Left and right of bookshelf speakers

[jonnythan]

If I asked a physicist how fast I would fall jumping out an airplane, I would expect a straight answer such as "about 120mph", not a list of reasons not to jump out of airplanes, advice on which airplane to buy or complaints about people who don't like gravity. Complaining I can't get a straight answer is not the same as saying the "expert" who answered knows nothing about gravity or air resistance.

1) Can speaker fabric in front of a speaker significantly alter the sound of a speaker or not?

2) Can any surface behind the baffle but forward of the rear of speaker significantly alter the sound of a rear ported speaker? If so, is this from interaction with waves from the driver, waves from the port, or through other means?

I am actually baffled most non-expert enthusiasts (including myself) don't have a good answer to 2), as almost every setup has surfaces in these areas other than the walls and floors of the room.

Poor analogy. You're not asking "how will the speakers sound if I do this?" - you're asking how best to do it. So a better analogy might be "if I asked a skydiver how I should jump out an airplane with no parachute, he would just list reasons not to do it instead of giving a straight answer."

The answer to your question is "there is no answer, because no matter how you do it, it will suck. Really, we promise, it will not sound good at all." If you insist on doing it, with the knowledge that it will sound bad, why even bother asking how much space to have around the speakers? You are sacrificing good sound for appearance, so just make them look good.

 

[TLS Guy]

If I asked a physicist how fast I would fall jumping out an airplane, I would expect a straight answer such as "about 120mph", not a list of reasons not to jump out of airplanes, advice on which airplane to buy or complaints about people who don't like gravity. Complaining I can't get a straight answer is not the same as saying the "expert" who answered knows nothing about gravity or air resistance.

1) Can speaker fabric in front of a speaker significantly alter the sound of a speaker or not?

2) Can any surface behind the baffle but forward of the rear of speaker significantly alter the sound of a rear ported speaker? If so, is this from interaction with waves from the driver, waves from the port, or through other means?

I am actually baffled most non-expert enthusiasts (including myself) don't have a good answer to 2), as almost every setup has surfaces in these areas other than the walls and floors of the room.

You don't tell us much and pending further sensible information from your quarter will run out after this reply.

For one, obviously fabric in front of a speaker does and can effect sound.

However we know nothing of the nature of the fabric and nothing about its form, stretch, proximity to the drivers and whether your existing speakers have their grills on.

Fabrics vary enormously in the way they modify sound, depending on fabric type weave and other issues.

Your next question is even more complicated as you have given us no visual plan.

The port is the easiest to answer, and the port should ideally be 10" away from a rear boundary. However on a shelf you can get away with about 4" depending on the speaker. Front porting is preferred.

However your question is much more complicated than you think, as we know nothing much about the space you intend to put the speaker in.

The problem then becomes that the cavity behind the speaker will react to modify the properties of the port. This is called end correction, and would be impossible to predict, and only quantifiable by measuring the effect on box tuning after you built the contraption.

The effect of the reflections by your structure is hard to quantify as again we know next to no details of your plan.

However, it seems you may be creating some unusual close proximity boundaries. This is never a good idea, because they are close and so sound intensity is high and so the reflected intensity of sound is high, increasing interference with the direct radiated sound of the speaker.

Now lets take your airplane example. That is not so simple either, unless you jumped in a vacuum.

Newton's formula for velocity under gravity is fairly simple.

Your final velocity = The force of gravity(your weight) X the time you were falling + your initial velocity. And velocity is not the same as speed as velocity is a vector and has to have a direction.

Now no physicist could ever say about 120 mph. He would want to know your body habitus, your clothing, how much it would billow out in the wind, whether your head was covered and by what. The there would be imponderables, such as whether you fell vertically or with a more horizontal profile. This latter would be highly random.

You see all of the above and some I have not thought of will vary the wind resistance. These factors will subtract from the force of gravity in complex ways in the above formula and defy an answer that is any use to you. The only thing that could be said with certainty, is that unless you have a parachute, you will kill yourself.

Your question about boundaries is the same.

All I can say is you are setting up a system of complex interacting variables and your plan is a bad one. Further I seriously doubt your ability to quantify the effects of your build and structure. Your problem is you have no clue as the huge array of interacting variables in this case.

 

[BradB]

Sound does actually leave the sides and back of the speaker, especially if you're using a rear-ported design.

I thought I made it very clear I was aware sound left the port. I am talking about surfaces in front of the port. I am also aware sound leaves the sides, however I don't think this sound is important.

Placing a speaker into any enclosure which will distort and capture/refocus the sound will make the speaker sound worse.

Everyone keeps stumbling on the semantics of "enclosure". Consider placing a 1" aluminum pole to the left of a 12" speaker. This is not an "enclosure" by any reasonable definition. What I want to know is how (and how much) that pole colors the sound from the speaker.

 

[jonnythan]

I am also aware sound leaves the sides, however I don't think this sound is important.

What makes you think you know enough about sound and loudspeakers to make that judgment? You are, of course, wrong. It is extremely important. Speakers are not flashlights.

Everyone keeps stumbling on the semantics of "enclosure". Consider placing a 1" aluminum pole to the left of a 12" speaker. This is not an "enclosure" by any reasonable definition. What I want to know is how (and how much) that pole colors the sound from the speaker.

