Folks,
there were a number of very interesting posts that talked about the use of the analog Radio Shack SPL/dB meter to get an idea what kind of frequency response one is getting in their control room. The gadget is rather inexpensive so I went for it and gave it a go.
I have to say that I have not been able to get any consistent readings. I am not saying that my speaker system is crap and the FR is all over the place (which it might be but that is not the issue), but tiny variations in holding the unit or positioning myself (...I know about the effect at low frequencies) can result in up to 6 or more dB of difference. With speakers (hopefully) in the 1-3 dB tolerance range this renders the results obviously useless.
What am I missing?
Is it my room (only 8'x12', IMO pretty well "foam-controlled")?
Any advice on how to conduct some useful measurements will be greatly appreciated.
Thanks in advance,
MisterBlue.
Topic Tags
Comments
You are not going to get usable results using the Radio Shack un
You are not going to get usable results using the Radio Shack unit in that fashion. Why? Even though the specs say that the units SPL is fairly accurate (+/-3dB or so), the microphone element has not flat from 20Hz to 20kHz. At some frequencies the mic itself is of in excess of 20dB. How can this be? The unit is sensitive to a narrow bandwidth. It is not falt from 100Hz to 8kHz, but that is the bandwidth that is needed for measurement.
Anyone that tunes a room with this is a nut.
He is talking about the SPL meter. Many people think that they
He is talking about the SPL meter. Many people think that they can set up a speaker system or a room eq with this. They sinewave sweeps or in some cases narrow bands of pink noise from test CD's. They look at the SPL meter to tell them how far up or down they need to adjust the EQ. The SPL meters are only using 100Hz-8kHz. The mic element is not flat. They only guarantee the unit will detect the greatest SPL in that 100Hz to 8kHz, not which frequencies are loudest. It cannot provide that kind of resolution.
SIA SMAART lies at frequencies below 100Hz. So don't even try to work out the bottom end with it. It is a great tool for live sound and installs. I use it alot.
The next step up would be the TEF system. It is licensed by Crown, Goldline Loft, etc...Then comes the grandaddy Meyer system.
:roll: :d: It did not make a lot of clarity to me...
:roll: :d:
It did not make a lot of clarity to me...
Talk to the Man Kevin.
We all know to sound "good" on an RTA, the bottom around 40 to 60 must be 7 to 9dB UP from midband average. Only the peaks in midband..."can approach" the level of the sustained bottom and if you want the crowd to not have a massive migraine, that 2 to 4K region....******MUST****** have a slight dip...at concert dB's, It would kill me to have 110dB at 3K hit me. I would not stand for it at all...
Kevin...Hope you got some words to the Man..
Originally posted by Kevin M.: [qb] Hi lowdbrent, Thank you for
Originally posted by Kevin M.:
[qb] Hi lowdbrent,Thank you for your reply. There's just a few things I want to point out.
"They look at the SPL meter to tell them how far up or down they need to adjust the EQ."
I'm confused on this one. How can they tell from a SPL meter what frequencies to EQ. Do you mean a RTA (Real Time Analyzer)? The control room monitors are leveled by the engineer.
No, people actually try to balance a monitor and.or PA just as I described. They think that by doing a sweep that a deviation in dB's gives them the amount to go -/+ on an EQ. It is spooky.
"SIA SMAART lies at frequencies below 100Hz. So don't even try to work out the bottom end with it. It is a great tool for live sound and installs. I use it alot."
Come on brother, you should know better if you work with it. PM me and we can rap in private.
It is true. SMAART's engineer/support staff will confirm. I use it for coherency testing mostly from 100Hz to 8kHz. Bass, IMO, for concert sound is personal preference.
"They only guarantee the unit will detect the greatest SPL in that 100Hz to 8kHz, not which frequencies are loudest. It cannot provide that kind of resolution."
It's true. The unit provides RELATIVE measurements, not ABSOLUTE measurements. Do the research. This is a difference between Class 1, 2 and 3 SLM's.
