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Old 25th May 2010, 01:18 AM   #1
Rudy216 is offline Rudy216  Canada
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Default 18" Cerwin Vega info?

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Anyone familiar with this old 18" Cerwin Vega speaker? Model number 188C 4 ohms

I have a couple in folded horn cabinets (and an extra driver) that were used for PA use. I would like to put these in cabinets as subwoffers. I was thinking bass reflex cabinets. I haven't done any measurements on these yet so I don't know if I'm woofing up the wrong tree.

Any information or opinions would be welcome.
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Old 25th May 2010, 04:11 AM   #2
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Cerwin Vegas with the accordion surround are quasi PA drivers. I don't think you'll find them very successful as subs.
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Old 25th May 2010, 06:01 AM   #3
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Put it on a U or H frame OB, then add a 6dB/ctave low pass filter starting at the lowest frequency you'll want out of them (30Hz is a good start).

Play around with the crossover control on Foobar.
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Old 25th May 2010, 07:41 AM   #4
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I think the T/S parameters will be more suited for a horn than a reflex box.

A tapped horn might be the best application for these, take some measurements.
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Old 25th May 2010, 02:42 PM   #5
Rudy216 is offline Rudy216  Canada
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Yeah I kind of had my doubts that they would work well in a "reasonable" sized ported box.

Quote:
Originally Posted by chris661 View Post
Put it on a U or H frame OB, then add a 6dB/ctave low pass filter starting at the lowest frequency you'll want out of them (30Hz is a good start).
Sorry I'm new here and haven't picked up much terminoligy yet. "U or H frame OB"?

I would be happy with 40Hz. While I often need my Rock fix I tend to listen mainly to Classical music now. Keeps the blood pressure down.

I've been doing a little reading and the tapped horn seems interesting. But I've got a lot of reading to do yet before I understand what's going on. Things are a bit different then when I was interested in DIY audio 30+ years ago. I haven't been on this site much but I'm surprised and thrilled by what I have found.

Since this is my first (now second) post I'll add that I have an electronics background. I work for a small electronic controls manufacture designing new products. I have done very little with amplifiers mainly digital and power controls. Some of the posts here on amplifiers blows me away.
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Old 25th May 2010, 03:37 PM   #6
Pano is offline Pano  United States
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OB= Open Baffle. U and H mean a baffle with side wings. U has wings in the back only, H in front and back.

As chris says, try the low pass trick on open baffle. It really works. Even with low Qts drivers. A sub plate amp can be your friend, here.

See this thread for some ideas:
Big OB fun. Come hear!
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Old 25th May 2010, 05:29 PM   #7
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I used Foobar's crossover add-on to create a 6dB/octave low-pass, then used my amplifier's 12dB/oct variable crossover (set the roll-off to 15Hz now - scary on movies).

I use an Eminence Beta 12A. It goes lower on it's little U-frame than my pair of 8" drivers with equilisation.

The different terminology.
OB - open baffle - just a driver mounted on a flat piece of wood.
U-frame - in a plan view, picture the speaker on the horizontal of the U, with the verticals as "wings". This lowers the roll-off frequency
H-frame - similar to U-frame. The speaker on the horizontal stick, then sides that extend forward as well as backward.

Here's a page on different speaker types...
LDSG Appendix A - Enclosures

Chris
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Old 25th May 2010, 09:14 PM   #8
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Now I have a little more time, here's some advantages and disadvantages of these designs...

Advantages
- Allows the use of a physically small cabinet
- doesn't require the same amount of eq as a sealed box
- you can choose the lower cut-off easily
- below your specified cut-off, the bass output will roll-off by 6dB per octave (a half or double of frequency) lower you go. For example, you choose the cutoff to be 40Hz. At 20Hz, it will be 6dB quieter. Your -10dB point (some consider this important) will be somewhere near 13Hz, which is very very low. I chose the cut-off at 20Hz, so I'm -6dB at 10Hz, and -12dB at 5Hz. Very few standard (sealed, ported) subwoofers can match that.

Disadvantages
- they need careful positioning
- getting low bass at decent SPLs will require a lot of displacement (with an 18" driver, you'll be fine).
- bass is pretty localised - you will get a dipole-shaped output. If you need to fill every inch of the room with bass, this isn't the way to do it.
- the lower you choose to make it, the less efficiency you get. For example, a speaker with efficiency of 95dB/w, and began rolling off at 400Hz, would be 89dB efficient at 200Hz, 83dB at 100Hz, 77dB at 50Hz, 71dB at 25Hz.
Because of this, in order to make the roll-off frequency lower, a larger baffle is needed. Also, you'll need something of decent power to drive it properly (a tube amp will struggle).

In my opinion, the advantages outweigh the disadvantages, but then again, I listen from one position, and have over 100w RMS to power a subwoofer, which is enough for a bedroom system.

Chris
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Old 26th May 2010, 12:43 AM   #9
Rudy216 is offline Rudy216  Canada
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Thanks for the posts guys. Before I would never have even considered an open back design. Still not sure if I'll go that way but it sure sounds interesting. The main concern is the positioning issue. I have two main seating positions. One might be a problem.
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Old 26th May 2010, 06:20 AM   #10
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Hmmmm....

I suppose you could do what I did.
I played with positioning until it sounded right, then remembered roughly where it was.
Then I push it back to it's corner at the end of each listening session.
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