Sensitivity Ratings

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DMurphy

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Re: Sensitivity Ratings
« Reply #40 on: 24 Jan 2009, 04:13 pm »
Thanks for the great post.  I'm sitting here taking some preliminary measurements, and then I'll let it rip.  Or damp.  Or whatever. 

DMurphy

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Re: Sensitivity Ratings
« Reply #41 on: 24 Jan 2009, 05:56 pm »
OK.  I did the test.  First I installed two Seas CA12 4.5" midbass-midrange speakers in extremely rigid double walled cabinets that I had built to help develop a midrange design for the as-yet unfinished HT4.  I measured each (they were almost identical), and lugged them into my listening room to see if I could hear any difference between the two unmodified speakers.  I have a comparison preamp machine with a remote control that allows instantaneous, volume compensated (though that wasn't necessary in this test) comparisons between up to 4 speakers.  The two Seas units sounded the same to me, and not as good as the HT3 sitting next to them.  But pretty darn good for raw drivers running full range.  I then removed one of the Seas and wrapped mortite tightly around as much of the basket as I could without interferring with the spider or cone surround (that wasn't easy, and I can't swear that I succeeded 100%).  I then listened to the same music slections as before (mostly a variety of stuff on the Iowa DIY2007 test disc and some Tchaikovsky at full cry).  This was not a blind test.  I obviously knew which was which.  I didn't expect to hear anything, because the Seas frame is quite rigid to start with, and it's small.  But there was an obvious difference this time around.  It wasn't really that subtle, and I'll keep this experiment set up in case anyone else in the area wants to hear it.  The modified unit had more presence.  In comparison, the unmodified Seas sounded somewhat hollow.  Maybe that was due to some kind of basket resonance.  I'm not sure everyone would say the modified Seas sounded better, although I think it did.  But there was a distinct difference, and there wasn't before.  I thought it was probably just a change in frequency response due to some ill-placed mortite, so I measured that unit again in the same position as before.  Really no difference, except at the very top, and in a direction that wouldn't explain the character or magnitude of the difference I heard, and was probably due to a slight difference in the mic position.   Am I 100% sure the effect was due to mortite damping vibrations rather than just restricting cone movement? No--and I would have to repeat the experiment with a larger driver that was easier to work with.  But I'm pretty sure.  Unfortunately, I can't write to Jim telling him to wrap clay around all of the baskets, because it could very well come loose in the field or during shipping, and that would be a disaster.  So I'm not sure this can be implemented as a post-mod.  But it's certainly worth exploring (after I expermiment some more, which won't be anytime reall soon due to other demands.)  If someone will remind me how to post images here, I would be happy to show you the relevant plots.     Thanks for the suggestion, Frank. 

martyo

Re: Sensitivity Ratings
« Reply #42 on: 24 Jan 2009, 06:09 pm »
Posting the plots.
I have the image saved on my computer.
go to my gallery here and click the upload file button and continue to follow the prompts.
After the plots are in your gallery, open the image and right click properties, then highlight and copy the address
Then use the image icon in the post reply window, 2nd from the left in the 2nd row, and paste the copied address between the brackets.

good luck
 

DMurphy

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Re: Sensitivity Ratings
« Reply #43 on: 24 Jan 2009, 08:41 pm »
Hmmmmm.   I guess I don't have a gallery.  I went to "gallery," then "my gallery" and then upload, but it just told me I didn't have a gallery.  And then I clicked on create, and that's where I deadended.  I couldn't figure out how to create one, and I didn't see any prompts. 

R Swerdlow

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Re: Sensitivity Ratings
« Reply #44 on: 24 Jan 2009, 08:46 pm »
Dennis

Is it possible to export the numerical data from those mortite tests in text form (CLIO files?) and send it to me.  I can put them together in one graph showing the plots with and without mortite in different colors.  And depending on the numbers, I can also make a plot of the difference between the two.  It is easy to do and it might help.

