Speaker Dispersion

[bruce egnater]

More useful information.

TECH NOTE #102

Sound dispersion

November 2008

Ever wonder why your 4x12 cabinet sounds better when you stand off to the side? Did you wonder why the pros mic a speaker from the edge instead of in the center? Ever have people in the audience tell you your guitar tone is really shrill but it sounds great to you onstage? This is a result of the directionality of loudspeakers. Speakers inherently do not project all frequencies equally. As the frequency increases, the dispersion decreases. In non technical terms, this means the higher you play on your guitar, the more directional your sound will be. By nature, speakers tend to be somewhat non-directional at lower frequencies. This means you can stand off to the side of your cabinet and you will hear basically the same bass and lower mids as your audience is hearing right in front of your speakers. On the other hand, and this is where the trouble starts, higher frequencies tend to “beam” from the center of the speaker. While you are standing off axis from your cabinet (not directly in front of it) you are hearing an even balance of lows, mids and highs and feeling pretty pumped about your awesome tone. Unfortunately, unbeknown to you, the listeners directly in front of your cabinets are being killed by the high end that is “beaming” from the center of the speakers. FYI, contrary to what one might deduce, having four speakers in a 2 by 2 arrangement, as in a 4x12 cabinet compounds the problem and makes the beaming even worse. Next time you play take a moment to walk from side to side and squat down in front of your speakers. You will be amazed at the difference between listening off axis (to the side) and listening on axis (directly in front). Have you ever seen a band in a small place where you are hearing the stage volume and wonder why the guitars sound so bright? Doesn’t that guitar player hear that obnoxious high end? That knucklehead must be deaf!?!? More likely he is standing close to his cabinets and all that high end is just blowing past his/her legs so he/she doesn’t even hear it.
OK..so now I’ve pointed out how we’ve all been playing for years believing everyone in the crowd thinks our tone is as awesome as we think……or is it? Great, so what can you do about it? The key is to place your speakers so you are hearing the same thing as everyone else. If you can get the cabinets far enough behind you, you probably will pretty much hear everything just fine. If that is not possible, try placing the cabinets pointing across the stage sideways instead of forward at the audience. At least then you will only be killing your other band members instead of the audience. Chances are you often want to kill the drummer or bass player anyway, right? The best thing you can do is to tilt your cabinets so that they are pointed at your head. I guarantee you will set your controls way different from what you normally do.
There are a number of companies who are now offering a cool new solution to the beaming problem. A few companies make a disc that you install in front of the speakers to help disperse the high end. These discs have met with some success though they do introduce some phasing issues. Also, because there is a solid piece in front of the speaker, if one places a microphone in front of the disc (which happens quite often at shows), it can sound weird because the disc is blocking the sound into the mic. The one that we find works best is called the “Tone Bra” by Music Products Group. The discs are made of special foam that attenuates the beaming highs instead of blocking them.
I’m always surprised whenever this subject is discussed and most guitar players make the statement “I hate the way my guitar sounds when I stand in front of my speakers”. The answer is not to simply stand off to the side so it only sounds good to you. Remember why we play music? It is for others to enjoy. We should always make a conscious effort to think about what the audience is hearing, too.


On that happy note……………

Be the one who makes the shovels, not the one who digs the ditches (Ed Kreske)

Thanks

Bruce Egnater

[reo73]

Great post! This should be one of the first things guitarist learn when they start to play live. I make sure I always set my amps controls and do my sound check standing right in front of my amp and then walk away as far as my guitar cord will let me in-line with the amp and see how it sounds. It is amazing the difference in tone between being in-line and off axis, and it is easy to never realize it if you are only standing off-axis. I also like to use my stage positioning in relation to my amp to control how loud I hear my guitar...solo time, step more in-line...quiter section, step more off axis.

