3 x LM3886 one transformer for active triamp system

[Tex Houston]

Hello all. I'm wanting to build a tri-amp active speaker. Would it be possible to run three amps off one power supply using boards from chipamp? I'm figuring the tweeter will be use much less power than the mid and the mid less than the woofer.
It would also be nice to run the crossover from the same power supply - regulated after the amp power supply. Too ambitious? Any comments appreciated!

[AndrewT]

Hi,
If you pick three drivers with the same sensitivity then all three drivers require the same voltage from the power amp.

Tri-amping will require a similar constant voltage drive for constant SPL.

However, you can and should adjust the voltage to take account of sensitivity of your chosen drivers. i.e. a 100db tweeter will require half the power of a 94db mid and quarter of the power of a 88db bass driver. These are strictly voltage sensitivity SPL/2.8Vac not SPL/W.

If you mix drivers of different sensitivity, your amplifiers will require different transformer voltages. This makes sharing less manageable.

[WE91]

Hi.

The different requirements to each driver is best taken care of in an active crossover, thus taking care of crossover-slopes and sensitivity. There are several analogue active crossovers for DIY out there. There are several advantages and many traps. One of the most noticeable advantage is less distortion/coloration from passive parts. One of the traps is having control over the crossover-slopes, phase and characteristics of your driver through the funtions of the active electronics. The easiest way of having control with an active crossover, is choosing a digital one. There are several out there to be had. Some have measuring microphones and will adjust to the correct parameters for your speakers and room. The coloration and general effects of a passive filter is by magnitudes worse than what a good digital crossover adds.

Good luck with your project.

Regards
Aril

[WE91]

Hi again.

Alternatively, just keep your passive filters.
The various sections in the passive filter, supplies the driver with the correct frequencies, EQ and are matched to the sensitivity of the other filter and driver "sections" in your speaker. So, parting your passive filter up into sections for low-pass, band-pass(?) and high-pass, you will get a bi amplifiable (two way speaker) or tri-amplifiable (three way speaker) passive crossover, and this really does the trick for you, allowing you to tri-amplify!

I forgot to say that implementing an active crossover means bypassing your passive filters (connecting the amp directly to the speaker units). If some EQ should be impossible to implement in the active crossover, it may be that you need some passive components to do this, - but with the DSP filters of today, you should be fine. Another problem is that you may need to measure the performance of each driver in the speaker without the passive filter, so that you know what you are doing in the digital crossover. You then have to measure during the process of doing the EQ in the digital crossover, to verify and know what you're acheiving. The best of the DSP filters of today, does the measuring and corrections themselves, making it much, much easier to implement such a filter.

I found some products, articles and links:
http://home.pacbell.net/donwm/
http://www.americanmusical.com/item--i-BEH-CX2310.html
http://www.abesofmaine.com/item.do?item=RNAC24#detail
http://www.musiciansfriend.com/produ...496-Crossover?
http://www.americanmusical.com/item--i-BEH-CX3400.html
http://www.newformresearch.com/tweaks.htm
http://www.proacousticsusa.com/produ...l.php?pId=1543
http://www.qscaudio.com/products/dsp/SC28/sc28.htm
http://www.theelectronicsshop.co.uk/...io%20acx23.htm
http://highlite.omc.net/index.php/hi...cessing/dlm_26

Or have a look at, among others, this thread:
http://www.diyaudio.com/forums/showt...?postid=691851

[runebivrin]

Originally posted by AndrewT
Hi,
If you pick three drivers with the same sensitivity then all three drivers require the same voltage from the power amp.

Tri-amping will require a similar constant voltage drive for constant SPL.

However, you can and should adjust the voltage to take account of sensitivity of your chosen drivers. i.e. a 100db tweeter will require half the power of a 94db mid and quarter of the power of a 88db bass driver. These are strictly voltage sensitivity SPL/2.8Vac not SPL/W.

If you mix drivers of different sensitivity, your amplifiers will require different transformer voltages. This makes sharing less manageable.

This is really confusing the issue more than necessary. It's true that drivers of different sensitivity should have their amplitude adjusted to reflect this.

But this has little to do with power supply voltage. It's a matter of gain structure.

The supply voltage for each driver depends on the maximum amplitude sent to that driver, but it's safe to assume that the bass driver will be fed with the greatest amplidude. One could therefore argue that the amplifiers for mids and tweeters could be supplied with a lower voltage, but there's nothing other than slightly smaller heat generation to be gained from that.
So by all means, share the power supply. Just make sure it's beefy enough to reduce interaction between the amps.

Rune

[ttan98]

look at this site:
http://www.linkwitzlab.com/xo_eq.htm


particular at the bottom of the page on amplifier, lots of details, read carefully you will find lots of useful info. No ******** here.

Mr Linkwitz has 35-45 years of designing experience.

[ttan98]

******** means b**l s**t

[WE91]

Hi ttan98.
My answer above also takes into consideration that drivers not necessarily measures flat. They may have ressonances in addition to many other effects. A correct EQ means that you have to measure your drivers. With an analogue filter it may be, depending on driver units, very difficult and complex to make a correct EQ. I'm not responding to attempts at muscle-flexing (my fathers stronger than yours stuff), I'm merely pointing out that optimum results can be had doing this many different ways, but that there's two ways that stands out. One is to do it simple, and use your existing passive filters, the other is going digital.

[ttan98]

I am not refer to you.

I just want to direct Tex to the site in designing integrated/power amplifier correctly, and not with reference to designing op amp. for x-over or equalizer.

[AndrewT]

Originally posted by runebivrin


This is really confusing the issue more than necessary. It's true that drivers of different sensitivity should have their amplitude adjusted to reflect this.

But this has little to do with power supply voltage. It's a matter of gain structure.

The supply voltage for each driver depends on the maximum amplitude sent to that driver, but it's safe to assume that the bass driver will be fed with the greatest amplidude. One could therefore argue that the amplifiers for mids and tweeters could be supplied with a lower voltage, but there's nothing other than slightly smaller heat generation to be gained from that.
So by all means, share the power supply. Just make sure it's beefy enough to reduce interaction between the amps.

Rune

Hi Runebivrin,
yes, designing is not straight forward.
No, bass drivers with equal sensitivity to the other drivers do not need more amplitude. That is going to be the point we will have to disagree on.
If you use a widebandwidth bass driver it will by design have a lowish sensitivity. Some can be around 80db/2.8V to 84db/2.8V.
Choosing a treble driver with a sensitivity of 100db/2.8V will require one tenth the amplitude to one fifth of the amplitude sent to the example bass driver. That equates to 1% (-20db) to 2.5% (-16db) of the power.
If instead you chose drivers with the same sensitivity then all the drivers will require the same amplitude (=voltage).

Finally, if one decides to use mixed sensitivity drivers then one has a choice:-
Supply the same power and the same amplitude to each but, turn down the gain setting (your gain structure) on each of filters feeding the drivers of high sensitivity,
or,
Supply each driver from an amplifier with the correct potential maximum amplitude and the matching PSU voltage. This option more closely matches the requirement that Tex was asking for when he said

I'm figuring the tweeter will be use much less power than the mid and the mid less than the woofer.

If one chooses the first option then much of the power designed into the mid and treble amplifiers never gets used.
Choosing the second option will very likely require different PSU voltages. This second option also allows high quality mid and treble amplifiers and go for a lower quality brute force bass amplifier.