Speaker Matching

[milsman2]

Currently I am in the planning stages of a 2 way actively crossed over bookshelf speaker. I plan to power these by 4 LM 3886 gainclones and 2 seperate PSU both using kits from chipamp.com. What are your thoughts for these two being my drivers?

Dayton RS150S-8 6" Reference Shielded Woofer 8

Tang Band 25-1166SJ 1" Neodymium Tweeter

I would most likely cross them over at about 2500 Hz.

[milsman2]

Any suggestions or comments?

[wintermute]

Hi Milsman2, it's a bit hard to comment when there are no FR plots to look at. One observation is that the tweeter is roughly 5db more sensitive than the woofer so you would want less gain on the tweeter amp.

What are you planning to use as the active crossover?

edit: found this for woofer. breakup is very nasty, high slope probably required. http://daytonaudio.com/files/specs/R..._specsheet.pdf

Tony. .

[milsman2]

http://www.parts-express.com/pdf/295-354s.pdf

http://www.parts-express.com/pdf/264-834s.pdf

I would like to use a miniDSP actually. I'm a little new at this so how would I go about producing less gain? Can't I use to miniDSP to create baffle step correction for this? I appreciate the help.

[milsman2]

http://www.parts-express.com/pdf/264-850s.pdf

http://www.parts-express.com/pdf/264-868s.pdf

I'm contemplating using these two drivers in my 2 way now. Both have fairly flat frequency responses and fit my power needs and I think these may be the ones I want to use. Tell me these speakers will work for my project! XD

[wintermute]

Hi Milsman2 There are two ways you can deal with the difference in sensitivity, one is to have a small pot on the the high pass section of your active crossover to reduce the incoming signal level. The other is to change the gain setting resistors in your amp to lower the overall gain. See Michaels excellent article for why you might want to do the latter. There is a third, which doesn't really make sense in an active setup and that is to use an lpad on the tweeter, that is what is done in a passive crossover setup.

You have a massive overlap to play with with those two drivers. should allow you (especially if you use a mini dsp) to experiment with different crossover points.

You could easily use the original tweeter with the new woofer you have shown, just make the crossover 3Khz or a bit higher. You could probably go up to 4Khz, but directivity will start to be an issue.

The berilium tweeter is pretty interesting! I'm not sure I'd personally like it as I generally don't like metal domes.

Tony.

[milsman2]

That actually makes a lot of sense and cleared up a few things. I now plan to adjust the gain of the tweeter amp accordingly. However, one of my other issues here is if I indeed use

http://www.parts-express.com/pdf/264-834s.pdf and

http://www.parts-express.com/pdf/264-850s.pdf

the tweeter will in fact be a 4 ohm load necessitating a small supply voltage to the power amp to produce the correct power output. I realize that power is taken and not given so they say but if you look at the lm 3886 output power vs. supply voltage curve, the voltage I would give to the 8 ohm load will not play well with a 4 ohm load at the same rail voltage. Any thoughts on this problem as well?

Also, why would there not be a need for a zobel network in an active crossover as some people have told me?

[wintermute]

Hi Millsman, Yes if you have a 4 ohm driver then the chipamp should run at lower voltage raills.

This will only be an issue if you run the same power supply for the tweeter amp channels as you do for the woofer amp channels.

Even then it may not be an issue as the high frequencies actually have much less power draw from the amp so it won't be working so hard on those channels.

A zobel is generally used to flatten the impedance of a driver so that it works properly with a standard passive crossover network. If you have an active crossover then I don't believe there is any need for the zoblel, as all it will do is increase the amount of current drawn from your amp.

Tony.

[Francec]

Tony,
What do you mean by this;
"as all it will do is increase the amount of current drawn from your amp"?

Frank

[wintermute]

Hi Frank, the normal impedance curve of a woofer goes up as frequency goes up (due to the inductance of the voice coil), meaning at higher frequencies less current is being drawn from the amp.

If you put a zobel on the driver then at higher frequencies (that aren't blocked by the cap) some of the signal gets shunted off to ground, via the resistor in the zobel. The load presented to the amp is more constant (ie it is a flat impedance, rather than rising) but more current will be drawn at the higher frequencies than would be if running just the driver without the zobel.

Edit: maybe I should have left out the "all it will do"... I'm not aware of any benefit for a zobel with an active crossover, the traditional use is to keep passive crossovers happy

Tony.