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[Ivan Beaver]

Last time we had a big techno name in the club we rented what you see in the picture (just withouth tops, we used our yamaha mid-hi boxes)

http://www.uesmag.com/wp-content/uploads/2014/10/boca_zvuk.jpg

These boxes were cut, hog scoops: 30-65hz, kickers 65-150hz i think with a slope of 24dB/octave.
Pushed them with MC2 amps.

With them i could reach some actual sub, not molded energy. Amazing transient response, fantasticaly fast drivers. I think some B&C 18's.

In many cases it is NOT the driver-but rather the cabinet and how the driver is loaded that makes the difference.

Take the same driver-put it in a different type of cabinet and you can get different results.

Typically bass horns have less distortion than front loaded boxes.  This is because of 2 reasons.  One is that the cone is not moving as far.  With any loudspeaker, the further the cone moves-the more distortion it has.

Second is that the higher freq (the distortion components) do not "make it around the bends" in the horn-so they are physically attenuated or not as noticeable.

In a horn, the driver/cabinet combination has to be closely matched to get the best response.

With a ported box, the cabinet more or less determines the tuning/response.  You can swap drivers around in ported cabinets much easier than in horns.

In most cases putting "better" driver in a ported cabinet will result in better performance.

But horns are different.  Often putting "better" driver in a cabinet designed for a different type of driver will result in LOWER performance.

But good drivers in cabinets designed for their parameters will result in better performance.

Sometimes the "fast sound" is associated with lower distortion.  But some people like the extra distortion that comes from front loaded cabinets.

[Stephen Kirby]

I see another term used here a bunch, that is a driver or sub system is "fast" or "slow".  As was explained, a bass reflex cabinet is a resonant cavity.  At some frequency the combination of the compliance of the air in the cabinet and the compliance of forcing air through the port will resonate.  Which creates output at the port instead of physically coming from the surface of the driver.  This resonance can be adjusted to be very severe or more moderate.  More severe resonance can produce more output but mostly at that particular frequency.  The old "one note wonders" that boom at one frequency and sound loud but any other note drops off appreciably.  Like blowing over a bottle, that sound doesn't happen instantly.  And as also pointed out, below that point, at high levels the cone is flapping around uncontrolled producing lots of distortion.

The net is that the more you try to get out of a driver by tuning a cabinet low and with a high Q, and then try to eq more low end out of it, the "slower" or more boomy it will sound.

Also, pretty much every low tone has higher frequency components.  When these get smeared in time compared to the fundamental the tone becomes muddled and incoherent.  Audiophiles refer to this as "pace".  Music loses it's timing and groove as the low frequency cues we rely on are not in time with the rest of the sound.

As was pointed out, there are a number of phase inversions going on in a system with a ported cabinet sitting on top of a ported sub.  The crossover also creates some.  If you had Smaart or something you would see the phase slope going one direction and then the polarity flipping back until the next point.  Probably several times in the region where both sub and top are playing.  At every point along this, the combining sounds are going to have cancelations and additions at some point in the room.  These sounds in the 50-150Hz range have to be coherent with the other upper harmonics of the sound as well as any 30-60Hz fundamentals (if you're doing electronic music where these are artificially generated) for the timing of the sound to appear "fast" or together.  If they are smeared in time or canceling out parts of the sound, the result will sound "slow".

Some of this can be mitigated by system alignment.  But you cannot get 30Hz EDM out of your boxes at any appreciable levels.  If you redirect your efforts to optimizing the setup within it's capabilities, you may find that the "slowness" is reduced and even though their may not be the extreme lows the music has more visceral punch and is more enjoyable for the audience.

[Eugen Jeličić]

Another two really usefull posts.

Let me check if im getting this right. I knew that a horn loaded and a bass reflex box have a completly different principal of working but it think i get it now.

The biggest problem with big slow 18 inch sub drivers is that they move slow and air it not thick enough to let that slow driver push it with high efficency. If the 18 inch driver worked under water, it would have a much easier task of pushing the medium around it. However we are not fish so it would be great if we could make the air thicker for that 18 inch driver...

