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Author Topic: Ideas for Subwoofer Upgrade  (Read 16883 times)

John Chiara

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Re: Ideas for Subwoofer Upgrade
« Reply #30 on: March 02, 2017, 08:31:12 PM »

Has anyone compared the TH118 and the PG118?
Cost difference?
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Ivan Beaver

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Re: Ideas for Subwoofer Upgrade
« Reply #31 on: March 02, 2017, 08:48:33 PM »

Has anyone compared the TH118 and the PG118?
Cost difference?
I have no idea on price-but you know that.

The PG118 goes a good bit lower than the TH118.

At 30Hz it is 3dB louder (due to the longer horn path).

Above 35Hz, they are essentially the same.

The PG118 also has the Sentinel thermal protection built in, the TH118 does not.

The PG118 has a lot more handles than the TH118.

It is also orange-but can be ordered in any color.
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Ivan Beaver
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Ivan Beaver

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Re: Ideas for Subwoofer Upgrade
« Reply #32 on: March 02, 2017, 08:59:57 PM »


Edit: Whenever you double speakers, you add 3db. So 2 LS1208's would be 139db, 4 would be 142db, 8 would be 145db. So on and so forth down the line.
No.

For a limited number of cabinets at a specific distance, you will gain 6dB (not 3) every time you double the number of cabinets and double the power.

This works for a little while.

But as you start to add more speakers, since the cannot occupy the same space, you start to run into "problems".

One of them is the fact that the cabinets start to be further away than the ones you started with.  So the outside ones contribute less and less to the total output.

The next problem is also due the cabinets being further away.
You start to get combfiltering (two or more signals arriving at a single location at different times), which is notches in the response-ie cancellations.

You will get a little bit of addition (when the signals are the same level-which would not happen because the ones with the late signals are further away and lower in level), and deep cancellation.

You will get maximum cancellation when the levels are equal, but once again-the levels will not be equal.

It is for these very reasons that louder single subs are often a better solution than trying to pile up-or spread out- multiple quieter subs.

The exact same thing happens with full range line array boxes-just at different freq.

You do NOT get the summation that you "think" you should.

That cancellation is also what give the line array some of its pattern.

If you ever line up (space out) a number of subs and then walk the pattern, you will find that just after you get to the end-the bass drops off dramatically-especially outside or in a very large room.

This may be good or bad-depending on what you are trying to accomplish at the particular stage.

If you are trying to keep the bass energy off of another stage in a festival or away from the food vendors-this is a very good thing.

But if people are seated/standing off to the side-this is a very BAD thing.

So-once again-it depends.
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Ivan Beaver
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Jake R. Trutt

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Re: Ideas for Subwoofer Upgrade
« Reply #33 on: March 02, 2017, 09:32:10 PM »

No.

For a limited number of cabinets at a specific distance, you will gain 6dB (not 3) every time you double the number of cabinets and double the power.

Interesting. Initially I left it off because I'm not that great with the math for coupling and such. I know the single SPL numbers are accurate because they were tested as such. I don't know exact physics behind multiple cabinets but I found this and used it: http://myhometheater.homestead.com/splcalculator.html

Seems as though their calc is off. I also did the calc to disregard placement and in 1/2 space. It showed the same results. Although there might be a disparity between doubling power and speakers that I did not account for in the calc (I assumed it would correct it and give the same wattage to all the speakers). By your statement, that means that 4 LS1208's should beat out a DBH218 then. I know about the rest you are referring to, there is also cardioid to direct the bass energy as well.

