Testing Cheap Thrills with REW - AVS Forum
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post #1 of 163 Old 10-13-2013, 09:17 PM - Thread Starter
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I built a set of Cheap Thrills that I am putting head to head with my old DCM KX-12 speakers. I have 2 Onkyo 818s and I am splitting the HDMI signal to both receivers, allowing me to A/B compare the speakers quickly with just the mute button. Something doesn't seem/sound right. While I listen to various songs I would level match the 2 speakers by ear and things sounded close. The next song however might need one of the speakers adjusted 6-8dB to sound matched.

Here is my attempt to do a REW sweep from 20-20,000 on both speakers. The mic on the CT is between the waveguide and woofer and about 1 - 1.5 feet away. The mic on the DCM is 1-1.5 out from the tweeter because it is a MTW. I smoothed both curves 1/6 because they are very jagged raw.

I may not be performing the test correctly because when I have seen the omnimic, the results are much smoother with less smoothing.

This test is in my unfinished basement, very near a corner boundary with exposed concrete.
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post #2 of 163 Old 10-13-2013, 09:32 PM - Thread Starter
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I forgot to say that my mic is the umik-1.
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post #3 of 163 Old 10-14-2013, 01:28 AM
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just eyeballing your data, this is how i'd guesstimate the ct's are performing. red dashed line.

the peak at 40hz is a room resonance.

the suckout around 200hz is one or more reflections off the walls near the speaker.

the suckout up around 1.7khz is simply a measurement artifact based on where you have the microphone located.


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post #4 of 163 Old 10-14-2013, 06:38 AM - Thread Starter
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Thanks LTD, do you know of a better way to measure them? The sky is clear today and I've got 10 acres so I could test one outside if that makes a big difference.

Here is what my basement is shaped like, however it is completely unfinished, so none of the walls that are shown are there. The speaker is in the bottom left of the plan, maybe 2.5 - 3 feet off the back wall and only 6" off the side wall, toed in a fair amount.


I could center a speaker along the bottom wall and let it shoot across my basement, except for a couch, it is pretty long, only 13' wide in that area though. Would that help with measuring the speaker?
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post #5 of 163 Old 10-14-2013, 06:50 AM
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if you do them outside, you want to raise them off the ground a bit (this can get annoying) and measure like you just did

some people use stools some use ladders, some build custom stands ect


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post #6 of 163 Old 10-14-2013, 06:59 AM
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You need to move the mic further back. Move the speaker away from reflections. Going outside is definetly a good way to do it. If you can't raise the speaker up, lay it on its back and place the mic 4' above it. I prefer to raise the speaker up.
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post #7 of 163 Old 10-14-2013, 07:07 AM - Thread Starter
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I just performed a test with the speaker 2.5 feet off the ground, near the center of the front of my HT area. Mic was 30" out and 6" above tweeter, just like Bills measurements show. I'll take it outside to really test it, however this doesn't look anything like Bills.


Here is Bills.


When I take the speaker outside, can I place it on the roof of a Bobcat or similarly a tall car or should it be on something skinny like a ladder like Sibuna mentioned?
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post #8 of 163 Old 10-14-2013, 08:48 AM - Thread Starter
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I just ran the test outside. The CT was on top of 2 stacked KX-12s so about 5.5 feet in the air. The mic is about 10-12 feet away at roughly the same height as the bottom of the waveguide. The kids playground is about 50-60 feet away, about 20 degrees in front and to the right. My house is about 25-30 feet behind the speakers.

I am still getting the ugly area in the crossover region. I also took the response curve and 1/6 smoothed it and shifted it down so that it would be more visible.
If I can, I'll attach the raw REW file.
CT outside.zip 1814k .zip file
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File Type: zip CT outside.zip (1.77 MB, 5 views)
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post #9 of 163 Old 10-14-2013, 09:03 AM
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post #10 of 163 Old 10-14-2013, 09:38 AM - Thread Starter
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I'm not sure if you can still make this design because Bill said the following,
Quote:
It might take it a notch down on the bang per buck (bpb) competition, but I think the Celestion TF1525 will work in there, too. Not as much Xmax, though. Oh, and almost twice the $. Still, compared other 100buck drivers, it doesn't look too bad.