[hamfist]

I agree with every word Bruce ! That is why I now use a 4x12 plus a 2x12 on top (minimum) for gigs, so I can get some speakers pointing somewhere near my head level. SOunds very different to a cab on a stand pointing at your head. With a cab or combo on a stand you lose all bass response. Tilting back amps on the floor is a much better solution than a stand, IMO, but not as good as having a stack that starts on the floor and reaches up to your head level.
I don't play particularly loud, but just want to hear roughly what the crowd is hearing. A full-stack would be ideal, but I just couldn't fit it all in the car.

[Jay Mitchell]

Speaker directivity is the bane of a consistent guitar sound. That much is correct. However, there are several audio myths that continually get repeated, and they should be be corrected:

1. High frequencies come from the center of a cone speaker, and that's why they beam.

Nope. If you could actually get the high frequencies to be radiated by the "center" of the speaker - say the dust cap - you'd find them being radiated over a greater angle, not a smaller one. A number of past cone speaker designs actually had compliance elements built into the cone in an attempt to create this exact scenario: the size of the cone effectively getting smaller at higher frequencies. They didn't work particularly well.

2. Placing an obstruction in front of the center of the cone "blocks" these "beaming" frequencies and makes the speaker's directivity (the word "dispersion" does not actually apply to radiation pattern) broader.

Nope again. The "blocker" will indeed change the on-axis response and directivity of the speaker, but the effect is not consistent or necessarily useful. The directivity will actually be made narrower at some frequencies.

The mechanisms whereby an obstruction placed in front of a speaker changes its response and directivity are complex and counterintuitive. "Blockage" has nothing to do with it, however.

An obstruction will reflect sound back towards the cone, which will "re-reflect" the sound forward. The time it takes sound to make this extra trip means that the reflected sound will be delayed by some amount compared to sound that didn't make the extra trip. The response of the combined sound - slightly delayed plus undelayed - will contain interference ("comb filters"). The "phasiness" some folks describe when they install beam blockers is due to these comb filters.

A portion of the outgoing sound will diffract around the obstruction. This sound is also delayed and will cause an additional set of comb filters. The diffracted sound also has a different radiation pattern from that of the speaker, since it comes from the edge of a small disc. Taken by itself, the diffracted radiation has a strong beam directly in front of the disc. Combined with the other radiation (direct and reflected), the radiation pattern will vary widely with frequency - even more than the pattern of the speaker with no blockage. If you find these effects desirable - as a number of players apparently do - then there is nothing wrong with the use of "blockers," but they don't cause the directitivity changes their makers attribute to them.

If you want to alter the directivity of a guitar speaker in a favorable and frequency-consistent way, I've developed a means to accomplish that, and it can easily be tried by any reasonably competent DIY type. I'll be happy to share it if there's any interest. I've used this method on my tube amps, and it works beautifully.

[doublee]

^

Would love to hear about it....

[Jay Mitchell]

I've got Thanksgiving duties for the rest of the day. I'll try to post a description sometime tonight.

[somedude]

This is my solution..... having a speaker aimed right at your head tends to keep the whole treble/presense thing under control, and oddly enough, I can generally play a little louder since I'm not killing people with top end.

http://i104.photobucket.com/albums/m197/screamingdaisy_album/Other/thIMG_0925-1.jpg

[Artimus82]

not to sound like a rookie here (been playing live for about 10 years)... but that explains SO much for me~

thanks for the post!

can't wait to try a few things out next weekend ;)

[KBN]

Jay,
I too would love to hear what you have come up with when you get some free time.

[Randy Van Sykes]

I dial in my amps with them pointed right at my head...when playing live I tilt them towards my head side-washed so when I move left to right I still hear it very well. Sounds great all the time and I keep my stage volume down for others, so soundmen love it and put my guitar tone loudly in the mains for all to hear.

When I was young I used to stand to the side of my amp and thought it sounded good, what did I know then. :NUTS:crazy

[bruce egnater]

Jay. Please share your solution with all of us.

