10 Hertz FLAT!

I just purchased an RTA program that allows analysis down to 10Hz. The previous RTA software I had had a lower limit of 20Hz. Since I could now see what exactly was going on in the region between 10Hz and 20Hz, I decided to see what improvements I could make to my four JBL 18" subs. I did modifications to the electronic crossover's extreme low end active EQ frequency and slope, lowering it from 20Hz to 10Hz and increasing the "Q" of the circuit so it would be more selective.

The result? Well, using pink noise and the spectrum analyzer, and measuring at the listening position, at 10Hz the in-room response is absolutely dead flat relative to the higher frequencies! Not 10db down, not 3db down, but dead flat. I don't know what the actual lower limit is since the RTA software only goes down to 10Hz, but I shudder to think

How does it sound? Well.... I played some organ music I recorded of an organ that has a genuine 32 foot rank of pipes which yields a 16Hz lowest pitch, with "beat" frequencies of even lower pitch. The difference was remarkable. I didn't expect that opening up the low end from just below 20Hz down to below 10Hz would make that much difference - I was wrong, it makes a huge difference.

This could get scary

[This message has been edited by soundhound (edited August 14, 2003).]

Wrong, Bass Breath, this is ALREADY scary!

I happened to go over to Hound's place about an hour after he finished tweaking his system and heard that same organ recording.

This wasn't bass. This was a Full Body Massage. You could literally feel the individual pulses of the soundwaves at that frequency. And I suuuure hope the contractors did a good job building Hound's studio because those subwoofers definitely were moving the foundations around.

The most surprising thing is that this wasn't obnoxious, overstated or pugnacious bass at all. It was just suddenly THERE when that bass-crazy organist opened up the 32-foot ranks.

I heard this system MANY times before today's tweak and I can say that this latest refinement has made a HUGE difference in the last time I heard these bass demos. And it sounded pretty damned great before.

Too bad Peter missed this latest innovation when he made the Outlaw field trip to Soundhound's studio.

Yipes.

I assume you're talking about an active high pass filter. Adjusting it lower and to a higher Q not only extended the low end response, but boosted it at the HP filter's corner.

My sealed subs are flat (in room) to 10 Hz. (also as low as I have tones to chart), but they can't take too much power at that point. It's too cool to feed a 10 Hz. tone into them and watch the cones move at 10 cycles per second while you only feel it and hear nothing.

I KNEW those dual 18 beasts could be flat to 10 Hz., corner loaded, in room!

Try DareDevil. I wasn't too fond of the flick, but in the first chapter at about 4:40 there is about 5 seconds of sub-sonic tone that actually moved my floor like the ocean.

Yeah...many times I've pictured the maniac Soundhound with 4-18s. It's a beautiful thing.

Yes, it is a beautiful thing! The filter was modified as you imagined. The problem before was that since my RTA software only went down to 20Hz, I had no reliable method to see what was actually going on down below that frequency. I did some speaker only, without crossover measurements, and modified the crossover to accommodate what the speakers needed. Seeing that flat line at 10Hz on the RTA and going strong to gawd knows how low is, FUN!. I think I would run into room structural limitations before I ran out of speaker SPL capabilities!

[This message has been edited by soundhound (edited August 14, 2003).]

I do not understand why the software has a lower frequency limit unless the software creator chose to place a limit on the low frequency limit so as to decrease the response/update time. I would have expected a user option to set a lower limit, if one is desired, at the expense of response/update time.

I have a set of speakers that have response down to DC. I put in a big DC voltage and the (woofer) speaker responed by moving outward and then giving off a lot of smoke for a while. After that, it (the woofer) responed by just ignoring the input signal.

Paul

The organ recording that I used in my original post is by far the most impressive bass-wise that I have ever encountered. It is what results when you combine 3 spaced omni-directional (pressure) micorphones, a huge stone church, and an organist who loves bass

I have made an edited version of this track and encoded it into mp3 at the highest bit rate of 320kb/sec from within ProTools using their excellent encoding algorhythm, and posted it here:

http://home.earthlink.net/~soundhound/Organ.mp3

The bass on this track goes well below 20Hz - well below. It will give your subs a workout, and if they do venture into the sub-20Hz regions, you're in for a real room rattling experience. Have fun


[This message has been edited by soundhound (edited August 16, 2003).]

