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post #61 of 144 Old 01-21-2010, 09:18 PM
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I am not understanding how you have it connected. Do you have two AV receivers, one driving main speakers, center and surrounds, with the sub output going to a second receiver that is eventually driving this sub?

A little bit of clarification would be good here.

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post #62 of 144 Old 01-22-2010, 01:36 PM - Thread Starter
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Okay, I can clarify.

The receiver subwoofer output IS going into the multi channel input of another receiver. I have my receiver set to send 80hz and below to the subwoofer, as well as to the speakers. I have also tried 50hz, but 80hz works better.

I play a 27hz sine wave, the meter reads 18v from the speaker output, 27hz, and the dB meter (C, fast) reads ~90dB (+6 = 96dB) at my listening position. My laptop that I use for the sine waves keeps freezing and I have not been able to do any more testing yet.

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post #63 of 144 Old 01-22-2010, 11:10 PM
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18 v into 2.8 ohms is around 115 watts... however you would have to see what the actual impedance at 27 hz is... WinISD should give you a value... I am willing to bet the actual impedance around that frequency would be around 20 hz at least, so 18V ^2 / 20 would be about 16 watts.

The only time the impedance will drop near the Re would be right at your tuning frequency, you will have peaks below and above that in frequency.

Bottom line, the receiver is pretty sub par. Test with an actual amplifier that can put out at least 60 volts into the load.

If you are cascading crossovers, you will also be rolling off the high end.

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post #64 of 144 Old 01-22-2010, 11:24 PM - Thread Starter
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Today I decided to fight the laptop in the name of bass

I got these graphs with an SPL meter and REW, but I forgot to have the meter calibration file activated for all the measurements. Is there a way to go in afterwards and fix it?

What I can say is that I still have a bit of the tube resonance (98hz). Would more padding help the sound, really?

In the outdoors measurements, I seem to lose a bit of output in the low 20hz high teens. Inside, I also lose a lot here, with a bump at 27hz. The 40-50hz range is a big peak.

At 1 watt/meter outside (ground plane WinISD?), I get 84dB sensitivity (not 90? Whatttt?), and then it gets down into the mid-low 70s in the 20s and teens? What is the meaning of this LOW sensitivity? It's nightmareishly low?



Any ideas on the sensitivity (corrected). Is it a problem with the enclosure or the driver? A nearfield of the driver looks correct, save for a bit of resonance at 98hz. Same with the port.

So what is the deal here? Am I losing output somewhere?

My room also seems to have a bad low freq problem <.<<br />
Get more data... fix the problem

...
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post #65 of 144 Old 01-23-2010, 07:36 PM - Thread Starter
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Am I not giving enough information? Not the right information? Do people not know how to answer?

I know my room only partly has something to do with it, as the subwoofer output is not correct for what is going on.

It does not matter how much power I have if something is seriously wrong with the overall response?

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post #66 of 144 Old 01-23-2010, 09:52 PM - Thread Starter
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I see.

I will go ahead and say I raised the tuning from 12.7hz to 15hz. It improved things, and the use of the 11.5-14hz range is sparing enough that it is an improvement.

Although - to get anyone to say anything about what they think is the problem, I think I will post an outdoor response graph vs. an indoor response graph

And yes, I figured out how to make it correct the data after the measurement has been taken. Thanks a lot.

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post #67 of 144 Old 01-23-2010, 10:17 PM
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Quote:
Originally Posted by arande2 View Post


What I can say is that I still have a bit of the tube resonance (98hz). Would more padding help the sound, really?

In the outdoors measurements, I seem to lose a bit of output in the low 20hz high teens. Inside, I also lose a lot here, with a bump at 27hz. The 40-50hz range is a big peak.

At 1 watt/meter outside (ground plane WinISD?), I get 84dB sensitivity (not 90? Whatttt?), and then it gets down into the mid-low 70s in the 20s and teens? What is the meaning of this LOW sensitivity? It's nightmareishly low?

I don't know how you are arriving at a sensitivity figure, are you using a digital multimeter to get voltage?

The 98 hz resonance will be healed with absorption in the box, yes, that is possible with a big, long sonotube, infact I had one very similar.

See here: http://www.avsforum.com/avs-vb/showthread.php?t=1141956

Ok. Measure the box outside at 1 meter from the cone, and then again 2 meters from the cone, outside... you will get two different curves. The 2 meter curve will look a lot smoother without a big hump.

The port and driver will be a lot closer path length to the microphone, when you measure farther away.

