[aceinc]

There are a few BG style ribbon tweeters which have a rise in frequency response between ~4khz & ~12khz. One of the typical ways of resolving this issue is to create a notch filter.

Is there another way of resolving the problem such as a wave guide to boost the lower frequencies?

For the sake of this discussion let's use one GRS PT6816-8 8" Planar Slim Tweeter. https://www.parts-express.com/GRS-PT6816-8-8-Planar-Slim-Tweeter-8-Ohm-272-128. For this design we will crossover the tweeter at ~800hz with a sealed back chamber.

The frequency response dips down to 88-89db in the 1500-2500hz but peaks at about 100db ~9500 hz.

[FullRangeMan]

There are a few BG style ribbon tweeters which have a rise in frequency response between ~4khz & ~12khz. One of the typical ways of resolving this issue is to create a notch filter.

Is there another way of resolving the problem such as a wave guide to boost the lower frequencies?

For the sake of this discussion let's use one GRS PT6816-8 8" Planar Slim Tweeter. https://www.parts-express.com/GRS-PT6816-8-8-Planar-Slim-Tweeter-8-Ohm-272-128. For this design we will crossover the tweeter at ~800hz with a sealed back chamber.

The frequency response dips down to 88-89db in the 1500-2500hz but peaks at about 100db ~9500 hz.

which have a rise in frequency response between ~4khz & ~12khz.
This excessive increase in amplitude is more than common in tweeters.
Is there another way of resolving the problem such as a wave guide to boost the lower frequencies?
Place a black felt cloth in front of the tweeter which should decrease the high SPL level, which also will prevent dust from getting inside the ribbon.

[Wayner]

Most planar tweeters have a 94db/m/w efficiency, so they are already too loud for lots of mid and low frequency drivers. Thus, they will likely need an L-pad to knock them down to a more useable level (like 89-90db/m/w). The L-pad can be either mechanical (the usual rotatory dial), or electrical, one resistor is series, one in parallel to the driver. If you look on line, you will find several free softwares to calculate the resistor values based on the db of reduction in output needed.

That is the first problem.

[aceinc]

Most planar tweeters have a 94db/m/w efficiency, so they are already too loud for lots of mid and low frequency drivers. Thus, they will likely need an L-pad to knock them down to a more useable level (like 89-90db/m/w). The L-pad can be either mechanical (the usual rotatory dial), or electrical, one resistor is series, one in parallel to the driver. If you look on line, you will find several free softwares to calculate the resistor values based on the db of reduction in output needed.

That is the first problem.

One way to level the efficiency playing field is to use multiple squawkers and/or woofers. Where possible I would like to avoid additional electronic components. If physics doesn't allow that, then c'est la vie.

[DannyBadorine]

I think the answer to this is "yes".  Check this video as I think it's been done.  Joseph Crowe is fun to watch.  Smart guy.
https://www.youtube.com/watch?v=f_nO7kymm84

Also, not to nit-pick you, but these speakers are planar.  They're different from a ribbon.  I mention this because I think this detail is important in what you're asking.  They will act differently in a waveguide from a ribbon speaker.  These planar are a bit wider and go a lot lower than ribbon speakers, which gives you different options in the design.

[aceinc]

I think the answer to this is "yes".  Check this video as I think it's been done.  Joseph Crowe is fun to watch.  Smart guy.
https://www.youtube.com/watch?v=f_nO7kymm84

Also, not to nit-pick you, but these speakers are planar.  They're different from a ribbon.  I mention this because I think this detail is important in what you're asking.  They will act differently in a waveguide from a ribbon speaker.  These planar are a bit wider and go a lot lower than ribbon speakers, which gives you different options in the design.

Oops, yes they are planar. I suspect this mistake is often made.

[wingsounds13]

It is PAINFULLY common for manufacturers to misrepresent planar tweeters as ribbons.  I suspect that this is normally a marketing ploy because the supposed advantages of ribbons are commonly known (but not really understood) and many people do not know the difference between a ribbon and planar speaker. 

J.P.

[DannyBadorine]

Oops, yes they are planar. I suspect this mistake is often made.

I didn't know the difference until I made speakers with both different tweeters.  I like both but the planar is definitely my favorite and has different characteristics. If you dive into it, I think you will be delighted.

[Danny Richie]

The real problem is that the tweeter you are referring to is 8" tall. That is WAY too tall for a single tweeter. It will have considerable beaming and have no real output above or below the on axis point.

These are designed to be used in line sources where a long continuous line is made by using 6 to 9 of them in a line. Using a line of them also increases the whole lower range as the longer wavelengths will couple and give an increase in output while the upper ranges will not.

When using a single tweeter don't use anything any taller than the Neo 3 model (ours or any other brand). 

[aceinc]

The real problem is that the tweeter you are referring to is 8" tall. That is WAY too tall for a single tweeter. It will have considerable beaming and have no real output above or below the on axis point.

These are designed to be used in line sources where a long continuous line is made by using 6 to 9 of them in a line. Using a line of them also increases the whole lower range as the longer wavelengths will couple and give an increase in output while the upper ranges will not.

When using a single tweeter don't use anything any taller than the Neo 3 model (ours or any other brand).

Danny, do you know what the vertical "spread" would be?

My main application is HT where a lot of vertical spread is not needed because of folks being seated, and the listening positions are more than 10' away from the drivers.

Vertical beaming does have the advantage of reducing floor & ceiling reflections.

[Danny Richie]

The top octave will drop off as soon as your ear leaves the height of the tweeter.

It will also cause a very uneven room load and room response.