4x isobaric - 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 10th May 2005, 05:29 AM   #11
Jennice is offline Jennice  Denmark
diyAudio Member
 
Join Date: Jun 2003
Location: Planet Earth
Issue A:

Quote:
Originally posted by azrix
Depending on frequency and driver layout, though, you can have lobing issues with that many drivers.
Maybe it's a language thing (english isn't native to me), but I don't understand this part. Is there another way of describing the phenomenon you're referring to?

Issue B:
You refer to the impedance not being changed... so what matters really is the "available" membrane area (factor relative to a single driver), and the power drawn from the amplifier (factor relative to power into a single driver)?

Jennice
__________________
I get paid to break stuff. My g/f gets paid to play with children. Life is good.
  Reply With Quote
Old 10th May 2005, 06:18 AM   #12
simon5 is offline simon5  Canada
diyAudio Member
 
Join Date: Nov 2004
Location: Québec, Québec
Frequency lobing is when the off-axis response is alot quieter than the in-axis response.

This is not a concern when designing a subwoofer.

Since you keep the impedance at 8 ohms, then yes, you only need to consider the membrane area and the power drawn from the amplifier.
__________________
DIYaudio for President !
  Reply With Quote
Old 10th May 2005, 06:44 AM   #13
Jennice is offline Jennice  Denmark
diyAudio Member
 
Join Date: Jun 2003
Location: Planet Earth
Hi Simon5,

If I was to use 4 drivers all facing out (useable surface area), I would try to design the X-over at the baffle step frequency, so that the rear facing drivers would assist in making a (close to ideal) point source, radiating all 360 degrees.

Maybe I didn't explain that part originally... my plan was to either make a smallish enclosure with 2 x 2 drivers isobaric, or make use of all 4 drivers, 2 facing front, and 2 facing rear.

I think it was Dave (Planet10) who makes the baffle step compensation for a 2-way with an addidional woofer that is mounted at the rear. The rear driver would have a simple LP filter, letting the driver play as the baffle step reduces the apparent output from the front driver.

Jennice
__________________
I get paid to break stuff. My g/f gets paid to play with children. Life is good.
  Reply With Quote
Old 10th May 2005, 07:50 AM   #14
azrix is offline azrix  United States
diyAudio Member
 
Join Date: Oct 2004
Quote:
Originally posted by simon5
Frequency lobing is when the off-axis response is alot quieter than the in-axis response.
Not exactly, at least that's not what I meant by lobing. What I was refering to is when you have phase cancelation at certain frequencies and certain angles off-axis. For example, say you have a speaker that's -3db at 30deg off axis at a certain frequency, -20db at 45deg off axis, and back up at -6db at 60deg off axis. If you were to plot this kind of response on a polar chart, you'd have three teardrop shapes, or 'lobes', that connect at your point of origin. This polar response will change and become less of a problem as you go down in frequency. It's mostly an issue with lines arrays of dynamic drivers. But, it can happen with only two drivers if they're trying to reproduce the same frequency and are far enough apart.

Quote:
Originally posted by simon5
This is not a concern when designing a subwoofer.
No, it wouldn't be, but if you're using a large woofer as a bass driver in a speaker design, which I believe is the case here, you can have problems if you crossover high enough and use more than one or two drivers. It probably isn't going to be an issue in this case, so forget I said anything . Just trying to be thorough.
  Reply With Quote
Old 10th May 2005, 08:00 AM   #15
azrix is offline azrix  United States
diyAudio Member
 
Join Date: Oct 2004
Quote:
Originally posted by Jennice
Maybe I didn't explain that part originally... my plan was to either make a smallish enclosure with 2 x 2 drivers isobaric, or make use of all 4 drivers, 2 facing front, and 2 facing rear.
Oh, I didn't realize this. This is generally refered to as a bi-pole arrangement, I believe. You can run the front and rear speakers in phase, so that all the drivers are going out as the same time, or out of phase, so that when the front speakers go out, the rear ones go in. That's about all I know of that. If you are going to do that, you might look at mounting the woofers on the sides of your cabinet so that you can have a more narrow front baffle. By doing that you might also be able to get away with larger drivers, if you want.
  Reply With Quote
Old 10th May 2005, 08:42 AM   #16
Jennice is offline Jennice  Denmark
diyAudio Member
 
Join Date: Jun 2003
Location: Planet Earth
I figured I'd let the drivers play in phase if I were to go for the "4 drivers facing out" solution. This could compensate for baffle step I suppose, giving the 6dB gain which would otherwise be lost.
(Isn't baffle step -6dB).

