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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Subwoofer Forum => Topic started by: Trevor Jalla on February 22, 2017, 04:29:49 am

Title: 21" subwoofers - opinions
Post by: Trevor Jalla on February 22, 2017, 04:29:49 am
I've been contemplating a pair of double 18s to upgrade from the four PRX718XLFs I have.

I now have a line on 4x 21" units (dB Tech S1521N - powered, bass reflex). Does anyone here use 21s and in what situations would these present an advantage over 18s? Are 21s overkill or unsuited for rock/R&B bands?

Mostly, I operate and supply for 6-10pc bands for corporate events and weddings although I would absolutely be looking for wider applications - maybe EDM or outdoor cinema clients, council festivals etc. I'm wondering if 21s might be too specialised.

Mains are 4x dB Tech D12HP, and they outrun the JBLs. Thanks for any input.
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 22, 2017, 07:26:13 am
I've been contemplating a pair of double 18s to upgrade from the four PRX718XLFs I have.

I now have a line on 4x 21" units (dB Tech S1521N - powered, bass reflex). Does anyone here use 21s and in what situations would these present an advantage over 18s? Are 21s overkill or unsuited for rock/R&B bands?

Mostly, I operate and supply for 6-10pc bands for corporate events and weddings although I would absolutely be looking for wider applications - maybe EDM or outdoor cinema clients, council festivals etc. I'm wondering if 21s might be too specialised.

Mains are 4x dB Tech D12HP, and they outrun the JBLs. Thanks for any input.
I would look closely at the response graphs and specs and make sure they will do what you need them to do.

I have no opinion about the specific products mentioned, but there are a good number of 21" cabinets that don't actually go as low as people would like to think.

People often "assume" that a larger driver will give more "bass".

That can be true, and it ALSO can be false.

It all depends on how the particular driver is used in a particular cabinet.

There are advantages and disadvantages to larger drivers.

I honestly feel a number of manufacturers simply make cabinets with 21" drivers because they assume people will buy them because they are "better" than smaller drivers.

You MUST dig into the specs (for any product) to see if it is suitable for YOUR applications.

Think of it this way-if bigger was better-why are so many companies making "mini" line arrays.

BTW-it goes the other way also.  Smaller is not always better.
Title: Re: 21" subwoofers - opinions
Post by: Don T. Williams on February 22, 2017, 01:10:44 pm
+1 for Ivan again!
Title: Re: 21" subwoofers - opinions
Post by: lindsay Dean on February 22, 2017, 02:39:32 pm
"specs" can be " embellished by the marketing depts. to make the product seem more competitive, in theory.
   maybe see if you can rent or audition ?
Title: Re: 21" subwoofers - opinions
Post by: Luke Geis on February 22, 2017, 04:15:48 pm
From a theory standpoint, the 21" should be able to produce more low end at a higher level, but how much more is the question. The next issue is box design. People like the idea of the larger drivers, but it also makes for a non standard box size. So did the company try and repackage a 21" driver into a box more standard to an 18" driver? The proof is in the pudding. The last thing That I would consider is quality of sound. 21" drivers are pretty big in comparison to 18" ones and there is that much more mass to move. So it will react slower to the electrical input from the amp. Many 18" boxes these days will get right around 35hz these days and some even breach the 30hz zone in double 18" form. Shoot the JBL SRX-728's were rated down to 27hz. My question would be more how loud do I really need it to go and will 5hz lower make or break the show? 
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 22, 2017, 05:23:57 pm
From a theory standpoint, the 21" should be able to produce more low end at a higher level, but how much more is the question. The next issue is box design. People like the idea of the larger drivers, but it also makes for a non standard box size. So did the company try and repackage a 21" driver into a box more standard to an 18" driver? The proof is in the pudding. The last thing That I would consider is quality of sound. 21" drivers are pretty big in comparison to 18" ones and there is that much more mass to move. So it will react slower to the electrical input from the amp.
There are a number of double 21" boxes that barely get to 40Hz.  SO that kinda blows the whole "going lower" theory.