And that's just about what a horn does right? The initial opening (the throat) of the horn is very small in the place where it connects to the chamber that the driver is in. When it starts moving air, that opening resist that amount of air from going trough it, it's like when you are trying to blow very fast trough a small hole. It's hard.
So pressure and air thickness inside the chamber where the driver is rises when the driver is moving and then that driver starts turning mechanical energy into acoustical energy much easier. The air has no where to escape so fast because the small opening of the horn is resisting.

What i don't get here is... the horn needs to get wider when you get closer to it's mouth, that's how it slowly adjust impedance of air to the outside air impedance. But why is this needed. Wouldn't the driver work efficient if the mouth and the throat diameter were the same size? Or would this be a problem because then the horn wouldn't fit as much air so it would start escaping it much sooner and the pressure inside would drop?


Talking about bass reflex box. It's principal is completly different. The box does hold air around the drivers but that only rises efficiency a lot when the antinode, the pressurised area inside the box, is in the same place as the port opening. And that's only at the tunning frequency. Would this be the correct vision of things?

I see why a horn has many benefits over a bass reflex box. The driver will automaticaly sound more precise when working under higher pressure/air impedance because it will move less.
But of course the drivers parameters have to be mached to the horn parameters. And yes... if we would want a horn going lower then 30hz we would need something bigger then a standard HOG folded horn. Which then couldn't go trough the door of a standard club and would be very impractical.

Now can you just correct me at all the things i just wrote wrong? That way i will understand my own misinformations the best.

[Eugen Jeličić]

Stephen:

So the thing is, every system where there is a bass reflex box on top of another bass relfex box will not be perfectly in phase in the 50-150hz area where the crossover comes in.

If i delay one of the boxes what can i get? I can't get perfect summation but can get some frequencies in phase right?
At what price?

If i try getting them perfectly in phase at 100hz that might give me some more sharpness that but will cost me something?

Also. You are basicaly saying the more low end i try to EQ out of the system the slower it will sound. Especially if i try pushing below tunning frequency which i shouldn't do? 

[Ivan Beaver]

You need to stop using the terms "fast and slow".

I know they are "popular" but have no real meaning.

The rate at which a cone moves is based upon the freq that is applied.

A horn is an impedance coupling device between the air and the driver.

With a good coupling, then it takes less driver excursion to reach a certain SPL.

But just like an electrical transformer that can change voltage, there are tradeoffs.

Yes you can get a horn that is flat to around 20Hz and loud, through a normal door way.  It just has to be designed that way.

There are some advantages to a bass reflex cabinet as well.

It all depends on what the end result is and what is most important.

[Tim McCulloch]

Another two really usefull posts.

Let me check if im getting this right. I knew that a horn loaded and a bass reflex box have a completly different principal of working but it think i get it now.

The biggest problem with big slow 18 inch sub drivers is that they move slow and air it not thick enough to let that slow driver push it with high efficency. If the 18 inch driver worked under water, it would have a much easier task of pushing the medium around it. However we are not fish so it would be great if we could make the air thicker for that 18 inch driver...

And that's just about what a horn does right? The initial opening (the throat) of the horn is very small in the place where it connects to the chamber that the driver is in. When it starts moving air, that opening resist that amount of air from going trough it, it's like when you are trying to blow very fast trough a small hole. It's hard.
So pressure and air thickness inside the chamber where the driver is rises when the driver is moving and then that driver starts turning mechanical energy into acoustical energy much easier. The air has no where to escape so fast because the small opening of the horn is resisting.

What i don't get here is... the horn needs to get wider when you get closer to it's mouth, that's how it slowly adjust impedance of air to the outside air impedance. But why is this needed. Wouldn't the driver work efficient if the mouth and the throat diameter were the same size? Or would this be a problem because then the horn wouldn't fit as much air so it would start escaping it much sooner and the pressure inside would drop?


