Left and right of bookshelf speakers

[BradB]

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

I am building an entertainment center - a series of plywood shelves to hold my TV, speakers (left, right, center and subwoofer), computer and other equipment. Each speaker will be inside a plywood "box". The back of the box will be open, and the speaker will be 24" from the wall behind the entertainment center. The front of the box will be speaker fabric to hide the speaker but let the sound through. The bottom and sides of the box will likely be solid plywood. Does the width and height of the box matter at all?

This is part of a post I made on the Emotiva forum that I didn't get a complete answer to.

 

[j_garcia]

First, are you saying you are going to install drivers into one of these "shelves", basically building them into the cabinet or you are going to place existing, complete speakers into the shelves? If the first DIYing into the cabinet, then there are a LOT more factors than just slapping a speaker on a piece of wood if you want good sound. If the second, there are definitely some things to consider to do this.

 

[BradB]

I am going to place existing, complete speakers into the shelves. Can you be more specific about things to consider?

 

[j_garcia]

Wanted to know what you meant first, because they are two very different things. To do this, rear ported speakers would be a bad idea. You will want front ported or sealed speakers to reduce issues with being placed inside a secondary enclosure like this. Typically you want a few feet from the walls in all directions, but if you are going to enclose them like this, I'd say about 6" around them and make it so they can be pulled as far forward to the front of the shelf as possible so the sound is reflecting off the inside of the shelf as possible. A friend of mine had a built in unit like this before and did something similar with his speakers and it sounded pretty good.

 

[lsiberian]

Very few speakers sound good enclosed in a cabinet. On wall would be a better option. Unless you build the cabinet for tornado safety it will color the sound badly.

If you have no other options then make sure you line the cabinets with thick foam. Be sure tweeters are aimed at ear height were possible. Make sure to be vertical were possible too.

 

[BradB]

I have rear ported speakers, and am not buying new speakers.

"Enclosed" is a matter of semantics. Outside of a zero gravity environment, it is not possible to avoid having anything near your speakers. "Near" is also relative. Obviously blocking the rear of the speaker is bad, and blocking the front is worse. Almost everyone has something touching the bottom of their speaker (floor, stand or shelf), and they don't think about it.

This gives me:
Front : Clear path to listener
Back : 2 feet minimum is the general recommendation
Bottom : Zero distance required.

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

 

[j_garcia]

When I said at least 6" around them, that means to the sides and top, obviously not to the bottom. Nobody said you can avoid having the speakers near something and that wasn't the point. The point was that putting a speaker inside another small space WILL compromise the sound to some extent no matter what you do. Giving the speaker a little breathing room will help to minimize this. A speaker sitting a few feet from any wall is a lot different than one sitting in a cubby hole. The ideal situation would be to not have them setup like this, though it will still work and we are just offering some thoughts on how to get better results, since that is what you asked. As I've already said, I know you can do this because I've seen/heard it done first hand; I just wouldn't do it myself.

 

[BradB]

6" inches is a good answer, but how are you coming up with this? How do you know I won't hear noticeable improvement with 12" or that I will notice "coloring" with only 4"?

Other than by actually building a variety of set ups and measuring, I don't know how to do this, but I am surprised no one has done that before. I would also think there would be some theory of physics that gives a reasonable sounding answer (other than 0" should be fine).

 

[TLS Guy]

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

I am building an entertainment center - a series of plywood shelves to hold my TV, speakers (left, right, center and subwoofer), computer and other equipment. Each speaker will be inside a plywood "box". The back of the box will be open, and the speaker will be 24" from the wall behind the entertainment center. The front of the box will be speaker fabric to hide the speaker but let the sound through. The bottom and sides of the box will likely be solid plywood. Does the width and height of the box matter at all?

This is part of a post I made on the Emotiva forum that I didn't get a complete answer to.

The worst place to put a bookshelf speaker is on a shelf!

You need to understand Baffle Step loss and its compensation, BSC

Now decent speakers are step loss compensated, so if you make an adjacent boundary, the range below 600 Hz will be boosted.

In your case the worst thing you could do is allow reflections from the cabinet behind the speaker, which will make for an irregular response.

You need the softest backed books you can find right up to the speakers both sides, to absorb the first reflections as much as possible.

The speakers will still sound on the "chesty" side, but the only way you could deal with that would be crossover modification.

It would have been better had you purchased in wall speakers, as these are obviously designed without BSC.

Book shelf speakers should be placed on stands, with the tweeter 36" above the floor and at least 10" to 14" from all boundaries.

The rear port must be at least 4" from the back of the cabinet.

By the way don't build a box, that is absolutely the worst thing you could do. You don't want a box within a box.

