Multiple Tweeters

[GranteedEV]

Loudspeakers with multiple tweeters are few and far between. Yes, there are bi-pole and di-pole and line-array speakers which do in fact use 2 or 50 tweeters very specifically. That's not really what I'm refering to though... Convention wisdom suggests that two tweeters on the same baffle is a just plain bad idea. That the wavelengths of high frequencies become so short that virtually any spacing becomes too far away, and lobing ultimately comes into play.

We know that lobing of a mono source can lead to cancellation of frequencies - surely this would be audible, right?

Perhaps the most popular speaker I can think of which defies the laws is the Axiom M80. A so-claimed "dumb design" for more than one reason. That people seem to love.

Axiom's defense to the criticisms is that a microphone may pick up comb filtering, but humans, with two ears separately placed as opposed to one, are much more forgiving. Shouldn't this still sound unnatural?

There are two other companies I can think of who have used this in their with apparently positive results. RBH's T1 is said to have a "dispersion averaging array" but they don't really give us any real scientific argument backing it up. The T1 takes this one step further with the top and bottom woofers being rather spaced apart themselves. Dynaudio's equally ultra high end Evidence Temptation does something similar, with a crazy 5-way WWMTTMWW arrangement.

Personally, I've never even heard a loudspeaker with more than one tweeter on the same baffle plane, or even an electrostat which is supposed to have similar effects. But the idea has always intrigued me. That is to say, are these lobing artifacts just overstated? Or is it just a worthwhile yet ever-present tradeoff? I appreciate any and all in-depth responses on the matter. I'd like to think that these speaker companies know what they're doing; it's just that there's always a certain... sentiment of dismissal I've found... that these high end designs are exotic for the sake of being exotic.

 

[JerryLove]

It depends on design. I have a pair of McIntosh XR-5's that use dual tweeters set both off-axis so that the sound fields don't directly, significantly overlap.

My major experience (outside of electrostatics / large ribbons) is with the McIntosh Xrt2k (which uses 40 tweeters and 64 midranges). I found the effect on that particular speaker... diffuse. Like the difference between hearing a single violin and a bank of violin's all trying to sound like one.

I'm sure someone with far more knowledge on the nature of such designs will chime in... I can only really speak in "like" and "dislike".

 

[Alex2507]

I can only really speak in "like" and "dislike".

... but did you? I mean like or dislike the multiple tweeter thing?

I've heard and liked a triple tweeter center over at Walter's and sort of honed in on this post by Gene regarding this multi tweeter issue.

I saw an interesting article regarding lobing here on AH but lost track of it because it had too much English for me. I guess if somebody located it I might try to read and comprehend it again but I'm not making any promises.

 

[JerryLove]

... but did you? I mean like or dislike the multiple tweeter thing?

I disliked the mid-to-upper sound of the XRT2k. It was by no means "bad", but was "lacking". (The bass on the XRT2k is my favorite of any speaker so far)

For reference: I far preferred the mid-to-upper sound of the B&W CM9's in the neighboring room.

 

[GranteedEV]

I disliked the mid-to-upper sound of the XRT2k. It was by no means "bad", but was "lacking". (The bass on the XRT2k is my favorite of any speaker so far)

For reference: I far preferred the mid-to-upper sound of the B&W CM9's in the neighboring room.

That was a proper line array, right? I was discussing something more conservative on the number of tweeters... 2 or 3

 

[JerryLove]

That was a proper line array, right? I was discussing something more conservative on the number of tweeters... 2 or 3

I will say that I still wish I had picked up the McIntosh XR-19 from eBay a couple years back when it went for $200. I wonder, though, to what extent that might also be excluded as the multiple-tweeters are angled away from one another and crossovers have been carefully used to prevent comb-filtering problems.

If you have a local McIntosh dealer: they have current designs with 2-4 tweeters you could listen to. I'm not of another available brand that uses multiple tweeters.

 

[Alex2507]

I'm not of [aware of] another available brand that uses multiple tweeters.

Maybe fixed and this is what I listened to. It did sound pretty good too with The Blue Man Group and Venus Hum screaming her head off.

