Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Cone has a small dent/scratch. Audible?
Cone has a small dent/scratch. Audible?
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 May 2020, 11:11 AM   #11
Scottmoose is offline Scottmoose  United Kingdom
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
Quote:
Originally Posted by system7 View Post
Back in the day, de Havilland unveiled the terrifically shiny de Havilland Comet Aeroplane. Unfortunately, "Widowmaker" might have been a better name.

The wings fell off after a few flights. This was not good. We started to understand metal-fatigue.
Actually, to be pedantic (me? never), the most famous issue was a result of over-stressing via regular pressurisation / depressurisation, causing fatigue around the punch-rivets around the supports & corners of the sharp, square-cut ADF window in the cabin roof and a general explosive decompression. In [George] Yoke Peter a window struck the elevators, likely causing severe uncontrolled pitch, tearing off the rear of the fuselage, with finally the wing structure, forward fuselage and fuel tanks failing. Not a nice subject, and my prayers are still with those who lost their lives, and their families. Ditto for 783, where the elevator spar was probably overstressed by a hard pull-up in bad weather, causing / followed by a wider structural failure.

These applied only to the Comet MkI, and the lessons learned from that (everything being new) fed into revised stress requirements, changes to construction requirements, and the subsequent models of the Comet and the Nimrod that was based upon it were very different aircraft. Sadly, commercially speaking, it was too late to save its reputation. And as you say, the early losses (not including unrelated accidents) provided through bitter experience an understanding that the stresses in large jets were higher than had been originally anticipated, with metal fatigue being a critical component. No more rivets of that kind in places like that, no more sharp cutouts, higher stress requirements &c. all came from it.

Be that as it may, re the driver, if the VC has sagged fractionally & is rubbing because the driver has been mounted the same way up for a long time (it does occur), as Steve suggests, try turning it 180 degrees. It may prevent rubbing etc. Worth a shot, since it costs nothing.
__________________
www.wodendesign.com (commercial site)
www.frugal-horn.com www.frugal-phile.com (community sites)

Last edited by Scottmoose; 22nd May 2020 at 11:27 AM.
  Reply With Quote
Old 22nd May 2020, 02:45 PM   #12
system7 is offline system7  United Kingdom
diyAudio Member
 
system7's Avatar
 
Join Date: Aug 2008
Location: Portsmouth UK
That was very interesting, Scottmoose! You can never discount the unexpected in engineering. Called "The Law of Unexpected Consequences" back in my day.

Long story short: The office manager decided to install water-saving throttle devices on our Urinals. Saved money. What could go wrong? Everything! All the flippin' toilets started horribly overflowing during the night! Turns out Uric acid crystals were building up and blocking them!

My favourite (exciting) engineering book is about Operation Black Buck.

Quote:
Originally Posted by Rowland White in "Vulcan 607"

Synopsis

It was to be one of the most ambitious operations since 617 Squadron bounced their revolutionary bombs into the dams of the Ruhr Valley in 1943...When Argentine forces invaded the Falklands in the early hours of 2 April 1982, Britain's military chiefs were faced with a real-life Mission Impossible. Its opening shot, they decided, would be Operation Black Buck: to strike a body blow at the occupying army, and make them realize that nothing was safe - not even Buenos Aires...

The idea was simple: to destroy the vital landing strip at Port Stanley. The reality was more complicated. The only aircraft that could possibly do the job was three months from being scrapped, and the distance it had to travel was four thousand miles beyond its maximum range. It would take fifteen Victor tankers and seventeen separate in-flight refuellings to get one Avro Vulcan B2 over the target, and give its crew any chance of coming back alive. Yet less than a month later, a formation of elderly British jets was launched from a remote island aribase to carry out the longest-range air attack in history.

At the tip of the spear was a single aircraft, six men, and twenty-one thousand-pound bombs, facing a hornet's nest of modern weaponry: the radar-guided guns and missiles of the Argentine defences. There would be no second chances...It was the end of an era - the last time the RAF flew heavy bombers into combat before they were replaced by their digital, fly-by-wire, laser-guided successors.

There were many who believed it couldn't be done. Drawing on extensive interviews with the combatants, Falklands residents and British High Command, and with unprecedented access to comtemporary military records, Rowland White takes us, for the first time, to the beating heart of the legendary raid. "Vulcan 607" is a story of ingenuity, courage and sheer bloody-mindedness that's destined to become a classic.
Nothing to do with speakers, but engineering. The main trick was to thieve refuelling nozzles from Vulcans in our US cousin's museums... we'd run out of them in Dear Old Blighty, and the museum security guards had been given the night off...

Quote:
Originally Posted by Kustomize123 View Post
Its the Zaph ZA5. I purchased it from Madisound 2 years ago. I am not sure they’ll change it for me now. What so you mean rotate the driver?
Scottmoose has answered it, though I often try 90 degrees as a start. Theory is speakers sag a bit with age, and rub voicecoil occasionally. Especially if tolerances or manufacture is poor.

What else might go wrong here?

Rocking mode?

Click the image to open in full size.

Another sort of rocking mode? I prefer series wiring.

Click the image to open in full size.

General cone breakup issues:

Click the image to open in full size.

Click the image to open in full size.

