passive radiator excursion - Page 2 - diyAudio
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 18th August 2010, 06:34 PM   #11
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally Posted by jaybee View Post
I've seen the method proposed, where the required PR mass is calculated by designing a port with the same effective diameter as the PR - it's simply the mass of the air enclosed in the volume of the port. Sounds good, although I'm somewhat concerned that it doesn't seem to agree with the datasheets Seas publishes for their Prestige line PRs.
Remember to add ~0.8 times the diameter to the length a port program spits out for calculating mass of the air in the port. In my sheets there is very little difference between the "port method" and a much more complicated method, in terms of getting the right mass to add.

Make sure you use PR's with an Fs well below your intended tuning frequency and a large Vas. Very few premade PR's (usually based on woofers) follow this advice and can be hard to use.
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  Reply With Quote
Old 19th August 2010, 02:06 AM   #12
jaybee is offline jaybee  United States
diyAudio Member
 
Join Date: May 2008
gentlepersons of DIYaudio, thanks for taking the time to respond, I appreciate it.

The rough rules of thumb have merit I'm sure but I guess I was looking for something more specific. The easiest way is definitely modelling software, but for a Mac user options look really sparse. I've got one spreadsheet working okay, called "ported.xls", but no PR functionality. I'm not sure why the Unibox.xls doesn't work.

Then there's all the web-based "applets", they never seem to agree with each other. This is one reason I thought it's better just to know the formulas. There's a couple technical papers I've tried to find online but I guess they're not hosted anywhere Google can see.

Another reason is, the added complexity I'm considering in an active filter. The alignment I'm working on is a sub-chebyshev (k>1) with a fairly slow roll-off, which a peak-y 2nd order active HPF would flatten out really nicely. I've got that bit all worked out using this spreadsheet, it looks good with no driver excursion problems. With this kind of alignment the system tuning is pretty far below f3, which the filter only moves down a couple Hz. With the filter, the response is more than 20dB down at system resonance.

This clearly relaxes the woofer excursion requirements at very low frequencies, and my assumption is that it does the PR likewise. Outside resonance, the PR doesn't get pushed that much, but I don't know how fast it falls off. My intuition is that this PR just isn't going to get worked that hard. I just now thought of another way to figure it. I'll be around.
  Reply With Quote
Old 19th August 2010, 04:17 AM   #13
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally Posted by jaybee View Post
The rough rules of thumb have merit I'm sure but I guess I was looking for something more specific. The easiest way is definitely modelling software, but for a Mac user options look really sparse. I've got one spreadsheet working okay, called "ported.xls", but no PR functionality. I'm not sure why the Unibox.xls doesn't work.

My intuition is that this PR just isn't going to get worked that hard.
Maybe you should ask specific questions Unibox doesn't work on macs because it uses VBA.

Here's the same size box, same tuning, modeled with a port, a loose and a stiff PR. I can also show PR excursion if you are interested...
Attached Images
File Type: png Clipboard01.png (12.5 KB, 103 views)
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  Reply With Quote
Old 21st August 2010, 01:05 AM   #14
jaybee is offline jaybee  United States
diyAudio Member
 
Join Date: May 2008
Ron E, I am definitely interested to see excursion, if you would be so kind. Please! I'm still grokking what I see in that chart, since I thought a stiffer suspension would be better in a PR. Thanks for that.
  Reply With Quote
Old 21st August 2010, 05:36 PM   #15
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Here's a graph of PR and diaphragm excursion. Same loose and stiff - this time Stiff is alignment 1 and loose is alignment 2.

You can see that stiff PR reduces both diaphragm and PR excursion, at the expense of frequency response. The loose PR has better damping on the active diaphragm and more output and better frequency response.

In reality, the excursions would be lower at this power level because the transducers are not linear and this is a linear simulation. But the trending is likely the same. Note, I have Qp set to 15 for both, where the stiffer PR might be lower, and the looser one might be higher, which would also likely give greater output near resonance for the looser PR. I haven't added a filter or modeled the driver you will be using. It wouldn't be too difficult to cascade a filter in here - let me know what the parameters of your design are.

This is a simulation for an old driver - Adire Shiva
Fs=22
Qts=0.38
Qes=0.4
Vas=144
Xmax = 15mm
Re=2.7

Vb= 150liters
Fb=20Hz

Pr1 has Fp=15, Vap=117liters, Diameter 33cm
Pr2 has Fp=8, Vap=1000liters, Diameter 33cm

Driven by a 75 watt/8ohm amp ~35Volts peak
Attached Images
File Type: png excursion.png (17.2 KB, 77 views)
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  Reply With Quote
Old 22nd August 2010, 12:28 AM   #16
jaybee is offline jaybee  United States
diyAudio Member
 
Join Date: May 2008
Very interesting Ron E, thanks a lot for showing me that. Adding mass to a PR moves it's resonant freq lower doesn't it? I'm far from home now but one of the things I'm going to do when I get back is order the Vance Dickason book.

