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-   -   I finally designed and built my first crossover! (http://www.diyaudio.com/forums/multi-way/32287-i-finally-designed-built-my-first-crossover.html)

Jim85IROC 15th April 2004 12:30 PM

I finally designed and built my first crossover!
 
A few weeks ago I bought some of the Parts Express Buyout onkyo drivers to fool around with. I built an MTM using 2 of the 4" "NSB" onkyo/pioneer drivers (PE# 269-570), and an Onkyo tweeter with a neo magnet (PE# 269-776).

For now they are taped into a cardboard box, but hopefully I'll have enclosures built this weekend.

Anyway... an explanation of my development process. After asking a bunch of dumb questions here and getting good feedback, I started to design an excel spreadsheet that would let me play with various crossover values. Here are the CLIO responses of the raw drivers:

http://www.sover.net/~lirace/Jim/onk...ered-graph.gif
As you can see, neither driver exactly has an ideal curve, nor does there seem to be an ideal crossover point.

One of the suggestions that I latched on to was one by Sreten that suggested that I choose individual low-pass and high-pass filter frequencies. That's what prompted me to design this spreadsheet. It allows me to do exactly that, and gives decent visual results.

I wound up settling on crossover points similar to his original suggestion. I'm running the woofers with a 1400hz low-pass 2nd order electrical, and I'm running the tweeter with a 4500hz first order electrical high pass. The approximate result can be seen here:
http://www.sover.net/~lirace/Jim/onk...over-graph.gif
I wouldn't pay much attention to the red "summed" line... I don't trust it, but you can see what the two filtered responses look like individually.

Here's the crossover I constructed:
http://www.sover.net/~lirace/Jim/onk...neer-xover.gif

I don't have any measurement equipment, so I have no idea what the frequency response looks like. it sounds like the upper midrange is lacking, but since this driver is so harsh in the upper mid, I'm not sure that it's a bad thing. I think the problem is that the paired woofers are quite a bit more efficient than the tweeter, and since the tweeter has a bump at the very high frequencies, everything inbetween is getting lost. I may toss some resistors in line with the mids to bring them down a few dB, and remove the phase plug on the tweeters which will provide a much smoother high frequency response. I'm also going to fool with different component values so that I can begin to hear their individual effects on crossover frequencies & slopes.

But overall, I'm quite happy. :smash: Now I'm going to move on to the vifa/jbl buyout mids, which should be a bit easier to work with.

SimontY 15th April 2004 12:42 PM

Hi!

Cool stuff, how much do all the drivers and other parts cost altogether?

Now, I'm no expert so please don't shoot me down... but, I think your lacking midrange could be due to phase difference between the two drivers - you probably ought to have both drivers 2nd order, or just the tweeter 2nd order and bass driver full range (as I have currently) connected with inverse polarity.

I used my speakers FR on the bass and 1st order on the tweeter for a while, and when I added an inductor to the tweeter and adjusted the values I found a more open and pleasing midrange. I suspect one reason for this *could* be the better phase coherance at the crossover/overlap region.

Just an idea anyway. Thanks for sharing your project with us.

sreten 15th April 2004 01:04 PM

Re: I finally designed and built my first crossover!
 
Quote:

Originally posted by Jim85IROC
I don't have any measurement equipment, so I have no idea what the frequency response looks like. it sounds like the upper midrange is lacking, but since this driver is so harsh in the upper mid, I'm not sure that it's a bad thing. I think the problem is that the paired woofers are quite a bit more efficient than the tweeter, and since the tweeter has a bump at the very high frequencies, everything inbetween is getting lost. I may toss some resistors in line with the mids to bring them down a few dB, and remove the phase plug on the tweeters which will provide a much smoother high frequency response. I'm also going to fool with different component values so that I can begin to hear their individual effects on crossover frequencies & slopes.

But overall, I'm quite happy. :smash: Now I'm going to move on to the vifa/jbl buyout mids, which should be a bit easier to work with.

Glad to be of some help, from what I remember one mid/bass unit
crossed over as a I suggested would ~ match the tweeter level.

I don't think I clouded the issue with baffle step correction.

So time to ;). Build a 2.5 way. One of your bass units should be
rolled in 1st order much lower, the other driver keep the crossover
the same so you need new values for the higher impedance.

The frequency of the 0.5 unit is generally held to be 130 /
baffle width, both in metres, I think its nearer 100 / width.

Try tweaking that. Certainly you should try inverting the phase
of the tweeter also, one connection is likely to sound better than
the other but there are cases when it doesn't matter so much.

Also you can consider a TMM for a 2.5 way. If you build a
MTM 2.5 way which way up it is will also affect the sound.

:) sreten.

edit : P.S. which Vifa JBL buyout ? one of them is a nightmare !

Jim85IROC 15th April 2004 01:50 PM

SimontY:

The drivers cost $.87 each, and the crossover parts are a few bucks... maybe $5 total.

The phase difference could certainly be a part of it, and next time I get a chance to play, I'm going to try to reverse the polarity of the tweeter to see how it effects the sound. Since my spreadsheet is rather crude, it doesn't take phase issues into account.

