Nonexistant Mid-Bass - AVS Forum
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post #1 of 24 Old 06-09-2012, 12:49 PM - Thread Starter
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Complete System Setup (I know its not all perfectly matched, my system is still a work in progress)

Reviever: Yamaha RX-V667
Center: Paradigm CC-170
Fronts: Paradigm Towers, titanium dome tweeter, 5 1/4s, powered 10" woofers
(unsure of model)
Sides: Polk TSI-200
Rear: Polk OMW3
Extra Subwoofer Polk PSW125
(Explained below)

Room: About 20x30, hardwood floors, 12' ceilings, open archway to dining room, open staircase upstairs

When I first set up this system, I did not have the additional polk subwoofer. I ran the reciever's YPAO setup, then manually tweeked distances, levels, and eq.
Center/Front/Sides set to large, Rears set to small, Extra bass from said speakers off.

Highs and Deep bass performs wonderfully for both music and movies, but there is almost no mid-bass in the living room. If you walk into my dining room or upstairs it' almost overpowering, so I assume there some sort of wave cancelation. I have tried putting the TV, center, and fronts in 2 different location, but it didnt help. I added the Polk sub and moved it around the room to see if it would fill in the missing tones, but it barely helps. Any advice on what i could do?

Thanks
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post #2 of 24 Old 06-09-2012, 02:07 PM
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So you've tried adjusting the subwoofer distance in the AVR and/or reversing the phase? A subwoofer with reversed phase at the problem frequencies can act like a "powered" bass trap. Of course, you could try a bass trap too. I'd have to be there to hear it for myself >_>

...
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post #3 of 24 Old 06-09-2012, 02:17 PM - Thread Starter
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The YPAO had the subwoofer distance just about perfect, but I did play with the setting manually to see if it would help at all (it didnt). The Polk has a phase switch which I have adjusted to sound best, but the Paradigms towers do not have a phase adjustment, and If the Yamaha has a phase adjustment for the LFE channel, I cannot for the life of me remember where its at...
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post #4 of 24 Old 06-09-2012, 02:20 PM - Thread Starter
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And to be honest I do not fully understand how to use/place bass traps properly
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post #5 of 24 Old 06-09-2012, 04:23 PM
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Did you measure the frequencies with an SPL meter and what did it tell you exactly? Where is the "hole"?
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post #6 of 24 Old 06-09-2012, 07:23 PM - Thread Starter
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No as of right now I don't own a SPL Meter, I've made all my adjustments by ear. Should that be my next purchase? And what would you recommend, budget friendly?
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post #7 of 24 Old 06-09-2012, 10:51 PM - Thread Starter
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My fronts, btw, are Paradigm Legend V2s

I've found a solution that seems to be working a lot better, although I'm still not completely satisfied.
Instead of running the Paradigm towers' 10" woofers off the 0.2 LFE I now ran them to the left and right pre-outs on the Yamaha, with the towers set to large with "extra bass" enabled. The Polk 12" is now alone on the LFE, and pushed a little harder. The 10s are pretty much focused on mid-bass and the crossover on the polk is set at 60 to just handle very lows. Still not perfect but the sound is greatly improved...
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post #8 of 24 Old 06-10-2012, 10:44 AM
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I have an older RadioShack meter ($50) and a cd from Reeves Audio with frequencies beginning at 20 or 25 Hz that adjusted already for the sensitivity fluctuation of the RS meter.
I don't know whether the current version of the RS meter is more prezise or not, but the Reeves cd has also "unadjusted" frequencies.
There are also adjustment tables for the RS meter on the web, but my knowledge of the meter is from 2005, when I bought it. Somebody else might have more up-to-date info on the current meter.
Without meter and frequency cd, it will be pretty much impossible to really see where peaks and troughs are. I thought it was well worth the money.
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post #9 of 24 Old 06-10-2012, 11:09 AM
 
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If you are going to buy any additional equipment, may I suggest investing in equipment which enables far greater utility and is far more future oriented...