Oh, did you go from a backless plywood box to a 1" aluminum pole? This is progress! Now just get rid of the pole.

 

[BradB]

Continuing the airplane example, you are correct it is more complicated than Newton's formula, but simple compared to many things physicists do.

It is reasonable to assume the questions implies I am not jumping in a vacuum from the context of the world "airplane". I could theoretically jump from an airplane (which could not be flying the way they do on earth) on a planet without an atmosphere, however the lack of this qualification in the question implies this is not the case I am interested in.

So while there may be many forces at work, the 2 most important ones are air resistance and gravity. Gravity can be calculated with Newton's laws, Einstein's, or other methods, all of which are imperfect and some of which are very complicated. The physicist knows the Newton's method is a reasonable approximation for the precision again implied by the context of the question.

Now my body and clothing are somewhat relevant. A physicist could ask me some more details, or calculate a range for reasonable bodies and clothing. If asking for details, eventually he would have to stop and work with a range. I might be wearing 200 thread count nylon tights, and not all 200 thread count nylon tights have the same air resistance, however a physicist knows the difference is negligible, and eventually further questions about the tights won't add value.

Most importantly, a physicist who took the question even slightly seriously, would avoid spending the bulk of his time on irrelevant details. Why do I want to jump from an airplane? What color are my tights? From the context of the question, the physicist might assume I am doing something similar to jumping out of an airplane - however this does not imply he should focus his time and effort on convincing me not to do it.

People have fallen from airplanes without parachutes and not been killed. A physicist may or may not know this, but most physicists would probably consider the effect of the fall on my body outside their expertise.

Most importantly, the physicist could explain how I can come up with the answer on on my own, and where to plug the variables in.

My question about boundaries is the same.

 

[lsiberian]

If you put a mirror next to a bright light does it influence the amount of light in the room?

If you put a piece of plywood next to your speaker you can have a similar effect. The problem is that the full spectrum of sound may not be reflected evenly.

Grill fabric is normally okay in front of a grill less speaker. Do you understand the concept of having open sides around the speakers instead of putting wood next to them. This would allow them to radiate better. You could even use books or other more absorbent material for a better look and sound performance.

For the port make sure you have a vent behind the shelf for it. Also give the gap as much space as you can. Honestly you'd probably be better angling the speakers down toward your position from the top of the shelf or something similar.

Use of an EQ system and an external amp should help correct some of the issues.

What speakers are we using?

 

[Adam]

Brad, you're building an entertainment center, right? I'm sure that it has other considerations, such as aesthetics. Will it affect the sound? Sure, but so does the room. My advice is consider what's been said here as well as how you want it to look, then use a receiver that has auto equalization to help deal with these effects (hopefully you already have one - sorry if I missed where you posted your electronics). I use Pioneer's MCACC and am very happy with it.

Sorry. Didn't mean to interfere with this fine intellectual p*ssing contest. Back to people jumping out of airplanes...

 

[BradB]

Poor analogy. You're not asking "how will the speakers sound if I do this?" - you're asking how best to do it.

Jonnythan - this is my point exactly, except backwards. I am not asking how to do anything best, that is the question everyone is trying to answer instead of what I asked. I was asking "how will the speakers sound if I do this" (and why).

 

[TLS Guy]

Jonnythan - this is my point exactly, except backwards. I am not asking how to do anything best, that is the question everyone is trying to answer instead of what I asked. I was asking "how will the speakers sound if I do this" (and why).

I have absolutely no clue, of the total effect. Nor does anyone else on Earth who is honest.

I do know it will have an adverse effect, degree, how what where is impossible to predict.

Good design predicates simplicity and minimizing confounding variables, always.

 

[jonnythan]

Jonnythan - this is my point exactly, except backwards. I am not asking how to do anything best, that is the question everyone is trying to answer instead of what I asked. I was asking "how will the speakers sound if I do this" (and why).

Well here was the real initial question:

"Assuming something is to the left, right or above a bookshelf speaker, does it matter at all how close it is?"

The answer is "yes - but be sure you keep in mind that any distance remotely reasonable within the confines of an entertainment center will make the speakers sound significantly worse."

This question was then followed with:

"Which leaves me with needing distances for left, right and top, as well as some idea of how important those distances are."

To which the answer is "any distance is a bad idea, because the entire idea of putting a plywood box around a speaker is a bad idea to begin with."

 

[lsiberian]

Sorry. Didn't mean to interfere with this fine intellectual p*ssing contest. Back to people jumping out of airplanes...

I've never understood jumping out of an airplane, but if that's what interests these folks then by all means have at it.

 

[lsiberian]

Good design predicates simplicity and minimizing confounding variables, always.

With this in mind go forth. Simple is your friend. A solid 13ply cabinet braced with oak should do best for materials. Give the speakers as much gap to the sides and top as you can spare. Since it's going behind grill cloth you can even use a stand within the structure. I can toss out numbers, but use what is reasonable with your design. I suggest lining the back sides and top bottom of the shelf with r19, foam or rockwool.

I hope you can see this picture in your head. A speaker on a pedestal with a decent gap from the top, bottom and sides. Lining the insides of the shelves with r19 or rockwool to help absorb sound and I also recommend using a sandwiched piece of rubber between the speaker and the stand it sits on.

Is any of this making sense?