What is frequency response? Bass amps, speakers, cabs.

[Ögon]

Hello,

I have been wondering about frequency response. Amps, cabs and speakers have a frequency response in their technical data. For example, a popular cab: Aguilar SL 112 cab: 37 Hz – 16 kHz.

The reason i am asking this is a device called "SFX micro-Thumpinator v2". They say it enhances the sound of your rig and suggesting it improves the live-span of your speakers/amp, less movement, less heat etc.. but the technical data graph provided and the YouTube video, raised a few questions:

This is the frequency response of the device:

The YouTube video is interesting: without the device the speaker moves more then with the device. But how is this possible? I know i do not know everything about audio yet, but when i look at the graph: the device provides a gradual cut below 25 Hz and a slight boost between 25 Hz - 100 Hz. So why it's not moving more, but less?

The setup they used and frequency responses:

• Fender TBP-1 (preamp)
  20 Hz - 20 kHz
  Specifications - Fender TBP-1 Service Manual [Page 3]
  
  
• Glockenklang poweramp ( I assume the Glockenklang Heart-Rock Poweramp? )
  25 Hz - 20 kHz
  https://www.glockenklang.de/pdf/en/GL Heart-Rock Poweramp Technical Data + Garantie.pdf
  
  
• Glockenklang cab ( I assume the Glockenklang Take Five 4x10" )
  36 Hz - 18 kHz
  take_five

The gradual cut of the SFX micro-Thumpinator v2 from 25 Hz and below, is beyond the frequency response of the Glockenklang Heart-Rock Poweramp and the Glockenklang Take Five 4x10" cab.

Does a frequency range mean that below and above the specified range nothing is coming out of a specific amp/cab/speaker?

Or is based on an average, meaning that MOST of the sound is between the bottom and top limit? (For example it might be putting out 1-2 dB of 20 Hz, but that is not seen as important because between 37 Hz - 16 kHz it's 10 dB on average.. )

I know that in general audio cabs/speakers, frequencies are divided/set so for example the low/sub speaker only receives 50 - 500 Hz, the mid speaker 501 Hz - 1500 Hz and the tweeter 1501 Hz - 20 kHz. Is this true for bass cabs / amps as-well?

If so, in bass-amps, are frequencies removed right after the input or at the end of the circuit before the speaker out?

It's nice to gain knowledge about this, it helps me (and others) in finding the right gear and making the right decisions.

@agedhorse: You are an expert from Mesa Boogie, can you provide us with answers about this?

 

[Mike Caldwell]

Going by their graph the "Thumpinator is just a 25hz high pass filter that applies a slight boost at the cut off frequency.

Reason the cones don't move as much is the sub low frequencies that cabinet can't really reproduce well anyway are being reduced in level with greater level reduction as the as the frequency lowers as indicated by the cut off slope on the graph.

A speaker with a low frequency response rating of say 30hz will attempt to reproduce frequency lower than the rated 30hz at the the expense of speaks mechanical limits, the sound of the speakers straining as they try not to fly apart, the wasted power/amp headroom from amplifying the sub low frequencies.
You have to look at the full speaker specs, it may say in bold print the 30hz number but looking closely the real spec maybe -10db at 30hz.....if they even publish that in the first place. That 30hz speaker may actually be closer to an actual 50hz usable rating.

All told the Thumpinator's 25hz high pass would still be too low for many cabinets.

More often than not bass guitar cabinet speakers are ran full range with the high end naturally falling off. Cabs with a horn or mid driver just high pass that driver and bring it in over the top of the cone speakers.

There are very few PA sub cabinets that even come close to flat at 25hz

 

[BoogieZK]

Hello,

I have been wondering about frequency response. Amps, cabs and speakers have a frequency response in their technical data. For example, a popular cab: Aguilar SL 112 cab: 37 Hz – 16 kHz.