Most pro stuff is measured at 10 meters with 28.3 volts input and calculated back to 1 meter / 2.83 V.

I can't say that the Rat Shack or even the Galaxy meter is accurate at low frequencies.... even the Behringer ECM8000 I don't trust down low, unless you are measuring with a lot of voltage into the cabinet. IE: almost full tilt operation.

Gain structure in REW matters, especially when you have multiple gains as some of us do. If your soundcard clips, or in the case of ECM8000 mic / mixer, if you clip that it will affect what REW measures.

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post #68 of 144 Old 01-23-2010, 11:53 PM - Thread Starter
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Quote:
Originally Posted by michael hurd View Post

I don't know how you are arriving at a sensitivity figure, are you using a digital multimeter to get voltage?

The 98hz resonance will be healed with absorption in the box, yes, that is possible with a big, long sonotube, infact I had one very similar.

See here: http://www.avsforum.com/avs-vb/showthread.php?t=1141956

Ok. Measure the box outside at 1 meter from the cone, and then again 2 meters from the cone, outside... you will get two different curves. The 2 meter curve will look a lot smoother without a big hump.

The port and driver will be a lot closer path length to the microphone, when you measure farther away.

Most pro stuff is measured at 10 meters with 28.3 volts input and calculated back to 1 meter / 2.83 V.

I can't say that the Rat Shack or even the Galaxy meter is accurate at low frequencies.... even the Behringer ECM8000 I don't trust down low, unless you are measuring with a lot of voltage into the cabinet. IE: almost full tilt operation.

Gain structure in REW matters, especially when you have multiple gains as some of us do. If your soundcard clips, or in the case of ECM8000 mic / mixer, if you clip that it will affect what REW measures.


Hi, thanks

Yes, I am basing the sensitivity figure on 2v input (4-ohm driver), so unless the sensitivity is always based on 2.83v, even with 4-ohm, it is 6dB low. Otherwise, it is right on the money...

I tried measuring the subwoofer at 18v and noticed the smoothing of dips and peaks, but I did not save the measurement.

After correcting the data of my outdoor measurement, I found the response was actually pretty close to what I modeled, except for somewhat of a dip at 23hz.

I use a pre-amp between the meter and the soundcard input to give full input before clipping, thus maximizing S/N ratio and accuracy as much as I can..



-----------

I am continuing to experiment, but trying more spots for the subwoofer would be tiring. I've moved it over 10 times already and it does get tiring. However, I have only had it in one spot since I got the SPL meter. It may be worth trying more spots..


-------------

Everything I have tried so far seems to point to EQ and a second subwoofer before getting more power. I think making better use of the power I have would be more advantageous than brute force.


Off to read that link..

EDIT: Yes, I have read that before. It is weird because yours measures very well and mine does not. I don't know if it is a measurement problem or sub problem..

...
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post #69 of 144 Old 01-24-2010, 12:12 AM
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Quote:
Originally Posted by arande2 View Post


Yes, I am basing the sensitivity figure on 2v input (4-ohm driver), so unless the sensitivity is always based on 2.83v, even with 4-ohm, it is 6dB low. Otherwise, it is right on the money...

After correcting the data of my outdoor measurement, I found the response was actually pretty close to what I modeled, except for somewhat of a dip at 23hz.

I use a pre-amp between the meter and the soundcard input to give full input before clipping, thus maximizing S/N ratio and accuracy as much as I can..



Are you placing the SPL meter on the ground when testing outside?

How deep is the dip, and how wide of a bandwidth is it? IE... if it's 2 hz wide, etc...

Sounds good... are you using a loopback on L channel on the soundcard?

I am sure that there will be a lot of people that will disagree, but you won't get meaningful data below about 20 hz outside, unless you are driving the cabinet close to it's limits... and make sure nothing in the signal chain is clipping.. mixer etc.

Trust me, you need more power, as well as some eq in room.

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post #70 of 144 Old 01-24-2010, 12:19 AM
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Did you throw some low frequency sines on it to break in the driver suspension when you got it, or just threw it in the box?

What's your noise floor like?

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post #71 of 144 Old 01-24-2010, 04:38 PM - Thread Starter
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"Are you placing the SPL meter on the ground when testing outside?"

No, I was doing a diagonal 1 meter to driver/port, but I am guessing on the ground farther away is more accurate (in terms of absolute spl and relative spl)


"...loopback..."

Since I don't know what you mean, probably not. If you are asking if I am using the left channel to measure, yes.

"...meaning data below about 20hz outside..."