It is a myth that larger drivers move "slower" than smaller drivers due to the mass.

ANY driver will move back and forth at the same speed as the freq applied.

For example-they will move back and forth at a 50Hz rate-if 50Hz is applied.

If it moved "slower", then the freq would change.  That would be VERY noticeable.

As the freq goes lower the "speed" will be slower and as the freq goes up the "speed" will go up.

But the speed is solely dependent on the freq applied.
Title: Re: 21" subwoofers - opinions
Post by: Scott Holtzman on February 22, 2017, 06:50:51 pm
There are a number of double 21" boxes that barely get to 40Hz.  SO that kinda blows the whole "going lower" theory.

It is a myth that larger drivers move "slower" than smaller drivers due to the mass.

ANY driver will move back and forth at the same speed as the freq applied.

For example-they will move back and forth at a 50Hz rate-if 50Hz is applied.

If it moved "slower", then the freq would change.  That would be VERY noticeable.

As the freq goes lower the "speed" will be slower and as the freq goes up the "speed" will go up.

But the speed is solely dependent on the freq applied.


However a 21" driver will require a much more powerful motor and amplifier to accelerate the greater mass.  Is there a practical point where the driver can't articulate fast enough and small transient and detail are lost?


How would one measure such a thing?


I am sure like anything that better materials are making this a non issue. 



Title: Re: 21" subwoofers - opinions
Post by: Marjan Milosevic on February 22, 2017, 07:06:51 pm
Eeerm, 21 inch have about 50% more cone area, so they need to move less to shift same amount of air. :-)
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 22, 2017, 07:23:59 pm

However a 21" driver will require a much more powerful motor and amplifier to accelerate the greater mass.  Is there a practical point where the driver can't articulate fast enough and small transient and detail are lost?


How would one measure such a thing?


I am sure like anything that better materials are making this a non issue.
Very often people confuse "speed" with freq response.

They "assume" that the loss of HF is due to "lack of speed".

But in reality it is a combination of the self inductance of the voice coil (that acts like a low pass filter-knocking out the higher freq) and the mass of the cone (not being able to vibrate as easily).

Years ago-whizzer cones were popular.  They were very light and stiff.  They moved along with the cones-but were able to vibrate easier than the main cone body-so it added some more highs.

As usual-it is a combination of several factors, and not a single one.

Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 22, 2017, 07:28:00 pm
Eeerm, 21 inch have about 50% more cone area, so they need to move less to shift same amount of air. :-)
The old EV 30W (a 30" woofer) did not have very much excursion, yet could go quite low.

They were limited in max output.

Something else that is often forgotten is the fact that the more a woofer moves-the more distortion it produces.

 Large drivers moving a small amount or woofers that are properly horn loaded produce less distortion than woofers that are "flopping around".

Of course some people associate the distortion of woofers as "normal"-because they are not used to clean accurate sound.
Title: Re: 21" subwoofers - opinions
Post by: Bill Hornibrook on February 22, 2017, 09:43:36 pm
Thanks for any input.

I'm just a guy in the field and not a pro like many in this forum, so with a bit of reluctance here goes...

As a DJ I own and use a couple of 21" subs in boxes very similar in size to the ones you are considering. I built them primarily for contemporary hip-hop - which brutally and relentlessly dips into the low 30s on a continual basis. They work great for that.

I've used them a few times for bands. The kick is definitely there, but with tonal characteristics that are a bit different than 18s. They sound cleaner but not as warm (for lack of a better word).

That said, I don't think my 21" subs are unsuitable for bands, and don't imagine those dB Tech subs would be either. I also think most bands would be very happy to see them replace your PRXs. And as far as DJs are concerned (if you end up doing some festivals) they are always impressed with 21" subs... just because they are bigger. And I'm not going to explain any further than that...

