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In Reply to: RE: Your best tweaks for fullrange posted by moray james on May 07, 2015 at 21:06:11
So what are your receipe?
Follow Ups:
damp mechanical resonance with the best available constrained layer damping material this will provide maximum reduction in mechanical vibration. Damp acoustical resonance/reflections with acoustical felt which has the widest possible absorption coefficient. The best time to do theses things is when you are building the driver or when you are rebuilding the driver so you will have full axis to the pole piece the top plate and the basket, otherwise you will need to remove the dust cap to access the pole piece. After the fact damping can be applied to the top plate by incisions in the side of the spider. Available space under the spider will be the limit as to what you can do there. Acoustical damping can be installed between the cone and the spider to absorb reflections between the top plate and the cone, this is also very effective in catching reflections between the basket and the cone. Felt can be applied to the inside of the basket as well. Each driver will offer its own unique set of conditions so there is no one recipe. I use these techniques to treat woofers mids tweeters cone/dome and compression drivers. Cost will often dictate what and how much you do to a given driver. I like to damp both sides of a basket with CL damping and felt but this is not inexpensive to do so you need to decide if the driver is worth it. This is a time consuming method and it is not inexpensive but it is very effective. Non treated drivers will soon become very unattractive to you. This is a very powerful system for the improvement of drivers. Hope that this helps. Best regards Moray James
moray james
the best available constrained layer damping material . . .
Such as?
TIA
dynamat or hushmat there are many such products and availability will usually determine what people will use. F-11 Acoustical felt is the very best possible felt (real wool) it has the widest bandwidth of absorption available. I like to use three layers of 1/8" F-ll looses around the cone so that it damps both cone and spider energy. this makes for a huge improvement in bass SQ. Hope that helps. Best regards Moray James.
moray james
there are many such products and availability will usually determine what people will use
Thanks for that. As it goes, I put plenty of a local Dynamat equivalent on my drive units several years ago but I'd not thought of using felt.
D
I bond about a 1/4" layer of F-11 on the inside of the baskets on top of the CL material. The felt used around the cone needs to be free of the cone and the spider so I cut doughnuts each is a different size ID to track the cone expansion. By the way synthetic felt like acrylic craft felt and some of the packing felt is a wast of your time synthetics do not work or sound (absorb) anywhere near natural wool felt.
moray james
moray james:
I bond about a 1/4" layer of F-11 on the inside of the baskets on top of the CL material, etc, etc.
I reported earlier that I'd fitted CL damping to my drive units. Well, so I had but, as it turns out, to speakers I sold some ten years ago. As the frame on my "newer" drivers is made of diecast aluminium and as the arms are short, I'd not bothered this time round.
So, this afternoon and in light of your tip, I fitted as many strips of Dynamat equivalent as I comfortably squeeze onto to the frame and put 1/8" (3 mm) wool felt on top where appropriate.
Yes, it's made a very worthwhile improvement - smoother sound, more of that "in the room" feel. I don't think I'm finished yet but it's been a good start. Many thanks to all for the ideas.
Dave
I bond about a 1/4" layer of F-11 on the inside of the baskets on top of the CL material. The felt needs to be free of the cone and the spider so I cut doughnuts each is a different size ID to track the cone expansion. By the way synthetic felt like acrylic craft felt and some of the packing felt is a wast of your time synthetics do not work or sound (absorb) anywhere near natural wool felt.
moray james
Moray,Used some spare 'Madisound Sound' felt to line both sides of the mid-range basket arms as I understood you to recommend; a fiddly procedure that took three hours and yet such was the improvement in natural tone that I much look forward to repeating the task on the woofer basket arms when new felt arrives. Many thanks.
Have found that two layers of Neoprene 60 Gasket Duro Rubber between the tweeter and speaker cabinet protect the sensitive treble from the bombardment of neighboring heavy mid-range vibrations and allow it to produce well-focused notes. You write with a technical familiarity that I lack and so am left unclear as to whether you offer a better tested solution there.
DG
Edits: 05/09/15 05/11/15
Aupiho,
It costs approx. $76.50 to buy 14 feet of MagnetShield (@$4.50 per linear foot + $13.50 USPS Priority Mail) from www.lessEMF.com) in order to enclose two pairs of mid-range and woofers each with four layers around the outside and back separated by strips of 1/8" cork to maximize its effectiveness. Such enclosures block much of the 'fringing effect' that causes 25%-30% of the speaker magnetism to escape. Make sure to leave a hole in the back to equalize air pressure or you will throttle the drivers... The large increase in driver and therefore speaker efficiency is proportionately reflected in increased dynamics and slam.
Hopefully these pictures will give you the idea. Don't forget to take the opportunity to re-orient each speaker 180 degrees and demagnetize the brass wood screws before re-installing it with the enclosure.
DG
Well that's a very impressive tweak!!!
But I don't understand why shielding the speaker is good for sound?
You have to constrain magnetic fields to maximize power?