Is this because of background noise, wind, etc..?

"...trust me..."

I still think 2 subs will be needed (weird pressure difference between ear) so I don't get distracted by noises (rattles etc..) where the subwoofer is...

I was planning on more power and EQ anyway


"...break in the driver suspension..."

Yes, I broke it in for 3 weeks.

"What's your noise floor like?"

I assume you mean what the VU meter says on the input without any signal. -42dB


------------

Some graphs to aid...

The measurement I got outside... 1 watt of input...



Nearfield measurement of subwoofer driver before raising tuning to 15hz, 80hz low-pass



Nearfield measurement of port (not absolute SPL)



In-room current ilstening position, 4 watts input, 80hz low pass. I think you can see the problem...

...
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post #72 of 144 Old 01-24-2010, 06:58 PM
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[quote=arande2;17995056]
No, I was doing a diagonal 1 meter to driver/port, but I am guessing on the ground farther away is more accurate (in terms of absolute spl and relative spl)

Since I don't know what you mean, probably not. If you are asking if I am using the left channel to measure, yes.

Is this because of background noise, wind, etc..?

I still think 2 subs will be needed (weird pressure difference between ear) so I don't get distracted by noises (rattles etc..) where the subwoofer is...

I was planning on more power and EQ anyway

Yes, I broke it in for 3 weeks.

I assume you mean what the VU meter says on the input without any signal. -42dB
"

Pro stuff is measured farther away to get away from the 'velocity' issue that will affect the measured FR. Tom talked a bit about this issue, but I don't recall where the post was placed.

Place the mic on the ground when measuring the cabinet outside.

Measure on the right channel, and tick the box that says "use left channel as calibration reference" You will find this under 'settings' in REW.

I use an RCA>RCA cable that physically connects the soundcard output on the left channel to the left channel input. This is what is meant by a 'loopback'.

Yes, I was meaning that outside wind noise, trains / traffic will affect the measured FR down low.

Use the sine wave generator in REW to sweep for rattles and go around, fixing them. Rattles will totally ruin the perception, fix them or you will go loopy...

A little bit of thin foam weatherstripping tape can do wonders for hanging pictures, etc.

Can you post graphs of the measurements with the suggested settings for REW? 15-200 hz, 45-105db. Alternately, you can PM me, and I will give you my email, you can send the .MDAT file ( measurement file ) and I can take a look at it.

Some absorption inside the sonotube will be needed to kill the end to end resonance.

42 db noise floor is pretty decent, you should be able to get relevant measurements.

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post #73 of 144 Old 01-24-2010, 11:09 PM - Thread Starter
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Cool I'll see if I can try that stuff (not sure my input is stereo... )

Funny you should mention trains/traffic and wind noise... When I was trying to measure 3 trains went by and it was rush hour, plus it was windy Needless to say, it took a while to get a good measurement. But now that you say it should be on the ground, it's a moot point.

Speaking of absorption, I got some pillows and put them in there. It took care of the resonance

The top endcap already had some foam on it, but it probably did almost nothing being at the end.

I measured the driver again and it showed what I expected (less of a dip at tuning due to higher absorption (and slightly lower tuning), without the nasty resonance. Also it gave a slightly smoother response, but the weird dip around 30hz is still there.


You also mentioned rattles. I just got rid of a few more rattles than I had. After listening very closely everywhere, I realized that the large unbraced metal panels (like 6ftx4ft) on SIX large filing cabinets are vibrating a lot. I would believe this might cause a lot of trouble for bass!

I also have like 30 pictures in the room (no exaggeration). Sadly, it is the only room I have for an HT/music system.


Do you think if I can brace/stop vibration on all the metal panels maybe it would help the bass? They have a lot of rattle, but it's not obvious. More like a 2nd/3rd harmonic distortion thing. Probably not good...

I also have trouble telling if sounds are from the driver or things around it.

...
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post #74 of 144 Old 01-25-2010, 03:26 AM - Thread Starter
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Tests in my room are showing 84dB with 1 watt from one meter. This is with the subwoofer in the corner. What gives?

Why is the sensitivity so low?

Is it all the metal panels absorbing the energy? Then again, it was also low outside.

I should also say when I got the driver it showed an FS of 38hz. I am questioning the driver... Surely there is nothing wrong with it?

Also I found it is still 38hz after being in the enclosure, so maybe it is the meter. It is one of those clip-on meters that measures the current through the magnetism from the wire. Maybe I need to try a hardwired setup.