Bruce

[Galo]

“Tone Bra” by Music Products Group

link please..

[gag halfrunt]

Jay. Please share your solution with all of us.

Bruce

Yes, please do.

And Bruce's main point remains correct, of course. Your sound directly in front is much brighter than off axis, and should be seriously taken into consideration when playing live, whether mic-ed or not.

EDIT: this refers to an unaltered speaker, of course.

[Jay Mitchell]

OK, back from Thanksgiving dinner with inlaws. Here's the deal:

Cut out a doughnut-shaped piece of acoustically absorbent foam. The diameter should be the same as the speaker cutout in the baffle in your cab, and the diameter of the center hole should be ~3". Attach it to the rear side of your cab's grille using spray contact adhesive (e.g., 3M Super 77, available at Lowe's). Spray a light coating of adhesive on the foam only, and press it against the grille cloth within about 30 seconds of spraying it. You can easily remove the foam with no ill effect on the grille material, if you decide you don't like the effect.

The material you want is open-cell polyurethane foam in sheet form, and there are a number of sources for it. McMaster-Carr is one. I use acoustic foam that the company I own purchases for use in my loudspeaker designs, but that is a matter of convenience. I have tested and subjectively evaluated two thicknesses: 1/2" and 3/4". The limit on maximum thickness is the thickness of your baffle, so make sure you don't exceed that.

With the material I use, the 3/4" doughnut produces the most consistent response at different angles. A 12" speaker has huge variations in its response above ~1200 Hz within just 10 degrees of the speaker's axis. With the 3/4" foam doughnut in place, the on axis response and the response at 40 degrees off axis are almost identical. This is a huge improvement.

If you think about the subject of directivity, you'll easily recognize that there are two ways of saying the same thing: when you say a speaker becomes "beamy" at high frequencies, you're also saying that its on axis response is much brighter than its off axis response. For example, if you equalized the response to be flat on axis (a hypothetical exercise, as that's never what you actually want from a guitar speaker), you'd find that the response off axis falls off pretty rapidly at higher (> 1200 Hz) frequencies.

The reason for the preceding paragraph is to point out that making directivity more consistent over frequency requires that either the on axis or off axis response change. The foam doughnut causes a change in the on axis response, while leaving the off axis response alone. This means that, if you've tweaked your tone with the speaker aimed at your ears, it's now going to sound darker, and you'll need more treble, presence, and/or midrange, depending on the design of your amp's tonestack and other tone-altering circuits. If you're placing your amp on the floor facing the audience, the response you hear will change little or none, but the response the audience hears will now match what you've been hearing all along.

[gag halfrunt]

Very cool, Jay. Thanks. :AOK

[cram]

For all interested in how sound and perception of sound is managed by our minds - http://www.thegearpage.net/board/showthread.php?t=459022&highlight=ethan

Ethan Winer has a lot of great info. They guy is a wealth of information.

What your doing there with your solution is aiming at absorbtion for a frequency range that's not desirable. Glad it works for you.

I've gone through aiming my cab at the ceiling, at the back corner of stage and I am now using a plexiglass baffle with it mic'd. This has worked the best for me.

[userd]

For all interested in how sound and perception of sound is managed by our minds - http://www.thegearpage.net/board/showthread.php?t=459022&highlight=ethan

Ethan Winer has a lot of great info. They guy is a wealth of information.
.

Great info.

I noticed that often when AB testing different power cords etc,
Thinking B is better than A, then again when changing position slightly I thought: "oh no, its the same".

[Matybigfro]

i don't understand any of the physics but it sounds cool
basically much like these but the other way around tp what these do
http://www.tube-town.net/ttstore/product_info.php/info/p1687_TT-Diffusor-12-.html

[Jay Mitchell]

What your doing there with your solution is aiming at absorbtion for a frequency range that's not desirable.No. It's much more involved than that, and there's quite a bit more insight and understanding in the method than you apparently grasp.

