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Multi-Way Conventional loudspeakers with crossovers

A tricky question from a novice
A tricky question from a novice
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Old 28th May 2006, 04:38 AM   #11
jleaman is offline jleaman  Belgium
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Default Re: Combing, Resonance, other things

Originally posted by chewrock
Hello, I hope I'm not seen as raining on your parade. There are some limitations you should know about.

- Using two speakers that cover the same range of frequencies from the same source can cause an effect called "combing", or "interference banding". Let's assume that both speakers have almost identical characteristics and tone quality. Essentially, the 6" round speaker and the oval speaker will sometimes be in a space and time where they will help each other. From other points in the listening room, or at different frequencies, they will cancel each other out. The reason it is called "combing" or "banding" is that if you plotted the frequency response of the speaker from every different spot in the room, you would see bands of areas that had no sound, and other areas that were 3dbs louder than either of the speakers alone. The solution? Pick the speaker that sounds the best and use that one, only. The other speaker doesn't add anything to sound that you would really need.

- OK, what happens if we assume that the speakers do NOT have the same characteristics and tone quality. Well, now the two speakers will fight each other in the time domain / phase domain. This can cause something called "smearing" in which the location of the sound source becomes difficult or impossible to determine. In effect, the space and time differences between the speakers will cause them to create the illusion that the sound is not coming from any particular location. The solution? Pick the speaker that sounds the best and use that one, only. The other speaker is simply smearing the sound source so that you can't tell where the instrument is, or where the explosion just happened.

Bottom line? Put the speakers on a large baffle and listen to each of them in turn for several minutes at a time. Decide which one is most natural, and then go looking for the characteristics of that speaker, only. Sell the other speakers, give them to charity, or set them aside for another project.

Another thing about car stereo speakers; many of them were designed to be used without a box at all. especially the smaller ones that you are talking about. Have you considered getting an "infinite baffle" design of cabinet? They are very handy for using car stereo speakers, because the mimic a great big sheet of plywood.

Is this like how some *caraudio Tech that call them selve's smart * would say its best to use 15" sub and 2 8".. Kinda pointeless to me.. I've seen soem guys say oh it's the best thing out there.... and how they say it is behond me......
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Old 28th May 2006, 05:04 AM   #12
jamikl is offline jamikl  Australia
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With reguards to the comments made by Ron E about round versus oval speakers I must say I tend to agree. This is the second time I have seen oval speakewrs bagged lately. Back in the fifties, sixties it was mentioned by one or two designers, particularly in U.K. that ovals had some breakup advantages over round speaker if well made. As we seem to be looking back to those times a lot now perhaps it is time to examine, reconsider oval cones again FWIW.
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Old 28th May 2006, 06:18 AM   #13
poobah is offline poobah  United States
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I would agree that they could be made to a higher standard.

To visualize things, take a standard cone shaped paper cup found at a water cooler. Fill with water and squeeze into an ellipse. Now release the pressure... the cup wants to restore its shape to a circle. That is essentially the effect the air has on the cone when it tries to move. In this situation the mass of the water exceeds that of the cone by a long shot.

The mass of the cone, acting alone, exerts an opposite effect.

These effects occur when the cone is traveling out... toward the listener... imagine what happens in the other direction.

It all a balancing act. A round cone certainly doesn't solve all problems. But why invite problems if dimensions aren't an issue?

The "high end" bozos doing this are only seeking differentiation.

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Old 28th May 2006, 07:33 AM   #14
msharpe is offline msharpe  United States
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Wow, it sounds like I have several options here. I think I'm most likely going to just scrap the 4X6's for the time being and just focus on making a set of boxes for the Alpines. The idea of the "infinite" baffle sounds interesting to me. I never even realized you could make a cabinet with a partial back. I'm thinking that this might be a really good option, as I should be able to mount the boxes in some built-in cabinets around the room. So with this sort of system, is the size relatively arbitraty? I think I might just base the dimensions off of my current set of speakers which are also 6.5's. Also, if I were to use an infinite baffle system, could I still use dampening material to make any adjustments?
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Old 28th May 2006, 07:41 AM   #15
poobah is offline poobah  United States
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Yeah... you could mount things anywhere you want. Forget about damping material in the regular sense... you won't damp jack. But rather, think about a non-reflective surface behind your boxes. Plaster/tile is bad... curtains/carpet are good.
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