ohms

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 10:03 am

I have a pair of old school Boston's that say they are 3 ohm. What would the amp ohm load be and watts produced from a ms-275?

Post by **kg1961** » Tue May 26, 2009 10:17 am

3ohm stereo and about 90watt a side would be my guess?

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 11:10 am

would you use passive crossover (xvr2) and also the crossover that is provided by the boston's?

Post by **fuzzysnuggleduck** » Tue May 26, 2009 11:33 am

XVR crossovers are for running a whole system straight from a single amp. If you're not interested in that configuration then stick with the boston crossovers.

Post by **stipud** » Tue May 26, 2009 11:35 am

fuzzysnuggleduck wrote:XVR crossovers are for running a whole system straight from a single amp. If you're not interested in that configuration then stick with the boston crossovers.

If you are doing this, you would use the XVR and boston crossovers together.

Post by **fuzzysnuggleduck** » Tue May 26, 2009 12:01 pm

stipud wrote:
fuzzysnuggleduck wrote:XVR crossovers are for running a whole system straight from a single amp. If you're not interested in that configuration then stick with the boston crossovers.
If you are doing this, you would use the XVR and boston crossovers together.

Oh damn, I guess I should have checked the manual but I was under the impression that the XVR models had separate driver and tweeter outputs.

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 12:28 pm

the reason is that I have a sub that will have 250-275 watts which I think would use up the crossover wattage of 250 watts and I would have to buy another for the boston's?

Post by **fuzzysnuggleduck** » Tue May 26, 2009 12:33 pm

Hmmm, don't quote me on this but I don't think your XVR2 is going to work as expected unless you hookup a load to the "left" and "right" outputs as the xover points are determined by the load placed on the outputs.

I could very well be wrong but I don't think the XVR is meant to be used as a sub-only xover.

Also, if you hookup the front stage on the XVR, it's sharing the power from the amp, so the amount of power the amp puts out is distributed amount the different outputs of the XVR. So just don't exceed the XVR total power handling at the input side and you're ok.

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 12:42 pm

so you think I can run two ms-275 on one xvr, sub on one and boston's on the other ?

Post by **fuzzysnuggleduck** » Tue May 26, 2009 12:56 pm

jwilson273 wrote:so you think I can run two ms-275 on one xvr, sub on one and boston's on the other ?

You could likely run each MS275 bridged into the two XVR inputs, then your sub on the sub output, your boston xovers on each left and right output then your drivers and tweets off the boston xover.

One MS275 is rated for 280W bridged, so times two that might be too much for the XVR. Nothing wrong with scaling them back though... but in that case you almost just may as well run a single MS275.

If you're not looking to run the whole system off the XVR and be limited by it's maximum power handling, I would suggest you look for another xover unit.

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 1:17 pm

your right about the limited power, what xover would you suggest?

Post by **fuzzysnuggleduck** » Tue May 26, 2009 1:51 pm

jwilson273 wrote:your right about the limited power, what xover would you suggest?

If you want to stick with PG and stay with the same era of gear, the AX204a would be a good choice, although it use RNETs (resistor networks) to set the xover points instead of easy to use potentiometers (knobs).

There's also the MX2 which uses knobs instead of RNETs but it's a little rare I think, I don't see them for sale all too often. There's also the MX3i which is just the big daddy of the MX3 and meant for 3-way setups.

If you don't care if it's PG or not, AudioControl makes a bunch of great units as well.

Post by **stipud** » Tue May 26, 2009 2:11 pm

jwilson273 wrote:so you think I can run two ms-275 on one xvr, sub on one and boston's on the other ?

Hold on a sec.

The XVR was designed so you can run components and a sub off of a single stereo amplifier. This was desirable back in the early 90's when stereo amps were common and bloody expensive. A little thing like an MS275 could power a decent setup like this.

However, with multiple amps, there is no use for an XVR. Instead you would need to split your sub/component signal up before it goes into the amp. Some headunits can do this, or you need a crossover like the AX204/MX3i/etc.

Let us know more about your setup. All the gear you have, what you plan to run, etc.