The reason i am asking this is a device called "SFX micro-Thumpinator v2". They say it enhances the sound of your rig and suggesting it improves the live-span of your speakers/amp, less movement, less heat etc.. but the technical data graph provided and the YouTube video, raised a few questions:
The gradual cut of the SFX micro-Thumpinator v2 from 25 Hz and below, is beyond the frequency response of the Glockenklang Heart-Rock Poweramp and the Glockenklang Take Five 4x10" cab.

Does a frequency range mean that below and above the specified range nothing is coming out of a specific amp/cab/speaker?

Or is based on an average, meaning that MOST of the sound is between the bottom and top limit? (For example it might be putting out 1-2 dB of 20 Hz, but that is not seen as important because between 37 Hz - 16 kHz it's 10 dB on average.. )

Well every speaker is capable of delivering an audio range but not at the same level/power that isused to be called the frequency range.

Take a 15inch driver, it will be rated from 35Hz to 3000kHz. But nothing will block all other frequencies to pass thru.
And yes, below 35Hz the level/power decrease but is still there if not filtered.
Below 40Hz, you'll need a lot of power to move the mass of the cone because of the length of the wave.
So cutting below 31Hz which is the fundamental frequency of the low B string, might be a good idea.

Most the time preamps and poweramps are designed with a safe guard below 20Hz to avoid DC to pass thru speaker.
Plus another safe guard (filter) above 20kHz to avoid self resonances.

So frequency response without a graph showing the level is pointless.

My smartphone speaker is Highres 20Hz to 20kHz.... Yeah much like 200Hz to 8kHz within 3dB.

A great bass speaker must be IMHO 31Hz to 3000Hz within 3dB.
+3dB in power means double the power. (1x15" speaker = 96dBSPL ==> 2x15" speaker = 99dBSPL).

 

[Ögon]

Well every speaker is capable of delivering an audio range but not at the same level/power that isused to be called the frequency range.

Take a 15inch driver, it will be rated from 35Hz to 3000kHz. But nothing will block all other frequencies to pass thru.
And yes, below 35Hz the level/power decrease but is still there if not filtered.
Below 40Hz, you'll need a lot of power to move the mass of the cone because of the length of the wave.
So cutting below 31Hz which is the fundamental frequency of the low B string, might be a good idea.

Most the time preamps and poweramps are designed with a safe guard below 20Hz to avoid DC to pass thru speaker.
Plus another safe guard (filter) above 20kHz to avoid self resonances.

So frequency response without a graph showing the level is pointless.

My smartphone speaker is Highres 20Hz to 20kHz.... Yeah much like 200Hz to 8kHz within 3dB.

A great bass speaker must be IMHO 31Hz to 3000Hz within 3dB.
+3dB in power means double the power. (1x15" speaker = 96dBSPL ==> 2x15" speaker = 99dBSPL).

Okay.. Without a graph it's clear? So... Is there a way of knowing if an amp/cab has filters that avoid it to go below/above certain frequencies? (besides measuring it with an audio device.) Or do all the amps/cabs have the filtering build-in that actually hard cuts / limits the frequency response to it's given frequencies?

Going by their graph the "Thumpinator is just a 25hz high pass filter that applies a slight boost at the cut off frequency.

Reason the cones don't move as much is the sub low frequencies that cabinet can't really reproduce well anyway are being reduced in level with greater level reduction as the as the frequency lowers as indicated by the cut off slope on the graph.

A speaker with a low frequency response rating of say 30hz will attempt to reproduce frequency lower than the rated 30hz at the the expense of speaks mechanical limits, the sound of the speakers straining as they try not to fly apart, the wasted power/amp headroom from amplifying the sub low frequencies.
You have to look at the full speaker specs, it may say in bold print the 30hz number but looking closely the real spec maybe -10db at 30hz.....if they even publish that in the first place. That 30hz speaker may actually be closer to an actual 50hz usable rating.

All told the Thumpinator's 25hz high pass would still be too low for many cabinets.

More often than not bass guitar cabinet speakers are ran full range with the high end naturally falling off. Cabs with a horn or mid driver just high pass that driver and bring it in over the top of the cone speakers.

