12" PA woofer in vented 3.5 ft3 cabinet = good idea? - diyAudio
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Old 4th September 2011, 08:00 PM   #1
dbrose is offline dbrose  Belgium
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Default 12" PA woofer in vented 3.5 ft3 cabinet = good idea?

I'm looking for full-range PA speakers that produce well controlled bass down to 45Hz (F3). Max spl does not need to be very high, 120 db/W/m will do (I'll use them primarily in our 4000 ft3 cellar and for small parties). My 1000$ budget doesn't allow to use subwoofers. Commercial full-range PA speakers generally use a 12" woofer in a 1-2 ft3 cabinet or a 15" woofer in a vented 1.5-3 ft3 cabinet. This results in an F3 somewhere between 55-80 Hz. That's why I got the idea of using a decent 12" woofer (like an RCF LF12G301, fs 43 Hz, Qts 0.22, Vas 3.5 ft3 and Xmax 0.27") in a 3.5 ft3 cabinet together with a CD and big horn. This should result in a low enough F3 but I wonder whether such an over-sized cabinet (RCF recommends 0.8-2 ft3) will affect bass reproduction quality. My experience with building hifi speakers learned that "there's no substitute for cubic feet". Growing enclosures really enhances bass quality. But maybe things are different with PA speakers. Has anyone experience with this?
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Old 5th September 2011, 04:25 AM   #2
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I would recommend an Eminence 12lta in a 4cf or larger box with a compression tweeter to fill in the highs.

Eminence Beta 12LTA 12" Twin-Cone Woofer, 8 Ohm, 225 Watt at Performance Audio
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Old 5th September 2011, 04:33 AM   #3
freddi is offline freddi  United States
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for just woofer consideration, ~ 4cubic foot with a pro 15" , qts ~0.3and 6th order assisted reflex (typically tuned 1/2 octave below 4th order fb and with Q=2/6dB boost at 1.03*fb) can be a nice compromise. 12LTA may work decently in a Karlson K15 but those are 7.3 cubic foot external bulk. 12LTA have a voice coil overhand of~ 0.080" and could use a least another pound of motor.
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Old 5th September 2011, 05:15 AM   #4
freddi is offline freddi  United States
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a Karlson with 15" coax or woofer can pound quite well with very little excursion - no need to go to 0.25" xmax which robs midrange sensitivity. K15 is 33" high 22.5" wide, 18" deep. Cheap Eminence can suffice but their 15" coaxial are out of production. A Karlson slotted pipe waveguide on the top will work. You could load K15 with 12LTA. I'm not sure how well 12LTA's little voice coil would hold up with 120dB levels. It lacks magnet but is cheap and cheerful. Making reflex cabinets too large (for parameters) robs dynamics.

that RCF has decent specs - ask over at Audio Asylum's High Efficiency Speaker Forum and Wayne's Pi Speaker forum

Last edited by freddi; 5th September 2011 at 05:20 AM.
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Old 5th September 2011, 05:49 AM   #5
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Quote:
Originally Posted by dbrose View Post
My experience with building hifi speakers learned that "there's no substitute for cubic feet". Growing enclosures really enhances bass quality. But maybe things are different with PA speakers. Has anyone experience with this?
So you'll get experienced also in PA systems !!
I'm not ( nor in hi-fi )
I see that some factors such power handling and reliability over time are the things that differentiate pros from home hi-fi speakers . So , a tougther construction leads also to a more 'resistive' membrane motus ( high Qms ),always compensated by huge amplifications .
I guess that you could have fun if you built a well sized BR box and play with active equalization .
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Old 5th September 2011, 05:51 AM   #6
Up_3dB is offline Up_3dB  United States
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I recently built a pair of 2.2 cu. ft., sealed and heavily stuffed, Eminence Beta 12LTA cabinets out of 1/2" plywood. Finished, they weigh 27 pounds. They sound very uneven with a straight flat signal. But when I EQ'd the speakers for a flat response using a cheap Radio Shack 15-band graphic equalizer, and then run the same flat signal, they become the most clear, and big sounding direct radiators I've ever heard. The bass is immense and perfect (45 Hz is no problem). They also have sweet air even though they roll off above 8 KHz. My ears do not get fatigued listening to these. They go concert loud, and still every instrument and voice is clear and gorgeous.

