The importance of measuring your sub+room response (1 Viewer)

[BruceD]

Paul,

A program I purchased and have been using for the last 5 years ETF will measure the RT-60 of your room.

You can even downloaded the ETF program for free and use a radio shack SPL meter (with it's RCA output jack) as the measurement microphone/preamp.

 

[paul clipsel]

Chu I don't think its the fundamental.
Bruce great stuff I will try it out.


PC

 

[Wayne A. Pflughaupt]

I'm not sure how you came up with that, Chris, but that’s not what I said.

Regards,
Wayne A. Pflughaupt

 

[Chu Gai]

You might find some of the freeware apps at http://www.acoustics-noise.com/ like the room modes & reverberation time calculator to be of some interest. Also the newsgroup, alt.sci.physics.acoustics can be a fun place to poke around in.

 

[ChrisWiggles]

You said this wayne:



Which is why I am very wary to let that float out there. Problems that are as long in terms of absolute *seconds*, are not really as bad in small rooms as big auditoriums, but a "good" proper decay rate will also shorten for smaller rooms. A much longer decay is ok for larger rooms, there is no fixed proper decay rate, it varies by room size, and preference(and also *very* heavily on the use of the space, but assuming the same uses in different sized rooms the ideal RT60 should change depending on the room).

 

[Edward J M]

Sure it will save money (and I'm sure this was Bruce's good intention), but if you're going to go to the trouble of measurement software, buy a decent measurement mic and preamp and get the combo professionally calibrated.

Also realize the sound card in your PC can be a significant source of error depending on its quality. If the software can correct for soundcard FR anomalies in a closed loop mode (i.e., where the software generates and reads the signal), all the better. Even then, it's best to use an aftermarket sound card with audiophile grade DSP and DACs.

 

[Chu Gai]

ETF sells a calibrated mic and preamp ($250)...Father's day is coming.

 

[BruceD]

Ed,

No disrespect, but I think you're a little off on your recommendation. I simply don't agree that a calibrated mic/preamp is necessary to measure the RT-60 of a room. The Radio Shack SPL meter will do just fine.

Yes, I have a professionally calibrated mic and preamp myself, and as I said, I bought the ETF software ($150). By the way, I also disagree with the need for an audiophile grade soundcard (especially for an RT-60 measurement), as the ETF software uses a closed loop calibration procedure. The software was tested with both low-end soundcards and high-end audiophile sound cards with no difference in results.

ETF is generating MLS test signals that simply don't require a soundcard with audiophile grade DSPs and DACs to work accurately. IIRC, these MLS (Maximum Length Sequence) test signals are shaped pink noise.

For more extensive room analysis like frequency response, impulse response, energy time curves, and 3D waterfall charts (also part of the ETF software) a calibrated mic/preamp will be helpful.

 

[Edward J M]

Bruce:

My apologies for skimming the thread; I wasn't aware this was specifically for the RT-60 measurement. In that case - agreed, the RS meter will do the job.

When I changed sound cards I did notice a change in its response to a digital FR chirp with TrueRTA, despite having sound card calibration/correction in both cases. The TrueRTA chirp is gated, but not nearly narrow enough to be considered MLS (it does allow room effects to fully develop), and it is also not pink noise - so apples to oranges really. Again, that's what I get for thread skimming. Thanks for clarifying and carry on!

 

[CurtisSC]

A little OT, but do you guys have preferences in sound cards? Which brands and models?

 

[Edward J M]

Creative Labs Audigy 2 ZS

 

[BruceD]

Edward,

Just wanted to says thanks for all the information and commentary you have provided with your sub reviews, etc.

I found it fascinating and useful, including the methodologies and testing tools.

 

[Edward J M]

Thanks Bruce - stay tuned for the PB2-Ultra review - I've got a few extra's planned beyond what I've included thus far in my reviews. I wish I could ground plane it, but grass stains and dog poo don't mix well with a furniture grade finish.

And while we're dishing out compliments, I often follow your posts in other forums and have saved (and rely upon) several of your posts on equalization, crossovers, and filter theory.

Wait......I feel a group hug coming on. Have a great weekend guys!

 

[Richard_M]

While we are way OT...

Just a couple of quick questions.

Ed

You recommend the Creative Labs Audigy 2 ZS as a sound card to be used in conjunction with RTA software; did you consider the M-Audio range of cards? The reason I am inquiring is that I have been considering a new sound card, currently using onboard SoundMax (Intel M/Board), and was interested in why you went the way you did.

Bruce

How did you go with the midi & BFD, get it all working?


Dick

 

[Ned]

I wouldn't recommend any Creative Labs soundcard as they resample everything to 48khz when using the digital output. It is also rumored (hard to confirm this) that the live/audigy cards operate internally at 48khz so even playing 44khz through the analog outputs may suffer resampling. The Maudio cards like the Revo and 2496 can use ASIO or Kernal Streaming to bypass resampling. If you want to spend even more, the RME and Lynx cards are even better than Maudio (for analog out).

 

[Edward J M]

My primary reason for upgrading the sound card was to obtain a much lower noise floor (higher S/N ratio) for observing low level spectra on THD analysis. The new card certainly accomplished that (it probably exceeds the old card by at least 30 dB S/N), and it has a ruler flat FR to boot.

The sampling frequency issue Ted noted is not a concern in my particular case since I'm only doing low frequency work testing subs. It might be a concern to others, though, and is worth researching and confirming.

The card handles all HT formats and DVD-A and and even has bass management; it's like a little pre/pro. I'm building a little HT system in my office and this card is the core.

So for me, the card served a few purposes and the price was right. No complaints thus far with its performance, but I'm far from an expert in sound cards.

TrueRTA is also set-up for an Audigy2 card as a default, and apparently is popular with TrueRTA users. There is even a special set-up section on the TrueRTA website for Audigy 2 cards, and recommended settings too.

 

[Richard_M]

Thanks Ed for the very informative reply (As usual), I will look at the info on the TrueRTA site.

Ned thanks for the information on the sound cards, I don't want to spend a fortune, but will do some investigation into the M-Audio range as well as the others. I already have a HTPC using DVI etc just the audio needs upgrading, also I will be using it in conjunction with RTA software.

 

[BruceD]

Richard,

I had to put the BFD exercise on hold (packed up most of my audio stuff) as I'm preparing to sell my house.

Will let you know how it goes when I get resettled, and then just buy an 1124 to replace my 1100 if I can't get the 1100 to work correctly with the MIDI software.

 

[Craig Chase]

To all you computer gurus... When you use an external microphone pre-amp through the USB inputs on the computer... does that mean you are bypassing the internal sound card ? Specifically... for going into the TrueRTA software ?

 

[Richard_M]

Bruce...

No worries, thanks for the update, good luck with your sale & move.

BTW I think it maybe your Midi interface could be the culprit, is there any Audio/Computer retailers that allow you to buy products and let you have seven days to return it for a full refund if you don't require the goods. We have several here in Oz so I presume you have them in the US, get a USB-Midi interface and give it a test.

Craig...

Does the USB interface have a sound card built into it?

Where do you plug your Pre/pro or sub into the external box or line out of your sound card in the computer?

I just checked TrueRTA, and it appears to use what the default settings are from windows for its sound in/out, where as some of its opposition programs allow you to select the source, from within the program.