I looked these up online. If you are spending over $12,000 on subs there are many excellent choices out there. I'd suggest that you don't zero in on one product in particular until you've done some research. You mentioned that you "have a line" on 4, so maybe for considerably less?
Title: Re: 21" subwoofers - opinions
Post by: Mac Kerr on February 22, 2017, 09:53:21 pm

However a 21" driver will require a much more powerful motor and amplifier to accelerate the greater mass.  Is there a practical point where the driver can't articulate fast enough and small transient and detail are lost?

What transient program would make it past the crossover that sends all higher frequencies to a different speaker? Any transient that does make it through doesn't belong there so isn't a concern.

Mac
Title: Re: 21" subwoofers - opinions
Post by: Trevor Jalla on February 22, 2017, 10:06:03 pm
Thanks all for your input. More contentious that I had imagined, and these are not my sole consideration for upgrading from the PRX subs. Yes I concede it comes down to box design, but I can barely find any info on the DVA range of subs (except the S30, which is popular in the field). Also these are an out-of-state buy with no means to demo. I'll ask around rental houses to see if anyone has stock to rent - but I'm doubtful! I'll also look around for response graphs. The on paper specs put +/- 3db at 30-105hz, fwiw.
Title: Re: 21" subwoofers - opinions
Post by: Scott Holtzman on February 22, 2017, 10:29:28 pm
What transient program would make it past the crossover that sends all higher frequencies to a different speaker? Any transient that does make it through doesn't belong there so isn't a concern.

Mac


The transient could be in the pass band of the filter.  What I am trying to say is you have a pounding kick with a fundamental of say 45hz and it each hit is pushing the driver to say 75% of Xmax.  Then the bass player plays a more nuanced note with a fundamental of around 80hz.  Just for giggles let's say that that note is 9db down from the kick signal.  A smaller cone could more easily be accelerated and managed by the motor to create that complex waveform.  The larger driver has so much more compliance volume, shear weight and resistance for the motor to work against. 


Just like a small car can more easily navigate a winding road than a tractor trailer. 





Title: Re: 21" subwoofers - opinions
Post by: Mac Kerr on February 22, 2017, 10:32:16 pm

The transient could be in the pass band of the filter.  What I am trying to say is you have a pounding kick with a fundamental of say 45hz and it each hit is pushing the driver to say 75% of Xmax.  Then the bass player plays a more nuanced note with a fundamental of around 80hz.  Just for giggles let's say that that note is 9db down from the kick signal.  A smaller cone could more easily be accelerated and managed by the motor to create that complex waveform.  The larger driver has so much more compliance volume, shear weight and resistance for the motor to work against. 


Just like a small car can more easily navigate a winding road than a tractor trailer.

The small car doesn't have the advantage of a filter that straightens the road for it. Frequencies in the sub bass range are by definition slow moving. actual impulses go to a different driver.

Mac
Title: Re: 21" subwoofers - opinions
Post by: Craig Hauber on February 22, 2017, 10:41:25 pm
The small car doesn't have the advantage of a filter that straightens the road for it. Frequencies in the sub bass range are by definition slow moving. actual impulses go to a different driver.

Mac
which is exactly why that really slamming kick-drum hit also requires output from the mids and the highs too -all in proper alignment.
Title: Re: 21" subwoofers - opinions
Post by: Tim McCulloch on February 23, 2017, 01:11:29 am

The transient could be in the pass band of the filter.  What I am trying to say is you have a pounding kick with a fundamental of say 45hz and it each hit is pushing the driver to say 75% of Xmax.  Then the bass player plays a more nuanced note with a fundamental of around 80hz.  Just for giggles let's say that that note is 9db down from the kick signal.  A smaller cone could more easily be accelerated and managed by the motor to create that complex waveform.  The larger driver has so much more compliance volume, shear weight and resistance for the motor to work against. 


Just like a small car can more easily navigate a winding road than a tractor trailer.

