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Author Topic: Under Stage Sub Advice  (Read 11241 times)

Rufus G. Crowder

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Under Stage Sub Advice
« on: November 27, 2011, 09:31:54 pm »

Looking for options, choices, and MSRP pricing on small subs to potentially be placed under a 21" stage in an approx. 90' W x 60' D room.  Some I have looked at are the Danley THMinis and the JBL VRX918S.  Is it possible to obtain similar performance of a couple of Danley TH118's or other dual 18 boxes by using multiples of any small sub that would fit under this stage?

I am checking to see if the ceiling deck would support flying a system that I could use flown subs also.
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Ivan Beaver

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Re: Under Stage Sub Advice
« Reply #1 on: November 27, 2011, 09:44:46 pm »

Looking for options, choices, and MSRP pricing on small subs to potentially be placed under a 21" stage in an approx. 90' W x 60' D room.  Some I have looked at are the Danley THMinis and the JBL VRX918S.  Is it possible to obtain similar performance of a couple of Danley TH118's or other dual 18 boxes by using multiples of any small sub that would fit under this stage?

I am checking to see if the ceiling deck would support flying a system that I could use flown subs also.
Is the 21" your actual clearance or the top of the stage?   Do you have any width or depth limitations?

Remember that it is a GOOD idea to fully enclose an under stage sub with double wall sheetrock (at a minimum) on all sides except the front and bottom.  So you are going to lose another 1.5" on the height.  Just something else to consider.

There are a number of various subs available, but there is always a tradeoff.  As you go lower, (for a given size) typically you lose sensitivity.

You say that you are looking for the performance of a couple of Danley TH118's.  Are you looking to match all the performance (low freq extension-max power output etc)?  Or would something that didn't go as low, but was as loud do the job for you?

It is important to accurately define the needs/expectations/limitations of a result, then look towards that end.

In the Danley line, the TH212 is a good "middle" between the TH118 and the THmini and would fit into the space.
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Ivan Beaver
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Rufus G. Crowder

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Re: Under Stage Sub Advice
« Reply #2 on: November 28, 2011, 12:32:32 am »

Is the 21" your actual clearance or the top of the stage?   Do you have any width or depth limitations?

Remember that it is a GOOD idea to fully enclose an under stage sub with double wall sheetrock (at a minimum) on all sides except the front and bottom.  So you are going to lose another 1.5" on the height.  Just something else to consider.

There are a number of various subs available, but there is always a tradeoff.  As you go lower, (for a given size) typically you lose sensitivity.

You say that you are looking for the performance of a couple of Danley TH118's.  Are you looking to match all the performance (low freq extension-max power output etc)?  Or would something that didn't go as low, but was as loud do the job for you?

It is important to accurately define the needs/expectations/limitations of a result, then look towards that end.

In the Danley line, the TH212 is a good "middle" between the TH118 and the THmini and would fit into the space.
21" is the top of the stage and is max height due to space restrictions of a drop down projection screen.  We wanted to use 28" but just cannot make it work.  I am currently using two JBL SR4719X dual 18's (30 inches laid on their sides) in a school commons environment and they are ok.  Was considering their 728's as they were 24" laid on their sides but they will not fit either.

I do understand the tradeoffs as I stopped packing around my dual 18's and went to some smaller singles and I really miss them but they were not practical for the rooms I was playing.  I suppose something not as low but was as loud would suffice.  Looking for some quality low end (contemporary Christian rock music).
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Ivan Beaver

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Re: Under Stage Sub Advice
« Reply #3 on: November 28, 2011, 09:21:17 am »

21" is the top of the stage and is max height due to space restrictions of a drop down projection screen.  We wanted to use 28" but just cannot make it work.  I am currently using two JBL SR4719X dual 18's (30 inches laid on their sides) in a school commons environment and they are ok.  Was considering their 728's as they were 24" laid on their sides but they will not fit either.

