OB W-frame build

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aceinc

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Re: OB W-frame build
« Reply #60 on: 9 Apr 2017, 04:25 am »
Are you saying that all I need to do is reverse the sensing leads on the forward facing driver, which is "Speaker 1" in the drawing?


Danny Richie

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Re: OB W-frame build
« Reply #61 on: 9 Apr 2017, 04:30 am »
Are you saying that all I need to do is reverse the sensing leads on the forward facing driver, which is "Speaker 1" in the drawing?

No, on both drivers.

You have red to red on the top woofers driver coils and black to black. But on the sensing coils you have them flipped.

You need to wire red to red on the top woofers sensing coils too. Then wire black to the black of the lower woofer (it's flipped) and then red back to the black wire of the amp.

aceinc

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Re: OB W-frame build
« Reply #62 on: 9 Apr 2017, 07:15 pm »
Well I'm finished round one, the woofer cabinets.

Here are a few pictures. I am currently using the KEF 101/2s that are on top to test them. The speakers I am aiming to replace are in the background (B&W 802 Matrix), these are awesome sounding speakers in their own right.

Here is a couple of shots of one of the woofer cabinets, the cloth under the woofer cabinets is to protect from scratching until I get the feet built.





Here are the speakers as I am currently testing them, the towels are to keep the KEFs from sliding off, which one almost did playing some classical heavy on the Tymapnis.






Here is the test rig, an Emotiva UMC 1 for pre-amp, an Adcom GFA 555 II for power and a Yamaha DVD player.




Now I need to finish the upper cabinets. These will be a an open baffle of my own design (I use the term "design" loosely) using 2 - 8" mid-woofers and a B&G Neo 8 clone for each one.



aceinc

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Re: OB W-frame build
« Reply #63 on: 10 Apr 2017, 12:54 pm »
BTW, the second cabinet I had wired correctly. The first cabinet I had wired the woofer power incorrectly as the wiring diagram I provided shows. I rewired the woofers in the first cabinet to match the wiring diagram provided by Ed and everything was wonderful.

That is one nasty noise you get when wired incorrectly.

Lesson learned, triple check your wiring before turning anything on.

When I received the amplifiers, all of the documentation included referenced "Sealed Enclosure." How can I tell if an amplifier is properly tweaked for open baffle?

Danny Richie

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Re: OB W-frame build
« Reply #64 on: 10 Apr 2017, 01:05 pm »
Quote
When I received the amplifiers, all of the documentation included referenced "Sealed Enclosure." How can I tell if an amplifier is properly tweaked for open baffle?

The quick guide that goes out with each amp is the same for all amps. The shelving circuit is added to all amps going out that are used with the open baffle drivers.

Send me a picture of the back of the amp and I can confirm the circuit has been added.

Danny Richie

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Re: OB W-frame build
« Reply #65 on: 10 Apr 2017, 01:09 pm »
Now I need to finish the upper cabinets. These will be a an open baffle of my own design (I use the term "design" loosely) using 2 - 8" mid-woofers and a B&G Neo 8 clone for each one.

That will require a fairly complex crossover and baffle design to make that work. Let me know if you need assistance with it.

Keep in mind that the height of the Neo 8 (or clone) is too tall to use as a stand alone tweeter. So it will have very limited vertical off axis. The highs will fall right out if you get just above or below on axis.

rythmik

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Re: OB W-frame build
« Reply #66 on: 10 Apr 2017, 01:45 pm »
The feedback connection does matter. If the polarity is incorrect, the negative feedback will become positive feedback.

Put a 20 ohm/5W or 10W resistor in-line in the driver coil can reduce the oscillation noise in case of incorrect wiring.   

aceinc

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Re: OB W-frame build
« Reply #67 on: 10 Apr 2017, 02:31 pm »
Danny, it will take a bit of unscrewing to get one of the amplifiers off the cabinet.

I will try to get to it in the next day or so.

Another lesson learned;

Follow the instructions for pre-drilling the holes for the amplifier. I did not drill the holes deep enough and sheared the heads off 6 screws (I don't learn quickly). Also set the tension on your drill/screw gun to a low number (I finally set mine to 3) to protect against shearing heads off.

One thing I would like added to the "kit" for a dual driver system. Extra wire and 4 (2 each size) male spade connectors. I think about 2-3' of each gauge wire would be  great. For me it would have made things neater.

Danny Richie

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Re: OB W-frame build
« Reply #68 on: 10 Apr 2017, 02:42 pm »
One thing I would like added to the "kit" for a dual driver system. Extra wire and 4 (2 each size) male spade connectors. I think about 2-3' of each gauge wire would be  great. For me it would have made things neater.

When you place an order for this stuff by phone I ask if you'd like the four pole SpeakOn connectors with them. That's what we use for connecting them.

I take it that the placement of your amp at the back of the box was just for the picture? It needs to be away from the back of the woofer when playing.

aceinc

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Re: OB W-frame build
« Reply #69 on: 10 Apr 2017, 03:04 pm »
Danny, no I have the amp mounted just like you see it.

What artifacts should I look/listen for with the amplifiers mounted this way?

Are there any other problems I should know about?

Danny Richie

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Re: OB W-frame build
« Reply #70 on: 10 Apr 2017, 03:29 pm »
Danny, no I have the amp mounted just like you see it.

What artifacts should I look/listen for with the amplifiers mounted this way?

Are there any other problems I should know about?

You can't leave it there like that. You are blocking the rear output of the driver and changing the way the driver is loaded.

aceinc

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Re: OB W-frame build
« Reply #71 on: 10 Apr 2017, 04:10 pm »

Yes, I understand that restricting the air flow will change the loading of the driver. A couple of things;

I believe that even with the amplifier in its current position the open area that would allow air to escape is at least the surface area of the 12" driver. I will confirm that when I get home.

