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frank23
06-05-2005, 06:57 AM
hi,

I have a pair of 2420 drivers where I can see into the horn throat. I also have a pair of 2425 drivers where the horn throat is covered by a perforated mesh. This is the same as with a pair of 2416.

Now I came upon an item of a new 2426 on ebay that carries a sticker that covers the horn throat that says "pull, to remove perforated center before installing horn".

Does this mean, the horn throats of the 2425, 2426 and 2416 are meant to be open like the old 2420's?

for pics see this ebay item:

http://cgi.ebay.nl/ws/eBayISAPI.dll?ViewItem&category=3276&item=5779386862&rd=1

Greetings, Frank

Mr. Widget
06-05-2005, 09:43 AM
The screen is to prevent bugs and other debris from entering your driver... not a bad idea. Many older drivers do not have these screens, most new drivers do. Some audio tweaks (you know who you are) carefully remove the screen so as to have even less between their music and themselves. Personally I'd rather not risk getting debris in my driver.

Now, the "pull" sticker is something else entirely. That is on the gasket. A brand new driver will have that, and so will one that has a new gasket. You must pull out that center plug or the sound will not come out of the driver very well... it will be blocked by the donut hole of gasket material.

Widget

frank23
06-05-2005, 10:53 AM
thanks! now I understand.

and since I am "one of those" I think I am going to remove the anti-bug mesh

I use mine only indoors in a home environment, in the years I've used the 2420 I never saw a bug in my phaseplug, so I'll take the chance with the 2416's

greetings, Frank

Mike Caldwell
06-05-2005, 04:27 PM
Hello
The 2420, 2416, 2421 and the older LE series series
drivers do have a fine mesh screen deep in the throat directly
in front of the phase plug, maybe some one removed it on the
drivers you had looked into. All of the newer 2425 and the current 2426
drivers have the screen at the front edge of the throat at the
mounting flange.

Mike Caldwell

johnaec
06-05-2005, 08:09 PM
How do you remove those screens? 'Careful cutting with an X-Acto knife? I sure wouldn't want to try that, especially on a new driver...

John

Maron Horonzakz
06-06-2005, 06:41 AM
By removing the screen you,r taking the chance of getting iron paticles down in the voice coil gap. You,d be suprised at what floats around in your home. I recommend not removing the screen. Sonicley your not going to hear any improvement. But over time without the screen you,l have problems.

Alex Lancaster
06-06-2005, 07:04 AM
:) I think Maron is a 100% right, in 25+ years I have not done an A/B test, as I use them, get rid of them, and go on, but I do not recall a sonic diff.; Maybe some guys here have?

Jakob
08-12-2005, 03:14 AM
Hi!

I have the mesh in my 2441's, and over the years quite a lot of debris have come to rest along the edge. How do You get rid of this?
I was thinking compressed air, but maybe you then push some of the debris inside the driver? Any tips?

Regards: Jakob

stevem
08-12-2005, 06:48 AM
:) I think Maron is a 100% right, in 25+ years I have not done an A/B test, as I use them, get rid of them, and go on, but I do not recall a sonic diff.; Maybe some guys here have?

At the risk of being labeled a "tweak", :spin: I have removed the screens and do hear a slight difference. A little less "hash" if you will. Of course YMMV.:scoot:

Mike Caldwell
08-12-2005, 09:37 AM
Hello
I would use a vacume to suck the dirt and dust away, like you said
using compressed air could blow the dirt on into the phase plug and
then work it's way to the voice coil. You would want to reduce a normal
vacume cleaners hose down to a half of an inch or less in diameter to be
able to reach in and easly go around the edges of the screen. You could remove the diaphragm and then use compressed air blowing it through the slits in the phase plug. You would want to clean out the voice coil gap if you did it that way.

Mike Caldwell

Mr. Widget
08-12-2005, 09:48 AM
I wouldn't use a vacuum... you'd be surprised at the power of a vacuum... I once tried to make a dust collection system for my shop on the cheap and used a galvanized steel trash can as a collection tank... when the hose got clogged with debris, the power of the vacuum collapsed the steel can in about a second.

I have done as you described using compressed air. Remove the diaphragm and blow the air through the phase plug and the debris will come flying out the throat.

If you are not equipped to remove and replace your diaphragm, you can use bits of aggressive double faced tape on the end of a dowel. Gently pressing it against the screen to stick the debris on to the tape.


Widget

Mike Caldwell
08-12-2005, 10:15 AM
Hello
That's why I suggested reducing the vacuum hose down very small, to avoid sealing the throat completly with the hose and turning the diaphragm into a piece of wrinkled tin foil.

