Dumb question about 2 way towers with multiple woofers

[goldark]

So as I understand it, the problem with 2-way MTM center channels is that the multiple woofers cause acoustic interference with each other which causes a narrowing of the response off axis, correct?

So why isn't this a problem with 2-way towers with multiple woofers? Why does changing the orientation alleviate this? Or does it? Does it still exhibit comb filtering but in the vertical plane instead?

Sorry if I'm getting my terms mixed up - just a bit confused at the moment.

 

[Deleted member 21219]

Does it still exhibit comb filtering but in the vertical plane instead?

If it's a vertical MTM, then yes, it still exhibits the same problem. However ... our auditory system is more sensitive to horizontal cues than vertical cues, so the MTM center channel, with the array laying on its side, has characteristics that are more noticeable. The vertical, not so much.

Jim

 

[middlemarch]

My understanding is that the MTM is OK on axis and within about +/- 10 degrees or so off axis. After that is where the comb filtering really becomes an issue.

When the thing is vertical, with the axis (tweeter center line usually) typically at about seated ear height, most folks will find themselves within that 20 degree cone of goodness (unless you lie on the floor or take up flying or something), but that same speaker on it's side, the likelihood is much greater that folks may be seated outside the cone of goodness and thereby experience the problems caused by the cone filtering.

 

[Sancus]

Sitting inside the "good part" of the on axis is just a mitigation though, it doesn't make the speaker actually perform equally well. Bad off-axis still causes bad reflections which make speakers sound worse, same as with any other kind of speaker. If you have a very heavily treated room it will mitigate that but that comes with other downsides obviously.

Vertical MTMs just become like normal designs really because non-coaxial designs all have poor vertical off-axis response and it is true that that's less audible than poor horizontal off-axis.

 

[thewas]

Often towers with such driver configuration are also 2.5 instead of 2 ways which reduces the vertical lobe problem.

 

[valerianf]

Let us take a practical case.
Focal Sopra N°3

Here is the horizontal measurement between -90 and 90 degres:

Here is the vertical measurement between 0 and 15 degres:

There is no comb filtering effect between the dual woofer and the midrange that is placed far from them.
There is a small dip at 15 degree between the midrange and the tweeter around 3Khz.
The complete test is available at Stereophile:
https://www.stereophile.com/content/focal-sopra-no3-loudspeaker

At home I got a similar tower speaker from another manufacturer and there is no noticeable comb filtering effect.
Low frequencies are not as directive as high frequencies.

I do not have any measurement for a 2 way speaker that got a dual woofer configuration.

 

[somebodyelse]

Let us take a practical case.
Focal Sopra3

There is no comb effect between the dual woofer and the midrange that is placed far from them.

That's a 3 way though, not an MTM. The crossover from woofers to midrange is just below 200Hz so the woofers and mid are still 'close' relative to wavelength. That's also below the minimum frequency in the vertical off axis plot you show, so it wouldn't appear even if it were an issue.

 

[ZolaIII]

Let us take a practical case.
Focal Sopra3

Here are the measurements between -90 and 90 degres:

There is no comb effect between the dual woofer and the midrange that is placed far from them.
The complete test is available at Stereophile:
https://www.stereophile.com/content/focal-sopra-no3-loudspeaker

At home I got a similar tower speaker from another manufacturer and there is no noticeable comb effect.
Low frequencies are not as directive as high frequencies.

I do not have any measurement for a 2 way speaker that got a dual woofer configuration.

That's really, really bad example. Those have beryllium long horn guided tweeters and very wide coverage and even on long trow, are three ways and proper crossed and besides really don't need sub's and if you do want to cross them then one is enough as ideal crossover is at 60 Hz. I am not selling kidney for those.
@goldark to reciver any valid answer you need to provide details and your in room measurements including; waterfalls, clarity, RT60 decay times.
Edit: @somebodyelse first crossover is at 250 Hz.

 

[valerianf]

Here are the measurements for a 2 way tower.
Marten Parker Trio Diamond edition

https://www.stereophile.com/content/marten-parker-trio-diamond-edition-loudspeaker

Horizontal dispersion:

Vertical dispersion:

There is no sign of comb filtering issue.
The crossover design may need some phase optimization.

 

[valerianf]

Let us finish with a 2 way in MTM configuration.
Q Accoustic Concept 50
https://www.stereophile.com/content/q-acoustics-concept-50-loudspeaker

Horizontal dispersion:

Vertical dispersion:

No sign of comb filtering issue.

 

[thewas]

There is no sign of comb filtering issue.
The crossover design may need some phase optimization.

There is, look at -15°.

No sign of comb filtering issue.

The Stereophile vertical measurements are unfortunately limited to +-15°, in decent designs like this the lobing appears just at higher angles.

Here for example the full vertical measurements of the similar Q Acoustics 5040:

 

[ZolaIII]

Let us finish with a 2 way in MTM configuration.
Q Accoustic Concept 50
https://www.stereophile.com/content/q-acoustics-concept-50-loudspeaker

Horizontal dispersion:

Vertical dispersion:

No sign of comb filtering issue.

About those I can speak a lot as I have Q3030i's. Not a great design and hard to control big back port's, sweet spot is 12~15° vertically it's soft dome not guided tweeter. Again it all depends on room and placement. You work concretely on what you are getting. I have good clarity and great RT60 decay with mine after lot of work in small room siled, crossed with two sub's and cut at 120 Hz.

 

[valerianf]

I agree that the Q Acoustics 5040 shows some vertical comb filtering.
But the Q Accoustic Concept 50 does not seem having several peaks cancellation.
May be the crossover design is different: there is a big difference of price between the 2 models.

 

[thewas]

I agree that the Q Acoustics 5040 shows some vertical comb filtering.
But the Q Accoustic Concept 50 does not seem having several peaks cancellation.
May be the crossover design is different: there is a big difference of price between the 2 models.

It will definitely have at least one dip at each vertical direction as the drivers spacing is larger than half of the wavelength of their radiated frequency band, this is physically inherent to all such designs as almost all of them don't really fulfill the original D'Appolito requirements to avoid such, now how much this is audible is a different topic. Also in the end actually almost all non coaxial designs show some vertical lobes, the important issue is though how deep and at which angles they appear, I recently designed a 2.5-way floorstander for a friend where I minimised it as much as I could given the drivers dimension but still there is one, it is at high angles though so it shouldn't have a very audible impact:

 

[somebodyelse]

Edit: @somebodyelse first crossover is at 250 Hz.

I was going by the Stereophile measurements page which says:

The woofers are crossed over to the midrange drive-unit (green trace) just below 200Hz

 

[goldark]

Often towers with such driver configuration are also 2.5 instead of 2 ways which reduces the vertical lobe problem.

Interesting you mentioned this. In his interview with Erin, Greg Timbers said that he was surprised his Studio 590 was the big seller over the 580, considering the 580 measures better and has better driver integration.

The 590 is a 2.5 way and the 580 is a 2 way. Even within the same line, it seems like the effect varies.

 

[thewas]

Interesting you mentioned this. In his interview with Erin, Greg Timbers said that he was surprised his Studio 590 was the big seller over the 580, considering the 580 measures better and has better driver integration.

The 590 is a 2.5 way and the 580 is a 2 way. Even within the same line, it seems like the effect varies.

Often it is also cost decision as the extra inductor needed for the 2.5-way adds some significant weight and cost when chosen of good quality.