Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th February 2011, 08:16 PM   #341
soho54 is offline soho54  United States
diyAudio Member
 
Join Date: Nov 2005
Location: Georgia
Quote:
Originally Posted by jbell View Post
nope... so you want to take that reading and multiply by .707?
Voltage Conversions
Peak= 1.414*RMS
RMS= .707*Peak or Avg*1.11
Avg= .637*RMS
With sine waves only.

Last edited by soho54; 4th February 2011 at 08:45 PM.
  Reply With Quote
Old 4th February 2011, 08:53 PM   #342
jbell is online now jbell  United States
diyAudio Member
 
Join Date: Apr 2003
Location: .
Quote:
Originally Posted by soho54 View Post
Voltage Conversions
Peak= 1.414*RMS
RMS= .707*Peak or Avg*1.11
Avg= .637*RMS
With sine waves only.
Any time I post a spl measurement, it's always volt meter, sine wave, and spl meter, 28v10m.

Beckman is the poor mans fluke... I have great confidence in it.

Maybe runrod's 111db measurements aren't as far off as I thought..... hmmm.....
  Reply With Quote
Old 4th February 2011, 09:00 PM   #343
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by jbell View Post
nope... so you want to take that reading and multiply by .707?

That'll make the numbers look even better....

That was at the end of my sidewalk... about 20' from the house, nothing in front for about a half mile. You can see the toyota off to one side, that's about it.
The pic a few posts back (#331) was 28v10m, I don't see much difference to what I did today.

excuse the 'non-scientific' measurement that was obviously rushed.... it was cold, and snowy, but at least no wind.
A dB meter reports level at the frequencies that are loudest, the response peaks around 160 and 260 Hz are 3 dB above the 55-120 Hz range.

An unweighted SPL reading of 105.4 would put the response in the pass band of 55-120 around 102.4 dB, about three dB more than a similar sized ported box with the same speaker .

Even with a calibrated dB meter, the calibration only insures the dB meter is accurate at the test tone frequency, usually 1K, a decade away from sub frequencies.

A relatively small meter (or test voltage) error could mean the box actually has little or no advantage over a ported design of similar size.

I found measuring about 6 feet away from outdoor buildings lifted the response of subs by 4 dB in the octave around 40 Hz, not sure what influence walls 20 feet away would have, but the wall being within a wavelength of the DUT will definitely have some effect. Even small objects by the test microphone can have several dB influence.

Using the magnitude response will show coherence, very helpful to see if what you are testing is valid.
Windscreens are a must outside too, just do an indoor measurement with it on and off to find if it affects the response. The standard ones I use have virtually no effect on frequency response, but make all the difference when testing outside.

Getting reliable measurements without a known benchmark is virtually impossible, the reason I asked l the questions in post #334 and 339.

The comparative tests I posted in #339 were an eye opener for me, I would have thought the front loaded and tapped horns would have performed better than they did, but the JBL SRX 728 proved otherwise, it is 98 dB one watt one meter in the 80 Hz range

Donít want to sound like a ďdoubting ThomasĒ but until I see a relative comparison, I find it hard to accept test results, including my own. I went through a period of frustration building and testing dozens of boxes (and freezing my what off), finding they fell far short of predicted results, only to later find the test microphone I was using read way low in the low frequencies.

I hope you will mount a 3015LF in a standard box, or better yet the one like below (well under one sheet :^) ), and do a comparison to the tapped horn.