I should also mention that I had the crossovers wired wrong; I had wired one connection to Tweeter + instead of ground. It was after the protection capacitor so I don't think I damaged the compression driver.

Here is where I goofed up.
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post #11 of 163 Old 10-14-2013, 10:22 AM
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humm in interested to how you think they sound after you fix that, the CD seemed fine on Sat and measured like it should have at pops. I can post up that curve when i get home if you want it


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post #12 of 163 Old 10-14-2013, 10:49 AM - Thread Starter
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They are much less bright and have bass now. I think I was bypassing the tweeter padding before. They sound a little dull now and audysee actually brightens them up now.
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post #13 of 163 Old 10-14-2013, 11:17 AM
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thats good to hear


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post #14 of 163 Old 10-14-2013, 01:32 PM
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Quote:
Originally Posted by NathanJ View Post

They are much less bright and have bass now . . They sound a little dull now and audyssey actually brightens them up now.

Interesting that you would characterize these as 'dull'. I have a Umik-1 on the way and will post some test results after I get it.

I am driving these with a Denon 4311 and find they have just the right balance of mid-bass and clarity in the upper frequencies. I haven't run Audyssey and am just setting levels to my liking from the MLP. I will run Audyssey at some point, problem is I like to fiddle with settings.

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post #15 of 163 Old 10-14-2013, 01:48 PM - Thread Starter
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I found a problem with at least this one Cheap Thrills I am testing. It needs the compression driver polarity reversed. Look at this graph, the mic didn't while I was reversing polarity on the tweeter. I also found that I was using my UMIK calibration twice, once for the mic and once for the sound card. Once I removed the sound card calibration things looked better. MiniDSP also provided me with a calibration from 5hz up as I was an early adapter of the mic, now they only provide it from 20 and up. If I download the calibration they have now, it produced a different response in the upper frequencies than the one I received when I purchased the mic. The original calibration produces a much flatter line in the upper region, much more similar to Bills.

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post #16 of 163 Old 10-14-2013, 02:13 PM - Thread Starter
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My number 2 CT is testing exactly like the first, so it needs its polarity switched, too.

I am also noticing that the CT roll off very early. I pulled the stuffing out of the woofer area of mine, but the upper area around the horn is still insulated. That gained 2-3 dB in some regions, but it still rolls off fast. I may try building a ported box at some point...

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post #17 of 163 Old 10-14-2013, 04:07 PM
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the response that you are getting in #15 looks quite nice. what conditions were in play for that sweep?

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post #18 of 163 Old 10-14-2013, 04:13 PM
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Double check your crossover assembly to be sure it's correct.


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post #19 of 163 Old 10-14-2013, 04:28 PM
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I want to see more KX-12 measurements for comparison. I've been rocking a pair of those in my shop for years. Preferably "on top of 2 stacked KX-12s so about 5.5 feet in the air" once you get your measurements figured out. :-D
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post #20 of 163 Old 10-14-2013, 04:29 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

the response that you are getting in #15 looks quite nice. what conditions were in play for that sweep?
For that sweep the box was stuffed and the tweeter polarity switched. The mic was about 10 feet away and in line with the bottom of the waveguide and tested outside 5.5 feet off the ground.

The sweep in post 16 is the same except I pulled the insulation out of the lower 2/3 of the cabinet in the woofer area. That added up to about 3dB in the lower region and the upper region didn't change if I remember correctly.
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Originally Posted by Erich H View Post

Double check your crossover assembly to be sure it's correct.
I went through the crossover last night and found the one problem I highlighted above. I copied to large extent mhutchins crossover he posted on this forum. The back side of mine isn't as pretty as his, but I can post a picture to get some more eyes on it.
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post #21 of 163 Old 10-14-2013, 05:19 PM
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did you perform and speaker break in?

if not, that could cause a lessening of the bass response.

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post #22 of 163 Old 10-14-2013, 05:30 PM
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winisd (thiele small) model for under 200hz tends to be pretty accurate. matches your measurement pretty well.

not sure what is going on with your speaker around 300hz.


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post #23 of 163 Old 10-14-2013, 06:03 PM - Thread Starter
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Here is the KX12 vs the Cheap Thrills, they both show the same dip at 300. I have always loved the amount of bass the I get from the KX12s and it appears from this curve that the cheap thrills keep up fine up until my crossover to my subs. The DCM was placed on top of the other DCM and the the CT, that put the tweeter at the proper region for the mic.

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post #24 of 163 Old 10-14-2013, 06:07 PM
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so you are going to hear deeper bass and more shimmer with the dcm, while the ct appears to have a smooth response. the way the room effects are captured in each always amazes me, though it shouldn't. really goes to explain just how much we are actually hearing "the room".

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post #25 of 163 Old 10-14-2013, 06:08 PM
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if it wouldn't be a pain in the butt, could you post up the .frd files? i'd like to plop them in excel and monkeying around a bit.

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post #26 of 163 Old 10-14-2013, 08:01 PM - Thread Starter
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Not a problem at all LTD. I've never used the FRD format, but it appears that it is a tab-delimited text file. Here it is for the KX12 and CT with a pretty generous amount of fiberglass insulation. The second file is just the CT with minimal stuffing. You probably didn't want the KX data, but it isn't very large so I'll attach it anyway.

I can attach the REW mdat file if I haven't given you what you wanted/needed. It is interesting to see the same dips and peaks in both speakers, but these were tested outside. I was only about 20 feet off the side of my house, projecting into the yard. There is also a 2 level playhouse 50 feet away 30 degrees to the right from the speakers. I'm sure each one of those peaks relates to a reflection off of something. REW exports for Cheap Thrills and KX12.zip 6k .zip file Cheap Thrills - minimal stuffing.txt 6k .txt file
Attached Files
File Type: zip Rew exports for Cheap Thrills and KX12.zip (6.0 KB, 6 views)
File Type: txt Cheap Thrills - minimal stuffing.txt (5.6 KB, 3 views)
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post #27 of 163 Old 10-14-2013, 08:11 PM - Thread Starter
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This is nearly a repeat of what I posted in #16, however the colors on the graph made it hard to differentiate. This graph is smoothed more than the others at 1/3.



Does the minimal stuffed box, purple above, look better? They are side by side above 600Hz. Except for 400-500, the minimal stuffed one has more output down low.
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post #28 of 163 Old 10-14-2013, 08:29 PM
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The polarity definitely needed to be reversed it seems.

The reflections are from the ground. The other objects are to far away.

Ya, the less stuffing looks much better. Should probably have some stuffing in there to kill internal reflections, but maybe less that what you originally had.
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post #29 of 163 Old 10-14-2013, 09:01 PM
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so here is some confusing stuff. :-)

first pic, red and blue are your raw measured responses. red is ct. blue is kx12.

then I attempted to identify your measurement setting transfer function using a 20 period moving average window around both of the speakers tested. essentially, the idea is that if a peak appears in both speakers at the same frequency (poking through the 20 period m.a. for each speaker), it is probably an environmental influence. crude and not exact, but rough ballpark. the transfer function is plot two.

in the third picture, the before (raw) and after (subtracting environment transfer function, mod) of the ct is shown.

in the last picture. the ct (raw and mod) is shown against bwaslo's measurement of the ct (heavy blue). resized and rescaled to be the same.

2khz tracks really well. bass on yours seems a little shy. you seem to have a little more energy from 800hz to about 1.6khz.








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post #30 of 163 Old 10-14-2013, 10:56 PM - Thread Starter
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Very interesting. The speaker is nearly brand new, maybe it needs to be broken in?

I should look at my mic calibration to see if it could be off.
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