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Old 29th November 2012, 03:29 PM   #1
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Default Question about passive radiator and enclosure bracing for surround speakers.

I'm thinking of building the surround speakers based of the CHR-70 splayed surround plan from planet-10, but with a twist of adding the passive radiator to the enclosure.

Click the image to open in full size.

kind of like in the picture above. If I want them to be 8ohm impedance, what choice of combination should I go for.

  • 1 of the CHR-70A on the front with 2 of the 830878 Peerless 3.5" on both sides.
  • or 2 of the Alpair-6M on both sides (wire them in series) with 1 of the 830880 Peerless 5.25" on the front.
Last question about the bracing inside. I never build speaker enclosure using the bracing inside before. Should the bracing board be place right next to the back of the drive, or should it has some space or gab in between?

If anyone could help me with my questions, that would be nice.

Thank you,
^_^
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Old 29th November 2012, 05:02 PM   #2
chrisb is online now chrisb  Canada
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The Peerless part numbers you quote are not passive radiators, and unless for very large room or high volume levels, you might not need that much LF response from surrounds? Certainly that would sound a bit of overkill considering your question in other thread about single driver CHR70s for fronts and surrounds - or is that for an entirely different system / concept.

EDIT: as noted, clearly this is a BRAIN FART, Chris - yes these are PRs, but for me that just raises the question as to why you'd think that a CHR or pair of 6Ms would need a PR in a small wall mounted enclosure for surrounds? With wall mounting and the ability of most HT processors to HP filter/XO all channels, the bandwidth requirement of rear and front height surrounds can readily be accommodated by a CHR. As mentioned in the other thread, I haven't played with every drawn or proposed Planet10 enclosure.


The idea of bracing to driver could probably devolve into a much broader debate on "the best" mounting arrangement, but to answer the specific question, Dave's approach is to have "snug" contact of the brace to the magnet when the driver's mounting gasket is sealed, but not over compressed. The composite plastic frames of Marks' drivers are compliant enough that when you see any flexing around the area of mounting screws, you've over-tightened, and need to back off.

The more important function of the off-center brace in question is to couple the adjoining enclosure panels, divide them into smaller unequal areas and distribute energy of their resonance over a wider range of higher frequencies.
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Last edited by chrisb; 29th November 2012 at 05:30 PM. Reason: BRAIN FART
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Old 29th November 2012, 05:55 PM   #3
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[
They are both for completely different spaces.

for this thread I was gonna use them in the close space (room with 4 walls) about 4 by 7 meters wide and 3 meters tall

for the front and surround back speakers I'm aiming at the mMarS for CHR-70

http://frugal-phile.com/boxlib/P10fr...map-231009.pdf

to hang them from the front and back walls.

and the splayed speakers is for the surround speakers to be hang on the side.

but to my understanding if I use 2 CHR-70 speakers, I'll end up getting 4ohm (wire them in parallel) or 16ohm (wire them in seires) correct?

So I preferred to use 2 Alpair 6M in each box instead, wire them in series and I'll get 8ohm correct?

Not sure on how to re-size the plan down to suit 6M instead of CHR-70.

If the idea of adding the small passive radiator is not gonna cut it.

What should I go for?
  1. using all 3 pairs (in this 7.1 system) of the mMarS for CHR-70
  2. or, go for the sprayed surround with Alpair 6M
  3. or, use the CHR-70 wall mount plan instead?

http://frugal-phile.com/boxlib/P10fr...dix-191209.pdf

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Old 29th November 2012, 09:58 PM   #4
chrisb is online now chrisb  Canada
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Quote:
Originally Posted by nowobody View Post
They are both for completely different spaces.

for this thread I was gonna use them in the close space (room with 4 walls) about 4 by 7 meters wide and 3 meters tall

for the front and surround back speakers I'm aiming at the mMarS for CHR-70

http://frugal-phile.com/boxlib/P10fr...map-231009.pdf

to hang them from the front and back walls.

and the splayed speakers is for the surround speakers to be hang on the side.

but to my understanding if I use 2 CHR-70 speakers, I'll end up getting 4ohm (wire them in parallel) or 16ohm (wire them in seires) correct?
Depending on the power supply capacity of amp/receiver driving the mains, you might be fine with the 4ohm load of parallel wiring. Assuming that the impedance of the 70A is similar to the CHP , CHR and CHS, the nominal 8ohms is the minimum, and curve looks benign enough to not cause major reactance issues.

My own Denon receiver is rated at "6ohms or more", and I've been using for well over a year now with Alpair 7.2 in the front row with no issues.

Quote:
So I preferred to use 2 Alpair 6M in each box instead, wire them in series and I'll get 8ohm correct?
yes - and don't worry about sensitivity issues when using different drivers - the speaker level calibration of today's processors makes that easy enough for a klutz like me to get it close (once you figure out how to access and navigate the on-screen set-up menus - not always as easy at it sounds)


Quote:



Not sure on how to re-size the plan down to suit 6M instead of CHR-70.

If the idea of adding the small passive radiator is not gonna cut it.

What should I go for?
  1. using all 3 pairs (in this 7.1 system) of the mMarS for CHR-70
  2. or, go for the sprayed surround with Alpair 6M
  3. or, use the CHR-70 wall mount plan instead?

http://frugal-phile.com/boxlib/P10fr...dix-191209.pdf

^_^
I didn't mean to imply that passives wouldn't "cut it", just that they'd perhaps be unnecessary, and I'll admit that after using them in a different application in the distant past, I'm not particularly a fan, so some negative bias is certainly involved.

In any case, compared to floorstanders you're contemplating for the system described in the other thread, the mMarS are small / light enough that using them for all 3 pairs and center shouldn't be much of a problem size wise; but depending on the layout of the room, I'd still be inclined towards a splayed / angled surround, whether using a single CHR or dual 6Ms. Dave could better answer the question regarding "scaling" enclosure for dual 6Ms
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Old 30th November 2012, 05:52 AM   #5
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I think I'll stick to Dave's plans for now, and see if they suit my need or not.

My last concern now is finding sub-woofer to match these 2 sets.

Will keep update my progress, incase any one will help with any more suggestion.

^_^
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Old 30th November 2012, 08:28 AM   #6
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One more question before getting start, Between these 4 (in the pics below) which is the best choice to use as a surround speaker?

Click the image to open in full size.
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Old 30th November 2012, 11:17 PM   #7
chrisb is online now chrisb  Canada
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I've not heard the enclosure in bottom sketch, but am quite familiar with the milli-Fonkens in top row ( Fostex FE127E), and the larger VG fir MarKen enclosure with Alpair12. Presuming this question is regarding the smaller system, I'd tend to go with whichever of the smaller enclosure best fits the "ergonomics" / placement considerations of the room.

I spent more time than I wished on a pair of corner mounted angled enclosures for 6Ms for my own rear surrounds, and if I had it to do over would probably go for a simple rectangular box and swivel brackets.
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