Alpair 12 with passive radiators for near field monitor? - diyAudio
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Old 25th June 2011, 07:06 PM   #1
18Hurts is offline 18Hurts  United States
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Default Alpair 12 with passive radiators for near field monitor?

Hello All,

Want to dip my toe into the swimming pool water of full range/wide band speakers and figure a set of near-field monitors would work well. My plan is use a Topping USB T-amp connected to my computer driving a pair of full range speakers. It will generally run CDs from an outboard source. I do have a 12" subwoofer that I can turn on when needed for games etc, but prefer not to run it for music.

The Alpair 12, the 6.5 inch full ranges seems to be what I would need. Since it is near-field, it will be always on axis so the larger FR beaming issues won't be a problem. Noted the Fs of 46 Hz and the 9mm Xmax so 10 watts from a T-Amp won't overdrive it in music. So far so good.

QTS indicates a ported box but those speakers will be moving around. My plan is a outside size of 9.5 inches wide, 12 inches high and 14 inches deep for around 0.6 cu ft. Since I'm out in the country, "things" love to crawl into ported boxes so I use sealed or passive radiator designs to prevent that. With that box size, I'll use two 8" passive radiators, one on each side of the box for balance, then tune them for 30 to 35 Hz. I'll tune them for the desk corner they will generally call home for the smoothest response.

Would this work well with Mark Audio full ranges? Are MA drivers recommended for listening at distances less than a meter? Anyone ever try a FR-PR combination or is it a no go from the start.

My reasoning to tune it as low as I can go (in place) is the Xmax of the Alpair 12 combined with the passive radiators should give me great response for music. 10 watts from a T-Amp and the listening levels with monitors at less that a meter away should avoid any speaker damage.

Thank you for any information you can provide--both good and bad.
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Old 26th June 2011, 07:46 PM   #2
18Hurts is offline 18Hurts  United States
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Survey says?

I would guess no. Oh well, my JBLs sound decent enough to keep reading, learning and eventually I'll find a FR with passive radiator design that will work. The Alpair 12 with two 8" PRs looks like it should work--but I'm not blowing $375 on the build just to satisfy my curiosity.

Back to the drawing board
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Old 26th June 2011, 09:36 PM   #3
zman01 is offline zman01  Bangladesh
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18Hurts,

There already is an Alp 12 Studio Monitor design as far as I can remember - have you checked that out?
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Old 26th June 2011, 11:03 PM   #4
18Hurts is offline 18Hurts  United States
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Thanks zman,

Seems the Alpair 12 can be used as a monitor and sounds good when doing so. If it works in a double-bass reflex, passive radiators should not be an issue. Went to Planet 10's site and checked the interior volume of some of the very tall, narrow towers and will run with that for box volume. (~0.8 cu. ft. ported) On the high side of a desk top speaker but such is life and I can tune the passives for the location.

Thanks again!
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Old 26th June 2011, 11:19 PM   #5
CSS/XBL is offline CSS/XBL  Canada
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Hi,

I know you mentioned dual 8" but have you considered one of my APR10s? The easy adjust ability from the front would give you maximum tuning choice. By putting 1 on opposite sides they could fire in or out as needed or preferred.

Bob
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Old 26th June 2011, 11:20 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

IMHO PR's are only good when you have no other choice but use them,
the required port being far too big for the (small) speaker design. If this
is not the case then using ports is usually a better idea, noting that you
are not designing a subwoofer, for a full range speaker you will never
have all the power going to the bass, IMO port size dimensioning for
1/2 power is about right, and this can make port size workable.

rgds, sreten.
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Old 27th June 2011, 12:43 AM   #7
18Hurts is offline 18Hurts  United States
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The APR10 seems like a really nice option,

The reason I use passive radiators is they are easy to tune/re-tune and "seal" the box to prevent ants/spider and dirt from getting in. They are a physical weight sitting there to slow down the main driver driven below tuning, it also prevents sound from traveling through an open port.

If the speakers sound great and I want to spread the FR "religion", I'll send them to a audiophile type friend of mine for a few weeks to see if he likes them. The guy has a pair of JBL monsters with passive radiator, he re-tuned it to his preferences. He will play around with the tuning of the PR (cough, cough OCD cough, cough) and test them with the Topping USB T-Amp and his regular Yamaha M series monster amps.

Bob, one APR10 on the back would do it--I don't think the 124mm cone of the Alp 12 would get it jumping too far on 10 watts of motivation from a T-Amp. Correct me if I'm wrong?
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Old 27th June 2011, 01:17 AM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by 18Hurts View Post
They are a physical weight sitting there to slow down the main driver driven below tuning,

Hi,

No they are not. They act the same way as ports. They do have the
advantage of adding their stiffness to the driver stiffness for very
low bass below the PR tuning, unlike a port. How well that works
is related to the PR diaphragm mass to the drivers mass, and
hence the suspension stiffness ratio of the two parts.

rgds, sreten.
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Old 27th June 2011, 04:00 AM   #9
18Hurts is offline 18Hurts  United States
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My sub PR is an Exodus Audio 18" beast with a total cone weight of around 1,220 grams, a very stiff beast of a radiator tuned to 21Hz. It goes below 20Hz, shakes the floor when the passive is in operation (kids like it) and anything below 20Hz is gravy.

I did find this statement though:

Better driver stability below fB due to increased damping on the driver below fB. This is because of specific compliance characteristics of the PR which help to keep the driver under better control at subsonic frequencies.

Audio Innovation - by Dan Marx www.danmarx.org

Have no idea how well PRs will translate to full ranges--it will keep the bugs/dirt out, I can easily tune it and it will help keep cone motion damped. I'm very aware of many speaker enthusiast's dislike of passive radiators--but the same thing applies to full ranges also. That is why I want to build one, to see if it works.

Maybe it would be a better idea to build a CHR-70 ($72 a pair) and team it with a pair of Peerless 5.25" PRs, ($15.60 a pair) one on either side of the cabinet? Tune it for around 50 Hz which would be fine with music, I have a subwoofer if I need more. The CHR-70 4 ohm load would be a better match for the 15W at 4 ohm T-Amp anyway (besides being much more desk friendly)
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Old 27th June 2011, 09:37 AM   #10
sreten is offline sreten  United Kingdom
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Hi,

I don't dislike PR's, they work well in small cabinets. The Peerless PR's
look well priced, and AFAICT will suit your CHR-70 plans very well.

rgds, sreten.
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