Richard

jsalk

Re: Sensitivity Ratings
« Reply #45 on: 24 Jan 2009, 09:39 pm »
Dennis -

Hmmmmm.   I guess I don't have a gallery.  I went to "gallery," then "my gallery" and then upload, but it just told me I didn't have a gallery.  And then I clicked on create, and that's where I deadended.  I couldn't figure out how to create one, and I didn't see any prompts. 

If you want to send me the files, I will upload and post them.

- Jim

DMurphy

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Re: Sensitivity Ratings
« Reply #46 on: 24 Jan 2009, 09:51 pm »
I hate to bother you, but I will anyhow. They will be on their way shortly.  Richard--I can save them in text file as I go, but I didn't, and I don't have time to remeasure and unmod right now.  But thanks for the offer. 

avahifi

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Re: Sensitivity Ratings
« Reply #47 on: 24 Jan 2009, 09:54 pm »
Thanks very much for running the tests Dennis.

I can assure you that plastic modeling clay (available in 5 pound bricks at art stores) will not ever come loose or fall off of the speaker metal parts if properly installed in the first place. You can actually carefully heat it up in a microwave oven to make it very soft and workable.

We have used this on the little Biro L/1 speakers we built for Mithat Konar for years without ever a field problem.

The test I ran at B&W in Worthing, England years ago was a true double blind test.  John Bowers gave me a matched set of their little CM-1 bookshelf speakers to play with in their lab.  I had brought a half pound of plasticlay along with me when invited to a factory visit.  I pulled the driver assembly from one and damped it thoroughly and then put it back together very privately.  Since they had identical cabinets and no serial numbers yet, not even I could tell which one I had worked on.

We set them side by side in their sound room and A-Bd them with mono material using the balance control of the drive preamp to switch from one to the other.

The whole tour group got to listen.  I asked everyone to write down the answer to two questions.  First, can you hear any difference?  Second is it a better worse difference and which one do you like better?  After everone voted, I opened up one of the speakers again.

The results, much to B&W's surprise, was that the damped speaker was by far preferred by nearly everyone.

Again Dennis and or Jim, I urge you to try this on the midrange basket of a HT3 or Songtower.  It is a very easy and inexpensive way to build a better speaker.  The sonic result can most accurately be described as having stuff that was obvioulsy not supposed to be there go away, leaving more of the music, less garbage, and better sound.

Best regards,

Frank Van Alstine

P.S. DO NOT TRY THIS WITH PLAYDO.  THAT IS A FLOUR WATER PASTE AND SETS UP LIKE A ROCK AND IS USELESS FOR THIS PURPOSE.

The scientific principal behind this proceedure is simple.  Meatballs don't bounce.  :)

Nuance

Re: Sensitivity Ratings
« Reply #48 on: 25 Jan 2009, 02:39 am »
Wow, this is quite intriguing.

Is this something that a DIYer could do to his own speakers/Salk's?

Zheeeem

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Re: Sensitivity Ratings
« Reply #49 on: 25 Jan 2009, 02:10 pm »
Wow, this is quite intriguing.

Is this something that a DIYer could do to his own speakers/Salk's?

Yes.  Assuming you got reasonably good grades in kindergarden.

Seriously, Frank wrote this up at some length in early Audio Basics, and you can track down the articles for free on his website.  He has many helpful hints there.  The key thing, of course, is to not impede any moving parts. 

I found that patience in working the plasticlay up to a nice consistency for applying is the key.  There is really no substitute for hand-kneading.  A relatively thin, even coat seems to do the trick, say around 1/4 inch - unless you are also trying to add mass to whatever you're working on.  You may also want to think about "reversibility" issues.  Plasticlay is removable, but only with great difficulty if you cram it into every nook and cranny.  And the colours do not easily come off of unfinished MDF.  So if you're planning to undo this to sell your stuff in a couple of years, I'd suggest only treating relatively smooth metal parts.


fishinbob

Re: Sensitivity Ratings
« Reply #50 on: 25 Jan 2009, 02:34 pm »
Nuance -  maybe you go first  :lol:

AliG

Re: Sensitivity Ratings
« Reply #51 on: 25 Jan 2009, 03:57 pm »
If anyone decides to try it, please kindly show some pictures.

jsalk

Re: Sensitivity Ratings
« Reply #52 on: 25 Jan 2009, 04:24 pm »
Here are Dennis Murphy's measurements...