Talking about bass reflex box. It's principal is completly different. The box does hold air around the drivers but that only rises efficiency a lot when the antinode, the pressurised area inside the box, is in the same place as the port opening. And that's only at the tunning frequency. Would this be the correct vision of things?

I see why a horn has many benefits over a bass reflex box. The driver will automaticaly sound more precise when working under higher pressure/air impedance because it will move less.
But of course the drivers parameters have to be mached to the horn parameters. And yes... if we would want a horn going lower then 30hz we would need something bigger then a standard HOG folded horn. Which then couldn't go trough the door of a standard club and would be very impractical.

Now can you just correct me at all the things i just wrote wrong? That way i will understand my own misinformations the best.

A smaller, lighter piston mass can be accelerated faster than a more massive piston when the same motive force is applied.  As with cars, greater mass requires greater force to achieve the same results.  As Ivan alludes to, though, it's a matter of what frequency is being reproduced; your concern seems to be how soon (relatively speaking) the transducer produces the onset of the waveform from the time voltage is applied.

In that regard, filters will have a far greater impact.  A HPF, 48dB/oct at 20Hz, for example, is going to introduce more group delay than the same filter at 80Hz, or 12dB/oct at 20Hz.  The more times you have to make a trip around the Phase Wheel, or the slower (lower frequency) your trips, the greater the delay.

As for why a horn acts as a transformer, you have to think of air in a planar sense.  Air in not "pumped" out of a horn.  Sound propagates when air molecules bump into each other, so the smaller throat expands into the mouth, and the area of the transducer becomes "virtually" bigger.  You now have a much larger radiating area than you have with just the transducer's piston.  Also, because there is no "pumping" of air, the air in the horn, from transducer entry to mouth, is essentially captive, and it has it's own mass and compliance (just like the air on the back side of the transducer).  To achieve the same SPL with a raw transducer would require much greater drive voltage and tolerance of greater distortion as well.

If you have some basic electronics theory in your background you might find it useful to look at various types of subwoofers as their schematic equivalents.  Cabinet design (bass reflex, band pass, horns, tapped horns) all have acoustic behaviors that can be modeled as electronic circuits.

[Ivan Beaver]

A smaller, lighter piston mass can be accelerated faster than a more massive piston when the same motive force is applied.  As with cars, greater mass requires greater force to achieve the same results.  As Ivan alludes to, though, it's a matter of what frequency is being reproduced; your concern seems to be how soon (relatively speaking) the transducer produces the onset of the waveform from the time voltage is applied.

People also associate "speed" with higher freq reproduction.

The issue starts when you look at drivers.  Typically larger heavier drivers have larger voice coils (and magnets).

The larger voice coil is going to have a greater self inductance.  This means it has a "natural" high freq rolloff (the inductance is effectively in series-just like a coil in a low pass crossover).

You don't see heavy drivers with small voice coils (they would not work well due to the lack of driving force)

And it is very rare to find a light cone with a large voice coil.  But some exist.  And of those-the xmax is very small-limiting them to non sub freq.

Everything is a trade off-so you have to figure what is best for a particular situation or usage.

[Eugen Jeličić]

When i say a fast driver i don't mean fast in terms of speed that the driver is moving at. I mean, how fast will a driver accelerate to a certain movement and how fast will it stop once it stops getting signal due to it's dullness which is effected by the materials of which the membrane and suspension/surround are made. And of course it will depend on the box that the driver is in.

Yesterday we had a party. The last DJ was playing dnb, a bit of noisia a bit of pendulum, it was a slightly more commercial party this time, usually we do only underground stuff.
I tried the different EQ approach we talked about. Yes, if i low cut them at about 37-38hz there is not much loss in sub frequencies and there is a slight gain in precision but they still will sound very floppy and wont hit you in the chest nice and sharp.