Download the free RoomEQWizard software (it also has a built in tone generator) as well as the ability to generate a wide selection of the most useful frequency and time domain measurements.

Along with a computer, you will need a calibrated Dayton EMM6 mic (uncalibrated from Parts Express (~$48) or calibrated from Cross Spectrum ($70)) and an ART Dual USB Pre mic preamp ($69).

This will avail you with much greater capabilities that will enable you to not only definitively troubleshoot this situation, but also to completely evaluate your system within the room and effect proper treatment as necessary.

If you later desire more capabilities, consider ARTA for ~79 Euros or ~$98.75USD.
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post #10 of 24 Old 06-10-2012, 11:19 AM
 
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As general as the problem is described, it may be as simple as a modal null, SBIR, or even a driver/crossover out of polarity.

But few if any sources of a problem will result in lack of the energy in the entire room yet present outside of it. Any of the aforementioned issues will result in a variable response based upon location within the room.

You can quickly make near field measurements of each speaker to determine polarity of the individual drivers and then run waterfalls and possible impulse and ETC responses at the listening positions for each speaker to determine what is going on after you have a more defined concept of the actual problem now too amorphously defined.

Once the precise nature of the problem is known, specific steps for correction can be specified and their optimal effectiveness verified using the same measurement setup..
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post #11 of 24 Old 06-10-2012, 11:32 AM
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Quote:
Originally Posted by cardshark2048 View Post

And to be honest I do not fully understand how to use/place bass traps properly

Acoustics and treatment are nowhere near as complicated as many people believe. This is short and gets right to the point:

Acoustic Basics

Further, this is surely what you need most, along with optimizing placements.

--Ethan

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post #12 of 24 Old 06-10-2012, 03:08 PM - Thread Starter
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I work for a division of RadioShack, so I picked up an spl meter there ($20 with my discount) and used NCH Tone Generator on my laptop, connected via HDMI to my Receiver. Just from moving my head to look at the meter and back to my laptop its pretty obvious my living room is an acoustic nightmare... Not only were there noticeable differences in volume at certain frequencies, just moving my body around would cause 3+ decibel shifts on the meter (I made sure to keep myself out of any direct speaker lines to it). Here are my readings at various frequency's. All readings were double checked with me standing in a different location also.
Laptop volume was at max, and the Yamaha was at -12.0db the whole time
20 hz 90
22 hz 89
25 hz 94
28 hz 99
31 hz 104
35 hz 101
39 hz 105
44 hz 105
49 hz 107
55 hz 104
61 hz 100
69 hz 96
78 hz 101
87 hz 97
98 hz 102
110hz 98
123hz 97
138hz 102
155hz 99
174hz 99
196hz 78
220hz 77
246hz 91
277hz 90
311hz 98
349hz 94
392hz 94
440hz 95
493hz 87
554hz 91
622hz 85
698hz 85
783hz 86
880hz 87
987hz 82
1180 81
1244hz 89
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post #13 of 24 Old 06-10-2012, 03:47 PM
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The room having all hard wood floors as well as its size and 12' ceilings are the main problem that I see. It also has openings to other rooms. So you have reflection issues from the floor and high ceiling and dips in mid bass most likely from the size of the room. How far away is the main listing position from the center channel and mains? The closer the better in your case.
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post #14 of 24 Old 06-10-2012, 04:52 PM - Thread Starter
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Originally Posted by Secret Squirrel View Post

The room having all hard wood floors as well as its size and 12' ceilings are the main problem that I see. It also has openings to other rooms. So you have reflection issues from the floor and high ceiling and dips in mid bass most likely from the size of the room. How far away is the main listing position from the center channel and mains? The closer the better in your case.

I sit roughly 10' from my center/mains.
Basically adding a rug of some sort, along bass traps and other acoustic aids should go a long way towards fixing my issues then?
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post #15 of 24 Old 06-10-2012, 05:09 PM
 
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Aside from not plotting them in order to easily show visual trends…

We have the frequency response that only shows us the result of various possible direct and indirect signals superposing (combining).