...
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post #75 of 144 Old 01-25-2010, 06:00 AM
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Did you get your amp yet? You should really hold off on conclusions until you get a proper amp. Its like saying I have a corvette and its not really going fast. It has a go cart engine in it, but it should still go very fast.
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post #76 of 144 Old 01-25-2010, 01:35 PM - Thread Starter
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Quote:
Originally Posted by brandonnash View Post

Did you get your amp yet? You should really hold off on conclusions until you get a proper amp. Its like saying I have a corvette and its not really going fast. It has a go cart engine in it, but it should still go very fast.

No, but would an amp really help the issue of noticing the bass come from one side of the room more than the other?

Even if I did get the amp, 98dB max output (20-25hz, very important range to me) is crap for an 18" driver with over 1kW of power in a giant enclosure. Obviously I should be getting at least 105dB (if not more) with my current power, which I am not.

Surely you don't get 98dB at 20hz with 1000 watts? Surely not? Surely more like 120dB? Certainly you wouldn't accept 98dB at 20hz with 1000 watts? Brute force can only do so much if something is wrong in the first place.

Right now I am experimenting to see what I have to do to make this work once I get full power.

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post #77 of 144 Old 01-25-2010, 02:07 PM - Thread Starter
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Another thing - If my subwoofer is supposed to be 90dB sensitivity and act like this, and reads like 95dB with 100 watts (60hz), why does a single mains speaker read 111dB when I give it 100 watts? (or 115dB for all the speakers together). Listening position ---

I believe either my build quality (how would I tell?) or the driver itself is to blame here.

"You need more power. Give it more power."
Brute force won't fix a build/driver problem

My goal here was to extended the response an octave or two, not build a subwoofer that isn't working right.

I have an idea - go to the local car audio place and listen to a driver free air.. Maybe that will help me decide whether it's the driver or enclosure. I am thinking both...

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post #78 of 144 Old 01-25-2010, 05:40 PM
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What happens when you have a lot of distortion in a speaker, it will measure louder than it actually is. ( it will also sound louder ) An SPL meter reads all frequencies together, so if you have high 2nd and 3rd harmonics, the meter will read artificially high.

I don't think there is a build quality problem, unless you have leaks, even then you should be able to generate half decent levels. Can you give us more details about the room... if it's a main floor with lossy construction, you can be losing output through the floor in the low end.

Pictures are worth a thousand words here.

The only way you can really audition a subwoofer is with decent mains, and having a good blend to the main speakers. It should sound like you have gigantic mains, that dig deep when the need calls for it, not like a 45 hz tuned prosound sub. 'thump thump'

PM me, I will give you my emaill address and look at the .mdat file... you have to save the measurement, and then attatch it to the email.

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post #79 of 144 Old 01-26-2010, 04:29 AM - Thread Starter
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Hmm maybe I should see what it sounds like on its side..

Should probably get it outside again for testing.. today is my last chance this week


I can get pics, cell phone pics though.. Pics of what exactly?


Right, that's what I want, sound like I have big mains that go all the way down.

I can't hear the distortion the speakers put out at 115dB, so it can't be above the threshold (surrounds 75rms, 150cont. mains just say 5-350 watts recommended). The drivers are barely moving at '115dB'

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post #80 of 144 Old 01-26-2010, 09:01 PM
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Arande, I took a look at the picture you posted, and it's really not that bad indoors.... you don't have a lot of gain down low, but if you pull that 40~ hz peak down a bit, you fit within a + 3db, -3db window from about 17 hz to 70 hz which is quite respectable, as long as the measurement is valid.

Don't forget that the shape of the graph will look a lot different when you set the graph limits to the REW defaults, 45-105 db, and 15-200 hz, the peak will 'look' a lot less than what shows up in your settings.

I would do a bit of investigation with a sine wave generator parked at your 22 hz dip... something must be vibrating sympathetically to get that deep of a dip. If you don't end up healing it, not a huge problem because the bandwidth of the dip is pretty narrow... you'd likely never notice it.


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post #81 of 144 Old 01-27-2010, 01:32 PM - Thread Starter
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Thanks for taking a look at it and reminding me of that

I will do what I can about the dip.

My main problem right now is the 14dB efficiency problem. (equal to less than one 20th of the power). That's like...err...uhh... not good!

I also found that turning it on its side either A) got rid of rattling or B) made it quieter... I think it was B.

Also I am getting a (corrected) reading of 102dB with one watt at tuning at the port (15.5inch/8.5inch ratio)

...
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post #82 of 144 Old 01-27-2010, 02:00 PM
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Are you using the correction tables for the Radio Shack Spl meter, if that's what you are using?

