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Author Topic: subwoofer position - opinions  (Read 3405 times)

Robert Weston

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subwoofer position - opinions
« on: April 25, 2011, 11:25:04 am »

Provided sound for band last weekend.  Subs are 2 x SRX728 – each powered with their own PLX-3602 (bridged).  Everything sounded great, plenty of “chest-slamming” kick and toms.  Received complements on sound quality and the "feel" of the music.  Subs were positioned about 2” above the ground (sitting on 2 x 4”s) horizontally (dirt floor – no pavement, asphalt, etc…) and spaced about 13’ apart (center of sub to next center of sub) directly in front of a 4’ raised stage.  No rear solid surface behind the subs.

Here’s my question – could the subs perform better (in an audio physics way) if they were elevated say 12” off the ground?  Maybe 18” off the ground?  I’m aware of the ¼ wave cancellations, which is why I usually keep the subs close to the ground; however, could I be missing out on a few db increase in “perceived” output by not raising the speakers?  Does a dirt floor (i.e. ground) work the same way in ¼ wave cancellations as solid surfaces do? 

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Art Welter

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Re: subwoofer position - opinions
« Reply #1 on: April 25, 2011, 12:34:33 pm »

Provided sound for band last weekend.  Subs are 2 x SRX728 – each powered with their own PLX-3602 (bridged).  Everything sounded great, plenty of “chest-slamming” kick and toms.  Received complements on sound quality and the "feel" of the music.  Subs were positioned about 2” above the ground (sitting on 2 x 4”s) horizontally (dirt floor – no pavement, asphalt, etc…) and spaced about 13’ apart (center of sub to next center of sub) directly in front of a 4’ raised stage.  No rear solid surface behind the subs.

Here’s my question – could the subs perform better (in an audio physics way) if they were elevated say 12” off the ground?  Maybe 18” off the ground?  I’m aware of the ¼ wave cancellations, which is why I usually keep the subs close to the ground; however, could I be missing out on a few db increase in “perceived” output by not raising the speakers?  Does a dirt floor (i.e. ground) work the same way in ¼ wave cancellations as solid surfaces do?
A dirt floor is basically the same as a concrete floor on dirt regarding low frequencies, it is solid.
Dirt is far more solid than a suspended concrete or wood floor.
Other than temperature gradient effects, there is little difference between sand, dirt, concrete or asphalt regarding low frequencies. Temperature gradient effects are more prevalent at higher frequencies.

Raising the subs off the ground does result in a cancellation above the subs, so the reverberant field is driven a bit less hard at whatever the distance related cancellation frequency turns out to be.

There will be virtually no difference out front raising the subs in the small increments you are speaking of, though raising the subs can decouple them from a resonant surface like a wood floor, giving less of a "foot massage".

If you continue using the PLX-3602 bridged mono with a four ohm load (equivalent of 2 ohm stereo) for sub use, I'd suggest an outboard fan.

Art Welter
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Tim McCulloch

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Re: subwoofer position - opinions
« Reply #2 on: April 25, 2011, 12:35:20 pm »

Here’s my question – could the subs perform better (in an audio physics way) if they were elevated say 12” off the ground?  Maybe 18” off the ground?  I’m aware of the ¼ wave cancellations, which is why I usually keep the subs close to the ground; however, could I be missing out on a few db increase in “perceived” output by not raising the speakers?  Does a dirt floor (i.e. ground) work the same way in ¼ wave cancellations as solid surfaces do?

No, and no.
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Robert Weston

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Re: subwoofer position - opinions
« Reply #3 on: April 25, 2011, 01:59:36 pm »

Thanks for the replies.  I'll keep the subs "on the ground"; there was certainly some "foot massages" taking place from them.  And thanks to Meyer Sound for the use of their MAPP Online program; moving the subs in closer certainly helps with the bass.

The cooling issue you brought up has been mentioned before (I think from the older forum).  The amps (all of them) were running fairly warm; though, it was about 80 degrees outside with 70% humidity (no direct sunlight on the amps); so I guess some heat can be expeced.

Speaking of cooling, (Bob Lee are you lurking...?) is there anything like an upgrade for the cooling fan of a 3602?  Maybe there's not enough air flow over the fins.


Maybe a fan cliped to the back of the case and angled to the air intake of the amp will help.