Was the software you bought some fancy schmancy pro stuff? I've been pondering picking up a copy of TrueRTA from True Audio. Any of you have any experience with it?

[This message has been edited by Ellen (edited August 16, 2003).]

Ellen:

It is TrueRTA that Hound is using.

It was TrueRTA that I was using.....echo.....echo.....echo.....

It seems to be pretty darned good. For analysis with 1/24th octave resolution you need the $99.99 version, but I think it's money very well spent. My only wish list would be for it to have a comparison function where you could subtract one set of measurements from another, and also that you could save the screenshot as-is so you could look at the graph later. It does have an "export" function but this is a listing of numbers for each frequency and the level at that point. Not very easy to compare with other data, especially if the absolute level is lower or higher between the two charts

[This message has been edited by soundhound (edited August 16, 2003).]

hound...you are my idle..'nuff said

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Play it LoUd!!

SoundHound,

You could always do a print-screen, paste the image into your favorite graphics program, and save it from there. I forget the key sequence: Alt-PrtScr, or Ctrl-Alt-PrtScr, or something like that. One captures the entire desktop and the other captures just the active window.

BTW, which do you think is better for my purposes: this RTA program or an actual RTA, such as the Audio Control one? I have the AudioControl, but if the software version is more versatile, it might be worth it to switch.

Jeff

It depends on if you have a measuring microphone that is flat enough to do the measurements. The RealRTA does give 1/24th octave resolution which is basically as good as a frequency response plot. It also has a "chirp" function where you can do a frequency response sweep quickly across the entire frequency band. For $99 it is a bargain I think. Personally, I like software implementations because they are more upgradable. And in addition, the RealRTA program does have a function to calibrate for the deficiencies of your soundcard in frequency response.

I have used a Panasonic condenser microphone capsule available from Digikey electronics (www.digikey.com) part # P9959ND that is accurate to less than 2db in the extreme high end. In the low end and midrange, it is within 1db, even down to below 20Hz. Of course you will need to power it but this involves nothing more than a 9 volt battery, a 2k2 ohm resistor and a 220uf capacitor (to isolate the DC from the sound card input). You will also need a 100k ohm resistor after the capacitor to discharge the DC, so the input of your soundcard doesn't have to do this!


[This message has been edited by soundhound (edited August 24, 2003).]

I have a calibrated mic and battery powered mic preamp to go with it, so I guess I should get off my duff and get a copy of TrueRTA.

As Jeff indicated, you can do screen capture of the active program by pressing Alt-PrtScrn. This copies a bitmap to the clip board which you can paste into your favorite image editor. I use a screen capture utility called Screen Seize that I got from PC Magazine. It allows greater control over what you can capture, from the full screen, the active program window, current dialog box, or any area of the screen thay you select with the mouse.



[This message has been edited by Ellen (edited August 24, 2003).]

SH, I just came upon TrueRTA, and was going to try the free demo to see if I like it. Could you share the details about that little circuit you described so I don't have to drive to Jeff's and steal his mic whenever I want to use it?

Thanks!

-Joe


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Remember the Intellivision?
http://www.gotmaille.com/nostalgia/

The bass on the organ recording is very nice. At my normal bass level, set by ear, it blends beautifully with the higher frequencies. Having some fun, I raised my subwoofer output to about twice it's normal level and proceeded to shake the floor! Very Sweet!

Overall, that's a great two-channel recording. Playing that back gives a great sense of space without even needing surrounds. Please feel free to post more examples.

One question: What was your recording path and mic set-up? That's only if you can give away your secrets...

Can you “import” your “exported” number sets into Excel or some other spreadsheet/database that has graphing capabilities? That way you could have multiple sets of information posted in varying colors in just about any two or three dimensional graphing style, even within the same graph/chart, to make direct visual comparisons. If you are savvy enough to enter formulae into your spreadsheet, graphs displaying differentials, etc. are possible.

[This message has been edited by bestbang4thebuck (edited August 17, 2003).]

Even if now, Excel is very smart at how it inputs data. If the exported data is CSV (comma-separated values) or space- or tab-seperated, Excel should be able to make sense of it.