We are unable to determine the response of each speaker independently, and how the measured response in the room may be a result of the interaction of the speaker and the room, and, if two speakers were driven simultaneously in the measurements, the destructive interaction of the two direct (as well as various indirect reflected) signals.

We still cannot knowledgeably distinguish between the response of each individual direct source and the various interactions with the space and each other in the form of a baseline speaker response, modes, SBIR and the comb filtering that necessarily results from the superposition of the energy from two direct spaced sources (not even to mention the additional associated reflected energy of each, being driven simultaneously.

In other words, in order to whittle the possible causes down, and identify the degree that each, if it is a factor, contributes, we need much more information. And since you are choosing to do this manually in the frequency domain, it will require a bit of busy work.

As instead of using an automated sweep, you are plotting the gain at each discreet frequency manually. So the workload grows exponentially.

Additionally, the region between 174 Hz and 248 Hz may very well correspond to a crossover region with a number of possible contributing issues.

The fact is, we are still guessing as the data is not sufficient to isolate and eliminate sufficient variables in order to narrow the source of the problem to one that can be specifically addressed. We are still at the point of guessing and trying various steps that unfortunately will not respond in a manner sufficient to eliminate individual variables.

If you think the problem is modal, you would do well to construct a grid on paper and in the room such that you map the surrounding listening points relative to the current listening position and play the tones and determine the modal distribution at those points. Typically, if left right symmetry has been maintained in the room setup, moving forward or back a short distance should be sufficient to move out of a null and into an intermediate point prior to encountering a peak.

Otherwise, you will likely need to further investigate, which if done in a brute force manual method will be tiring at best…obtaining a baseline nearfield frequency response for each speaker and subwoofer (if used), the response at the listening position for each speaker individually (without a separate subwoofer), again with the subwoofer. You can also measure each speaker source individually, moving the speaker out from the front wall while maintain the same distance to the side and floor/ceiling, and then again maintaining the spacing and height with the front wall while varying the side wall distance, and then once again maintaining eh front and side wall spacing while varying the height in order to determine the contribution of SBIR.

And then we have the issue of crossover alignment in the time domain between various spaced sources reproducing the same passband out of phase. A classic recipe for comb filtering…

And if you have open spaces into adjoining rooms, you have the contribution of additional modal behavior due to coupled spaces in addition to the behavior of the room itself.

But the fact remains; you have too many contributing variables included in the basic measurements you are making to be able to isolate any of them. In effect, instead of constructing an experiment where you solve for a single variable, you have a multivariate equation such as: a + b + c –d +e –f = 15. …Solve for c.

In such a fashion you can iteratively determine the degree to which the speaker itself, modal, SBIR, or finally the superposition of specular reflections are contributing to the creation of the frequency anomalies.

Not quick or elegant, using only an SPL meter and tones, which is about all you have. Conversely, with a tool like REW the process would be done very quickly

The problem is not that necessarily that difficult to address once the causal factors are known. But narrowing the actual casual variables down to the actual factors as it stands may prove to be a pain.

And if this is the way you will go, You would do well to sit down and begin to map put small systematic experiments that will serve to isolate one variable at a time, while keeping track of the rationale for such an exercise and keeping track of each bit of data so that it can be used in what will prove to be a rather tedious process of elimination. Until you can narrow the focus, you will be subjected to myriad well-meaning suggestions to try different things based on whatever aspect of many that one might chose to focus upon... ....Me?...I would get REW a preamp and a mic. ;-)


addendum:

A thin rug that will do little more than EQ high frequencies while doing nothing to the mid and low frequencies will have NO effect on low frequency or modal anomalies, and it will only tend to EQ the highs. Nor will thin wall treatments do much of anything to control reflections at the frequencies of concern! As Ethan has pointed out earlier, for low frequency issues, assuming they are due to speaker room interaction and not driver-driver or speaker speaker interactions below about 300 Hz are in the realm of BASS traps, not thin panels/rugs that function effectively only against high frequencies..
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post #16 of 24 Old 06-10-2012, 06:16 PM - Thread Starter
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I had to get rid of all external noise to concentrate on that post enough to where I could understand what you were saying. I swear I have ADD... anyways
Essentially, taking manual measurements like I did confirms there is a problem but does nothing to move towards a solution?
I'm now going to take the advice posted a couple times and use REW... Ive downloaded and installed the proper software. Is it possible to use my RadioShack meter as the input device with REW? I only ask this because they had the calibration file for said meter posted on the site. Or should I still invest in a nicer mic?
Also what might you recommend as a preamp to use with REW? budget friendly please...
And in the meantime what can I do to further figure out what the problem is and possibly work towards a solution just with the tools I have? dragonfyr might have already told me this in the above post, but as I am sure is painfully obvious, I have a rather limited working knowledge of most of this, and if I was given the answer I did not understand it.
Any resources that could further my knowledge in these areas would be appreciated too. I do enjoy learning more.
Thanks
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post #17 of 24 Old 06-10-2012, 06:50 PM
 
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Yes, a RS SPL meter can be used (assuming it has an output). Just realize that it is a large diaphragm omnidirectional mic and is suitable only for low/mid frequencies and is therefor limited in its application.

For more universal broadband use you would want a calibrated small diaphragm omni mic, the lowest priced 'best deal' of which is the Dayton EMM-6 available in the basic calibration package from Cross Spectrum for ~$70.

But for your purposes here to ID the variables and specific issues at hand at this point, the RS SPL meter should get you going just fine.

If you have a Mac, you can also use the internal soundcard of the unit as a stopgap mic preamp (although I would seriously suggest considering getting the similarly 'lowest cost best buy pre-amp' that supplies phantom power and accommodates balanced interconnects in the form of the ART Dual USB Pre for ~$69 from B&H Photo.

(Just as a head's up, last year prior to Christmas quite a few places had the unit on sale for $49! A literal steal of a deal! So we will be keeping a weather eye out to see if that was a one time only deal or perhaps such will happen again this fall...)




And for those so interested, a bit more info - and maybe a bit to consider before you run out and buy a limited package such as Omnimic or XTZ...:while saving the money involved in buying a 'large' more expensive package such as EASERA, SMAART or TEF, etc... with features you may not need.

I will also mention for the record that if folks seriously consider pursuing the measurement route that they consider getting a matched pair of the Dayton mics and purchasing the Art Preamp and also the ARTA measurement package for about $100 USD.

The advantage is that this platform not only adds significant (and useful!) capabilities (many of which you may never use but its nice to have them should you get a wild hair and choose to investigate them), but it is also a 2 channel FFT unit that allows you to compare one channel with another - a feature that has infinite practical uses and very significantly extends the power and capability of the system over a single channel FFT rig. I will also note that the 'joke' in the industry has been that if the folks in Croatia ever realize the market value of the ARTA platform (along with the STEPS and LIMP modules), that they will add $1000 to the price to make it commensurate with the other 'big' platforms commercially available. ARTA is a another best buy in the field that will give you plenty of room to grow into. ...But I am not pushing, this is just meant as an FYI. (Note that REW is always advisable as well, if for no other reason than its additional ability to identify low frequency minimum phase modal filters for LF EQ use...so in the least, REW can do the fundamental frequency and time domain measurements, while you add binaural inter-aural cross correlation and 2 channel FFT abilities as well as still more capabilities with ARTA.

Its nice to be afforded such powerful tools that go FAR beyond the alternatively mentioned products for such a small investment -essentially $100USD for both programs plus mic and preamp (total $140 + 3-4 interconnects from MonoPrice)- for those so interested...
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post #18 of 24 Old 06-10-2012, 08:00 PM - Thread Starter
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Probably a really stupid question, but because I'm not really going for perfection here, out of curiosity, why couldn't I plug the SPL Meter's output into my laptops mic input and use REW to take the measurements that way?
I only ask because its going to be about a week and a half before I'll have a chance to pick up the ART Preamp...
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post #19 of 24 Old 06-10-2012, 08:39 PM
 
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No.
First the laptop's audio input has neither the frequency range not the linearity to make accurate measurements.
And you will need to allow the system's frequency response and hardware propagation delay to be calibrated and corrected using the 2nd channel. And if you make time domain measurements you will need to use a loop back on the 2nd channel to compensate for hardware propagation delay errors.

