3 way open baffle with Eminence and Skytronic - Page 35 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

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 22nd October 2010, 01:23 AM   #341
diyAudio Member
 
Kim Schultz's Avatar
 
Join Date: Feb 2003
Location: Hundested, Denmark
Hi again.

Now Ive made two different spacers and measured both.
As you can see the spacer with the plug into the driver make a huge difference.

The mic was placed 30cm from the horn mouth and the signal was gated, no smoothing was used.

That little driver actually measures pretty good on a waveguide.

Can you post a link to where you found the foam ?
Attached Images
File Type: jpg spacertest1.jpg (97.0 KB, 590 views)
File Type: jpg spacertest2.jpg (104.2 KB, 568 views)
File Type: jpg spacertest.jpg (135.5 KB, 563 views)
File Type: jpg csd.jpg (268.6 KB, 545 views)
  Reply With Quote
Old 22nd October 2010, 01:41 AM   #342
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Default Kim has overtaken me

There is indeed a cavity inside.

I drew some rough sketches (just about when you discussed the above):

The first is the ATP-50 with APT-3 adaptor, like I said it's straight:
Click the image to open in full size.
I don't think there's any proper horn with a throat that is perfectly straight. There should be at least a little angle at the starting point. So with this adaptor, there's inevitably dffraction happening here - the transition of straight/angled wall. What a bad and irresponsible design!

But there's catch. Look carefully, there's a tiny step at the edge of outer slot. APT-3 (and APT-80 horn) has that proper little rim to fill that step properly and make the passage perfectly smooth.

I think this is critical. As the very high frequency sound is mostly comming from the outer edge and surround of the dome, i.e., the outer slot of the phase plug. So anything unsmooth here is not welcome.


The second, Simon this is what you do (I suppose):
Click the image to open in full size.
Please don't overlook anything (big or small) near the throat. Everything is critical near here. Anything breaks the continuity is not good.

In addition, I hate to say that, but, Simon your WG looks not smooth to me (or have I already mentioned that?).

The contour of an OS waveguide is based on an assumption that the waveform at the throat is flat. At this APT tweeter, I can't point out where the wave is flat Maybe it's never flat

I'm not sure it's the shooting angle or what, it seems the expansion at your throat of WG is quite 'sudden'. To my eyes, it's almost a right angle with slightly rounded edge. It's different from other OS WG's I've seen around here.

And back to the 'starting point' of the WG, I think it's worth further discussion....


The following is what Kim mentioned, APT-80 horn:
Click the image to open in full size.
As you can see (or better yet, your own ones), the flare starts very early, near the base of phase plug. I think, the shape of the phase plug and the contour of this horn must be considered together. Or, they should be.

Ironically, this is quite different from the very first drawing with APT-3 adaptor. I can't tell which is correct. (Or they're both wrong? )


I myself use Dayton's WG, which needs that lousy straight PT-3 adaptor to assmebled properly. However the throat of Dayton's WG is 29mm I.D. instead of standard 1" (25.4mm), so there's a 2mm step at where they joint. This happened to give me a chance to flare out the APT-3 a little, so this is what I do:
Click the image to open in full size.
And luckily it's plastic and quite easy to file and sand to make them smooth (well, as much as I can).

Again, I still don't know exactly which is correct (or none of them is). Waveform can't be seen and I can't measure, either

To my ears, APT-80 is smooth, straight or stepped throat of APT-3 is not (and very audible), modded and flared APT-3 with Dayton is smooth again. So, at least it's worth the effort, to me.

For your reference.
  Reply With Quote
Old 22nd October 2010, 02:01 AM   #343
diyAudio Member
 
Kim Schultz's Avatar
 
Join Date: Feb 2003
Location: Hundested, Denmark
CLS, the OS WG is nearly straight sided, it is only at the start of the throat it curves out, so it is hard to see in pictures. And if Simons WG is 45 then it looks very much like the expansion is quite sudden.

Geddes also mentioned that wood is not the best solution for OS WGs as it is hard to make a perfect throat, but I think it looks so much better than the resin ones.

Those are some nice drawings, but your drawing of the APT-80 is not entirely correct, as the first about 15mm of the horn is straight, just as the APT-3.

I dont think the straight sides matter much as long as the contour is set by the phaseplug, but it looks like the APT-3 adapter goes further out than the phaseplug.
The OS WG can be made to fit a driver with 0 at the throat.

Last edited by Kim Schultz; 22nd October 2010 at 02:24 AM.
  Reply With Quote
Old 22nd October 2010, 02:58 AM   #344
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Quote:
Originally Posted by Kim Schultz View Post
...your drawing of the APT-80 is not entirely correct, as the first about 15mm of the horn is straight, just as the APT-3.
Yes, you are right.

Quote:
Originally Posted by Kim Schultz View Post
I dont think the straight sides matter much as long as the contour is set by the phaseplug....
I agree, to some extent. As I've mentioned, I think the overal expension should be set by the combination of phase plug and the surface around it, be it any adaptor or the throat passage of the driver itself. The APT seems a very special case in this regard.

APT-3 maybe make the passage too long and narrow, thus different loading to the driver.

However, in reality, this APT with straight adaptor sounds somewhat nasal to me. It smooths out and opens up quite a bit with the adaptor flared. And I tried different Dayton's WG's, I like the bigger one which flares out faster (shorter and wider). It's less colored and more open.