Mike Caldwell

Zilch
08-12-2005, 11:58 AM
Buy the mini-accessory kit available at your vacuum store. It has a neat little brush extension that reaches right in there. The suction is adjustable. Several forum members use it for throats and screens routinely:

http://store.yahoo.com/eurekaservice/minitoolset.html

Does LE85's quite nicely, for example.

See also: http://audioheritage.org/vbulletin/showthread.php?p=50197&highlight=attachment#post50197

Removes dome dents, too! :)

John
08-12-2005, 12:04 PM
I will back Widget up on the sticky tape method, works great. And when it looks clean use a few cotton swabs dipped in thinner and the screens will look like new.:applaud:

sonofagun
08-13-2005, 08:33 AM
Might I suggest a small "plug" of the acoustically transparent open cell foam which I sell? I'll send you all you should need for multiple horns for $5 (and up) depending on your location and amount needed (recommend 1/2", 3/4", or 1" thick please specify) - you can cut to fit using scissors. It will keep debris, bugs, etc. from entering into the horns internals and could be easily removed or replaced at will.

Alternately I can provide a sheet of 1/4" or other thickness foam which you can cut to cover the entire mouth of the horn.

sonofagun
08-14-2005, 08:14 AM
Never ceases to amaze me that whenever I post on any forum thread on any discussion site, that ends the thread.

:wtf:

Am I noticing a pattern?

Maybe my new on-line name should be something like "Final Commenter"

:blink:

richard c.
08-14-2005, 12:11 PM
Sonofagun,

Yeah, it happens to me, too...But, I am not going to stop posting.

I think you will find there are TWO, (and only two) different thoughts on removing the screen.

1. those who would rather leave it in for various reasons.

2. those who would rather remove it for various reasons.

I have never heard anyone say they wanted to place anything else in the throat to be between the diaphragm and their ears. Many people won't even use "grill cloth" or "foam" for this same reason. evidently, some people can hear the difference - a few on this thread can.

I have several Altec 902 drivers that still have the screens, and I seem to have "pretty good" highs. I know, how can a 2-way be any good?;)

Oh, I did remove the screen from the mass air flow sensor on my '86 Vette, and it runs 200% better, now!

Richard C.

Richard Long
01-15-2010, 05:18 PM
hi,

any ideas how to remove the mesh in a 2445j ? is it possible to remove the phase plug ?

badman
01-18-2010, 11:41 AM
Might I suggest a small "plug" of the acoustically transparent open cell foam which I sell? I'll send you all you should need for multiple horns for $5 (and up) depending on your location and amount needed (recommend 1/2", 3/4", or 1" thick please specify) - you can cut to fit using scissors. It will keep debris, bugs, etc. from entering into the horns internals and could be easily removed or replaced at will.

Alternately I can provide a sheet of 1/4" or other thickness foam which you can cut to cover the entire mouth of the horn.

I wouldn't be surprised if there were membrane resonances in 1/4" applied as a cover over the horn mouth. And if this is plain-jane open cell polyurethane.... it's not acoustically transparent, at all. Geddes uses the reticulated stuff for a reason, the other foams have a lot of loss in the top octaves. Even the reticulated, after a certain length, has quite a bit, 1-2dB @ 10k.

Allanvh5150
01-18-2010, 12:02 PM
I wouldn't be surprised if there were membrane resonances in 1/4" applied as a cover over the horn mouth. And if this is plain-jane open cell polyurethane.... it's not acoustically transparent, at all. Geddes uses the reticulated stuff for a reason, the other foams have a lot of loss in the top octaves. Even the reticulated, after a certain length, has quite a bit, 1-2dB @ 10k.

When you say "quite a bit", you can see 2 db on an analyzer but to the human ear, 2dB is only just percievable to some people. Sure there will be people out there than think they can hear way less than that but in reality they cant. I would have a crack at what you wish to try but obviously you cant put it back in.

Allan.

sonofagun
01-18-2010, 12:13 PM
I'll provide some material n/c if someone wishes to run a test.

LE15-Thumper
01-18-2010, 01:50 PM
I will back Widget up on the sticky tape method, works great. And when it looks clean use a few cotton swabs dipped in thinner and the screens will look like new.:applaud:

Are those the "Gold-Tipped" Audiophile grade Q-Tips ? :blink:

http://gadgets.boingboing.net/bmagic.jpg :bs:

badman
01-18-2010, 03:56 PM
When you say "quite a bit", you can see 2 db on an analyzer but to the human ear, 2dB is only just percievable to some people. Sure there will be people out there than think they can hear way less than that but in reality they cant. I would have a crack at what you wish to try but obviously you cant put it back in.