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post #83 of 144 Old 01-27-2010, 05:51 PM - Thread Starter
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Right, yes, the correction tables for their SPL meter.

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post #84 of 144 Old 01-30-2010, 04:46 PM - Thread Starter
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Testing reveals that the voltage on the output of the amp is reaching a full out clipped 27v from the amp during loud scenes.

I may go ahead and take the easy way out with brute force and get the EP2500 first. But then I'd be worried about blowing the driver..

I really did expect a lot more from an 18" driver, 100 or 1000 watts. Surely there is something wrong here. But how do I figure out the problem?

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post #85 of 144 Old 01-31-2010, 01:00 AM
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You will not regret buying the amp, I believe it will solve all your problems. I think the ep2500 will clip much before you blow your driver as they are incredible subs. My 2c's.
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post #86 of 144 Old 01-31-2010, 11:13 PM - Thread Starter
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Considering that I am not having problems with localization now (except for rattles, can't really do anything about them atm), I think that may be a good idea.

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post #87 of 144 Old 02-09-2010, 08:22 AM - Thread Starter
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I have watched probably 50 movies now with the sub and it makes a good difference.

Of course, the bad response is a problem and I am aiming to fix it.

Due to laptop problems, I have not been able to do any testing, but I DID get a blu-ray player and although I don't have much use for blu-ray functionality (except DTS discs with a 1.5mbps core, I returned the HDMI cable I bought in favor of an equalizer sooner), the USB port, streaming, and other features are very nice to have!

I can now put all my test files on a USB and not worry about computer problems (or soundcard noise).

I am working on testing with sine sweeps to find rattles right now. During 25hz sweeps and below, I can actually see my hair moving in some parts of the room, even with 100 watts

The next step that I can do requires an equalizer and probably some re-arranging.

I am still wondering if anyone in the area has a system with a (properly set up) large LLT that I could hear to know what I am shooting for (or beyond).

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post #88 of 144 Old 02-16-2010, 11:07 PM - Thread Starter
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Keeping it updated here until I am happy...

I still think something is wrong with the sub, but troubleshooting has led to a dead end. I would expect 90dB outside at one watt/meter WITHOUT an early roll-off at 40hz (light roll-off), NOT (and I say NOT) an average of 80dB.

The receiver has shut off 3 times so far during movies, and no, I didn't really notice. In fact, I didn't know until after the movie when I saw the receiver had shut off.


If you tell me I 'need more power' you're right, but we can't just ignore sensitivity. I can't really test the driver except by going somewhere to see a similar sub playing with similar power.

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post #89 of 144 Old 02-16-2010, 11:17 PM
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1) Radio shack spl meters aren't accurate at low frequencies... even with using the tables to add to make up for the lack of meter sensitivity down low. Individual units can be off 3-4 db easily. I think it was Ricci that posted a picture of two different Galaxy meters and a couple of rat shack meters that had different readings... which one do you trust?

2) Stiff spiders can rob you of some output at low drive levels. Temperature will affect the compliance as well. Cold temps, the surround and spider will be stiffer than room temp.

I dunno what to tell you other than I don't feel you have a problem with sensitivity.. if you add up all the factors that can be accounted for.

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post #90 of 144 Old 02-27-2010, 11:18 PM - Thread Starter
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The last post made me go get rid of more rattles... (which helped) and re-calibrate the system. Somehow it seems better, but anything but low volumes gives a rattle.

The driver itself gives a little bit of rattle, but I have trouble telling how much or why.

I decided to get some measurements of input vs. output, what the meters said, no corrections.. Taken 1m from the driver in-room.

20hz Test

1.97v = 72dB
3.94v = 79dB
8.85v = 85dB
17.7v = 91dB
19.83v = 91.5dB

15hz test

1.95v = 69dB
4.38v = 75dB
8.75v = 82dB
19.56v = 90dB

30hz test

2.1v = 81dB
4.17v = 88dB
8.34v = 94dB
23.5v = 103dB


These tests showed me that input vs. output scaling is pretty consistent. The last of each test is the point where I noticed distortion.

The maximum corrected output would be 102dB (15hz), 99dB (20hz) and 105dB (30hz). Add maybe 10-13dB from an amp and I'm 5dB shy of my output goal, meaning a second subwoofer. I still think that the fact that it's in a corner would give me more SPL, at least at 30hz.

The next 'free' step would be re-positioning the sound system and listening position.

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