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I just got my RLP-18 in and I'm going to make a 24" Sonotube. Mike says I can use between 13-23 CuFt which if my calculations are correct would make it about 7.5 feet tall? Dunno if the wifes gonna like that.
 

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Discussion Starter #145
That's pretty tall... should be awesome! Be sure to start up a new thread with your build... :T
 

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:devil: :bigsmile: Compression, the silent killer. There's a lot of people out there who just don't know what they are missing - I think today you just found out :R
Though it may seem that I'm arguing with you more than usually, I wanted to grab on this when I noticed that you brought it up again in Rodny's thread. :R :kiss:

"If he was somehow experiencing any compression previously, like you unknowingly were with even two Plus/2s, that won't be the case anymore."

We should remember that even if those two subs were calibrated at the same level, he would still have a ~6 dB gain when both are playing at the same time. So it doesn't mean that the SVS' were compressing by 122.8-114.5 dB=8.3 dB. When you subtract the 6 dB you'll have 2.3 dB, and that can be explained by the different frequency responses.

So nothing shows that Sonnie's SVS' were yet compressing. Based on experience with my own Plus/2, I'd say he will have to push them over 120 dB until any major compression sets in. It can be easily tested by running the same scene at rising output level (for example -10RL, -5RL, RL and so on) with an RTA running (peak hold on) behind.

 

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Discussion Starter #147
It can be easily tested by running the same scene at rising output level (for example -10RL, -5RL, RL and so on) with an RTA running (peak hold on).
Running just the pair of SVS subs? I can probably test this Friday since I'm taking off to fiddle with the room some.

Steve, I can also test that tuning frequency... I'll just use my CM-140 with the ECM8000 cal file. It will tell us what we wanna know anyway.
 

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Elite Shackster
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Running just the pair of SVS subs? I can probably test this Friday since I'm taking off to fiddle with the room some.
Yes, just SVS subs. When you find their limits, you can add the DIY sub and see how much higher it can take you. Though it's not healthy to push SVS' into more than ~5 dB of compression.

I assume you also have TrueRTA since it can't be done with REW.

Steve, I can also test that tuning frequency... I'll just use my CM-140 with the ECM8000 cal file. It will tell us what we wanna know anyway.
Yup.
 

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Sonnie, was the ~123db achieved with the SVS AND LLT running, or just the LLT? I was under the impression it was from just the LLT. And if both, was the sub level knocked down 6db before replaying the scene or lef as is?

Ilkka said:
Though it may seem that I'm arguing with you more than usually
Again, no worries, it's not arguing, it's discussing :wave: :rant:
 

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Discussion Starter #150
Yes, just SVS subs. When you find their limits, you can add the DIY sub and see how much higher it can take you. Though it's not healthy to push SVS' into more than ~5 dB of compression.

I assume you also have TrueRTA since it can't be done with REW.
No, I don't have TrueRTA... I though you meant using an SPL meter... :huh:

Sonnie, was the ~123db achieved with the SVS AND LLT running, or just the LLT? I was under the impression it was from just the LLT. And if both, was the sub level knocked down 6db before replaying the scene or lef as is?
Yes.... both subs running. Both subs were level matched and left the same. All we did was hold up the SPL meter during the same ~30 second scene and played just the SVS subs to start with, got the max reading and then turned on the LLT with the SVS subs and got another max reading.

I can do each separately if it will help to determine something useful.
 

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Again, no worries, it's not arguing, it's discussing
Agree! You guys create some very healthy discussions IMO... if others followed your style in other forums, we'd have quite a few very fine forums. Unfortunately for some... and fortunately for the Shack... that will probably never happen elsewhere. :bigsmile:
 

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No, I don't have TrueRTA... I though you meant using an SPL meter... :huh:
Okay. It can be done with an SPL too, of course then you won't be able to see where it starts to compress because SPL meter grabs only the peak SPL (total power), not the frequency response. Just monitor the master volume vs. SPL relationship. When the SPL doesn't rise by 5 dB or what ever you are adding, that's the point where your subs are starting to compress.

Yes.... both subs running. Both subs were level matched and left the same. All we did was hold up the SPL meter during the same ~30 second scene and played just the SVS subs to start with, got the max reading and then turned on the LLT with the SVS subs and got another max reading.
This was the exact scenario I was thinking about.

I can do each separately if it will help to determine something useful.
I would be most interested if you could measure them separately. Though it would require that their frequency responses should be EQ'd as similar as possible.
 

