Topic: Built-in mics baffle

[Billy Mumphrey]

I picked up a Tascam DR-05 for $20 on Facebook Marketplace and I've always wanted to make a little baffle for the built-in mics. I had a bit of leftover rubber mat (made from old tires, often used for gym floors) and used a grinding wheel to shape up a little circular baffle that squeezes onto the recorder and will stay in place without any tape or anything. I tried it onstage at a jam last night and here's a sample:

https://samply.app/p/VbnIYE7mNsUh70COoTLi

The first sample is mastered, the 2nd is raw except for normalization.

The jam started out as a trio; drums in center, guitar to the left and bass on the right. But a keyboardist jumped in and sounded surpisingly fine, considering it was mostly coming from PA and only a little bit of monitors.

[robgronotte]

Great deal on the recorder, but something like that came with it when it was originally purchased.

[Billy Mumphrey]

oh nice i didn’t know that. I looked up baffles and didn’t find anything.

I’ve listened on a few different playbacks by now and honestly not sounding as good as i thought it would; the stereo separation is kinda non-existent for some things but also a weird stereo image for other parts. It’s not a bad recording, especially on monitors, but I’m not getting the clear sound stage that I normally get from stage lip recordings. No worries tho, I’m just gonna keep this recorder in my car for any last minute shows.

[aaronji]

Perhaps I am mistaken, but I think a baffle that small only affects quite high frequencies, so I am not surprised it doesn't create much additional "stereo-ness". It would be interesting to AB it with/without the baffle to see if the difference is audible.

[beatkilla]

I strongly prefer the RAW over the mastered.

[Billy Mumphrey]

Perhaps I am mistaken, but I think a baffle that small only affects quite high frequencies, so I am not surprised it doesn't create much additional "stereo-ness". It would be interesting to AB it with/without the baffle to see if the difference is audible.

Yes I wanted to try removing it for a little AB action but I didn’t want to be onstage during the performance.

I might try to find a performance where I can take some video with my phone of me removing the baffle (while the band is playing) and then syncing my DR-05 recording with the video, so you can watch me physically pull of the baffle and you hear the difference as you watch.


beatkilla, appreciate the feedback. I think I like the raw on headphones and monitors, it sounds a bit more natural. For the mastered version I tried to process it for cheaper speakers that my intended audience will probably use, but it is a bit bright. I think I prefer less bass in my recordings than others, to my ears it can interfere with other frequencies.

The song in the sample was a pure improv started by the bass player. Good stuff.

[aaronji]

^ Maybe you can do a test at home? You could play the same music, at the same volume, with the recorder in the same location, once with the baffle and once without.

[Gutbucket]

Good ideas based on the fundamentals always never die.  Here's some photos and write up on doing more or less the same with an Edirol R09 back in 2006, which may be of interest-
https://taperssection.com/index.php?topic=70134.msg939769#msg939769

The post linked and the one following it are the two most relevant in that thread.  I came to essentially the same conclusion as you, which lead to the larger wedge-shaped cardboard baffle in the second post working significantly better. The key is making the baffle as large as practical.  Wedge shape helps if positioning it relatively close to the source. The further step for me was external mics on either side of a larger hemispherical head-sized Nerf basketball baffle cut in half, which worked pretty well for my intended use. However, if I were doing it again today I'd just make a simple flat baffle that's taller/larger, or put a slot in it that hemispherical Nerf ball so a larger flat baffle could to be slipped in.

[Billy Mumphrey]

Thanks for the link, nice to know that other people are thinking the same thing. It seems like, when it comes to baffles, size matters. Sound waves do a great job of "wrapping around" physical barriers.

I'm curious how much the materials matter. I helped a friend soundPROOF a room for a home theater (with a subwoofer) and we learned A LOT about how different frequencies behave. It should come as no surprise to many of us that low frequencies are the most difficult to control. It comes down to DENSITY (and de-coupling, but that's a whole other can of worms, PM me if you want to learn more). Basically, only more dense materials will have any chance of impeding low frequencies: cement, brick, drywall (crushed rock) will have the lowest resonance points and therefore will have the most effect at containing bass. Rockwool insulation and rubber are fairly dense and can have an effect. Foams, styrofoam, and heavy fabrics/blankets will not really do anything. Using a foam baffle will theoretically block all high and (most) mids, creating stereo separation for those frequencies, but will not impede the lows. It's entirely possible this may not be a deal breaker. Especially when PA recording from back of the room, appropriately-sized cardboard and foam can separate enough of the room and crowd to create the stereo image we seek.

I suppose I am thinking more of the stage lip example I posted above, where the bass amp was off to the right, and yet you would not know that when listening to the recording. I have one last piece of rubber and I am going to make a bigger baffle. However it is approaching the point where it's becoming visibly obtrusive, at least for onstage stuff. It will also be heavier, so we'll see.

I do remember Moke's baffles from back in the 2000's, I still have a circular piece of plywood in a basement somewhere that was supposed to become an omni mic baffle, inspired by Moke.

aaronji, I think I'll wait for a live performance, where there is room ambience and maybe even instruments on different sides of the stage. I want to do the video thing with no baffle, small baffle and then the larger baffle and our ears will tell us the results while we watch the baffles being changed out. I wish youtube allowed control over audio resolution....

[Gutbucket]

Yeah, unless using part of the room itself as baffle or some large item in it like a wall partition or something, any reasonable sized portable baffle is only going to be effective from the midrange and up.  The sonically absorbent surface treatments on baffles such as foam or felt or blanket material or whatever is intended to attenuate the reflected sound bouncing off the baffle that would otherwise interfere with the same sound-front's direct arrival to the microphone element.  If the microphone is mounted flush against the baffle surface, the geometry doesn't create a situation where that reflected interference occurs. So setting it up that way is one way of simplifying things by allowing for a harder, more reflective untreated baffle surface.

