Couple Simple Dipole Question... - 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 21st November 2005, 02:36 AM   #1
santiu is offline santiu  United States
diyAudio Member
 
Join Date: Feb 2005
Location: Los Angeles
Default Couple Simple Dipole Question...

I'm building a pair of H-Frame dipole woofer with some budget 10" drivers I picked up.

From pictures I've seen it looks like the wires pass through the baffle. I just want to make sure okay to drill a small hole in the baffle to pass wires through.

Also, I'm wondering about the active EQ. I'm using drivers that have a fairly low Qts. Linktwitz mentions that for the Peerless 830500 (which also has a low Qts) you need extra equalization beyond the 6db/oct but doesn't mention what. Is it on his site somewhere, or am I supposed to buy the MT1 PCB & documentation to find out? Do any of you out there know what sort of EQ I might need.

thanks a bunch
  Reply With Quote
Old 21st November 2005, 03:45 AM   #2
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
1. Yes, you can drill a small hole to pass wires through.

2. There's no way to answer your second question until you identify the Qts and response of your particular driver. The Q-correction equalization for the 830500 is 8Hz-80Hz (20db gain.) This equalizes the Q to approximately 0.5 from 0.2. If your drivers Qts is similar then you're probably in the ball park.

Cheers,

Davey.
  Reply With Quote
Old 21st November 2005, 03:54 AM   #3
santiu is offline santiu  United States
diyAudio Member
 
Join Date: Feb 2005
Location: Los Angeles
Is that 20db independent of frequency?

Here's the driver I'm using:
Fs 26.6 hz
Re 3.2 ohm
Qts 0.23
Qes 0.24
Qms 5.7
Vas 2.2 ft3
Sd 346 cm2
Xmax 13 mm (p-p)

Thanks again for the help!
  Reply With Quote
Old 21st November 2005, 04:25 AM   #4
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
No, it's not independent of frequency. The 8-80Hz I mentioned for the 830500 is specific to that driver. Yours will be different (higher in frequency.) You'd need to measure to verify.

The 10" driver you listed with Xmax of 6.5mm will have limited output capability in a dipole configuration relative to some other 10" drivers that have twice that much. You're going to use up that Xmax very quickly when you apply both Q-correction and dipole correction to the system. You SPL capability will be pretty low.

I take it you're aware of this, and this is a get-your-feet-wet project?

Cheers,

Davey.
  Reply With Quote
Old 21st November 2005, 06:08 AM   #5
santiu is offline santiu  United States
diyAudio Member
 
Join Date: Feb 2005
Location: Los Angeles
Yeah, I realize the limited output. But I got these 4 drivers for $100 shipped to my door, so I figured I'd give it a shot just to hear what this dipole bass is all about. I tend to listen at fairly low levels anyways.

WHOA... never mind on that X-max number though. When I bought them, the person told me 12mm xmax, and I assumed that was p-p. But I'm just reading the manual now and it says the xmax is 2.4cm! So i guess 12mm is just one way! Yippee, extra travel I've attached some pictures of the driver for your viewing pleasure.

Also, I when I said frequency dependent. What I meant to ask is, is that 20db just a constant gain applied, or does it has some sort of slope (sorry, I'm still learning about EQs, so I'm a bit confused). Or is it 20db constant gain on top of the 6db/octave standard

Thanks again
Attached Images
File Type: jpg img_6787.jpg (100.0 KB, 305 views)
  Reply With Quote
Old 21st November 2005, 06:11 AM   #6
santiu is offline santiu  United States
diyAudio Member
 
Join Date: Feb 2005
Location: Los Angeles
.
Attached Images
File Type: jpg img_6788.jpg (98.0 KB, 266 views)
  Reply With Quote
Old 21st November 2005, 06:20 AM   #7
santiu is offline santiu  United States
diyAudio Member
 
Join Date: Feb 2005
Location: Los Angeles
one last one with the rubber magnet cover removed.
Attached Images
File Type: jpg img_6789.jpg (89.9 KB, 277 views)
  Reply With Quote
Old 21st November 2005, 11:59 AM   #8
diyAudio Member
 
Join Date: Oct 2002
Location: France
where did you get those drivers? website? link?
  Reply With Quote
Old 21st November 2005, 04:15 PM   #9
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
Santiu,

The 20db gain is a 6db/octave slope from a (6db/octave equals 20db/decade) 8-80Hz shelving filter. The 8Hz and 80Hz define the 3db points where the shelf begins and ends. (At 80Hz the response would be +3db and at 8Hz the response would be +17db.)

The dipole correction will also be a 6db/octave shelving filter, but it may not "line up" over the same frequency range you need for the Q correction. This will depend upon the shape/size of the H-baffle you create. A nominal value for baffles similar to the Linkwitz-sized ones would be 20Hz-320Hz which is a four octave range which means the 6db shelving filter would have a gain of 24db.

To implement this you'd build two shelving filters one 8-80 (20db gain) and one 20-320 (24db gain) and cascade them together to achieve the final result. At low frequencies you'd be boosting 44db, and somewhere in the middle of those two filters the slope would be 12db/octave...you can see where the very large excursion requirements come from.

The surround on those drivers looks fairly small to me.
I would hook those up in free-air initially and play a 20-30Hz tone through them at excursions near the rated Xmax to see if they make any aerodynamic noise. Drivers that are acceptable for dipole usage are very quiet with this test.

Cheers,

Davey.
  Reply With Quote
Old 21st November 2005, 11:06 PM   #10
santiu is offline santiu  United States
diyAudio Member
 
Join Date: Feb 2005
Location: Los Angeles
exipnos, I bought these from an individual, so sorry, I don't have a source for you. They are made by NEXT in germany, which I believe is a company owned by FIAMM. Here's some more details on their products: http://www.fiamm.com/en/3/prod.php/22;224 (too bad the guy didn't have any of the AL woofers. Those frames look nice and open)

Davey, thanks again for all your help. Yeah, you are right, the frames look a bit constricting. Luckily, with only $100 invested in drivers, I'm not worried if I get less than optimal results. I guess I'll just deal with having limited excursion (and consequently levels) due to any aerodynamic noise I might get. Hopefully, I can get some non-ugly sound out of them at 30.87hz.

Hopefully I can get these things built before the end of the year (things just always get so busy around the holidays).

Anybody have any suggestions for free or cheap speaker measuring software for Macs (preferably something that runs under OS X)? I think I want to build the microphone listed on Linkwitz site and try to measure the response I'm getting with these uber cheap dipole woofers.

Thanks again for all your help I'll keep you all posted as I make progress
  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
NAD 3020 with loud hum. A couple of simple questions. KingOfMyCastle Solid State 14 23rd January 2012 01:04 AM
ACROSOUND direct-couple EL84 amplifier question vaslejean Tubes / Valves 18 12th May 2010 02:30 PM
cap couple or direct couple class A SE amp? AudioGeek Solid State 7 7th May 2005 06:16 PM
A couple question regarding speaker design audioaction Multi-Way 2 27th January 2004 12:14 AM
Simple answer required for a simple question... rabbitz Multi-Way 4 31st August 2003 10:05 AM


New To Site? Need Help?

All times are GMT. The time now is 08:01 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