|   Standing wave question for all you speaker smart guys | eric the red
Mar 8, 2001 2:52 PM | | There has been some talk in here about the demise of intelligent posts or intelligent replies to posts, and I think the solution is this: Want an intelligent reply? Ask an intelligent question on something you are interested in. That said...
After reading the comments on standing waves that m.barnes posted on his norh website, it got me to thinking. I can't quote verbatim what he says at the moment, but simply put, he thinks that the standard box or coffin shaped speaker design is very bad at eliminating standing waves (I imagine surfers LOVE standing waves). And his solution to the problem is his Prism design for norh floor-standing speakers. My question is this, and I would love to hear from people who are directly involved with the designing and building of speakers: 'If standing waves are a big problem in music reproduction, why haven't the majority of speaker builders moved away from the box or coffin shape and tried new shapes for their speakers?' I realize that some companies (think of bi-polar Mirages, Maggies, Nautilus etc etc) have designs that are outside the box, but many, many highly regarded speaker companies still make the same coffin shaped speakers that sound wonderful. I also have done enough reading to know that many companies put different bracing and damping materials inside their speakers in order to address the standing wave issue, but the basic shape remains the same. Speaker companies have very highly-trained engineers that design their products, and if standing waves are such a problem, why haven't these same engineers changed the basic speaker shape that has been around for many mnay years? Thanks in advance |
| re: Standing wave question for all you speaker smart guys | oron
Mar 8, 2001 3:46 PM | | Not sure exactly, but I know my Infinity Delta towers are specifically designed in their "Delta" shape to eliminate (or at least reduce) standing waves. |
| It sounds like... | Azuth
Mar 8, 2001 4:23 PM | | It sounds like most companies go to great lengths to convince the waves that they really aren't in a box at all. |
| re: Standing wave question for all you speaker smart guys | oron
Mar 8, 2001 4:31 PM | | I'm just conjecturing here, but I have some ideas:
1. These companies have been designing for the standard "box" style cabinet for so many years that they have it perfect down to a science, not to mention that their engineers and design software are going to be oriented to that type of enclosement.
2. I'm not sure, but I would guess the math involved in a non rectangular box must get a lot more complex and confusing.
3. There are a lot of companies out there who generally use box cabinets who are also experimenting with different cabinet shapes (like my Infinity Delta's, for example).
4. With all the refinements made in cabinet design, bracing, acoustic dampening, etc., these higher end speaker manufacturers have probably worked ways around standing waves while still using the box style cabinet.
Just some thoughts. |
| re: Standing wave question for all you speaker smart guys | mbarnes
Mar 8, 2001 11:53 PM | | The reason why most speakers are made in box styles is that is is cheaper to do so and because there is no waste of material. The math for calculation a loudspeaker doesn't change with the shape. All loudspeakers are calculated for the woofer. The tweeter doesn't play in the calclution for the size of the cabinet. The specifications of the woofer determine the volume of the cabinet and the tuning of the port.
Given a specific volume, the most efficient (cheapest) way to create this volume is a box. Boxes are also easy to pack. You put them in another box.
If you take a large rectangular piece of MDF, you can cut a loudpseaker with almost no waste. If you try to create another shape, you will waste material.
Standing waves are created by any two parallel surfaces. What happens is that the waves reflect off the surface. The waves that are "out of phase" cancel each other out and the waves that are in phase add to one another.
This does not include deep bass because the standing waves for deep bass can't be created inside the cabinet as the waves are too long to create standing waves. |
| I'm not the intelligent guy you're looking for, but... | gijoe
Mar 8, 2001 6:07 PM | | and I don't have much experience either...
if you open these speakers... are they empty boxes? or they got something inside (besides the drivers, etc) that... man... I wish I studied vocab harder (english isn't my 1st language)... makes the inside not so cubelike...?
I dunno if you get what I mean... |
| Standing wave answer | Richard Greene
Mar 9, 2001 10:14 AM | | Standing waves inside your listening room are much more important,
much more audible, and extremely difficult to eliminate compared with standing waves inside a speaker enclosure.
Standing waves inside a speaker enclosure can be controlled by
stuffing the enclosure with polyester or fiberglass.
For three-way speakers with ported bass drivers, stuffing the entire enclosure would be counterproductive (absorbing energy that you want to exit the port), so a good speaker designer will isolate the mid-range driver and stuff its sub-enclosure with polyester
(if it is large enough to develop standing waves).
Standing waves inside a rectangular enclosure can be spread out evenly
by using golden ratio (0.62x by 1.0x by 1.62x) enclosure dimensions.
