Newbie question about output power...

[Bill622]

So, here's the thing, i'm planning my very first build of custom made loudspeakers and I have a few questions that maybe someone around here will have the answers.

My home theatre amplifier is a Sony STR-DE445. The output is 80W on all 5 channels. Can't say if it's peak or RMS. I'm guessing it's peak.

I want my loudspeakers to be tall (around 48") and slim so I'm limiting my choices to one 6½" sub woofer combined with a tweeter. They are both 8ohms, by plugging them in parallel to have 4ohms of impedance at the connectors.

Based on a catalogue from my local electronic store, I can only rely on a Goldwood GW-6PC8 sub woofer (100W peak) combined with a Pioneer BDE75-52F (100W).

So my questions are:

1) should both of the drivers allow a power output greater than what my amp. can push (Tweeter and sub)? I just can'T understand how Samsung, Sony or Yamaha can build super slim speakers with 5 drivers in it and claiming it can it can output 150W ?

2) If i'm using 4 drivers: 2 group of drivers in series and then those groups are connected in parallel, i would end up with 8ohms in total, but what would my output be if i use drivers of 80Wpeak ?

3) what's the trick to have the right impedance with many drivers?

I have the software to help me calculate the volume of my box, i just need to choose the right drivers. I want a good frequency range, and flat response...

Thanks!

[Cal Weldon]

Originally posted by Bill622
So, here's the thing, i'm planning my very first build of custom made loudspeakers and I have a few questions that maybe someone around here will have the answers.

Maybe but...

[i]My home theatre amplifier is a Sony STR-DE445. The output is 80W on
all 5 channels. Can't say if it's peak or RMS. I'm guessing it's peak.[/B]

I'm guessing it's RMS

[i]I want my loudspeakers to be tall (around 48") and slim so I'm limiting my choices to one 6½" sub woofer combined with a tweeter. They are both 8ohms, by plugging them in parallel to have 4ohms of impedance at the connectors.[/B]

No, each driver is covering a different part of the spectrum so when paralleled the impedance remains 8 ohms

[i]Based on a catalogue from my local electronic store, I can only rely on a Goldwood GW-6PC8 sub woofer (100W peak) combined with a Pioneer BDE75-52F (100W).[/B]

It helps to provide links so other don't have to look up your drivers.

Woofer: http://www.partsexpress.com/pe/showd...number=290-306

Tweeter:http://www.partsexpress.com/pe/showd...number=270-035

[i]So my questions are:

1) should both of the drivers allow a power output greater than what my amp. can push (Tweeter and sub)? I just can'T understand how Samsung, Sony or Yamaha can build super slim speakers with 5 drivers in it and claiming it can it can output 150W ?

2) If i'm using 4 drivers: 2 group of drivers in series and then those groups are connected in parallel, i would end up with 8ohms in total, but what would my output be if i use drivers of 80Wpeak ?

3) what's the trick to have the right impedance with many drivers?

I have the software to help me calculate the volume of my box, i just need to choose the right drivers. I want a good frequency range, and flat response...

Thanks! [/B]

1) Speaker don't output 150 watts, they take in 150 watts and power ratings are notorious exaggerated.

2) If you connected the 8 ohm drivers that way you would end up with 8 ohms and a power handling of 320 watts peak.

3) The trick is simple addition and subtraction. You already seem to have the basics covered.

Now before you go further you must realize there is a lot more to building a speaker than the questions you have asked. First off, the drivers don't seem well matched. The low cut off for the tweeter is 3K. That's also the upper limit of the woofer. That's not going to work. The drivers should overlap. The woofer should be cut off lower than that or you will end up with cone break-up. They don't include the Fs for the tweeter. This is important to know as you don't really want to XO it below two times the Fs.

You have not mentioned what you plan to do with the XO. Once you have drivers that are more suited to each other, you then have a long process of getting the XO, L-pads, BSC, notch fliters and zobel networks right. This is a very big task and not for the timid.

It sounds like you have good intentions but there's much more to it than what's been asked and spelled out here. I think you should consider a kit speaker. For the extra cost, you get the engineering required to get it right. Much more satisfying than the hit and miss route you're are on now. Trust me on this one. Nothing worse than laying out some good cash to find you headed down the wrong path. I have headed down that path too many times myself to see a fellow addict get hooked on the wrong drug.

If you agree with the kit idea, let us know. there are lot's of good ones out there. Peter McK has a good post with links to see what you're up against.

http://www.diyaudio.com/forums/showt...84#post1606084

My name is Cal and I'm a speakerholic.

[Bill622]

Originally posted by Cal Weldon

I'm guessing it's RMS

Good to know...

No, each driver is covering a different part of the spectrum so when paralleled the impedance remains 8 ohms

I assumed it reacted like in DC, my knowledge of AC is limited...

It helps to provide links so other don't have to look up your drivers.

Woofer: http://www.partsexpress.com/pe/showd...number=290-306

Tweeter:http://www.partsexpress.com/pe/showd...number=270-035

Thanks for those links. I made these choices to have 100W per driver which i think was a bad idea. I originaly made a design with those:
McBride Linear B 6.5, 8 ohms, 80W (peak, based on the sales man), 40hz to 10khz, Fs=50hz.
+
Goldwood GT-520 tweeter, 8 ohms, 50W / 12db / 2.0khz, 2.0khz to 20khz, FS=1000hz.

