OB5 Center ideas

Anthony · « **on:** 28 Nov 2006, 02:59 pm »

Hey all,
after reading the reviews and seeing Rocket Ronny's OB5 build, I am sold. I have been wanting to replace my Magnepan home theater. Don't get me wrong, I like the Maggies a lot, but the expensive center channel that does not voice exactly like the mains (and the ultra expensive center they are offering next year) have led me to look elsewhere.

Right now I run a 4.1 system with a phantom center and it works well for the back row and sweet spot, but off axis in the front row, you can get sound anchored to the speakers. So I need a center, but for the price of the Maggie center, I can build a pair of OB5 mains and possibly a center.

So I'm sold, I have a lot of woodworking experience (built my own sub, some Adire HE 10.1's, bar, cabinets, equipment racks). I'd say my worst skill is finishing, but I'm even improving there.

So hopefully early next year I can start building these. My first question is center channel design.

What I'm imagining is an inverted |__| shape, with the bass modules on the side, doubling as a stand and the open baffle portion horizontally between them with the tweeter rotated so that it remains vertical. If the sides are sized properly, the frequency response should still remain the same, but I'm worried about the directionality.

With the tweeter vertical, it will beam vertically (fine for a center) and be wide horizontally (great for a center), but being flanked by the other drivers should cause some beaming horizontally, which may anchor the image too much. The mains (regular OB5's) are already in a D'appolito array, which limits the vertical beaming and keeps the wide horizontal. But when turning it sideways (even with the tweeter rotated) it may still narrow the off axis response considerably.

An alternative may be to curve the open baffle a bit to compensate, something I wouldn't mind tackling in the wood shop. But I'm not sure if that would work.

Right now I can't seen any arrangement keeping the baffle vertical (which would be ideal) due to projection screen height issues.

Any thoughts on this? Thanks,
AC

Brucemck · « **Reply #1 on:** 28 Nov 2006, 03:14 pm »

I'm similarly intrigued by how to construct a good center to match an OB5 or OB7

Would an O-3 be a good matching center? What would be benefits of "turning an OB5/7 on it's side" as described in post above vs. just going with an O-3?

Anthony · « **Reply #2 on:** 28 Nov 2006, 03:32 pm »

Well the only real reason to turn it on its side is to go atop or underneath a screen, flat panel, or RPTV. Ideally, if you had the space, you would put three of the same speakers across the front with no geometry change.

But failing the slight form change, using a speaker will all exactly the same drivers, crossed over at the same points should yield the best timbre matching across the front sound stage.

What I'm worried about here is that the sound would beam and be so anchored to the center that a panning noise (say car driving from off screen left to off screen right) would appear to jump to the middle of the screen instead of gradually transitioning from Left to Center then to Right.

I know Magnepan fixed this with a curved design. Many other centers fix this with the D'appolito array for the tweeter and small low-treble drivers (see pics of Atlantic Technology HT speakers). It's the toughest part of center channel design: wide horizontal, narrow vertical across all frequency ranges. Open baffles do this by default -- but I'm not sure what happens when the speaker is sideways.

Rocket_Ronny · « **Reply #3 on:** 28 Nov 2006, 03:33 pm »

Why build a center channel. It's pointless to me.

I could see it if you needed distributed sound, like in large theater, but not in a home setting.

4 channel is plenty-0.

We don't have a home theater set up. Heck, we don't even have a t.v. But I do watch videos off of my 17" laptop on occasion, and run it through the OB 5 mains. 2 speakers, no center channel. There is no need for the center channel. It will just mess up the nice stereo image I would think.

Glad you liked the OBs. They truly are nice.

Rocket_Ronny

Brucemck · « **Reply #4 on:** 28 Nov 2006, 03:46 pm »

I'd like to have a "closely matching" center for three reasons ...

(1) I've had great two channel and great multichannel. In my experience, and here's the biggest caveat "properly implemented", two channel Redbook CDs through Meridian's "Trifield" mode sounds markedly better than great two channel. I've tested that to my satisfaction with big Genesis ribbons, with home brewed Accuton two ways, and with Salk HT2s; with VTL tubes and with solid state; with dCS and AR Ref front ends and with Meridian front ends. I have/had a "custom designed room", with great dimensions, extensive room RPG treatment, etc. The center provides an "anchoring" to the center image that's just not there with even great two channel, and the subtle side and rear ambience channels (via Danny's great surrounds) really adds an "envelopment" that straight two channel lacks.

(2) Being selfish and a perfectionist, I don't care all that much about the sound for those folks not sitting in the sweet spot, but, a center channel does improve the "wow factor" for those sitting to my immediate left and right.

(3) A lot of my listening is to multichannel mixes: movie soundtracks, high def music feeds, etc. Those sources "downmixed" to a two channel front end just never sound right.

Danny Richie · « **Reply #5 on:** 28 Nov 2006, 04:26 pm »

I see the need for the center as well. If watching a movie or TV, the center will anchor the sound to the center regardless of seating position.

There are several ways to go and match the sound of the OB-5's.

First off you can rotate an OB-5 onto its side and move the woofers to a configuration that puts one on each end. You then rotate the tweeter 90 degrees as well. You can do this with no crossover changes too. Since the lower woofers are only covering from 200Hz and down, moving them has little effect.

Since the tweeter is only 2.125" tall it does not have a very limited vertical dispersion so beaming in the vertical range is not an issue. It has great vertical dispersion.

