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Old 16th February 2008, 06:32 AM   #1
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Default First DIY - bi amped 2-way standmounts

Hi

I've been lurking here for a while, reading and absorbing the info on offer and I think it's time for my first post.
I'm a student at the moment and term ends in a few weeks then I'll have 6 weeks off some of which to devote to this project, so despite this being ambitious for a first project I think I'll be ok as I have plenty of time.

The idea is to go with an active crossover. I have picked the Behringer CX2310. I can pick it up here in the UK for £60 and by all accounts it's a very decent piece of kit.

For the amplification I have a Harman Kardon HK680 whose bass reproduction I love so much I won't part with it so that will be driving the midbass driver.
I have yet to decide between a T-amp and an LM3886/3875 for the tweeter.
I have seen some debate between these two, but would be glad to hear peoples thoughts. Given it will be driving the tweeter is either one known to be better at treble reproduction?

On to driver choices...

For the tweeter I was thinking about the Peerless 810921. Seems decent value for money and I'm hoping will give me what I need.

For the midbass I am looking at the Scanspeak 18W/4531G 7" Revelator 4 ohm. This driver is expensive but I have read very good things about it and I'm willing to invest the money.


The cabinet then is the next barrier. The speakers might well be placed close to walls so a front ported design is preferable.
I will probably try to use a design I can find. I'll do some more investigation, but I'd appreciate some help with the kind of size of cabinet I might need.

Many thanks in advance, this is a big project for me so all input is very much appreciated.
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Old 16th February 2008, 11:54 AM   #2
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Here is a nice design that uses your prefered mid/bass driver:

http://www.humblehomemadehifi.com/Optimo.html

There is an option to use the Vifa XT25TG30 (much cheaper) with only a small change to the crossover if you decide to go passive at some stage.

http://cgi.ebay.co.uk/2-Vifa-Peerles...QQcmdZViewItem

I know that this is a floorstander, but it does not take up any more space than a standmount, and it is arguably less "messy" looking. The transmission line will get the best low end out of the Scanspeak driver and the "port" faces upwards,
making placement flexible.
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Old 16th February 2008, 01:58 PM   #3
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Unfortunately you won't find too much in the way of active XO designs. Those of us who prefer an active crossover are a distinct minority.

Your chosen XO is pretty basic - although its sound quality is decent, It is better suited to main-sub crossover duty. Without the ability to add EQ, delays or baffle step compensation you're limited to the basic textbook matched slopes.

Not that it cannot work if your drivers have plenty of overlap, but chances areit will be less than optimum. If you can afford the DCX2496 you'll be able to get better results with the flexibility it offers. There is also a group buy brewing for active crossover boards, but t probably won't be completed in time for your break.

My preference would be an LM3886 for the tweeters. I haven't heard the T amp, but I'd like the extra headroom that the LM3886 would offer. It's not that much more expensive.
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Old 16th February 2008, 02:33 PM   #4
eStatic is offline eStatic  United States
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AFAIK ( which is not very) the only problem with using an active xover like the Behringer CX2310 (which I use for my surround speakers) is that they donítí invite response tweaking. Dedicated Xovers usually incorporate corrections to match the drivers and tweak the overall response. For my mains I use the dbx xover with RTA that accomplishes that for you. (Behringer also makes an excellent one) IMIO* muti-amping and active xovers are definitely the way to go.

IMIO = In my ignorant opinion.
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Old 16th February 2008, 04:49 PM   #5
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Many thanks for the input. Unfortunately I really can't accomodate floorstanders, but I could probably live with tallish standmounts. The problem is, being a student, I move about a bit, changing rooms etc and floorstanders are simply too impractical for this.

With regards to the crossover... The DCX2496 is only £140. Admittedly that's quite a bit more, but not excessive in the grand scheme so I will definitely give it proper consideration.

From what I can tell, this is also a 3-way XO. The question then is should I go 3-way instead. This would certainly help with the integration, and with a 3 way system I could set the lower XO point in the middle of the baffle step and simply give the woofer a little extra power. This seems to me quite an elegant way of dealing with the necessary correction.

If I were to choose a 3 way design I would need to choose some cheaper drivers. I have never bought a driver before, but I feel fairly sure that, for instance, a SEAS driver coming in below $100 isnt really going to be that much worse than the Scanspeak costing more than twice that.

So for a 3-way I could go with:
Peerless 810921
MCA12RC (H1304) 4.5" Coated Paper Midrange
For the woofer I would then be looking at the CA18RNX or the P18RNX/P. I think this is just the coated paper/poly versions of the same driver.
The paper version has a more similar Fs to the original scanspeak while the poly cone is higher.

I would then need a couple of T-amps or LM3886s or maybe one of each, and stick to using my HK as a pre and power for the woofer.

That optimo cabinet design looks good, despite the fact I cannot accomodate it. I'll quickly sketch a version I could accomodate in a moment and post it for criticism.

Once again, thanks very much, I really want to do this project and I won't be able to without help. I'm not expectine anyone to design this for me, but these kinds of comments are just what I need.
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Old 16th February 2008, 05:21 PM   #6
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The great thing about active crossovers is that you can easily change your set up without wasting money on expensive crossover components.

If you buy a good mid/woofer like the Scanspeak and build a bookshelf/standmount then you can add a bass driver at a later date and build a three-way floorstander. I think three-way standmount will be hard to achieve and may limit future potential.

Do not be put off good compact speakers. They can go deep and sound every bit as good as larger units.

You should also consider the 15W4531 driver too, along with its sisters, 15W/8530 etc. It may be more suitable in the long run.

http://www.troelsgravesen.dk/Ellam.htm
http://www.troelsgravesen.dk/W1501_95.htm
http://www.zaphaudio.com/ZD5.html
http://www.lautsprechershop.de/english/index_hifi.htm See "Studio 12" under "Scan Speak kits"

The 18W4531 is also used in AOS Studio 22M in the german section here http://www.aos-lautsprecher.de/index.html

The Delta 3 project here http://www.gattiweb.com/index.html demonstrates how you can "grow" from two-way to three-way, by adding the bass driver section at a later date when you have more space and funds available.

I would aslo recommend going for the DCX2496. It is much more capable and will be able to serve your needs for many projects in future years.
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Old 16th February 2008, 06:20 PM   #7
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So Here's the picture I've come up with and a scribble to the side showing the possible eventual arrangement.
Sorry about the crummy photo - finished the sketch, put it in my scanner and a nice little message popped up declaring the scanner is dead...


Also dublin I think I may well go for those tweeters you recommend too, thanks.
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Old 16th February 2008, 07:42 PM   #8
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You could also use that third crossover to go to a sub or two
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Old 17th February 2008, 03:36 AM   #9
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OK. You're definitely right, the DCX2496 is a better idea. I'm fairly sure it has a sub out too, so I can add a sub later if I like in addition to the 3 drivers.

Is there any obvious reason the design I posted above would not work? Is it a problem to have the tweeter so low and might I be better going for WTM?
Also any thoughts on maybe a 3 driver copy of the ZD5?
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Old 17th February 2008, 01:49 PM   #10
eStatic is offline eStatic  United States
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Hard to tell from the drawing but it looks like the cabinet is part of the port. Dont' you wan't to check out the port length and volume needed for your woofer before deciding how to best do that?
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