I have thought about placing the drivers on the side, but wouldn't that mess up the sound stage? If placed side-ways, I thought the drivers should only play below 100Hz or so (where you start hearing directivity)...?

Jennice
__________________
I get paid to break stuff. My g/f gets paid to play with children. Life is good.
  Reply With Quote
Old 10th May 2005, 08:48 AM   #17
Jennice is offline Jennice  Denmark
diyAudio Member
 
Join Date: Jun 2003
Location: Planet Earth
Quote:
Originally posted by azrix


No, it wouldn't be, but if you're using a large woofer as a bass driver in a speaker design, which I believe is the case here, you can have problems if you crossover high enough and use more than one or two drivers. It probably isn't going to be an issue in this case, so forget I said anything . Just trying to be thorough.

I appreciate all the input I can get

My plan was to cross somewhere around 2-300 Hz if I went for the 4-driver-out solution, depending on the baffle step, and hence the width of the cabinet.

However, due to the use of the room (and spouse!) the speakers wouldn't be too far from the wall, so maybe baffle-step isn't a real issue here. (in real life considerations)???

Jennice
__________________
I get paid to break stuff. My g/f gets paid to play with children. Life is good.
  Reply With Quote
Old 10th May 2005, 09:38 AM   #18
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Ron seems to have a decided dislike for isobariks...

I went thru an isobarik phase... the design has a place and i really enjoyed those speakers.

I also think the design brings more to the party than just 1/2ing the box and paying the price. The extra layer of cone isolating what's on the inside from the outside tends to make the boxes sound less boxy for one.

and it allows me to put 4 12" (a lovely semi-vintage Foster) into a 42 litre box -- a pair of 6 ft^3 boxes is something i don't want to contemplate.

push-pull push-push

dave
Attached Images
File Type: gif push-pull-push-push-fosters.gif (8.5 KB, 279 views)
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 10th May 2005, 09:44 AM   #19
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Yes, 3dB max SPL gain and 2x power handling over an isobaric pair. As already mentioned, with small boxes the space taken up by the 'hidden' driver and/or it's connecting tunnel becomes significant and you often hardly end up with a smaller box and you have wasted all that money on an extra driver. IMO isobaric only comes into real use if you refuse to use any active EQ and your box is bigger than 75 litres. I go with the LT every time.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 10th May 2005, 10:08 AM   #20
Jennice is offline Jennice  Denmark
diyAudio Member
 
Join Date: Jun 2003
Location: Planet Earth
I have played with WinISD, and come up with compromised at about 20 liter for isobaric (plus some extra for the spacing between the drivers), and 80 liter for 4 drivers. these two should give the same response/roll-off, but at 4 times the enslosure size!!!
The ideal flat roll-off happens at 41 liters and 164 liters, respectively. There's no chance that I'm going to build speakers this size.

Considering that I want to make a sub-inclosure inside the main box, containing the mid- and tweeter driver, I would end up in excess of 100 liter with the 4 "visible driver" option.

Actively compensating for an error that could be avoided with a different speaker design, is not a thought I like.
__________________
I get paid to break stuff. My g/f gets paid to play with children. Life is good.
  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
isobaric keyser Subwoofers 9 9th December 2010 01:35 AM
isobaric any info on how? newfinish Multi-Way 38 18th January 2008 02:04 AM
isobaric damping.. ChesterFuzzin' Subwoofers 9 4th January 2006 12:30 AM
isobaric resonator? tade Subwoofers 6 17th August 2005 07:24 AM
Isobaric for subs only? speekergeek Multi-Way 8 13th January 2004 03:15 AM


New To Site? Need Help?

All times are GMT. The time now is 07:55 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