Is full baffle step compensation always the way to go?

[fjhuerta]

Hi there,

Although I haven't built anything in quite a while, I've been listening (for a change!) and wondering about what I hear and whether I've been doing things the right way...

This time, my question is about BSC, and how to treat it properly.

I always design my speakers considering a 6 dB baffle step. Lately, though, I've been wondering whether in-room response needs a different kind of approach.

I don't want to design a speaker that only works in one room. I'd like something more flexible. So, measuring in-room and tweaking as I go along isn't an option.

Anyway... considering that bass is severely reinforced in small to medium rooms... wouldn't a less severe BSC model should be used? 3 dB? 4 db? Also, when using tower speakers with drivers closer to the floor, and obviously closer to the walls, should baffle step be even less? I'm thinking about this as I listen to a pair of tower speakers with a pair of 8" woofers very close to the floor - maybe the bass reinforcement is too much!

I also remember reading that speakers with a "rising" frequency response tend to sound balanced in room because bass reinforcement tends to flatten out the response.

What are your thoughts on this subject?

[Forte_II]

The 6 dB loss is correct for a speaker enclosure in free space.* When the enclosure is placed in a room it will encounter various effects due to the room
(reverb, standing waves, boundary effect, cavity effect . . .)*

Diffraction loss and room effects are independent and completely different effects.* The diffraction loss is nicely predictable whereas the effects of the
room are highly variable, not only from room to room but also with speaker placement and room furnishing.* This typically means that each listening environment
will be unique and will require unique compensation.

I suggest the 6 dB diffraction loss correction as a correction for the diffraction loss alone.* I don't suggest that it will neutralize all the effects
due to a unique listening environment.* Others suggest you "deal with diffraction" in the crossover, usually by just lowering the tweeter level a bit.

In some situations* 3 or 4 dB of diffraction loss correction may result in an overall response that is closer to neutral (flat).* But the most correct way
to compensate the room would be to do it separately from any diffraction loss correction.* Room compensation might take the form of several notch filters
tuned to the worst peaks resulting from room modes.* Next you might want to tilt the treble up a smidge to compensate for reverberation that has significant
treble loss.* Dark room reverb will make the playback sound a little darker. Bright reverb . . .* bright.* Next, depending on the size of the room and
speaker response, you might need to compensate for the cavity effect.* In larger rooms cavity effect can be ignored but in vehicle cabins it is a major
effect.*

John Murphy

http://www.trueaudio.com/st_diff1.htm

[Kevin Haskins]

No.... the way to go is to make measurements and then adjust accordingly. You also have to consider where the loudspeaker is going to be used. If its a wall mounted unit, you effectively don't have a baffle step. If you place the loudspeakers near a boundary, you get re-enforcement.

The bottom line with any design is that you have to consider the environment that its going to play within and you need to make corrections in the crossover based upon the acoustical measurements in that environment. You never get a loudspeaker perfect for every environment to fit every style of music and taste. Its just not possible with our current design methods.

What we need is a system that measures the user's environment and then adjust the baffle step, or other room gain/re-enforcement type effects based upon the user's positioning of the loudspeaker. Then we wouldn't have to guess in the design. Of course there is the Fletcher-Munson curves, and preference to deal with also. So in reality, we need a bass adjustment that is dynamic, and changes with loudspeaker position, volume level and user preference.

[cjd]

This is very very simple for anyone using real measurements:

Forget about baffle step. It's already there in your measurements.

C

[Mark K]

This is very very simple for anyone using real measurements:

Forget about baffle step. It's already there in your measurements.

C

Well, that's not quite the right way of looking at it. Typically, when you measure, you look at the free space, 4pi measurement. Assuming the gating is adequate, most typical configurations will show the 6dB drop. But the real world drop is much more complex, due to boundry reinforcement.