No, the cone is already moving, whether at 45Hz or 80Hz.  What you get is intermodulation.  You're mixing wave forms not creating discrete events.
Title: Re: 21" subwoofers - opinions
Post by: Tom Bourke on February 23, 2017, 04:34:41 am
The on paper specs put +/- 3db at 30-105hz, fwiw.
at what output?  With how much distortion?  Is that distortion "good sounding?"  How big of truck do I need to move it?

Once you get out side of the engineering department the size of the cone is just a marketing thing.  The frequency range stated is easy, depending on output needs.  I have a set of computer speakers that have a 6.5" sub that can hit that.  It just can't cover much more than a small office or bedroom doing it.  The 15" subs I designed years ago can also hit that, and cover a good size room doing it, provided I  add some filtering and EQ.  Speaking of processing, ever hear of BagEnd?  They had a processed system that could get 8 Hz out of very small drivers and boxes.  They had single 18" and dual 12" boxes that were not much bigger than the drivers alone.  I use to run a rig that had 9 18" drivers PER SIDE that would make you feel like the earth it self was opening up right under your feet.  The trade off was the distortion was high enough to fill the next octave above them.

What's the need of your business?  21" drivers in huge boxes because your clients are running EDM shows and like big?  Or like my former biz where renting out a bunch of smaller systems paid the bills?  Or my current situation where one week I have a designer that did not plan for speakers existing  yet the CEO wants to feel the stage shake when he walks on and the next week the client saw there favorite band and HAS TO HAVE!!! the same brand speaker system?

Any sub can make you money, it just has to fit your clients needs, real or imagined.
Title: Re: 21" subwoofers - opinions
Post by: John Ferreira on February 23, 2017, 04:43:02 am
About size, there are subwoofers that are less than one inch in diameter, but of course with low wattage capacity.

For sub frequencies it is more important the inherent resonant frequency of the woofer, than its size.



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Title: Re: 21" subwoofers - opinions
Post by: Chris Grimshaw on February 23, 2017, 05:26:56 am

The transient could be in the pass band of the filter.  What I am trying to say is you have a pounding kick with a fundamental of say 45hz and it each hit is pushing the driver to say 75% of Xmax.  Then the bass player plays a more nuanced note with a fundamental of around 80hz.  Just for giggles let's say that that note is 9db down from the kick signal.  A smaller cone could more easily be accelerated and managed by the motor to create that complex waveform.  The larger driver has so much more compliance volume, shear weight and resistance for the motor to work against. 


Just like a small car can more easily navigate a winding road than a tractor trailer.

Cones being fast/slow is a myth and needs to be sorted IMO.
The motor in any modern driver is more than capable of keeping control over the cone and accelerating it as fast as needed.

Here are two drivers that use pretty much the same motor, one 18" and one 21":
http://bcspeakers.com/products/lf-driver/21-0/4/21sw115?impedence=4
http://bcspeakers.com/products/lf-driver/18-0/4/18sw115-4?impedence=4

The difference we are talking about is more like this:
One has a moving mass of 304g, and the other has a moving mass of 335g. That's about 10% difference.
Subwoofers are like having a car being asked to accelerate to 30mph in about 30 seconds, and then smoothly decelerate. That car will not care if it has a couple of passengers that add 10% to the total weight. It's still well within the capability of the engine.
Low frequencies do not require a fast-moving cone. If the cone is moving quickly, it's producing treble and your crossover is set incorrectly.

High-frequency drivers need to be small and light. Here's an example.
A 21" driver moving 10mm one-way at 50Hz has a peak velocity (as it passes through the zero position) of just over 3m/s. The acceleration is around 1000m/s/s, so the voicecoil is exerting just over 300N of force (about 30kg, 66lb). That will result in an SPL of a smidge over 121dB at 1m, groundplane. That's around 1KW power input.
That same cone producing 121dB at 5kHz would be moving 0.01mm, with peak accelerations of 15000m/s/s, requiring 4500N of force (992lb). To produce that force, you'll need to put around 60KW in there and hope it survives.

A 4.5" driver producing 121dB at 5kHz needs to move 0.07mm one-way, requiring a larger acceleration of 77,000m/s/s. The moving mass is about 3g, though, so you only need 231N of force to get it there. That particular driver would need around 5KW input power to manage that, which it won't survive. Dropping the moving mass further (thin titanium diaphragms) and bolting a horn on the front would improve efficiency and reduce the power requirements, though.


Edit - couple of people have posted while I typed that.
Free-air resonance is not more important than the size of the driver. Resonance (Fs), among a bunch of other parameters, will help determine the shape of the response of the driver in a given cabinet. The size and linear excursion, and thermal power handling of the driver will tell you how loud it can go.

Chris
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 23, 2017, 07:32:13 am
I'll also look around for response graphs. The on paper specs put +/- 3db at 30-105hz, fwiw.

The response graph will tell you more than "simple numbers".

I have seen some spec sheets in which the "claimed -3dB point", is actually 9 to 20dB down from the rated sensitivity.

The -3dB MUST be tied to something.

There is no such thing as "-3dB",  It MUST be 3dB down from "something".

Knowing what that "something" is, is VERY important.

Also be wary of just a processed graph.

If they are doing a boost at the low freq (VERY popular these days to get lower numbers), REMEMBER that whatever boost they are applying, MUST be subtracted from the maximum output.

So if there is a 10dB boost down low, and the claimed max output is 130dB, then at the boosted freq, the max output will be 120dB.

This is NOT what you want or expect.

Hence the reason to dig a little deeper to see the ACTUAL performance.

Simple numbers give all sorts of wrong answer.

I have no idea about the product in the post-so have no opinion how accurate it may be.

But just stating things to look for when comparing "simple numbers"

Any car can easily get 100 miles per gallon.  As long as it is coasting down a hill.  But you will probably not always drive down a hill.   Same sort of thing.

Title: Re: 21" subwoofers - opinions
Post by: John Rutirasiri on February 24, 2017, 11:51:05 pm
FWIW, I have a pair of old K-Array KL21ma powered subs.  21" Faital Pro neo driver powered by 1500W RMS Powersoft plate amp.
IMO the much cheaper JBL PRX718XLF whips its butt when it comes to output and low-end.

Driver size is not everything.

John R.

Title: Re: 21" subwoofers - opinions
Post by: John Ferreira on February 25, 2017, 07:06:19 am
Cones being fast/slow is a myth and needs to be sorted IMO.
The motor in any modern driver is more than capable of keeping control over the cone and accelerating it as fast as needed.

Here are two drivers that use pretty much the same motor, one 18" and one 21":
http://bcspeakers.com/products/lf-driver/21-0/4/21sw115?impedence=4
http://bcspeakers.com/products/lf-driver/18-0/4/18sw115-4?impedence=4

The difference we are talking about is more like this:
One has a moving mass of 304g, and the other has a moving mass of 335g. That's about 10% difference.
Subwoofers are like having a car being asked to accelerate to 30mph in about 30 seconds, and then smoothly decelerate. That car will not care if it has a couple of passengers that add 10% to the total weight. It's still well within the capability of the engine.
Low frequencies do not require a fast-moving cone. If the cone is moving quickly, it's producing treble and your crossover is set incorrectly.

High-frequency drivers need to be small and light. Here's an example.
A 21" driver moving 10mm one-way at 50Hz has a peak velocity (as it passes through the zero position) of just over 3m/s. The acceleration is around 1000m/s/s, so the voicecoil is exerting just over 300N of force (about 30kg, 66lb). That will result in an SPL of a smidge over 121dB at 1m, groundplane. That's around 1KW power input.
That same cone producing 121dB at 5kHz would be moving 0.01mm, with peak accelerations of 15000m/s/s, requiring 4500N of force (992lb). To produce that force, you'll need to put around 60KW in there and hope it survives.