I never like the sort of tank notch that Zaph and Paul Carmody use. A simple capacitor across the bass coil. Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter

I prefer an LCR as used by SEAS in the Thor: THOR

Tank notches break up badly at high volume, IMO. Sounds horrible. See, breakup is highly non-linear.

Michael Chua uses the same Zaph ZA5 drivers. It might be a better circuit, but I really haven't seen it yet: Swift 2.5 (Zaph ZA14W08 with Peerless DQ25SC16-04) – AmpsLab

My longest post ever! Keep you entertained in lockdown I hope.
__________________
Best Regards from Steve in Portsmouth, UK.
  Reply With Quote
Old 22nd May 2020, 05:00 PM   #13
plasnu is offline plasnu  United States
diyAudio Member
 
Join Date: Jan 2011
Location: NY USA
This distortion chart is from 2 vintage German SABA FR speakers. One has much higher distortion due to voice coil rubbing. Those 2 units look the same, almost mint condition.
Attached Images
File Type: png SABA.png (45.8 KB, 51 views)
  Reply With Quote
Old 22nd May 2020, 05:05 PM   #14
Scottmoose is offline Scottmoose  United Kingdom
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
There you go. Good illustration of what can happen.

Ah, Black Buck. How they pulled that one off was -'impressive'. Still more that they got authorisation for it.

Re breakup, is it the tank notch itself Steve, or is it the fact that the filter no longer has a monotonic or similarly progressive rolloff? I find variations useful, but you need to be careful to ensure you don't end up with insufficient suppression above / below the zero pole frequency. Depends on the driver's response & your crossover frequency in relation to whatever you're stamping on.

Equally, a simple notch (bottomless or otherwise) may not adequately deal with cone resonant amplification in the passband -you can take out, say, a midbass driver's main cone mode, but the HD products lower down are still present, & the harder you crank it, the more likely it is you'll hear it. Depends on the baseline distortion performance of the driver of course -if it's low enough in the first place, may not be a problem. Rare for that to be the case though, which is one reason I tend to like low XO frequencies providing the tweeter can handle it at the desired limits.

However. Sorry about the OT!
__________________
www.wodendesign.com (commercial site)
www.frugal-horn.com www.frugal-phile.com (community sites)
  Reply With Quote
Old 22nd May 2020, 11:53 PM   #15
Kustomize123 is offline Kustomize123
diyAudio Member
 
Join Date: May 2019
What is this? Is this glue sticking out or what? this is about the only thing I could find abnormal. The VC is not rubbing or anything I checked. And I can't exactly figure out how to "rotate" the driver. Sorry I am pretty much a newbie if you all haven't figured already.
Attached Images
File Type: jpeg WhatsApp Image 2020-05-23 at 4.51.29 AM.jpeg (85.4 KB, 26 views)
  Reply With Quote
Old 23rd May 2020, 12:48 AM   #16
Galu is offline Galu  Scotland
diyAudio Member
 
Join Date: Apr 2018
Yes, looks like magnet glue. Nothing to worry about there.

By rotating the driver we mean mounting it back on the enclosure so that it is upside down compared to the way it was mounted previously.
  Reply With Quote
Old 23rd May 2020, 12:54 AM   #17
Kustomize123 is offline Kustomize123
diyAudio Member
 
Join Date: May 2019
Quote:
Originally Posted by Galu View Post
Yes, looks like magnet glue. Nothing to worry about there.

By rotating the driver we mean mounting it back on the enclosure so that it is upside down compared to the way it was mounted previously.
Yes. I have done that! Took it out, mounted it back in the enclosure in a different way.

Is it possible too much glue is causing this issue as mentioned by Steve earlier?



Quote:
Originally Posted by system7 View Post
Maybe too much glue?
  Reply With Quote
Old 23rd May 2020, 01:13 AM   #18
Galu is offline Galu  Scotland
diyAudio Member
 
Join Date: Apr 2018
I think Steve mentioned glue in relation to it preventing the free movement of the front suspension (the roll surround) or the rear suspension (the corrugated 'spider').

I don't know if it is possible that magnet glue has got into the narrow magnet gap that the voice coil vibrates within. If it is possible, there would be no way of telling without destructive dismantling of the driver.
  Reply With Quote
Old 23rd May 2020, 01:17 AM   #19
afa is offline afa  Australia
diyAudio Member
 
Join Date: Jul 2008
But then it would be causing voice coil rub, and Kustomize has ruled that out in post#15
  Reply With Quote
Old 23rd May 2020, 01:18 AM   #20
Galu is offline Galu  Scotland
diyAudio Member
 
Join Date: Apr 2018
Indeed!
  Reply With Quote

Reply


Cone has a small dent/scratch. Audible?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Can a small inhomogeneity in the voice coil cause audible distortion (in a sub)? guferr Subwoofers 2 24th April 2020 06:03 AM
Small format cone driver in horn thread frangus Multi-Way 120 23rd July 2019 03:16 PM
Avermetrics AverLAB Scratch and Dent Sale AverPaul Vendor's Bazaar 0 8th August 2018 07:20 PM
Will a small cap value difference be audible? jb0194 Multi-Way 2 8th February 2012 05:39 PM
Dent in D6.8 Speaker Cone excetara2 Multi-Way 0 28th August 2009 06:22 PM


New To Site? Need Help?

All times are GMT. The time now is 03:43 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki