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Discussion Starter #1
Hi guys.....

The first thing I want to do with REW is complete a full and accurate speaker distance measurement for each speaker and the sub.

Now I understand how one does this within REW. Loop backs etc.

But my query is in regards to what best I have my processor set to interms of speaker distance settings.

I have an Ada suite 7.1 HD and for eq purposes I use mono 5 as the surround setting. This basically sends the same signal to each speaker at the same delay rate. Taking into account the speaker distance delay... And this is where my query is.

Now as I understand it, to measure every speaker acurately I need to ensure that the ony latency in play is that of the actual processor and not any physical distance delays that I may have already have in place in the Ada.

So I was thinking the best way to complete a distance measurement would be to reset each speaker to 0 feet so as the latency is the same on each channel. From there I can then measure every channel and input the measurements into my Ada, save them and then continue on with the eq side of things. The peq, with the most accurate speaker distance settings I can have.

And also on this, I am going to be playing with an audyssey sub eq for the sub channel.

Now during the setup of this it will give me a suggested speaker distance to put into the Ada. I was wondering, again, the most acurate measurement of sub distance would be to complete the sub eq, have it engaged and then run REW distance measurement thru the Ada to the sub via the sub eq. This is going to give the most acurate result over the audyssey result as it will be taking into account the latency caused by the Ada and cables etc?

Surely all this will give me the greatest most acurate results for completing an eq, in regards to phasing / delay timings.

Many thanks
 

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Discussion Starter #3
I think I understand what your saying.

But interms of using the REW without processing, that is not possible with the Ada. It has no real analogue domain. It has 4 analogue inputs that get instantly processed. And the cleanest, least processed path is to choose mono 5. This is the setting Ada suggest one used for calibration purposes.

Essentially I send a test tone to all speakers then solo each speaker in turn and measure.

This is why I ask whether I should set the speaker delays in the processor to 0 feet before speaker distance measurement is completed. Or, should I have the speakers delays in the Processor set to their physical distance and then run the speaker distance measurement in REW. IMO, that will give an inferior result to running it from speaker distances of 0 foot.

I would imagine the absolute best way of measuring the speaker distance would be to actually connect REW straight to the poweramp. And ensure the volumes on the external sound card are low to start with so as not to destroy the speakers and my ears. But do not worry, I will not be doing this.
 

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That makes perfect sense. Thanks sac.
LOL - on the contrary, it makes no sense if you understand the question correctly!

The analogue inputs can not bypass the a/d converter but this does not mean that the signal is altered via DSP unless you set the Ada to a mode where that would happen. Mono 5 is a special mode that routes an analogue signal on the LR analogue input to all other channels on the device. When used with individual channel muting it can be seen this is entirely useful for device setup with REW signals.

The one thing that Mono 5 does is reduce the channel level when compared with single channel being driven and I can't remember if that is by 3 or 6dB. Simply place the mic and measure the left or right channel in direct mode then in mono 5 to get the exact offset that you should be aware of for SPL related measurements.

The Ada uses relative distances for speaker delay not absolute distance. For that type of setting knowing the propagation delay of each channel is ideal - find the shortest total time then the relative additional delay for all of the other channels. The channel outputs from mono 5 Are perfectly time aligned for this purpose.

To get a correct result it should be pretty obvious that all channels should be set to zero delay before hand.

Have fun

Neil
 

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Discussion Starter #7
Thank you Neil. You are the first person to state that my theory is correct on the setting the Ada to 0 and using mono 5 etc for speaker distance. Thank you.

One thing I find on the Ada. Is if I balance the sub from the internal test tone and then balance using an external tone, the sub is way to high. I generally have to set the internal Ada test tone to about 10db lower on the sub than the reference I am trying to reach. Ie, if I set all to 80 db and then test them again using an external tone, soloing inputs and no peq. I find all channels are equal and balanced except the sub which will be about 10 db too high.

Most odd.
 

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Discussion Starter #9
So do I understand this right.......

