Using multiple tweeters in parallel

[gnalbant]

I've searched the forum but I couldn't find a matching topic.

There are loudspeaker designs that use multiple midrange or mid bass drivers or an array of them in parallel for the same frequency range. I do not mean the d'appolito design, I mean using four drivers parallel for midrange frequencies, for example.

The motivation for using more than one driver is to avoid some off-axis problems and balancing the power distributed to the drivers.

What is the reason that more than one tweeter is not used in those designs? I know some Kenwood speakers that use three tweeters connected parallel or serial.

Thank you.

[BHTX]

When the center-to-center distance between drivers becomes greater than one wavelength, lobing/cancellation/dips/suckouts will occur. Obviously, with tweeters, it'd be an absolute worst case scenario, as they're playing highest in frequency.. likely up to 20KHz+ (20,000 cycles = only 1.72 centimeter wavelength, for example). This would cause a phasey/lobey/combed response as you move around anywhere in front of the loudspeaker, becoming worse as frequency increases, depending on the center-to-center distance between the drivers radiating areas. This effect is VERY noticeable, as well as easily identified. I've always loved some aspects of large planars/electrostats, but this issue is a common trait that I've never been able to stand, and I soon become irritated.

edit:

Originally posted by gnalbant
The motivation for using more than one driver is to avoid some off-axis problems and balancing the power distributed to the drivers.

Using more than one driver would inevitably CAUSE off-axis problems, not avoid them. As for "balancing the power distributed to the drivers", I guess I don't know what you mean.

[Cal Weldon]

I think he might mean that the power handling is increased when spread among multiple drivers.

gnalbant, I agree with what BHTX has written. IMO, the only justification for using more than one tweeter on the same baffle plane is for power handling, unless you are smitten with the line array idea, but that's a different matter.

[terry j]

I don't have as much experience as you guys, and I find it very interesting that BHTX says that with the tweeters the lobing etc is very noticeable (irritating as well, tho I guess that noticeability and irritation would vary greatly from person to person...trouble is you may not notice at first if you've never experienced it, but once you notice anything the it becomes obvious. Imagine one day suddenly noticing this phenomenon and the speakers you once loved you can no longer stand!! ).

But here is my question, do not Dynaudio use two tweeters in some of their top of the line stuff?? And they would not exactly be cheap either. I don't know much about them, but I think that one of them is designed to only start operating above a certain frequency, ie they don't track across the entire tweeter range. But in any case, when the second one does come in it comes in at exactly the worst time, that it higher up in the FR.

The engineers there would be no dummies, do they ignore the bad and take the good thinking the benefits outweigh the drawbacks?

The problem noted is most apparent when moving around I guess, but if it is used as a dedicated stereo setup where you just sit and listen, are the drawbacks still apparent??

What about the rear firing tweeters in some designs. I think they are there usually to balance the spatial distribution of sound in certain designs, so are doing a different function than what is being asked here...right?

[D OB G]

Hi terry j,

If I'm not mistaken, the Dynaudios use the new neodymium, unobtainium, Esotars (very small diameter) in parallel up to about 8 kHz, then a single one takes over above that.

Maybe because the domes are so close together, lobing is not considered a problem at that freq, although I personally believe that using 6 dB per octave crossovers at high frequencies invites problems.

We are only, say, 9 dB or so down at 16 kHz, so lobing is progressively occurring up from 8 kHz in a way that wouldn't occur at 24 dB per octave. (Not a problem at low freqs given the driver sizes and proximity for the wavelengths under consideration).

Just an opinion.

David

[LineArray]

Using a manyfold of tweeters opens some interesting
design options.

For example one could wire two small nedymium tweeters
in series mounted close to each other and realize a
lower crossover frequency because distortion is reduced.

In a 2 Way speaker the manyfold could be designed to match
the dispersion of the mid-bass unit at XO ...

Lobing can be avoided by rolling some of the tweeters off at
higher frequencies, only one of them transducing the upper
range of the spectrum. Dispersion and overall performance
in the upper range may be improved when compared to a
larger tweeter.

So this concept is very interesting, when executed well.