 

[JerryLove]

Maybe fixed and this is what I listened to. It did sound pretty good too with The Blue Man Group and Venus Hum screaming her head off.

That raises an interesting point. Banks of speakers (including tweets) are common in commercial productions as well.

Was there anything in particular that you feel that more tweeters brought to the table? In other words: and specific strong point to that driver you would equate to the tweeters being in multiples?

 

[Alex2507]

That raises an interesting point. Banks of speakers (including tweets) are common in commercial productions as well.

Was there anything in particular that you feel that more tweeters brought to the table? In other words: and specific strong point to that driver you would equate to the tweeters being in multiples?

Now I'm back to using your 'I like' phrase. What I thought I knew about multiple tweeters told me it's wrong but Venus Hum's voice on Walter's center sounded better than on my Infinity PC350. More forward, more present, less laid back ... I think I have gotten better at identifying how well a speaker reproduces let's say low', mids and highs from paying attention to what I hear. I think I've gotten better at noticing what different rooms sound like. I have for sure gotten better at identifying how well a speaker reproduces the human voice. That speaker just did a better job than mine ... plus Walter had that cranked loud enough to shake loose the popcorn on his ceiling but that's a different matter. Who knows, maybe my center just sucks. Let's face it, that center retails for more than I paid for all my speakers ... including at least one of my subs. So ... it should sound better than my center.

To answer the question, her voice sounded like it was more piecing, present, real especially with the hard 'e' sound. However this comparison is quite unfair. It should be done in the same room with the same equipment driving it. Which brings me to how this thread gets jacked.

I recently got a couple of rec'rs off eBay for Eddie's shop. Both of them together cost $38. I think they were 70 watt and 85 watt Yamahas. Testing them with 6 Ohm Aiwa (screw those jerks for having a name that is unpronounceable and spelled wrong even when it's spelled right) bookshelf speakers revealed that the 85 watt one got the test tune much louder with much less distortion than the 70 watt one. This was a night and day difference that went well beyond the difference of 15 watts but yes when they were played at low levels there was no preference.

The good one ...

To bring my point back to the topic I'll say that Walter has an amp rated at 350 watts pushing his center.
What a maniac.

 

[woofersus]

That raises an interesting point. Banks of speakers (including tweets) are common in commercial productions as well.

Was there anything in particular that you feel that more tweeters brought to the table? In other words: and specific strong point to that driver you would equate to the tweeters being in multiples?

Commercial productions use constant directivity horns with spacing set to limit overlap as much as possible. The limited dispersion characteristics of horns makes it possible to use multiples like this. There can still be some comb filtering audible at certain places in the room though. You just try to minimize them as much as possible. More and more, large commercial productions are moving to line arrays anyhow, which helps maximize coverage and has less of that issue. Regardless, in those cases it's a necessary evil.

There are a number of ways a designer can use multiple tweeters in a way that makes sense, such as a dipole, a (properly designed) line array, or McIntosh's Bessel arrays, but in any of those cases, the potential issues that multiple tweeters can cause are taken into account and dealt with. (of course you may or may not like those designs based on your own preferences) They aren't just slapped next to each other on a baffle. If you do that, it WILL cause problems. There's not a great reason to do so either, since the tweeter is rarely your source of limitation with regards to dynamic range or power handling.

For some reason, Axiom talks about the comb filtering induced by their multiple tweeter designs as "artifacts" that are difficult to hear in real life, but let's talk about what comb filtering is and what it does. The cancellation caused at certain physical alignments with the tweeter(s) causes the frequency response to vary depending on where in the room you are. If we look at off-axis measurements and think they matter, then how can comb filtering not matter? If you lose 6db at 16k when you move 20 degrees off axis, that's not a very good result. If you lose significantly more and then get it back on an inch by inch basis won't your ears notice that? I've seen this in "high end" designs too, and the laws of physics seem to hold fast there as well...

Take a look at the measurements of the M80ti and VP150 in this thread.

 

[AcuDefTechGuy]

I tried using 2 identical (CLR3000) center speakers vertically once, each speaker having 1 tweeter. I hated the result.

I've listened to the RBH T2-P speakers, and I thought they sounded very good.