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-   -   A tricky question from a novice (http://www.diyaudio.com/forums/multi-way/80386-tricky-question-novice.html)

msharpe 27th May 2006 10:41 PM

A tricky question from a novice
 
I've been researching and working on my first project for a couple of months now. I plan to finish the thing this Summer. I have a sytem of car speakers that I'm going to use indoors. I was lucky in that the Subwoofers came with a full data sheet, so I already have dimensions for those boxes, but the speakers pose a serious problem. I plan to make four boxes each with a 6.5" two way and a 4X6 three way in each box. Naturally, none of the speakers came with any data. So what should I do to figure out dimensions for these boxes? And also, would it be wiser to give each speaker its own seprate box?

poobah 27th May 2006 10:59 PM

I wouldn't use the 4 x 6 speakers at all. Oblong speakers have issues... they make them that way so they are easier to fit into a car. Also you really don't want 2 different types of speakers sharing the same portions of the frequency range. nor do you want multiple tweeters unless the physical layout is done correctly.

Tell us make, model, and part number for the 6.5's. Someone here may have the specs. Can the tweeters be separated from the 6.5's, and could the tweets then be panel mounted?


;)

PeteM 27th May 2006 11:33 PM

Quote:

I wouldn't use the 4 x 6 speakers at all. Oblong speakers have issues
Oh I thought they were the bees knees

http://www.worldsbestloudspeakers.com/

poobah 27th May 2006 11:46 PM

Round speakers begin to distort when the power reaches a certain level.

Oval speakers are distorted at any power level... the unequal distrbution of cone mass around the voice coil ensures this. It's not a horrible thing... just not good thing.



;)

msharpe 28th May 2006 12:05 AM

The 6.5's are Alpine SPS1629's. I don't think the tweeters can be dismounted. I'll probably just sell the 4X6's, they are a lousy brand anyway. Would it be a good idea to maybe buy a set of tweeters to mount seperately? Thanks for the advice.

PeteM 28th May 2006 12:07 AM

Quote:

Round speakers begin to distort when the power reaches a certain level.

Oval speakers are distorted at any power level... the unequal distrbution of cone mass around the voice coil ensures this. It's not a horrible thing... just not good thing.
It's a sure thing we know the facts those speakers in the link sell for almost 2000 on eBay, what I find strange is all the buyers that have purchased them have been power sellers with +5000 to their name,with 70% feedback or no longer registered users.

Ron E 28th May 2006 12:18 AM

Quote:

Originally posted by poobah
Round speakers begin to distort when the power reaches a certain level. Oval speakers are distorted at any power level... the unequal distrbution of cone mass around the voice coil ensures this. It's not a horrible thing... just not good thing.;)
The distortion from round speakers comes from suspension and BL nonlinearities primarily, not from cone shape.

There is nothing inherently wrong with making an oval driver. In fact, if executed properly cone resonances can be somewhat distributed by the non-circular shape.

Admittedly, most oval car drivers are poorly made, but the limitations are not due to the shape or "unequal distribution of cone mass", but rather due to cost limitations.

poobah 28th May 2006 12:37 AM

ms sharpe

No need to go crazy about the tweeters. Someone will come along here with some rec's for the 6.5's.

If you assume the cone to be a rigid structure (it is not) then any shape with mass-moment symmetry about the voice coil would work. Cones are membranes of sort i.e. not so rigid

chewrock 28th May 2006 12:57 AM

Combing, Resonance, other things
 
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.

poobah 28th May 2006 03:19 AM

Chewrock makes an excellent point...

An infinite baffle is probably best for a car speaker... you don't need a true infinite baffle (ain't such a thing anyway). Just build a box to your liking and put a partial back on it... like a guitar amp.

Consider this also; before you spend alot of money on materials for boxes, think about just buying some new drivers that are intended for the purpose. My point being, if you spend $200 dollars to build boxes... you'll wish someday that you bought proper speakers and designed a box to match.

It all depends, but car speakers are either low efficiency or low fidelity... because they are infinite baffle (stiff suspension).

Decent sounding mids and tweets don't have to cost alot.

;)


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