Compute D for dipole speaker - Page 2 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

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 21st September 2005, 02:25 PM   #11
Rudolf is offline Rudolf  Germany
diyAudio Member
 
Rudolf's Avatar
 
Join Date: Mar 2003
Location: Germany
@MBK

__________________
www.dipolplus.de
  Reply With Quote
Old 21st September 2005, 02:58 PM   #12
MBK is offline MBK  Singapore
diyAudio Member
 
Join Date: Apr 2002
Location: Singapore
Alright, I'll explain:

The Edge page didn't open on the link you gave at first try. So I read a short summary somewhere else on that page and then wrote my first reply w/o actually trying the program, and w/o reading your original link where the author explains the capabilities in detail...

(now it makes sense does it? )

Anyway: it worked eventually, so I tried and played with both the spreadsheet and the Edge, and compared to my actual measurements in half space outdoors and indoors. Not bad, hits the general looks of the real measurement, but major peaks and dips differ from reality. Then again I have a (shallow) U-frame (about 15 cm), and real life MLS resolution does not come close to the simulation's "exact" prediction.

I'd say all in all Linkwitz gives quite a good approximation with his formulas using "D", and real life from this short experiment still differs from both by enough a margin to warrant a lot of experimentation, guesswork, and tacit knowledge.
  Reply With Quote
Old 21st September 2005, 03:16 PM   #13
Rudolf is offline Rudolf  Germany
diyAudio Member
 
Rudolf's Avatar
 
Join Date: Mar 2003
Location: Germany
Hi MBK,

there is no need to explain. I just wanted to show how happy I was to get someone on the right track regarding EDGE.
Thought, those emoticons would transport that.

Time to give this thread back to Doug!
__________________
www.dipolplus.de
  Reply With Quote
Old 21st September 2005, 03:33 PM   #14
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by Rudolf
To find out, how the OB response is boosted by the floor and how the driver height on the baffle is interfering with the floor, I simulate with Thorsten Loesch´s xlbaffle.xls:
http://baseportal.de/cgi-bin/basepor...rt~=Excelsheet
Just to add, the XLBaffle Spreadsheet was written using a first approximation of the dipole rolloff and based on an AES Preprin and simplifications of the math in that, the room effect is largely fudged, the end result remains REMARKABLY close.

I have previously criticised the math and detail given on Siegfried Linkwitz's site as being not useful insofar, as it does not predict what really happens.

I have noticed more or less recently that SL himself includes the issues that cause the diations in his analysis elsewhere on his site. When combining these with his basic math we arrive back at similar results to my own spreadsheet and experience in performance.

The key difference is that Mr. Linkwitz treats these effects as undesirable deviations from the ideal that must be equalised out in order to allow the equalisation to applied such as i we where to equalise an ideal dipole while I treat them as usefull resources to minimise (or eliminate) the need for equalisation on Dipoles.



Some of this "it's an error so let's remove it" philosophy can be noted here:

http://www.linkwitzlab.com/models.htm#D

This section also covers some of the desirable properties of dipole cone drivers (rear radiation rolloff at high frequencies, increased beaming at higher frequencies).

The differences overall acrue as follows:

1) Mr. Linkwitz's Math assumes more or less a round baffle with D(iameter) equal to the smalles baffle dimension, one might call this worst case condition. Using "The Edge" (yummy when from Pizza the Hut) gives a more accurate result.

2) HOWEVER both "The Edge" and Mr. Linkwitz's pages assume a dipole in completely open space, which is simply not present in a normal audio system. In reality we have two more effects.

3) First, for a wavelength with a length longer than than two times the distance to the floor (eg, 65cm floor distance, critical frequency around 260Hz) the floor reflection begins to be progressively in phase with the direct radiation, giving a boost of around 3db at the critical frequency and levels out at a total of 6db LF gain one octave below. The bottom line is that we have 6db more SPL at all frequencies more than one octave below the critical frequency and a 3db boost at the critical frequency not accounted for in traditional dipole theory.

Mr. Linkwitz covers this in some detail:

(see http://www.linkwitzlab.com/models.htm#F1 )

It should be noted that sidewall reflection invariably happen too and usually happen at a lower frequency and will add another up to 6db LF SPL

4) We have so far assumed that the rear wave of the dipole either wraps around forward arund the baffle or is "lost in space", but in reality we have a rear wall which will reflect back our rearwave towards the listener.There will be some attenuation and (obviously) some delay, if we take our exampe of 1m distance to the rear wall the sound will be delayed by 6mS.

As our rear-wave is in opposite polarity to the frontal one at around 90Hz (for our 1m distance) we can conclude that it will re-inforce our front wave at 90Hz, BUT it will cancel it at 45Hz, of course in reality the rear wave is somewhat damped and will thus not lead to such extreme problems and more interesting, by tuning the rearwall distance carefully one should be able to "fill in" the combfilter response caused by the floor reflection to a good degree, usually a "golden ratio" placement of the speaker which accounts for the inverted polarity of the rear wave makes for a rather smooth response.

Anyway, the above items are intended to illustrate why a dipole that SHOULD roll off at 200Hz and SHOULD be down 12db at 50Hz may very well be flat at 50Hz, in room.

Sayonara
  Reply With Quote
Old 21st September 2005, 06:02 PM   #15
AJinFLA is offline AJinFLA  United States
Banned
 
Join Date: Feb 2005
Location: Tampa
Ok Doug,

posting at lunch again . Aren't you glad it's so simple ?
Dipoles are definately fun to play with. Empirical results are often the most important. Enjoy.

cheers,

AJ
  Reply With Quote
Old 22nd September 2005, 05:37 PM   #16
reins is offline reins  Germany
diyAudio Member
 
Join Date: Mar 2004
Location: Bayern
Quote:
Originally posted by AJinFLA
Ok Doug,

posting at lunch again . Aren't you glad it's so simple ?
Dipoles are definately fun to play with. Empirical results are often the most important. Enjoy.

cheers,

AJ
I have to agree, simulation could only give you a hint what will go on, but reallity will be different.

Stephan
  Reply With Quote
Old 23rd September 2005, 04:57 AM   #17
DougL is offline DougL  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Wheaton IL.
Blog Entries: 31
Thanks for the reply’s.

As usual, I learned something from the board.

AJinFLA, posting at lunch seems hazardous.

The XLBaffle Spreadsheet is an excellent tool.

Quote:
Anyway, the above items are intended to illustrate why a dipole that SHOULD roll off at 200Hz and SHOULD be down 12db at 50Hz may very well be flat at 50Hz, in room.
This is the main reason I am avoiding "alphabet" baffles.
The simple ones seem to have many advantages.

Again, thanks all.

Doug
  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
20 Hz to 20 kHz Dipole Speaker System MJK Full Range 69 29th September 2008 01:37 PM
how to compute for fuse amperage? jarthel Parts 32 2nd August 2006 01:06 PM
how to compute the rms output of audio amp mozikluv Everything Else 26 4th September 2003 09:45 PM
DIY stepped attenuator (how to compute resistor values?) jarthel Solid State 8 16th June 2002 09:54 AM


New To Site? Need Help?

All times are GMT. The time now is 10:24 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki