21626
From: Brian, [gnd210-95.caribsurf.com]
Subject: TrueAudio's TrueRTA Software (take II)
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Today I had the opportunity to put the 1/3rd octave version of TrueAudio's TrueRTA software to the test. We've got another car audio show coming up on Monday, and one of the potential competitors wanted me to tune the system. He'd just swapped out his previous subwoofer box for a new one, and the installer had made a few other "adjustments" to the system. The result was a sonic nightmare. Boomy bass, piercing highs, no midrange to speak of, distortion at any volume level above 5 (volume control goes up to 30) and loud background hiss, no matter what the volume was set at. After sorting out the gain settings on the amplifiers (the source of the hiss), and fixing the phase problem with the main speakers and the subwoofer, the system was sounding a bit better, but the highs were still a bit piercing in nature. So I brought out my laptop with the TruRTA software and used my Monacor SPL meter in its C-weighting setting as the pickup. With the C-weighting, the response of the meter is rolled off at either end of the spectrum, but that didn't bother me too much, as the intent here was to smooth the response, not flatten it. For the measurements, I set TrueRTA's range from 50 Hz to 10kHz, put the SPL meter on top of the driver's set (no headrest) then used a slow sinewave sweep as the source signal. Normally pink noise is used for these types of measurements, but the advantage of the slow sine wave sweep is that you can also quickly identify problem areas caused by distortion, either from the drivers or from the environment itself (e.g. vibrating panels, etc.). Apart from being audible in most instances, this distortion shows up on the RTA as any response above the fundamental frequency (during this test we quickly identified one source of distortion - loose protective covers over the 4" drivers on the dash). Well, TrueRTA immediately identified a number of problems, including a gap between the low bass and midbass and a "hump" in the response stretching from about 3kHz up to 8kHz. The former was caused by the subs being out of phase with the rest of the system, which was easily corrected. The latter was caused by two name-unknown tweeters mounted on the dash, which were basically overpowering everything else up front. To fix this, basically all I did was adjust the EQ's upper bands until the "hump" disappeared entirely from the response as measured by TrueRTA. It took a little time to do, but the end result of all the tweaking was a downward-sloping but smooth response, with two or three response peaks that were too narrow to be effectively dealt with by the system's 12-band EQ. Note that trueRTA's settings for frequency and SPL ranges are easily changed in the main window, and this definitely came in handy when dealing with the problematic areas in the frequency response. Well, after about an hour of tweaking, we were getting a littled tired of all the test tones and sine sweeps, plus we were anxious to test the results of all the tweaking, so the test CD was replaced with some music. Note: up to this point we hadn't listened to ANY music on the system - all the tweaking was done using the slow sine sweep, plus test tones (for setting x-over points). And damn, did we ever hit the sonic jackpot! Nice smooth response, from the bass all the way up through to the highs, with nothing sounding out of place. The system's owner was incredibly pleased with the results, as was I. I think I've definitely got one more useful tool in my audio toolkit :-). Best $40 I've spent in a while. If you've got a laptop with a decent sound card, and you're trying to get the best out of your car audio system, you might want to have a look at it. Regards, Brian Steele www.diysubwoofers.org |
Responses:
[21655] [21656] [21671] [21681] [21690] [21823] [21713] [21653]
21655
From: freddyi, [port-1-26-56k.huntington.zoomnet.net]
Subject: Re: TrueAudio's TrueRTA Software (take II)- what stuff is needed?
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Hi Brian this might be more useful in someways than Speaker Workshop - my use would be with clunky desktop computer for home sytems/subs typically, what is needed for interface? - will preamp and decent mic suffice? also - do you think there's much point to higher res versions when tweaking a full-range DIY speaker? Freddy |
21656
From: Brian, [gnd210-123.caribsurf.com]
Subject: Re: TrueAudio's TrueRTA Software (take II)- what stuff is needed?
