Couple plate and front firing

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Droogne
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Couple plate and front firing

#1 Post by Droogne » Fri Jun 21, 2019 2:28 pm

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Hey

I just read through the subwoofer placement post, and found it really helpful. I did wonder if all horn couple plates are applicable to regular subs with sealed/vented configurations. I have 4x 18" subs at my disposal outside, and wondered how I can get the most of them. I was thinking about a square with the 4 of them, and was wondering if a plate an "v formation" would help.
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Grant Bunter
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Re: Couple plate and front firing

#2 Post by Grant Bunter » Fri Jun 21, 2019 3:29 pm

I'm probably wrong, but the way I see it is, the V plate is about creating a larger mouth area.
That makes a different in horns.
I'm not sure it does for DR's though.

But wall loading and corner loading will, if you're inside.
The best you could do would be to make sure the 4 cabs are stacked together for coupling..
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DR 250: x 2 (melded array) with March 2012 plans. 2 more under way with CD horn
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Bill Fitzmaurice
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Re: Couple plate and front firing

#3 Post by Bill Fitzmaurice » Fri Jun 21, 2019 3:55 pm

What he said.

Droogne
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Re: Couple plate and front firing

#4 Post by Droogne » Fri Jun 21, 2019 4:03 pm

Yeah, coupling them is logically a thing, but as it wasn't specified further I was "hoping" the hornloading with a plate would help. As you're saying, it would expand the horn mouth area, but as there is no horn to start with I think you're right in thinking the horn you create with the plate would not be big enough to support any low frequencies. Just wanted to be sure.

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Re: Couple plate and front firing

#5 Post by ACUA » Fri Jun 21, 2019 5:48 pm

I think that v-plating does positively effect the situation ie better impedance matching effect. but how much in that situation, I’m not sure. If it were me I would try to experiment by finding something, a sheet of wood or something and see if a plate helps. If it does I would be inclined to build a v-plating system for the sub bank.
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Bill Fitzmaurice
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Re: Couple plate and front firing

#6 Post by Bill Fitzmaurice » Fri Jun 21, 2019 9:03 pm

Droogne wrote:
Fri Jun 21, 2019 4:03 pm
as there is no horn to start with I think you're right in thinking the horn you create with the plate would not be big enough to support any low frequencies.
Correct. Even if you added a three foot long horn to the 18s it would only load them above 100Hz, where they're not working anyway.

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Re: Couple plate and front firing

#7 Post by Droogne » Sun Jun 23, 2019 4:33 am

[]

Yes, no way I can create a long enough horn.

Thanks in any case, we will just do stack on one side. It's just a couple of rented subs, and I just wanted to be sure I was correct in assuming it wouldnt work with a reflex sub.

Our mainstage uses 6x "dB Technologies DVA S30 Bassreflex-horn subwoofer, 2 x 18″, 3000 Watt" subs, but that horn looks wayyy to shallow, and the specs look unrealistically ( [+/- 3dB]30 – 120 Hz
Max SPL141 dB). Could this be correct? Or did they use some magic corner placement to get these specs?

In any case, real horn it not, would a V-plate help here? I'm guessing it's not of much help either?
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Re: Couple plate and front firing

#8 Post by CoronaOperator » Sun Jun 23, 2019 5:10 am

Droogne wrote:
Sun Jun 23, 2019 4:33 am
[]

Yes, no way I can create a long enough horn.

Thanks in any case, we will just do stack on one side. It's just a couple of rented subs, and I just wanted to be sure I was correct in assuming it wouldnt work with a reflex sub.

Our mainstage uses 6x "dB Technologies DVA S30 Bassreflex-horn subwoofer, 2 x 18″, 3000 Watt" subs, but that horn looks wayyy to shallow, and the specs look unrealistically ( [+/- 3dB]30 – 120 Hz
Max SPL141 dB). Could this be correct? Or did they use some magic corner placement to get these specs?

