I had a theoretical question about micing a ported guitar cab. My understanding is that at the port's tuning frequency, the port is actually producing the sound and the driver is producing next to nothing. So if I try to mic it using the traditional method - SM57 close miced to the center of the speaker - wouldn't that mean that at the frequency where I want enhanced bass response, I'm actually getting even less through the mic?
yes.
but if you look at how the sound is radiated you will find that you will still hear the output from the port rather well... otoh, a bit depends on what you are trying to capture in the recording, and where the port is tuned. IF the port is tuned below the lowest open freq of the instrument (bass guitar?) then the port is not doing anything except on "slaps" where it makes something of a "whoomp" sound or "thump"...
Most "ported" bass guitar cabs (Hartke, for example) are not really "tuned" to anything much, they just are there...
Best to investigate by trying mic placement and listening in your monitors, or off your recording for the best sound and best placement... close up is frequently not the best sound anyhow - it is done that way in LIVE PA/SR situations to keep the S/N and feedthrough minimized (you want the instrument you are mic'ing not the rest of the band).
_-_-bear
but if you look at how the sound is radiated you will find that you will still hear the output from the port rather well... otoh, a bit depends on what you are trying to capture in the recording, and where the port is tuned. IF the port is tuned below the lowest open freq of the instrument (bass guitar?) then the port is not doing anything except on "slaps" where it makes something of a "whoomp" sound or "thump"...
Most "ported" bass guitar cabs (Hartke, for example) are not really "tuned" to anything much, they just are there...
Best to investigate by trying mic placement and listening in your monitors, or off your recording for the best sound and best placement... close up is frequently not the best sound anyhow - it is done that way in LIVE PA/SR situations to keep the S/N and feedthrough minimized (you want the instrument you are mic'ing not the rest of the band).
_-_-bear
with some woofers it could make sense to tune relatively low, to get tighter bass and maintain control, and keeping the woofer within its Xmax limit
depends on woofer
simulation needed
or choose closed box
ahh, you are asking how to measure a ported design, where to place the microphone
I would suggest about 1 meter distance
closer to the driver its mainly the higher frequency
but actually, I know next to nothing about measurements
I dont know really
but maybe it would make sense to measure impedance ressonance peak
and for the lowest frequency I suspect a simple simulation to be more accurate
that is if its based on accurately measured driver specs
Well see, that's when it starts getting complicated, to me at least. Sure you can double mic it, but how do you place each one for optimal quality? I imagine tweaking it is much more complicated than if you just had one mic. For live situations, forget it. Soundmen in venues don't have the time to mess around with mic placement.
You definitely do NOT want to double mic a bass cabinet or a guitar cabinet or any other cabinet unless you know precisely what you are doing and what you want to get soundwise and are getting soundwise.
The two mics will have "bleed" from each other's source plus everything else on the stage. In an iso booth in a studio, then two mics MIGHT be useful IF you know exactly how to deal with it - or, if you have to ask, don't!
So, if it is a commercial cabinet, likely the best thing to do is to ignore the port. In the case of a guitar cabinet, the port has no meaningful sound to record (unless ur doing something unusual, in which case you know what you are doing already and don't need to ask!!). In the case of a bass cabinet, the port may or may not be doing something useful, best check. But two mics open on the same source are problematic, so you have been warned!
Live sound is a different animal than studio sound...
_-_-bear
The two mics will have "bleed" from each other's source plus everything else on the stage. In an iso booth in a studio, then two mics MIGHT be useful IF you know exactly how to deal with it - or, if you have to ask, don't!
So, if it is a commercial cabinet, likely the best thing to do is to ignore the port. In the case of a guitar cabinet, the port has no meaningful sound to record (unless ur doing something unusual, in which case you know what you are doing already and don't need to ask!!). In the case of a bass cabinet, the port may or may not be doing something useful, best check. But two mics open on the same source are problematic, so you have been warned!
Live sound is a different animal than studio sound...
_-_-bear
I'm actually in the process of designing my own guitar cabinet. My goal is to optimize the design for applications I will encounter - live and studio.
Originally I was thinking of making a ported guitar cab, because it will be used with 8 string guitar, but after considering the micing issues, I think I'll go with a sealed cab using some wider range 12" speakers.
I think that with an 8 string guitar (what you might qualify as unusual), the port would have some meaningful fundamentals. But if I were to play an 8 string through a ported cab and just miced the speaker, I think I would lose quite a bit of useful information, especially since the speaker itself is not doing producing much at the lower freqs. Right?
That depends on the situation and your mic technique... in a studio close mic'ing is not always required or even good... so then the issue goes away.
I presume you have two lower strings, or an upper and a lower?
But anyhow, even with two low strings added, the lower string will still be WAY above the open E on a standard bass, so the port is only going to reproduce stuff that is not the fundamental of the string. Effects and octave dividers can change that...
The requirements for a MI speaker are quite a bit different than a hi-fi driver... the MI speaker tends to be "stiffness" controlled, meaning the mechanical aspect, not the electrical aspect or the box loading (air in a sealed box) is the primary control over the cone.
Can you use a hi-fi type driver in a sealed box? Maybe. Better have oodles of power handling (or a critically matched power amp) and not be able to be overdriven out of Xmax range by lower frequency information, like thumps, etc...
I'd not worry too much about the mic'ing of a port on a guitar amp, live or in the studio. Just put up a mic, listen, move it around until you like it (in the studio). Live, just go for being heard, unless you have some very exotic PA it doesn't matter that much. If ur recording live, then you have to make your compromises anyhow, so just make the ones that you prefer and go with it.
_-_-bear
I presume you have two lower strings, or an upper and a lower?
But anyhow, even with two low strings added, the lower string will still be WAY above the open E on a standard bass, so the port is only going to reproduce stuff that is not the fundamental of the string. Effects and octave dividers can change that...
The requirements for a MI speaker are quite a bit different than a hi-fi driver... the MI speaker tends to be "stiffness" controlled, meaning the mechanical aspect, not the electrical aspect or the box loading (air in a sealed box) is the primary control over the cone.
Can you use a hi-fi type driver in a sealed box? Maybe. Better have oodles of power handling (or a critically matched power amp) and not be able to be overdriven out of Xmax range by lower frequency information, like thumps, etc...
I'd not worry too much about the mic'ing of a port on a guitar amp, live or in the studio. Just put up a mic, listen, move it around until you like it (in the studio). Live, just go for being heard, unless you have some very exotic PA it doesn't matter that much. If ur recording live, then you have to make your compromises anyhow, so just make the ones that you prefer and go with it.
_-_-bear
Again bear is right - guitar speakers are excursion limited by their non-linear suspensions. The reason for this is that even dropping needle on a record doesn't put out the spike that plucking a guitar string does. Guitar speakers are also designed to dissipate the heat of double digit distortion from the amplifier, as well as add a little distortion of their own to smooth out the non-harmonic components of the amp's distortion.
It's a darn good thing Leo Fender did what he did when he did, because if he'd waited much longer, the euphonic console radio speakers he needed to make his guitar amps work would have been off the market.
Anyway.... there's one speaker that will do what you need - an EVM12L in a TL806 cabinet. Or, if you actually do have two extra bass strings, the EVM15L in a TL606 cabinet. Otherwise, it's hard to find a guitar speaker that benefits from a ported box. And one can argue that a 2nd order alignment is more musical, and more amenable to EQ. In fact, that last is important, as you'll find all guitar amps have a huge bass boost designed in. "Flat" is with the bass control rolled down to '0'. But the most damning thing for a guitar speaker in a closed cabinet is the non-linear suspension I mentioned. To get things right, you need a non-linear port.
In short, other than the EVs which were designed for a 6th order reflex cabinet, your best bet is one of the 55Hz coned speakers in a closed box. This isn't an acoustic suspension design, so simply make the box as big as you can carry. And don't try to use hifi speakers, they'll have a very short half-life.
Regarding your micing concerns, simply close mic the speaker as is normally done, and fix the low end with EQ.
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Anyway.... there's one speaker that will do what you need - an EVM12L in a TL806 cabinet. Or, if you actually do have two extra bass strings, the EVM15L in a TL606 cabinet. Otherwise, it's hard to find a guitar speaker that benefits from a ported box. And one can argue that a 2nd order alignment is more musical, and more amenable to EQ. In fact, that last is important, as you'll find all guitar amps have a huge bass boost designed in. "Flat" is with the bass control rolled down to '0'. But the most damning thing for a guitar speaker in a closed cabinet is the non-linear suspension I mentioned. To get things right, you need a non-linear port.
In short, other than the EVs which were designed for a 6th order reflex cabinet, your best bet is one of the 55Hz coned speakers in a closed box. This isn't an acoustic suspension design, so simply make the box as big as you can carry. And don't try to use hifi speakers, they'll have a very short half-life.
Thanks for the tips. I was actually looking at the Eminence Delta Pro 12a and the Eminence Deltalite 2512, both of which are high excursion speakers designed for MI applications. They are both supposedly good replacements for the EVM12L, just much cheaper. They both have resonant frequencies down in the 40 and 50 Hz range, so I'm guessing in a sealed environment I might be able to achieve something around 70 Hz.
As for acoustic suspension systems, what exactly makes an acoustic suspension different from a small sealed enclosure? Is it just that the speaker being used has a high excursion but is able to handle it due to the enclosure regulating the excursion? In such a small enclosure, wouldn't the transient response be terrible?
It has to do with an acoustic suspension speaker having a very soft suspension designed to be augmented by the compression of the air in the cabinet. They also have a low resonance, as we know when the cabinet increases the compliance the resonance will increase.
The Delta is a great speaker that slipped my mind, and will also work well in a ported cab.
The Delta is a great speaker that slipped my mind, and will also work well in a ported cab.
Probably have phase cancellation issues too.
I agree about guitar cabinets being better sealed and nearly all of the ones you can buy are.
I think I disagree with you guys on mic placement. Micing the center of the speaker sounds tinny. The speaker puts out the most sound in the middle meaning the middle between the center and one side not the center of the whole speaker. So say on a 12 inch speaker the center of the whole speaker is 6 inches from the edge. Id say put the mic 3 inches from the edge. Also you will get more bottom end and richer sound the closer you put the mic to the speaker. I put mine as close as I can get it without it ever actually touching the speaker.
That one looks to have great specs, but according to the Eminence tech guy, it's roll off on the high end may not be suitable for guitar. It looks like a great bass speaker though.
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