[hurdy_gurdyman]

Does anyone here know where the chart/graph showing baffle roll-off figures for different frequencies? I have seen it somewhere, but can't find it now.

Dave

[OZZIOZZI]

Try Planet10.com or frugalphile or Dave Dlugos on DIYaudio forum he published a chart at one stage HTH
Ozziozzi

[hurdy_gurdyman]

Someone was nice enough on a different forum to point to the Edge program. I remember seeing it years ago, but had forgot about it. I haven't been active in audio forums for several years and am slowly getting back into it. Thanks.

Dave

[nicoch]

is relate to qts and some other t/s data

[JohnH12]

The edge will give you the baffle response.  ABC dipole will give you a driver plus baffle

[hurdy_gurdyman]

The edge will give you the baffle response.  ABC dipole will give you a driver plus baffle

Thanks, but I already have the drivers and have been running them on a baffle I've had for several years now that has 18 inch square removable panels in it with a 12 inch removable panel between them. They were built for Hawthorne Audio 15 inch Sterling Silver Iris coaxial and 15 inch Augie bass augmenters on the bottom. I have panel cutouts for 15". 12" 10" and 8" and for a 10"x16" horn. I recently decided to dig out my EV LS12's again and give a listen. These decided me on trying a fullrange driver again. Bought a couple of 8" Betsy's from Caintuck Audio. Couldn't be happier. Now I'm thinking about building a smaller set of baffles for the 8" Betsy and a pair of 10" Augies. This would make the living room a lot less crowded. Edge is supplying me with what I need. To use ABC dipole pole would require me to go back to collage, and would probably end up directing to a pair of drivers I'd have to take a 2nd mortgage out on my home, motorcycle and both dogs. 

Dave

[tru168]

[Scott L]

Interesting, but the dimensions given require a bit more explanation. For example, is that 200 by 200 inches ?

[Scott L]

After further research, I would have to answer my own question as a "yes". I have found other resources that suggest a VERY large baffle is required
for anything approaching decent bass response. I suppose you could extrapolate from the graph to determine just how much e.q. would be required
if you were to choose a much smaller baffle. Also,  in the "Briggs" article, he mentions that floor coupling also has an effect.

http://jelabsarch.blogspot.com/2012/06/open-baffle.html

[opnly bafld]

Don't go by that chart as there are too many variables in drivers and position on the baffle.

[Bob in St. Louis]

Don't go by that chart as there are too many variables in drivers and position on the baffle.

^^ This.
But I'm sure Dave knows that. He's been around the block a time or two. 

[opnly bafld]

^^ This.
But I'm sure Dave knows that. He's been around the block a time or two. 

Scott L seems to be new to the game, unlike HG man.

[Scott L]

I found some more information right here at Audio Circle:
     

Re: OB theory: Baffle width and roll-off (Jeff B.)
« Reply #5 on: 10 Aug 2012, 10:53 pm »

    Quote

I did an open-baffle build a while back.  It showed promise, but I now think my biggest problem is that I need to deal with the roll-off.  This is my current understanding.  I hope someone will correct me if I am wrong.
If we have speed of sound = 1135ft/sec, then an 1135Hz tone is 12" long.
If I have an 18" baffle, then the 6db per octave roll-off will begin at 12"/18" * 1135Hz * 2 = ~1500Hz.
How many octaves can I stretch a driver across, seems like 2 at the most, however if I want a smallish mid-range driver like 3" or 4", these are normally not very efficient and so would only be good for 1 octave.  I mean if I start at say 86 db, then I will be down to 81db after correcting for the 6db roll-off.  I chose 18" here because that is what I used originally, but now I think maybe I should go narrower.  If I use 16", so that I can still use a 15" woofer, then I get the following:
12"/16" * 1135 * 2 = ~1700Hz.
Now I can use a tweeter from 1700Hz without the need for baffle step correction.
I can use a 3" driver for one octave from 850Hz to 1700Hz.
I can now bring in something bigger with high efficiency.  Some sort of pro-audio 8" or 10" to cover two octaves from 212Hz to 850Hz.  Then I can use a 15" to cover two octaves from 53Hz to 212Hz.
I am now up to 4 drivers and still don't have the bottom 1.5 octaves.
If I go with a wider baffle, then my 3" driver covers a range where it will change from 2pi space to 4pi space.
This might be advantageous though as it could run lower.  So lets try a 24" baffle and see what happens.
Now the 6db roll-off starts at 1135.
So now I need to deal with the 3" in both 2pi and 4pi space. I think I will just it run without a tweeter to save 1 speaker.  I can now run the 3" driver from 567Hz all the way up.  A high efficiency 10" for two octaves from 142Hz to 567Hz, and a 15" from 35Hz to 142Hz.  Ok, this is starting to look doable.  How come most of the open baffle designs I see are 2-way.  Seems like 3-way is the bare minimum.  Unfortunately, I think 24" is a bit too wide for my room.  18 is really about the max.  Maybe 20".  Perhaps the 15" could be stretched a little beyond 2 octaves.  Or perhaps I am ok with the bass rolling off a little early.  It is kind of nice not having bass bother the neighbors.

