Author Topic: 2 x frs 8 in parralel with w 170 s 8  (Read 5876 times)

Offline tangmonster

2 x frs 8 in parralel with w 170 s 8
« on: November 21, 2011, 03:11:45 PM »
High all the speaker builders and designers.

I like the simplicity of the Stella light design from visaton.

http://www.visaton.de/en/bauvorschlaege/2_wege/stella_light/index.html

Although the crossover seems a little bit simple.

So I was toying with this idea. Why not use TWO frs (8ohms) in parralel with a w 170 S 8ohm for woofer and make the crossover point at around 300 to 500hz.

I was messing around with visaton's boxim software. And came up with this:





What are the cons of using two drivers in parallel next too each other  for higher frequencies? I have read some stuff about lobing issues which i am not sure i inderstand and not sure how to solve in an enclosure design?



I have also toyed with the idea of building a bipole for my rear channels using this same setup. Looking something like this:




Since I am using a low frequency crossover the capacitors sizes is high. I might even use the 4th order crossover and actively biamp this speaker.

But before I build all that. I would like to run my idea past all the experienced builders. Is it viable to put the two frs 8's close to each other on a single baffle?

Offline JimGore

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #1 on: November 21, 2011, 05:49:46 PM »
Hi,

Not really a good option - you will have comb filtering issues with 2 drivers doing mid and tweeter duty.

You may find your configuration will work well with just one FRS because of baffle step.

Ian.

Offline tangmonster

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #2 on: November 21, 2011, 09:49:14 PM »
Thanks

For the bipole idea? With the 2 drivers pointing more or less in different directions? does comb filtering have less of an effect there?

Offline Timber_MG

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #3 on: November 21, 2011, 11:01:06 PM »
Nothing preventing you from making a 2.5 way with the .5 on the mid-tweeter. The interference with both drivers running paralell would be somewhat aided by the bi-pole and the baffle step is somewhat free to an extent (somewhere the delayed radiation to the rear can wrap around the rear baffle and cause cancellation).

Looks like a very nice small driver that and iirc it's the original Buschhorn driver?

Offline Atjan

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #4 on: November 21, 2011, 11:20:12 PM »
I also like this project for its simplicity. Doing all that....well that kind of makes it complicated. Nothing wrong though. The drivers are cheap as anything else so why not!
It's only hifi people....

Offline JimGore

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #5 on: November 22, 2011, 07:53:08 AM »
Thanks

For the bipole idea? With the 2 drivers pointing more or less in different directions? does comb filtering have less of an effect there?
Comb filtering will still have play a major role on the off axis response.  You will most probably have timing and phase issues as well in a bipole.  No problem at all if it's for your side surround speakers, but if it's for your main listening stereo setup then I would rather try a different approach.

Sorry, I know it's not what you want to hear.  That being said - nothing stops you from trying it out!  You can do some experimentation and report back here so we all learn some new things.

Ian.

Offline tangmonster

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #6 on: November 22, 2011, 08:18:03 AM »
My idea was to use the same setup and build all 5 speakers. The surrounds will be like the ones in the picture to disperse it.

And for the front and center just use the two frs 8's front firing.

My plan was to build the surrounds first , since I really want wall mounted surrounds.

The w 170 s 8 will do great with a 20 l ported design as stated on the visaton website.

On the other hand one frs 8 (4 ohm) might do just fine. The only reason i really want 2 x 8ohms is too split the energy so they won't go close to distorting on high volumes.

Long story short. I should get a frs 8 4ohm , put it in a little 1Liter enclosure, and drive it with a 300+hz signal and see how loud it goes and see if I am happy with it.

30W rated power with a 82db 1w / 1m speaker is not all that much so I am just not sure if they will cut it... but it could just be if they only get 300hz and up?

Offline JimGore

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #7 on: November 22, 2011, 10:26:33 AM »
Firstly, is the driver 82dB, or the entire speaker with crossover 82dB?

If my math is correct, then 30W RMS will give you around +14.5dB.
This added to the starting point of 82dB = 96.5dB (at one meter distance, using the full 30W).
Next, for each doubling of distance, you subtract 6dB.  If your seating position is 3m from the speaker, you will subtract around 9dB from that, meaning you end up with an approximate 87.5dB at listening position while driving the speaker at full tilt.

87.5dB isn't particularly loud to be honest - not sure if it will cut it when watching movies?

Ian.

Offline tangmonster

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #8 on: November 22, 2011, 10:37:38 AM »
yes the 82db  is the speaker spec itself

long story short. This speaker won't do.

even if I crossover at 500hz and lets say 500hz up is around 40-50% of the total energy. It still is a bit on the low side.

back to the drawing board for me.....

Offline Timber_MG

Re: 2 x frs 8 in parralel with w 170 s 8
« Reply #9 on: November 22, 2011, 11:05:17 AM »
My B3N speakers currently have full BSC and run somewhere in the high 70dBs @ 1W sensitivities yet crossed @ 160Hz they get to reasonable levels up close, though dynamics fall well short of the 96dB system set up next to it when listening from further away. The upshot is a very coherent soundstage. For low to intermediate levels it's quite likable.

Cross it at 200Hz+ LR24 as opposed to 160Hz But12 and matters change somewhat and it can play a whole lot louder, though the dynamics are still limited, even if distortion measurements are surprizingly low at close to full power. Note that this is an almost 20dB less efficient a speaker than I am used to. Rod Elliott's article on bi-amping has good info on power distribution and crossover choice.

Bipoles work well if you place them well into the room and if the rear speaker is not further behind the front radiating unit than the width of the baffle. I've had reasonable success with a bi-pole using 2x2 4.5" drivers. Interrestingly running the rear set almost fullrange was better sounding to me (no tweeter at the back) and phase better integrated with the set than crossing them with the fronts. The presentation is very different from the highly directional front facing setup I am accustomed to. It works for some things, but it adds a lot of reverb in more live rooms. It's quite nice for a hybrid DR/di-pole rear speaker setup though.