First home DIY project - need guidance

[Lusso5]

After scouring this board for about half a year, and digesting as much as I can - I'm going to build my first loudspeaker system this month.

I'd like to build a center-channel, to start, next will be a pair of rear channel speakers to add to my fronts I already own, then a sub, to round out a 5.1 HT system.

From Partsexpress:
I bought four of the 4.5" Vifa/JBL 4ohm Mids from the buyout.
And the Dayton 1/2" tweeter 275-065.
I'd like to use these drivers for the center channel, and try to build it first.

My idea was to series-wire the mids into pairs, then parallel-wire the pairs to get one 4ohm group. Then I could use one of the pre-built Dayton crossovers. Per Sereten's advice, I will add "padding" to the tweeter - I'm guessing this is a resistor to attenuate the level? - need guidance here. And will add a parallel series resistor and capacitor to "compensate" for the mids. - I need guidance here too, because I'm not sure what this is. Sounds kind of like a Zobel, but like I said - I need instruction.

I see again and again that a purpose built crossover, tailored to the drivers will be much better, but I'm at the mercy of my limited knowledge. So if someone would like to help me/walk me through building one - I'd be all over that plan. There may be a good x-mas present in it for ya...

As far as cabinets go - I plan on building something slim. MMTMM. But I need guidance on how best to space the drivers from each other.

Well, that is where I'm at now. Temptation wants to push me to build a cabinet and throw these things in there with an off-the-shelf x-over, but I really want to do this right. Any and all help would be greatly appreciated, and recognized as the project progresses.

Thanks.

[michael]

sounds good, id build your own crossover that is simple, dont worry about the tricky things, just make sure the sensitivities of 4 woofers matches the tweeter, if it dont then make an Lpad.
see how it goes and if it sounds good leave t.
you can always change a XO, its actually the easiest thing to change in a speaker other than wire.

[sreten]

will look through this tomorrow, sreten.

[sreten]

Originally posted by sreten
will look through this tomorrow, sreten.

From Parts Express:
>>>>>>>>>>>>>>>>>>>
I bought four of the 4.5" Vifa/JBL 4ohm Mids from the buyout.
And the Dayton 1/2" tweeter 275-065.
I'd like to use these drivers for the center channel, and try to build it first.
<<<<<<<<<<<<<<<<<<

http://www.partsexpress.com/pe/pshow...number=275-065
http://www.partsexpress.com/pdf/275-065g.pdf

5,000 - 20,000 Hz * Magnet weight: 1/2 oz. * Fs: 2,600 Hz * SPL: 90 dB 1W/1m

Very basic tweeter, originally designed by Audax / Polydax.



http://www.partsexpress.com/pe/pshow...number=299-495
http://www.partsexpress.com/pdf/299-495.pdf

Frequency response doesn't look too promising at all.

Power handling: 35 watts RMS/70 watts max *VCdia: 1" *L1: .5 mH *Znom: 4 ohms
*Re: 2.95 ohms *Frequency range: 65-5,000 Hz *Fs: 65 Hz *SPL: 88dB 2.83V/1m
*Vas: .16 cu. ft. *Qms: 1.44 *Qes: .34 *Qts: .27 *Xmax: 3.5 mm

Lets see if we can find the Vifa part equivalent.
Nope, but judging by the frequency responses something in common with TC11WG49-04,
this also has a kink in the impedance, but both occur an octave higher.

Judging by the kink in the impedance curve and the steep drop in the
frequency response there is definitely something going on at 700 to 900 Hz.
It drops 5dB over the octave 600Hz to 1.2kHz.

Not an easy driver to use for midrange at all.

Possibly designed to be used as the bass / midrange for
dipole rears, with two cone tweeters crossed over low.

I can't see an easy way of using these at all.

Except possibly a (B)T/M(B) or (BB)T/M(BB).

sorry, sreten.

[kevyjo]

You could always check out thos little powered speaker modules from apexjr. There very inexpensive, could always try one and see how it worked. www.apexjr.com the are $49

[mpm32]

I too was looking at doing a similar project for a center MMTMM, front ported using 4 TANG BAND W4-656S 4" sheilded drivers wired in a combination of series and parallel to get me 8 ohms, and a TANG BAND 28-847SA sheilded neodymium dome tweeter. Crossed at 2,500. The enclosure would also be narrow; external dimentions of 5"h x 30"w x 19.5"d. Internal volume of around 1 cubic foot. This needs to fit in an available spot due to the wife factor. That's the plus of diy, you can build to fit.

