the second curve is 30 degrees). 6 degrees off axis the drop is likely to be far less than 1 dB, so directivity appears not to be important.

At 3kHz, wavelength is 11.5 cm, a quarter of a wavelength is 2.9 cm. If two equally strong, in-phase signals (as at the crossover frequency) are shifted by 90 degrees the level drops by 3 dB. So, moving the acoustic centre of the driver 2.9 cm back or forth *can* give a response change of 3 dB.

Now, there are all sorts of other things that can happen near the crossover frequency, and the drivers are not nessecarily in phase. It may turn out that a flat baffle is either better or worse when all aspects are considered.

Bottom line here is that you would probably have to build it and see what happens. The bent baffle need not be the best.

[sreten]

JM Labs have angled baffles that have no engineering justification.

For the bass / midrange c/o its laughable.

Nevertheless the marketing claims all units are equidistant from
the user, and thus "critically aligned".

Acoustically this is total nonsense.

sreten.

[Svante]

Originally posted by sreten
JM Labs have angled baffles that have no engineering justification.

For the bass / midrange c/o its laughable.

Nevertheless the marketing claims all units are equidistant from
the user, and thus "critically aligned".

Acoustically this is total nonsense.

sreten.

Probably yes, and in the case there IS a difference, the flat version may very well be the best.

But not in the marketing of course.

[BobEllis]

Originally posted by sreten
JM Labs have angled baffles that have no engineering justification.

For the bass / midrange c/o its laughable.

Nevertheless the marketing claims all units are equidistant from
the user, and thus "critically aligned".

Acoustically this is total nonsense.

sreten.

Maybe the marketeer misunderstood what the engineers told him and the drivers are time aligned?

At least for the Mini Utopia, I figure that with the midbass centered about 4" below the bend, roughly 15 degreees of kink would align the voice coils (assuming that the voice coils are the acoustic centers of the drivers and the midbass voice coil is an inch behind the flange.) It looks like about that angle on the Mini Utopia cabinet. Of course, we are now dealing with off axis response for the midbass....

[RussianBlue]

Well, there are some designers who I respect that do tilt their drivers: George Augsburger and Dunlavy for instance. In one of his studio monitoring systems Augsburger use 4 X JBL 10" with a TAD horn centered in the middle with two 18" subs on the bottom. The 10" speakers are all angled in to focus on a specific spot in the listening position. The big Duntech Sovereigns and the SC V-VIs are also slightly angled.

[kingdaddy]

Depending on the crossover frequency (the higher the X-point the closer the drivers need to be) angling the drivers can help lobbing errors. Some Tweeters physical size makes it difficult to mount close enough to the Midrange drivers so some manufacturers tilt the mid baffles to bring the drivers acoustic centers closer together for both Time alignment and lobbing errors. I have designed a DIY monitor with midrange cabinets that can be tilted and have noticed a audible difference when they are in full tilt as opposed to plumb, so I can say from experience that something is going on here.

[pinkmouse]

Originally posted by RussianBlue
Well, there are some designers who I respect that do tilt their drivers: George Augsburger and Dunlavy for instance... The 10" speakers are all angled in to focus on a specific spot in the listening position.

Hmm, in most of the big studios I have ever worked in, the idea of a sweet spot at the console is pointless. The only one likely to be sitting there is the engineer, the producer/ manager, etc. are all likely to be in big comfy chairs away from the main axis, and they are the ones that make the critical decisions on the mix.

I suspect that these designers know that such things make little real difference to a well designed system, but they also have Product Design and Marketing types or influences involved as well.