I have designed loudspeakers for a living for the past 25 years. During that time, I have designed, engineered, prototyped, analyzed, and implemented for production a number of mechanisms for controlling directivity, including horns, line arrays, and the strategic use of acoustic absorption. Those interested in learning more about the mechanisms involved in this approach are encouraged to read this white paper: http://frazierspeakers.com/download/bounds.pdf , as well as the chapter on loudspeakers I authored in the current (fourth) and just-prior (third) edition of Glen Ballou's Handbook for Sound Engineers.

If absorption of "a frequency range that's not desirable" were all that is happening here, then a doughnut shape would not work as well as a solid disc. In fact, the center hole is essential to the device working properly, and its size is important. Geometry is a major factor. This technique corrects directivity issues that are in large part caused by the geometry of a cone transducer, and the geometry of the absorber is essential to that purpose.

I've gone through aiming my cab at the ceiling, at the back corner of stage and I am now using a plexiglass baffle with it mic'd. This has worked the best for me.However, you clearly have not tried the solution I just suggested, so you're really in no position to pass judgement on it. A plexiglass barrier is the most problematic "solution" possible, because it profoundly alters your tone in ways that EQ cannot recover.

If anyone is interested in learning how and why this works - not just hand-waving speculation, but a real explanation from someone with an education and professional experience in the field - I'll be happy to provide one. Guesses such as this one are bound to be oversimplified and incorrect.

More importantly, if anyone is interested in verifying whether this works, there's one way to find out: try it for yourself. Rather than package a device for retail sale, I have chosen to pass along a valid, useful technological development for free. It will be interesting to see if this "marketing" approach is as effective as making wild, unsupported claims and overcharging by an order of magnitude. :roll

[somedude]

More importantly, if anyone is interested in verifying whether this works, there's one way to find out: try it for yourself. Rather than package a device for retail sale, I have chosen to pass along a valid, useful technological development for free. It will be interesting to see if this "marketing" approach is as effective as making wild, unsupported claims and overcharging by an order of magnitude. :roll

It is TGP. I suspect the latter woul be more effective. Particularily if you somehow managed to include a swirly and/or tie died finish.

Anyway, amp I reading you correct when you say that the donut should be about 12 inches outer diameter, with an ~3 inch inner diameter, and 1/2 to 3/4 inch thick?

Also, it's connected to the back of the grillecloth and should not touch the speaker?

How much does blocking off that much of the cone reduce the overall volume?

[cram]

No. It's much more involved than that, and there's quite a bit more insight and understanding in the method than you apparently grasp.
...
However, you clearly have not tried the solution I just suggested, so you're really in no position to pass judgement on it.


You're misunderstanding my earlier post and it seems that you're taking it as an acusation or insult of some sort. This is entirely not the case. I was just trying to help in providing related information in what I've tried and read about acoustics.

I understand and appreciate your past work and history. I didn't mean to insinuate that you were only absorbing a frequency range. It's simply that from your first post and the information you provided in example - it was the main portion of it.

Your reply has a tone of insult taken and condescension given back that I really didn't expect. Based upon what I wrote. I'm glad you've worked out a problem and have shared the information and perhaps I'll go through the work to experiment with it.

[Jay Mitchell]

Anyway, amp I reading you correct when you say that the donut should be about 12 inches outer diameter,Its o.d. should be a match for the baffle cutout (maybe even 1/16" smaller), so that it sits entirely within the cutout without being stuffed. If the cutout isn't round - some cabs have cutouts with a flat - then you should cut the foam to match the actual shape.

with an ~3 inch inner diameter, and 1/2 to 3/4 inch thick?Yes.

Also, it's connected to the back of the grillecloth and should not touch the speaker?Yes.