In any case, real horn it not, would a V-plate help here? I'm guessing it's not of much help either?
All lies but every manufacturer tells the same lies: First off to get to 141 dB's on 3000 watts you would need 107 dB-1w-1m sensitivity. Only way that cabinet could pull that off would be where the cones would break-up. 800-1000 hz or so. That doesn't even matter because to pull 3000 watts from a 1850 watt 15amp, 120v outlet you could only do that for 20ms at a time (energy stored in capacitor bank) or you would trip the breaker. 20ms is less than 1 wavelength at bass frequencies. So if they measured max sensitivity at 1 frequency and CALCULATED the spl increase for 5ms at 3000w, then they wouldn't be lying. I said CALCULATE because that's how everyone publishes max spl. Seriously go to any sub website, look at the specs and look at the fine print - they ALL say CALCULATE. Calculating max spl that way conveniently gets around the reality that your woofer has a maximun travel xmax before it self destructs. It also forgets that 3000w into a voice coil heats it up fast and then its dc resistance drastically increases (power compression, you don't keep getting a 3db increase for every doubling of power once it starts to get hot, there comes a point where you double power and you get no increase in spl due to heating). Keep that power there for more than a second or 2 and you will melt the voice coil. Your red-hot stove top elements don't get 3000w, how is that voice coil goes to handle dissipating more heat than that? That 141 dB rating is "on paper". Real world not without a solid concrete corner.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

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Re: Couple plate and front firing

#9 Post by Bill Fitzmaurice » Sun Jun 23, 2019 8:09 am

CoronaOperator wrote:
Sun Jun 23, 2019 5:10 am
Calculating max spl ...forgets that 3000w into a voice coil heats it up fast and then its dc resistance drastically increases (power compression, you don't keep getting a 3db increase for every doubling of power once it starts to get hot, there comes a point where you double power and you get no increase in spl due to heating).
+1. Thermal power compression is one of those dirty little secrets that manufacturers, including driver manufacturers, tend to sweep under the nearest rug. I'd tell you how much power compression those dB Technologies suffer from if RCF had it on their data sheets, but they don't. It won't be much different from a Beyma 18P 1200ND, which I do have power compression specs for. After only five minutes at full power the power compression loss is 5.5dB. Once you get above 500 watts power compression losses become significant enough that there's very little to be gained with more power.

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Re: Couple plate and front firing

#10 Post by ACUA » Sun Jun 23, 2019 9:15 am

Good right up Corona, it was music to my ears. Can’t think of a better first read waking up in the morning to!!!
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Droogne
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Re: Couple plate and front firing

#11 Post by Droogne » Mon Jun 24, 2019 6:18 am

CoronaOperator wrote:
Sun Jun 23, 2019 5:10 am
Droogne wrote:
Sun Jun 23, 2019 4:33 am
[]

Yes, no way I can create a long enough horn.

Thanks in any case, we will just do stack on one side. It's just a couple of rented subs, and I just wanted to be sure I was correct in assuming it wouldnt work with a reflex sub.

Our mainstage uses 6x "dB Technologies DVA S30 Bassreflex-horn subwoofer, 2 x 18″, 3000 Watt" subs, but that horn looks wayyy to shallow, and the specs look unrealistically ( [+/- 3dB]30 – 120 Hz
Max SPL141 dB). Could this be correct? Or did they use some magic corner placement to get these specs?

In any case, real horn it not, would a V-plate help here? I'm guessing it's not of much help either?
All lies but every manufacturer tells the same lies: First off to get to 141 dB's on 3000 watts you would need 107 dB-1w-1m sensitivity. Only way that cabinet could pull that off would be where the cones would break-up. 800-1000 hz or so. That doesn't even matter because to pull 3000 watts from a 1850 watt 15amp, 120v outlet you could only do that for 20ms at a time (energy stored in capacitor bank) or you would trip the breaker. 20ms is less than 1 wavelength at bass frequencies. So if they measured max sensitivity at 1 frequency and CALCULATED the spl increase for 5ms at 3000w, then they wouldn't be lying. I said CALCULATE because that's how everyone publishes max spl. Seriously go to any sub website, look at the specs and look at the fine print - they ALL say CALCULATE. Calculating max spl that way conveniently gets around the reality that your woofer has a maximun travel xmax before it self destructs. It also forgets that 3000w into a voice coil heats it up fast and then its dc resistance drastically increases (power compression, you don't keep getting a 3db increase for every doubling of power once it starts to get hot, there comes a point where you double power and you get no increase in spl due to heating). Keep that power there for more than a second or 2 and you will melt the voice coil. Your red-hot stove top elements don't get 3000w, how is that voice coil goes to handle dissipating more heat than that? That 141 dB rating is "on paper". Real world not without a solid concrete corner.
That the specs were hugely deceiving was clear to me, but I thought it was gonna be more about using "peak" value and cornerloading, than thermal compression. So thanks for the explanation. I'm learning something every day ;)

