Trying to interpret measurements for baffle step loss

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Hi,

I'm trying to figure out what kind of baffle step loss I'm seeing, and have done a bunch of measurements.
Based on calculation (11500 / 36,8 cm) I should see baffle step occur at ~312 Hz.
But other than the amplitude drop around 400 Hz which is driver related (by looking at the near field measurement), the only other place we see a drop is ~170 Hz.

Could someone help me interpret my measurements to try and make some sense of them?

They are done at distances of 1 cm, 12 cm, 23 cm, 33 cm, 51 cm, 68 cm, and finally 1 meter.
First with no gate and 1/12 smoothing. Then no smoothing with a 10ms gate and then a 5ms gate.

Also added a picture of the speaker in question.
 

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I assume the floor and rear wall are a fixture in this design.

I reckon what you're asking is if the woofers close placement to the floor and the enclosures close placement to the back wall are intentional?
If so, then yes they are intentional as a way of reducing floor bounce and boosting bass due to the enclosure being sealed.

Considering the dimensions involved I'd consider moving the mic further back.

The furtherest measurement above is 1 meter. I have an averaged measurement from listening positions below.

It may become difficult to gate out the ceiling and side walls.

You mean the floor? Ceiling and side walls should be more than far enough away to easily be gated out no?
 

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diyAudio Moderator
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the woofers close placement to the floor and the enclosures close placement to the back wall are intentional?
Ok, then maybe they should be included.

How far is it from the driver around to the wall and back to the baffle (maybe 1.2m)? You have the potential for a hole at 145Hz and 430Hz. To measure this properly you should not be too close to the speaker. As you can see from your measurements the relative intensity of the direct sound and the reflection are changing at a different rate due to the different path lengths.
 
Ok, then maybe they should be included.

How far is it from the driver around to the wall and back to the baffle (maybe 1.2m)? You have the potential for a hole at 145Hz and 430Hz. To measure this properly you should not be too close to the speaker. As you can see from your measurements the relative intensity of the direct sound and the reflection are changing at a different rate due to the different path lengths.

The measurements (with exception of the averaged one) are of the left woofer. In other words the one furthest away from the side wall. It's about 1.4 meter from the center of the woofer to the side wall (I'm not home at the moment, so can't measure exactly).

This is excellent. If you have done proper averaging then you should be able to add a sub to fix your <200Hz response.

I'm thinking of converting the enclosure to a ported design tuned to about 50-60 Hz so I can get a needed boost in that area. I'm curious if that will have any effect on the 180 Hz dip also. Probably not...

But we're get off topic here. What I'm really after is seeing what baffle step loss I have.
 
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Baffle step loss isn't a single number or slope, but if you want to see it in that form you'll need to go outside or at least go in to the middle of the room.

Further, it would also be interesting to measure with the back wall and floor because these reflections are near to the drivers, meaning they may have a significant effect on room power and on response.
 
Further, it would also be interesting to measure with the back wall and floor because these reflections are near to the drivers, meaning they may have a significant effect on room power and on response.

Not sure what you mean. All of my measurements are with the speaker placed as in the picture. In other words, the room effect is already included in my measurements.

Baffle step loss isn't a single number or slope, but if you want to see it in that form you'll need to go outside or at least go in to the middle of the room.

I was hoping my combination of near field and far field measurements could give an indication through deduction. For example, we can see that the 400 Hz drop is driver related by looking at the near-field measurement, so we can exclude that from being baffle-step related.

That leaves the drop at ~170 Hz, which starts to show up from a measurement distance of 20 cm and above. But seeing the null gets deeper the further away we measure, it seems like its room related and not baffle step related.
 
Baffle step loss isn't a single number or slope, but if you want to see it in that form you'll need to go outside or at least go in to the middle of the room....

Defo's classy and careful lab work shows that effects like baffle step are trivial compared to room acoustics and other influences. Important to marketing departments mostly.

I like to put the mic where my head normally is. That's the "bottom line", hoping my use of the term "bottom" won't be misunderstood. I use 3 mic locations spread over 3 feet.

My guess is the dip at 62 and the boost at 42 Hz are major room factors and/or related to location of speakers (location of speakers makes a big difference, even just dozen inches). Maybe can only be moderated.

I'd just remove the back from a speaker and see what you get. Even if the bass isn't better the ambience might be.... carefully measuring before and after, of course.

Given the monumental differences between the acoustic needs of sub speakers and main speakers, seems irreconcilable to put them in the same box.

B.
 
