Baffle step compensation (sound absorption instead of electrical attenuation)

[peter190e]

Hi to all full-range lovers!

I am a rookie in speaker construction, and even moreso as far as FR is concerned. My first FR project is about to begin! I got myself a pair of Fostex FE164 drivers. I specifically sought out these drivers because they have a very smooth roll-off in the bass region ( less than 10db difference between response at fs and at mid frequencies) and higher Xmax than the newer 166/167 drivers. I also "feel" that 6,5 inch FR drivers are the best compromise.

My heart is set on building a BIB, mainly becaues of the ease of constuction and the apparent great results that can be had.

The reason for this post is that I have been running things through my mind before beginning construction. Initially I had thought/hoped that I would not need to insert anything between amp and driver, but as I searched, discovered this "nasty" called baffle step and the need for a BSC and so on and so forth.

The question that I want to ask is this:

What if we make the baffle, or even better the entire enclosure very very absorptive? Would that not attenuate the mid/high frequencies in the same way an attenuation circuit would. In this way we avoid any inductors, caps and resistors in the signal path, AND, we create a better point source( the source of sound will be the driver cone, not cone+baffle).

One fleeting idea I had in accoumplishing this is by using small felt pyramids that would be glued to the baffle/enclosure covering the entire surface. There may be better materials or methods of achieving what I am proposing.

Please share yout thoughts and knowledge regarding this idea, and my proposed project in general.

Best wishes to all

Peter

[rjbond3rd]

Hi Peter, I also am finishing up some BiB's for FE164 and FE166ES-R's. I've never heard of anybody using BSC on a BiB, actually. Placed in corners, the issue is often an excess of bass. What a great dilemma!

Check out the simulation made by Martin King -- he modeled using the FE167E which is pretty close to the FE164, and taking the corners into account as he does, he got tremendous bass:

General Speaker Related Articles (last article in the list)

Of course this is easily cured with stuffing and/or repositioning the BiB's. Mine should be done this weekend. Let's compare notes!

[Dr.EM]

Interesting idea. The wider the baffle is, the thicker (and/or more absorbent) the treatment will have to be. You'll want to keep the baffle as narrow as possible, even with just the width of the driver itself you're looking at baffle gain starting from ~250Hz. This, I would expect, will require 50mm+ of high density acoustic foam; normal felt will only do much at 10kHz+ really. It'll be hard to figure out the exact quantities required I think. The alternative is in-wall mounting, as studio monitors often employ

[rjbond3rd]

Would applying something to the baffle really attenuate the directly radiated sound? I think it would merely attenuate the diffracted energy which is already much lower in amplitude. But "mechanical eq" is a great idea.

GM has said a few times something to the effect that for acoustical problems, acoustical solutions are preferable to electrical or something like that (sorry GM for the misquote).

[pjanda1]

AFAIK, BIB's don't typically need BSC. (Acronyms galore!) They have plenty of bass gain, as you can see in the sims The also require placement against the wall, or preferably, in corners, which also reduces the need for BSC. My BIB's actually produced too much bass for my room, and I had to use a bunch of stuffing to tame the bass. So, while your idea merits some discussion, I wouldn't worry about any form of BSC with this build.

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

[peter190e]

Very encouraging that we BIBers don't need no BSC! Do we need zobels and/or notch filters though?

Another thing: would an offset driver not be a good idea? Heard it helps with baffle step. Have not seen any BIBs with offset drivers.

Regarding the absorption theory, I just try and think of it as a ''stealth'' baffle or enclosure: invisible acoustically. So yes, an acoustical solution to an acoustical problem. Very well put. I believe that with the right material, you could dampen(?) the baffle and/or enclosure to such an extent, that any reflected, refacted, diffracted etc. sound is totally absorbed/eaten up/vanished etc. so as not to interfere with, or have any influence on the sound coming directly from the driver cone.(IOW an anechoic baffle/enclosure!) I am confident that the desireable 'single point source' will be enhanced, by getting rid of the ''other sources".

[peter190e]

RJ, my BIBs will take a while to be up and running. Haven't receive drivers yet! Thinking of making rough/temp enclosures as a start out of paricle board/mdf to play around with, and then make ones out of BB( or even Aquapanel concrete sheets! Is that a good idea?). Placement will not be in corners,but against the long wall of a room about 6,5mx4,5m. Hope I get enough bass.

Dr EM, thick acoustic foam would probably work. My initial idea was of using tall(+-40mm) felt pyramids. Not that I've seen these pyramids as been available, but just imagined it as a rough/eneven absorptive surface-''stealth''!

Paul, great to know that BIBs don't need a BSC. The idea of a "stealth" baffle/enclosure could be very beneficial in other types of builds though. I'd like to see where this idea may lead ( I am not proposing that this is a new concept, or has not been discussed/done before)

Anyone else have any thoughts as to how to make, or benefits of, a ''stealth'' baffle/encloure?

Thanks

[Scottmoose]

Originally Posted by peter190e

Very encouraging that we BIBers don't need no BSC! Do we need zobels and/or notch filters though?

Think about what you're saying. If your driver requires a zobel to sound half decent to your ears, then it requires a zobel. Ditto for notch filters. Both are issues with the driver's innate response, whatever the box it happens to be mounted in.

[peter190e]

Hi Scottmoose!

Glad to see you taking inerest in my rookie questions!
You're right-I should have thought more about asking that. I'm a noobie and at the moment everything I'm saying/thinking is theoretical. I haven't glued two planks together yet! I'm just gathering info/knowledge in order to be able to make the best BIB I can. You have been a great influence in my decision to build BIBs in the first place!

What's your take on this ''stealth'' baffle/enclosure?

Thanks

[rjbond3rd]

Originally Posted by peter190e

RJ, my BIBs will take a while to be up and running. Haven't receive drivers yet! Thinking of making rough/temp enclosures as a start out of paricle board/mdf to play around with, and then make ones out of BB( or even Aquapanel concrete sheets! Is that a good idea?). Placement will not be in corners,but against the long wall of a room about 6,5mx4,5m. Hope I get enough bass. ...

Hi Peter, building a prototype sounds like a good idea to me. If I can afford it, I would remake them out of BB. I have no experience with concrete board.