The filter I was planning was pretty carefully tweaked to flatten out the response of my alignment, but it was done with a port. I see now that a PR will change things, maybe alot.

Ron, maybe I can ask you for a big favor, to plug in my driver there, please. You can say "I don't have time for that you dick".

It's Seas H1192.
Fs=20Hz
Qt=0.24
Vas=108 l
xmax=14mm

Fb=20.7Hz
Vb=27.7 l

The filter is a 2nd order Sallen-Key with q=1.27 f=36.7 Actually I'm not sure how ported.xls specifies the frequency, but that's the number that's in there now. Chart shows -3dB from 0dB about 26.5Hz, -3dB from the peak is 31Hz.
  Reply With Quote
Old 22nd August 2010, 03:18 AM   #17
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally Posted by jaybee View Post
You can say "I don't have time for that you dick"
Well, I am not one who makes such statements. It might take a while to get to this, but just remind me if I forget. I am not sure what your background is, but the book "Theory and Design of Loudspeaker Enclosures" is a good reference for those who understand Laplace transforms and circuit analysis.

Total mass for the stiff PR is ~1kg and the loose PR is ~480g, IIRC.
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley

Last edited by Ron E; 22nd August 2010 at 03:21 AM.
  Reply With Quote
Old 22nd August 2010, 04:23 AM   #18
jaybee is offline jaybee  United States
diyAudio Member
 
Join Date: May 2008
Pardon my crudeness then. I appreciate what you've already done.

My background is in music performance, jazz guitar. I'm this guy: jeffreyburrjazz.com

I have decent general math skills but no calculus. So, some of the papers I've been reading by Small, Thiele et al are pretty well over my head. That said, I have been learning a fair bit from these, and I'd love to find a particular one by Thiele from 1965 which describes SC4 alignments, "Filters with Variable Cut-off Frequencies". It is referenced in a four part paper by Small that seems widely available in PDF. Maybe some of these books have this information as well.

Thanks, speaking of books, for the recommendation. I'll look into it. The circuit style analysis kind of boggles my mind but I understand there are losses which may be modeled as various types of reactive impedances.

Last edited by jaybee; 22nd August 2010 at 04:27 AM.
  Reply With Quote
Old 22nd August 2010, 11:48 PM   #19
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally Posted by jaybee View Post
It's Seas H1192.
Fs=20Hz
Qt=0.24
Vas=108 l
xmax=14mm

Fb=20.7Hz
Vb=27.7 l

The filter is a 2nd order Sallen-Key with q=1.27 f=36.7 Actually I'm not sure how ported.xls specifies the frequency, but that's the number that's in there now. Chart shows -3dB from 0dB about 26.5Hz, -3dB from the peak is 31Hz.
I haven't added the filter section yet, but here it is without. This is with the 8" and 10" SEAS prestige PR's with parameters from madisound - if you have a fair deal of cut below 20Hz, you may be fine with either, but it is probably best to follow their selection guide. The vented sim for this driver is not much different from the looser of these and the stiff PR problem is not an issue because your box is quite small, so you will be fine just simulating frequency response with ported.xls. I'll get to the filtered PR excursion sim later.

Note SEAS publishes xmax as peak-peak, whereas I use one way xmax (7mm) Note that for every 6dB of boost or cut at any single frequency, your excursion will be changed by a factor of 2. This may be enough to answer your question about PR suitability.
Attached Files
File Type: pdf passivebeta2.pdf (146.6 KB, 10 views)
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley

Last edited by Ron E; 23rd August 2010 at 12:05 AM.
  Reply With Quote
Old 23rd August 2010, 01:25 AM   #20
jaybee is offline jaybee  United States
diyAudio Member
 
Join Date: May 2008
Wow, Ron you are a prince among men. Thanks so much for doing that.
It looks like a pretty sophisticated program, all the enclosure losses are broken out. That's nuts!
I've been putting the peak to peak linear excursion in ported.xls because that's what I thought they were asking for. I see now this thing isn't going to be quite as wonderful as I thought. That's going to get even worse with the active filter, since it has a 2.8 dB bump before rolloff.
Are most manufacturers quoting one-way xmax? If so, I feel misled by Seas.

Last edited by jaybee; 23rd August 2010 at 01:35 AM.
  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
Passive Radiator Excursion HTRookie Subwoofers 13 17th December 2008 09:05 PM
Passive radiator Chris8sirhC Subwoofers 4 5th August 2008 05:49 PM
XLS passive past excursion Kram Subwoofers 21 29th November 2007 05:59 PM
Passive radiator jamikl Subwoofers 1 3rd June 2006 09:23 AM


New To Site? Need Help?

All times are GMT. The time now is 02:01 PM.


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