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Discussion Starter #153
When the SPL doesn't rise by 5 dB or what ever you are adding, that's the point where your subs are starting to compress.
Is -10 to -5 supposed to be 5db... or does that depend on the receiver? I guess I can measure it and see... :duh:
 

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I -10 to -5 supposed to be 5db... or does that depend on the receiver? I guess I can measure it and see... :duh:
Yeah, going from -10 to -5 will get me a 5 dB measured increase on my SPL meter. If your receiver is showing dB, you will probably have the same thing going on, but measuring will let you know for sure.

That thing looks awesome, Sonnie (and Rodny). Sometime when I'm in Alabama...
 

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Discussion Starter #155
I'd much rather be in Colorado than Alabama, but we'd love to have you visit with us sometime.

Yep... 1 notch on the receiver is 1db... :T


I took a couple of measurements with REW on the Behemoth.

I did scroll the chart up so that you could see the full measurement, but the proportion is our standard.

Blue is 3" from center of driver
Red is center of port exit



 

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So with a ported design, where does someone correctly take a nearfield measurement to ensure optimum assist from the port effect while eliminating as much effect as possible from the room?

Your graph shows exactly what I would expect.

Right at the cone, we see the pure speaker output without the port effect (more like sealed I suppose).

Then right at the port output, we see the port assist.

Where do they combine to produce the pure speakers total output before the room wrecks it?

My limited knowledge of speaker design is showing.... Steve? Ilkka? Sonnie?

brucek
 

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Discussion Starter #157
Though it would require that their frequency responses should be EQ'd as similar as possible.
That part is going to be a challenge.

I did play around with just the SVS subs and the SPL. I got them to 118db at max volume on my receiver. Funny thing is when I cut my sub pre-out up, my max volume reduces. Of course just sitting here thinking about it, the subs are only 1/4 volume, so I can turn them up too. They didn't flinch one teenie weenie bit at 118db though... they were doing well as far as I could tell.

I turned on the behemoth and reached 125db on the same scenes at max volume. Man, it was loud! This little SBS-01 speakers didn't flinch either.... I was impressed at how loud they will play.

I'll turn up the volume on the Plus/2's and see what else I can learn.
 

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Discussion Starter #158
My limited knowledge of speaker design is showing.... Steve? Ilkka? Sonnie?
lol... my knowledge is much more limited than yours, so I eagerly await Steve or Ilkka.
 

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Discussion Starter #159
Max I could ever get from the Plus/2's was 118.6db. After turning the volume up on the subs to 12 o'clock, I was able to go from -5 to 0 and it reached about 117db. When I went from 0 to +5, the SPL meter peaked at 118.6db.
 

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Wow, that's a nice and low tune :cool: :R I actually forgot you were going for a 13hz tune as opposed to something like 16hz in the other two dual RL-p15 LLTs (steve's and ryan's). After eliminating that dividing wall from your original design, what would you estimate the final effective volume came out to be? If you are using two 6" diameter ports that are 34" long with roundovers, I'm guessing ~575 liters. Whatever it was, it seems to have worked perfectly :T

brucek said:
So with a ported design, where does someone correctly take a nearfield measurement to ensure optimum assist from the port effect while eliminating as much effect as possible from the room?
Unfortunately you can't really. You have to merge a driver close mic and port clos emic like Sonnie did. You'd have to test it outside from a good distance (considering how large the sub is) to allow the port and driver output to merge completely.

brucek said:
Right at the cone, we see the pure speaker output without the port effect (more like sealed I suppose).

Then right at the port output, we see the port assist.
Yep, a close mic of the driver should look almost exactly like the box were sealed until you get around tuning. Above that point, the driver is moving too fast to effectively couple with the air in the port.

brucek said:
Where do they combine to produce the pure speakers total output before the room wrecks it?
Not sure what you are asking - do you mean what is the lowest frequency in which only the driver is still providing nearly all the output? At about an octave above tuning, the simulation shows the port output to be about 12db down and the difference in group delay when comparing to a similarly sized sealed sub is only about 0.001 second, so for all intents and purposes, I use one octave above tuning as the point where port output isn't significant anymore. Ilkka can correct, clarify, or expand upon that better. This is a main reason why I set one of the requirements for a LLT to have a simulated tuning <16hz. By doing this, the port won't be playing much of a role anymore at 30hz, and the majority of music doesn't dip below 30hz. I try to retain all the benefits a port can yield while eliminating or stifling the drawbacks :T
 
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