There are very few PA sub cabinets that even come close to flat at 25hz

Yes.. I've watched a few youtube vids about frequencies past 6 months, have seen a video from Adam Neely or some-sound-engineer.. Anyways, he was talking about frequencies and told that for example.. (i don't remember correctly how it works, bear with me) if you have a 50 Hz sine wave or a certain note on a piano: C4 for example, and cut the 50 Hz or the center of the certain note completely but you leave the other frequencies untouched, (if you dont remove 100 hz but only 50 hz for example) your brain/ear will automatically fill in those frequencies and you will think they are there while they are not? (yes i am extremely vague because i dont remember every bit of info, i hope to find this youtube video again sometime.. ) Do amp / cab / designers use this knowledge to design things?

 

[Aloe]

Okay.. Without a graph it's clear? So... Is there a way of knowing if an amp/cab has filters that avoid it to go below/above certain frequencies? (besides measuring it with an audio device.)

typically if the amp has a band-pass (like Genzler MG) or high-pass (like Phil Jones BP800), it's noted in the user's manual. not all amps do have it.

 

[BoogieZK]

Okay.. Without a graph it's clear? So... Is there a way of knowing if an amp/cab has filters that avoid it to go below/above certain frequencies? (besides measuring it with an audio device.) Or do all the amps/cabs have the filtering build-in that actually hard cuts / limits the frequency response to it's given frequencies?

Without a graph or a electronic schematic of the gear, i will not know.

Simply put: If you are using a BASS cab (with bass speakers), don't bother to know what is filtered or not.
At least you will not damage anything.

8 ohms cab into 8 ohms amp output / 500W amp into 500W cab.

If you want to know, you can use your phone and download signal generator amp, get a cable to connect the output of your phone headphone jack to the input of your bass amp.
Then try to generate a sinusoidal signal constant level and try to sweep from 100Hz to 0Hz, you will hear and see the speaker move a lot below 20Hz.
If not, it's filtered.

There is other method but this is fairly simple.

 

[Ögon]

Without a graph or a electronic schematic of the gear, i will not know.

Simply put: If you are using a BASS cab (with bass speakers), don't bother to know what is filtered or not.
At least you will not damage anything.

8 ohms cab into 8 ohms amp output / 500W amp into 500W cab.

If you want to know, you can use your phone and download signal generator amp, get a cable to connect the output of your phone headphone jack to the input of your bass amp.
Then try to generate a sinusoidal signal constant level and try to sweep from 100Hz to 0Hz, you will hear and see the speaker move a lot below 20Hz.
If not, it's filtered.

There is other method but this is fairly simple.

Oh that seems like a fun experiment.. It is a good way to test the lower-limit, because you can see the speaker moving when applying low-frequencies. I will try that out for fun and of curiosity with my bass-amp, and will be easy on the volume levels, so I'm not destroying something.

 

[agedhorse]

Okay.. Without a graph it's clear? So... Is there a way of knowing if an amp/cab has filters that avoid it to go below/above certain frequencies? (besides measuring it with an audio device.) Or do all the amps/cabs have the filtering build-in that actually hard cuts / limits the frequency response to it's given frequencies?




Yes.. I've watched a few youtube vids about frequencies past 6 months, have seen a video from Adam Neely or some-sound-engineer.. Anyways, he was talking about frequencies and told that for example.. (i don't remember correctly how it works, bear with me) if you have a 50 Hz sine wave or a certain note on a piano: C4 for example, and cut the 50 Hz or the center of the certain note completely but you leave the other frequencies untouched, (if you dont remove 100 hz but only 50 hz for example) your brain/ear will automatically fill in those frequencies and you will think they are there while they are not? (yes i am extremely vague because i dont remember every bit of info, i hope to find this youtube video again sometime.. ) Do amp / cab / designers use this knowledge to design things?

Many amps do have high pass filters, some are very effective, some are not. It depends on the quality of the design.