How much does blocking off that much of the cone reduce the overall volume?None, if you're accustomed to playing in an off-axis position. Open cell foam in this thickness has almost no effect on sound passing through it at frequencies below ~1kHz. The doughnut will therefore cause no change in off axis response or sensitivity. It will reduce higher-frequency content directly on axis. If you're accustomed to playing with your cab aimed straight at your head, the doughnut will make it sound darker by reducing the on-axis sensitivity of the speaker in the higher frequency ranges. If you've adjusted your tone to remove the "ice pick" effect on axis, you will need to brighten it with the doughnut in place. The advantage you will gain is that your position relative to the cab will no longer matter so much: it will sound the same off axis as when you aim it at your head.

[rhythmrocker]

Thanks Jay, great reading here.

Question - I have round metal covers on one of my cabs. Do you think your disspersion method will work if I attach the foam to the inside of the metal grill? Any suggestions for when I try this out? Thanks.

[swimrunner]

I really need to try this sometime. Thanks for sharing this little mod.

[Tone_Terrific]

Very interesting and quite counterintuitive that the center is left open.

How close to the speaker does the device have to be? Could I hang one aginst the grill of a borrwed amp in the practice room, say, and still get a reasonable benefit? The size would be an approximation as well.

[Jay Mitchell]

To answer a couple questions: to try the idea, you could temporarily attach the doughnut to the front side of the grille. Just make sure to center it over the speaker cutout. If your cab has metal speaker protectors, you can attach the doughtnut to those.

The spacing of the foam off of the speaker cone is not critical, but you do not want it to make contact with the cone, and you also do not want there to be a flanking path (i.e., a large gap around the outer edge of the doughnut) that sound can take without passing through the foam.

In order to understand why/how it works, you have to understand a bit of the geometry and acoustics in a cone transducer. The cone is driven very near its center (where the voice coil former is attached to the cone). The mechanical excitation (the vibration of the cone) is not instantaneous. It moves outward in the cone with its own characteristic velocity, which is geater than the velocity of sound in air. As the excitation moves outward, the air in contact with the segment of the cone that is moving is also excited, and sound is radiated from that segment. If the angle of the cone is "just right" for the properties of the cone material, the sound that is radiated from each section will be almost perfectly in time with the sound that was radiated earlier, from a portion of the cone that is set further back.

When all this sound adds up out in front of the cone, you get a coherent wavefront to a relatively high frequency (as high as ~5kHz), but only on axis. At off-axis positions, the synchronization falls apart very rapidly, to the extent that a typical guitar speaker will see its output above 1200 Hz fall off by as much as 15-20dB within just a few degrees off axis. The effects on directivity due to mis-synchronized off-axis arrivals are much less at lower frequencies, because the wavelengths of sound are larger than the cone, and the speaker is therefore not "beamy" at these frequencies.

Placing an absorber doughnut in front of the cone has almost no effect below 1kHz, because the material is too thin to have a significant effect at lower frequencies. This is good, since, as we've seen above, the speaker's behavior below 1kHz is not a problem. At higher frequencies, the radiation from the outer portions of the cone is progressively absorbed, whereas the portion of the radiation from the center of the cone which moves straight forward is allowed to pass through the opening in the doughnut unattenuated. The result is that there is a net reduction in high-frequency content on axis, but the high frequencies that do get through are now radiated by a virtual source - the opening in the doughnut - which is much smaller than the actual speaker, and they are therefore radiated over a greater angle. The speaker's directivity is now essentially the same over the entire range of interest for electric guitar, and you're out a few bucks for a piece of foam and a few minutes to cut out and attach the doughnut.

[K-man]

Thanks for sharing the info Jay.

[somedude]

That's pretty cool, and makes alot of sense when put that way.

What is your opinion on grille cloths? I've taken to using cane/wicker (like that used by Orange) as I feel it knocks off some top end.

[FortinAmps]

To answer a couple questions: to try the idea, you could temporarily attach the doughnut to the front side of the grille. Just make sure to center it over the speaker cutout. If your cab has metal speaker protectors, you can attach the doughtnut to those.