I am very new to this, the box building won't be an issue, I feel I will have problems designing my own crossover so I thought I'd try a prebuilt one.

Anything to look out for when I try this idea?

[Lusso5]

First off, thanks for your responses - I'm glad there are those who will give me the fact to learn from.

I'm still trying to figure the acronyms, so I'm not sure what (B)T/M(B) or (BB)T/M(BB) means.

I gather:
T - tweeter
M - mid
T/M - tweeter-midrange (a cone tweeter?)
(BB) - ?????

Also, Im not sure of the implications of the dip in the impeadance curve on the driver means. I know what it means from a power-supply standpoint, but not from a freq. response standpoint.

Well, looks like from digesting your comments and then looking at the freq. response, this is a dedicated midbass. Not a total waste though - I can put them in the rear deck of my daily driver for rear-fill and build a band-pass x-over for them. What do you think - 150-500hz?

OK, since those drivers are worthless for anything else - I'll move to my rear-channels (which may be my fronts if they end up sounding better than my old Advents).

I have two of the Infinity/Vifa 7" 299-493
http://www.partsexpress.com/pe/pshow...299-493&ctab=2

Specifications: *Power handling: 35 watts RMS/100 watts max *VCdia: 1" *L1: .8 mH *Znom: 8 ohms *Re: 5.45 ohms *Frequency range: 40-4,000 Hz *Fs: 41 Hz *SPL: 86dB 2.83V/1m *Vas: 1.03 cu. ft. *Qms: 2.96 *Qes: .63 *Qts: .52 *Xmax: 4 mm

The response is much smoother, and hopefully I can use it to 2.5-3khz.

If the consensus is that this is a decent driver - I would like to buy two more, to use them in a MTM configuration.

If useable, would someone recommend a good, but relatively inexpensive, tweeter to match up with them? What about the shielded soft-dome and the ribbon at http://www.apexjr.com/speakerstuff.html ?

[kelticwizard]

One piece of advice I can give. You are making both an array-I assume your 4 inchers are in a vertical line, with the tweeter in between the two pairs-and a crossover. That can be tricky.

After examining the crossovers of various center channels, my advice is: go steep slope. Like third order at least. Maybe fourth order.

The interaction of the various 4 inchers can be a pain itself, the last thing you need is to add crossover interaction. On a first order slope, (6 dB per octave), there has to be smooth response for the drivers over a course of four octaves. Which isn't going to happen in a configuration like this.

The steeper the slope, the less interaction between the drivers in different bands, which is what you want.

[SY]

To amplify kw's comments, you also need to understand the difference between an acoustic slope and an electrical one. The acoustic slope is what your real target is, and it will be comprised of the electrical slope of the crossover (including its interaction with the driver's complex impedance) and the acoustic slope of the driver itself. One nice feature of steep slopes is that the alignment of driver acoustic centers is much less critical.

Trying to design a custom crossover is quite a challenge! If you're not comfortable with the idea of measuring complex impedance and using crossover optimizers, you might try something less ambitious the first time around, like a kit. If you're up for the challenge and don't mind doing the hard work of learning all this stuff, you'll find the path frustrating and ultimately very rewarding.

[mpm32]

Thanks for the responses and taking the time to answer the questions of a complete newbie. It figures that what I want to do would be complicated. I am learning - somewhat - about building crossovers and I think I need to do some more reasearch.

About crossover slope;

First order=6db/octave
Second order=12db/octave
Third order=18db/octave? or 24db/octave? or something else
Fourth order=????

I think I need to get a book.

or better software.

Any suggestions on some freeware that will help me make this type of crossover? I was going to start by just buying a dayton premade 2-way at 2,500 hz and seeing how it sounded. Plus it would help me see how these things are put together. I am very good at modifying things that are pre-built, and even better at copying something when I have it in my hand.

I don't expect it to sound good right from the get go but if it helps me learn....