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Old 10th July 2004, 12:23 AM   #1
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Default possible active system

recently i heard an active speaker system, and thought it would be really nice to make one. It was a 2 way active system, and the treble and mids were absolutely amazing! Bass was there too, and nice. Would it be possible to make an active system using the following drivers:
Seas H1212 Tweeter
Seas H571 6.5" woofer

and a dbx electronic crossover:
http://www.zzounds.com/item--DBX223

Any thoughts?? TIA

Dave
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Old 10th July 2004, 02:59 PM   #2
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looks petty good

definitely ok from the electonics end but it may be cheaper to build your own crossover.... if you are going to build the amps. If you are going to use off the shelf amps the pre built xover is the way to go from the time money prespective. I would set the xover point at about 1.5 to 2k. If you use off the shelf amplifiers be care ful of their gains, the two speakers you selected are 91 and 92 dB spl units and would need the their amplifiers to have the same gain.

Some notes on the speakers...
tweeter - Seems like a good unit, you may want to look for a speaker with a better off axis response. The last ime I looked the reasonably priced speakers with really good off axis response typically had a difficult impeadance cure, which isnt a problem for an active system. There may be something better out there but then again there may not.

Woofer - when you design the box use a speaker design program that will let you input the accoustic response data. Then design a ported box such that it has a peak to counter the roll off from the speakers. This keeps the speakers response flatter longer, but it hurts the deep bass response. Powered subwoofers are so cheap now that i never saw this as a ral problem though.
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Old 10th July 2004, 05:12 PM   #3
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Here is the amp i'm currently running (and would probably run the woofer on, with the power turned down a bit)
http://128.134.140.230/en/product/r-150_300_500.html
That amp is the R500. For the tweeter, i would probably use an R300, which run for about $200.

Suppose a different tweeter was used, like maybe the ScanSpeak D2008/8512. The price is almost double, at $52.75 each. It seems to have a better off-axis response though:
http://www.d-s-t.com/scs/data/d2008_851200a.htm
go there, and then click where it says frequency response. The thing i'm wondering about is how to match the woofer to the tweeter, and whether this scanspeak would match well to the seas woofer.

As far as the box design, Winisd shows the correct box size to be about 0.33 cubic feet for a ported box. This gives a tuning frequency of 57.30 Hz. Where would you like the peak to be, and how large? A subwoofer would definitely be easy. A local dealer around here has some nice B&W's for about $350, so that should be all set.
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Old 12th July 2004, 03:21 AM   #4
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The tweeter is pretty much your choice, in my setup I used a speaker from Focal which had really good off axis response but since then they killed it. How much off axis response you want should be based on two factors, cost which you seem to have a handle on, and what you need in your listening space. Why pay to put high frequencies in a part of the room you will never be in?

As far as matching the two speakers there are two main components. Sensitivity or volume and with the crossover above the matching should be trivial. The second is the frequency division, that may give you some problems as the crossover seems to only go as high as 950 - 1K. So to use this crossover the two speakers have to have a flat response at this point to work together perfectly.

About the speaker box sizes - I am not too familiar with WINISD but the last time I used it I was unable to enter the frequency response curve. Thus it assumes a perfectly smooth one, a speaker which I have yet to see. If you get the software to design a ported box then reduce the volume you will start to notice a hump in the response curve. I use this hump to extend the range of the speaker, the hump makes the speaker louder as its loudness diminishes. Usually this is only good for a few hertz maybe 120HZ before to 80Hz after the tweak. Im sure this adjusts the transient response but I haven't yet figured out how to model this.

My best advice is to use a sealed box (If the form factor is good for you) and buy a good sub that reaches the higher frequency range.
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Old 12th July 2004, 03:42 AM   #5
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From the specs, here are the possible crossover frequencies:

Crossover Frequencies
Stereo Mode:
Low/High: 45 to 960 Hz or 450 Hz to 9.6 kHz (x10 setting)

the X10 button enables you to use higher frequencies.

As far as the box, once you simulate a woofer box and specify whether it is ported or sealed, if you enter a new box size where they suggest box size or tuning frequency where they suggest a tuning frequency, then the response graph will change correspondingly. For instance, they suggest a .34 cubic foot box for the Seas H571 woofer. That gives a tuning frequency of about 57Hz. The only problem with a smaller box, is that it might get impractical to build one so small (i.e. you couldn't possibly fit a woofer in that!!) Here is a modeled response of the same woofer in a 0.2 cubic foot box, with the same tuning frequency.
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File Type: jpg new speaker response.jpg (60.0 KB, 56 views)
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Old 13th July 2004, 03:41 AM   #6
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I did not catch the 10x button, seems like smooth sailing as far as system integration goes. I looked at the plot, that seems pretty in line with what I remember. Another way to get the hump is to change the port size, which I had to do originally because it would not fit into the box. Some things never change with small woofers. My last project packed two amps, a crossover, tweeter, port, and a 6 inch woofer into a box 10.5in tall box. I was 7.5 wide and about 8.75 deep - all external measurements.

Sounds like you have a project. Play around with the port and box size if you are interested, but like I said I usually do it to get the size down while streching the frequency response. Small boxes that people can see with improved integration to the large box they usually don't. By the way I have been extremely happy with my active system and good luck.
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