And what about the "horn" part? Would you consider this a horn, and would you expect it to ameliorate with a V-plate / v formation? Apparently our hired soundguy is gonna place the 6 we have as a 2(wide)x3(high) stack, with 2 facing backwards. I figure this help with baclwaves from the front firing, but is this the correct way to go?

And if this subs, like the other one I mentioned, is no real horn, and would benefit from a plate, would making a cake corner help? And if so, how big would this need to be to support 40hz? I'm guessing it depends on the WL of that 40hz wave? 1x WL on each side? 1/2? 1/4?

Thanks!

Droogne
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Re: Couple plate and front firing

#12 Post by Droogne » Mon Jun 24, 2019 6:23 am

Bill Fitzmaurice wrote:
Sun Jun 23, 2019 8:09 am
CoronaOperator wrote:
Sun Jun 23, 2019 5:10 am
Calculating max spl ...forgets that 3000w into a voice coil heats it up fast and then its dc resistance drastically increases (power compression, you don't keep getting a 3db increase for every doubling of power once it starts to get hot, there comes a point where you double power and you get no increase in spl due to heating).
+1. Thermal power compression is one of those dirty little secrets that manufacturers, including driver manufacturers, tend to sweep under the nearest rug. I'd tell you how much power compression those dB Technologies suffer from if RCF had it on their data sheets, but they don't. It won't be much different from a Beyma 18P 1200ND, which I do have power compression specs for. After only five minutes at full power the power compression loss is 5.5dB. Once you get above 500 watts power compression losses become significant enough that there's very little to be gained with more power.
Thanks to you too! Love the explanation. I'm trying to understand specs more and more, and even though I have known for quite some time that manufacturers exaggerate and 'cheat' their numbers , it's nice to know, how.

I originally thought the RMS was the rating specifying how much the driver could take electricaly before overheating, so thanks for correcting that misconception I had

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Re: Couple plate and front firing

#13 Post by Bill Fitzmaurice » Mon Jun 24, 2019 6:35 am

Droogne wrote:
Mon Jun 24, 2019 6:18 am
And what about the "horn" part? Would you consider this a horn
It is a horn, but since it's far too short to load within the subwoofer pass band its main purpose lies in advertising.
I originally thought the RMS was the rating specifying how much the driver could take electricaly before overheating
It is. That's not useless information by any means, but it doesn't say anything about how low or loud the speaker is actually capable of.

CoronaOperator
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Re: Couple plate and front firing

#14 Post by CoronaOperator » Mon Jun 24, 2019 7:16 am

Droogne wrote:
Mon Jun 24, 2019 6:18 am
Apparently our hired soundguy is gonna place the 6 we have as a 2(wide)x3(high) stack, with 2 facing backwards. I figure this help with baclwaves from the front firing, but is this the correct way to go?
He is doing a "cardiod array". Where you flip 1/3 of the cabinets around, reverse the polarity of the backwards cabinets and delay them by the depth of the cabinets. Cardiod arrays will make the bass forward directional. It is generally used to keep the bass from building up on stage. Generally used very successfully outdoors, indoors the reflection off the back wall almost always ruins the effect. Also cardiod arrays will always have less output than having all cabinets forward facing. You are giving up some output and sound quality "less impact" in order to get some control over the direction of the bass.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

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