DG is NOT shielding the speaker. The flux fields will stretch out forwards and backwards. To shield the speaker you need to completely enclose the magnet and to be honest regular iron will work just as well,
Magnetically conductive material tends to capture the "lines" of magnetic force and within that material moves faster than through air speeding up magnetic efficiency.
MJ has a point : since we are working with magnetic fields there is an associated E field generated by the magnetic induction. Mumetal manufacturers recommend layering the mu metal with copper foil and it speeds up the magnetic field even more.
Even when wrapping the magnet, it is important to eliminate sharp corners. Even a small radius on the corners seems to "sweeten" the sound.
two decades ago I was attempting to build shielding for some of my favorite speakers for use as center channels. It was a great learning experience.
One of the best tweaks was to imagine two lines tangent to the magnet of , say the tweeter and midrange. Now place a few layers of mumetal and copper perpendicular to the centerline of the magnets but within the tangents (sorry scanner is down, but I will send a picture later), and halfway between the drivers. ACtually placement is similar to how I recommended the putty be placed on the front baffle, except the mu metal strips should be placed parallel to the magnets and in the line of sight of them.
There is a tremendous increase in detail within the crossover points. The magnetic fields of each driver is actually affecting each other and a lot of what we consider crossover distortion disappears, even though we may have not even noticed it before
Of course YMMV and FWIW
Hi Stu
You mean iron works good in theory or you actually used iron for capture the magnetic lines?
Would be iron useful in right place?
please send the photo if you can.
thank you
mehrdad
tweaker
A good source is old transformers. Normally silicon steel, they are highly permeable and can direct magnetic fields quite nicely. A bit more work, but I like to cut off the coil windings and just use the laminated sheets. It enables me to experiment with more precise placement of the lamination orientation. You can also simply short out the windings ( For me it depends on the size of the transformers).
Over motors or under, I often used to use large steel washers. These will absorb the magnetic fields and work well but even better with copper tape bonded to the top and bottom. Works well for TT's and CD spin motors.
If you use the copper tape I like to run a ground wire to the component
Hi
Silicon steel of old Transformers is very good idea.
Thanks so much
tweaker
Stu,
"DG is NOT shielding the speaker. The flux fields will stretch out forwards and backwards. To shield the speaker you need to completely enclose the magnet"
Four layers of 'MagnetShield' wrapped around the side and back of each of my mid-range and woofer magnets has resulted in a 25+% increase in dynamics and slam so, if it's not the magnet-shield minimizing the 'fringing-effect', what else does your testing suggest is energizing their drivers?
DG
Going back to physics class:
Remember those magnetic lines of force when sprinkling ferrite powder on a piece of paper above a magnet? They would rather travel through ferrous metal rather than through air, and you could demonstrate this by placing a piece of ferrous metal above the magnet on the paper. The lines of force want to move towards the ferrous metal.
In fact, you can greatly extend the range of the magnetic field this way.
In using concentric layers of magnetic material around the speaker magnet, the lines of force move closer together, thus simulating a more powerful magnet. A comparison of ceramic magnets to something like neodymium will show many more and denser "lines of magnetic force.
I would prefer the layers of magnetically conductive material to be as close as possible (think laminations in a transformers). In such a case, I use the copper foil only on inner most and outermost layers and ground them to gain a a bit more "speed" to the drivers. Actually, come to think of it, alternating copper and mumetal will provide magnetic isolation between the mu metal layers. You wouldn't want the magnetic field of one layer bleeding into the adjacent ones.
Thinking of magnetic fields and their interactions was very difficult for me. Voltage and resistance is much more easier to comprehend and measure. Although eventually I did get a gaussmeter, by that time I had sort of started to comprehend magnetic fields. Incidentally you can use a simple compass as a sort of gaussmeter
YMMV and FWIW
Stu,
So differentiating between 'shielding' and 'enclosing' is largely semantics since it's impossible to 'seal' the front of the speaker?
Emil Detoffol of LessEMF Inc. advised that the effect of MagnetShield or MuMetal was virtually doubled when leaving a gap between each layer. That was the reason for the cork strips but copper foil sounds like an excellent idea. The only limitation is the space restriction in re-installing the speaker through its hole in the cabinet. Certainly blocking the central air hole at the back completely throttles the driver.
All I know is that wrapping the sides and back with layers of MagnetShield puts the performance of my speakers (that have a good reputation) on steroids.
DG
Magnets are weird things
Alnico drivers basically use slugs, and the Alnico elements are located where the pole pieces are normally located. The Outer shell of the magnet structure forms a sort of "keeper" like what you are making pulling the magnetic field closer to the slug and thus increasing the magnetic intensity.
Funny budget alnicos like in TV sets use a u shaped keeper with two ends open. Still work but not very efficient Just slapping on a couple pieces of steel to the open sides helps a lot. The good drivers, Altec, Bozak, etc. use rings ( looks like steel pipe to me), and afford better shielding ans well as stronger magnets.
Less emf is correct, you don't want direct contact with the magnetic material as the "lines " of force can cross over and muddle the field intensity. In pulling the lines closer together, you are reducing the overall magnetic field extension, and increasing the intensity at the same time, at least at the magnet core.
