Basic question on OB

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oon_the_kid

oon_the_kid

Member
Joined 2008
Hi,

I am planning an open baffle with the SEAS FR22 full range with a extra woofer.

There are a few things I would like to know?

1) Is there a minimum distance from driver back to wall? Is there a recommended this?

2) For an open baffle, if I have additional fold/wing to the baffle at the sides that is perpendicular to the front baffle, to make it look somewhat like a 3 sided box, does the bass response go lower, as if it is wider baffle?

Thanks ahead,

Oon
 
oon_the_kid

oon_the_kid

Member
Joined 2008
gooki said:
1, yes, 1 to 2 meters.
2, yes, wings create larger baffle.

What you a building sounds like a u-frame open baffle. Google it to see its effects.
Click to expand...

Hey,

Now I know what it is called. U frame.

Is there a reason why there needs to 1~2m from the wall. Still trying to understand the physics of the problem. What are the consequences of it being too near the wall? My primary concern is mostly the mids, will be using something else for the bass....

Many thanks.

Oon
 
badman

badman

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Joined 2003
pothaudio.com
454Casull said:
OB bass costs more (sometimes much, much more) for the same SPL and distortion.
Click to expand...

Oh, I dunno. The price of one nice Seas 8" that would be sufficient in a box, in some people's rooms, more than pays for a couple of Alpha 15A.


Regarding distance to the wall- you need the time delay for the summation peaks and dips of the reflection off the back wall to be smoothed, and delayed so as to have precedence on the forward radiation. If you wanted to be closer you'd have to start damping the back wall.
 
oon_the_kid

oon_the_kid

Member
Joined 2008
a_tewinkel said:
Please note that with wings, you create a resonating pipe with one closed end. In theory the resonance would be 1/4 lambda, although in practice it is lower with relatively shallow U-frames. See Frontiers . Also, front-back symmetry will be slightly diminished at higher frequencies.
Click to expand...

That would explain why most of those baffles are tapered with the shape of the wings a triangle. That would distribute the resonant frequency over a range of frequency instead of one, and would reduce the height of the resonant hump.

So if I were to build 12" wide U baffle with sides that are tapered to the top with a base of about 12", The bass should be more than a 12" wide normal baffle only right? And since it is tapered at the top, it will not have a peak resonant frequency. Is this correct?

Oon
 
Rudolf

Rudolf

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Joined 2003
dipolplus.de
oon_the_kid said:
So if I were to build 12" wide U baffle with sides that are tapered to the top with a base of about 12", The bass should be more than a 12" wide normal baffle only right?
Click to expand...
Yes.
And since it is tapered at the top, it will not have a peak resonant frequency. Is this correct?
Click to expand...
The peak will be distributed over a wider hump, based roughly on an averaged U depth of 6".

A nice introduction
 
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Godzilla

Godzilla

Member
Joined 2005
speakerprojects.wordpress.com
>>> Yes, but not a Beta-8, which would be the appropriate analogue, I think.

The Beta 8 can't match the Alpha 15 for reproducing rich, full bass tones. I've not encountered an 8, 10 or 12" powered subwoofer that's as satisfying as the H-frames in my den using relatively inexpensive Alpha 15s. If space is an issue a hi end driver like Seas, Scan Speak, etc. does a great job but if space is not an issue the Alpha's in H-frames rock... My son's 15" buyout Jamo's also do a wonderful job in a simple OB which cost $20 each. I'm sure there are more expensive drivers that can be used successfully but I'm content at the moment.
 
oon_the_kid

oon_the_kid

Member
Joined 2008
Hi godzilla,

I was planning to supplement the seas fullrange with another 4 pcs 8" woofer, possibly a jamo from PE buyout. Might go with a line array or a slot loaded open baffle. Presently they are about 8 bucks each.

That should give me the same area as the beta 15. Will probably boost the speakers electronically and biamp. I am trying to push the bass from SEAS driver lower so I can cross the speakers lower.

Oon

Sent from my Milestone using Tapatalk
 
R

rvsixer

Member
Joined 2008
454Casull said:
OB bass costs more (sometimes much, much more) for the same SPL and distortion.
Click to expand...
In the average/smaller living area, and staying within safe SPL limits, I have experienced the opposite (albeit I prefer lean clean bass, not overemphasized thump thump thump).

For example my setup is Peerless 12" SLS times two on flat baffles ($160USD the pair when I bought them), miniDSP for crossover/OB rolloff EQ ($135), and an old receiver for amp worth about $50. That's less than $175 a side, and is the cheapest best sounding bass I have achieved to date (which includes trying several high $$$ boxed driver solutions, both DIY and store bought).

I do however find myself wanting more for HT movies, so am adding a high-excursion 15" OB sub in the center (my HT receiver can route 120Hz and below L/R content to all three woofers). May experiment with U and H frames too.

Just my experience, and trying to keep away from blanket statements with no intended mission target stated. OB bass meets both my "quality" and low budget target.
 
4

454Casull

Member
Joined 2004
rvsixer said:
In the average/smaller living area, and staying within safe SPL limits, I have experienced the opposite (albeit I prefer lean clean bass, not overemphasized thump thump thump).

For example my setup is Peerless 12" SLS times two on flat baffles ($160USD the pair when I bought them), miniDSP for crossover/OB rolloff EQ ($135), and an old receiver for amp worth about $50. That's less than $175 a side, and is the cheapest best sounding bass I have achieved to date (which includes trying several high $$$ boxed driver solutions, both DIY and store bought).

I do however find myself wanting more for HT movies, so am adding a high-excursion 15" OB sub in the center (my HT receiver can route 120Hz and below L/R content to all three woofers). May experiment with U and H frames too.

Just my experience, and trying to keep away from blanket statements with no intended mission target stated. OB bass meets both my "quality" and low budget target.
Click to expand...
Nobody said that OB couldn't be "good enough". But the fact is, a monopole sub with less displacement would've done the same job, at least where SPL is concerned.
 
oon_the_kid

oon_the_kid

Member
Joined 2008
Dear Rudolf,

I was reading more of your posting in the MA 10.2 OB project. I can't understand german unfortunately but i could see you are a proponent on narrow baffles. I am planning to build a fairly narrow baffle about 1' wide and 3' high. It would be a U baffle with a tapered wing from 6" to 12". In that baffle I plan to use 4 X 8" Jamo speaker per side with an xmax of 3mm.

JAMO 20318 8" Treated Paper Cone Woofer 12 Ohm 299-934

It would be biamped with an additional amplifier and some additional bass boost. There will a SEAS FR22 full range on a 1' wide baffle on top of that, without and U. I plan to have the the bass come from the 4 Jamos at about 100Hz and below and let the SEAS run full range.

the 4 X 8" hopefully should have enough bass to handle since the displacement is roughly equal to eminence 15" which has an xmax of 3mm.

I would like your opinion on this design.:eek:

Oon
 
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