Yes, some amp/cabinet know all about this stuff, but some don't. Again, it comes down to the quality of the designer, their knowledge and experience.

Oh that seems like a fun experiment.. It is a good way to test the lower-limit, because you can see the speaker moving when applying low-frequencies. I will try that out for fun and of curiosity with my bass-amp, and will be easy on the volume levels, so I'm not destroying something.

Yes, be very conservative because speaker power handling decreases as frequency decreases below the -3dB rolloff point of the speaker. It's a good way to damage a speaker if you are not careful.

 

[Eadger]

It doesn't really matter that most speakers don't have a frequency response below 25hz....as mentioned, if they get sent a signal below that, they'll still waste efficiency trying to reproduce it. And regardless, it's almost as important to note that not sending those frequencies to the power amp/head means the amp is also being much more efficient by not having to power and push those frequencies.

On both accounts, even if the speaker is rated with a much higher frequency cutoff and can't extend that low anyway, it will be more focused on the audible range that it can produce (which should result in more accurate, tighter response), and be able to handle more power (output volume) as well as protecting your gear. Yes, some amps do have that in place already....but usually I don't believe at a -36dB/octave slope (which I would not call a "gradual cut"). And if the amp does have a similar steep HPF built in, it really doesn't hurt anything to have another one in front of it.

 

[Passinwind]

A great bass speaker must be IMHO 31Hz to 3000Hz within 3dB.

Please name any that achieve that figure, or preferably several.

 

[Erithon]

Going by their graph the "Thumpinator is just a 25hz high pass filter that applies a slight boost at the cut off frequency.

The micro-thumpinator is more than that. It's also extremely good buffer meant to drive the end of your signal chain: input impedance of ~2MΩ to output impedance below 150Ω. Also its slope is 36 dB/oct versus, say, the 12dB/oct of the Broughton filter. So the attenuation of the frequencies below its filter is much more aggressive.

Reason the cones don't move as much is the sub low frequencies that cabinet can't really reproduce well anyway are being reduced in level with greater level reduction as the as the frequency lowers as indicated by the cut off slope on the graph.

A speaker with a low frequency response rating of say 30hz will attempt to reproduce frequency lower than the rated 30hz at the the expense of speaks mechanical limits, the sound of the speakers straining as they try not to fly apart, the wasted power/amp headroom from amplifying the sub low frequencies.

Excellent response - well said, Mike!

All told the Thumpinator's 25hz high pass would still be too low for many cabinets.

Even if cabinet can't produce frequencies at 30Hz, the thumpinator will still help it mechanically by attenuating some of the infrasonic frequencies with which it is struggling. I use a Barefaced Big Baby 3 (30-20kHz) and I can hear the difference the micro-thumpinator makes. I thought it would be subtle, but when I tested thuminator versus no thumpinator the difference was pretty obvious. Enough so that I ordered a second micro-thumpinator v2 from Max for my mini-board.

 

[brianrost]

do all the amps/cabs have the filtering build-in

Passive cabinets never have any filtering built in. The speaker's frequency response itself is the filter!

 

[seamonkey]

This is the frequency response of the device:

Right this is the frequency chart of the device. They show the levels all the way to zero hz. The amp and speaker are probably not going to go there.

It is a High-Pass-Filter (aka Low Cut) with some marketing spin on it.

Charts are great and convey a lot of useful information, but there are a few that will exploit and misrepresent the charts. This is why we can never have good things. One or two spoil it for the rest

 

[J Wilson]

You also have to remember that just that one octave (45hz/2=22.5hz, or 25hz for this discussion) below 45hz is one engineering challenge to add that into a driver/cabinet. Usually we only see cabinets that approach those frequencies in huge multipass traveling FOH systems, usually on the order of a subwoofer with multiple 18's and huge power and speaker controllers. This device may be able to suggest that deeper end in a bass guitar cabinet, but actually making it in the real world is one hell of a job.