Using an external pre-amp is not simply an unnecessary step that someone dreamed up to make things unnecessarily difficult.... ;-)

Also, I am not sure what you mean by you 'not going after "perfection"'. I would hope that you are going after "accuracy" in measurements - otherwise just sit back and enjoy the imperfect response that you have already achieved....

In the meantime you might want to review REW help configuration pages and the wiring configuration, as you will need a mic cable to connect the mic to the pre-amp, a USB cable to connect the Pre to the computer, an adapter to change the pre-amp output to an RCA compatible fitting and an ~10' male-male RCA cable (for the AV receiver input), and you will need an appropriate short 1.5-2foot 1/4" balanced male TRS to XLT male loopback cable for both preliminary frequency calibration as well as for hardware propagation delay compensation during measurements for impulse and ETC responses.
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post #20 of 24 Old 06-10-2012, 08:52 PM - Thread Starter
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Alright I suppose I can wait. I've just never really mastered the art of patience...
My "perfection" comment was along the lines of using the RS SPL Meter as the mic... not the best option but will acceptable results.
Looks like my free time will be occupied reading up on REW for the time being... thank you
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post #21 of 24 Old 06-10-2012, 10:12 PM
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Don't tell anyone... but I just use my AVR's YPAO calibration mic plugged into the PC's soundcard and TrueRTA.

It works good enough for frequency response measurements and how it changes relative to adjustments I make. wink.gif
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post #22 of 24 Old 06-11-2012, 08:52 AM
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Quote:
Originally Posted by cardshark2048 View Post

I swear I have ADD... anyways

It's not you. biggrin.gif
Quote:
Essentially, taking manual measurements like I did confirms there is a problem but does nothing to move towards a solution?

Regardless of what you measure, the solution is the same: speaker / sub placement and bass traps. But your measurements are inadequate because 1) They show only spot frequencies with large gaps between them, and 2) they don't show decay time which is just as important.
Quote:
I'm now going to take the advice posted a couple times and use REW

Exactly. This will help:

Room Measuring Primer

When you measure using REW, it's not wrong to measure each speaker separately just to have the added info. But when assessing low frequencies both speakers should play at once. Most music recordings are mixed so bass frequencies emit equally from both speakers, so that's the way you should measure too.

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post #23 of 24 Old 06-11-2012, 09:42 AM
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Quote:
In the meantime you might want to review REW help configuration pages and the wiring configuration, as you will need a mic cable to connect the mic to the pre-amp, a USB cable to connect the Pre to the computer, an adapter to change the pre-amp output to an RCA compatible fitting and an ~10' male-male RCA cable (for the AV receiver input), and you will need an appropriate short 1.5-2foot 1/4" balanced male TRS to XLT male loopback cable for both preliminary frequency calibration as well as for hardware propagation delay compensation during measurements for impulse and ETC responses

The behringer uca202 takes all of these other things out of the mix as the soundcard already has usb to pC built in, rca in and outs. This is what I use with my RS meter, and it can be had on the SUPER cheap. works fine for measurements for me smile.gif I have confirmed all measurements with omnimic as well, which is also a great quick-setup rig for simple FR. The new disc also has L/R tracks that can show you how comb filtering and such is affecting your system. so in my case to reiterate, I have REW (free), two rca cables (maybe $10), RS meter, berry mic uca202 ($30) and that is it. works great, all that I need at this point is more time to play biggrin.gif

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post #24 of 24 Old 06-11-2012, 11:14 AM
 
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Quote:
Originally Posted by beastaudio View Post

