PC into RTA?

[JonFairhurst]

Originally posted by Giskard
"These days I've been tuning to taste. As long as it sounds good to me, what more could I want :-)"





The other stuff can be quite fun though if not taken too seriously

Very true. And after doing some RTA work you will calibrate yourself, as well as the speakers/system/room. I find that I want to roll off the high end slightly, and want to bump the low-end *for some source material*. It's like adding salt and pepper to your food.

My high-end tuning stays contant for most any decent recording. But I find that I want to customize the bass on nearly every CD - even if by a dB or two. The difference between weak bass and flabby boom can be very subtle. At least for my ears in my room with my speakers.

[Ian Mackenzie]

Interesting Jon,

I made a laboratory mic using a Panasonic insert which is known to be flat within a 1dba over most of the range, it is used in the popular Mitey mic marketed for speaker testing in the speaker diy field.

Basically you put the insert into a thin length of brass or aluminium tube about a foot or so long to avoid difraction effects.

The peamp with phantom PS is nothing more than a two transister gain stage with phantom supply via the nine volt battery and a resister. (can scan the design for those interested)

The PC RTA look fun and pretty, however non appear to have variable gating windows, and non appear to use FFT pulse .

There in lies a problem for a speaker builder if you require true speaker only measurements on the mid and top end without room effects or other early reflections.

The convenience of being able to selectively remove room effects is crucial for speaker testing.

I can't possibly see any one lugging a 200lb speaker out into their drive way everytime you wana do a frequency run..muhhahah frighten the neignbours away.

This the data from JBL of the 4345 measure in open air.

macka

[Ian Mackenzie]

Attached is a gated measurement using Winairr,

The top curve is the time response and the vertical lines are the gates or time sample I have chosen.

The immediate wiggley lines on the time curve after the initial pulse are baffle reflections (being cardboard at the time..muhhahahah) and time displacement of the various drivers (over a millisecond), everything else is chopped out.

The second curve is the response, and you can see the clear thin line except the very top end which could be further gated but we would loose details of the lower midrange.

The lower curve is the system calibration curve

If this curve were not gated, the mid and high frequences (and low ) would be an unreadable blurr and usefuless.

Also you can do far field measurements lie this one @ 2.5 metres which are more meaningful, particularly with horns when near field are influenced by the immediate pressure zone of the flare.(and still gate out room interference)

The mid range can be independantly analysed by also gating out reflections from the floor, walls and ceiling around 300-1000 hertz.

Low frequency measurements to me are a bit of a waste. The modelling of the LF on bassbox is a far more accurate indicator than any measurement. There are so many influences from your room modes its easier to work out the main resonances with a pocket calculator, and you really can't fix them properly with EQ, hence the use of tube traps and refractors to absorb LF content.

Ian

[boputnam]

Originally posted by Oldmics
Measurement taken with Shure 58s always bring a chuckle to me.A great mic,not slamming the 58 but not quite right for this application.

I certainly wasn't - nor wouldn't - use an SM58 for that. That'd be dumb-is-as-dumb-does. I must've confused by even mentioning a vocal mic in this Thread. I didn't fugire anybody here would misinterpret that. The rest of your post is quite iteresting.

Originally posted by JonFairhurst
And after doing some RTA work you will calibrate yourself, as well as the speakers/system/room.

As posted on a very similar thread some time back, after flat to Pink Noise I toss the RTA and fine-tune to ear. I find the RTA is most useful for identifying the large reflections/standing waves of the room acoustics. After that, nothing beats painstaking tweaking over the course of a few days. And I'm still using my Gold Line - Link with it's reference mic. Good enough for now. Not gone PC, yet...

[Ian Mackenzie]

Here is another screen dump after some tweeking of the faders.

Not bad for $50 bucks when all we need to know is if there are any major peaks, dips building an assumed design from JBL.

Granted however, if your into graphic and parametric EQ, the RTA is still a useful tool.


Ian

[Oldmics]

Hey boputnam,I knew that you were only doing a tongue in cheek kinda comparision about the 58.Please do not think I was trying to cast dispersions towards you regarding my comments about the use of a 58 for measurement or regarding the comment about encounters that I have had with 98% of Smaart users.I think that this is a more in touch forum with the way things are correctly done.Some of the exacting measurement that I do regards arrays of systems.Its a diffrent mindset when you are measuring a stereo cluster with a six box horizontal trapazoidal array that is multiple rows hi on each side.Trying to achieve null free coverage in both near and far field listening positions in combination with high SPL is like a quest of the Holy Grail.Thank God for line source array technology.As an experiment place your home stereo speakers together and see what I am talking about.Start listening and then try to correct for that mess.Upon measuring you will see phase goes right out the window and comb filtering becomes a new factor to deal with.Add in humidity and altitude outside and you have just another day at the office for me.Thats why I need exacting measurement.While it can be fun ,I do take it seriously.Best regards,Oldmics

[boputnam]

Hey, Oldmics...

Thanks, and no dispersions hit me - but I was compelled (after Jon's comment on the 58, too) to ensure we here were in-no-way suggesting that application! Hell, next-up, someone'd be doing RTA with a RadioSchucks Hi-Z hard-wired Karaoke mic. Boy-howdy, that'd be it.

I love your comment about line arrays - not the end-all, but heaps better than the stacks-of-the-past. My friends think I'm nutz (OK, so they're right...) to seek seating in "null free coverage" areas, and they give me the Homer Simpson "blink" when I try and explain it all (maybe it is just me, after all...)

All I'd add, is after all the "ringing the house" (if you will forgive the use of the term), it's back to square-one the minute the audience arrives and adds their acoustical damping to the room. Yikes...

Anyway, if you're ever doing FOH at a show I happen to be at, know that your work is mighty appreciated!

[JonFairhurst]

A Radioshack mic? No way. To really save money, just use the microphone in your telephone. Your wife won't mind.

[boputnam]

Originally posted by JonFairhurst
A Radioshack mic? No way. To really save money, just use the microphone in your telephone. Your wife won't mind.

Ha! You prompted an even better idea - a grid of cell phones! Think of the cost savings in relieving all that troublesome wiring...

Can you hear me now...?

Can you hear me now...?

Can you hear me now...?

[Alex Lancaster]

Thanks everybody!

I think I know what I want, now comes the slow process of getting it down here, but I will.

Alex.

[JonFairhurst]

Buena suerte, Señor Lancaster.

[Mr. Widget]

As a long time reader of "Speaker Builder" and now "AudioXpress" I have been meaning to get a Mighty Mike. Has anyone used one. They are based on a cheap (possibly the same Panasonic unit) condenser mic, but are tweaked and available in a calibrated version that seams to be quite the deal.

http://www.audioxpress.com/bksprods/kits/kd-4.htm