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my new OBs!

rogerfederer

rogerfederer

determined amateur
Subscriber
just picked these up yesterday and so far i love them. here is the thread where i asked for your advice:

http://www.audiokarma.org/forums/showthread.php?t=501663

thanks again for all the great ideas! per suggestions from MJ King and others i went with a 2-way design. I’m using a rane active crossover (bought on BT from dc270). My excellent builder helped set up the crossover points but I will probably play around with them. The eminence alpha 15s come from tomlinmgt and the betsy 8" full rangers come from opa1.

Here are some pics: http://albums.phanfare.com/isolated/Jm0OUCMO/1/6040798

My builder is a local audiophile, speaker builder, turntable whisperer, artist and professor – Fred Markham. Fred is registered on AK, though I’m not sure what his handle is.

These were Fred’s 1st OB speakers so he built a mock-up to test the sonics. We ended up closely copying the project 9 from Martin’s quarterwave site: http://www.quarter-wave.com/Project09/Project09.html

will cycle in several SE amps for the top end. Right now using a RCA single-ended pentode el-84 based amp. Couple of watts; needs a lot of gain. Very detailed sound. Using an old technics integrated amp for the bottom. Matches the tuner I’m using so why not!

i have some visaton b200s that fred is mounting on panels so i will try them soon.

Onward!
 
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Looks good.

Have you tried moving them a little farther from the front wall?

How would you compare the sound to the Klipsch?
 
Trying that now. Giving me more volume and soundstage.

I really like the fortes but prefer the open sound and big soundstage of the OBs. Cleaner sound. My builder did some fancy wiring and the active crossover has to be better then the stock klipsch crossover with original caps.
 
Hey. Hey, Rogerfederer. Fred here! Glad you like the build. If you have six to eight feet between them, they'll completely disappear and light up the room. The Eminence drivers should have very healthy bass, but tight. The crossover is around 120Hz, so they are only handling the really deep stuff. Most of what you hear is the Betsy, which is nice sounding driver. They shouldn't get boomy, but if so, play around with the distance from your wall a bit.

I'm also attaching a shot of the initial build. The dimensions and baffle placement were based off a Fibonacci sequence, but it had terrible peaks between 300-700Hz. I went back to the drawing board and put some measurements into "The Edge", a baffle diffraction simulator. I came out with a slightly taller baffle very similar to King's. Drivers moved a bit with the 15" coming up about two inches and the 8" driver coming up 4"-6", I believe. This smoothed the peaks a lot and the crossover did the rest.

In case any of you all are curious. The box at the back of the final build hides a concrete block wrapped in felt. The first build had "skis" which were very stable, but I wanted them to look a little cleaner from the front and needed about 20lbs back there to balance weight of the baffle. In addition, I felt the Eminence driver might have a tendency to vibrate the entire build and the extra weight should help stabilize it. I hated the bulk of it, but told R. he can always take the block out and put an amp in there to power that woofer! In retrospect, it doesn't look bad, plus it's nice plugging in binding posts from the top like that.

I've been playing with the mock-up today and am going to try to get them up and running with some old console 15"ers and a Fostex FE83En. I made a stop to a sporting goods store an picked up two 10lbs weights on sale so constructed a slightly different base. It's not as stable as the block, but has a lower profile. Been a bit busy with work, but will post some photos as I make progress.

Fred
 

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Fmlistener is a great handle!

Ok, moved them farther apart. I also have them arrayed so the full rangers are closer to the outside of the baffle, instead of closer to the inside. Gives them more separation...

Fun playing around with them
 
Curious what you think of those phase plugs. Kevin said he didn't use them that much. I found they would rub unless you have them placed just so...

Listening to moon safari right now and it sounds great
 
Great job and welcome to the wonderful world of OB. :thmbsp:

I really like your removalable panel which allows easy use of other drivers. From all I've read the B200, which seems to have the greater upside, may need more taming than the Betsy's. Anxious to read about your impressions with the B200/Alpha combo.

I have the Betsy's over Alphas on a more narrow flat baffle but run the Betsy's wide open off a Miniwatt SET amp. The Alphas I drive with either two Dayton APA150's using their crossovers or a Denon AVR with a low pass filter on the Alphas.

I use a Behringer electronic crossover on my 3 way OB's but when my Ashly arrives from PE I'll try the Behringer with the Betsy/Alphas. It's hard to beat the ability to tune the crossover on the fly.

I have all my OB's on furniture glides which makes it easier to pull them out into the room where they sound best.
 
This weekend I tried the Ashly with the Betsy/Alphas and found the sound to be very good but different. Before I ran the Betsys wide open and straight off the Miniwatt and the Alphas crossed over with their Dayton sub amps. On first listen the Ashly gives far greater integration/blend and better balance but a bit of the full range/SET magic may be lost. I'll have to keep listening and fiddling with the Ashly before I reach a final opinion.
 
I have never been a fan of having a crossover only on the bass driver of a two way OB speaker system. Having only one side of a crossover allows the two drivers to overlap and you end up with a combined SPL producing a "blooming" response centered around 100-150 Hz. At first it sounds great because the mid bass is strong and warm, but after a while it starts to sound confusing and artificial.

I have done this on a couple of my systems at the urging of fellow OB builders in private e-mails, my active crossover allows me to program this configuration easily. I can switch between a single sided crossover and my usual double sided crossover on the fly. It quickly becomes very clear that the double sided crossover sounds more integrated and natural, the drivers work better together.
 
Must have been Godzilla that emailed you. He uses the crossover only on the bass drivers with the Boomer kit he sells.
 
Not Godzilla. There are quite a few people who use the one sided crossover trick, it seems nice and simple not to have to worry about the details of a complete crossover design. Crossovers can be the toughest part of the design to get right and the cause of many poor performing systems. I have been questioned by a couple of different builders and finally tried it to satisfy my own curiousity.
 
Wouldn't the one sided crossover trick be the same as integrating a sub with a pair of full range single driver speakers?
 
Poultrygeist said:
Wouldn't the one sided crossover trick be the same as integrating a sub with a pair of full range single driver speakers?
Click to expand...

That's what I was thinking, Paul. So I guess with your Alpha H-frame based three-ways I built the Alphas are getting whatever slope is built into the crossover of the Dayton plate amps I'm using and the Eminence Betas being run full range are naturally rolling off on the bottom end with no matching slope to the Alphas. So, not good you say, Martin?

- Michael
 
In my limited, OK very limited, experience If the upper driver rolls off at about the crossover point to the sub a single ended is good. If it isn't rolling off, the overlap that Martin talks about can be an issue.
 
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