Jeff

Joe:

It's very simple, and if you order the mic capsules ($2.50 or so each) you can request a Digikey catalog which has the circuit drawn out with the mic capsule listings. Basically you want to run a single conductor shielded cable (up to around 15') from the "hot" tab on the mic and the "ground" tab (the ground tab you will see is connected to the shell of the mic capsule. Run the +9VDC through the 2k2 resistor to the "hot" lead and the -9VDC to the ground. At the junction of the resistor and the cable on the "hot" side, place the 220uf cap with the + side toward the 2k2 resistor. On the (-) side of the capacitor run the 100k resistor from there to ground. The output that goes to your soundcard is taken from across this resistor. It's much easier than it sounds! Your soundcard will need a microphone input because the microphone does not have it's own preamplifier.

There are really no secrets. The three omni directional microphones were placed at the front of the chruch, about 15' apart from each other, and 10' in the air on stands. The mics have low end response that goes WAY down since they are pressure type mics. The mics were fed to a mixer that was designed by a high-end audio designer friend of mine who designed the just released "Tampa" microphone preamp by M-Audio. It sounds very smooth. The center mic was split between the left and right channels and the stereo mix was run into a DAT recorder running at 48Khz 16 bit. The bitrate conversion was done in ProTools using the highest quality setting which is a non-real time process that takes about 6 hours for a CDs length of stereo to be converted.

I have tons of good organ recordings I've made through the years. Unfortunately I only have 10MB of webspace that I can upload to, otherwise I'd be happy to post as much as people can stand. If you can think of a solution, I'm game.



[This message has been edited by soundhound (edited August 17, 2003).]

I'd be willing to pay the cost to burn and ship some CDs. I'm a huge fan of organ music, as well as organs themselves. Some of the organs in the churches we saw in Ireland were amazing.

-Joe

------------------
Remember the Intellivision?
http://www.gotmaille.com/nostalgia/

Oh, and thanks for the info on the mic. I have a Digi-Key cat floating around at work, I'll check it out tomorrow.

-Joe

------------------
Remember the Intellivision?
http://www.gotmaille.com/nostalgia/

Why don't you email me your address and I'll put together a CD for you.




[This message has been edited by soundhound (edited August 18, 2003).]

Thanks for the info. That custom board sounds really sweet. At my job, we're looking into a rack mount mixer made by Dangerous Audio to handle some duties like that for us. It seems to be the best deal for the money.

Mic placement also helps...sounds like you know the room pretty nicely.

Let me guess....4006

Hi soundhound. I'm new here and love reading the post you put up. I would love one of those organ music cd's but i can't find your e-mail address How bout helping a new member out Looking forward to hearing from you!!

Lasher

I've been looking at replacing my current subwoofer... it's very musical, but it's lacking in the reall low bass...

So Soundhound or Bossobass, do either of you have designs for your subs?

Wow!

It looks like I sold my house, and Charlie HT 1.x goes with it, so I'm gonna need to start plotting HT 2.0. Suggestions are welcome, and I'd like to arrange to get a copy of that CD if possible, but I'd really like to pay something for it, or trade, or something. I hate to see you get 'SlashDotted' out of existence.

I think that there may be a "rip and pass it on" thread coming up Stay Tuned.

BTW for the copyright police - the contents of the CDs are NOT copyrighted and NOT commercial. So fuggaboutit!!

SH:
I have been using "TrueRTA" from True Audio for almost a year now. The creator, John Murphy, has recommended the Audigy 2 soundcard, used with a compatible and fast PC desktop computer for the best results. He also recommends calibrating the mic (creating a response profile) for certain analysis functions.

I was wondering what PC and soundcard you used for your analysis, as I believe I remember you are a Mac user. Since I use Mac's in my office, I have had to purchase a PC and soundcard to use "TrueRTA" to it's full potential for my work. My son uses the PC when I am not working with it, so it has utility beyond TrueRTA. GAMES, GAMES, and more GAMES.

Also... Mr. Murphy has contributed to some articles on tube vs. solid state amplification that you might find interesting, or perhaps irritating. They are found at the True Audio website under the Tech Topics section.

Thanks... knowing that you have found this software useful is reassuring to me, as I use it for both my work and home hobby.

Allan

Allan:

I use a Gateway 450XL laptop and it's line-in jack. I use the line-in calibration function, but the response already pretty flat. The mic is flat to something like 100Khz.