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>typically, what is needed for interface? - will >preamp and decent mic suffice? Yep, that should be enough. Note that this version is fairly simple in nature - there's no way to add in a "compensation curve" for your measuring equipment, for example. However, the producer has indicated that this issue will be resolved in v1.5, which will be a free upgrade for those owning v1.0. I'm not sure what the advantage would be to using anything higher than the 1/3 octave version - even if it was able to pick up a 1/6 octave resonance, how would you correct it? :-). Most active EQs are 1/3 octave or less. OTOH, if you're planning to use a PARAMETRIC EQ, to sort out room modes and the like, you might want to look at the higher resolution versions. |
21671
From: freddyi, [port-1-45-56k.huntington.zoomnet.net]
Subject: Re: TrueAudio's TrueRTA Software (take II)- what stuff is needed?
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Thanks Brian debatable over resolution - I had a test Karlson box built by a buddy - tapered panels pushed way too close together - on Speaker Workshop using 1/12 octave or higher resolution showed ~30dB notch - had to re-cut slot to alleviate the standing wave - a properly done Karlson has a nice bass-upper bass kick and will handle some powerful hip-hop/rap passages with good subjective pitch maybe 1/3 octave RTA version correllates decent with what we hear and eq standards - certainly saves a bit of $ do you know of any inexpensive software which can do real-time distortion analysis using sine? - it would be nice to have the ability to pick the filter notch frequency then see how bad things look as level is progressively increased. dunno 'bout parametric - Behringer's feedback-destroyer might be OK for home applications? - wonder how much internal processing delay it has? Freddy |
21681
From: ThomasW, [hh1124140.direcpc.com]
Subject: Re: TrueAudio's TrueRTA Software (take II)- what stuff is needed?
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Behringer is excellent for sub EQ. Don't use it for fullrange since it has a dddddigital sonic signature. Works well with the 1/24th octave TrueRTA version for super fine tuning the last few octaves. Also it's inexpensive, $129 from most of the internet retailers |
21690
From: freddyi, [port-1-09-56k.huntington.zoomnet.net]
Subject: Re: TrueAudio's TrueRTA as HD analyzer - what stuff is needed?
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Ttttttthomas - am not a fan of digital artifacts... tell me - can TrueRTA be used as a sort of distortion analyzer? - I'd like to feed some of my toys with sine and get an idea of harmonic distortion - is this something that might be done with TrueRTA? - if so would you need the highest resolution to get any meaningful display? Freddy |
21823
From: John L. Murphy, [host-216-78-28-52.tys.bellsouth.net]
Subject: Re: TrueAudio's TrueRTA as HD analyzer - what stuff is needed?
URL: About TrueRTA
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Freddy asked: tell me - can TrueRTA be used as a sort of distortion analyzer? - I'd like to feed some of my toys with sine and get an idea of harmonic distortion - is this something that might be done with TrueRTA? - if so would you need the highest resolution to get any meaningful display? YES! You can do very precise harmonic distortion analysis with TrueRTA. Take a look at the first screen shot on the TrueRTA info page below and you will see the result of a self-test of a sound card using a 1 kHz tone. The distortion products are easily seen as spectral lines at 3, 5, 7 and 9 kHz etc. (odd order harmonics) I just checked and at 1/3rd octave resolution it is hard to pick out the harmonics but 1/6th octave resolution starts to reveal the individual harmonics. So I'd recommend no less than 1/6 octave resolution for distortion analysis. Check it out here: http://www.trueaudio.com/rta_abt1.htm Regards, John ///////////////////////////////////// John L. Murphy Physicist/Audio Engineer True Audio http://www.trueaudio.com Home of WinSpeakerz, MacSpeakerz and TrueRTA. Check out my book "Introduction to Loudspeaker Design" at Amazon.com |
Responses:
None
21713
From: ThomasW, [hh1105126.direcpc.com]
Subject: Nope it can't do that, takes dedicated hardware $$$$$$$...nt
| nt |
Responses:
None
21653
From: chris, [dhcp024-209-035-016.neo.rr.com]
Subject: Re: TrueAudio's TrueRTA Software (take II)
| no lapop but i have a computer in my garadge hehe gonna look into it too |
Responses:
None
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