Coming Soon: Dipole/Bipole Surrounds *PIC*

[hongrn]

Provided Link: soundhobby


Those guys below need to stop bickering. If you spend as much time as I do cutting wood and breathing fumes, you wouldn't have time for silly arguments.

Anyway, I'm using Hi-Vi MN4 midwoofers wired in parallel with Peerless 811582 tweeters for my surrounds. 8-liter sealed cabinets, crossed at 2,500Hz LR2, although not finalized at this time. I did want something that will go below 70Hz, so I can set the crossover on my THX receiver to 80. The surrounds will be mirror images of each other. A switch will reverse the polarity of the rear tweeter (idea plegiarized from dB - Dave Brown). The cabinet idea was plegiarized from John Krutke. By the way, I broke a few panels bending the MDF before I got this right. Soak those suckers really wet before you bend. Let's see what else I plegiarized from this forum....

Hong

[hulan]

I like it so far. I havn't had the courage to try any designs with bent MDF yet. Many drawings haven't come to fruition.
I look forward to seeing progress pics.

[nick29498141]

They look great! That MDF bend looks pretty nice and evenly angled, too. have you thought about a tweeter on the front of the "cab" in reverse polarity? or did I just read your post too quickly? lol

Nice!

NK

[donparsons]

Hong,

You are some kind of speaker geek. Whilsome of us read and plan, you just do it. Very nice stuff. Where exactly are you? I am up in Santa Barbara.

Don

[hongrn]

Hey Don,

I'm down in Orange County. Thanks. This stuff keeps my sanity going...

Hong

> Hong,

> You are some kind of speaker geek. Whilsome
> of us read and plan, you just do it. Very
> nice stuff. Where exactly are you? I am up
> in Santa Barbara.

> Don

[donparsons]

Some people even proof read their posts fer stoopid errors. I am going to be going to San Diego a couple of times in August and September. I would love to hear your stuff in person if we could arrange it.

Excellent work.

[Wolf]

A switch will reverse the polarity of
> the rear tweeter (idea plegiarized from dB -
> Dave Brown).

You should probably have the corresponding midwoofer change polarity also, so it sounds right. If I understand it, you have a angle-front 2-way, and an angle-back 2-way, right? The 'null' should be opposite one-side to the other, or reverse polarity. In-phase/Bipole is same polarity for all drivers. In a TMT surround speaker, you would only have to switch a tweeter.
Later,
Wolf

[chichi]

Very nice...

Is that plywood or MDF?

Have you discovered a certain depth at which the cut will splinter on the round over?

[hongrn]

Thanks Wolf. I still have to experiment to see how it sounds. That's why it's such a neat hobby.

Hong

[hongrn]

Be glad to have you. Jon Pike is in Irvine also. We'll drag him up for a jam session.

Hong

> Some people even proof read their posts fer
> stoopid errors. I am going to be going to
> San Diego a couple of times in August and
> September. I would love to hear your stuff
> in person if we could arrange it.

> Excellent work.

[hongrn]

I used 1/2 inch MDF and cut it 7/16" deep, spacing is 1/4" apart. Thanks.

Hong

> Very nice...

> Is that plywood or MDF?

> Have you discovered a certain depth at which
> the cut will splinter on the round over?

[dB]

> A switch will reverse the polarity of

> You should probably have the corresponding
> midwoofer change polarity also, so it sounds
> right. If I understand it, you have a
> angle-front 2-way, and an angle-back 2-way,
> right? The 'null' should be opposite
> one-side to the other, or reverse polarity.
> In-phase/Bipole is same polarity for all
> drivers. In a TMT surround speaker, you
> would only have to switch a tweeter.
> Later,
> Wolf

If he reverses woofer polarity, there'll be no low freq output. That's assuming the two drivers share the same enclosure volume. If the woofers were each in their own enclosure, he'd still get some broad cancellations across the listening area. Could be worth a try though -- there are alot of things going on with wall and ceiling reflections so it would be interesting to hear the results.

dave

[markwortham]

> Those guys below need to stop bickering. If
> you spend as much time as I do cutting wood
> and breathing fumes, you wouldn't have time
> for silly arguments.

> Anyway, I'm using Hi-Vi MN4 midwoofers wired
> in parallel with Peerless 811582 tweeters
> for my surrounds. 8-liter sealed cabinets,
> crossed at 2,500Hz LR2, although not
> finalized at this time. I did want something
> that will go below 70Hz, so I can set the
> crossover on my THX receiver to 80. The
> surrounds will be mirror images of each
> other. A switch will reverse the polarity of
> the rear tweeter (idea plegiarized from dB -
> Dave Brown). The cabinet idea was
> plegiarized from John Krutke. By the way, I
> broke a few panels bending the MDF before I
> got this right. Soak those suckers really
> wet before you bend. Let's see what else I
> plegiarized from this forum....

> Hong

Nice work Hong! I'm diggin' it. I've got to give those kerf cuts a try sometime...

[Dirk]

> If he reverses woofer polarity, there'll be
> no low freq output. That's assuming the two
> drivers share the same enclosure volume. If
> the woofers were each in their own
> enclosure, he'd still get some broad
> cancellations across the listening area.
> Could be worth a try though -- there are
> alot of things going on with wall and
> ceiling reflections so it would be
> interesting to hear the results.

> dave

One of these days I'm actually going to try implementing the all-pass lattice filter I've had on the shelf. I think it'd have some real merit. It really shouldn't be difficult to do, because it looks like it'll work with even just nominal impedance values (assuming both woofers are identical). The phase-flip frequency might move around, but not more than a 1/6 octave.

[Wolf]

> Thanks Wolf. I still have to experiment to
> see how it sounds. That's why it's such a
> neat hobby.

> Hong

Di-pole creates a NULL at the seating position, so both would switch out.
Bi-pole lets you hear a diffused surround channel for better ambience, and room fill. If it were me, I'd internally baffle/separate the 2-way sections if you haven't already.
Later,
Wolf

[Wolf]

> If he reverses woofer polarity, there'll be
> no low freq output. That's assuming the two
> drivers share the same enclosure volume. If
> the woofers were each in their own
> enclosure, he'd still get some broad
> cancellations across the listening area.

That's the point in the di-pole (reverse)configuration, to create a null at the listening position across the bandwidth. This is why most people don't prefer the di-pole arrangement, even though THX regulations state this is the better strategy.

> Could be worth a try though -- there are
> alot of things going on with wall and
> ceiling reflections so it would be
> interesting to hear the results.

They both add rear-ambience to a surround soundtrack, but your opinion is usually the kicker.
Later,
Wolf