What are the pros and cons of mic'ing a bass port rather than the speaker?

[jazzyvee]

I posted a picture of the rig I was using for a reggae gig last weekend on a facebook group and one of the bassists there suggested that for reggae I should put the mic in the speaker port. Now that is not something I have ever thought of doing on these BF or my previous Mesa boogie cabs. My understanding is that bass ports are tuned ports so i think sending that signal to the PA would possibly be void of frequencies that are needed for a decent FOH sound.
 

I haven't ever had any complaints about my sound so i have no plans to try his suggestion but my curiousity is aroused and I just wondered if anyone here has an experienced view on this. 

[Stub Mandrel]

I would imagine you get a very dark sound, possibly with a big hump at the port tuning frequency as you suggest. No harmonics or top end to speak of...

 

The port resonance affects the driver so dont expect more bottom end than you'd get from micing the speaker - just less top.

 

For reggae my instinct would be to set crossover frequency high, mic the speaker fairly close to the dust cover. Maybe mix in a bit of di.

 

I’m not a reggae bassist but my impression is that the sound is more in style/technique than in eq settings despite the reputation of just being bottom end.

[Bill Fitzmaurice]

If all you want to hear is boom-boom-boom then it's OK. Otherwise don't.

[SumOne]

Being a tuned port I don't think it'd work very well. For live use I'd stick with what you're doing. 

 

I guess they might have heard that some old reggae recording studios mic'd the back of cabs and might be assuming it's the same. 

[Downunderwonder]

I don't know what you are doing with such a big cab when getting PA support.

 

You may as well DI it as the cab reproduces flat enough that the DI would likely be closer to the cab sound than best mic job you could do. 

[BigRedX]

In the days when I was still using a traditional bass rig I found that there was a lot of air movement from the ports which I doubt most mics would be happy with.

 

We tried mic'ing the speaker closest to the port once in the studio for exactly the reason suggested in the OP. The static peak frequency produced by the port was not particularly pleasant and that idea was quickly abandoned.

[itu]

It could be feasible only, if the response could be filtered dramatically, and the actual speaker elements wouldn't mix/mess the trial completely.

[nilebodgers]

There is a cable in the DI output of that preamp, so no mic strictly needed anyway.

 

Sticking a mic in front of a port will give lots of signal around the tuning frequency of the port and not a lot at other frequencies. Probably plus a load of wind noise to boot. Not normally what is wanted.

[bremen]

1 hour ago, nilebodgers said:

 

 

Sticking a mic in front of a port will give lots of signal around the tuning frequency of the port and not a lot at other frequencies. Probably plus a load of wind noise to boot. Not normally what is wanted.

Last few gigs I've been to sound like that's exactly how the bass has been mic'd.

[Bill Fitzmaurice]

3 hours ago, bremen said:

Last few gigs I've been to sound like that's exactly how the bass has been mic'd.

That's on the FOH crew, when they don't know what a bass is supposed to sound like and therefore neglect to EQ the bass channel appropriately. 🤥

[bremen]

Indeed.

 

The same geniuses who think kick drum should have nothing above 200Hz and be 6dB louder than the rest of the band.

[Chienmortbb]

On 08/08/2024 at 21:28, bremen said:

Indeed.

 

The same geniuses who think kick drum should have nothing above 200Hz and be 6dB louder than the rest of the band.

....and compressed to hell.

[jazzyvee]

On 08/08/2024 at 08:33, nilebodgers said:

There is a cable in the DI output of that preamp, so no mic strictly needed anyway.

 

Sticking a mic in front of a port will give lots of signal around the tuning frequency of the port and not a lot at other frequencies. Probably plus a load of wind noise to boot. Not normally what is wanted.

This picture is from one of my gigs and is my regular setup with the DI out going to the FOH. Sometimes the cab gets mic'd also. Depends on the sound engineer. But it never crossed my mind to mic the port. Not something i'd do so my post really was to find out what the pros and cons of doing it would be. 

[Bill Fitzmaurice]

This is why you don't mic the port.