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My understanding is that baffle step calculations are based on the speaker being in free space. The proximity of the floor will have a big influence on the need in practice. (This is why wall mounted speakers need little on no BSC)

The speaker does not "know" which is the near boundary so the floor would have a major effect in your design. I think the distance to the back wall could mean that when the reflected sound distance is half a wavelength out with the direct sound it can cause a dip in response. Someone with more knowledge might be able to confirm/shoot down in flames my statements.
 
The measurements if post #1 can not show baffle loss, because long gating grabs rflfecions and room modes, and short gating is not able to show low bass response right at all.

Theoretically in your case, because of the construction and placement, baffle loss is compensated by boundary reinforcement pretty well now. Sealed box woofer has also low bass loss which gets partially compensated as well.

Only measurements done outdoors or in a large hall can show low bass response "right" - but in-room "room response" is what we are listening, so only that's what we should look at.

This is typical scenario of boundary/room effect to bass response (simulation).
room-gain.png
 
Defo's classy and careful lab work shows that effects like baffle step are trivial compared to room acoustics and other influences. Important to marketing departments mostly.

The whole baffle step might indeed be a bit exaggerated.
But I guess it all depends on the application of course. Such as a small bookshelf speaker on a stand versus something wall mounted or close to the floor like my setup.

Looking at the 5mS gate, which I assume includes the rear wall, the 400Hz drop changes frequency with distance?

Yeah, that's indeed a bit strange... On the other hand, such a small gate kind of invalidates data in this frequency area.

My understanding is that baffle step calculations are based on the speaker being in free space. The proximity of the floor will have a big influence on the need in practice. (This is why wall mounted speakers need little on no BSC)

The speaker does not "know" which is the near boundary so the floor would have a major effect in your design. I think the distance to the back wall could mean that when the reflected sound distance is half a wavelength out with the direct sound it can cause a dip in response. Someone with more knowledge might be able to confirm/shoot down in flames my statements.

Since my design don't have any baffle step correction taken into account in the crossover, this seems indeed to be true.

Due to the proximity to the floor, and the theoretical baffle step f3 frequency wavelength being larger than the gap (where the shelf is) between the two woofer enclosures, we should in theory only see loss from two out of four sides of the baffle. In other words about half the loss.

Theoretical loss is 6 db, while the actual real world loss seems to be 3 db. So maybe 1.5 db in my case?

The measurements if post #1 can not show baffle loss, because long gating grabs rflfecions and room modes, and short gating is not able to show low bass response right at all.

Theoretically in your case, because of the construction and placement, baffle loss is compensated by boundary reinforcement pretty well now. Sealed box woofer has also low bass loss which gets partially compensated as well.

Only measurements done outdoors or in a large hall can show low bass response "right" - but in-room "room response" is what we are listening, so only that's what we should look at.

This is typical scenario of boundary/room effect to bass response (simulation).
room-gain.png

Thank you for the excellent reply and illustration. Seems free air is indeed the only way to go then for an accurate measurement.
 
....Seems free air is indeed the only way to go then for an accurate measurement.
Yes in the sense that a dynamometer is the only way to know how fast my motorcycle will do the Pacific Coast Highway.

Just to give a nutty example of important influences, my speed will depend on how many speeding infractions I've gotten recently (OK, none on the many quiet back roads of Ontario). Hard to enter that into a sim or to assess with a dynamometer.

B.
 
Take one speaker outdoors. Do ground plane measurements of it (mic laying on ground)
- first put the speaker on a 2-3 meter high stand far away from any buildings, driver facing down to the mic that is on ground below the speaker
- then carry the speaker next to a building/wall as it is in your room, mic distance same as previously, on ground

Now you can use long IR gating, at least 50-100ms to see bass similarly, but with the ground surface boosting low frequencies a little. You will see what the front wall and the floor make. You will skip the effect of floor bounce, ceiling bounce and all other wall bounces ,as well as room modes.

The_Floor-Bounce_Effect-fig2.png


Often it is said that the speaker should lay on ground too. This way it will get boundary gain from the ground plane, as well as the mic. Only reflection/cancellation because of bounce elimination will disappear. this is the most practical and easily repeatable way to make measurements of different speakers, used eg. for these tables dB v2
 
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To me your measurements look like what you'd expect. Boundary reinforcement plus a high Q alignment on the woofer used. This effectively negates typical bafflestep although the proof is always in the listening.

You may, or may not need compensation. And by compensation I mean 0.5-2dB of it until things sound right. What are the drivers are they coaxial?
 
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