# Acoustic effect of placing speakers against wall or on shelves?



## PuckDaddy

I've read that stand-mounted monitor speakers (many of which are called, ironically, bookshelf speakers) should be mounted some distance away from the back wall when used as L & R speakers. I've also read that there should be some space between them and the side walls as well.

What is the effect of placing such monitors directly on a shelf or countertop within 1' (or less) of a rear wall?

What effect is there of having them within 1' or less of a side wall?

In my case, I have a pair of ACI Sapphire 25th Ann. speakers that I'm using for my L & R speakers (along with an ACI Protoge center). I would prefer to stand mount them, but that is just not practical for WAF and kid-friendly issues.

How much am I losing by placing them close to the rear wall?

Thanks!


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## bpape

I know the Sapphires very well. I displayed with Mike D several years at RMAF. Great speakers. The rear port will not be happy that close to a wall so you will lose some bass extension and get an exaggerated midbass hump from the boundary reinforcement as well as losing their tremendous ability to through an extremely deep soundstage.

Bryan


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## PuckDaddy

Wow, I suspected I asked this question in the right place! I love the Sapphires and don't want to part with them, so I need to find a kid and WAF-friendly way to give them some air to breathe. How much space behind them is ideal for the rear port?

Along the same lines, I have my Protege mounted on an open shelf beneath my plasma with about 1' of space between it and the rear wall. Am I losing much by having it on a shelf?










Thanks!


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## tonyvdb

Two things that dont work well with speakers. Having the sides or the top and bottom of the front of the speaker recessed in a shelf will cause some degradation of the sound as well. Always have the speaker sticking out not recessed if possible. another issue with rear ported speakers in a shelf is that the sound coming out the back of the speaker should be in the open allowing that sound to reflect naturally off a rear wall.


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## bpape

If there is a full foot behind them, the ports will breathe OK so that's not a huge problem - just not as open as with a few feet behind them.


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## PuckDaddy

tonyvdb said:


> Two things that dont work well with speakers. Having the sides or the top and bottom of the front of the speaker recessed in a shelf will cause some degradation of the sound as well. Always have the speaker sticking out not recessed if possible. another issue with rear ported speakers in a shelf is that the sound coming out the back of the speaker should be in the open allowing that sound to reflect naturally off a rear wall.


Understood. Eventually I will wall-mount my plasma and move my gear to a different rack, which will allow me to get the center channel out from its shelf. Luckily, it is a sealed box design so it has no rear port.










The Sapphires (L & R) are rear-ported will need some space behind them, so I'll try to figure out a way to secure them. The last thing I need is a heavy (40lbs) speaker falling over on a kid!

If I have to place them approximately 1' from the rear wall, would adding acoustic treatment to the rear wall help? If so, what kind of treatment is recommended?


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## Skylinestar

I have a similar question but it's about a dedicated speaker stand vs a cheap table.

Currently I have a set of Klipsch bookshelf speakers sitting on cheap Ikea Lack side tables. Will I get big improvement if I place them on a rock stable speaker stand?


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## bpape

Any time you have a large surface close to the speakers (like a table top) you'll get boundary interactions from that surface in the midbass through the lower midrange in the form of reinforcements (peaks) and cancellations (nulls). Dedicated stands which are very rigid and have a small base for the speakers to sit on avoid that problem as well as concentrating the speaker's weight so it's harder for any of the driver motion to move the cabinet and stand/table itself. That helps to reduce muddiness and improve focus.

Bryan


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## PuckDaddy

bpape said:


> Any time you have a large surface close to the speakers (like a table top) you'll get boundary interactions from that surface in the midbass through the lower midrange in the form of reinforcements (peaks) and cancellations (nulls). Dedicated stands which are very rigid and have a small base for the speakers to sit on avoid that problem as well as concentrating the speaker's weight so it's harder for any of the driver motion to move the cabinet and stand/table itself. That helps to reduce muddiness and improve focus.
> 
> Bryan


Center channel speaker placement often suffers from the same problem. In my case (see photo a few posts up), I have a shelf above and below the speaker. I can isolate the speaker from the lower shelf with something like an Auralex foam pad, and can also move the speaker so that it is flush with the edge of the shelf, but would that help the situation at all?

Thanks,
Ken


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## Skylinestar

bpape said:


> Any time you have a large surface close to the speakers (like a table top) you'll get boundary interactions from that surface in the midbass through the lower midrange in the form of reinforcements (peaks) and cancellations (nulls). Dedicated stands which are very rigid and have a small base for the speakers to sit on avoid that problem as well as concentrating the speaker's weight so it's harder for any of the driver motion to move the cabinet and stand/table itself. That helps to reduce muddiness and improve focus.
> 
> Bryan


The bookshelf speakers are placed close to the front edge of the Lack side tables. Currently I don't have Auralex Mopad or anything expensive to isolate the speakers. I do place them on top of a packaging hard sponge. Sometimes I do wonder if those sponges are doing anything to isolate.

Currently, I think I have poor mid. I'm hoping that changing whatever that the speakers rest on will help improve the sound.


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## bpape

Bass radiates spherically in 3 dimensions. Close to the front is better than back farther but the larger top is still causing boundary interactions.

Bryan


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## PuckDaddy

bpape said:


> Bass radiates spherically in 3 dimensions. Close to the front is better than back farther but the larger top is still causing boundary interactions.
> Bryan


Understood. Thanks for the explanation. I suspect that poor placement of my CC is part of the reason why dialog is difficult to hear, even with Audyssey applied. Eventually I'll mount the TV on the wall, rackmount the gear, and put the center on its own stand. For now, though, I'll settle for moving it closer to the edge of the cabinet and elevating it slightly to decouple it from the cabinet.

Ken


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