I planned a second order XO at 4khz. I have BassBox 6 Pro and the frequency response of the subwoofer seams very wide and flat, something i'm looking for.

1) Speaker don't output 150 watts, they take in 150 watts and power ratings are notorious exaggerated.

2) If you connected the 8 ohm drivers that way you would end up with 8 ohms and a power handling of 320 watts peak.

3) The trick is simple addition and subtraction. You already seem to have the basics covered.

So if I understand well, i can connect the two drivers mentionned above (first design) in parallel and i would end up with 8ohms of impedance with a power handling of 130W (80+50)?

Just when i though i had almost enough knowledge to build my new set of speakers, i realize how ignorant I am...

The idea of a kit is something i never though of. But on the other hand, i feel like i'm following a recipe instead of making my own stuff.

I'll think about all that...

Thanks for answering!

[sreten]

Hi,

Output is 80Wrms per channel into 8 ohms and 4 ohms is not allowed.
Your speakers must be an easy load, i.e. solidly 8 ohm for best results.

Your main question is will you use a subwoofer or not. If yes then
small boxes on stands are more sensible than 5 floorstanders.

Tweeters should be at ~ ear hieght, or lower if angled baffle.

Your driver choice is somewhat unknown and therefore difficult to
work with, though they are not particularly expensive, but you
can use known quantities that are very likely much better for
not much more and the end result will turn out vastly better.

http://www.zaphaudio.com/blog.html

The Seas L15 system will be replaced by a MCM 55-3870 / DQ25SC16
system which will sound just as great but cost a lot less.
That will be the next project that shows up on this web site.

Both great high value drivers :
http://www.mcmelectronics.com/product/55-3870
http://www.madisound.com/catalog/pro...oducts_id=8352

See Zaphs driver and tweeter tests at that site

They will be very good but suited to 5 sealed satellites + subwoofer.
A design well worth waiting for. (and buying the drivers
in advance for, before they sell out when it is published).

5 floorstanding high value 6.5"/1" is more difficult in
finding one were the hard work has been done for you.

for no subwoofer :

The Dayton DA175 http://www.partsexpress.com/pe/showd...number=295-335
Can be tuned low in a decent size box, not many 6.5" can.
Around 30Hz in an around 1cuft or so box.

Sticking to PE :
http://www.partsexpress.com/pe/showd...number=297-416 HiV,
see Zaphs tests , it is good value , goes lowish.

If you ask nicely on the forum someone may model the crossover
for you. you should not use an off the shelf c/o or cookbook values.

The resulting speakers will have excellent bass but not be particular
efficient (at all, the price of bass and 8 ohms) or have particulary
high power handling, they will work well with your reciever.
They are however not the way to do it if you add a subwoofer.

/sreten.

[AndrewT]

Originally posted by Bill622
..... my choices to one 6½" sub woofer combined with a tweeter. They are both 8ohms, by plugging them in parallel to have 4ohms of impedance at the connectors.

no, use a crossover to select which frequencies go to the appropriate driver.
Then the speaker consisting of the combined crossover plus two 8ohm drivers will have an impedance of 8ohms.

Buy a ready built or kit. No other choices at this stage of your hobby.

[Bill622]

It seems it's getting worst and worst...

You realize i'm new to this wonderfull world and most of you are suggesting me to buy kits instead of trying something that will most likely fail... I did a few research on Parts Express about DIY speaker kits. I just don't get it. I mean, what's the point of buying something almost already made with fixed parameter and pre-decided look and shape. I'd rather go to Futureshop and buy any pair of speakrs for the same price. I just need to assemble the whole thing.

I want to thank you all who took time to answer me. I must admit i'm a bit disapointed because it seams like i need a much higher level of knowledge to do something. I though i could rely on volume box calculators, XO calculators and a few books about speakers i've found at the library to learn the basics of custom made speakers.

I'll have to think about all this. My goal was to complete my 5.1 system. I currently have 2 Paradigm Titan speakers since 2001. Back then I was in an appartment and I did'nt had the place to do a nice movie room. Now that I have a house, I though I could complete my set by making two front and using my Paradigm at rear.

I opened my Paradigm speaker to see how it was inside. The port is made of a cardboard tube, the crossover is only first order, there are no internal brace of some sort, just a plain box. The result of these speaker are very satisfying for my needs. I know i can't do better than that, but how worst could it be?

I must sleep on this...
Thanks!

[AndrewT]

Hi,
start your speaker project, but accept you may go through a lot of components and boxes before you get what you require.
By then you will have learned a lot about speaker design and building. Put the extra cost and all that time down to acquiring your new skills.
Just don't expect (unless you are very lucky and very talented) to get good results from your first assembly and certainly not cheaper than a ready built.

[PeteMcK]

"I though i could rely on volume box calculators, XO calculators and a few books about speakers i've found at the library to learn the basics of custom made speakers"

Bill622, you can, trust your instincts... learn by doing, like most of these other guys have, and be sure to ask heaps of questions here (just don't expect everyone to have the same answer )

[Bill622]

I think what i'll do is putting everything on paper, well on PC: box design, size, schematic, specs, anything. Before i spent a penny on equipement, i'll ask what you all what think about it....

I think it will be a better approach.

Thanks!

[AndrewT]

= informed decision making.