[jrebman]

Starting this thread to continue the discussiongoing on in the "favorite single drivers" thread.

-- Jim

[JLM]

Perhaps we (someone who knows what they're talking about) should clarify why I always see BSC brought up in context of single driver speakers (and not other speaker types).

I suppose that in theory only infinite baffle designs (or those with drivers that don't go low enough to be affected) wouldn't need BSC.

[markC]

Most wide range drivers have a rising frequency response, (as frequency increaces, so does SPL). The BSC is implemented to tame the SPL as the frequency rises giving a flatter overall response. Now that the mids and highs aren't louder than the lows, bass seems greater.

[MJK]

Perhaps we (someone who knows what they're talking about) should clarify why I always see BSC brought up in context of single driver speakers (and not other speaker types).

It is definitely a very real problem for all speakers. I once used a BSC filter on a two way speaker design. But since two and three way designs have a crossover between drivers, if you design the transition region to be around the baffle step region you can use the crossover to correct the rising response. So a lot of time the BSC circuit is built right into the crossover design and is not so obvious by looking at the crossover circuit.

For a full range driver in an enclosure you get the rising response of the driver and the rising response of the baffle step adding and if you do not do something to rebalance the SPL response you will end up with thin sounding bass. You can use a correction filter, like the ones in my designs, or try and design an enclosure that will produce more efficient low frequency output to make an electrical filter unnecessary. Sometimes placement in the right type of room might be all that is required, but my guess is that this is the least likely to work for most people.

I suppose that in theory only infinite baffle designs (or those with drivers that don't go low enough to be affected) wouldn't need BSC.

Agreed.

[Ed Schilling]

Martin, you wrote......"But since two and three way designs have a crossover between drivers, if you design the transition region to be around the baffle step region you can use the crossover to correct the rising response. So a lot of time the BSC circuit is built right into the crossover design and is not so obvious by looking at the crossover circuit."[/u]

EXACTLY. It (BSC) should be part of the overall design of any speaker, not addressed as a separate "problem".

And this....."or try and design an enclosure that will produce more efficient low frequency output to make an electrical filter unnecessary."

There you go. We agree again. You are making progress.

Ed

[MJK]

It (BSC) should be part of the overall design of any speaker, not addressed as a separate "problem".

We almost agree. I consider the design of a BSC filter as part of the design of a speaker system. I also consider the type of amplifier to be used as part of the design of a speaker system. If you want to exclude the BSC as part of the speaker design process, why not also exclude the box since it is an acoustic filter and the placement of the box in a corner which is another acoustic filter.

As far as I am concerned, anything that influences the sound of a speaker is part of the design process. Anything that improves performance, and therefore the listener's enjoyment of music, is a good thing even if politically incorrect. To ignore something that would improve performance is ______ (fill in the blank). If you choose to restrict your options and limit potential improvements in your speaker design, that is up to you. I will take any improvement available to get the best optimized total performance that meets my goals.

[Vapor Audio]

To answer the thread subject, when is BSC needed?  That's simple ... always.

Now, how you accomplish that can be any number of different ways.  And how much you choose to implement depends on a lot of conditions.  BSC can be achieved simply by room placement.  Changing the size of the baffle obviously has an impact as well.  A good example was Scott F's system we listened to Saturday using Lowthers.  He has no crossover on the full-rangers, but had a woofer cabinet actively crossed at 250hz ... and lots of wings on his Lowther baffles.  Both of those things accomplish BSC.

I don't know anybody who uses a separate contour filter in multi-way speakers designs to accomplish BSC.  Of course you can, but that's over-thinking the issue.  It's simple to just shape the response, typically by slightly oversizing the coil on your woofer. 

One thing I will say, 6db of BSC is almost always too much.  Real systems are in rooms with walls, and reinforcement.  3-4db typically sounds better, unless you're building speakers for your patio 

[Ed Schilling]

Martin,
Now you are back to making no sense. You wrote....."If you want to exclude the BSC as part of the speaker design process, why not also exclude the box since it is an acoustic filter and the placement of the box in a corner which is another acoustic filter."


I never said it was not IMPORTANT or that I don't (try to) fix it. I said it should not be a separate issue. And you even wrote...."."or try and design an enclosure that will produce more efficient low frequency output to make an electrical filter unnecessary."

Which is EXACTLY what I have done. You of all people should know that. I understood this concept decades ago. And again....BS is just one part of ANY design. It must be dealt with. My issue is that it is not more important than any other aspect of speaker design but yet seems to come up because it is "catchy" and gives the impression that certain speaker types are in need of "special attention". This is not the case. It is just what happens to a driver on a narrow baffle. BFD.

Anyone trying to design a speaker will not have found a bit of help in these discussions.

How about some math to predict the effect with a driver of a certain size on a certain width and depth enclosure over a stated response? Instead of talking about it, why don't you simply tell the guys that need to know  what it is the  info (math) on how to predict the "problem"?