I don't want to run the mid full range because it sounds terrible that way. There is a ton of breakup above 7khz that I want to filter out.

sreten:

I do have intentions to build a 2.5 way as well, but I want to tweak the MTM first. Since I'm doing this strictly as a learning experience, I'm going to try out as many combinations as I can.

The Vifa that I just bought is the 4.5" jbl/vifa jobber. PE # 299-495. Other than a massive dip above 1khz, it doesn't look all that bad. Maybe it'll give me an education on notch filters! I'm going to be using 2 of them in an isobarac sub enclosure that I designed to mate to my tangband full range speakers. I figured that at $6 each, I'd get 2 more to play with.

How much do you think keeping the MTM arrangement for the 2.5 way would effect the sound? I'd rather do this with one baffle if I can help it, and the tweeter is so small that the woofers are still spaced less than 6" apart, center to center. That's closer than a pair of 7" woofers in a typical 2.5 way system.

SimontY 15th April 2004 01:52 PM

Hi Streten,

I think your comments are a little more meaningful than mine were, lol. :rolleyes:

In your opinion, is it reasonable to make a '2.5-way' with MTM positioned drivers? I can't see why it wouldnt be, and I am in an experimental sort of mood :D (currently using electronic BSC and 2-way MTM layout) Apologies for threadjacking, I can just never help myself!! :)

Ooh, one reason it'd work in some cases (mine) - if your seating position fits either the top or bottom mid better than it does the tweeter...

Thankyou

SimontY 15th April 2004 01:56 PM

Ah, we posted almost simultaneously

Jim85IROC - what a bargain!!!

If you can get good sound from such cheap drivers, some wonderful things must surely be waiting round the corner...! ;)

Jim85IROC 15th April 2004 02:25 PM

Well, I wouldn't call this "good" sound. It's tolerable considering what the drivers cost. These mids offer minimal detail, and the highs are very bright.

I'm sure not replacing any of my other speakers with this little experiment, although I do plan to a/b it with my tangband full range speakers when I get those done.

However, I am very happy with my results considering that this is my very first crossover design. As I tweak it, I hope to be able to improve upon it. My only wish is that I was able to measure the frequency response so that I could correlate what I hear to what the response looks like.

sreten 15th April 2004 02:54 PM

Nothing "wrong" with a MTM 2.5 way, usually the top unit
is the midrange so T&M are inverted compared to TMM.

Same issues as a TM versus MT.

IMO if you want to tweak your MTM 2 way then you still
need to implement BSC by cutting the midrange back by
6DB by oversizing the series inductor and possibly adding
a parallel resistor to it.
Again you need to be 3dB down at the baffle frequency,
6dB in the midrange and then c/o as you currently do.
IMO 2.5 way is more elegant, but a BSC'd 2 way MTM
can take more juice in the midrange.

The vifa/JBL is a nightmare as a bass/mid unit, in a sub it will be
fine. It is however entirely unsuited to an isobaric sub and will
work much better reflexed in parallel. We are hardly in subwoofer
territory, 2 litres per driver tuned to 80Hz is about as good as it
gets, unless you drop the port tuning and add active bass boost,
going over 2 litres per driver is not sensible.

:) sreten.

SimontY 15th April 2004 04:11 PM

Ugh, you make it sound so complicated. :bawling:

6db sounds like major overkill to me. I'm only using a little bit right now, too much killed the life totally, god only knows how much in db tho, hehe.

The basic idea though:
Slap an inductor in series with one mid/bass driver (at about 300hz or so), which then becomes the 0.5. Leave the other mid/bass to do everything it was doing already, but connect it in series with a small resistor to balance the sounds out.

Please confirm!!! :xeye:

Thanks!

Jim85IROC - sorry if this is not relevant to your thread

Jim85IROC 15th April 2004 05:06 PM

sreten,

what's so bad about the isobarac arrangement? The box size with the isobarac alignment was very small, which is exactly what I was aiming for with the design. I used an EBS alignment, which yielded a fairly flat response between 45 and 130hz, all in a 4.2 liter enclosure. Since I'm going to be running the sub passively (plus this is $$$$ driven), I don't think active equalization would be realistic.
http://www.sover.net/~lirace/Jim/vifa-jbl-isobarac.jpg

I posted a question about cone excursion last week, and the resulting information indicates that I should be able to get 90dB of output above 50hz, which will be more than enough for the intended use.

Getting back to BSC... that's definately something I want to tackle, but I think that first I should hone my basic crossover skills before getting involved in BSC. These speakers have a very high qts, so their bass response isn't exactly going to be "lean" to begin with. Here are a couple alignments that I've modeled in WinISD. Box volume is 1 cubic foot (28 liters).
http://www.sover.net/~lirace/Jim/onkyo-pioneer-box.gif
To get any flatter, I need to double the volume, which is already excessive for 2 4" drivers. With a narrow (5") front baffle, I suspect that this bloated response should provide reasonably adequate BSC as long as they stay relatively close to a wall.

SimontY:

Don't worry about if it's relevant or not. We're both learning here, and thankfully sreten has the patience to help us with our questions.


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