 

 

[Stub Mandrel]

22 minutes ago, Bill Fitzmaurice said:

This is why you don't mic the port.

 

 

 Very interesting. Below about 40Hz the driver would appear to be acting against the port, presumably due to the phase shift.

 

Thinking about it that would be expected...

Edited August 10 by Stub Mandrel
looking at the diagrams total output is less than port output below ~40Hz

[Bill Fitzmaurice]

Yes, the port output shifts 180 degrees below the port tuning frequency, so the combined result of the port plus cone output falls at twice the rate of the port or cone output alone. That's the downside of a ported enclosure. However, compared to a sealed enclosure it still has higher sensitivity to at least an octave lower than sealed, along with far lower excursion.

[itu]

I read those graphs and for me they look like (+/- 3 dB):

- the full response is 40 - 800 Hz

- port response something like 27 - 75 Hz

 

If we choose +/- 6 dB, we get around:

- the full response 32 - 1000 Hz
- port response 20 - 100 Hz

 

(What should be taken into account is that the max level of the port is some 4 dB less than the whole system.)

 

@Bill Fitzmaurice please throw some comments on this.

[Bill Fitzmaurice]

The top chart is the modeled response of a typical twelve loaded cab, but it's not accurate above 200Hz or so. That's because modeling software uses Thiele-Small specs, which are only accurate to 2 octaves or so above the driver resonant frquency, in this case around 50Hz. A measured response chart would show the sensitivity increasing above 200Hz, with useful (-10dB) response to at least 3kHz. You shouldn't run this speaker much below 40Hz, as while sensitivity is dropping excursion is rising. Amp designers usually put in a high pass filter for this reason. Mine doesn't, but it does have full EQ. I pull the 32Hz slider all the way down.

[mazdah]

Pros:

- none

 

Cons:

- the sound

[bremen]

It's 100% agreed here that there's nothing to be gained by micing the port.

 

So I guarantee that sometime soon, some "renegade" producer is going to be questioned about how he gets his awesome bass sound and he says: -they said it couldn't be done, but rules are just there to be broken....

 

I'm going to have to try it now 😀

[agedhorse]

Another ridiculous urban myth that I’ve never seen at a pro gig ever. 

[Downunderwonder]

5 hours ago, agedhorse said:

Another ridiculous urban myth that I’ve never seen at a pro gig ever. 

Define pro gig. 

 

One would hope that any gig that required a mic on bass cab would have paid sound crew doing it. Never mind the band of wannabe pro musicians.1 

 

I guess it shows you don't need to get paid very much to call yourself professional sound crew and not all pro gigs are equal.

 

In case of OP I am not too sure but I think he is used to being paid? Perhaps the folks that comment on his FB feed are mere wannabes who only get volunteers for sound crew.

[agedhorse]

A pro gig is gigs by pro musicians (who earn a substantial portion of their living in the music industry) and pro sound guys make their living providing sound to mostly professional acts.

 

There is a HUGE difference between real pros and those who think they are pros. Unfortunately you often discover the difference  between pros and non-pros after it's too late to do anything about it.

[Stub Mandrel]

6 hours ago, agedhorse said:

A pro gig is gigs by pro musicians (who earn a substantial portion of their living in the music industry) and pro sound guys make their living providing sound to mostly professional acts.

 

There is a HUGE difference between real pros and those who think they are pros. Unfortunately you often discover the difference  between pros and non-pros after it's too late to do anything about it.

 

I think we should (1) be clear that @jazzyvee is very much a pro and (2) his post was a reaction to a response to his rig when he posted it on Facebook, he already concluded the port would be 'devoid of many frequencies' and wondered why anyone would want to mike it up.

[Dan Dare]

Mic'ing the bass rig in any manner is not the best way to go, imho. DI is better. Before anyone starts talking about "my tone/sound", it needs to be realised that the sound that works onstage often doesn't work in the mix out in the room - different acoustics, different rig, etc, etc. It's better for the sound man/woman to have a clean slate to work with.

Edited August 12 by Dan Dare