A 4.5" driver producing 121dB at 5kHz needs to move 0.07mm one-way, requiring a larger acceleration of 77,000m/s/s. The moving mass is about 3g, though, so you only need 231N of force to get it there. That particular driver would need around 5KW input power to manage that, which it won't survive. Dropping the moving mass further (thin titanium diaphragms) and bolting a horn on the front would improve efficiency and reduce the power requirements, though.


Edit - couple of people have posted while I typed that.
Free-air resonance is not more important than the size of the driver. Resonance (Fs), among a bunch of other parameters, will help determine the shape of the response of the driver in a given cabinet. The size and linear excursion, and thermal power handling of the driver will tell you how loud it can go.

Chris

Chris that's not what I said, and by omitting the first three words of my sentence, you are taking my statement out of context.
 I said (and did not edit) "For sub frequencies..." meaning relative to, and did not say that it is just "more important".

I also did mention low wattage handling for the mentioned  example size.
As an example, you can have a perfect 1" subwoofer on a headphone. Obviously many other TS parameters are relevant, as I also mentioned in the same post.

The reason I mentioned that particular example, is because, as you probably know, too many people get hung up on the  12" or 15" versus, for example, a 21", and automatically think bigger is better.

Of course there are many other factors that dictate which subwoofer is better suited for a determined enclosure, a determined SPL, and a determined frequency range.



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Title: Re: 21" subwoofers - opinions
Post by: Chris Grimshaw on February 25, 2017, 08:11:29 am
Chris that's not what I said, and by omitting the first three words of my sentence, you are taking my statement out of context.
 I said (and did not edit) "For sub frequencies..." meaning relative to, and did not say that it is just "more important".


Sorry John, looks like I misinterpretted you. Thanks for clearing that up.
I find the amount of misinformation around with speakers in general quite frustrating, which is probably why I jumped on your post.

Chris
Title: 21" subwoofers - opinions
Post by: John Ferreira on February 25, 2017, 01:41:22 pm
Sorry John, looks like I misinterpretted you. Thanks for clearing that up.
I find the amount of misinformation around with speakers in general quite frustrating, which is probably why I jumped on your post.

Chris

No problem Chris.

Your analogy about the accelerating car to 30mph and the extra 2 passengers relate to two parameters (there are a few more of course) in the power amp itself:

One is Slew rate (how fast an amp reaches full power, and usually 100V/microsecond would be typical of higher end amps)

The other is Damping factor, (the ability to stop the speaker cone, or the "breaks" and "torque" in your car analogy, before you put it in reverse and accelerate negatively, a typical example being 800 to 1 at 400Hz).

EDIT: Chris your first link does not work.
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 25, 2017, 02:02:50 pm


One is Slew rate (how fast an amp reaches full power, and usually 100V/microsecond would be typical of higher end amps)

The other is Damping factor, (the ability to stop the speaker cone, or the "breaks" and "torque" in your car analogy, before you put it in reverse and accelerate negatively, a typical example being 800 to 1 at 400Hz).

What I find funny is that one line of amps that has been considered to be "great" has one of the worse slew rates.

The old Crown MA series had a "terrible" slew rate, as compared to others.

Damping factor in amps is also highly over rated.

The "system" has a MUCH larger effect than the amp itself.

Years ago (late 90s) I did some testing (just listening-no measurements) and we had a decent variety of amps by different manufacturers.

The amp that had the highest damping factor (by a good bit) had the "loosest" sound.

The one that had the lowest damping factor stood right up with the highly regarded Crown MA2400.  This amp was also the next to the cheapest one in the test.

Historically, the amps with the best damping factor had the most "controlled" sound-so that was "assumed" to be, because of the damping factor.

The speaker wire and connectors is much bigger factor.

Often the "simple numbers" will result inaccurate assumptions.



Title: 21" subwoofers - opinions
Post by: John Ferreira on February 25, 2017, 02:50:43 pm
What I find funny is that one line of amps that has been considered to be "great" has one of the worse slew rates.

The old Crown MA series had a "terrible" slew rate, as compared to others.

Damping factor in amps is also highly over rated.

The "system" has a MUCH larger effect than the amp itself.

