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PostPosted: 07 May 2016, 05:56 
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Joined: 26 Sep 2015, 13:59
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I've just completed a pair of Zigmahornets as my fisrt speaker build. They are indeed very impressive but definately need bass reinforcement. I'd like to build a sub but don't really know where to start. I am using the speakers in a small room so space is a big issue. I have some 8" B&W bass units from a pair of DM220s it would be great if I could use these. The DM220 is an infinite baffle design, is it likely that the bass units could work in a ported design? I'm thinking possibly about a dipole arrangement. Or would it be better simply to put them both in a sealed box? Beyond that I have no idea how to design a suitable cabinet, all the designs I can find use a minimum of 10" units and I have no desire to shake the foundations!

Any assistance or advice much appreciated.

Thanks,

Mark


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PostPosted: 10 May 2016, 20:29 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Mark. How were you planning to power the subwoofer? Also, what were you planning to use to process the signal (ie low pass / high pass).

Cheers

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PostPosted: 11 May 2016, 03:17 
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Hi,

I have an LM3875 Gainclone I'm currently not using which I thought I could use. I would plan to take the sub output from the back of my Forewatt preamp and put it through a low pass filter, then through the amp, then to the bin using one speaker in the sub for each channel. I have found a low pass filter circuit using a couple of op-amps that I would plan to build cutting off at around 100Hz. I would leave the Ziggys to roll off.

Does this seem reasonable?

Mark


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PostPosted: 12 May 2016, 10:32 
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Hi Mark.

That seems reasonable. However, since you will have good gain with the preamp in place and the LM3875 does not really require much gain, you can get but with a passive line-level crossover.
http://www.t-linespeakers.org/tech/filt ... eHLxo.html

In order to come up with a box design, you will need to know the T/S parameters for the drivers. Do you have a way to measure?

For matching up with a full range unit, 8" can work well. I actually use a sealed 8" to match up with Fostex FX120 speakers.

Cheers

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PostPosted: 12 May 2016, 12:21 
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Thanks.

Unfortunately I do have the T-S params for the drive units and no way to get them. Is it possible to measure them or estimate them in some way?


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PostPosted: 13 May 2016, 11:55 
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Hi, It sounds a bit non-diy, but Parts Express carries a whole line of sub woofer amps....some with very good crossovers that have gain, cut off and variable phase controls. One of these would power your speakers. I would try a ported box pretty much as large as you can use in your space and try a simple vent for the port. An old school way was to make the vent opening equal to 1/2 the area of the speaker cone and then use a sliding cover over it and move it back and forth until the sound was right. Certainly not high tech but with a microphone or sould level meter it can work. BTW they make fairly good external mics for smart phones now that are quite inexpensive and would do the job for this build.

Good listening
Bruce

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PostPosted: 14 May 2016, 04:36 
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Thanks Bruce, I think I might just give this a try.
B&W say they don't give T-S parameters except to their R&D department! Looks like trial and error then unless I can find some way to get hold of measurements.

Mark


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PostPosted: 16 May 2016, 17:41 
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You can measure the parameters following these instructions: http://sound.westhost.com/tsp.htm

And if you plan measure a lot of speakers, http://diyaudioprojects.com/Testeq/DATS/
can make sense.

If space is not a issue, it might be worth considering an enclosure with a similar volume and box tuning of the original speaker cabinets.

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