[LostInPA]

I have wondered if the horizontal placement of two [sort of] mid frequency drivers was a good idea.   The JBL Project Everest DD67000 uses two 15 inch drivers in staggered 150 and 850 Hz crossover points.   What, if any, are the limitations here of off-axis listening on directivity, soundstage, lobing,etc.   My crazy dream is to use two 10 inch or 12 inch drivers in horizontal placement for the range of  80 Hz up to 640 Hz minimum/1,280 Hz maximum.   I would certainly like to hear from those of you who are willing to share your technical thoughts.   I would even like to hear from those of you who have semi-technical opinions.   It is all grist for the idea mill.

[FullRangeMan]

This H position  was very well implemented by Polk Áudio in the 1980/90, I have listened the SRS and the sound was 3D filling room.

[dB Cooper]

The SRS (which has just been reintroduced)used a form of 'crossfeed' though. The two drivers weren't playing the exact same thing. What you're describing would be akin to an 'MTM' setup on it's side. Have seen few layouts like that.

My personal experience has generally been that the more complicated the driver layout, the harder it is (from a design standpoint) to make the sound 'cohere' and the smaller the 'sweet spot' over which it does.

Also, 10-12" sounds very large for a midrange these days.

Interesting topic.

[richidoo]

I have wondered if the horizontal placement of two [sort of] mid frequency drivers was a good idea.   The JBL Project Everest DD67000 uses two 15 inch drivers in staggered 150 and 850 Hz crossover points.   What, if any, are the limitations here of off-axis listening on directivity, soundstage, lobing,etc.   My crazy dream is to use two 10 inch or 12 inch drivers in horizontal placement for the range of  80 Hz up to 640 Hz minimum/1,280 Hz maximum.   I would certainly like to hear from those of you who are willing to share your technical thoughts.   I would even like to hear from those of you who have semi-technical opinions.   It is all grist for the idea mill.

Try to keep the center to center distance between any two adjacent drivers sharing bandwidth smaller than the shortest wavelength in their shared bandwidth. <1/4 wavelength distance is ideal and supposedly makes no lobing, but apparently it's not a big problem until distance exceeds 1 wavelength.

The Everest woofers are within 1/4 wavelength so there is no lobing <150Hz and only 1/3 wavelength at -24dB. It's easier to avoid lobing at bass freqs because wavelength increases exponentially with falling freq. But the falling acoustic impedance with increasing wavelength is a major drawback. The reason you want dual 12" mids is because of the very high acoustic impedance at midrange freqs. There are some great midrange 12" pro drivers like those used by Gedlee designs. Beaming is the limiting factor with large midrange cones, but you could angle them outward slightly to widen the beam.

Consider how dual horizontal mids will interact with a single tweeter above. Will the ceiling reflection patterns affect stereo imaging?

Some designs deliberately violate the 1 wavelength rule when there are more than two drivers in the array sharing same bandwidth so they can control directivity, floor bounce, SBIR etc. Bill Duddleston of Legacy Audio is an innovator in this area. He uses side by side double and quad midrange drivers in his top models.

Wavelength calculator

[nickd]

Sounds like you want the “Rodspeaker” made for Rod Stewart by Ric Riccio back in the 70’s.
Built using Altec Lansing drivers and horn.
There were some some Altec bridge monitors that used horizontally mounted mid woofers too.  Polar response measured quite well.

Altec Lansing / Great Plains Audio woofers provide some of the most dynamic midrange you will ever hear. Big paper drivers also have amazing tone.

[JLM]

Have heard the Polk SDS, they produced an effective but artificial and exaggeratedly wide sound stage that only worked if if you sat exactly in the middle of them.  Yes they used a special cross feed circuit.

Years ago was invited to a presentation of expensive WMTM loudspeakers.  Went forward to snap a couple of images of the listening group and observed heads bobbing up and down.  The listeners were of varying heights sitting in a variety of chair heights but all were struggling to avoid the lobbing effect of the MTM phenomena.  It reminded me of the prairie dog carnival game you play by bopping the dogs with a mallet.

Here's a review of a typical MTM center channel loudspeaker:

https://www.audiosciencereview.com/forum/index.php?threads/ascend-cmt-340-se-center-channel-speaker-review.11797/

[LostInPA]

Thanks to all who replied.   Thank you!   I was certain that there would be useful knowledge somewhere on Audiocircle.
  Clearly, I need to do some more technical research.   The practical part of the research is in process.   Two of the specific drivers that I propose to use are on order.   They will be mounted in boxes, analog electronic crossover set to the required low frequency and one of the probable high frequencies.   They will be listened to in stereo to evaluate the driver, with the crossover varied to listen at a range of high frequency cutoffs.   Later, the two boxes will be moved together as mono to experiment with frequency and toe out to evaluate the sense, or nonsense, of my idea.   I expect that this process should take approximately two weeks.   Then, I will have some decisions to make.

[LostInPA]

FYI, 2 drivers in horizontal placement, crossover frequency 1.3kHz:

https://www.jblsynthesis.com/products/loudspeakers/type/in-wall-loudspeakers/SCL-3-.html?dwvar_SCL-3-_color=Black%20Matte-GLOBAL-Current&cgid=in-wall-loudspeakers 

[FullRangeMan]

The mentioned Rod Stewart speaker and some vintage Westlake:

Westlake BBSM-15F

[planet10]

I have wondered if the horizontal placement of two [sort of] mid frequency drivers was a good idea.

Any time the centre-to-centre distance starts getting less than the quarter wavelength of the sound being reproduced you will start to get combing. This is usually a greater problem if the drivers are aranged horizontally than if vertically.

dave

[FullRangeMan]

Dave,
How does comb effect sound like ?

[planet10]

It increases as frequency increases. Effect is heavily dependent of the listeners ear/brain sensitivity to the phenomenon. And the recording.

It looks worse in measures than what the brain decodes, it has evolved to deal with this.

If you can pick it out, one gets a blurring of detail and a loss of DDR (small details) so harms the end resolution.

dave

[FullRangeMan]

Wow Its very Interesting.
Thanks Dave

[planet10]

I forgot the picture (from Taylor):



dave