Years ago (late 90s) I did some testing (just listening-no measurements) and we had a decent variety of amps by different manufacturers.

The amp that had the highest damping factor (by a good bit) had the "loosest" sound.

The one that had the lowest damping factor stood right up with the highly regarded Crown MA2400.  This amp was also the next to the cheapest one in the test.

Historically, the amps with the best damping factor had the most "controlled" sound-so that was "assumed" to be, because of the damping factor.

The speaker wire and connectors is much bigger factor.

Often the "simple numbers" will result inaccurate assumptions.

Ivan the Crown MA 2400 had a slew rate of 75V/microsecond, which in the early 90s was not so bad for the price point.  Also the damping factor was a lot higher than, for example, a Bryson 4B (400:1 at 400Hz for the Bryson)

The Slew rate would probably impact latency more than anything else.

However, the higher damping factor made the bass frequencies sound better.

EDIT: The MA 2400 I owned also had PIP cards in the back of the amp, that you could replace and affect the its response. I replaced mine, (PIP) and compared to other amps I tried at the time, was like turning off "reverb" and increase a dry low frequency punch. In 1995 I found that amp sounded way better on Apogee 18" subwoofers, than most other amps I had tried.
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 25, 2017, 03:14:19 pm
Ivan the Crown MA 2400 had a slew rate of 75V/microsecond,
Where are you getting that number from?

The spec sheet says 13v/microsecond.

That is what I was going by
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 25, 2017, 03:17:57 pm

However, the higher damping factor made the bass frequencies sound better.


But as I said in my test, amps that have a much lower damping factor can sound as "tight" and amps with a much higher damping factor can sound looser.

Damping factor is greatly over rated-at least in terms of amplifiers.

It is basically a measurement of the output impedance of the amp relative to the load impedance.

The cable makes a much larger difference in the overall system than the amp itself.
Title: 21" subwoofers - opinions
Post by: John Ferreira on February 25, 2017, 11:55:08 pm
But as I said in my test, amps that have a much lower damping factor can sound as "tight" and amps with a much higher damping factor can sound looser.

Damping factor is greatly over rated-at least in terms of amplifiers.

It is basically a measurement of the output impedance of the amp relative to the load impedance.

The cable makes a much larger difference in the overall system than the amp itself.

Ivan you are correct, at least on line they are rated at more than 30V/microsecond , and some models at 13V/microsecond. I had all my gear stolen in 1997, and I could swear that is what the manual said. I suspect dementia.

But to use your words, "it depends" :()

I don't know how you tested the amps, but remember that when you bridge an amp, damping factor goes to 1/2 value, and also at what frequency was the number obtained.
Damping factor values at 400Hz should not be compared to a 40Hz measurements, where the cone movement has a much lower inertia, and  it is so much easier to apply the "breaks"  (damping factor) before the cone reverses direction. But then again, you already know all that.
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 26, 2017, 09:27:31 am
Ivan you are correct, at least on line they are rated at more than 30V/microsecond , and some models at 13V/microsecond. I had all my gear stolen in 1997, and I could swear that is what the manual said. I suspect dementia.

But to use your words, "it depends" :()

I don't know how you tested the amps, but remember that when you bridge an amp, damping factor goes to 1/2 value, and also at what frequency was the number obtained.
Damping factor values at 400Hz should not be compared to a 40Hz measurements, where the cone movement has a much lower inertia, and  it is so much easier to apply the "breaks"  (damping factor) before the cone reverses direction. But then again, you already know all that.
I remember "Back in the day" that Crown was ridiculed for having such a low slew rate.

But it did  not hurt the popularity-nobody seemed to notice.

All of my tests were done single channel.

Agreed the damping factor goes in half when bridged.

That is because the output channels are in series with each other-so the "total loop resistance" is doubled-at least for the amplifier part.
Title: Re: 21" subwoofers - opinions
Post by: John Ferreira on February 26, 2017, 02:04:19 pm
I remember "Back in the day" that Crown was ridiculed for having such a low slew rate.