Those of us who do this for a living (Duke, for instance) already know. But my job is not to teach speaker design and I don't make formulas for that stuff up.

So, again Martin, we do agree, You just seem to think "I don't get it". I do. I did.

We may differ here though....I do not think a system should be designed for one's "taste". By doing that everything else will be wrong. I think instead the system should reproduce the signal as closely as possible. Bad recordings will and should sound bad in all their glory. And great ones will sound great. If one wants pleasing over accuracy then a pair of Advents is the way to go.

Turbo, Excellent. You seem to get it too. I bet you did not read that...... "6db of BSC is almost always too much.  Real systems are in rooms with walls, and reinforcement.  3-4db typically sounds better, unless you're building speakers for your patio" in a book or on the internet either did you?

Ed

BTW....I should mention "Chrisby" (I am pretty sure) asked me a few years ago how I dealt with BSC. I was for a couple minutes confused! I NEVER had even thought of it as a separate issue! I had always just dealt with "response using a narrow baffle". It took me a minute or two to realize what he was talking about! EVERYTHING about my little speaker is for a reason, and that includes the narrow baffle and the overall resulting response. They are corner horns, remember. I hope that is clear enough.

[MJK]

Anyone trying to design a speaker will not have found a bit of help in these discussions.

Not sure I agree with that statement, but I will stop now and move on to doing something else.

[Ed Schilling]

Martin, Please don't "move on". Do you have any "math" to help the budding designer predict where and how much to comp. to apply for a (as I asked before) certain cone diameter with a given freq. response on a baffle of "X" width and depth? This of course would assume flat response across the driver intended range.

This I am sure would be VERY helpful as a starting point and will be something we will (assuming your math is correct  ) agree on completely. That is ....the need to comp. and what and where to do it.

People need to learn something other than our ability to antagonize one another. Although that has never been my goal. Math is you area. Should be easy for you.

Thanks,

Ed

[Vapor Audio]

Turbo, Excellent. You seem to get it too. I bet you did not read that...... "6db of BSC is almost always too much.  Real systems are in rooms with walls, and reinforcement.  3-4db typically sounds better, unless you're building speakers for your patio" in a book or on the internet either did you?

Haha, no ... I think it was a realization I made awhile back after hearing many commercial 2.5 way speakers - which of course gives a full 6db of BSC - that they all sound fat and slow, of course phase and group delay problems play into that as well, but it's primarily from too much mid-bass energy. 

BTW....I should mention "Chrisby" (I am pretty sure) asked me a few years ago how I dealt with BSC. I was for a couple minutes confused! I NEVER had even thought of it as a separate issue! I had always just dealt with "response using a narrow baffle". It took me a minute or two to realize what he was talking about! EVERYTHING about my little speaker is for a reason, and that includes the narrow baffle and the overall resulting response. They are corner horns, remember. I hope that is clear enough.

That's essentially how I think of it as well.  I don't say to myself during the design stage, "how much BSC should I build into this speaker".  BSC is simply a part of the voicing process, however much it ends up being isn't a conscious decision, but it is there.

[Ed Schilling]

Turbo,
I like you already. We agree on a very simple concept. It should be obvious to anyone (serious) in this field. I hope.

And you got the concept of what I was trying to say perfectly. I wish I could have done it in so few words!

Ed

[Vapor Audio]

Turbo,
I like you already. We agree on a very simple concept. It should be obvious to anyone (serious) in this field. I hope.

And you got the concept of what I was trying to say perfectly. I wish I could have done it in so few words!

My choice of few words is from lazyness, not eloquence

It looks like we're all agreeing that it's an inherent part of the design process.  When I'm building something, I don't consciously think about BSC past my initial 'ideas bouncing around in the head' phase.  After that it's just a matter of meeting the target through response shaping, voicing, whatever you wanna call it.  Some examples

- A small sealed 2-way bookshelf.  You don't want to reduce sensitivity too much through excessive BSC, or cause over-excursion to meet SPL goals, so build a touch less in.  Design them to be used closer (relatively) to walls, also because small bookshelves can still image like crazy close to a wall. 
- An open baffle midrange design just gets even more 'open' sounding if you can move it out from the wall a bit, so in that case you're probably going to want a bit more fullness on the bottom end.  Full dipoles require a totally different set of paradigms however.
- Surround speakers meant to be mounted on the wall, or right up against them on stands, just make sure and do your voicing with them up against a wall ... or when you do put them against a wall they're going to sound like mud.

[planet10]

http://www.t-linespeakers.org/tech/bafflestep/intro-bds.html

There is some more detail i need to add to this, but it is generally accurate & has links to other articles & circuits

dave

[jimdgoulding]

Perhaps I can help.  I'd like to try if someone would indulge me.  There is no good reason not to.  Doubt or disbelief are not good reasons.