Testing autotuba responses?

Karanael · 21st June 2005, 10:39 PM

Hello all.

I'm now the proud owner of one of Bill Fitzmaurice's wonderful horn-loaded enclosures

One problem... the decibel meter I have is suspect.

It's a £50 digital run-of-the-mill job, and appears to have some serious inaccuracies below about 65Hz. Ie, the horn's output sounds flat, but the reading is at least 25dB down from what it should be!

Is there an easier way of doing this than a frequency generator, decibel meter and a pad of paper?! I haven't been able to find anything software-wise that seems to do the job. Either far, far too confusing, or otherwise unusable (ie, expensive).

On a related topic, would a 'vanilla' condenser microphone insert be accurate enough and/or calibratable for low, low bass frequencies? I'm looking at stuff from about 150Hz downwards (limit will probably be about 20Hz or so).

Thanks everyone

Karanael

qi · 22nd June 2005, 02:46 PM

This MAY be what you are looking for...

Radio Shack Sound Level Meter (Model 33-2050) correction chart:

http://www.hometheaterhifi.com/utili...load-page.html

Puggie · 22nd June 2005, 03:06 PM

I'd suggest you find a car Audio shop who has an Audiocontrol or better Termlab SPL meter, and ask if you can use their meter to test it.

A Termlab would allow you to just play a sweep tone and it would give you a nice bar chart of SLP Vs Hz (1Hz divisions I think too). as the Termlab seems to be the industry standard now (in car audio) you would have something as a reference too.

tiroth · 22nd June 2005, 03:18 PM

Compare my measurements and see what you think. Bill's quarter-space estimates are rather enthusiastic in my mind. I don't know how much cabin gain improves this.

It's a good design but there isn't much output below the horn cutoff ~35-40Hz. (as expected -- you can't cheat the physics of it)

Autotuba measurements, plus shiva

simon5 · 23rd June 2005, 05:43 AM

Hi tiroth, just saw I was supposed in that thread to give you the graph of the Shiva. The girl did a graph, I'll try to post it for you. Sorry for the awful long delay.

simon5 · 23rd June 2005, 06:22 AM

Hi again tiroth, I posted the information you wanted in the relevant thread.

Sorry to hijack your thread Karanael.

morbo · 23rd June 2005, 06:42 AM

what ever happened to Bill anyway? He used to post around here all the time

Netlist · 23rd June 2005, 07:57 AM

Quote:

Originally posted by morbo
what ever happened to Bill anyway

people can get banned from diyaudio.com?

/Hugo

morbo · 23rd June 2005, 03:40 PM

LOL!!! That is hilarious. So the 'Jim York' persona that made all those ridiculous claims (ie, autotuba w/10" driver will 'destroy' a ported tempest) was really Bill? I always thought 'Jim' was a bit over the top...

morbo · 23rd June 2005, 05:47 PM

Since posting the above I got an email from an 'interested party' who pointed me to a message on another forum from Bill, who has his own version of events, in which Jim merely posted from Jim's home as he often visits with him. He feels he was banned without warning or explanation.

I find all of this somewhat suspect, but as there are 2 sides to every story, it seems only fair to mention it.

21st June 2005, 10:39 PM	#1
Karanael diyAudio Member Join Date: Aug 2004 Location: East Ayrshire, Scotland	Testing autotuba responses? Hello all. I'm now the proud owner of one of Bill Fitzmaurice's wonderful horn-loaded enclosures One problem... the decibel meter I have is suspect. It's a £50 digital run-of-the-mill job, and appears to have some serious inaccuracies below about 65Hz. Ie, the horn's output sounds flat, but the reading is at least 25dB down from what it should be! Is there an easier way of doing this than a frequency generator, decibel meter and a pad of paper?! I haven't been able to find anything software-wise that seems to do the job. Either far, far too confusing, or otherwise unusable (ie, expensive). On a related topic, would a 'vanilla' condenser microphone insert be accurate enough and/or calibratable for low, low bass frequencies? I'm looking at stuff from about 150Hz downwards (limit will probably be about 20Hz or so). Thanks everyone Karanael

23rd June 2005, 05:43 AM	#5
simon5 diyAudio Member Join Date: Nov 2004 Location: Québec, Québec	Hi tiroth, just saw I was supposed in that thread to give you the graph of the Shiva. The girl did a graph, I'll try to post it for you. Sorry for the awful long delay. __________________ DIYaudio for President !

23rd June 2005, 06:22 AM	#6
simon5 diyAudio Member Join Date: Nov 2004 Location: Québec, Québec	Hi again tiroth, I posted the information you wanted in the relevant thread. Sorry to hijack your thread Karanael. __________________ DIYaudio for President !

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22nd June 2005, 02:46 PM	#2
qi diyAudio Member Join Date: Oct 2003 Location: .	This MAY be what you are looking for... Radio Shack Sound Level Meter (Model 33-2050) correction chart: http://www.hometheaterhifi.com/utili...load-page.html

22nd June 2005, 03:06 PM	#3
Puggie diyAudio Member Join Date: Oct 2004	I'd suggest you find a car Audio shop who has an Audiocontrol or better Termlab SPL meter, and ask if you can use their meter to test it. A Termlab would allow you to just play a sweep tone and it would give you a nice bar chart of SLP Vs Hz (1Hz divisions I think too). as the Termlab seems to be the industry standard now (in car audio) you would have something as a reference too.

22nd June 2005, 03:18 PM	#4
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Compare my measurements and see what you think. Bill's quarter-space estimates are rather enthusiastic in my mind. I don't know how much cabin gain improves this. It's a good design but there isn't much output below the horn cutoff ~35-40Hz. (as expected -- you can't cheat the physics of it) Autotuba measurements, plus shiva

23rd June 2005, 06:42 AM	#7
morbo diyAudio Member Join Date: Sep 2004 Location: Guelph, Ontario	what ever happened to Bill anyway? He used to post around here all the time

23rd June 2005, 03:40 PM	#9
morbo diyAudio Member Join Date: Sep 2004 Location: Guelph, Ontario	LOL!!! That is hilarious. So the 'Jim York' persona that made all those ridiculous claims (ie, autotuba w/10" driver will 'destroy' a ported tempest) was really Bill? I always thought 'Jim' was a bit over the top...

23rd June 2005, 05:47 PM	#10
morbo diyAudio Member Join Date: Sep 2004 Location: Guelph, Ontario	Since posting the above I got an email from an 'interested party' who pointed me to a message on another forum from Bill, who has his own version of events, in which Jim merely posted from Jim's home as he often visits with him. He feels he was banned without warning or explanation. I find all of this somewhat suspect, but as there are 2 sides to every story, it seems only fair to mention it.

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