The shape of the enclosure has only a small correlation with controlling standing waves because you must absorb energy
to control the standing waves. Changing the shape of an enclosure is not likely to absorb any more energy, although extra diffusion of the reflections inside the enclosure may reduce the strength of the standing waves somewhat (My B&W DM302 speakers make that claim).
There are some enclosure shapes that cause overlapping standing waves from internal reflections. A spherical enclosure, for example, would be the worst for standing waves because all surface-to-surface dimensions are identical, so all surface-to-surface relections would be at the same frequency. A cubical enclosure is bad too -- all three surface-to-surface reflections would be at the same frequency.
I don't know of any enclosure shape that would do much to control standing waves unless there was sound absorbing material inside.
Standing waves develop for frequencies whose 1/2 wavelength dimension
is equal to an internal enclosure surface-to-surface dimension.
For subwoofers, the enclosure is rarely large enough for internal standing waves to develop at the very low frequencies coming from the sub driver (I'm assumimg a low pass filter prevents the sub driver from playing up to mid-range frequencies where a standing wave could develop). |
| Excellent-Thank you :) nt | eric the red
Mar 9, 2001 4:25 PM | | nt |
| What about a 2 way ported speaker? | Tyson
Mar 9, 2001 6:21 PM | | I see the validity of the stuffing approach for a 3 way speaker with a sealed mid driver, or even a 2 way speaker that is not ported. But most 2 way speakers are ported. What do you think the best way to deal with standing waves in them would be? |
| What about a 2 way ported speaker? | mbarnes
Mar 10, 2001 5:25 AM | | Stuffing a port does not reduce standing waves. It does raise the resonate frequency. |
| What about a 2 way ported speaker? | Tyson
Mar 10, 2001 10:19 AM | | I was really wondering what Richard would say about the best way to deal with standing waves inside a 2 way ported loud speaker, since he does not feel that cabinet enclosures make all that much difference. Since 2 way ported speakers are a majority of the speakers made, especially in the medium price ranges, what would he consider the best way to deal with standing waves in such a speaker, as he did not post anything about it in his original post. And also, the point about standing waves in the room is a bit of a red herring. This info, while true, is more relevant to a question on room acoustics than with loudspeaker design. Besides, most room modes are affective only in the bass region & will not affect things like midrange purity or detail, or "boxiness", they way cabinet design, materials, and speaker shape will. Besides, every speaker is going to have problems with bass response in room, unless people either EQ or listen in an anaechoic chamber. |
| Ignore them. Work on standing waves in your listening room. | Richard Greene
Mar 11, 2001 6:29 PM | | I have to assume the speaker manufacturer is smart enough to
build the enclosure in a shape that evenly distributes internal standing waves rather than a cube shape.
There are energy absorbers used in car audio that could be used
to line a ported enclosure rather than 1" thick fiberglass but
they are expensive and the improvement may not be audible.
These absorbers won't soak up much deep bass that you want to exit the port -- actually no thin sound absorber will soak up much deep bass.
It's tough for me to worry about internal speaker enclosure estanding waves when standing waves in a listening room often make the frequency response worse than +/- 10db measured with a slow sine wave sweep at the listening position. |
| Standing wave answer | mbarnes
Mar 10, 2001 5:48 AM | | The standing wave issue is only one issue. All dynamic drivers need some sort of enclosure--unless it is an infinite baffle. The first is the contain the "out-of-phase" information that would otherwise cancel out the primary sound.
The second is to encapsulate a given volume to allow the speaker to control the response characteristics in order to achieve a desired Q that will determine your frequency response characteristics.
Stuffing a speaker will convert some of the energy into heat but not all of it. Using stuffing can reduce internal reflections but it also decreases the volume of your cabinet.
There are many articles that say it is a bad idea to damp behind the woofer as it restricts airflow.
The idea behind the nOrh is to force the energy through a horn backwards. This increases the impeadance for the entergy inside the speaker. The design doesn't allow energy to reflect back on the woofer. In standard boxes, the energy that reglects off the back wall will reflect back to the woofer. The woofer is less rigid than the rest of the cabinet. Therefore, if the woofer tries to work harder, the impeadance increases, meaning it takes more and more energy to produce the more sound.
I think that it is fair to say that if you can reduce reflections and standing waves without resulting in stuffing a speaker, the results will be better. |
| Standing wave answer | Richard Greene
Mar 11, 2001 6:37 PM | | Some dipole speakers have no enclosure and sound good,
such as the dipole 15" bass spesakers in the Legacy Whisper,
the best sounding speaker I've ever heard in a private home.
Stuffing increases the effective volume of an enclosure
(you incorrectly wrote "decreases").
Stuffing a ported enclosure is obviously not a good solution
to internal standing waves because it would restrict port
output. |
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