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Discussion Starter #1




The top image is my 1.2-3 ft^3 towers with one RS180 woofer (with matching tweeter, although still tweaking the crossover) and I seem to be down 10-20dB in the low end and I'm not sure why. I know my room isn't optimal. It's 11*12 with a large desk in the center of one wall with the speakers a foot out from the side walls but beside the desk (1.5 feet beside the desk).

The bottom image is the same exact setup, except with a 100Hz 12dB boost. I'm not sure of the Q on the filter, because it's from my Realtek soundcard (which measures +/- 0.5 db from 1-16k Hz).

Modeling the driver in this box, ported with the same 1.5 port 2-2.5 in. long looks to be flat to below 40 Hz, and sealed the F3 is below 80. is the port that too small for the woofer, doesn't seem to be a problem with the boost? Is the room just sucking all the <200Hz out? is there port reflection from the desk perhaps? There is only 2.5dB BSC, but with the speakers almost up against the wall, that doesn't seem to be it and with the 9.5 in. baffle width the BSC F3 would be above 500. Measuring with the port plugged, and I didn't seem to lose any low end? Is the port too low? I didn't figure that would be a/the problem but maybe? The mic (RatShack) is level with the woofer, and the port is roughly 9 inches below the woofer, but above the desk level by an inch or two.

I'm at loss as to what it could be, should I take close-mic measurements? should I measure outside without the BSC filter?

Sorry for the seemingly dumb post, but I'm stumped. I don't think I'd use a sub if I could get these flat to ~40-50 Hz. -_- *sigh*
 

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yes, would you take close mic measurements?, that would give more info.

as far as you measurements being 10 or so db's low, it seems to me that your settings might be set a little low, or maybe a lack of calibration?

sometimes, when using a small woofer, on the inside of the cabinet where the driver is cut out, if the opening is not chamfered at a 45 degree angle or at least rounded over, then the Q can spike causing a drop in low end, similar too a small enclosure. this could possibly explain the premature lowend drop.
looking at your graph, that doesn't look like the case to me, but i dont know, could be anything.

thats all i can think of
keep us posted
 

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Discussion Starter #3 (Edited)




Top picture is the driver, and port without the the boost. The bottom, with. So it looks to me like the port isn't even doing anything at all? Which would explain why there wasn't a difference when I plugged the ports, but still doesn't explain why I'm getting such bad low end response. Maybe I need to make sure the enclosure is 100 percent sealed, aside from the port? But besides, even if was a "sealed" build, wouldn't the low end still be better? I mean, models F3 is below 80, not above 150. I wasn't planning on getting everything 100% before getting everything right with the crossover, etc, but I may want/have to?

I don't think it's faulty calibration because it even sounds super weak on the low end without the boost, but with my sub on it sounds pretty fine since I'm down flat to 10 hz in this small room.
 

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How long have you had these drivers, and what use have they seen? I recently made a pair of NatalieP's (RS180-based MTM) with very different results, attached (done with an EMC8000 mic, not the RS SPL meter). Your low end looks like mine sounded for the first few minutes, and your high end looks like there's no tweeter.

Since the port only makes sound when the woofer backwave resonates in the box, the lack of driver low end means there's no back wave to resonate and so no sound augmentation through the port.

And then perhaps there's an issue in the measurement system, or the XO design. Can you test response of another full-range speaker? What do you get from the RS180s with the XO bypassed? What's the story on the XO design?

I'm also confused by the pair of curves; is one the port? It almost looks like a muted version of the driver output, with a complete lack of normal port resonances. I'm sorry if this seems confusing, but I haven't made a speaker from scratch yet, so everything I've done has worked well!

Frank
 

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Discussion Starter #5
I've had the woofers a few weeks, and they've been broken in thoroughly (almost xmax for a few hours) and had over 100 hours of music put through them as med-high levels. They should be moving more, they aren't moving hardly at all until I get the levels above 95-100 db, even running full range.

Those last two graphs might look like there's no tweeter, because the mic was about two inches away from the woofer, so the tweeter was over 75 degree's off vertical axis, and I haven't taken on axis tweeter measurements yet, so that's why it may look like that (rolls off at 8k). Don't mind the 1-2k hz dip, that's where I'm tweaking the crossover, even though the dip changes when I move the speakers around...

I can test a pair of Celestions later today. Maybe it's my amp? I'm powering these with the Dayton APA150, and my last pair of speakers seemed to have the same problem (rolling off at 200-300 Hz) but they were a vintage pair of Pioneer studio monitors from the 70's.
 

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Actually, that's why I suggested a second test speaker. A driver can be defective, and many failures are obvious, but it's highly unlikely that two mid-woofers would have the same low-end fall off you're seeing.
Frank
 

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Maybe it's my amp?
More likely it's the cheap Radio Shack meter you're using to measure full range.

Buy or borrow someones Galaxy CM-140 or ECM8000/preamp and then you can have some confidence in your results.

brucek
 

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Discussion Starter #8 (Edited)




Top is the RS180 + RS28 in box, 5-6 inches away. BSC, crossover, in box, against a wall.

Bottom is the same thing but at the listening position. I guess I had my crossover wired wrong last time. Oops. Still, I'm more focused on the *below 500Hz*

I'll find get those celestions to test.
 

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Discussion Starter #9 (Edited)




First image is a celestion SL6S nearfield, the second is at the listening position. On those graphs, they seem to stop at 100, which they very well might as it's a single 6.1/2 woofer and 1-1.5 in. metal dome tweeter.

I'm concerned it's my amp, because I know the RS meter is the more logical culprit, it just doesn't sound like it. Everything sounds very lacking without my sub, to which everything measures just dandy when it's on.

I haven't learned much today, other than that I had my crossover wired wrong, and that I'm still frustrated.
 

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Discussion Starter #10
I just talked to my father about it, (he's the one who helped me with the boxes and whom I ramble about speaker stuff to, because he'll listen) and he knew what I was saying about the chamfering because they do the same thing in dentistry, so he said he'd help me with that, and make sure everything's sealed up.

We may have to chop the bottom off, because due to my new subwoofers the speakers are going to be placed on top of those, and at 49 inches tall + 24 inches of sub, 73 inches is pretty tall! Shorter box, chamfered, all sealed up. Sounds good, and hopefully will fix the problem, otherwise it's on the drivers themselves and since I've had them for a while - I don't think I can send them back. Or the amp, but I'll test the speakers with another amp tomorrow to make sure.
 

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Yes, the high end looks a lot better, and with 2 speakers showing the same lack of LF, my money's on the amp. Mine's nothing great, but it does let me set them to large so the low end's not truncated.

Trust your ears, and try the generator function in REW to convince yourself they're right.

frank
 

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Discussion Starter #12
Here's an updated graph. I took 15 inches off the bottom, taking off .4 ft^3, raising the tuning 10 or so hz, AND "chamfering" the woofer hole. Being as the box was already constructed, I couldn't router it out, so I took a drill and a large egg shaped burr bit and ground a ton of MDF off making it almost a 45 degree angle, but not quite. Cutting it down, making sure the bottom was at least temporarily sealed against another piece of wood, and chamfering the woofer cutout all helped a little bit - BUT NOTHING'S SOLVED MY PROBLEM. =(

The mic is 1 meter away, 10-15 degree's down, 15 degree's off axis, with the tweeter on the outside.



Should I just start over with the enclosures? That'd hurt, but I'd get a change to do it right, and I may just make a small sealed box, since I'm going to be crossing them over to a sub at 100-140 Hz. The speakers would sit directly 2 feet above the subs. I'd love some feedback from more than one person, although I'd like to thank you Frank for your help.
 

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Discussion Starter #13
As you can see, it would seem the woofers have room to breath, and yes that's the port a bit below it.

I also got.. frustrated? and duct taped the box seems to make sure there weren't any air leaks there didn't appear to be.

Still no luck.

 

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You are using REW correct? Are you measuring inside or outside with no reflections? If I were you I would take a look at the waterfall tab. ( have to hit the 'generate waterfall' button )

Keep in mind that placing the speaker on a stand can rob you of output. Does it sound like it should, or does it really lack bass? If it sounds OK, I would suspect your measurements. On the other hand, if it sounds anemic, I would want to check everything out.
 

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Discussion Starter #15
I'm measuring inside, at my listening position.

What would a waterfall tell me?

How would putting it a foot off the ground take that much out of it, especially in the 100-500 range?

IMO, it sounds weak, but not anemic. I might take it outside sometime when I can put REW on a laptop.
 

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Waterfalls can be valuable, they what happens to the initial signal in many slices of time, if you know how to interpret that you can find problems with the room. The placement upon a stand will have effect on the lower bass and up over the omnidirectional limit for the driver size.

You need to measure outside away from boundaries, at least 20 feet if you can make it happen. Put the speaker on the ground, measure with the mic 1m away on the ground. Repeat at 2 meters. Repeat with the speaker up against a large boundary, a garage door will work fine.

Now you have a bunch of measurements that you can sift through. What mic are you using? Do you have a cal file loaded?
 

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Discussion Starter #17
Alright I set the meter to C weighted, took the calibration file off, and then checked the "C weighted meter" box. Ran another sweet and had to turn down my sub 1/4 to a 1/3 of the way to get it level, lol. I've been used to my brother's car.

Again, this is at the listening position, with 1/3 octave smoothing.

 

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Here's the critical question - did you change anything other than the meter? Does it sound any different? Are you now thinking your ears were badly calibrated?

And have you ever read this?
http://www.audioxpress.com/magsdirx/ax/addenda/media/koya2811.pdf

I've been thinking the only thing that could cause your problem is an amp with a really high subwoofer crossover - I never considered you might be using A-weighting for your measurements. If that's the case, I've learned something , too!

Have fun,
Frank

PS I retrospect, this comes across a little harsh. No offense intended, just venting a bit of exasperation.
 

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Discussion Starter #19
No it's okay. Um, well I had to scoot the speakers further away from the wall, and thus only about a meter away from the LP. The subwoofer did not move, only turned the gain down, and the crossover frequency down.

Live music, acoustic music, classical, etc. all sound more natural with the lower crossover point, and less bass emphasis, but rap/techno music sounds.. well sounds like I don't have my sub on, but then again I've been around unbalanced (if you will) speakers for the past years.

I'm using an old, analog meter, BTW. Not digital.
 
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