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Willy said:
I'd say the Rl-p's are middle of the road. So yeah, that FR does look quite flat in the upper end, but hey, I don't believe many Rl-p 18s have been measured to determine their natural upper frequency response, so we don't really know.
Right, for all we know it could be very linear up top. Now that I think about it though, he's taking that measurement from his seat - which is absolutely the only place that matters - but to get an apples to apples comparison, we'd need a close mic sweep.

Bradely, any way you could do a close mic sweep (position the tip of the mic 3-4" away from the center of the cone) with something like a folded up blanket behind and or around the mic?
 

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Discussion Starter #122
Because there is no adjustment to the start of sweep, only end of sweep...

Do an REW electronic sweep of your AVR in a loop from the soundcard to check its low frequency extension. It may be providing free HPF protection.
I did that and the sound card is pretty [email protected] flat. It was down not even half a dB at 10Hz.

Maybe it's time to buy some op amps and bread board up a 4th order activer HPF. ;)
 

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Discussion Starter #123 (Edited)
Bradely, any way you could do a close mic sweep (position the tip of the mic 3-4" away from the center of the cone) with something like a folded up blanket behind and or around the mic?
Here you go. I plugged the sound card directly into the power amp for this one to make sure no crossover was being done through the AVR. Judging from the big dip at 13 Hz, that would appear to be the tune, correct? Strange that it is still so low.

 

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Here you go. I plugged the sound card directly into the power amp for this one to make sure no crossover was being done through the AVR. Judging from the big dip at 13 Hz, that would appear to be the tune, correct? Strange that it is still so low.
Yes, the tune seems to be around 13 Hz. And the roll-off above 50 Hz looks as expected.
 

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Interesting how the amps roll off below 10hz appears to be protecting you.......... doesn't appear that you require an HPF........
 

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Discussion Starter #126
How do you know it's the amp that is rolling off? At least when you model it, the output from the sub drops like a rock at 10 Hz while cone excursion soars.
 

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Discussion Starter #128
OK, just can't stop playing with REW. :p

I stood the sub up and moved it into the corner of the room to see how that would affect FR. Previous measurements were with the sub "horiztonal" and beneath the screen (as pictured earlier in this thread).



Moving it into the corner made a big difference. The graph below was done with the mic in the exact same position as the first graph I did with the big dip at 58.5 Hz, but there is no trace of that dip now.



Also note I changed the scale to 5 dB increments instead of 10.
 

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Also note I changed the scale to 5 dB increments instead of 10
Usually best to display about 60dB swing in the vertical scale.

The standard we usually use is 45dB to 105dBSPL on the vertical axis...... This places the 75dB target at center scale.

brucek
 

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Discussion Starter #131 (Edited)
Usually best to display about 60dB swing in the vertical scale.

The standard we usually use is 45dB to 105dBSPL on the vertical axis...... This places the 75dB target at center scale.
OK, thanks. I've just been messing around and having fun with it so far but I do remember reading somewhere that Dolby Labs and/or THX recommends a 75 dB target. I guess if I want anyone to take me seriously, I better get with the program. ;)
 

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Thanks for the close mic measurement Bradley - looks like a 5-5.5db rolloff to 100hz.

The Conquest won't be nearly as linear into the infrasonic range as your beast. Considering you'll have built two of them for roughly the cost of one Conquest, you'll have it beat by plenty in all regards :T
 

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Discussion Starter #136
Oh, that deal where he got one quick sweep in as it was starting to rain? I'll have to go take another look at that. Did you see the in-room test Tom Nousaine did on the Conquest?

Also, do you find that subs with the port on the rear or side of the cabinet don't do (as well as they might be able to otherwise) in an outdoor ground plane measurements?
 

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Oh, that deal where he got one quick sweep in as it was starting to rain? I'll have to go take another look at that.
Yes.

Did you see the in-room test Tom Nousaine did on the Conquest?
I did. But unfortunately they are only comparable to other subs measured by TN.

Also, do you find that subs with the port on the rear or side of the cabinet don't do (as well as they might be able to otherwise) in an outdoor ground plane measurements?
I always try to place/orientate the subwoofer so that all the radiating elements (woofer, port etc.) are at 2 meter distance from the microphone. Of course this isn't always possible but the difference is very small.
 

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Discussion Starter #138
Well, that outdoors graph posted over on AVS shows the Conquest holding around 115-117 dB from 15 Hz on up. Pretty impressive if that is an accurate 2m ground plane measurement. I don't really care if I "beat" the Conquest. It's just fun to compare, since that's the closest commerical equivalent to what I've built. Like Steve said, I will have built two subs for the price of the Conquest (*if* you don't count the cost of all the *******' tools I bought) and it's been an interesting "adventure" so far to say the least! :)
 

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Discussion Starter #140
Yes... made some progress on the second subwoofer box over the weekend and posted new pics over on AVS.

Pretty happy with the first subwoofer. :) Even with one sub and 650 watts, pretty much EVERYTHING is rattling in my basement HT room. That drop ceiling has GOT to go!
 
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