For that reason, Moke's tiny baffles with the mics mounted directly to the surface on either side needn't have had the furry high-frequency absorbent surfaces he used on them.  In that case the soft anti-reflective surface isn't eliminating any reflective interference, but does change the timbre of diffuse off-axis pickup somewhat.  A mic placed up against a harder  more-reflective surface will invoke a bit of boundary layer effect in the mid and high frequency range which corresponds to the size of the baffle, making diffuse off-axis response sound somewhat "brighter".  And correspondingly, a typical absorbent-surface Jecklin disk will tend to sound a bit darker than the same pair of omnis would without the baffle between them.

So there can also be that kind of timbral aspect involved in addition to the stereo imaging effects.

[fanofjam]

I always thought the concept of the baffle was more about creating a little bit of sound delay and/or sound pressure difference between the two channels and less about sound absorption.  Nevertheless, FWIW the couple of times I tried baffled omni's, my baffle was a good 12 - 15 inches in diameter with the mics spaced something like 10 cm from each other (5 cm from the baffle) and I was significantly less than impressed with the results.  Plus, I tried this outdoor at a festival and the baffle made a really nice wind sail. 

[Gutbucket]

It's basically about creating acoustic shadowing which produces a level difference above a certain frequency on the opposing "dark side" of the baffle, opposite the direction of wavefront arrival.  Reflection attenuation (absorption) is just a further step nicety to make it work better when the mics aren't positioned tight up against the surface.

Yeah, a big enough baffle up on a stand is a PITA, visually intrusive and susceptible to wind.  Easier and better to just figure out how to space those omnis farther apart without a baffle, IMO.  Practically it makes more sense on a table or on-stage, sort as a potential improvement on "Healy method", and can improve narrow-spaced omnis built into a recorder like Chanher is doing. 

You might try boosting the upper midrange / highs on one of your old baffled omni recordings that were less than impressive and see if that improves them.  IME doing that tends to help some Jecklin disk taper recordings made on a stand from a position out in the audience.  In those situations the baffle improves imaging by reducing some of the cross-talk between close-spaced omnis but often makes the recording sound somewhat darker.

[fanofjam]

You might try boosting the upper midrange / highs on one of your old baffled omni recordings that were less than impressive and see if that improves them.  IME doing that tends to help some Jecklin disk taper recordings made on a stand from a position out in the audience.  In those situations the baffle improves imaging by reducing some of the cross-talk between close-spaced omnis but often makes the recording sound somewhat darker.

I've given thought to revisiting lots of my old recordings to see what I could do with improved software and whatnot.  I retire in July...I'll add this to the long list of stuff I'll probably never do.  LOL.

[Gutbucket]

Mixing and otherwise working the backlog of my recordings IS my future retirement plan.  Until then, the ongoing improvement in the capability of the tools used to do that somewhat eases the self-doubt I lay on myself for having not yet found the time to do so in a way that truly justifies the best of them, at least to my own satisfaction.

[Gutbucket]

Before I let it go, one last realization about my comments on tonal response above. 

[snip..] A mic placed up against a harder, more-reflective surface will invoke a bit of boundary layer effect in the mid and high frequency range which corresponds to the size of the baffle, making diffuse off-axis response sound somewhat "brighter".  And correspondingly, a typical absorbent-surface Jecklin disk will tend to sound a bit darker than the same pair of omnis would without the baffle between them.

So there can also be that kind of timbral aspect involved in addition to the stereo imaging effects.

It struck me this morning how all that is related to the difference between diffuse-field equalized vs free-field response equalized omnis, and also how it is not..

Perceptually, I suspect the "brighter" response of having the mics basically boundary-mounted against a hard-surface loosely approximates a diffuse-field equalization curve, generally appropriate when recording from farther away from the source, while the "darker" response more loosely approximate a free-filed equalization curve.  We have access to omnis with both types of equalized responses, and the application of EQ later can fully emulate the response of the other.  For instance, comparing the Schoeps omni caps, the difference between the free-field MK2 and the diffuse-field MK2XS is their overall response curve difference. The response of either mic on-axis verses off-axis still changes as expected of course, but the native, more fundamental free/diffuse response difference that differentiates the two capsules effects sound arriving from any direction.  That means either capsule can be made to sound essentially like the other with the careful application of EQ.

But with a baffled omni pair the situation is slightly different.  EQ remains a valuable tool capable of improving a recording, but it cannot fully emulate the effect of switching between a brighter boundary-mounted on a hard-surface type of baffle and a darker mics positioned somewhat off a sonically absorbent type of baffle.  The key difference as I see it is that the on-axis response remains more or less the same in both cases - because in that case wavefront arrival is primarily "edge-on" perpendicular to the baffle, so it doesn't effect sound arriving from directly in front, while the off-axis response response pickup of the room, ambience, audience, reverberant stuff is fully effected by the baffle and made brighter or darker.  EQ effects both responses equally, a baffle does not.

In other words, EQing a recording is going to effect direct arrival from the front as well as off-axis arrival from everywhere else in the same way, while altering the baffle surface and how the mics are mounted with respect to it is gong to effect the general off-axis response far more than the front-arrival response..  unless the mics happen to be positioned close to a furry baffle and buried deeply into fur or something, which would quite strongly effect front arrival.

Schoeps knowledge -base page on diffuse vs free response omnis- https://schoeps.de/en/knowledge/knowledge-base/technical-basics/diffuse-field-equalization.html
Plot from that page-