I do understand the tradeoffs as I stopped packing around my dual 18's and went to some smaller singles and I really miss them but they were not practical for the rooms I was playing.  I suppose something not as low but was as loud would suffice.  Looking for some quality low end (contemporary Christian rock music).
But we still don't know the height you have available.  Is the stage single layer or double layer construction?  Is it using 2x4 or 2x6 or other joist sizes?

Without knowing that height (and don't forget to subtract cavity lining) it is hard to start to search for a sub that will fit.
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Brad Weber

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Re: Under Stage Sub Advice
« Reply #4 on: November 28, 2011, 03:25:55 pm »

21" is the top of the stage and is max height due to space restrictions of a drop down projection screen.  We wanted to use 28" but just cannot make it work.
A typical stage construction might be something such as 3/4" hardwood on 3/4" plywood on 2x6 joists with 2x4 top and base plates for the face which would thus leave about 11" of open height at the front.  I've also seen stages that were raised slabs and other than a built up front facade and the floor construction itself there was no accessible space under the stage.  That is why it is important to know what clear height and depth is actually available and not to go by the overall stage height.

Also, the stage front and area under the stage is sometimes used as a return air path, which makes the area under the stage a plenum space and requires any speakers in that space to be rated for plenum installation or to be installed in rated enclosures.
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Rufus G. Crowder

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Re: Under Stage Sub Advice
« Reply #5 on: November 29, 2011, 12:24:42 am »

But we still don't know the height you have available.  Is the stage single layer or double layer construction?  Is it using 2x4 or 2x6 or other joist sizes?

Without knowing that height (and don't forget to subtract cavity lining) it is hard to start to search for a sub that will fit.
Ivan,
I was told that we only have 17.5 inches of height to use.  The stage will be double layered.  The width and depth and building an enclosure as you state is not a problem.  Brad, I am checking on your questions, however, I am 99% sure that this will not be used as a plenum space.
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Ivan Beaver

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Re: Under Stage Sub Advice
« Reply #6 on: November 29, 2011, 07:43:21 am »

Ivan,
I was told that we only have 17.5 inches of height to use.  The stage will be double layered.  The width and depth and building an enclosure as you state is not a problem.  Brad, I am checking on your questions, however, I am 99% sure that this will not be used as a plenum space.
So now that we have a height figured out, what about performance?  How low do you really need to go?  How loud do you need to go?  What is the size space (dimensions or seats?  What is the performance type (ie loudest)?  Is there a budget that guides this?

Without parameters, you can get all kinds of answers, that may or may not be related to each other in terms of performance.

With that height, the field gets narrowed down a good bit.
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Ivan Beaver
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Brad Weber

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Re: Under Stage Sub Advice
« Reply #7 on: November 29, 2011, 12:05:10 pm »

I was told that we only have 17.5 inches of height to use.  The stage will be double layered.  The width and depth and building an enclosure as you state is not a problem.
Maybe I'm missing something but you stated earlier it was 21" to the top of the stage floor.  A double layered stage is probably 1" to 1-1/2" thick, so that would leave 19.5" to 20".  If you have 17.5" clear that seems to leave just 2" to 2-1/2" for all of the actual stage structure and framing, which seems very limited.

Also think about the condition at the front of the stage.  Will you have to cut out vertical framing to create a speaker opening and would that require beefing up the header and/or framing to either side?  Do you need a runner or other framing at the bottom of the opening for either structural purposes or to provide a way to attach a grille?

It may sound like making a lot about nothing, but I've been the one in the field trying to figure out how to get subs under a church stage when the sub boxes were bigger than the openings provided apparently as a direct result of such issues not being properly considered.
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g'bye, Dick Rees

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Re: Under Stage Sub Advice
« Reply #8 on: November 29, 2011, 12:30:14 pm »

It may sound like making a lot about nothing, but I've been the one in the field trying to figure out how to get subs under a church stage when the sub boxes were bigger than the openings provided apparently as a direct result of such issues not being properly considered.

