Dipole bass or Ripole Bass? - 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 8th September 2008, 01:12 PM   #1
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Default Dipole bass or Ripole Bass?

Goodwill find: 4 - 15" woofers. No markings at all. No idea who made them.
The good news is that they were really cheap ($100.00 for all 4) and they seem to be in nearly brand-new condition.
The basket is thin stamped steel and the cone appears to be poly. A 2" (or less) voice coil and a smallish ceramic magnet show they have a weak motor.

I measured the T/S parameters with Speaker Workshop and have these figures to share (average of the 4 - not much deviation between drivers):

Fs = 30 Hz
Re = 5.7 ohm
Qms = 6
Qes = 1.5
Vas = 330 litres
Sd = 870 sqcm

Hard to judge just how much Xmax, but the wide foam surround and the fact that the voice coil is rather narrow suggests that there might be a fair bit of linear movement. A conservative estimate would be +/- 5mm.

I have mocked up a quick N-profile ripole to see how it performs.
I measured the Fs of this box combo and it shows that resonance has dropped to 18.6 Hz. This was lower than I expected (not disappointed).
When driven by the ordinary stereo output of my HTR without a crossover, the bass is strong but very low in level. There isn't enough output from one. When I drove it using my big sub amp with its Linkwitz transform, the bass was VERY strong and I could feel the amount of cone motion was quite large. The thin panels of the box were flexing, but I heard nothing bad from the driver itself.
The other possibility is dipole, with 2 drivers per side. For this, I'm thinking that a little EQ (from Rod Elliot's sub controller maybe or a low gain LT) will be needed. I'm not sure if these drivers will exceed excursion in this scenario though.

Another possibility is to lower the Q by damping the drivers and putting them in a sealed box. These would be suitable for infinite baffle too, but I don't want to go there.

Thoughts? Worth playing with or not worth the trouble?
Attached Images
File Type: jpg picture 018.jpg (97.3 KB, 633 views)
  Reply With Quote
Old 9th September 2008, 10:43 AM   #2
Piek is offline Piek  Europe
diyAudio Member
 
Piek's Avatar
 
Join Date: Oct 2006
Hi, I would check if all of them are "noise-free" at large excursions and then build very stiff (maybe braced, i would do nowadays)) ripoles when some bass boost is availabe <40~60Hz.

I had 15" 4,5mm XMAX Woofers in Ripoles(2) and they did work very well even beyond usual room SPL, its a matter of positioning, lowcut, bass boost and conservative (flat) connection to your tops.

Good Luck, Micha
  Reply With Quote
Old 9th September 2008, 06:05 PM   #3
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Quote:
Originally posted by Piek
Hi, I would check if all of them are "noise-free" at large excursions and then build very stiff (maybe braced, i would do nowadays)) ripoles when some bass boost is availabe <40~60Hz.

I had 15" 4,5mm XMAX Woofers in Ripoles(2) and they did work very well even beyond usual room SPL, its a matter of positioning, lowcut, bass boost and conservative (flat) connection

Thanks for the tips.
Yes, I think I will go with the ripole. I did some more listening last night, comparing it to a hasty-built dipole (half sheet of particle board, woofer in the middle).
The bass is much deeper and "tighter". Hard to define but now I understand what people have been saying about this type of sub and how it sounds and doesn't excite room modes.
It was eating a lot of power to produce reasonable spl, but I don't have any problem with suppling power.
The driver has shown no signs of distress, despite the power it was handling.

This sub system will be for lower level listening of music only and not for a demanding application like home theater.
  Reply With Quote
Old 10th September 2008, 03:28 AM   #4
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
I was interested as I've just discovered OB bass myself, I put those parameters into Jeff Bagby's box program, I got X-max limited power handling of 25 watts and 105 dB using 2 drivers in parallel, with in-line resistance of 0.5R for the inductor and wire; add the 3 dB form using 2 such panels and I'd be happy with that for music most of the time.

If you find you don't want them send 'em to me, I'll find them a home

I have very similar performance from a locally sourced driver from "Jaycar" but as 12 inch they are lower SPL and X-max limited to 12 watts, but they sound "GOOD" warm and friendly like grandma's old valve radio.
Regatds Ted
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 10th September 2008, 01:29 PM   #5
Piek is offline Piek  Europe
diyAudio Member
 
Piek's Avatar
 
Join Date: Oct 2006
I'd say don't worry about watts, the drivers will (mine did, i think they are comparable) reach maximum and beyond maximum excursion(who cares ) probably under 60W put into them.
I had ~80W at 8Ohm of power available per channel at the time and it was enough for all circumstances.

