CSS FR125S Splayed Horizontal Array

[xcortes]

I need a speaker (yes, only one) for a new system I'll be putting in place for a newly created space in my house. The speaker will be mostly used for background music but it looks like it will be the system we listen to the most. Requirements are: bookshelf (around 15 litres would be fine but could go for more if needed), parts cost around $200 (ex cabinets). I would like it to play loud in a big room and we listen to all kinds of music.

I originally considering Fostexes due to power limitations but since I redistributed amps and I'll have a stero gainclone at my disposal I'm now looking at the FR125S.

Duke at the high efficiency forum suggested a Splayed pair that sounds interesting. Since many people here have tried the FR125S I would love to hear your opinions.

In summary he proposes:

A horizontally splayed array would have one driver aimed 30 degrees to the left of center, and the other aimed 30 degrees to the right of center. I'm not sure what would be the best angle to use - 30 degrees is just a guess derived from eyeballing the published curves. If you look at the middle (dotted line) curve at the link below, that's the 30 degee curve. From straight ahead, you'd be 30 degrees off-axis to both the left and right driver, so the outputs would sum and pull that 30 degree line up a bit. From on-axis of one driver, the other driver is 60 degrees off-axis (the bottommost published curve) so it reinforces in the lower octaves much more than in the upper ones. The net effect is to tilt the frequency response slightly downward as compared to the normal on-axis curve. This is an improvement, as the driver is a bit on the bright side otherwise.

The drawback is that, to either side of the centerline, the output from the farther driver is delayed in time relative to that of the near driver. This will introduce comb filter effects, or narrow-band peaks and dips in the response. The ear is pretty forgiving of comb filter effects - every sound you've ever heard in a room with a non-carpeted floor was comb-filtered by the floor bounce. If the goal was ultra high fidelity I probably wouldn't recommend a splayed array, but since the goal is good sound from a mono source across a large area it's what I'd do.

So now you have improved the tonal balance and are getting a fairly uniform response over a much wider area than you would have with a single driver. If it works, should be nice.

Thanks a lot,

xavier

ps. The high efficiency thread can be found in: http://www.audioasylum.com/forums/hug/messages/101620.html

 

[Cal Weldon]

Hi xcortes,

First, the 125's are excellent sounding drivers, but...
They are not a high efficiency driver.
It won't go loud in a big room unless you have a bunch of them.
Horizontal alignment should be avoided as outlined in your quoted post.

Sorry to rain on your parade like that but I don't think you want that driver for your project. Perhaps reconsider the Fostex.

 

[xcortes]

Thanks for your answer Cal.

I don't need high efficiency drivers anymore since I'll be using gainclones now. Your comment regarding the horizontal alignment still applies though.

 

[happy.gringo]

Why avoid horizontal alignment, may I ask? I was planning on using two Pioneer B20 at 90 degrees as a cheap PA cabinet for acoustic guitar/voice, but maybe I should rethink that?

 

[Cal Weldon]

Lobing: The three-dimensional shape of how sound radiates from a multiple-point-source speaker. The sound will vary with different angles relative to the listening axis due to the separation of the acoustic centers. At some angles, there will be cancellations at certain frequencies. Lobing occurs vertically in vertically aligned speakers and horizontally in horizontally aligned speakers.

 

[Bas Horneman]

I don't need high efficiency drivers anymore since I'll be using gainclones now

Even so..the FR125's by themselves...won't fill a big room with sound. I tried...and did not like it..took the speakers to my kids's bedroom..liked them a lot.....a hell of a lot..they are a taste of high end ....great sounding speakers...in my computer room...perfect..but in my living room with open kitchen and dining room...no go. But that is only logical..you can't expect 3 inch cones to produce big sound pressure levels...

 

[Geek]

Even so..the FR125's by themselves...won't fill a big room with sound. I tried...and did not like it..took the speakers to my kids's bedroom..liked them a lot.....a hell of a lot..they are a taste of high end ....great sounding speakers...in my computer room...perfect..but in my living room with open kitchen and dining room...no go. But that is only logical..you can't expect 3 inch cones to produce big sound pressure levels...

I have discovered the max room for a pair to be about 250 sq. ft.

If you have a small listening room, there's few drivers better you could ask for under megabucks.

For bigger rooms and FR125S, has anyone tried TL or horn?