The spacing of the foam off of the speaker cone is not critical, but you do not want it to make contact with the cone, and you also do not want there to be a flanking path (i.e., a large gap around the outer edge of the doughnut) that sound can take without passing through the foam.

In order to understand why/how it works, you have to understand a bit of the geometry and acoustics in a cone transducer. The cone is driven very near its center (where the voice coil former is attached to the cone). The mechanical excitation (the vibration of the cone) is not instantaneous. It moves outward in the cone with its own characteristic velocity, which is geater than the velocity of sound in air. As the excitation moves outward, the air in contact with the segment of the cone that is moving is also excited, and sound is radiated from that segment. If the angle of the cone is "just right" for the properties of the cone material, the sound that is radiated from each section will be almost perfectly in time with the sound that was radiated earlier, from a portion of the cone that is set further back.

When all this sound adds up out in front of the cone, you get a coherent wavefront to a relatively high frequency (as high as ~5kHz), but only on axis. At off-axis positions, the synchronization falls apart very rapidly, to the extent that a typical guitar speaker will see its output above 1200 Hz fall off by as much as 15-20dB within just a few degrees off axis. The effects on directivity due to mis-synchronized off-axis arrivals are much less at lower frequencies, because the wavelengths of sound are larger than the cone, and the speaker is therefore not "beamy" at these frequencies.

Placing an absorber doughnut in front of the cone has almost no effect below 1kHz, because the material is too thin to have a significant effect at lower frequencies. This is good, since, as we've seen above, the speaker's behavior below 1kHz is not a problem. At higher frequencies, the radiation from the outer portions of the cone is progressively absorbed, whereas the portion of the radiation from the center of the cone which moves straight forward is allowed to pass through the opening in the doughnut unattenuated. The result is that there is a net reduction in high-frequency content on axis, but the high frequencies that do get through are now radiated by a virtual source - the opening in the doughnut - which is much smaller than the actual speaker, and they are therefore radiated over a greater angle. The speaker's directivity is now essentially the same over the entire range of interest for electric guitar, and you're out a few bucks for a piece of foam and a few minutes to cut out and attach the doughnut.

Stellar posts, Jay.

Thank you so much for sharing.

I've got my weekend cut out for reading and experimenting thanks to you:dude

Cheers,
Mike

[gag halfrunt]

Jay, thanks so much for the detailed explanation of WHY this works.


But what about PA speakers? Would you use the same 3" hole in front of a 15" driver? Would you change anything else about the dimensions/construction of your acoustically absorbent foam?

[Matt Jones]

A plexiglass barrier is the most problematic "solution" possible, because it profoundly alters your tone in ways that EQ cannot recover.

The plexiglass thing has always baffled me. A hard reflective surface right in front of a speaker cone is bound to wreak havoc on every frequency that hits it, even with a mic pointed 180 degrees away.

[Jay Mitchell]

But what about PA speakers? Would you use the same 3" hole in front of a 15" driver?No. If you were doing things conscientiously, you would cross over out of the 15" to a smaller transducer at a frequency well below the point at which the 15" speaker becomes too beamy. Whether a given manufacturer has actually done things well is an open question. You can't generally expect to be able to fix problems in two way speakers with this kind of simple measure.

[gag halfrunt]

No. If you were doing things conscientiously, you would cross over out of the 15" to a smaller transducer at a frequency well below the point at which the 15" speaker becomes too beamy. Whether a given manufacturer has actually done things well is an open question. You can't generally expect to be able to fix problems in two way speakers with this kind of simple measure.

I'm crossed over at 1,200 Hz and it's a two way system. Sorry - I should have included that in my question.

Do you have any recommendations about correcting beaminess from the the tweeter? I'm guessing it's a little more complex.

[JoeB63]

So where can we get just a few feet of this McMaster-Carr acoustical insulation?