Edit: I have adjusted my statement and removed the numbers for multiple cabs.
« Last Edit: March 02, 2017, 09:38:52 PM by ianzchurchill »
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Ivan Beaver

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Re: Ideas for Subwoofer Upgrade
« Reply #34 on: March 03, 2017, 07:47:54 AM »

Interesting. Initially I left it off because I'm not that great with the math for coupling and such. I know the single SPL numbers are accurate because they were tested as such. I don't know exact physics behind multiple cabinets but I found this and used it: http://myhometheater.homestead.com/splcalculator.html

Seems as though their calc is off. I also did the calc to disregard placement and in 1/2 space. It showed the same results. Although there might be a disparity between doubling power and speakers that I did not account for in the calc (I assumed it would correct it and give the same wattage to all the speakers). By your statement, that means that 4 LS1208's should beat out a DBH218 then. I know about the rest you are referring to, there is also cardioid to direct the bass energy as well.

Edit: I have adjusted my statement and removed the numbers for multiple cabs.
I have measured many subwoofers.  Typically they all get a 6dB increase in output (up to a certain physical size).

Some will actually get a little bit more.  This is due to additional forward directivity.  Not all or even most do this, but some do.

You CANNOT compare "simple numbers".

Unless you are comparing MEASURED freq responses, the SPL numbers could be way off.

Is the "SPL number" an average of the response within the intended freq range?

Or is it a Peak in the response?  I have seen QUITE A FEW spec sheets that state a Peak SPL and it is a very small freq range-often completely out of the range where the speaker would be used, but it does give a high number that some people like to use.

I have seen a 2x18" sub from a very respected manufacturer that state a "peak SPL" that they also showed on the spec sheet of the measured response, that was around 1,800Hz.

I don't know many people that run their subs up to 1800 Hz.

The spec is not lying-it WILL produce that peak.  It is just not usable.

I know a number of other subs that have a large peak between 100 and 200Hz.  So it gives a "big number", but is worthless when you are trying to see how loud it will get at 35Hz.

So unless you KNOW where the numbers come from (like a measured response) you have no idea if the number is valid or not.

So simply trying to compare peak SPL to peak SPL will often result in a complete misunderstanding of the actual performance.  Especially in the freq range of interest.

You have to compare apples to apples.
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Ivan Beaver
Danley Sound Labs

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Ivan Beaver

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Re: Ideas for Subwoofer Upgrade
« Reply #35 on: March 03, 2017, 07:53:12 AM »

there is also cardioid to direct the bass energy as well.


This is another misunderstanding.

I know a number of people think that cardioid is better because it is more "focused".

The "idea" is that the energy from the rear is "turned around" and "focused" forward so it is louder out front.

This is COMPLETELY FALSE.

In any directional setup, there is LESS energy out front-than the same number of cabinets all facing forward.

The loss of energy in the rear is a result of CANCELLATION-Not addition.

Cardioid also does not have as much punch or impact, because the higher freq of the bass region are actually REDUCED-due to the cancellation action.

I have measured this multiple times with different sub manufacturers and the results are the same.

I only do cardioid in very specific applications in which the rear rejection is more important than the sonic character out front.

I avoid it if possible.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

John Halliburton

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Re: Ideas for Subwoofer Upgrade
« Reply #36 on: March 03, 2017, 10:16:28 AM »

Oh I did!  I just like to poke around in here.  Been here a long time!  There's a lot of very smart folks in this particular forum, so pay close attention to what they say.  You'd be surprised who all has been here over the years!!  I have had the priviledge to have Tom Danley, Dave Guiness, Ken, Dave Rat, Tim, Bennett and a bunch of other very experienced folks chime in on posts.  This is probably the greatest live sound forum around!

It's usually Gunness, but for the next couple of weeks I'm sure this spelling would be acceptable to Dave.  ;)

Best regards,

John
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Terry Fryar

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Re: Ideas for Subwoofer Upgrade
« Reply #37 on: March 03, 2017, 10:43:58 AM »

Lol!  Mea culpa!

It's usually Gunness, but for the next couple of weeks I'm sure this spelling would be acceptable to Dave.  ;)

Best regards,

John
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Aaron Carian

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Re: Ideas for Subwoofer Upgrade
« Reply #38 on: March 03, 2017, 11:25:36 AM »

No.

For a limited number of cabinets at a specific distance, you will gain 6dB (not 3) every time you double the number of cabinets and double the power.