Brad..... 

What's the problem???
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Rufus G. Crowder

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Re: Under Stage Sub Advice
« Reply #9 on: November 30, 2011, 01:26:27 am »

Maybe I'm missing something but you stated earlier it was 21" to the top of the stage floor.  A double layered stage is probably 1" to 1-1/2" thick, so that would leave 19.5" to 20".  If you have 17.5" clear that seems to leave just 2" to 2-1/2" for all of the actual stage structure and framing, which seems very limited.

Also think about the condition at the front of the stage.  Will you have to cut out vertical framing to create a speaker opening and would that require beefing up the header and/or framing to either side?  Do you need a runner or other framing at the bottom of the opening for either structural purposes or to provide a way to attach a grille?

It may sound like making a lot about nothing, but I've been the one in the field trying to figure out how to get subs under a church stage when the sub boxes were bigger than the openings provided apparently as a direct result of such issues not being properly considered.

Brad, this is what I was told:
A stage heighth of 21 inches will have a clear space of 19 inches tall.
a stage heighth of 28 inches will have a clear space of 26 inches tall The floor of the stage will be 2 inches thick consisting of 1/2 inch sheetrock or deadening felt sandwiched between 3/4 inch plywood,.plus carpet, approx. 1/4 inch thick.

If I can find the best sub for this application, the stage will be built to accommodate.  The only non-compromise point is the stage height unless it is a minimal upward deviation.  Your observations with the front are spot on and have been discussed.  They are just waiting on me to specify a sub product with actual dimensions.  Definitely not a "win, win" situation here.
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Tim Padrick

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Re: Under Stage Sub Advice
« Reply #10 on: November 30, 2011, 01:45:04 am »

Brad, this is what I was told:
A stage heighth of 21 inches will have a clear space of 19 inches tall.

That would be the available height between the joists.  Under the joists will be at least 7" less.
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Rufus G. Crowder

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Re: Under Stage Sub Advice
« Reply #11 on: November 30, 2011, 01:46:59 am »

So now that we have a height figured out, what about performance?  How low do you really need to go?  How loud do you need to go?  What is the size space (dimensions or seats?  What is the performance type (ie loudest)?  Is there a budget that guides this?

Without parameters, you can get all kinds of answers, that may or may not be related to each other in terms of performance.

With that height, the field gets narrowed down a good bit.

Regarding performance, I can only state that my personal gear used that I mentioned before (JBL SR4719X's and SR4733X's) is ok but of course does not have the coverage (loud in front and drops off after about 30 feet) in a school commons environment.  I am certain that we exceed 100dB at about 40 feet easily but no one complains!  The new room is slated to contain about 300-350 seats.  All funding now is designated to the facility and $0 for sound reinforcement.  A future capital drive will fund the main system later.  The ceiling area will be addressed to support a LCR hang unless there is a system that can provide the proper coverage with just LR.  I am sure that we can use donated funds for the subs as soon as a decision is reached. 
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Ivan Beaver

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Re: Under Stage Sub Advice
« Reply #12 on: November 30, 2011, 08:10:59 am »

Regarding performance, I can only state that my personal gear used that I mentioned before (JBL SR4719X's and SR4733X's) is ok but of course does not have the coverage (loud in front and drops off after about 30 feet) in a school commons environment.  I am certain that we exceed 100dB at about 40 feet easily but no one complains!  The new room is slated to contain about 300-350 seats.  All funding now is designated to the facility and $0 for sound reinforcement.  A future capital drive will fund the main system later.  The ceiling area will be addressed to support a LCR hang unless there is a system that can provide the proper coverage with just LR.  I am sure that we can use donated funds for the subs as soon as a decision is reached.
Well if yo uput the subs under the stage, you are going to have exactly the same problem you have now.   Loud in front and quieter in the rear.  NO way around that. No mater what speakers you choose.

