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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
 

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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
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. :D

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.
 

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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?
 

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Discussion Starter #164
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.
 

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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.
 

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Discussion Starter #166
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.
 

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Discussion Starter #168
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.
 

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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
 

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Discussion Starter #172
The Bostons should be here first of next week... that will be one change I'll make. Who knows what else I am liable to do over the summer. :daydream:

Rodny's setup is going to be massively awesome! :yes:
 

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This thread was a good read and I must give my :T to Rodny's build quality :)

The only thing I'd be conserned with a box this long is standing waves developing on the inside of the box. I guess the longest internal dimension is 93" which would yield a first standing wave of 73Hz inside the box, but that's not visible in the FR plots you posted so it's all good. Happy listening! :bigsmile:
 

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8" would be too large for a single RLp-15 sub with a low tune.
What constitutes a port diameter being too large for a given Vd? I've asked around a lot in the past with no answer, and I've never heard anything about it till i saw this... but i've always thought, at some point, too much port area must create all sorts of issues.
 
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