I also tried delaying the tops or the subs to make them perfectly in phase just like art suggested but i couldn't get much. If i play a 100hz sinewave tough both the subs and the tops at the same level and then try delaying one of them... the results you get are not usable. You get a 1-2dB bump in one spot, but a loss in another. There was no combination that gives you some gain at around the crossover frequency at any or most spots in the club. The room is simply fucking things up way to much to hear these delicate differences.

I also tried delaying one side of the PA to move nodal/antinodal areas in sub frequencies. Yes i could affect the spots where subs summed or canceled out on a certain frequency. But again, not much can be gained. I create a nodal cancelation area close to a wooden resonating part of the club, great, it stops resonating, but now i have cancelation in front of the stage. More damage then good done...

And yeah, none of the things i try with this pa will give it a significant amount of sharpness. Most of theese kick transients in music like this look quiet much like...
there is a loud harmonic between 100-200hz that you hear like a snap and slightly feel in your chest. Then there is a subharmonic around 40-50hz that follows that upper kick tone.
That subharmonic has to punch you fast, it has to be a "bum" not a "wooofff..." the way i see it is, once that subharmonic hits the amp, the driver needs to accelerate from standing still to that 40hz hit as fast as possible and then stop as fast as possible once it stops getting signal. These emminence drivers in the combination of the boxes they are in are simply to dull for that.
It will be to slow in accelerating to reaching that 40hz vibration, which will mean it will basicaly be late to follow the upper ~150hz kick, and then when the transient ends the cone will keep flopping around for too long insted of stopping fast. No matter what i do this is the way these boxes behave.

The more load you give them the less precise they become. If it's only a fast 40-50hz hit it might be somewhat decent, if it comes on top of a lasting subline, it will drown even more. 


TIM: Can you explain the delay factor with high pass filters? I didn't understand what you are trying to say. 

[Ivan Beaver]

TIM: Can you explain the delay factor with high pass filters? I didn't understand what you are trying to say.

Don't think of it in terms of delay-but rather how long it takes them to "react".

As you go lower in freq-there is more phase shift/time in the filter.

As the filter gets steeper-there is more phase shift/time in the filter.

Put the the two together and it adds up pretty quick

I typically don't use more than a 24dB/oct slope.

If you need to get rid of lower freq and don't want to use a steeper slope (and the phase associated with it) a little trick is to put an eq point below the crossover filter.

You can do a lot of eq with minimal phase shift-at least as compared to the phase shift associated with a high or low pass filter.

Regarding "speed" the lower the freq the slower a driver will have to move.  at 40Hz it goes through 40 cycles in 1 second.  At 100Hz it must move much faster-because it has to go through 100 cycles in 1 second.

If your tops and subs are separated-then yes-at every seat you will need a different delay time.  No matter what speaker you use.

You have to choose a spot and live with it.

It is not just the delay time that works for alignment-sometimes you need to flip the polarity to get the best alignment-ALONG WITH the PROPER delay time.

[Eugen Jeličić]

I understood that part but i didn't understand why in the first place would a high pass filter cause phase/time shift?
It starts getting a driver quieter under a certain frequency, how is that related to moving the phase of what's coming out of the speaker, how does this work?

2. So if i want to avoid this phase shift, instead of using a high pass filter a take an EQ for that box and kill everything below the frequency i don't want? How, why, isn't a HPS basicaly also an EQ just in a more agressive version?

3. It's not about the speed at which the driver moves at the certain frequency, it's about how fast it gets there. You are constantly thinking that i literally mean "speed" when i say speed, but actually i'm talking about acceleration. If driver one, gets a signal of power X, with that power the driver will produce let's say 110dB of the signal. But driver one will need 2ms from the moment of getting the signal to the moment of producing that singnal at 110dB, driver two will need 10ms to reach the same thing. Then driver one is going to sound sharper and give you more punch in the chest because it will be less "late" to the upper kick harmonic that follows it and the change in pressure of air in front of you will be happen faster. The air around you can't just go from nothing to pressure X at frequency X. The pressure will slowly rise during the time that driver is accelerating.
The faster the driver accelerates and stops , the sharper the transients will be.

[ProSoundWeb Community]