Laying the OB-5 on its side will limit the horizontal coverage area due to the center to center spacing distances of the mid-woofers. If you sit within 20 degrees off axis each way then you are home free. If you sit further off axis than that you will begin to notice a slight dip in the 900 to 1000Hz range.

As suggested you could use a single O-3 as a center channel. This speaker has great off axis response in the vertical and horizontal plane and sounds much bigger than its size suggests. Its height can easily be adjusted to fit under a front projector screen or plasma. This speaker also easily matches the sound of the OB-7 and OB-5.

Anthony · « **Reply #6 on:** 28 Nov 2006, 06:18 pm »

Well, after some measurements, I think I can keep the baffle part completely upright for the center channel. However, to fit underneath the screen, the two lower drivers would have to move to accomodate. One option is to have them be very close to the floor (if all the drivers were kept in a straight line), then the cabinet would be wider to accomodate the volume and ports. Another is to let the bass drivers go to each side of the "stand", which would still have to be wider.

As long as the volume stays constant in the mid-bass section, it sounds like slight design tweaks like this shouldn't affect the sound much.

I think it's important to keep the MTM alingment intact for the open baffle to limit vertical dispersion. One of the worst parts of a poorly designed center speaker is the muddy voice regions caused by comb filter effects of floor and ceiling reflections. Granted, these can be fixed by room treatments, but I would still prefer to keep the vertical dispersion in check. The nice wide horizontal dispersion is necessary for any center speaker, since the screen is usually wider than the speaker.

I'll draw up some sketches of my ideas an you can let me know if you see any phasing, reflections, or constricted baffle problems from the design.

Thanks for all the feedback.

Danny Richie · « **Reply #7 on:** 28 Nov 2006, 07:22 pm »

Quote

As long as the volume stays constant in the mid-bass section, it sounds like slight design tweaks like this shouldn't affect the sound much.

As long as the lower woofer volume is maintained, you can do a lot of manipulating on the shape. What you are proposing will work fine.

Anthony · « **Reply #8 on:** 28 Nov 2006, 08:20 pm »

Thanks. For reference, this is what I had in mind. Ports would be on the back side after going through some baffling.

Now I just need to get all the little projects cleared from the shop, pay off the Christmas bills

, and I'll be ready to go!

Thanks again for all the feedback.

AC

klh · « **Reply #9 on:** 1 Dec 2006, 06:02 am »

I like that

. Three of them under a 120" wide 2.35:1 CIH screen would kick ass!!!

mnapuran · « **Reply #10 on:** 6 Dec 2006, 02:52 pm »

So is an OB5 Center design coming then? If not, what is recommended?

Danny Richie · « **Reply #11 on:** 6 Dec 2006, 05:12 pm »

There are a couple of options already. The short version that Anthony is working on will work fine as will the O-3 (the O-3 will actually work great). When I get time I will draw out the OB-5 on its side for those that want a side laying open baffle design.

mnapuran · « **Reply #12 on:** 7 Dec 2006, 02:59 am »

How would the AV-1RS work as a surround with the OB5?

Danny Richie · « **Reply #13 on:** 7 Dec 2006, 03:04 am »

Quote

How would the AV-1RS work as a surround with the OB5?

It will work fine together. It uses the same woofers and has a very similar sound.

tjt123 · « **Reply #14 on:** 11 Dec 2006, 02:20 am »

Danny,

At one point you said you had plans to create an AV1-RS speaker with the Neo 3 pdr to match with the OB-5 and OB-7 speakers. Are you still planning on doing that?

Danny Richie · « **Reply #15 on:** 11 Dec 2006, 02:32 pm »

Quote

At one point you said you had plans to create an AV1-RS speaker with the Neo 3 pdr to match with the OB-5 and OB-7 speakers. Are you still planning on doing that?

If I get enough interest for it I will.

tjt123 · « **Reply #16 on:** 12 Dec 2006, 12:47 am »

Well, I'll take 2 pair.

Anyone else?

phoenix_rising · « **Reply #17 on:** 12 Dec 2006, 02:46 am »

Quote from: Danny on 11 Dec 2006, 02:32 pm

Quote
At one point you said you had plans to create an AV1-RS speaker with the Neo 3 pdr to match with the OB-5 and OB-7 speakers. Are you still planning on doing that?

If I get enough interest for it I will.

I looked at these too but thought that they did not play low enough for a decent cross over point. Maybe with one of the new XBL woofers and the NEO would be more appropriate to match it with the OB5, or two woofers and make the cabinet larger so it can play lower, I think the design is an excellent one making it look like a sconce. Alternately I would love to see a larger speaker (O3 type) designed to be positioned close to a wall for rear surrounds. I think that this would have wider appeal due to WAF being low for speakers 2-3 feet oiut from the wall. Most surrounds are space constrained by the room, furniture etc so it is a big issue, most people I have seen park their rears fairly close to the wall when they are not designed for it and get badly compromised sound as a result. Just my 2c worth.

mnapuran · « **Reply #18 on:** 30 Dec 2007, 03:28 am »

Any follow up on the center channel design?

mcallister · « **Reply #19 on:** 30 Dec 2007, 01:25 pm »

as a newbie first off I know this is probably posted in the wrong thread and second I'm not sure if this has been asked to death so if it has my apologies, the question is is there plans in the works for an LS center?