Time of flight delay = time it takes for the sound to reach the mic from the actual speaker cone.

Propagation delay = delay imposed by electronic signal paths. Ie, dsps etc.

Reason one can not bypass propagation with the ada, I assume is because it has no direct bypass. Ie, it's always sends a signal thru the dsp.

So If I complete a speaker distance measurement using the loopback connected to the tascam as most do, then there will be an extra delay in place that would, intheory need compensating for. But,really, this delay must be tiny and so long as I complete each speaker measurement using the same method, then all channels would have this same delay imposed and surely cannot cause too much of an acoustical issue.

Transferring the loopback to the Ada pre out will get me a little closer to actual distance but will still include prop delay as the signal is still passing thru the Ada.

In practice, I think a standard sound card / tascam loopback should suffice?
 

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HI SAC,

Your post is a good one but as so often on forums you are hampered by only having half the data needed to give a correct answer.

An ADA Suite 7.1HD is the home cinema processor that Nick is using. This device has absolutely zero automated setup but does have exceptional flexibility for manual setup.

With the S7.1HD speaker delays are set using relative delays with the closest speaker being set to 0 then all the rest offset from that point.

The electrical delay on the signal as it travels from input to output is not insignificant (20-30ms) but IS identical on all channels. Thus for the purposes of setting delays on this device they can be ignored.

What the measured data will show is if any channel has hidden delays that tape measuring alone does not reveal - DSP induced delays on subwoofers for example.If you use this technique often enough it is still surprising how many unexpected results you find - but you do get very precise time delay settings.

I am not sure of how many other units would benefit from this technique now but the ADA is certainly much better for the use of it.
 

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Discussion Starter #12
Thank of Neil. That is what I wanted to hear. After reading all this I was just going to stick with using tape.

But I do feel that using REW to calculate distances with loopback on the tascam will be more acurate.

As said, tho only other way would be to bypass the ada completely and test directly to each channel of the poweramp. And then straight into the audyssey. As that is propagation delay that one does indeed want to included in the measurement.

What will be interesting is to see how different the figures are to my physical measurement..

The only thing I do not like about testing straight to the poweramp is the 8 times I'll have to turn it on an off between changing channels.

So, intheory, I could test all from the ada, then test one signal straight to the poweramp. The difference between the poweramp measurement and the Ada measurement will be the propagation delay, and this could intheory be removed from the Ada measurements.

All getting a little too much for just measuring distances when up until now a tape has always sufficed. Lol.

But I think I will just set all Ada speaker distances to 0 foot. Then measure distances via REW thru mono 5.

Hopefully should get my mic this week. Dam bank holidays slowing things up.
 

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Discussion Starter #14
Ha ha, the only place ill be moving my chair is to a new room in a new house which has a couple extra foot to go either side of my speakers. Lol.

Not very likely.
 

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Now for any additional specular analysis of direct and indirect signals within the space in order to determine and affect modification of the in room speaker-room response via the use of such tools as the ETC, the time display will still be corrupted by the hardware propagation delay, and the use of the time to determine distance will not be accurate, thus limiting and requiring one to resort only to the blacking method.

.
:yikes: come again!


Tape measure Nick :bigsmile:
 

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Discussion Starter #18
Yes, I think tape will be the way I will making my distance measurements.

I used the loopback, pretty sure I had all connected correctly and performed a measurement. The distances are crazy. Like 20m, when it more 20ft. Lol

Thanks for all the help on this one, now on to my next questions.
 

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I used the loopback, pretty sure I had all connected correctly and performed a measurement. The distances are crazy. Like 20m, when it more 20ft. Lol
I am having similar issues with the distance determinations. I'll stay tuned to your thread to see if we have similar causes but it looks like it may be receiver when set in stereo mode (Onkyo).

http://www.hometheatershack.com/forums/rew-forum/56427-im-back-but-confused-again-10.html#post515384

http://www.hometheatershack.com/forums/rew-forum/56427-im-back-but-confused-again-10.html#post515439
 
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