If you want more even coverage, then you will have to fly the subs-and now the conversation takes on a whole new set of parameters.

Changing the subject, if you look at a LR situation, then you have to consider what will happen right down the middle of the room.  Unless you do panning on every instrument or are seated directly in the middle of the LR, you will all kinds of interference.  OF course once you start to pan various channels, it will sound different on each side of the room.

For a low budget situation, you are MUCH better off to start with a center cluster and have fills as needs to the sides (NOT as a left /right speaker) but as fills pointed down and out from the main cluster.

Since you have no budget, you need to determine what is most important to you-loud or low?  I would argue that in most cases if you have subs that are actually flat to 40Hz (not 10db down-flat) you will be Ok.  If somebody wants deeper bass-ask them to pay for it.

I know it seems like petty things, but the arguments about stage height are VERY relivant.  It sounds like you are being told very different things regarding the ACTUAL AVAILABLE HEIGHT for a large speaker cabinet.

I can say without a doubt that the person who told you 19" on a 21" stage is completely wrong-there is no way you could put a cabinet under there-without the stage either falling or sagging when somebody walks on it.  The span is simply to long.  They were not taking into account the joists (which is what Brad and I have been trying to point out).

Those are VERY real and VERY much in the way and HAVE to be accounted for.
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Ivan Beaver
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Ivan Beaver

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Re: Under Stage Sub Advice
« Reply #13 on: November 30, 2011, 08:20:37 am »


If I can find the best sub for this application, the stage will be built to accommodate.  The only non-compromise point is the stage height unless it is a minimal upward deviation.  Your observations with the front are spot on and have been discussed.  They are just waiting on me to specify a sub product with actual dimensions.  Definitely not a "win, win" situation here.
In order to "find the best sub" you FIRST have to define what is "best".  Actual numbers-like SPL (be sure to conside what the number is A or C weighted-fast or slow or peak response-headroom etc)-freq response-room dimensions etc can go a long way towards defining this

Once you have those numbers (oh and don't forget budget-which may you biggest factor), THEN you can start to look for subs that will fit into the available space.

Other than that-you are just guessing and taking advice from people who have no real idea what your real needs are.

And then the other questions come up-like-is the whole front of the stage available to put the subs?  or are there steps in the middle?  How big/wide are the steps?  Are there any limitation on the width of where the subs can go? and so forth.

These are all things that HAVE to be considered if you want ot actually design something.  If you just want something that fits into a hole, without any regard as to whether or not it will have the desired performance, then put whatever in.  But don't come back and say it doesn't work well.

I know all this requires effort on  your part-and there are no simple answers.  But Brad and I DESIGN systems for specific uses, we  don't just throw stuff in a room and call it good.

I'm not trying to be ugly or anything-just trying to get you to think about the reality of this and what some of the problems may be-ahead of time.
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Mac Kerr

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Re: Under Stage Sub Advice
« Reply #14 on: November 30, 2011, 03:16:04 pm »

Brad, this is what I was told:
A stage heighth of 21 inches will have a clear space of 19 inches tall.
a stage heighth of 28 inches will have a clear space of 26 inches tall The floor of the stage will be 2 inches thick consisting of 1/2 inch sheetrock or deadening felt sandwiched between 3/4 inch plywood,.plus carpet, approx. 1/4 inch thick.

If I can find the best sub for this application, the stage will be built to accommodate.  The only non-compromise point is the stage height unless it is a minimal upward deviation.  Your observations with the front are spot on and have been discussed.  They are just waiting on me to specify a sub product with actual dimensions.  Definitely not a "win, win" situation here.

Were you told that by the builder? The Architect? I see no mention of the support structure that will hold up that floor. Maybe they got an advance copy of that new levitator, but all the stage floors I've seen have a structure of 2x4 or 2x6 on 16" or 24" centers construction underneath.

Mac
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Re: Under Stage Sub Advice
« Reply #14 on: November 30, 2011, 03:16:04 pm »


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