A-weighted frequency response for Ivie IE30 (red), SmaartLive with MK-10 microphone (green), Terrasonde Audio Toolbox (violet) and Radio Shack 33-2055 (blue).
What part of his fact did you not understand? Your post, just
What part of his fact did you not understand?
Your post, just repeating Kevins post is insulting.
I don't really think you know who we are or our expertise in acoustics, engineering, music or the recording arts. I was doing MAJOR mixing for groups you know (major 5 millions sold) in 1976.
I certainly hope you can bring something positive to tha table because what I have read so far is useless drivel.
Put up or go to another forum.
This is NOT what we founded RO about.
This is the first, and final warning of posting inaccurate deflamatory information.
I can provide many links for people that have your level of experience.
This is shameful, to just post a repeat of what the man said.
lowdbrent:
Ready to fess up or go crawl in a hole?
This is getting rather riduculous.
lowdbrent:
Kevin, I applogize for this craziness. Where the hell he get his education from...????
I am usually a guy that will not ever do anything but find good in a post and expound on that. You leave me no choice but to highly dissagree with your attitude and tactics.
Don't reply to this..lowdbrent.
Just heed it.
Sorry Kevin, Now you know how we really feel.
I hope you don't know this guy...
If so, pay him a visit on me. Just a friendly conversation will do fine.
[ March 17, 2003, 09:33 PM: Message edited by: audiokid ]
Ahhhh, I get it, go back over there, we do not subscribe to you
Ahhhh,
I get it, go back over there, we do not subscribe to your tactics lowdbrent.
I see you are totally on top of your game with the links:
[[url=http://[/URL]="http://www.handyaud…"]LBWP[/]="http://www.handyaud…"]LBWP[/]
Really, I mean it. This is not learning, this is harrassing people that know their business.
I will not have it.
I want to get along, I use to live near Tulsa, I feel you can be a fine asset...but not at this rate..we do things accurate, with compassion and feelings toward our fellow man.
[ March 17, 2003, 09:31 PM: Message edited by: audiokid ]
I quoted him in response, to answer him. Maybe you didn't read
I quoted him in response, to answer him. Maybe you didn't read what I said. I don't know. I don't see anything offensive in what I said.
He said surely they meant RTA, and I told him that no, people do attempt to use a SLM. I wouldn't do it. some do. What's the deal there. Then I identified that it wasn't class 2 or 3, and it makes relative not absolute measurements. The microphone element is a panasonic I believe, and is not flat, nor is the circuitry, and so I attempted to post a link to an article that had the AP graph. I didn't insult anyone. If I had, I would have talked about their computer or their hair. I clarified. That's it. I have read the F word by you and others. That's not offensive?
That's right, if you play the Rack, you gotta know how to swing
That's right, if you play the Rack, you gotta know how to swing that axe! Or mic stand, or barstool! Hey , did they have the chckenwire when you played there?
Was in town, had a cousin die a couple of months ago, burried her in the family plot outside of Drain. (my Mom's maiden name is Applegate, if you know any Ore. history)) I rode with my sister, and we only had a little while to get up and back, otherwise I woulda looked you up.
Thanks for the Velvet Turtle flashback, forgot all about that place. Has it stopped raining yet?
Aww mommy! I wanna stay up! Chris.. Yeah! the Velvet Turtle
Aww mommy! I wanna stay up!
Chris.. Yeah! the Velvet Turtle.. The name of that guitar shop... ROCKET GUITARS, right???