Allan.

I think that's an awfully aggressive statement- a 2dB shift in tonal balance is readily audible to many/most listeners. Most anyone who's ever used an EQ knows this.

4313B
01-18-2010, 04:00 PM
I think that's an awfully aggressive statement- a 2dB shift in tonal balance is readily audible to many/most listeners. Most anyone who's ever used an EQ knows this.I'm not buying that at all. I suspect most people wouldn't know a 2 dB shift if it sat in their lap and called them mommy...

Now a LOUDNESS button... that's a different tune... :rotfl:

badman
01-18-2010, 04:43 PM
We're not talking about Joe Blow listening on a Bose turdbox... we're talking about someone who enjoys spending time with their speakers, and a frequency dependent loss, a tonal shift that will act like an inverse loudness curve on the top end. Anyone who can't hear that shift... likely shouldn't be bothering with high quality audio. This isn't a high q shift, it affects several octaves of response.

And! We're talking about acoustic open cell foam (unless my understanding is wrong here) NOT the 2dB reticulated foam. The loss will be much higher, maybe as much as 6 or even 10dB.

Foamy feller, if you'd like, I'd be happy to tell you how much loss your throat plug has. But don't get upset if it's a lot more than you thought.

speakerdave
01-18-2010, 06:18 PM
When you say "quite a bit", you can see 2 db on an analyzer but to the human ear, 2dB is only just percievable to some people. Sure there will be people out there than think they can hear way less than that but in reality they cant. I would have a crack at what you wish to try but obviously you cant put it back in.

Allan.

Yeah, when JBL built a -1 dB adjustment into the mid-hi of the LSR32 they were just feature-mongering.

4313B
01-18-2010, 06:29 PM
Yeah, when JBL built a -1 dB adjustment into the mid-hi of the LSR32 they were just feature-mongering.And when that failed to sufficiently get a rise out of people they built in 0.5 dB adjustments into the E2...

Allanvh5150
01-18-2010, 08:21 PM
I will stick with my statement..............:)

badman
01-19-2010, 09:18 AM
Yeah, when JBL built a -1 dB adjustment into the mid-hi of the LSR32 they were just feature-mongering.

Or the 2dB horn level adjustment on the SR4725.... that's a PA speaker.... we all know DJs sit and listen to their setups and fiddle with them ad nauseum before a show.....

sonofagun
01-19-2010, 09:30 AM
Foamy feller, if you'd like, I'd be happy to tell you how much loss your throat plug has. But don't get upset if it's a lot more than you thought.

I need an unbiased tester.

badman
01-19-2010, 10:26 AM
I need an unbiased tester.

this isn't a subjective test..... and my biases are based upon measurements.... of foam. I have done a FEW things with foam.....

http://i42.photobucket.com/albums/e347/pothaudio/Horns%20and%20Waveguides/IMG_2202.jpg

sonofagun
01-19-2010, 11:12 AM
Actually being as (1) this thread goes back 5 years and (2) doesn't seem to be much of a demand or need, think it best to just let this pass.

Mike Caldwell
01-19-2010, 01:05 PM
Send me one your foam throat plugs for a two inch throat driver and I will measure it with SMAART with and without the foam and post the results.
I'll send the foam back after the test.

Let me know
Mike C.

sonofagun
01-19-2010, 01:13 PM
PM sent. Badman PM me your address for samples also.

badman
01-19-2010, 01:55 PM
PM sent. I'll run an averaged pink noise RTA on 'em and post results. Reticulated in small amounts has minimal effect, but as shown doesn't extend to the phase plug, only to the bug screen, and is reticulated foam with minimal resistive structure, rather than "acoustic foam" which retains cell walls and is much lossier.

badman
01-22-2010, 06:39 PM
Sonuvagun, you should have just said that your foam is reticulated. I already posted that it will have minimal if any effect. Oh well. I thought I was very clear in that I was being specific about which type of foam I'd have an issue with. Sorry for the inconvenience.