[Tone Loco]

The material you want is open-cell polyurethane foam in sheet form, and there are a number of sources for it. McMaster-Carr is one. I use acoustic foam that the company I own purchases for use in my loudspeaker designs, but that is a matter of convenience. I have tested and subjectively evaluated two thicknesses: 1/2" and 3/4". The limit on maximum thickness is the thickness of your baffle, so make sure you don't exceed that.

With the material I use, the 3/4" doughnut produces the most consistent response at different angles. A 12" speaker has huge variations in its response above ~1200 Hz within just 10 degrees of the speaker's axis. With the 3/4" foam doughnut in place, the on axis response and the response at 40 degrees off axis are almost identical. This is a huge improvement.

I checked McMaster-Carr and found 1/2" (and 1") but not 3/4", which I gather isn't as good as 3/4 according to your tests. How much worse did you think the 1/2" was? Its pretty cheap but I'm wondering if it's worth messing with.

[Tone Loco]

So where can we get just a few feet of this McMaster-Carr acoustical insulation?

http://www.mcmaster.com/

Due to the way they have their website set up I can't give you a more specific url. Just keep clicking on "polyurethane foam" (unbacked) and you'll get to a catalog page with sheets of it in different sizes. Its on catalog page 3464.

[JoeB63]

http://www.mcmaster.com/

Due to the way they have their website set up I can't give you a more specific url. Just keep clicking on "polyurethane foam" (unbacked) and you'll get to a catalog page with sheets of it in different sizes. Its on catalog page 3464.

Well, I didn't look too closely, but they seem like the kind of supplier that only sells large quantities of stuff to builders. I had the feeling that they would bother to sell me (or you) 4 square feet of the material. I could very well be wrong.

[Jay Mitchell]

Well, I didn't look too closely, but they seem like the kind of supplier that only sells large quantities of stuff to builders.Nope. You can buy a 12" square piece of foam. I buy small quantities of all sorts of stuff from them on a regular basis. They're the best hardware vendor I've ever found.

For 3/4" foam, try McMaster-Carr part no. 85735K72, 12" x 12" sheets of 3/4" poly foam, $5.20 each.

[Jay Mitchell]

I checked McMaster-Carr and found 1/2" (and 1") but not 3/4",See above. They've got 3/4" as well.

How much worse did you think the 1/2" was?I've still got a 1/2" doughnut on one of my amps, and it works just fine. With the 1/2" foam, the on-axis response is a bit brighter than with 3/4", and there is more of a change with 1/2" as you move off axis, but it is still a huge improvement over the untreated speaker. You might even end up preferring the 1/2" if you try both. It's certainly cheap enough.

Its pretty cheap but I'm wondering if it's worth messing with.The idea is free. If you're not willing to experiment a little bit to get a major improvement in your sound quality, then maybe you should just buy a beam "blocker" and be done with it. :dunno

[Stratofuzz]

Ok, I'll try this.
What is the recommended method for cutting this material-razor?

[Jay Mitchell]

Ok, I'll try this.
What is the recommended method for cutting this material-razor?Sharp scissors work very well, but, if you insist on the cleanest and most accurate cut, a really fresh utility knife blade and a good pattern of the shape you want to duplicate are the way to go.

For circular shapes, I find it easiest to scrounge a paint can or similar that is slightly smaller than the desired diameter and use that for a pattern.

[Cobra]

Jay, do you have any pix of your donut installed, or even better, any pix of the installation process?
Thanks!

[Tone Loco]

See above. They've got 3/4" as well.

I've still got a 1/2" doughnut on one of my amps, and it works just fine. With the 1/2" foam, the on-axis response is a bit brighter than with 3/4", and there is more of a change with 1/2" as you move off axis, but it is still a huge improvement over the untreated speaker. You might even end up preferring the 1/2" if you try both. It's certainly cheap enough.

