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Old 11th July 2012, 03:33 PM   #1
DrDyna is offline DrDyna  United States
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Default Open Baffle vs Infinite Baffle.

Hey guys.

This is a fairly simple inquiry, for anyone who has some insight. I've been reading a lot about big open baffle speakers. In thinking about it (a dangerous endeavor) I've been wondering if most or all of the positive things about a big open baffle speaker would also hold true for a big infinite baffle array.

I've designed my media room with a cavity behind the front wall in the hopes of installing a couple of Ficar IB318s in it, however, what would the drawbacks be to designing the front main speakers in there as well?

Would that offer some of the same benefits of open baffle? I realize it won't be dipolar (unless I get really creative with the mounting), but aside from that, is this a terrible idea? In my head, it looks awesome, but before I get too far into putting it on paper or simming some crossover changes, has anyone done this to satisfactory or even awesome results?
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Old 11th July 2012, 04:06 PM   #2
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A cavity at the back will trap the sound coming from the rear and is in effect sort of an infinite baffle WITH the addition of some rear radiated sound that might need to be absorbed as it will be transmitted through the cone again. In an ideal infinite baffle the sound from the rear doesn't return.
In an open baffle the rear sound does interact with the sound from the front and will measure and sound different from an infinite baffle. The radiation pattern will also be different.

That said , it probably is a nice idea to have a rear cavity . It will mean less or no equalisation than a dipole at low frequencies. That gives you more headroom in the bass. Mids and HF have ripples in an open baffle . Here you will have just the regular speaker response and hence easier to work with.
Don't see why you are worrying about it.

It probably will not sound like an open baffle but it should sound good with good drivers!
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Old 11th July 2012, 04:13 PM   #3
badman is offline badman  United States
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There is a little overlap. IB, due to low box pressure and long distances, seems to allow for low box coloration similar to dipole. IB also limits dispersion to a hemispherical wavefront- meaning that you don't have the baffle step compensation dilemna. With baffle step compensation, you are increasing the on-axis sensitivity but also the overall radiated power, in the bass, meaning the power response gets tilted towards bass.

With an infinite baffle you don't need the compensation, which saves some sensitivity (3-6dB) and avoids the discontinuity between power response and axial response.

Related to that, the concern of baffle diffraction is effectively solved.

There's a LOT to be said for IB.
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Old 11th July 2012, 04:14 PM   #4
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by ashok View Post
A cavity at the back will trap the sound coming from the rear and is in effect sort of an infinite baffle WITH the addition of some rear radiated sound that might need to be absorbed as it will be transmitted through the cone again. In an ideal infinite baffle the sound from the rear doesn't return.
In an open baffle the rear sound does interact with the sound from the front and will measure and sound different from an infinite baffle. The radiation pattern will also be different.

That said , it probably is a nice idea to have a rear cavity . It will mean less or no equalisation than a dipole at low frequencies. That gives you more headroom in the bass. Mids and HF have ripples in an open baffle . Here you will have just the regular speaker response and hence easier to work with.
Don't see why you are worrying about it.

It probably will not sound like an open baffle but it should sound good with good drivers!
I've been considering Dayton RS-180s and B&G Neo3s, I guess somewhat like the Cryolite, but modified slightly for having a 10 foot baffle. I think I'm going to go floor to ceiling with a strip of wood that I'll flush to the wall.

The pic is how my cavity looks for now. I'm planning on eggcrate foaming it before any drivers go in.

Thanks for the input! I'm always a little apprehensive before I try something new and I like to make sure nobody says "OMG, I did that once and it was terrible!"
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File Type: jpg cavity.jpg (173.3 KB, 400 views)
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Old 11th July 2012, 04:18 PM   #5
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Quote:
Originally Posted by badman View Post
There is a little overlap. IB, due to low box pressure and long distances, seems to allow for low box coloration similar to dipole. IB also limits dispersion to a hemispherical wavefront- meaning that you don't have the baffle step compensation dilemna. With baffle step compensation, you are increasing the on-axis sensitivity but also the overall radiated power, in the bass, meaning the power response gets tilted towards bass.

With an infinite baffle you don't need the compensation, which saves some sensitivity (3-6dB) and avoids the discontinuity between power response and axial response.

Related to that, the concern of baffle diffraction is effectively solved.

There's a LOT to be said for IB.
Perfect. Looks like I need to make a trip up to Lowes again today

Realistically, the only crossover changes necessary might be relaxing or eliminating BSC as a starting point?
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Old 11th July 2012, 04:22 PM   #6
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Cavity ? Wow that's a cavern ! I think some acoustic fiber sheets directly behind your driver would be sufficient.
Floor to ceiling panels ? Large panels vibrate unless they are pretty dense and/or thick. That adds to colouration. You might have to stiffen them if they are not very thick. I'm not an expert on US style plaster boards and walls.
So someone from there should comment on that.

Badman said that you will NOT have BSC with an IB . So you don't have to deal with it. Makes life easier !
I haven't looked up your driver specs. The bass driver better have a reasonably high Q ( like about 0.6 to 0.8 ). Otherwise you might have to use some bass boost ( a little bit ) . Hopefully it also has a low fs. Below 40 Hz for sure ! 30 Hz or lower would be fine.
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Last edited by ashok; 11th July 2012 at 04:27 PM.
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Old 11th July 2012, 04:29 PM   #7
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by ashok View Post
Cavity ? Wow that's a cavern ! I think some acoustic fiber sheets directly behind your driver would be sufficient.
Floor to ceiling panels ? Large panels vibrate unless they are pretty dense and/or thick. That adds to colouration. You might have to stiffen them if they are not very thick. I'm not an expert on US style plaster boards and walls.
So someone from there should comment on that.
Well, what I'm planning is a 2 foot wide panel that goes floor to ceiling, which I will run 5/8ths threaded rod through, and then on the rear of the wall, 2x4 that are placed horizontal and the bolts tightened to them, so the wall studs are sandwiched.

Kinda like this: (pic)

Edit: On the driver Q, I'll be using them as main speakers with 4 subs, so I only ask them to go down to about 70 hz or so.
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File Type: png studs.png (15.9 KB, 389 views)
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Old 11th July 2012, 04:37 PM   #8
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I think this should work out quite nice ! Make sure the drivers are at the right height from the floor. Typically tweeter at ear level when seated. Guess you are using multiple subs. Helps to even out the bass response in the room. Cross over as low as you can to the sub. Below 100Hz for sure. Your driver has a Qts of 0.45 and Fs of 44 Hz. You can design a 2nd order crossover to match this and get an overall Linkwitz Riley 4th order response . Then crossover to the sub at that frequency using a LR 4th order LP filter for the sub. All active crossovers of course !
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Last edited by ashok; 11th July 2012 at 04:43 PM.
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Old 11th July 2012, 04:55 PM   #9
DrDyna is offline DrDyna  United States
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My crossover to the subs is electronic cause it's part of my HTR, but the mains have a passive crossover.

My mains right now are ZX Spectrums. I might test this with them just for fun (I've built them with removable baffles), but in the long run, I do plan to buy new drivers.

I'm gonna go cut some baffles real quick and throw em in there and see what it sounds like O_o
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Old 11th July 2012, 05:38 PM   #10
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cool project! Ive often dreamt of doing this, (i havdm a small apartment) there are some Mivoc kits available for in wall IB, though i have no idea of their sound. In my situation i have drywall and around 4 inches of batten depth, and i have thought of cutting in, then mounting the baffle on the surface anchored into the batten. Once i suss how to toe them in i may try it.
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