Thanks.


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Steve Ferreira

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Re: subwoofer position - opinions
« Reply #4 on: April 25, 2011, 11:27:24 pm »

MAPP Online is for use with the Meyer gear.

I'm sure those amps get toasty warm..........

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Randall Hyde

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Re: subwoofer position - opinions
« Reply #5 on: April 28, 2011, 04:57:16 pm »

Provided sound for band last weekend.  Subs are 2 x SRX728 – each powered with their own PLX-3602 (bridged).  Everything sounded great, plenty of “chest-slamming” kick and toms.  Received complements on sound quality and the "feel" of the music.  Subs were positioned about 2” above the ground (sitting on 2 x 4”s) horizontally (dirt floor – no pavement, asphalt, etc…) and spaced about 13’ apart (center of sub to next center of sub) directly in front of a 4’ raised stage.  No rear solid surface behind the subs.
Maybe try shoving the subs together next time? I have four of them. I'd stack them 2x2 or 4x1 in front of the center of the stage if I could get away with it (2x1 in your case). If I had six and enough room in front of the stage, I'd even do a cardiod arrangement.  Alas, you can't always put the subs directly in front of the stage; in that situation, I'd suggest sticking both of your subs on one side of the stage (try these configurations out with MAPP or GPA).

Quote
Here’s my question – could the subs perform better (in an audio physics way) if they were elevated say 12” off the ground?  Maybe 18” off the ground?  I’m aware of the ¼ wave cancellations, which is why I usually keep the subs close to the ground; however, could I be missing out on a few db increase in “perceived” output by not raising the speakers?  Does a dirt floor (i.e. ground) work the same way in ¼ wave cancellations as solid surfaces do?

You will get cleaner sound if the subs are flown (but don't do this with 728s subs). Otherwise, keep them on the floor. You'll benefit from coupling (+3dB/+6dB) if you stick them together.

BTW, I used to run my 728s cabs off some  bridged XTi 4000 amps (roughly equivalent to your setup). Lit up the red clip LEDs every time the kick was hit. Bought some ITech-8000 amps (one 728s per channel). Amazing difference. Bigger amps should be your next upgrade. You should be providing at least 4000 amps continuous per cabinet; those cabs soak up a lot of power; fear not, they handle 6400 watts peak and they have damn good drivers in them. Lots of headroom is a good thing.
Cheers,
Randy Hyde
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Robert Weston

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Re: subwoofer position - opinions
« Reply #6 on: April 28, 2011, 09:42:39 pm »

Thanks for the info Randy.  Actually, I tried the 728's placed together and didn't notice too much of a difference in output (relatively speaking).  In fact the MAPP software shows minimal difference between one and two cabinets (using similar cabinets in MAPP compared with the 728s).  I placed the 728's apart based on what MAPP showed.  The spacing between the cabinets made a big difference.  I didn't need to run them as hard as I normally do when the cabinets are spaced anywhere from 20 to 35 feet apart.

Very true there are times when the subs can't sit in front of the stage area, though, I will always promote it.  A couple of ITech-8K would be nice, but the QSC's are doing fine.  From a wattage perspective, there's not really much of a difference between 3500 watts and 4000 watts. 

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Walter W Wright

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Re: subwoofer position - opinions
« Reply #7 on: April 28, 2011, 11:13:29 pm »

...spaced about 13’ apart (center of sub to next center of sub)...
what a vague way of describing it  ??? how much distance was there between the edge of one and the edge of the next?
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Robert Weston

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Re: subwoofer position - opinions
« Reply #8 on: April 29, 2011, 07:03:59 am »

what a vague way of describing it  ??? how much distance was there between the edge of one and the edge of the next?

The "center" was from the physical center of the cabinet to the next.  Therefore, the inside edge measurement between the cabinets would be less.  I didn't use a measuring tape... a 2 x 4 x 8 piece of lumber was "onsite" which was used to provide some rough measurements.
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luis Markson

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Re: subwoofer position - opinions
« Reply #9 on: April 29, 2011, 10:46:36 pm »

(try these configurations out with MAPP or GPA).

Cheers,
Randy Hyde

May I ask what GPA is?
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Re: subwoofer position - opinions
« Reply #9 on: April 29, 2011, 10:46:36 pm »


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