My 12LTA cabs do double duty... on weekends I use them as vocal monitors or mains for my blues band, while during the week they amaze me listening to CDs in my workshop. I'm surprised they don't get much mention in cyberspace.

Last edited by Up_3dB; 5th September 2011 at 05:58 AM.
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Old 5th September 2011, 07:20 AM   #7
freddi is offline freddi  United States
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~2 cubic foot would be a usable back volume for 12LTA in a Karlson-coupler - there's not enough motor on 12LTA to work well in K12 - in that case an 80oz magnet coax had imo better dynamics. I have run bass guitar with 12LTA in K12 and the mids were nice and loud. A new coupler based on Karlson's X15 size would work for 12LTA as it worked with Beta 12Cx. I still can't imagine it having a huge punch but have only tried it with open baffle augmented by a 21" cheap woofer and in a 4.6 cubic foot tapered pipe which was tuned too low to punch. Neither had the slam I"m used to with the 15"-18" Karlson or even the flabby/murky Klipschorn.

here's a little X15 copy with ~2.2 cubic foot rear chamber loaded with Beta 12CX - it didn't go low but it played the big odaiko drums on taiko cds at a surprising peak and not exceed 3mm Beta 12cx xmax - it got so loud I thought the cone would snap.- actual overhang on 12LTA IIRC is 0.08 inch.

28" by 19.25" by 14.25" - a slotted tube waveguide with APT50 would be good to augment 12LTA. This tube
is a copy of a Karlson tube probably from around 1966
Click the image to open in full size.

Last edited by freddi; 5th September 2011 at 07:29 AM.
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Old 5th September 2011, 02:07 PM   #8
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I think we need a little better 'focus' from you. On one hand "Max spl does not need to be very high". On the other hand we have "120 db/W/m will do" and "Commercial full-range PA ... with a CD and big horn".

In any case, pro-grade drivers generally are fairly efficient, and made to take a lot of power and produce high spls. Hoffmans iron law comes into play here. You have to juggle efficiency, box size and bass extension. You can have any 2 of the 3, at the cost of the 3rd one. For example, if you want deep bass and high efficiency you will need a big box. As you suggested, big boxes allow deeper bass. But this is true only to a point: you still need to start with a driver that can take advantage of the big box.

If moderately high spls are desired a driver like the Eminence Delta 12LF would meet your needs. If you want to be able to converse without having to shout during a party in your 4000cf room (more modest spls), the Beta 12LTA could do nicely.

If you clarify just what your needs are we can be more helpful.

Bob
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Old 5th September 2011, 05:21 PM   #9
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When freddi joined this forum he should have picked the name "KarlsonCouplerEvangelist."

I'm fairly convinced when people talk about larger cabinets and larger drivers being better at producing a "live" sound. To paraphrase Troels Graven, "don't expect tiny speakers to throw a huge soundstage; they can't." Also: "Put a 15" woofer on an open baffle - or a really big box - and see what it does to a kick drum." These aren't his exact words, but the point is the same. There is NO way my 5" full range drivers are going to give me the sound and dynamics that a 12" or larger driver is capable of.

So yeah, if you've got the space, then go for it! Big drivers and big boxes FTW!

Up_3dB, you're doing the same thing that Zilla's always doing to me: making me forget temporarily that I live in a cramped apartment and thus consider making speakers that are WAY to big and ugly for me to get away with!
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Old 6th September 2011, 03:46 AM   #10
Up_3dB is offline Up_3dB  United States
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Some pictures of my cabs...

Click the image to open in full size.

and...

Click the image to open in full size.

.
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