If you don't want to use stands, But them on a self with books either side of them.

 

[lsiberian]

You need to understand Baffle Step loss and its compensation, BSC

Now decent speakers are step loss compensated, so if you make an adjacent boundary, the range below 600 Hz will be boosted.

Does AS have the ability to help with BSC issues? I remember you saying it could help fix crossover issues at some point. Perhaps a minidsp is only 100 dollars and could be used with an external amp to help if not. I realize it's not ideal, but having an parametric eq might makes this an easier job.

Honestly this problem is ideal for custom audio IMO.

 

[BradB]

I am not sure how this article applies to speaker placement (versus speaker design). Diffraction from the baffle does play some role, and a close enough enclosure could act as an extension of the baffle, but this be a minor change and only happen if the surface were almost touching.

As far as I can tell, no sound, or at least no sound that we want, leaves the sides or top of a bookshelf speaker. Diffraction could theoretically play some role as I said above, and the shelf itself could have some effect on the reflected sound from the rear port - again minor. Are these the only 2 considerations? I guess I will need to build various "cabinets" and measure.

 

[BradB]

Please note by "side" I am not referring to anything that extends forward of the baffle and could cause a reflection.

 

[j_garcia]

6" inches is a good answer, but how are you coming up with this? How do you know I won't hear noticeable improvement with 12" or that I will notice "coloring" with only 4"?

Other than by actually building a variety of set ups and measuring, I don't know how to do this, but I am surprised no one has done that before. I would also think there would be some theory of physics that gives a reasonable sounding answer (other than 0" should be fine).

I never measured, but my friend's setup had less than 2" around and it sounded nasal. He was very pleased with it, so I didn't mention this to him because it really only mattered that he liked it because he is the one listening to it, and the same applies here.

In previous setups that I've done this in for friends who were setup like this, it seems like about 6" worked, thus the recommendation. It is going to vary depending on the speaker as well, so I can't say definitively this is the answer - some experimentation will be necessary as different speakers may have very different radiating patterns.

 

[TLS Guy]

Please note by "side" I am not referring to anything that extends forward of the baffle and could cause a reflection.

You don't understand. The problem is reflections At the frequencies we are talking about your speakers are spherical radiators.

So anything with a wave length longer than the width of your baffle will not be reinforced on a stand, but will be in your arrangement. The really "chesty area is 100 to 180 Hz or so. A 100 Hz tone has a frequency of 11" and 180 Hz 6".

Now away from boundaries the speaker is a half radiator (hemispheric), at a frequency above where baffle step loss starts to occur and a full space (spherical) below that.

For a small bookshelf with a baffle width of 6" the speaker is 3db down at 760 Hz and falls off 6 db per octave below that.

A larger one with a 9" baffle is 3 db down at 507 Hz.

Now these losses are compensated for in the crossover, or should be.

Now in your arrangement the speaker will be radiating in half space at all frequencies and if BSC compensated will have a rising response.

The next issue is your box you intend to construct. This will have a volume, and therefore resonance, and will also have parallel wall reflections.

I just don't understand why you want to put a speaker that is already a box with a grill, inside another box, with a grill.

If you have to put a speaker on a shelf of an entertainment, center, which is what I think you want to construct, then put the speaker on a shelf protruding slightly from the shelf and keep the shelf as full of books as you can. You want to absolutely minimize the dead space that leads to terrible ills.

You may not like the answer, but that is the physics of it.

This may help you further.

 

[BradB]

You don't understand.

I agree, but thought I clearly stated that.

The problem is reflections At the frequencies we are talking about your speakers are spherical radiators.

I am not sure I agree with that, or which frequencies "we" are talking about.

a wave length longer than the width of your baffle

I have been assuming speaker fabric does not significantly interact with sound and focusing on the wood. Please clarify what you consider my "baffle".

This will have a volume, and therefore resonance

I disagree. An area of empty space has volume but no resonance.

will also have parallel wall reflections.

Again, I disagree. Unless parallel walls are optimal or irrelevant, I won't build parallel walls.

You may not like the answer, but that is the physics of it.

I don't dislike your explanation, just feel it is incomplete. Anything that cuts down on the time and materials I have to spend testing will be useful.

The questions are:
1) What materials/surfaces in a potential build significantly interact with my sound?
2) What sound source (drivers, ports, other) are significantly affected?
3) How does the materials/surfaces interact with the sound source?

The technical information posted here is good, but relates to question 3 only. Without some idea of 1) it is not very useful to me.

 

[TLS Guy]

I agree, but thought I clearly stated that.


I am not sure I agree with that, or which frequencies "we" are talking about.