http://www.audiocircle.com/index.php?topic=108857.0

[Scott L]

but then, in a follow up:

Re: OB theory: Baffle width and roll-off
« Reply #7 on: 11 Aug 2012, 05:50 am »

    Quote

Ok, I must have read some bad info before.
From http://www.musicanddesign.com/Gradient_woofer_eq.html the dipole peak is computed as
C - the speed of sound
D - the effective separation of the speakers.
F = C / (2D).
So for 18", you get 1135/(2 * 18/12) = 378hz.  I was thinking it was 4 times higher.
I was using a basic surround sound receiver with a 200Hz cross-over point with a 3" and a 15".
The 3" was then down 6db at 200Hz.  This explains why it got close to working good, but not quite.

[Scott L]

So, guys, please help me to understand here:

An 18 inch wide baffle starts to roll off at 6 db/octave, starting at 378 Hz.
Such that, by 47.5Hz, the response is down 18 db, which needs to be corrected by e.q. right ?

So, plugging in these figures into a calculator, we get:

18 dB ->
  Voltage-ratio = 7.94328
  Power-ratio = 63.0957
  2.07233 Nepers

Thus, for every watt that would normally be sufficient in a traditional closed enclosure, you would now need 63.0957 times as much.

[Davey]

Scott,

The limitation is much more related to driver excursion capability rather than increased voltage needs from the amplifier.
Many users seem to assume open-baffle systems need more power.  (They don't....they need more equalization.)

Open-baffle systems are just not very (acoustically) efficient....relative to closed-box schemes. 
The general rule-of-thumb is.....if Driver X in a box yields adequate SPL and low extension, then you'll need 4 x Driver X in a typical open-baffle configuration to yield equivalent SPL and extension.

Cheers,

Dave.

[nicoch]

Many users seem to assume open-baffle systems need more power.  (They don't....they need more equalization.)

They need,  more eq=more power at that hz!
I preferred right qts  btw

[Davey]

They need,  more eq=more power at that hz!

No, I'm afraid not.  This is a basic concept, easily misunderstood.  You're not alone.
Driver X will require less power to achieve a desired excursion in an open-baffle than it would in a box.
Equalization extends the frequency range of the system/driver, but it doesn't increase the power demand to create a desired excursion.

This is why small-box sealed sub-woofers require so darn much power.

Dave.

[JohnR]

Also, efficiency increases with multiple drivers. And the 6dB/octave rolloff is at "infinity", it's less than that the closer you get. (Whitepaper on Kreskovsky's Music and Design site.)

[Scott L]

Okay, so taking this further.....
What does a proper enclosure do to the native response of a driver in free air ?
As I understand it, it raises the frequency of resonance, but at the same time, it lowers it's amplitude quite a bit.

Thus, open baffled drivers have a higher amplitude of resonance, as witnessed by the higher impedance peak.
If power is determined by the impedance of a system, and voltage squared over the impedance yields power, I can see where an amplifier is
yielding less power due to the restriction. For example 2.83 volts squared, over an eight ohm impedance, yields 1 watt
                                                               However, 2.83 volts squared, over an impedance of 50 ohms ( just as an example) equals .160178 watts
So, my question is, is this a result of what is required, or, rather is this a result of what is yielded ?