No they didn't have chicken wire at the Rack when I played there. Just the meanest g-d bouncers in town..They used to handcuff troublemakers to a metal grate in front of the club until the Cops showed up to collect them. They ended up getting sued for beating some guy up.. Man! That was a tough gig. 2 bands, 2 bandstands, three sets a night one hour on one hour off. Super loud Meyer speakers with Crest power amps. Speakers all over the place on delays to time align them. The monitor system did 120dB.. You can imagine how loud the mains were! No quiet place to go during your break. I used to go home with my head ringing. Polo Jones used to run sound. He played bass on the Bodyguard album for Whitney Huston, toured with Michael Jackson and Peter Gabriel.. He would have the mix cookin' and Hank (the owner of the Rack) would walk up to the console and push the bass guitar channel waaaaay up to get the dancers jumpin. Used to bug the sh*t out of Polo..hehehe Ahh the old days... Kurt
OK, friends. I started it, I finish it :D . First of al
OK, friends.
I started it, I finish it :D .
First of all many thanks for the posts that actually contained useful information ;) .
Although not being a multi-platinum engineer I still realize that the microphone element inside the RS unit is in all likelyhood not perfectly flat. It is also clear to me that a $30 gadget is not the final authority on straightening out room acoustics. It is also understood that the character of measurements needs to be relative to each other, not absolute.
Finally, I am not planning to "EQ-out" dips and overshoots, I just want to know if there are any serious deviations in my room. I quite like the sound I get, the mixes seem to translate well into the real world and so I considered the whole measurement thing more of a a "scientific experiment", geared at teaching me something interesting. I like learning.
What struck me and got me wondering (leading to this thread) was that playing a single sinewave (using the AT-Bench SW discussed in another thread here) gave me very inconsistent results. Small changes in the position of the unit or myself had a big effect. A simple task such as measuring whether both speakers were individually readiating the exact same volume, thus creating an image perfectly in the middle, seemed impossible (...the suggestion to use a tripod is probably the most valuable in this context and I will give it a go).
I will also check out the software packages that were mentioned earlier - they look interesting. I noticed that they have 30 day trial periods which should be plenty of time to collect some useful data. Connecting a more accurate mic is in this context also a problem that I can solve ;) .
In any case, don't hesitate to shoot me any questions or further suggestions.
In the meantime again many thanks for your posts and help!
Peace,
MisterBlue.
:w: MisterBlue, You are right in what you said about the
:w: MisterBlue,
You are right in what you said about the best advice was to use a tripod.
I had a grasp on what you were asking right from the start as did Bill. The reason you are seeing so much deviation with small moves is that’s what is really happening. Just a small amount of movement can make a big difference. We say this all the time about mics when we are micing an instrument or amp, why shouldn’t this hold true for a measurement device? The movement you see on the meter, when you move around beside or behind it, is reflecting how your body position is affecting the sound pressure. Try to stand as far away from the meter as possible when you are taking your measurements. Many of the higher priced RTA set ups provide remote viewing to overcome this problem. The Radio Shack meter is fine for what you want to do. Stand 3 meters in front of each speaker and point the meter directly at the speaker to measure the individual output. Be sure to only run tone to one speaker at a time. This will give you an output in dBs of each speaker. You can also run some bass tones 20Hz, 50Hz, 80 Hz and 100Hz and move around the room with the meter. This will show you if you have any bad modes (cancellations or reinforcements) in the room. That should give you a rough overall view of what is happening in your space. It’s true an RTA and pink noise would be better to do a more complete room analysis but cheap RTA ‘s are junk. Until you get into the $1000 range of these devices and a true calibrated mic, they are really worthless. The Radio Shack spl meter and a good tone generator can get you off to a decent start. Kurt
If you have a laptop, why not download SpectraFoo, SMAART, or Al
If you have a laptop, why not download SpectraFoo, SMAART, or Allen & Heaths free analyser and use that? Atleast you will have 31-bands on ISO centers to look at.
And hey Bill. My website is not an issue. that was being done gratis and the guy bailed. I have not taken it down. What does it hurt? Nobody knows it's there anyway?
Also Bill, you said that I was messing with people that know their business. You call measuring standing waves with an SPL "knowing your biz?"