For all: The foam he sent was of the reticulated style, which means that it no longer has cell walls. Foam is usually a cellular structure with one of several types. There is closed cell, which is fine for soft mechanical vibration absorbtion, as footers or pads, but is fairly reflective acoustically, as the cell walls are all present, which means that air cannot flow through, which is important for acoustic absorbtion. Normal "Acoustic foam" of the type I understood sonuvagun's product to be, removes SOME of these cell walls, allowing a restricted airflow and thus a balance of propagation loss aka absorbtion and reflection. Reticulated foam has very little of either of these properties, and has a bare minimum of absorbtion or reflection. It's described as being desirable in this app because reflections in the throat are described as bouncing around and thus encounter the foam many times increasing what little absorbtion there is to a useable factor, whereas the single incidence of direct waves are almost entirely unattenuated.

Anyway, my reservations are completely gone. I'd go so far as to ask what forming abilities our man has? Could you do an insert that would fill a horn?

Mike Caldwell
01-26-2010, 04:01 PM
A cold snowy day here in Ohio was the perfect day to do this test. Thanks "sonofagun" for supply me with a couple of foam samples for the foam throat plug test, 1/4 inch and 1/2 was tested. The test driver was an Electrovoice NDYM1 driver with a B&C ME60 horn, sorry no spare JBL parts laying around today. Reference mic was on axis about 4 feet away from the driver. Test input was pink noise high passed at 800hz. Testing was with Smaart 5 using transfer function measurement. The red trace is with no foam in the throat, the gold/yellow trace is with the 1/4 inch foam, the blue trace is the 1/2 inch foam. For fun I filled the throat up with foam plugs stacked one on top another, that measurement is represented in the green trace. As you would expect the throat full of foam did reduce the level and had some high frequency attenuation. With the single layers the difference is nill

The quality of the foam is very good, I will be contacting "sonofagun" when I need to re-foam any of my speaker grills or build new ones.

Thanks
Mike C.

Mike Caldwell
01-26-2010, 04:03 PM
A few picts of the test set up.

sonofagun
01-26-2010, 08:27 PM
Excellent and many thanks.

:applaud::applaud::applaud:

badman
01-28-2010, 10:58 AM
On the blue trace we see 2-3dB difference from 1500-2000Hz. That is a significant change.

Does your measurement system use time based averaging at all or are these "snapshots"?

Mike Caldwell
01-28-2010, 02:05 PM
Those are all random snapshots.

badman
01-29-2010, 09:44 AM
For this to be more meaningful, it should use averaging- pink noise tends to measure very inconsistently without averaging. I'd be surprised if the vast majority of those differences was not suppressed by incorporating averaging (time domain, not octave). The changes shown are not only significant, but likely inaccurate. If you're ever measuring a 3dB difference from 1/4" of reticulated foam, anywhere in the audible spectrum... something is very wrong.

Have you ever run multiple measures of the same thing, back to back, to confirm consistency?

Steve Schell
01-29-2010, 04:42 PM
I had a weird experience with a throat screen recently. A friend brought me a Lansing 285 field coil driver (circa 1938) that was bothering him with subtle buzzing noises from time to time. I pulled the top plate assembly and cleaned some corrosion off the center pole and ran paper around the gap between voice coil and top plate, but it still buzzed a bit down around 200-300Hz when swept. Then I happened to touch the throat screen while listening and the noise stopped. It seemed that the 72 year old screen had corroded enough to move as a solid and make "oil can" noises. I had to resort to removing the screen, which I ordinarily wouldn't do on a historic driver, to stop the noise.

Mike Caldwell
01-30-2010, 03:07 PM
Still cold here in Ohio and no sound jobs booked this weekend so I re visited the driver throat foam test. Same basic test setup only used a 2311 horn I dug up with no lens. The response this time was averaged to 128 frames or samples for the display. Each screen shot was taken after about a minute to let it stabilize after changing the foam.
Gold/yellow trace is no foam
Blue trace is the 1/4 inch foam
Red/pink trace is the 1/2 inch foam
Green trace is throat full of foam

badman
02-02-2010, 11:48 AM
Hi Mike:

Thank you for re-running with averaging. These are much more useful results, you can see that the changes shown are decreased in magnitude dramatically when the averaging is employed, thus, we were seeing mostly the noise of the measurement procedure before.

Your resolution is better than mine so I think we can use your results to put this to bed. If you have a few extra minutes again, it would be interesting to see how "normal" acoustic foam compares to the reticulated stuff. I'm betting we'd see some very large FR changes.

Best,
bad

lgvenable
02-02-2010, 05:05 PM
mike
what are you using to pull the mic signal in with (hardware)

Mike Caldwell
02-02-2010, 05:46 PM
It was a Presonus Firebox.
http://www.presonus.com/products/Detail.aspx?ProductId=4

It gives me the reference mic input to the lap top as well as the pink noise output from the internal generator with the SMAART software.
The was a Audix TR40.