There's a paragraph in the Lessemf catalog which states you should be directing magnetic fields not necessarily trying to eliminate them. That fact took me many years to sink in. so now I work on redirecting the magnetic fields and achieve much better results
YMMV
and FWIW
Too bad Radio Shack closed down. About 15 years ago they had a number of raw drivers, cheap and fairly good. RS 1354, IIRC a 5 inch full range with whizzer with tight voice coil spacing. Bought a dozen to play around with. They actually sounded pretty good. I cut off the dust caps, drilled the pole pieces, built phase plugs since at $7 each they were pretty much expendable. It was a great learning experience, since what I heard often contradicted standard wisdom and advice
unclestu,
FWIW
Too bad Radio Shack closed down. About 15 years ago they had a number of raw drivers, cheap and fairly good. RS 1354, IIRC a 5 inch full range with whizzer with tight voice coil spacing. Bought a dozen to play around with. They actually sounded pretty good. I cut off the dust caps, drilled the pole pieces, built phase plugs since at $7 each they were pretty much expendable. It was a great learning experience, since what I heard often contradicted standard wisdom and advice
I was wondering if I could contact you concerning the tweaks on that speaker. I have 5 or 6 of them. I dropped a lot of money on their selloff
of those and several other speakers often at a dollar apiece.
DagW00d
contact me at unclestu52@gmail.com
Aupiho,
Look at the first picture of the 'fringe effect' where there is all that magnetic flow outside the area between the two metals. Now visualize the loss of magnetism to the driver that exists when magnetism escapes from the sides and back... Wouldn't you want to stop a clutch from slipping and preventing a car engine from delivering its full performance? This is somewhat similar for coil speakers whose manufacturers have not enclosed their magnets.
DG
Why did you go with the magnetshield and not the Giron?
thanks
jhlrd,
Emil Detoffol (518) 608-6479, the principal of lessEMF Inc., strongly advocates MagnetShield for this application and can give you all the technical explanations for his recommendation. Giron is a stiff, thick material with which it is difficult to work and quite impossible to bend around a small speaker that has to re-installed through the existing cabinet hole. MuMetal is an alternative that you can buy from lessEMF or from eBay (MuMetal (Ultraperm) Permalloy Alloy Shielding Sheet; Mu Metal Audio Shield 80). Serrated scissors are needed to cut either material so that it will not later cut the user excessively.
www.ebay.com/itm/2PC-7-ANGLED-TIN-SNIP-SCISSORS-STAINLESS-STEEL-WITH-VINYL-HANDLE-FREE-SHIP-US-/271459213561?ssPageName=ADME:L:OC:US:3160
DG
driver design will dictate if you will enhance efficiency at all. Well designed drivers should be running either very close to or right at saturation so additional flux wont gain you much with those. Gains in driver efficiency tell you the driver was not as well designed as it could/should have been. Good way to extract all the flux that you can from a magnet and to provide shielding.
A layer of copper around the magnet can help reduce inductance a little as well. Every little bit helps, but how much you never know till you try. Best regards Moray James.
moray james
Moray,
So Vienna Acoustic Mozart Grands are poorly designed because they lack magnet enclosures to eliminate the 'fringe effect' and force virtually all their magnetism to the driver? I respectfully suggest that they are in good company with the vast majority of less expensive coil speakers in that respect. The increase in dynamics and slam from a 25%-30% in magnetic force behind the driver sounds like a complete upgrade in speakers! Incidentally I forgot to include pictures of mid-range and woofer cross-overs enclosed with MuMetal for achieving a significant increase in clarity.
Am now opening up the back of my mid-range/ woofer enclosures to test the effect of substituting wool-felt for the bottom layer of cork stripes that holds the first layer of MagnetShield off the back of each magnet to maximize its effectiveness.
DG
you are getting hot for nothing, I did not disagree with you I agreed with you, I simply said that the mod will only work with drivers that are not running at or near saturation (which is where a good driver should be and most are not as good as we are lead to believe). The comment was made to point out to people how a good driver is made. Your mod shows how lesser drivers can indeed be improved. I do not however favor shielding around inductors, given the option I would use spacing and correct orientation of the coils. Also inductors should not be mounted with metal inside of the winding ie. screws or bolts. Simply comments no disrespect intended here. Thanks for posting I do enjoy reading many of your insights. Best regards Moray James.
moray james
Moray,
My principal concern was the questioning of the general relevance of the tweak since there is such is an abundance of skepticism about tweaks in the first place. Please accept my apologies.
DG
I did not question the general relevance of the tweak nor was it my intention to do so I simply mentioned that it will only work on drivers which are not well designed in the first place which as we both know is a lot of drivers and now that I think about it I don't believe that was worth mentioning but perhaps for the fact that some might not have understood the difference between a good design and a poor one. A tweak worth trying in the right situation. Good to have in the handbook of tweaks. Keep posting I enjoy learning. Best regards Moray James.
moray james
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