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 2:40 pm

Sony CDX-GT320 head unit w sub out ( el cheap o )
Bostons Pro 6.4 125rms I think combined
Bostons 12" dvc 300rms sealed box
Bostons S85 35rms each
2 MS-275
1 MPS-2240

This is what I got! Thanks for the help!

Post by **stipud** » Tue May 26, 2009 2:55 pm

Ok... you will not be needing an XVR in your install whatsoever. It's designed for something completely different.

Your headunit does not have built in crossovers, so you will need an external one. From PG that means AX204 or MX3i. I also recommend Audiocontrol units.

Also, is your boston a DVC 4 ohm, or DVC 2 ohm?

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 2:57 pm

oh DVC 4 ohm

Post by **stipud** » Tue May 26, 2009 7:34 pm

4 ohm dvc means you can get 8 ohms (series) or 2 ohms (parallel)

In that case you should run it bridged at 2 ohms on the MPS2240. The components would be better off on the MS275. You could also run an MS275 at 2 ohms on the sub as well, but it's not an optimal impedance.

jwilson273 · Post by **jwilson273** » Tue May 26, 2009 8:13 pm

Thanks for your help! need to seek out a xover now.

jwilson273 · Post by **jwilson273** » Wed May 27, 2009 4:30 am

I found the manual for the ms-275/mps-2240. It shows that bridged in 4 ohms = 225 wrms but says its stable at 2 ohms without numbers.

Can you help me understand what that means? Is that like peakwatts/wrms!

knightrider358 · Post by **knightrider358** » Wed May 27, 2009 5:07 am

thats rms @ 4 ohms bridged w a 12V power supply so its actually around 375W x 1 @ 14.4V now Stupid correct me if Im wrong that amp should be ok @ a 2 ohm load and should put out "ROUGHLY" 500W rms bridged right.

knightrider358 · Post by **knightrider358** » Wed May 27, 2009 5:08 am

also that with the amp being updated with new guts almost to a new state since its so old it may not be able to function very long with a stress load like that

Post by **stipud** » Wed May 27, 2009 7:13 am

jwilson273 wrote:I found the manual for the ms-275/mps-2240. It shows that bridged in 4 ohms = 225 wrms but says its stable at 2 ohms without numbers. Can you help me understand what that means? Is that like peakwatts/wrms!

The MS275 is stable at 2 ohms, in that it can power that load without turning off. You can squeak out an extra few watts this way (on dynamic music NOT test tones), but probably not enough to audibly hear the difference. However it is less ideal, since you are running your amp right at the limit. Your amp will run hotter, and you may require additional cooling depending on how it is installed.

Similarly the MPS2240 is stable at 1 ohm bridged, but designed for 2 ohms. It makes the same power at 2 ohms that the MS275 does at 4 ohms. So, since you have a DVC 4 ohm sub, it makes more sense to run it at 2 ohms on your MPS2240. You could also run it on an MS275 for a TINY bit more power (likely not noticeable), as long as you can keep it cool.

Post by **kg1961** » Wed May 27, 2009 7:19 am

I have a white minty ax204a xover if you need?

jwilson273 · Post by **jwilson273** » Wed May 27, 2009 8:33 am

would I need the ax204a or the az406a? I have front, rear, and sub (three way?)

Post by **stipud** » Wed May 27, 2009 8:46 am

jwilson273 wrote:would I need the ax204a or the az406a? I have front, rear, and sub (three way?)

You would need the AX204a if you plan to run with your components passive crossover. The AX204 would split between your sub (MPS2240) and midrange/treble (MS275). Then the passive crossover splits the midrange and treble up to the mid and tweet.

However, you also have the option of installing all three amps, running one to the tweeters, one to the midranges, and one to the subs. In this case you would need the AX406. This is called running "active". It gives you a little more flexibility over your speakers (you can change the volume independently), and lets you modify your crossover frequency to taste, instead of using the factory setting (though in most cases the factory frequency is ideal already). It's a bit more complicated but can be rewarding if you have the proper know-how and equipment to tune it properly. Also depends if you want to install all three amps or just two.

Passive = split frequencies AFTER the amp
Active = split frequencies BEFORE the amp

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