But it did  not hurt the popularity-nobody seemed to notice.

All of my tests were done single channel.

Agreed the damping factor goes in half when bridged.

That is because the output channels are in series with each other-so the "total loop resistance" is doubled-at least for the amplifier part.

Technically, impedance and not just resistance.
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 26, 2017, 02:13:36 pm
Technically, impedance and not just resistance.
I would "argue" that the output stage of an amp is probably much more resistive than inductive or capacitive. 

But I have to admit, I have never measure the phase of the output "impedance" of an amp, which would tell if it had an "impedance character".

So I could be wrong.

But I guess if the phase was even a couple of degrees off, it would be considered impedance.
Title: 21" subwoofers - opinions
Post by: John Ferreira on February 26, 2017, 08:51:19 pm
I would "argue" that the output stage of an amp is probably much more resistive than inductive or capacitive. 

But I have to admit, I have never measure the phase of the output "impedance" of an amp, which would tell if it had an "impedance character".

So I could be wrong.

But I guess if the phase was even a couple of degrees off, it would be considered impedance.

Yes, but you love the correct numbers (   :)   ) and the amp "sees" an inductive reactive load, like a dancing moving target, and frequency dependent, plus the physical coil resistance. Since you love accuracy, when  you have inductive reaction plus resistance, it's then called impedance. But feel free to correct me.
Title: Re: 21" subwoofers - opinions
Post by: Ivan Beaver on February 26, 2017, 08:57:01 pm
Yes, but you love the correct numbers (   :)   ) and the amp "sees" an inductive reactive load, like a dancing moving target, and frequency dependent. Since you love accuracy, when  you have inductive reaction plus resistance, it's then called impedance. But feel free to correct me.
Yes-it depends on how things are "defined"

Since resistance is "basically" described as the opposition of flow to DC, and impedance is described as the opposition of flow to AC, then I "guess" it could be described as impedance-even if there is no reactive component in the actual value.

I am certainly not an expert in that specific regard, so could easily be wrong and would welcome correction.
Title: 21" subwoofers - opinions
Post by: John Ferreira on February 27, 2017, 09:16:55 am
Lol! I've read here how you love the words "it depends".
I am not an expert either, and my electronics courses are ancient from 1984. I'm still learning everyday, and specially from people like you.

Like I said, I was just being technical (and picky)
Just trying to stay in context, since we are talking mostly about sound and the effect of the damping factor on bass response, we are in the realm of AC.

Your statement about DC not being affected by impedance, again, "technically", if you have a variable DC, impedance will very much be a factor.
Title: Re: 21" subwoofers - opinions
Post by: Jay Barracato on February 28, 2017, 04:42:04 pm
My truck has a 4.11 to 1 rear differential. Can you tell me what performance I can expect?

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Title: Re: 21" subwoofers - opinions
Post by: Tim McCulloch on February 28, 2017, 07:45:59 pm
My truck has a 4.11 to 1 rear differential. Can you tell me what performance I can expect?

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With how may wheels at a time, and will red paint make my truck into a sports car?  You don't want to leave out anything, Jay!
Title: 21" subwoofers - opinions
Post by: John Ferreira on March 01, 2017, 09:33:36 am
My truck has a 4.11 to 1 rear differential. Can you tell me what performance I can expect?

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Again it depends how much you weigh, and bigger is not better.
Title: Re: 21" subwoofers - opinions
Post by: Teddy Murphy on March 04, 2017, 09:44:18 am
Message me if you have any questions.  I own 4 618xlf and 8 of the 1521s as well as 8 s30. I have used them all for different applications. 
Title: Re: 21" subwoofers - opinions
Post by: Trevor Jalla on March 04, 2017, 12:50:24 pm
Message me if you have any questions.  I own 4 618xlf and 8 of the 1521s as well as 8 s30. I have used them all for different applications.

I wish I had what you did. Message sent, thank you Teddy.