Quote:
In the meantime you might want to review REW help configuration pages and the wiring configuration, as you will need a mic cable to connect the mic to the pre-amp, a USB cable to connect the Pre to the computer, an adapter to change the pre-amp output to an RCA compatible fitting and an ~10' male-male RCA cable (for the AV receiver input), and you will need an appropriate short 1.5-2foot 1/4" balanced male TRS to XLT male loopback cable for both preliminary frequency calibration as well as for hardware propagation delay compensation during measurements for impulse and ETC responses

The behringer uca202 takes all of these other things out of the mix as the soundcard already has usb to pC built in, rca in and outs. This is what I use with my RS meter, and it can be had on the SUPER cheap. works fine for measurements for me smile.gif I have confirmed all measurements with o mnimic as well, which is also a great quick-setup rig for simple FR. The new disc also has L/R tracks that can show you how comb filtering and such is affecting your system. so in my case to reiterate, I have REW (free), two rca cables (maybe $10), RS meter, berry mic uca202 ($30) and that is it. works great, all that I need at this point is more time to play biggrin.gif

"The behringer uca202 takes all of these other things out of the mix "... It does not. But it does eliminate many capabilities of the rig.

I like saving money as much or more than the next guy, but when the tradeoff is a severe reduction in practical capability, that is where I draw the line on such imagined 'savings'.

First, it has no phantom power and does not accept balanced microphone inputs for a broadband measurement mic and limits you to the use of the RS mic that is anything but optimal or suitable for broadband measurements. And collecting all of this gear simply to make waterfall plots is a supreme waste of effort and time compared to what is otherwise made possible - but that is exactly what you get with either just the Behringer pre or OmniMic. And the ART USB pre comes with a USB cable as well - as if that makes or breaks the deal ... =S

So you 'gain' having to obtain an RCA adapter while sacrificing phantom power for condenser measurement microphones enabling broadband testing, balanced inputs enabling the use of broadband condenser microphones, and you necessarily limit yourself to low frequency waterfall tests that are but a smidgen of the useful capabilities that a platform such as REW provides...

The point is NOT to simply have a crippled rig capable only for simple low frequency frequency response measurements. Aside from the fact that the frequency response simply provides you with a summed result view of the myriad combination of variables without providing ANY insight into the nature or contribution or interaction of said discrete variables! The point of the measurement rig is to be able to look at the behavior in much more detail and to specifically identify the behavior of EACH of the contributing variables, to know each of their constituent parameters, and to thus be able to determine the nature, cause and subsequent solutions to the problems that are manifest as summed anomalies that is afforded by many more points of view than are afforded by a limited frequency or waterfall plot....The point is not to simply be limited to seeing only the resultant summed anomalies that result from superposition! In that sense the time domain view is causal and the frequency domain view derivative. And a platform limited only to the frequency domain view - and especially to the low frequency frequency domain - is a crippled platform compared to what is practical and useful.

IF the problem is simply one of the listening position being in a modal null at those frequencies, then it can provide an easier means of providing a quick mapping of the surrounding locations to see if moving the listening position forward or backward might avail a moderation of the effects of being located in a null.
Other than that, the fact is that we already know just about all we can tell by a simple frequency response measurement - and, except for the location of modal nulls, it is insufficient to isolate and determine any causal factors.

Folks would do well to spend a bit more time learning about the full range of behaviors and the measurements possible to evaluate them. And they would do well to familiarize themselves with the B&K Domain map that provides a simple overview of the various perspectives available by measurements and to what value such perspectives provide. There is MUCH more to the world of acoustics than the flatland that the simple frequency domain perspective provides - and I would suggest that folks examine and become aware of these factors before investing in alternative platforms such as XTZ and OmniMic that cost much more but provide a significantly restricted availability of important and necessary functionality.

Well, we would attach the Domain map, but we continue to get an error message that the PDF document "exceeds the maximum size of 0MB" - funny how that is a maximum that is bound to be exceeded.

So, if one is interested, I guess you can PM me with your email address and I could see if I can get around to sending a copy...
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