diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Multi-Way (http://www.diyaudio.com/forums/multi-way/)
-   -   Quick baffle step correction question. (http://www.diyaudio.com/forums/multi-way/188868-quick-baffle-step-correction-question.html)

digits 12th May 2011 05:31 AM

Quick baffle step correction question.
 
Hi, just a quick one.
I'm trying to understand baffle step correction a little better.
As far as I understand basicaly there is a reduction in sound energy at the listening position due to sound being radiated like a point source (like a lightbulb) at low frequencies, but then becomming directional at higher frequencies (like a car's headlamps), and the cutoff point is determined/influenced? by the baffle...

I hope I got it right so far to some extent.

Now my question relates to useing all the oline calculators etc. and comprehending the source papers most quote.... They refer to the width of the baffle. Is this litleraly the width, i.e. from left to right side, or just the longest dimensions? If not just the longest dimension, why is that not incorporated into the calculations also?


Then a second unplaned question that just occured to me.
In a multi-way system, is there any benefit in designing a a box with dimensions that creates the step at frequencies that are the same as the crossover network's switching points.

picowallspeaker 12th May 2011 05:49 AM

Quote:

... They refer to the width of the baffle. Is this litleraly the width, i.e. from left to right side, or just the longest dimensions? If not just the longest dimension, why is that not incorporated into the calculations also?
I think that it has to be related to what the loudspeakers are supposed to do , i.e. create a sound stage which may have 3D connotations ,like (other than the distance between the speakers ) depth and height .

Quote:

I hope I got it right so far to some extent.
:hypno2: me too ...reading here on the forum about the subject from enlightened minds makes me immediately comprehend the argument ,then ...next day is total dark !!

Well ,it is scientifically true everything that has been written on BSC ...
:deer:
For me it's just the lowpass of a woofer giving a certain Q ....:o

rabbitz 12th May 2011 06:48 AM

It's about baffle width and the space where the speaker is working. To calculate the F3 at the baffle step use 115/baffle width in metres.

I'll give you a visual example of baffle step using ants.

With a speaker against the wall (2PI space), picture the baffle covered in ants. As some ants escape to the back of the speaker they can't hide so you see them all (no baffle step reduction).

With a speaker in free space (4PI space), the escaped ants now can hide behind the box so you can't see them, only the remainder. That's the SPL reduction from baffle step.

chris661 12th May 2011 06:51 AM

This article covers issues such as baffle step very well.

Its certainly a handy reference to have.

rabbitz 12th May 2011 06:52 AM

Quote:

Originally Posted by digits (Post 2569335)
In a multi-way system, is there any benefit in designing a a box with dimensions that creates the step at frequencies that are the same as the crossover network's switching points.

That's generally used in 3-way designs. You address the baffle step issue by crossing over to a higher SPL woofer at around the baffle step F3. This provides the necessary BSC without needing additional crossover components.

An example is an enclosure 350mm wide, so the woofer would crossover at around 328Hz to help with BSC. The mids etc do not need correction as are operating far above the baffle step.

AllenB 12th May 2011 08:46 AM

Quote:

Originally Posted by digits (Post 2569335)
basicaly there is a reduction in sound energy at the listening position due to sound being radiated...

Not exactly. There is still the same amount of energy being radiated, it is just being spread at a wider angle at lower frequencies. To say that it will not be heard at the listening position is a little naive (for want of a better word ;)), especially at the lowest frequencies where it matters little where the sound went, only how much there is.

Quote:

Now my question relates to useing all the oline calculators etc.
Rather than use those, you might play around with a baffle diffraction simulator app or spreadsheet. These won't indicate the total sound put out into the room but only the direct sound to the listening position from the baffle, including edge diffraction which causes ripples higher up. I think this will teach you visually what is happening.

Charles Darwin 12th May 2011 09:04 AM

So from this I gather that BSC is only an issue if the speakers are free standing.
If they are positioned with their backs on the wall or even soffit mounted the problem should disappear and no compensation needed, right?

digits 12th May 2011 09:59 AM

Thanks for your time so far.

Ok so lets say I have the following, a driver in box 332mm from left to right.
It as an Re of 7.4R and is rated at 86db/W

According to the calculator the components I need for the correction is a147k resistor and a 65mH inductor. I assume it needs to be able to handle the current from the amplifier, lets say it can supply 4A, thats a GIANORMOUS inductor, certainly not in digikey catalogs etc.... am I doing something wrong?

bjorno 12th May 2011 10:12 AM

Hi,

I think, you are...Are you designing a passive or active compensation?

b:)

digits 12th May 2011 10:15 AM

I'm gonna make this a seperate post as I'm not sure to what extent these are linked yet. If the driver is 226mm wide (outer edge of frame) and you had a microscopicaly small tweeter (for the sake of the experiment), placed right on this border. The shortest wavelenght that could span from center to center would be just over 1500Hz. Does this mean that to approximate a point source, the highest frequency the woofer should cross at( Or possibly the correct frequency) would have to be under 1500, (under becasue as the tweeter size grows the frequency would drop a little). Which would correspond with the corner frequency of a baffle width of 22.9cm. (lol, thats less than the width of the driver, I think my brain just had a phase inversion...)


All times are GMT. The time now is 09:40 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2