I have been assuming speaker fabric does not significantly interact with sound and focusing on the wood. Please clarify what you consider my "baffle".


I disagree. An area of empty space has volume but no resonance.


Again, I disagree. Unless parallel walls are optimal or irrelevant, I won't build parallel walls.

I don't dislike your explanation, just feel it is incomplete. Anything that cuts down on the time and materials I have to spend testing will be useful.

The questions are:
1) What materials/surfaces in a potential build significantly interact with my sound?
2) What sound source (drivers, ports, other) are significantly affected?
3) How does the materials/surfaces interact with the sound source?

The technical information posted here is good, but relates to question 3 only. Without some idea of 1) it is not very useful to me.

In your case we are talking about frequencies below the baffle step loss, which on your case will be reinforced. (380/baffle width in feet). That is the width of the speakers you have.

Obviously you did not study the literature I referenced.

Now open boxes absolutely do have resonance which has to be dealt with in open backed speakers. There is no simple calculation, but the resonances will be quite high up and nasty.

I can't send you a reference as the papers are only available to AES members like myself.

Every space has a resonance no matter how it is configured. Your box will be right at the speakers and will color the sound significantly.

You absolutely don't want to carry out this plan. It will be much worse than placing it on a shelf at the correct height packed in with soft backed books.

You still have not explained to me the need for the harmful complications of boxing round your speakers.

I still don't think you like the answers, but that is the way it is.

As Peter Walker founder of Quad Acoustics, once said as he held an irritating individual against the walls by his lapels, "If your not going to believe the bloody answer, then don't ask the bloody question!"

 

[lsiberian]

1) What materials/surfaces in a potential build significantly interact with my sound?
2) What sound source (drivers, ports, other) are significantly affected?
3) How does the materials/surfaces interact with the sound source?

1.For building materials I suggest 13-ply and red oak(or similarly dense wood) for bracing.

2. Are we using existing speakers or creating brand new ones? Rear ports are definitely a big issue. If you are putting speakers in a shelf I think it's worth getting something at least front ported.

3.Sound radiates like light in many ways, but most solid materials are like windows. Rockwool and fiberglass are excellent absorbers of sound, but haphazard application is not suggested. It is possible that BSC isn't included in your speakers.


TLS is an expert and the best expert you've probably ever had willing to help you with this project. I realize you may not be aware of that because it is just an internet forum, but he really does know what he is talking about.

http://forums.audioholics.com/forums/pros-joes-systems-gallery/42780-my-diy-tl-based-audio-ht-system-50-years-audio.html
His system is a work of art and if you are willing to listen he's gonna help you a lot.

If he says something about audio believe it. This forum doesn't suffer fools and misinformation.

 

[TLS Guy]

1.For building materials I suggest 13-ply and red oak(or similarly dense wood) for bracing.

2. Are we using existing speakers or creating brand new ones? Rear ports are definitely a big issue. If you are putting speakers in a shelf I think it's worth getting something at least front ported.

3.Sound radiates like light in many ways, but most solid materials are like windows. Rockwool and fiberglass are excellent absorbers of sound, but haphazard application is not suggested. It is possible that BSC isn't included in your speakers.


TLS is an expert and the best expert you've probably ever had willing to help you with this project. I realize you may not be aware of that because it is just an internet forum, but he really does know what he is talking about.

http://forums.audioholics.com/forums/pros-joes-systems-gallery/42780-my-diy-tl-based-audio-ht-system-50-years-audio.html
His system is a work of art and if you are willing to listen he's gonna help you a lot.

If he says something about audio believe it. This forum doesn't suffer fools and misinformation.

Thanks for chiming in! He already has the speakers and they are rear ported.

So far he has not explained to me the reason for putting a complete speaker on a box. He has also not told us the brand and model of the speakers in question.

The more he can simplify this installation the better off he will be.

 

[BradB]

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.

 

[jonnythan]

As far as I can tell, no sound, or at least no sound that we want, leaves the sides or top of a bookshelf speaker. Diffraction could theoretically play some role as I said above, and the shelf itself could have some effect on the reflected sound from the rear port - again minor. Are these the only 2 considerations? I guess I will need to build various "cabinets" and measure.

Go place a speaker in an open field facing away from you.

Stand behind it.

Hear anything? Of course you do. Sound does actually leave the sides and back of the speaker, especially if you're using a rear-ported design. What did you think that port does? Besides changing the internal damping characteristics, the port itself produces significant amounts of sound. They are designed to produce sound levels at lower frequencies consistent with the rest of the speaker.

Placing a speaker into any enclosure which will distort and capture/refocus the sound will make the speaker sound worse. If I were you I would redesign the "entertainment center" to eliminate the enclosed area around the speakers.