And regarding experience. I have toured for the past 7 years with two grammy artists, and one CMA winner as FOH and prod. manager. Previous to that I worked for the largest A/V church contractor in the Southwest. I am a contractor. I use TEF, SMAART, Spectra Foo and Audio Control IASIS. There is no way that any SPL meter, unless you are using an IVIE, will have the resolution to do what this guy needs for room evaluation. It wouldn't even work in an anechoic chamber.
Just download a free trial version of the software and see if it works for you. Spectra Foo is the most user friendly, but it runs on a Mac. SMAART has a UC that you can get help from.
No, I meant Country Music Awards. I have Mixed the Tractors a
No, I meant Country Music Awards.
I have Mixed the Tractors and Junior Brown lately. I have two pages of clients before these guys.
I have done LOTS of Christian stuff. I would like to do lots more. Back in the 80's I worked for a Star Song records band that toured with Petra, Mylon LeFever, Shiela walsh and Morgan Cryar. The record company president gave me great help, and hooked me up with SAE. I did that, toured more, got married and settled in OK.
Currently I have a Pro Tools HD rental business, I do contract installs, and SR (32-box EAW, Crown, Soundcraft, yadda yadda). I would love to do more recording, I have worked with Word. One of their artists lives near, and they book the studio to do choir and solo overdubs annually.
Since I am not in LA anymore, and I hate to go to Nashville, the contacts are harder to maintain, and it is hard to be seen when you are on the road 200 plus days a year.
Where is the door?
Steve Ripley is a good friend, a mentor and yep, I know about th
Steve Ripley is a good friend, a mentor and yep, I know about the tractors are coming. He is a mad scientist. The Ripley Stereo guitar, the D-neck, etc. He has a great studio-Leon Russell's old church studio, in Tulsa. He has a Neve 8068, Studers, Ampex's, GML's, PT, ALL the toys and the place is warm.
Word on the street is that Louie Weaver quit Petra. That leaves John Schlit and Bob Hartman. What do you know? What do you know about Greg X Volz leaving? I only know what Jonathan D Brown has told me, and he held back.
Steve Ripley is a good friend, a mentor and yep, I know about th
Steve Ripley is a good friend, a mentor and yep, I know about the tractors are coming. He is a mad scientist. The Ripley Stereo guitar, the D-neck, etc. He has a great studio-Leon Russell's old church studio, in Tulsa. He has a Neve 8068, Studers, Ampex's, GML's, PT, ALL the toys and the place is warm.
Word on the street is that Louie Weaver quit Petra. That leaves John Schlit and Bob Hartman. What do you know? What do you know about Greg X Volz leaving? I only know what Jonathan D Brown has told me, and he held back.
Greg left in 85 I think. They got John schlit from Head East.
Greg left in 85 I think. They got John schlit from Head East. He is a great guy. Greg has been solo ever since, and is now calling what he does a ministry. Bob hasn't toured in years. John Lawry (former Joe English member) played keys for years, now he is a studio cat in Nashvegas.
Like Steve Martin said in My Blue Heaven: "I'm wit youse" Coun
Like Steve Martin said in My Blue Heaven:
"I'm wit youse"
Count me in with the idea that we're hear on equal levels .. the term is: peers. The way you truly learn is when people just talk truth and help, it's not about toys or anything, it's about sound, not oneself.
I'm from Brooklyn originally, so we know the drill when it's time to go from the stoop to the street to help a friend(s).
I would use a tripod. Attempt to place the unit where your he
I would use a tripod.
Attempt to place the unit where your head is during listening.
Their are some inaccuracies with them although a calibration chart can be found on the web with a search for "radio shack spl calibration"
When I compared one to my B&K calibration system, I found it to be amazingly accurate, within 2dB.
Some tips as per the azimuth of the mic to sound source needs to be studied as well. One person mentioned that pointing the unit strait upwards yielded the most accurate results.
It is a tool, not ideal but if their is a serious cancellation problem, the meter will show it.