Dont forget the bass boost... bass will drop at farfield, thats for sure. Chamber resonances at around 200Hz are also a sure thing and those need to be taken care of either passive, pllxo or active.

-Micha
  Reply With Quote
Old 14th September 2008, 06:13 AM   #6
mightym is offline mightym  United States
diyAudio Member
 
mightym's Avatar
 
Join Date: Feb 2008
Location: Checotah, Okrahoma former home of the Okra Fest
since the front chamber functions to both lower Fb, and as a side effect lowers output. would anyone care to hazard a guess as to what a small increase in the front chamber size might accomplish?

seems to me that the Fb could be controlled thusly, and return a portion of the lost efficiency too, I have no idea if this would be true in situ, just spitballin' here.
  Reply With Quote
Old 14th September 2008, 07:04 AM   #7
Rudolf is offline Rudolf  Germany
diyAudio Member
 
Rudolf's Avatar
 
Join Date: Mar 2003
Location: Germany
Quote:
Originally posted by mightym
since the front chamber functions to both lower Fb, and as a side effect lowers output. would anyone care to hazard a guess as to what a small increase in the front chamber size might accomplish?
What do you mean by "increase in ... size"? Cross area or depth? The effects would be different.
__________________
www.dipolplus.de
  Reply With Quote
Old 14th September 2008, 07:12 AM   #8
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
OK I'm new to OB's but I have been assuming all along that when you make a "U" frame the side of the frame are parallel, what happens when you make the sides as an expanding V

Like so \__/ is this no longer a "U" frame?? Where would you attach the wings in a baffle of this shape?? That is if you had wings
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 14th September 2008, 08:11 PM   #9
mightym is offline mightym  United States
diyAudio Member
 
mightym's Avatar
 
Join Date: Feb 2008
Location: Checotah, Okrahoma former home of the Okra Fest
Rudolph,

I haven't built or measured any OB speakers.

I was just wondering what would happen if you increased the size of the front and rear openings, Re: the ripole sub.

For example, if you were using the figure of 30 percent of Sd as the size for your openings ( which from what I read is an entirely reasonable number ), and this alignment gives you X extension of Fb, and Y loss of efficiency, then what would you get if you raised the percentage to say 35 percent?

I did say I was just spitballin' ( that means I just wondered what would result if you tried it), so I asked.

I'm trying to figure this out for an OB project of my own, I definitely will not attempt it until I have some kind of measuring gear. This will be some indeterminate interval into the future, as I'm still trying to decide what king of gear will provide the best bang for the buck.

I made an assumption that the depth was more or less controlled by the diameter of the driver, and that the cross section could be adjusted.

John
  Reply With Quote
Old 14th September 2008, 10:38 PM   #10
Rudolf is offline Rudolf  Germany
diyAudio Member
 
Rudolf's Avatar
 
Join Date: Mar 2003
Location: Germany
mightym,
I just wanted to be sure that I understood you correctly.

From my - limited - experience:

If you widen the opening, you will raise Fb and gain efficiency. By the same time the resonance peak of the chamber depth will be lowered. I donīt know of any formula describing the interaction of these effects in mathematical terms, so you will have to find your preferred combination by trial/measurement.

You are right in keeping the chamber depth as small as the driver allows. Setting the opening area below 25 % of Sd seems to be useless, like making a BR tube diameter much too small. Making it 50 % or larger, the cabinet would take up the same space as a H-frame. So I would consider that as the opposit limit of a W-frame.
__________________
www.dipolplus.de
  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
Sideways Dipole Bass sdclc126 Multi-Way 27 27th May 2013 05:47 PM
Raveland driver for dipole (ripole) bass Techz Subwoofers 41 17th May 2009 10:23 PM
dipole stereo bass? xstephanx Subwoofers 63 1st June 2006 12:19 PM
Some dipole bass measurements John Sheerin Multi-Way 19 3rd January 2005 06:48 AM
dipole bass help amo Multi-Way 11 17th September 2003 06:06 AM


New To Site? Need Help?

All times are GMT. The time now is 06:17 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2