Last edited by CLS; 22nd October 2010 at 03:05 AM.
  Reply With Quote
Old 22nd October 2010, 03:40 AM   #345
diyAudio Member
 
Kim Schultz's Avatar
 
Join Date: Feb 2003
Location: Hundested, Denmark
Ive also tried several horns and also turned two similar sized woodhorns, one with a tractrix contour and one with an OS WG 40 contour.
The OS WG sound so much better, it is more open and much less colored, but its also harder to make a crossover for it, as the tractrix loads the driver better.

I need to make some real adapters for the APT-50 drivers, so I can attach them firmly to the WGs and get some listening done.
  Reply With Quote
Old 22nd October 2010, 11:37 AM   #346
SimontY is offline SimontY  United Kingdom
diyAudio Member
 
SimontY's Avatar
 
Join Date: May 2003
Location: Sheffield, North England
Send a message via MSN to SimontY
Chaps, this is wonderful stuff, and I really appreciate the time you've taken to post about such things.

Firstly, I feel I do have a slight nasal colouration, as well as a slight grainy edge, coming from the APT-50, which is not seen in the axial frequency response curve.

Secondly, my waveguide is a careful (I would say damn close) copy of the designs produced by the Excel spreadsheet presented in the Geddes on Waveguides thread, believed to be a "proper" OS waveguide profile. The profile of this waveguide is indeed exactly straight in the middle. It is only the throat and mouth that have some "roundover" area, which only runs for a very short stretch. Maybe the photos are misleading.

Where my understanding of how best to implement this setup falls short is in knowing which part of the APT's phase plug should be level with the start of the throat. I think the B&C drivers (and others??) used by Geddes have a flatter phase plug section and apparently flatter wavefront, if my terminology is correct. I am trying to meld the APT into something that it is probably not 100% right for. Please do bear in mind, my longer term plan was to use a more esoteric tweeter later on, when funds permit.

All that said, I want to get a better result from this APT, so I am all ears. I will be investigating these steps and gaps. I must admit, I didn't realise that cavity off to the sides was of great consequence.

I still have my APT-80 mini-horns so I could do some chopping and re-working of those in order to gain a smoother transition into the waveguide, but I may need some guidance with regards to how far into the throat the phase plug's end should sit.

Many thanks,
Simon
  Reply With Quote
Old 22nd October 2010, 11:43 AM   #347
SimontY is offline SimontY  United Kingdom
diyAudio Member
 
SimontY's Avatar
 
Join Date: May 2003
Location: Sheffield, North England
Send a message via MSN to SimontY
Quote:
Originally Posted by Kim Schultz View Post
Hi again.

Now Ive made two different spacers and measured both.
As you can see the spacer with the plug into the driver make a huge difference.

Can you post a link to where you found the foam ?
Hi, your graph is most conclusive and interesting! Before I moved my tweeter back I had a bad response, but actually now it looks ok. I'd better take a fresh measurement with the driver in isolation.

Here's one place I saw the foam for sale: eFoam, all sorts of foam: Reticulated Aquatic Filter Foam
  Reply With Quote
Old 22nd October 2010, 12:03 PM   #348
diyAudio Member
 
Kim Schultz's Avatar
 
Join Date: Feb 2003
Location: Hundested, Denmark
Regarding where the phaseplug should be in the throat, I measured the APT-80 horn to start at about 13-15mm.
I would make a rough cut on the APT-80 horn and then sand it down until you got a 1" hole fitting you waveguide perfectly.
The B&C driver has the phaseplug hidden in the exit throat, and so does the BMS 4524 drivers I have.
But I dont think the APT-50 will benefit of this unless the adapter has a slight angle to it, causing the waveguide throat to be larger than 1" inch.
  Reply With Quote
Old 22nd October 2010, 01:07 PM   #349
SimontY is offline SimontY  United Kingdom
diyAudio Member
 
SimontY's Avatar
 
Join Date: May 2003
Location: Sheffield, North England
Send a message via MSN to SimontY
Measuring with inside callipers how far the 1" section goes (APT-80 horn) I'd agree it's about 15mm in. I will cut away slightly further than this and file it back and try to match it perfectly to my waveguide.

Here's one of my tweeters measured as-is, using the ~10mm wooden spacer with its probable issues. There's a fair old peak at 1.8Khz and a following null at 2.85Khz. Perhaps this is related to my dodgy throat.

Also attached, for comparison, is the APT-50 (not 80 as it says) in the waveguide before the spacer was introduced.

More to come later.
Attached Images
File Type: png With wooden spacer 1st ord.png (36.6 KB, 66 views)
File Type: png Tweeter_3u3.png (13.0 KB, 69 views)
  Reply With Quote
Old 22nd October 2010, 01:41 PM   #350
diyAudio Member
 
Kim Schultz's Avatar
 
Join Date: Feb 2003
Location: Hundested, Denmark
I think the dip you have is the same I have at 4khz, it's proberly just that my waveguide is smaller and therefore the dip is a bit higher in freq.
It is interesting to hear what changes in sound you hear with the new adapter.
  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
newbie eminence open baffle mrthieme Multi-Way 13 6th September 2009 05:26 PM
Eminence or P.Audio ? Open Baffle or Sealed Predator864 Multi-Way 0 23rd January 2009 11:51 AM
Fostex FE207E with Eminence Alpha 15 open baffle sharpi31 Multi-Way 15 21st September 2007 03:20 AM
Eminence Kappalite 3015 as open baffle bass? EC8010 Multi-Way 4 29th June 2007 08:05 AM
Australians- what solid timbers for baffle? (open baffle loudspeaker) tktran Multi-Way 13 29th November 2004 11:09 PM


New To Site? Need Help?

All times are GMT. The time now is 04:53 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