Another way of looking at it is that there is a 6 dB on axis rise as you rise above the bafflestep region, but the power response only rises 3 dB. There is no way to fully reconcile this. Basically, you've got to correct from 3-6dB based on your room, and your listening distance. The closer you are to the speakers, relative to the room boundaries, the closer to 6dB correction you should use. If you're relatively closer to the walls, or equal (see SL's page on direct spl and room spl), then you may want to only have 3-4dB.

Again. There is no perfect way to fix this. Practically speaking you have to try ~3.5-5.5dB and see what sounds realistic/best.

[Maximiliano]

I agree with Mark. Measurement with a particular amount of gating and boundary reinforcement makes things complicated. In my experience the best way is to adjust it through listening feedback.

[fjhuerta]

Thanks all for your suggestions,

I've been thinking a lot about it, and I believe this is an often overlooked part in speaker design...

If I understood correctly, there's no way of designing an "accurate" speaker without considering first the room it'll be used in. Likewise, 6 dB's of BSC seems to be too much in practically any situation (since floor reinforcement is unavoidable).

This would lead me to believe that the only way to deal with this issue correctly is via an adjustable active crossover (like the Behringer unit), and probably some room correction.

A less radical solution may be to design speakers with a certain amount of BSC, considering the type of room they'll be used in, as Mark said - 3 to 5 dB, depending on boundaries, etc.

Thank you all for your input - it was very thoughtful and insightful!

[---k---]

This would lead me to believe that the only way to deal with this issue correctly is via an adjustable active crossover (like the Behringer unit), and probably some room correction.

Tone control on your receiver??? Seriously. I know many think they are evil, but isn't this really what they are there for?

I would give CJD an opertunity to respond. I know he takes in room measurements in the real box. The measurements include the room gain. My speakers turned out great. His did also.

[fjhuerta]

Tone control on your receiver??? Seriously. I know many think they are evil, but isn't this really what they are there for?

I would give CJD an opertunity to respond. I know he takes in room measurements in the real box. The measurements include the room gain. My speakers turned out great. His did also.

CJD, if you do such a thing, how do you avoid ripples in your final measurements? I've tried taking measurements in baffle / in room, and they came out useless from all the reverberation the gating could detect...

[rc white]

If you look at the data published by Olsen the actual baffle step effect is manifested as a series of ripples with a general upward trend, the last dip corresponding to the baffle width.

On Rod Elliots page at esp I have described a small satellite speaker I built which has the woofer center in 1, 1:2, 1:6 relationship to the enclosure boundaries, this having the effect of smoothing out the diffraction field. This in conjunction with a slight over damping of the low pass crossover section is all that is needed for bsc.
rcw

[fjhuerta]

Hehehe. Apparently, John Krutke read this thread.

Be careful about generalizations of what a good number is for BSC. Some less than informed/experienced folks may immediately declare that full BSC is too much.

http://www.zaphaudio.com/SR71.html

[jkrutke]

Hehehe. Apparently, John Krutke read this thread.

http://www.zaphaudio.com/SR71.html

Nope but I did now. BSC seems to be a hot subject lately. I have room response curves for every system I design. Usually from several positions in the room too. Maybe I should post them, but it's of limited usefulness since everyone's room is different. I hate to say this, but on any particular project I do, only about 1/3 of the data gathered is posted. I don't want to kill people with information overload.

I posted one once in my L18 project, take a look. No gating. That design is near full baffle step. Warning: without gating the curve is real ugly.

My take on it is that full baffle step does not always work. It kind of depends on the system. With some systems it's the only way to get an enjoyable tonal balance. With other systems, 3dB may do the trick. Nobody should ever always do something, because that will sometimes result in a design that doesn't work well.

[fjhuerta]

My take on it is that full baffle step does not always work. It kind of depends on the system. With some systems it's the only way to get an enjoyable tonal balance. With other systems, 3dB may do the trick. Nobody should ever always do something, because that will sometimes result in a design that doesn't work well.

Thanks for your insightful post, John. It clears up a lot of things I had in mind - and I'll definitely consider it, since my last design was clearly very bass heavy!