 

[Erithon]

Right this is the frequency chart of the device. They show the levels all the way to zero hz. The amp and speaker are probably not going to go there.

You are right about the amp and speaker, but you have this backwards: it's precisely because an amp/cabinet/speaker cannot reproduce such infrasonics that a HPF is useful. If they could reproduce these low frequencies, and reproduce them well, there would be no reason to filter them out (depending on the room, mix, etc.) Sure, the human hear couldn't hear them, but the human body would feel them and that's a big part of our response to music. It's why us bassists are the ones who make people dance

But they cannot; filtering them out therefore renders the movement of the speaker more efficient and tightens up sound of the bass.

Anyway, Mike already explained this above:

Reason the cones don't move as much is the sub low frequencies that cabinet can't really reproduce well anyway are being reduced in level with greater level reduction as the as the frequency lowers as indicated by the cut off slope on the graph.

A speaker with a low frequency response rating of say 30hz will attempt to reproduce frequency lower than the rated 30hz at the the expense of speaks mechanical limits, the sound of the speakers straining as they try not to fly apart, the wasted power/amp headroom from amplifying the sub low frequencies.

 

[Pilgrim]

What I see in that graph is not much difference across the board. The very limited frequency range in which it appears to make the largest difference is 25-30 HZ and around 50 HZ. Aside from that there's no real difference in output because the effect drops quickly as frequencies move up.

A speaker will only reproduce what it's designed to reproduce. Whether one would hear any difference between output through this unit or not will depend on what you're playing through.

I play mostly through a Fender 100 Rumble. I found a frequency response graph (not necessarily scientific, but interesting) for that Rumble 100 here:
Fender Rumble 100 frequency response curves

Here's the graph:

You might notice that there is very little output from the Rumble 100 amp below 50 HZ. (And I bet it's far from the only amp and speaker cab that this is true of.

Therefore, unless you want to spend $$ to get a boost at 50 HZ output, it would be pointless to connect a Thumpinator to that amp. (Of course, it would seem pointless to try and use the Thumpinator with any low powered amp, right?)

Moving up the power pecking order, I have a Genz-Benz Shuttle 6.2 and a pair of speaker cabs for it. The Shuttle is capable of peak power around 600W @4 ohms, so it's by no means a low powered amp. I use a 12T Shuttle speaker cab and a Shuttle 210T speaker cab with it. The 12" cab has frequency response of 45-18 kHZ, and the 2x10 is listed at 50-18k HZ. Once again, it would seem like a marginal gain to use a Thumpinator just to get a bit of boost at 50 HZ. Below that frequency, nobody is home in those cabs.

Let's say that I am unimpressed, especially when you consider bang for the buck. I'd rather spend (less) money on good cables.

 

[agedhorse]

Moving up the power pecking order, I have a Genz-Benz Shuttle 6.2 and a pair of speaker cabs for it. The Shuttle is capable of peak power around 600W @4 ohms, so it's by no means a low powered amp. I use a 12T Shuttle speaker cab and a Shuttle 210T speaker cab with it. The 12" cab has frequency response of 45-18 kHZ, and the 2x10 is listed at 50-18k HZ. Once again, it would seem like a marginal gain to use a Thumpinator just to get a bit of boost at 50 HZ. Below that frequency, nobody is home in those cabs.

Note that the Shuttle 6.2's output power is 600 watts RMS (~1200 watts peak, but peak is a meaningless marketing number which is why we didn't use it).
The Shuttle amps already have a 4th order HPF built in, so the Thumpinator would not have any benefit in this application. The LF Boost (originally called LF Extend) switch does 2 things, it raises the HPF a little bit and adds some gain in the 50Hz range to counteract the typical rolloff of a compact or semi-compact bass cabinet (especially useful in large rooms or outdoors).

 

[Wasnex]

Understanding how a ported cab works should help understand why an HPF is useful.

Cabs have a usable bandwidth. Often usable bandwidth is considered the points where output is down by 10dB. When you see cab frequency response specs that do not include a qualifier, such as +/- 3dB, typically they are listing the usable response, I.E. +/- 10dB.