Pre-mod CA15...



Post-mod CA15...



Control CA15...



- Jim

DMurphy

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Re: Sensitivity Ratings
« Reply #53 on: 25 Jan 2009, 05:53 pm »
Thanks very much Jim.  Before anyone argues that I was just hearing the slight difference in response between the two Seas drivers around 1 kH, remember that I listened before I made the mod, and couldn't hear any difference between them  But this still isn't science.  And even Frank's B&W experiment lacked an essential step--they didn't actually listen to the pre-mod driver and the control driver before the mod.  The two units were "matched," but that doesn't mean they would have sounded identical.  So all of this is suggestive, but not ready for a journal article yet.  And not ready for anyone to yank out their midwoofs and start stuffing stuff on them (and maybe in then--not so good). 

avahifi

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Re: Sensitivity Ratings
« Reply #54 on: 25 Jan 2009, 06:43 pm »
One of the other listening tests I normally do is to white noise.  Either inter channel noise from an FM tuner or  a digital noise track on a CD I have.

The before and after results of resistive damping of speaker metal frameworks is pretty obvious with this test.

Again, if any of you readers want to try this, first set the speakers side by side and listen in mono with the balance control to switch back and forth.  Then do just one speaker, and make sure not to block any vents or do anything to obstruct speaker motion.  The have someone else make the setup again so you do not know which speaker is which.  Then test again on music and white noise.

I would definitely like to hear what results you come up with.

I noticed a small difference in the 7-8 KHz response on the graphs above.  But of course the acoustic measured response of the speaker is the sum of the output of the driver plus what ever stray resonant output is occuring from all the other things that might be vibrating.  That is where B&Ws use of a laser interferometer was useful, it could isolate the output from various parts of the moving system. Do note that we can easily hear differences in electronic circuit designs that we simply cannot effectively measure, I am not at a certain how much the response curves are actually telling us.  Not that they are wrong, of course not, but I suspect the resolution is not yet where it needs to be.

Regards,

Frank Van Alstine



DMurphy

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Re: Sensitivity Ratings
« Reply #55 on: 25 Jan 2009, 07:29 pm »
Thanks very much Jim.  Before anyone argues that I was just hearing the slight difference in response between the two Seas drivers around 1 kH, remember that I listened before I made the mod, and couldn't hear any difference between them  But this still isn't science.  And even Frank's B&W experiment lacked an essential step--they didn't actually listen to the pre-mod driver and the control driver before the mod.  The two units were "matched," but that doesn't mean they would have sounded identical.  So all of this is suggestive, but not ready for a journal article yet.  And not ready for anyone to yank out their midwoofs and start stuffing stuff on them (and maybe in then--not so good). 

Hi  The FR curves are just to show that I wasn't hearing a simple difference in frequency balance.  I didn't expect the damping to show up on the curves.  They really had the opposite purpose.  I do think that you should be able to run some kind of linear distortion test that would document an improvement.  And perhaps a waterfall, if I could achieve enough resolution (which I don't think I can).

Nuance

Re: Sensitivity Ratings
« Reply #56 on: 27 Jan 2009, 08:28 pm »
Nuance -  maybe you go first  :lol:
I'm scared to...   :| 

oneinthepipe

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Re: Sensitivity Ratings
« Reply #57 on: 27 Jan 2009, 08:45 pm »
Nuance -  maybe you go first  :lol:
I'm scared to...   :| 

I'll try it ..... on Nuance's speakers.  :D


Nuance

Re: Sensitivity Ratings
« Reply #58 on: 27 Jan 2009, 11:48 pm »
^ HAHA!   :lol:

Big Red Machine

Re: Sensitivity Ratings
« Reply #59 on: 28 Jan 2009, 12:55 am »
Modeling clay has been ordered.

Chickens! :flame: