Multiple tweeters

[Lopsided]

Just saw the pics of flagship McIntosh floorstander. The measurement for JBL CBT speaker, still can't wrap my head around the super narrow vertical dispersion. Does the graph only represent far field? If you're sitting and standing somewhere within the speaker height, does these tweeters beam and change the treble response? Looks like a recipe for severe comb filtering.

Would like some help for my understanding of this. Thanks!

 

[eddantes]

Sometime soon I'd like to run experiments, because I am extremely curious about is the audibility of comb filtering and its influence on subjective evaluation. My personal initial position, is that comb filtering is a concern of objective evalutation and that subjectively the story may be different.

Edit - I've not yet researched for any publications studying this, so this is an opinion purely out of my own ass.

 

[Trell]

View attachment 144079
Just saw the pics of flagship McIntosh floorstander. The measurement for JBL CBT speaker, still can't wrap my head around the super narrow vertical dispersion. Does the graph only represent far field? If you're sitting and standing somewhere within the speaker height, does these tweeters beam and change the treble response? Looks like a recipe for severe comb filtering.

Would like some help for my understanding of this. Thanks!

McIntosh is selling an accompanying head-vice that you can adjust with your toes. For an extra charge there is an Alexa integration as well.

 

[puppet]

In these designs the tweeters are really close together. I'd guess comb effects wouldn't be apparent until above 15khz or so .. maybe higher. So, below those frequencies, the tweeter "array" will act as a single unit that is very long. Vertical dispersion will be pretty narrow but not the horizontal. Looks to me though, judging by the height, that sit/stand shouldn't be an issue.

 

[Lopsided]

In these designs the tweeters are really close together. I'd guess comb effects wouldn't be apparent until above 15khz or so .. maybe higher. So, below those frequencies, the tweeter "array" will act as a single unit that is very long. Vertical dispersion will be pretty narrow but not the horizontal. Looks to me though, judging by the height, that sit/stand shouldn't be an issue.

So, as long as one is in the coverage of these tweeters the tonality won't change much? This is the part I found hard to understand. If we have a large enough driver with flat frequency response to envelop a man, the position one's at within the cone does not matter?

If we fill the distance between two sources with many more tweeters, or an entire membrane, what would the radiation pattern look like? Thanks!

 

[puppet]

What the pattern looks like would depend on their (McIntosh) implementation. If they shaded the array, the vertical dispersion may be increased somewhat. You'd have to see some measurements.

 

[fluid]

Just saw the pics of flagship McIntosh floorstander. The measurement for JBL CBT speaker, still can't wrap my head around the super narrow vertical dispersion. Does the graph only represent far field? If you're sitting and standing somewhere within the speaker height, does these tweeters beam and change the treble response? Looks like a recipe for severe comb filtering.

Would like some help for my understanding of this. Thanks!

There is a big difference between narrow vertical directivity in a conventional multiway and that which you get from a line array.

In a line array there are drivers above and below the usual tweeter height, so the narrow window of directivity moves up and down to a certain extent meaning the tonality does not change anywhere near as much as it does in a conventional multiway. You can listen lying down seated or standing and the sound is remarkably similar.

If shading has been applied then there will be more variation with height as not all the drivers are receiving the same signal.

The horizontal positioning of the mid and tweeter line can present something of an issue as far as horizontal directivity is concerned, in much the same way as it is for all speakers using horizontally split drivers.

My personal initial position, is that comb filtering is a concern of objective evalutation and that subjectively the story may be different.
Edit - I've not yet researched for any publications studying this, so this is an opinion purely out of my own ass.

Your ass is spot on. Comb filtering in arrays does not sound anything like it looks in a measurement. It would be better to be avoided if possible but by keeping the drivers as close as possible it pushes the effect to higher frequencies as noted above. As listening distance increases the effect also diminishes. At 1m listening with a tall array you can hear the sound change as you move your head up and down. By the time you get to 2 to 3m the effect has disappeared. The treble balance is harder to set by looking at measurements and usually needs some experimentation.

 

[escksu]

Sometime soon I'd like to run experiments, because I am extremely curious about is the audibility of comb filtering and its influence on subjective evaluation. My personal initial position, is that comb filtering is a concern of objective evalutation and that subjectively the story may be different.