The excursion plot for ported cabs tends to have sort of an "S" shape. The excursion starts to increase as the frequency drops below about 500hz. The excursion peaks somewhere around 100hz and then starts to decrease as the frequency drops lower. The exact frequency where the excursion peaks depends on how the cab and driver are tuned as a system. Cone excursion will continue to decline until Fb. Fb is the port tuning frequency.

The reason cone excursion starts to decrease is because the port is starting to become resonant. As the port becomes more resonant, it suppresses cone excursion and starts to produce more and more of the sound.

Well above Fb, the cab/driver system behaves pretty much like it is sealed. At a certain frequency the driver will begin to cut off. The port is tuned so that it begins to produce output to reinforce and extend the bandwidth of the cab to a lower frequency. At Fb the port is producing most of the cabs output and providing maximum suppression to cone excursion.

Below Fb, cone excursion increase very quickly and the output of the cab/driver system drops off. Usually the low frequency roll off of a ported system is 24db per octave below Fb. Because the cone starts jumping around like crazy, power handling is very limited. So you can't use EQ to compensate for the roll off without putting the driver to risk. This is where the HPF comes in.

One of the primary reasons to use an HPF is to protect the driver below Fb. However, a good HPF can also help tighten up the sound, and even give the perception that the cab/driver system has fuller lows. The reason is because you are not wasting energy trying to force the driver to work in a range where it is extremely inefficient. Also if the driver is not jumping around trying to produce super low notes, it will actually work better in the intended pass band.

Eminence Publishes cab design docs for most of their pro woofers. Each cab design doc has multiple models showing how the driver works in a range of different cabs.

Here is a link to the Eminence 2512 cab design doc: 290-593--eminence-deltalite-2512-cabinet-design.pdf (parts-express.com)

The 2512 has a 250W RMS power rating and Xmax of 4.9mm.

The second design in the document shows a -3db point at 58hz with a port tuning (Fb) of 50hz. Mechanical power handling is 100W and a steep HPF should be set to 40hz. Please notice this driver rated for 250W RMS/500W Program only has a 100W Mechanical power rating in this cab design, and it requires a steep HPF even at 100W.

Here is the output plot:

Here is the excursion plot:

Notice the dip in the excursion at Fb = 50hz. The excursion hits Xmax = 4.9mm with 100W just slightly above 40hz, and continues to increase quickly as the frequency goes lower.

The -3dB down point for the recommended HPF is 40hz. This basically means the HPF will reduce the applied power at 40hz by half. In order words if you are sending 100W and then apply a 40hz HPF, the power will drop to 50W at 40hz.

I believe the recommended HPF is 24dB per octave which implies the HPF will reduce the power sent to the driver to less than 0.2W by 20hz.

 

[seamonkey]

You are right about the amp and speaker, but you have this backwards: it's precisely because an amp/cabinet/speaker cannot reproduce such infrasonics that a HPF is useful. If they could reproduce these low frequencies, and reproduce them well, there would be no reason to filter them out (depending on the room, mix, etc.) Sure, the human hear couldn't hear them, but the human body would feel them and that's a big part of our response to music. It's why us bassists are the ones who make people dance

But they cannot; filtering them out therefore renders the movement of the speaker more efficient and tightens up sound of the bass.

Anyway, Mike already explained this above:

if I were to look at the Frequency response right out of the amp to the speaker, or out of the pre-amp to the power amp, I could very well see the amp/pre-amp already take care of the HPF function - in most all cases. In fact on a pre-amp it's probably filtered right at the input as it is simple and effective to filter first before any other processing.

Even power amplifiers these days have DSP and HPF built in.

 

[jdjk7]

Hello,

I have been wondering about frequency response. Amps, cabs and speakers have a frequency response in their technical data. For example, a popular cab: Aguilar SL 112 cab: 37 Hz – 16 kHz.