This works for a little while.

But as you start to add more speakers, since the cannot occupy the same space, you start to run into "problems".

One of them is the fact that the cabinets start to be further away than the ones you started with.  So the outside ones contribute less and less to the total output.

The next problem is also due the cabinets being further away.
You start to get combfiltering (two or more signals arriving at a single location at different times), which is notches in the response-ie cancellations.

You will get a little bit of addition (when the signals are the same level-which would not happen because the ones with the late signals are further away and lower in level), and deep cancellation.

You will get maximum cancellation when the levels are equal, but once again-the levels will not be equal.

It is for these very reasons that louder single subs are often a better solution than trying to pile up-or spread out- multiple quieter subs.

The exact same thing happens with full range line array boxes-just at different freq.

You do NOT get the summation that you "think" you should.

That cancellation is also what give the line array some of its pattern.

If you ever line up (space out) a number of subs and then walk the pattern, you will find that just after you get to the end-the bass drops off dramatically-especially outside or in a very large room.

This may be good or bad-depending on what you are trying to accomplish at the particular stage.

If you are trying to keep the bass energy off of another stage in a festival or away from the food vendors-this is a very good thing.

But if people are seated/standing off to the side-this is a very BAD thing.

So-once again-it depends.

Considering my specific situation, if I were looking at 8 TH118s vs 4 DBH218s clustered in the center in front of a stage outdoors, based on height limitations I would either have 90" wide x 45" tall cluster of DBH218 or 180" wide by 40" tall line of TH118s.  Since the 8 TH118s have an overall length approaching 1 wavelength at 60Hz I believe there would be substantial directivity at the "higher" frequencies near the crossover point and would require some beamforming if I desired wider coverage.  However, since the 4 DBH218 would be a much shorter cluster in the horizontal direction, I would obtain more even coverage at the sides without having to use delay that could impact the frequency response for some areas.  Also, it appears I would get 5-10dB more of output below 35Hz with 4 DBH218s clustered.  So, if I can deal with the weight and size of the DBH218 and am willing to compromise on not being able to as easily bring it indoors or up a flight of stairs then from a purely performance standpoint is that not the best solution?  Am I missing any other "it depends" factors?
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Ivan Beaver

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Re: Ideas for Subwoofer Upgrade
« Reply #39 on: March 03, 2017, 01:01:43 PM »

Considering my specific situation, if I were looking at 8 TH118s vs 4 DBH218s clustered in the center in front of a stage outdoors, based on height limitations I would either have 90" wide x 45" tall cluster of DBH218 or 180" wide by 40" tall line of TH118s.  Since the 8 TH118s have an overall length approaching 1 wavelength at 60Hz I believe there would be substantial directivity at the "higher" frequencies near the crossover point and would require some beamforming if I desired wider coverage.  However, since the 4 DBH218 would be a much shorter cluster in the horizontal direction, I would obtain more even coverage at the sides without having to use delay that could impact the frequency response for some areas.  Also, it appears I would get 5-10dB more of output below 35Hz with 4 DBH218s clustered.  So, if I can deal with the weight and size of the DBH218 and am willing to compromise on not being able to as easily bring it indoors or up a flight of stairs then from a purely performance standpoint is that not the best solution?  Am I missing any other "it depends" factors?
It looks like you are "right on track".

One of the biggest reasons to choose the TH118s is the ease of portability-especially when getting them up stairs (as compared with the DBH218).

I think (I am not sure) that the DBH218 is less expensive than 2 of the TH118s.

1 person can easily stack up a couple of TH118s.  Not so easy with the DBH218s.

The biggest drawback to the DBH218s is the size/portability for some people.  For others it is fine.

You are correct that having more output from a physically smaller setup will give a wider coverage.

In some rooms the DBH218 would simply be to large-specifically depth wise.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

ProSoundWeb Community

Re: Ideas for Subwoofer Upgrade
« Reply #39 on: March 03, 2017, 01:01:43 PM »


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