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Multi-Way Conventional loudspeakers with crossovers

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Old 5th January 2005, 01:34 PM   #1
bigerik is offline bigerik  Canada
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Default Would like advice on my new Seas project

Hi All
My first speaker project in almost a decade is up and running. Stumbled onto some Pro-Ac response 2 Cabinets that were about to be trashed, and seeing how I couldn't let that happened, I decided to build something into them. After some researching, decided to put some Seas CA 18RNX woofers and 27 TFFC tweeters into them.
Put them together first with just a 4.7 cap on the tweeter, and found a lot of detail, but INCREDIBLY bright sound. Measured the response in a local anechoic chamber, and found a big hump from about 3k on up.
With some local help, put a crossover together. 2nd order butterworth on the woofer (.72mh coil and 5.6 cap) and a 3rd order on the tweeter (7.1 cap followed by a 15 cap with a .29mh coil and a 2.2 ohm and 10 ohm resitor). Sounds much smoother now, with still some brightness/thinness. Letting them break in now. Still have to tune the port (impedance measurements showed that Pro-Ac tuned it to 50hz whereas the driver looks like it would be happier at 45hz). Oh, and the straws in the port are gonna go too!
Anyway, anyone have any thoughts or suggestions on this combo? Anything I have obviously done wrong?
Thanks!
Erik
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Old 5th January 2005, 02:28 PM   #2
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Has the reponse when the tweeter polarity is reversed been measures? You can most of the times always get a nice smooth response with the correct polarity, but when the polarity is reversed you can quite easily not get a notch.

What you want to see is a nice deep null around the xover frequency when you reverse the polarity, this shows that the drivers are in phase thru the xover region.
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Old 5th January 2005, 08:28 PM   #3
bigerik is offline bigerik  Canada
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Unfortunatly, I don't have ready access to the testing equipment. What I do wanna do is establish a baseline that sounds ok and then go back and re-measure again.
I do appreciate your tip. Will do so when I get the chance!
Erik
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Old 5th January 2005, 11:25 PM   #4
EspenE is offline EspenE  Norway
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These are very nice units.

.7mH on the woofer sounds a bit on the small side. No wonder that the sound seems bright. I would shoot for something like 2.5mH combined with 12uF, which probably would give a xover freq of about 2000Hz with a nice 4th order rolloff.

And to match that: a second order topology on the tweeter with around 10uF, 0.2Mh in parallell and some resistors for setting of level should be a good place to start.

Happy testing!

EE
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Old 7th January 2005, 08:32 AM   #5
bidland is offline bidland  Norway
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Dear bigerik,

I happened to have these drivers measured and ready for simulation, so I can give you a possible crossover solution for your drivers.

In series with the woofer a 2.4mH inductor, and in paralell a 10uF capacitor. Simple 2. order network.

For the tweeter also a 2. order with a twist....
Series cap 7.5 uF and in paralell a resistor and inductor (in series with each other) 3.6 ohm and 0.33 mH. The dc resistence of the inductor should be subtracted from the resistor value.

Say you have an inductor with a dc resistence of 0.6ohm , then the resistor should be 3 ohm. Not extremely critical, but it's a way to shape the highpass Q-factor to get a good phase transition between HP and LP.

Then in series with tweeter a 5.1 ohm resistor , and in paralell, forming an L-pad, a 10ohm resistor.

Both drivers should be connected with the same polarity.

This should give you a good starting point for some fine tuning. Maybe you have to adjust the series resistor for the tweeter to find the right balance that you like.

Remeber that this is a simulation and I have not listened to this, so don't be afraid to adjust the filter to your liking. This simulation works with a inter-driver spacing of 158.5mm center to center, and a baffle layout I also can send you, if you are interested.

Crossover frequency is 2.2 kHz, and system sensitivity with bafflestep compensation is 85 dB SPL @ 1m with 2.83V input.

Regards,
Bjorn Magne Idland
Lab technician
Seas Fabrikker AS
Attached Files
File Type: zip ca 18rnx & 27 tffc crossover.zip (37.1 KB, 448 views)
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Old 7th January 2005, 10:00 AM   #6
santi is offline santi  Thailand
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Hi Bigerik
Look at the datasheet. Your mid/woofer is 8 Ohms, 88 db. Your tweeter is 6 Ohms, 91 db. The tweeter is more efficient than mid/woofer. You need to attenuate level of the tweeter.
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Old 7th January 2005, 02:10 PM   #7
bigerik is offline bigerik  Canada
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Default Thanks!

Wow!
So much great advice. Thanks everyone!
Bjorn, I would love to see the baffle layout you suggest.
Now I just have to fin caps and coils locally of those values!
Thanks again
Erik
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Old 7th January 2005, 03:19 PM   #8
bidland is offline bidland  Norway
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I noticed that the attachment in my previous post wasn't downloaded with the right filename.

Just rename it with a .zip extension and unpack as normal.
It contains a MS Word document.

Bjorn Magne
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Old 7th January 2005, 04:17 PM   #9
bidland is offline bidland  Norway
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I'll get back on monday with the baffle dimensions.

BM
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Old 8th January 2005, 05:25 AM   #10
bigerik is offline bigerik  Canada
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Hi All
Looked all the great info you guys have given me and I must say I am confused. When we ran the speaker specs thru some software up here, it kicked out a .72mh coil and 5.6 cap for a 2.5k crossover, yet everyone here is recommending 2.0+ for the coil. Now my understanding is that this would be due to baffle step compensation. But it is a pretty huge difference! Now, using the numbers that originally got me the .72 coil, 2.4 would give me a 800 mhz crossover point. Just a little low for a 2 way, me thinks!
Anything else I am missing here? Just wanna make sure I understand!
Thanks
Erik
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