Spectrum analyzer software

[acre]

Hi everyone! I was wondering if anyone has come across some FREEWARE for sweeping our Altec speakers for frequency response? I would like to see a graphic version on my computer monitor of the frequency response being generated by my latest Altec creations. I recently completed these boxes with the help of Dave Fitts and GM. My main concern is phasing the 811B horn with the bass cabinets and the only way I've been able to do this is by guessing, using white noise and randomly moving the horn until I get a sort of homogeneous sound. A graph would be more revealing. Also, in setting the correct horn position, where should my HF attenuator be set? It is the N801-8A cross-over. Many thanks!...Lee

[bfish]

Hi, Lee,

TrueRTA has a freeware version which is somewhat limited, but might serve your purpose;

http://www.trueaudio.com/rta_down.htm

I've used their 1/3-octave version for over a year, and really like it. The UI has a hardware appearance, so it's easy to use, there are pink, white, and sine generators, and both scope and bar-graph display modes. The retail versions are priced according to their resolution.

For anything better than comparative-only testing, your hardware must be capable, and calibrated by the software used. Most use a loop-test cycle, which can compensate for everything but the mic. TrueRTA comes with a few mic cal files for certain mics, or you can write your own (text) cal files, if you have accurate response data for your intended mic. I found it much easier to buy a mic that matched one of the supplied cal files, a $69 Behringer.

The software does gobble RAM and resources, so if purchasing, read the sys requirements, no need to spend more on something you can't use.

[steveviso]

Hi,
I used Speakerworkshop, it is freeware and using you PC audio board.
Look at: http://www.speakerworkshop.com

Have you some frequency response graph of Altec components? Bye.

[acre]

Thanks very much guys! I'll give these resources a whirl and let you know. I have 1 Gig of RAM on my computer and an Athlon 2.9 GHz processor so hopefully it will work. I was intending to try a regular stage mic for the pick-up signal for now. Thanks again......Lee

[bfish]

Lee,

You're welcome. Sounds like you've got the PC angle more than covered, (didn't realize my 200Mhz P4/500MB RAM was that outdated!) and I'd expect with the setup you mentioned the soundcard will be more than adequate, too. Happy sweeping!

Steveviso,

I haven't saved any results that would help with your current project, and my only 416s (reconed 8As) and metal horns are now boxed up in storage (I decided reclaiming my bedroom was a more important project than any of the pending projects it contained!). Sorry.

[acre]

Hi BFish! Many thanks for the help and comments. I did download the True Audio freebie and it gives a good ball-park analysis of what my speakers are doing. I found a pretty big spike around 80 Hz and found that if I reduced the port size 50% it got rid of the spike. (The box is about 10 cubic feet, roughly 45"x22"x16". The port is a rectangle 15"x5"-no tube. The 811B horn sits on top and the bass driver is as high up on the baffle as possible.) I also found a bad spike at 900-1000 Hz. I assume this is due to the horn alignment relative to the cross over frequency. I tried moving the horn back and forth, to no avail. Finally, I set the flange of the 811B a wee bit behind the baffle and tipped it forward about 15 degrees, as to blend the cross-over frequencies of the LF unit with the horn and voila! The spike came down about 6 db!. The final test was to play a known CD track. Upon raising the volume higher and higher, the sound was amazing!! No fatique from the mids or highs. One thing I never mentioned at the begining of this post. I replaced my 416-8A bass drivers. I had an expert from the Toronto area examine them because I felt the "punch" had gone out of my drivers. He found that the spiders were pretty weak and one voice coil has a slight rub in it. So with regrets I have shelved my 416-8A (after 30 years) and installed a set of Eminence Kappa Pro LF models. They sound excellent in these boxes. I was in touch with the senior sound engineer at Eminence and he was very familiar with the A-7 line and suggested the Kappa Pro LF's. The fellow from Toronto said that he could re-condition my Altecs but couldn't guarantee that they would sound like the originals. The price was only marginally less than new, up to date Eminence drivers. I'm very happy with the new sound. In fact, they sound like my A-7's from the 70s. What do you think? Regards......Lee

[bfish]

Lee,

I think you found the satisfaction that many DIY'ers never achieve, something I feel may be caused by listening to opinions too much, and music too little. Congratulations!

Since you seem to be a competent and conscientious DIY'er, you might consider restoring your 416s yourself with GPA kits, whether you use them for this project or not. It's not difficult, but does require attention to detail. If you go that route, you should ask Bill about damping the cone surrounds, and get a bottle of compound (and glue) if you need it. You should end up with under $200 US in it, phone call, freight, and all. For practice, completely dissassemble the one that's rubbing, using acetone and/or MEK (and lots of patience) to dissolve the old glue. If you can reassemble it to perform as it did (hopefully less the rub), you'll be ready and able to install the kits.

Enjoy!

[donaldpatten]

I use FFT for frequency response curves in real time. No more hand plots or sweeps.
I use an eMac computer with SignalScope and SignalSuite software for an FFT signal and analysis. I burned a one minute FFT signal to a CD to avoid ground loops. Use Audio Hijack to capture the digital signal and send it directly to disk. I put my CD player on ?track repeat?. I use a small ( 1/2? ) omni electret microphone suspended 12 inches (30 centimeters) on axis in front of the speaker. Use a yard stick with the mic cable tied on the end. Adjust the cable length to position the mic. The mic preamp output is connected to the eMac Line Input for Scope FFT frequency response graphs. For a frequency response test signal use SignalSuite settings: Start , Swept Sine , On, Linear, Up, 1024 Samples, 20 Hz, 20,000 Hz, Repeat, On ( should sound nasty, not a chirp ). SignalScope settings: Input signals : Line in , 44100 , Both , Start , FFT, 22050, 512, dB, 10dB , -20 , Log, Uniform Exponential , 50.

The software I use on my Mac is SignalScope, SignalSuite, Peak 4 (G4+), Toast 6 Titanium , Perfect Pitch and Audio Hijack.
These give me an oscilloscope with FFT, power meter, tone generators, frequency counter, pulse generator, test CD generation, and more ; all I/Os use the eMac?s line in & headphone out jacks.
www.FaberAcoustical.com

[Jim Butler]

Must have posted my question before seeing your list of MAC analyzer appications. Thanks for the info. Will download them and experiment.

Jim Butler

[acre]

Thanks for the info Bfish. I may consider doing a re-vamp of my 416's. Also to Donald and Jim, thanks for chiming in regarding Spectral Analysis. I don't use a Mac but it would seem to my ear that the True Audio program helped level a few bumps in my creations. Regards....Lee