I ordered one of each thickness. This should be interesting. I've tried amp stands and pointing the amp backwards but this would be great. Now to find that spray on glue :-)

As far as McMaster-Carr's online retailing - I appreciated not having to guess at separate shipping charges and it was no problem that I only ordered those two small items.

[Jay Mitchell]

Jay, do you have any pix of your donut installed, or even better, any pix of the installation process?No.

[Jay Mitchell]

Now to find that spray on glue :-)The generic product description is "spray contact cement," and Permatex and 3m both make varieties of it. I believe Borden (Elmer's) also has one. Lowe's or Home Depot (or Wal-Mart, for that matter) are good places to look for it.

[JoeB63]

OK, one more question: What's the recommended micing technique once you have this ring installed?

[Jay Mitchell]

OK, one more question: What's the recommended micing technique once you have this ring installed?Depends on what you were doing before. If you were placing the mic dead center, nothing will change. If you were placing the mic near the edge of the speaker cone, the mic'ed sound will be darker than it was. If you can't EQ this to what you want, then you might try a position near the edge of the center cutout in the doughnut. As before, there really are no rules. Experiment until you find what works best for you.

[Luke Gibson]

Great reading guys, thanks for starting this thread!

[motis1953]

I've not heard anything mentioned about this but it seems that a Beam Blocker actually acts as a time alignment device as the higher frequencies travel faster through the air.

[Jay Mitchell]

I've not heard anything mentioned about this but it seems that a Beam Blocker actually acts as a time alignment device as the higher frequencies travel faster through the air.No. higher frequencies do not "travel faster through the air" - the velocity of sound in air does not vary with frequency - and beam "blockers" do not somehow magically create longer paths only at higher frequencies.

Beam "blockers" act as time misalignment devices, creating multiple added paths - all of which are longer than the direct one - due to reflection and diffraction.

[rhythmrocker]

I've not heard anything mentioned about this but it seems that a Beam Blocker actually acts as a time alignment device as the higher frequencies travel faster through the air.

Good stuff Jay - question: I mentioned that I have metal grills as speaker covers. Using these metal covers, will certain frequencies be reflected back to the cone, enough such that phase anomolies will occur?

Should I be concerned and dump the metal covers and go back to grill cloth? Will the foam you mentioned, applied to the inside of a metal grill, stop any foreseeable reflection?
Your thoughts . . .

[Jay Mitchell]

Good stuff Jay - question: I mentioned that I have metal grills as speaker covers. Using these metal covers, will certain frequencies be reflected back to the cone, enough such that phase anomolies will occur?Not if the covers are typical perforated metal parts. The solid (and therefore reflective) parts of a perf-metal speaker cover are spread out and interspersed with open spaces. The small amount of energy that is reflected is scattered in space and smeared in time to the extent that it will have no perceptible effect on the sound of electric guitar.

Will the foam you mentioned, applied to the inside of a metal grill, stop any foreseeable reflection?The foam will tend to reduce the magnitude of the reflections, but they won't be a problem anyway.

[Jay Mitchell]

It's interesting that this topic has been moved to the "Manufacturers' and Retailers' Forum." Why would that be? We're discussing an issue that is relevant in general to "Amps and Cabs," and nobody is selling anything or even discussing commercially-available products.

Anyone?

[Jay Mitchell]

I've started a new thread on this subject here:

http://www.thegearpage.net/board/showthread.php?t=470956

I have placed the information about how/why in that thread, and I would appreciate those who have questions or remarks participating in that thread, rather than this one.

I have no idea why this thread was moved, but I am certain that whatever content that caused to to be placed in the manufacturers' forum is absent from the new one.

[jzucker]

Thanks for the great tips Jay. Interestingly enough, the egnator tone-bra uses the opposite blocking pattern from your doughnut. I was almost ready to buy a tone bra before reading your thread but I ordered the open cell foam instead. Thanks again.