Edit - I've not yet researched for any publications studying this, so this is an opinion purely out of my own ass.

Maybe you can ask Mcintosh directly? I am very sure their engineers know about this when designing the speakers and how to resolve it.

 

[DonH56]

Comb filtering in my Magnepans (planar dipoles) is what caused me to learn about the effect and to treat the wall behind them decades ago. I couldn't stand the way it mucked up the sound.

 

[Jim Matthews]

I was under the impression that line arrays (in particular, Constant Beamwidth Transducers) have less power loss at a distance and reduce both floor and ceiling reflections.

http://www.acousticfrontiers.com/speaker-axis-constant-bandwidth-transducers/

 

[puppet]

https://engineering.purdue.edu/ece40020/Homework/SomeRefs/Line_Array_Theory.pdf
This was posted on DIYaudio by AllenB. Might help to visualize some of the design considerations re: line arrays.

 

[Lopsided]

Thanks for nice articles, going to work the brain hard to try to understand them

 

[puppet]

Join the club

 

[Jim Matthews]

Me, three.

 

[fluid]

Comb filtering in my Magnepans (planar dipoles) is what caused me to learn about the effect and to treat the wall behind them decades ago. I couldn't stand the way it mucked up the sound.

I've had both dipoles and a fullrange array. I would agree with you that treatment behind a dipole can be quite effective at getting rid of some of the muddiness that the rear radiation can give.

To me this is quite different in practice from the comb filtering that results from the use of multiple drivers in a line. I would suspect that it has to do with the amount of time delay involved.

I have attached a paper from David Smith from the time he was working at Mcintosh. One of the great speaker designers with a lot of array experience.

There is also this from Jim Griffin
https://audioroundtable.com/misc/nflawp.pdf

and a theory thread on diyaudio which may or may not be the best place to start
https://www.diyaudio.com/forums/multi-way/314917-infinite-line-source-analysis.html

 

[fluid]

I was under the impression that line arrays (in particular, Constant Beamwidth Transducers) have less power loss at a distance and reduce both floor and ceiling reflections.

http://www.acousticfrontiers.com/speaker-axis-constant-bandwidth-transducers/

CBT's are a little different to other line arrays. If the line is long enough then floor reflections will be non-existent, ceiling reflections are reduced but there can still sometimes be some ceiling splash where the drivers lose vertical directivity. This can all be simulated with Vituixcad or other tools.

 

[DonH56]

I've had both dipoles and a fullrange array. I would agree with you that treatment behind a dipole can be quite effective at getting rid of some of the muddiness that the rear radiation can give.

To me this is quite different in practice from the comb filtering that results from the use of multiple drivers in a line. I would suspect that it has to do with the amount of time delay involved.

I have attached a paper from David Smith from the time he was working at Mcintosh. One of the great speaker designers with a lot of array experience.

There is also this from Jim Griffin
https://audioroundtable.com/misc/nflawp.pdf

and a theory thread on diyaudio which may or may not be the best place to start
https://www.diyaudio.com/forums/multi-way/314917-infinite-line-source-analysis.html

Yes, comb filtering from dipoles is different than that from multiple driver interactions, agreed. I did not read the whole thread, just noticed a comment about not hearing comb filtering effects in practice, missed the context. My bad. IME the effect from multiple drivers is more subtle unless it is really bad, but like many things is easily recognizable by it's absence.

Skimming back a bit I see the discussion has evolved in line arrays and CBTs, which of course do not behave quite the same either (as planar panels or as each other). Speaker design is beyond my area of competence, bowing out to you experts.

Thanks - Don

 

[Hornlyd]

What about only two tweeter array?

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Are they connected in paralell? Then it will give comb filtrering?

Or is one of them lowpassed with just an inductor (no phase shift) in order to increase the relative sensitivity in the lowest frequencies so the distortion is reduced? Which will open for lower highpass crossover frequency.

It seems from the spec that Dynaudio is lowpassing one of the tweeters at 7000 Hz snd both at 2500 Hz.

I have an idea to use two Seas DXT tweeter crossed over to an 8 inch driver around 1500 Hz (active with dsp) and then a lowpass on the upper DXT around 2000-2500 Hz.