Thanks !
Attached Images
File Type: png 3015LFMed.png (72.4 KB, 444 views)
  Reply With Quote
Old 4th February 2011, 09:34 PM   #344
jbell is online now jbell  United States
diyAudio Member
 
Join Date: Apr 2003
Location: .
Here's a behringer 2031p... with well published specs. It's 89db 1w1m 4ohm. So... 2v should get something close to 89db.

well I'm within 2db of their published spec... on the cheap-o spl meter using the EXACT same setup as I did with the ss15.

now it's cold... I'm not dragging this stuff back out in the cold again.
Attached Images
File Type: jpg Picture 086a.JPG (314.7 KB, 461 views)

Last edited by jbell; 4th February 2011 at 09:53 PM.
  Reply With Quote
Old 4th February 2011, 09:38 PM   #345
diyAudio Member
 
Join Date: Nov 2010
Jim; I dont blame you its cold here in Pa. and more snow on the way. Andy
  Reply With Quote
Old 4th February 2011, 09:46 PM   #346
Djim is offline Djim  Netherlands
diyAudio Member
 
Join Date: Dec 2009
Location: 'Ollanda
For what its worth I used Jbells 2,83V and 28,3V measurements and put them in the same grafic model...
(The red line was just for reference)

Click the image to open in full size.
  Reply With Quote
Old 4th February 2011, 11:01 PM   #347
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by jbell View Post
Here's a behringer 2031p... with well published specs. It's 89db 1w1m 4ohm. So... 2v should get something close to 89db.

well I'm within 2db of their published spec... on the cheap-o spl meter using the EXACT same setup as I did with the ss15.

now it's cold... I'm not dragging this stuff back out in the cold again.
I donít blame you for not wanting to do more testing, I have not been out in my shop for days due to the cold.

Sensitivity specs without charts are always suspect, but letís pretend the Behringer spec is correct and the response is dead flat, and the proximity to buildings are having no effect on your readings.
I have not done that much pretending since I was a kid, this is fun!

So your meter reads 2 dB too high .

It reads 105.4 dB on the higher peaks of the one sheet sub, which are at least 3 dB above the range it is used in, so that puts the sensitivity at about 102 dB .

102 dB - the 2 dB meter variance =100 dB.
The 3015LF is almost exactly that sensitivity in a ported box of similar size.

Oh well .
  Reply With Quote
Old 4th February 2011, 11:19 PM   #348
jbell is online now jbell  United States
diyAudio Member
 
Join Date: Apr 2003
Location: .
Quote:
Originally Posted by weltersys View Post
I donít blame you for not wanting to do more testing, I have not been out in my shop for days due to the cold.

Sensitivity specs without charts are always suspect, but letís pretend the Behringer spec is correct and the response is dead flat, and the proximity to buildings are having no effect on your readings.
I have not done that much pretending since I was a kid, this is fun!

So your meter reads 2 dB too high .

It reads 105.4 dB on the higher peaks of the one sheet sub, which are at least 3 dB above the range it is used in, so that puts the sensitivity at about 102 dB .

102 dB - the 2 dB meter variance =100 dB.
The 3015LF is almost exactly that sensitivity in a ported box of similar size.

Oh well .
uh.... no. not even close.
  Reply With Quote
Old 4th February 2011, 11:41 PM   #349
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by jbell View Post
uh.... no. not even close.
Certainly the response above 125 Hz of the tapped horn will not be close, but below 125 Hz, your tests are not supporting your statement.

Should be easy enough for you to prove or disprove, perhaps you will do a test with the same speaker to verify how close or far apart the response is.

Based on what you have posted, my money is on a pretty close (within 2 dB) level between a ported cabinet and the tapped horn 45-125 Hz.

I hope you prove me wrong, I want to believe !
  Reply With Quote
Old 4th February 2011, 11:43 PM   #350
jbell is online now jbell  United States
diyAudio Member
 
Join Date: Apr 2003
Location: .
you show me the horn resp of your ported cab vs the ss15....
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Here is a Challenge latala Solid State 41 12th May 2011 01:13 AM
Renovation Challenge ZirconiumZephyr Multi-Way 16 1st September 2009 08:38 AM
Design Challenge #1 kgillies Subwoofers 12 13th June 2007 03:20 PM
a challenge --or I need help lawrence99 Car Audio 0 9th March 2005 04:44 AM
The challenge ! thylantyr Solid State 51 24th July 2003 08:41 PM


New To Site? Need Help?

All times are GMT. The time now is 11:31 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2