I use that technique in the backward tweeter panel of my
"Dipol 08" design too ...

Kind Regards

[gnalbant]

Thank you for all your comments.

I was curious about using more than one tweeter, in fact, very rare designs apply that but I didn't know the technic behind it.

As far as learned from your comments, it is not possible to use more than one driver 8 KHz because of the lobiying and other factors.

What I was trying to do is to widen the dispersion of the sound into the room by adding additional drivers. The first design was a d'appolito box and I thought using four midranges instead of two would lower the distorsion at higher volumes and disperse the sound into a wider area in the room. The same power would also produce a louder sound, I guess.

I saw some designs in the forum with eight drivers in a tower but they are used for low frequencies, I see now.

In fact, instead of using two tweeters, a dome midrange and one tweeter would be better in a four way system. But I am not that much experienced on passive crossovers and a four way seems a very critical design.

It is much better for me to stay in d'appolito design with two midrange and one tweeter.

Thank you again, I'll send the picture of it when it finished.

[BHTX]

Originally posted by gnalbant
What I was trying to do is to widen the dispersion of the sound into the room by adding additional drivers.

..If only it were that simple.

Originally posted by gnalbant
In fact, instead of using two tweeters, a dome midrange and one tweeter would be better in a four way system.

I'd agree, except that I don't care for dome mids, and I know a lot of other people don't as well, most likely for the same reasons. And.. why a 4-way? A 4-way isn't always necessary. I hope you're including very low frequency drivers in that 4-way.

Originally posted by gnalbant
It is much better for me to stay in d'appolito design with two midrange and one tweeter.

D'Appolito often suffers the same consequences as the configuration of tweeters in the title of this thread, and for the same exact reasons. Why D'Appolito anyway? If it's higher sensitivity you're after, go for it the real way and use real drivers.

Originally posted by gnalbant
But I am not that much experienced on passive crossovers and a four way seems a very critical design.

As stated above, "D'Appolito often suffers the same consequences as the configuration of tweeters in the title of this thread, and for the same exact reasons." Due to your above statement, I think it's very possible that it WILL suffer from slight lobing, especially if not crossed low enough. Regardless, vertical dispersion will also likely suffer.

For the record, I can't design a passive xover worth a flip either, so I'm not talking down to you or anything.. Just stating my opinion in hopes that you'll give it some thought.

[gnalbant]

Originally posted by BHTX


I'd agree, except that I don't care for dome mids, and I know a lot of other people don't as well, most likely for the same reasons. And.. why a 4-way? A 4-way isn't always necessary. I hope you're including very low frequency drivers in that 4-way.

Yes you are right, the design will include very low frequencies, that's way I consider about a four way system or focusing on the mid bass and mid range frequencies.

Originally posted by BHTX

D'Appolito often suffers the same consequences as the configuration of tweeters in the title of this thread, and for the same exact reasons. Why D'Appolito anyway? If it's higher sensitivity you're after, go for it the real way and use real drivers.

In fact simple is the best, I haven't tried D'Appolito before, but while listening to some midrange and midbass drivers, it sounded better to my ears, especially in classical music and jazz. I am also curious about the mid bass performance of the drivers, two would be a safer choice in terms of power handling.

Originally posted by BHTX

As stated above, "D'Appolito often suffers the same consequences as the configuration of tweeters in the title of this thread, and for the same exact reasons." Due to your above statement, I think it's very possible that it WILL suffer from slight lobing, especially if not crossed low enough. Regardless, vertical dispersion will also likely suffer.

There are meny D'Appolito designs, I am more optimistic about the results. What I am trying to do is to build the speakers first, then adjust the crossover frequencies by using an active crossover. Therefore I'll have some adjustment opportunities later.

Originally posted by BHTX

For the record, I can't design a passive xover worth a flip either, so I'm not talking down to you or anything.. Just stating my opinion in hopes that you'll give it some thought.

Thanks for sharing it helped a lot.

[jason_watkins]

I believe there is one vendor of home THX speakers that uses 3 tweeters. I can't recall the rational behind it.

Bessel arrays are another option.