The reason i am asking this is a device called "SFX micro-Thumpinator v2". They say it enhances the sound of your rig and suggesting it improves the live-span of your speakers/amp, less movement, less heat etc.. but the technical data graph provided and the YouTube video, raised a few questions:

This is the frequency response of the device:
View attachment 5043140



The YouTube video is interesting: without the device the speaker moves more then with the device. But how is this possible? I know i do not know everything about audio yet, but when i look at the graph: the device provides a gradual cut below 25 Hz and a slight boost between 25 Hz - 100 Hz. So why it's not moving more, but less?

The setup they used and frequency responses:

• Fender TBP-1 (preamp)
  20 Hz - 20 kHz
  Specifications - Fender TBP-1 Service Manual [Page 3]
  
  
• Glockenklang poweramp ( I assume the Glockenklang Heart-Rock Poweramp? )
  25 Hz - 20 kHz
  https://www.glockenklang.de/pdf/en/GL Heart-Rock Poweramp Technical Data + Garantie.pdf
  
  
• Glockenklang cab ( I assume the Glockenklang Take Five 4x10" )
  36 Hz - 18 kHz
  take_five

The gradual cut of the SFX micro-Thumpinator v2 from 25 Hz and below, is beyond the frequency response of the Glockenklang Heart-Rock Poweramp and the Glockenklang Take Five 4x10" cab.

Does a frequency range mean that below and above the specified range nothing is coming out of a specific amp/cab/speaker?

Or is based on an average, meaning that MOST of the sound is between the bottom and top limit? (For example it might be putting out 1-2 dB of 20 Hz, but that is not seen as important because between 37 Hz - 16 kHz it's 10 dB on average.. )

I know that in general audio cabs/speakers, frequencies are divided/set so for example the low/sub speaker only receives 50 - 500 Hz, the mid speaker 501 Hz - 1500 Hz and the tweeter 1501 Hz - 20 kHz. Is this true for bass cabs / amps as-well?

If so, in bass-amps, are frequencies removed right after the input or at the end of the circuit before the speaker out?

It's nice to gain knowledge about this, it helps me (and others) in finding the right gear and making the right decisions.

@agedhorse: You are an expert from Mesa Boogie, can you provide us with answers about this?

So... in this case, the speaker(s) is acting like a filter. Some frequencies pass, others don't. The mechanism by which the frequencies are filtered are the mechanical limits of what the speaker can reproduce. For the example of the figure of 37Hz to 16kHz, the likely context for these numbers is that this is the range of frequencies a speaker can reproduce without appreciably reducing the volume. You will still hear some sound that is outside of that range, but a) it will be reduced in volume as you go farther out of the speaker's response band and b), in the case of lower frequencies, you will drive the speaker harder and harder until it heats up and potentially damages something.

All that being said, just because the frequencies in between 37Hz and 16kHz pass doesn't mean they all pass equally. It's normal for speakers to emphasize or de-emphasize certain frequencies in the band. That's part of the character of the speaker. Some speakers can be very 'flat' and reproduce the signal accurately, others will impart their own sound upon the signal. There are reasons to prefer either one.

Some cabinets have what is called a crossover. The basic purpose of a crossover is to feed two distinct types of speakers: subwoofers and tweeters. A subwoofer reproduces lower frequencies while a tweeter reproduces higher ones. Feeding the same signal to both would be pointless; the lower frequencies would burn the tweeter out and the higher frequencies would be lost on the subwoofer. So, what a crossover does is separate the lower-frequency and higher-frequency components of the signal and routes them accordingly-- highs to the tweeter, lows to the subwoofer.

Amps can, in general, have features that remove extremely high or low end content as part of the preamp, such as high pass filters built into Mesa amps. High pass filtering (cutting the lows) is usually the major concern of bass players, because proper high pass filtering can make your speakers work much more efficiently and sound better in more acoustic spaces. Filtering the lows this way is better than letting the speakers do them by virtue of pushing them mechanically. Low pass filters are less common but are more of a tonal preference.