Since you know the author, could you bring up the possibility of having a "Calculator" function where you could subtrack one graph from another and do other comparisons? The "Mac RTA" I use on the Macintosh has this function but only goes down to 20Hz.

[This message has been edited by soundhound (edited August 22, 2003).]

I have no doubt that HT 1x had something to do with some fortunate person's decision to buy your house! Congrats!

It's always fun to spend OPM, so suggestions will be no problem.

Unferth,
What sub are you using now?

So the charlie sub setup will be passing on to someone else, eh? I'll be very interested to see what you put together at your new home, charlie.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

Sorry about that soundhound. I didn't want to give the impression i wanted a freebe. I just wanted to know where to send the money order and how much......lol Let me know your thoughts? I would like a copy to test and demo my system.

Thanks
Lasher

This time the preliminary plan is a dedicated room with a FP setup for video and handmade speakers all around, this time I'd like to use active crossovers and do all BM between the pre/proc and power amps. And with all actives, there should be lots of discrete power amp channels.....



I suspect so. The first folks to look at the house made an offer and it looks like we can reach terms soon. Partly the location, and partly the 'features' I think. The orginal offer specified the audio system was to stay as is, so I'm sure they noticed.

2.0 will take some time, but I'll be sure to give progress reports as needed.

Thanks for the help and support over the last project guys.

Okay Soundhound, I am going to go with the TrueRTA. I have one of the recommended Behringer ECM8000 Measurement Microphones and a phantom power supply. How do I get the balanced output of the microphone into the unbalanced input of the sound card? I am concerned that the adapters available may not be flat down to 10hz. Thanks for identifying this cool software.

Normally you would short the "low" side (pin #3 of an XLR) of the balanced line to the "ground/shield" (pin #1) of the cable, and take your signal from the "hot" side (pin #2). I don't know the specifics of your microphone's output, but this is the standard way of doing this.



[This message has been edited by soundhound (edited August 24, 2003).]

I'm not sure, SH, but I think THIS is bass! From Reuters news agency ...

Black Holes Sing Bass, But Humans Can't Hear Them

http://story.news.yahoo.com/news?tmpl=story&cid=570&ncid=753&e=1&u=/nm/20030909/sc_nm/space_bass_dc

"One particularly monstrous black hole has probably been humming B flat for billions of years ... But the pitch of the sound is about 57 octaves below middle C ... researchers said, and they believe it is the deepest note ever detected in the universe."

"Heavenly bass?"

You're darn right humans cant hear them...

A. It's in space. Since space is...well...a void, there isn't any medium to transmit sound through!

B. 57 octaves below middle C...that's so low that couldn't you hear, heck, you wouldn't even be able to time the pulses! C4 (middle C) is a frequency of 261.6 Hz. (261.6 vibrations per second) Octives are produced by doubling or halving the frequency in question, therefore the octive above middle C (C5)would be 523.2 Hz, and the octive below middle C (C3) would be 130.8. The smaller the number, the fewer vibrations per minute there are. 57 Octives below middle C would be a frequency of 6.9-n17. Thats .69 with 17 zeroes in front of it. Now my math may be a little off...lord know's I'm not a math major, but we aren't talking about a frequency that you can measure in seconds. It's not a frequency that you can measure in beats per minute, nor beats per days....or years...or even decades. We're talking one pulse (movement from peak to peak of a wave) per THOUSANDS of years. Why they decided to give it a musical connotation is beyond me.

[This message has been edited by fmcorps (edited September 10, 2003).]

Darn! I was hoping to be around to hear how the song ended! It starts off catchy enough. And the music video would have been a killer!

Jeff Mackwood

Wow! "How low can you go?" Our subs don't have a prayer.

OK, now you've got me curious. I had to dust off Excel for this one, but I think I've got it sorted out now. If we are 57 octaves below 261.6 Hz, that puts us at (261.1/(2^57)) -- or somewhere around 1.81*10^-15 Hz. That comes out to one cycle every 17,456.9 millennia - once every 17.5 million years. I don't think the Radio Shack SPL meter's going to know what to do with that test tone.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

More on "Sounds in Space" ...

http://www.space.com/scienceastronomy/mystery_monday_030922.html

Also:

http://rxte.gsfc.nasa.gov/docs/xte/learning_center/listen.html

Enjoy!

[This message has been edited by bestbang4thebuck (edited September 23, 2003).]