Dual RL-p15 D2 LLT Sub Project...

[Sonnie]

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.

[Ilkka]

Sonnie wrote:

No, I don't have TrueRTA... I though you meant using an SPL meter...

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.

[Sonnie]

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...

[Otto]

Sonnie wrote:

I -10 to -5 supposed to be 5db... or does that depend on the receiver? I guess I can measure it and see...

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...

[Sonnie]

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...


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

[brucek]

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

[Sonnie]

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.

[Sonnie]

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.

[Sonnie]

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.

[SteveCallas]

Wow, that's a nice and low tune 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

brucek wrote:

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 wrote:

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 wrote:

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

[brucek]

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?

No, I was wondering the best spot to place a microphone (with a ported design sub) to get the best indoor nearfield measurement (as compared to a sealed sub where you can simply rely on about a foot in front of the driver). But, you already answered my question. And the answer you gave above was also very interesting info... thanks

brucek

[Ilkka]

brucek wrote:

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

Unfortunately it's impossible to take an accurate near field measurement with a ported subwoofer. One needs to place the mic at least 2 meters away from the subwoofer in order to get a good summation of the driver and port output. Of course at that distance room does its thing and it can't be considered as a NF measurement anymore. So an anechoic or GP environment is your only chance. REW's averaging function shouldn't be used to predict the combined response, it's nowhere near accurate method.

It's not useful to try to measure only the port's output either. Port's output will be attenuated heavily around 1/2 octave below and 1/2 octave above the tuning frequency (already around 5 dB down). Anywhere else driver's output will be much higher. Around an octave above the tuning the port doesn't contribute to the combined frequency response at all (more than 10 dB down). So in order to get an accurate measurement of port's output, one would need to mute the driver. And we all know what happens then...or should I say, what doesn't happen.

In-room NF measurement is pretty tricky thing with sealed subs too. Almost every time some amount of room interaction is still being present and can be seen in the measured frequency response. One should understand that it's not easy to measure waves having wavelengths of several meters in small enclosed spaces.

[Ilkka]

Sonnie wrote:

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.

That's normal so don't worry about that.

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.

Which scene you were using?

I usually unplug my mains when performing max SPL tests. It's so much easier to hear any noises of distress then. One can pretty much tell by ear when the subwoofers are about to hit their limits. Is your crossover at 80 Hz?

[Sonnie]

Ilkka wrote:

Which scene you were using?

I usually unplug my mains when performing max SPL tests. It's so much easier to hear any noises of distress then. One can pretty much tell by ear when the subwoofers are about to hit their limits. Is your crossover at 80 Hz?

The scene is chapter 4 I think... it's the beginning when the machine first rises out of the ground and starts zapping folks. Generally the loudest SPL is right after Tom Cruise runs through the store (glass breaks) and after he exits there's one last couple of zaps before he hides beside a building while the machine walks by.

Yes, my crossover is at 80Hz. I had the subs jacked up probably 20db or more above the mains on the last test I did... the bass was all over me, obviously way louder than the normal. Really it seems like no matter how hard I push those Plus/2's they don't flinch. Of course there may be some distortion there that I just don't realize I'm hearing.

[Ilkka]

Sonnie wrote:

The scene is chapter 4 I think... it's the beginning when the machine first rises out of the ground and starts zapping folks. Generally the loudest SPL is right after Tom Cruise runs through the store (glass breaks) and after he exits there's one last couple of zaps before he hides beside a building while the machine walks by.

Okay, have you thought of trying out some other scenes? The good old LOTR "ring drop" is a pretty cruel ~25 Hz output test (remember to use the DTS soundtrack). Also Master and Commander's "first round" (just the first round of cannon fire) has lots of energy in 20-50 Hz range. If you have the Flight Of The Phoenix, try out the last sandstorm scene where the broken plane rolls over in the storm - high amounts of energy down to 15 Hz.

Yes, my crossover is at 80Hz. I had the subs jacked up probably 20db or more above the mains on the last test I did... the bass was all over me, obviously way louder than the normal. Really it seems like no matter how hard I push those Plus/2's they don't flinch. Of course there may be some distortion there that I just don't realize I'm hearing.

It's the 16 Hz tune that causes that. They will just compress but won't make much bad noises. Try the 25 Hz tune and you should get at least 5-6 dB more output.

[Sonnie]

I'll try out the LOTR "ring drop" scene. I don't have either of the other two.

What range are the depth charges on U-571?

What about the starship at the beginning of Star Wars III (or whatever that last DVD released was)?

Jurassic Park III maybe... seems like those dinosaurs always knock me around a little bit.

It's the 16 Hz tune that causes that. They will just compress but won't make much bad noises. Try the 25 Hz tune and you should get at least 5-6 dB more output.

I haven't really thought about that, but now that I have the dual 15's in the back, trying those front subs in a different tune might do well. Of course I really don't need it that loud, my max SPL at normal listening levels is around 115db. I don't think I could handle much more. None the less, it will be fun to experiment.

[SteveCallas]

Just one guy's opinion, but I'd RENT M&C and FotP if you want to check out those bass scenes.....the films themselves are very hard to stomach, skip the purchase FotP is still the rotten apple among my dvd collection

[Sonnie]

lol... I've seen M&C and it was so-so, definitely not worth buying IMO. FotP never interested me at all... never even rented it, and doubt I would just for a bass scene.

[aceinc]

I lost track of this thread for a while. I'm glad I found it again, it looks like you executed the design quite well. Quite a SUBstantial project, I'm envious.

You will want to make sure your home owners insurance covers seismic damage. Throw a quilt (or 3) over the Behemoth when the adjuster shows up.

The unfortunate thing is, what do you do for an encore?

Paul

[SteveCallas]

aceinc wrote:

The unfortunate thing is, what do you do for an encore?

Cough....replace the satellites with 3 way towers...cough