When playing the speakers as currently configured in my room, things sound pretty good.

I thought about moving the amplifier up so that it is centered vertically loading both drivers more or less equally.

For aesthetic reasons, I am not willing to have a separate amplifier box.

The difference between a mathematician and someone that is not;

The mathematician is put in a chair in a large empty room and a beautiful naked woman is placed on a bed at the other end of the room.
The psychologist explains, "You are to remain in your chair. Every five minutes, I will move your chair to a position halfway between its current location and the woman on the bed." The mathematician looks at the psychologist in disgust. "What? I'm not going to go through this. You know I'll never reach the bed!" And he gets up and storms out. The psychologist makes a note on his clipboard and ushers the engineer in.
He explains the situation, and the engineer's eyes light up and he starts drooling. The psychologist is a bit confused. "Don't you realize that you'll never reach her?"
The engineer smiles and replied, "Of course! But in less than half an hour, I'll be close enough for all practical purposes!"

Danny Richie

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Re: OB W-frame build
« Reply #72 on: 10 Apr 2017, 04:40 pm »
That's a funny analogy.

Seriously though, that is restricting way to much air. The lower woofer will act as if it is in a small vented box. So it will cause it to be loaded much differently than the other one and the sensing system needs for them to be the same so that it can make corrections that accurately effect both speakers.

Loaded this way, neither of them play the same.

And it will cause an uneven response.

Captainhemo

Re: OB W-frame build
« Reply #73 on: 10 Apr 2017, 04:46 pm »
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Davey

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Re: OB W-frame build
« Reply #74 on: 10 Apr 2017, 05:15 pm »
For aesthetic reasons, I am not willing to have a separate amplifier box.

All this trouble to build this excellent dipole woofer system, and aesthetics are ruling/ruining the day???

Since you already have a separate amplifier box, I suggest to disconnect it and lay it on its back behind the woofers.  It should not be visible that way and won't unduly effect the symmetrical operation of the woofer radiation.

This also has the benefit of not physically mounting the amplifier to the woofer enclosure.  Long term, that might have some positive effect on the longevity of the amplifier by reducing vibrations.
 
Dave.

Danny Richie

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Re: OB W-frame build
« Reply #75 on: 10 Apr 2017, 05:41 pm »
I agree with Dave today.

aceinc

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Re: OB W-frame build
« Reply #76 on: 10 Apr 2017, 05:48 pm »
OK, when I have completed my feet, which should be shortly, I will move the amplifier up to the middle of the cabinet, that should make the loading be the same on both drivers.

Based on my calculations the cabinet with no obstructions has an opening of 286 square inches. The piston area of both drivers is 152 square inches. The amplifier box covers about 130 square inches. 286 - 130 = 156 square inches of "covered space." Based on my limited understanding if the amplifier is moved to the middle it should cause little if any loading on the woofers.

Another little note about the my build. I built the cabinet based on the design on your site as accurately as my limited woodworking skills allows. I then wrapped that cabinet in a second cabinet that extends beyond  by 3/4" on the front & back. The amplifier braces are attached to the outside edge of the original cabinet with 3/4" (1x2) oak, so the box that the amplifier is in is actually 3/4" behind the rear opening of the original cabinet. The point I am making is that the calculations above are more conservative than the reality.

Irrespective of all of this, in its current configuration with the KEFs as mid/tweeters, I happily listened to all of my test recordings as well as some new fun stuff, and am pleased with the results.

The first thing I test with is a Sheffield Drum CD, then I play a cut off a Hybrid CD called "Alone Together" which is female vocal with acoustic bass to verify that the bass sound is well defined through various frequencies. Then I fire up 3 O'clock blues from the "Riding with the King" CD. For fun I played some CDs I picked up at a garage sale called "Classical Thunder I & II."

I will A/B them against the B&W 802s soon.


aceinc

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Re: OB W-frame build
« Reply #77 on: 10 Apr 2017, 06:06 pm »
Davey A few things;

I have a wife.

I do not consider myself an audiophile, but a person with an audio hobby, so aesthetics have a level of importance to me as well.

My hobby is full of trade offs, in this build for example I am using speaker level inputs for these cabinets and I am making feet that will not be attached to the cabinet so that if I decide to rotate the cabinet on its side, I can.

I will not be hammering these speakers often, so hopefully any cold solder joints will show themselves during my initial testing.

If I cannot keep the amplifiers mounted, then I made a costly mistake, because that is where they will stay, or I will sell them and recoup some of my loss.

Danny Richie

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Re: OB W-frame build
« Reply #78 on: 10 Apr 2017, 06:12 pm »
Quote
Based on my calculations the cabinet with no obstructions has an opening of 286 square inches. The piston area of both drivers is 152 square inches. The amplifier box covers about 130 square inches. 286 - 130 = 156 square inches of "covered space." Based on my limited understanding if the amplifier is moved to the middle it should cause little if any loading on the woofers.

Actually just extending the sides by an inch or so changes the loading on the drivers. Blocking that much of the back of the cabinet will change the loading on the drivers significantly.

aceinc

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Re: OB W-frame build
« Reply #79 on: 10 Apr 2017, 06:24 pm »
Danny, Were I closer I would bring them over so you could run tests on them. We could then see the impact that my foolishness has wrought.

Regarding the extra 3/4" in deciding the load it would present to the drivers, since it is also 3/4" out (from the center) I think it would act like a very short 45 degree horn. If that has an audible affect (on frequencies in the band pass), I would be very surprised.