# Help with cables for basic measurements



## cdanielski (Sep 11, 2010)

I'm completely new to all things audio and need your help with some cabling recommendations to take basic speaker and subwoofer measurements with REW. I've read through this forum as well as the REW cabling basics, but I'm not 100% confident in what to purchase (cheap newbie here!).

For starters, I'll be connecting a Radio Shack SPL (33-2055) to a Behringer UCA202 External Sound Card (both have yet to be purchased :spend. The SPL manual states the output jack requires an "audio patch cord" and the UCA202 has separate left and right RCA inputs. Based upon the REW connection diagram, is one of these the correct type - monoprice.com # 2680 or #2864 ?

Is it correct that only two cables are needed in total - including the setup for the loopback test? One from SPL to UCA202 and one from UCA202 to an available analog RCA input on the receiver?

I'm also confused if any Y adapters are needed for my configuration? The following note appears in the REW diagram, but I'm not sure what it means: "Optional Y splitter if you wish to feed both left and right channels."

Thanks in advance for all your help. I look forward to learning so much more...


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## SAC (Dec 3, 2009)

...Talk about a minimalist rig...

First, I would advise forgoing the RS SPL meter as an input source and_ at least_ going with a small capsule Behringer ECM8000 mic. And you might consider _at least_ an ART USB Dual Pre... That combination will at least afford you to opportunity to grow into the rig and not almost immediately grow out of it...

But..... if you observe the RS SPL meter, its output is either a 2.5mm or 3.5mm mono mini-jack (its nice of the user manual not to state which format it is), not an RCA jack. 

1. Thus your input cable is going to need to accommodate a male 2.5 or 3.5 mono mini-jack on the RS SPL meter end, and a male RCA jack on the other. Most likely you can achieve this with a mini-jack to female RCA adapter and then a male RCA to male RCA cable. (Monoprice 7174 or 7144 adapter)

2. Loopback is a short RCA male to RCA male cable.

And out put of the soundcard is a male RCA and a typical receiver input is a male RCA. 

3. Thus a male RCA to a male RCA will suffice.This will be sufficient for the basic connection from card to receiver/amp.

4. If you have a reason to drive both channels (most measurements do not use this), then you will need a Y cable that adapts the male RCA connector to 2 male RCA connectors. There are a number of cable and cable/hardware adapter combination that can achieve this. (example Monoprice 6261 or 326)

Note, you will want to make the interconnects longer than 6 feet, as you want yourself and the rig out of the measurement near-field - otherwise you become part of the measurement.


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## cdanielski (Sep 11, 2010)

Thank you SAC. Your future-proof recommendation drove me to look more closely at what I wan't to accomplish (and how much it will cost). Here are my goals on the learning curve ahead. I welcome all comments:

Goal #1, Calibrate speakers to the same dB level.
Equip I need: Radio Shack SPL Meter, 33-4050 $16.02.

Goal #2, Measure subwoofer FR and learn to use REW and associated gear.
Equip I need:	
Option A:	Behringer UCA202 $26.22
Adapter, RCA female to mini male (7174) $0.48
Cable, RCA male to male, 3' (2869, also used for loopback test?) $2.89
Adapter, RCA female to dual male (6261) $1.43
Cable, RCA male to male, 12' (2865) $5.06
Shipping from Monoprice $6.60
Total $42.68

Option B:	Art USB Dual Pre $67.96
Cable, USB A to B, 3' (5437) $0.99
Behringer ECM8000, not calibrated $50.00
Cable, 1/4" TRS male to male, 15' (4795, doubles for loopback test?) $6.92
Shipping from Monoprice $6.60
Cable, 1/4" TRS female to dual RCA (HOSA YPR-257) shipped $4.85
Total $137.32

Goal #3, Equalize subwoofer FR and optimize sub placement
Equip I need: 
Behringer DSP1124, used $50.00
Cable, RG6 Digital Audio, 25' (2683) shipped $13.13
Total $63.13

Goal #4, Full range equalization?
Equip I need:	
Calibration of Behringer ECM8000 $50.00
New Equalizer ???

Would anyone mind checking the cables and connections. Will they work? All show monoprice IDs in parenthesis, except the HOSA. I'm off to read REW docs because I still don't understand the connection diagram during the soundcard loopback test. Night!


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## SAC (Dec 3, 2009)

As far as "full range equalization", you seriously need to get out of the frequency domain and discover the primacy of the time domain.

The following reference may not yet mean much to you yet, but it nevertheless is critical.

You cannot equalize non-minimum phase signals. 
And you address issues resulting from the superposition - the proper term for the interaction - of non-minimum phase signals that manifest themselves as the comb filtering pattern in the frequency response by addressing this superposition of multiple direct and indirect specular signals in the time domain. 

Except for a _degree_ of modal improvement below ~80 Hz, EQ is *not* going to solve your frequency response anomalies!

Thus you will want to learn more about the practical uses of the Envelope Time Curve (ETC) response. 

Part of the strength of RoomEQWizard is that as you move beyond the derivative view afforded by the frequency response, you 'grow into' the causal power afforded by the time domain.

Stick with option B, and focus on the analysis of the speaker-room interaction and subsequent-room treatment.


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