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Old 14th June 2006, 08:28 AM   #1
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Unhappy Newbie Questions etc...

Hi all,

As I mentioned in my intro, Iím a mech engineer, but a total noob to DIY audio. I have a whole list of questions etc, and couldnít find the answers I wanted in a quick search. So I thought Iíd start a new thread. No doubt Iíll come up with a hundred more questions as we go along. So, right off the bat, Iíd like to thank anyone for any help that I get. And please excuse my total ignorance in some areas.

System Composition:

Firstly, I think my first DIY project will be a subwoofer. I will most likely incorporate a plate amp into the box. These have a built in crossover (active I believe). So does this mean that you use this amp to drive the sub plus the other speakers? Or is it simply to ensure that only the low freqís go to the sub? If this is the case, wouldnít there need to be another crossover that is matched to the variable one in the plate amp?

What Iím getting at is that I want to know how a standard system would fit together. Isnít a separate amp usually used to power the mid/tweeter speakers? If so, where does it go in the loop? The plate amps have high level in/out and line level in/out. I figure it would go something like:
Line out of PC/DVD/CD etc etc.. into sub, sub crossover splits frequency, amplifies the low part only, and mixes L/R channels. Take stereo line out of sub, which is now only high freq, into other amp with no crossover, which amplifies signal for other speakers.

I donít even know if this is how these amps workÖ

A guy at work is going to give me an old 40W RMS/channel 2-channel amp that he designed and built a few years ago. The way I figure it, this shouldnít be too bad, provided itís only processing the top end? Therefore, I need to make sure any crossover components filter the signal prior to feeding this amp. Correct? This is why I am looking at the option above. Is there an easy, better way to do this?

PC Integration:

If my PC sound card has a subwoofer output (line level), does this mean that the crossover component has been done? If so, is there a software way to alter the crossover frequency? Or is it a better idea to not use this output, and take L/R signals and do your own processing before feeding amp(s)?

Power/Frequency:

For a home system, what are reasonable power values to be driving to speakers for good quality sound at decent levels (ie: party-proof)?
Also, what are decent crossover points for sub, mid, tweeter? Bearing in mind that (to an extent) I can design my system around these if needs be. Or is it better to design the crossover(s) based on the system setup? Also consider that my components donít need to be pro quality, but Iíd like to get good sound, including good bass response for music, and possibly home theatre, for as little cash as possible (aah, the unachievable dream).

Anyway, thanks for reading my rantÖ if you can shed any light on any of this, thatíd be great.
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Old 15th June 2006, 08:58 AM   #2
AndrewT is online now AndrewT  Scotland
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Hi,
most of your questions are discussed at length by ESP http://sound.westhost.com/articles

The active sub with built in amp needs a line level signal.
A passive sub needs a speaker level input.

Some subs have an output to drive speakers, or to drive the higher frequency amplifier or not at all.

All addon subs have a crossover that removes the higher frequencies.

I would suggest that your build an active crossover that splits your frequencies before sending the music to your amps.
This allows the sub to be active but without it's own dedicated crossover. This is different from most of the retail versions.
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Old 15th June 2006, 09:11 AM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
forgot about party proof.
For domestic listening at normal levels i.e. talking seems to have the same volume as someone actually standing talking to you, you will need an enormous amount of power with uncompressed signals. This would try to reproduce the full range of SPLs found in nature.

We will have to settle for fewer SPLs.

Our normal domestic systems can mange with about 10W (+10dbW) to 100W (+20dbW) into speakers of 86db/2.83V to 90db/2.83V i.e. a total of about 100dbA to 105dbA.

For party levels you will have to settle for about 90dbA, anything more will annoy the neigbours. Unless you invite them along and then you could aim for 120dbA peak (with 90db/2.83V speakers you now need about 1000W peak. We are into disco levels now and probably disco quality.

If you look at passive bi-amping and active speakers (ESP) you should find that your individual amps can be substantially less than 1000W to achieve similar SPLs.

Sorry for all that, since I have given options and no real answers.
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Old 16th June 2006, 05:17 AM   #4
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Quote:
Originally posted by AndrewT
Hi,
most of your questions are discussed at length by ESP http://sound.westhost.com/articles

The active sub with built in amp needs a line level signal.
A passive sub needs a speaker level input.

Some subs have an output to drive speakers, or to drive the higher frequency amplifier or not at all.

All addon subs have a crossover that removes the higher frequencies.

I would suggest that your build an active crossover that splits your frequencies before sending the music to your amps.
This allows the sub to be active but without it's own dedicated crossover. This is different from most of the retail versions.
thanks for the assistance... will look into it in a bit more detail on the weekend

couldn't seem to get into that site though... haven't bothered visiting the root site yet (should really be working), is there a rego required or something?
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Old 16th June 2006, 06:23 AM   #5
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http://www.sound.westhost.com/articles.htm
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Old 16th June 2006, 08:34 AM   #6
AndrewT is online now AndrewT  Scotland
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Hi,
thanks for correcting my bad link.

I should have checked it while edit was still live.
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Old 16th June 2006, 09:36 AM   #7
Wombat2 is offline Wombat2  Australia
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What area of Brisbane are you? I'm in Chapel Hill.
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Old 20th June 2006, 12:30 AM   #8
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Quote:
Originally posted by Wombat2
What area of Brisbane are you? I'm in Chapel Hill.
Ferny Hills.


Thanks for the replies guys. I had seen that website before, but never spent a long time reading.

Still going
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Old 22nd June 2006, 07:50 PM   #9
preiter is offline preiter  United States
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There are several options for hooking up a subwoofer.

Most plate amps have the option of connecting a speaker level output from your amp into the subwoofer and sending speaker level outputs to your left and right mains. This is the easiest method to hook one up, and also the lowest sound quality. It also has the drawback that your amplifier is still driving the full range signal.

Some plate amps I have seen have a built-in active crossover. Pre-amp output goes to the subwoofer in, the sub-woofer line level output goes to the main amplifier. This is a good option if your plate amp has this feature and you have a discrete pre-amp. It will depend on the quality of the crossover built into the amp, however.

Some home theater amps have a built in active crossover with a subwoofer output. This is the easiest option, just hook up the subwoofer to the sub output. Your computer has that as well it sounds like. Be aware that this locks you into using the computer's sound card and volume control. It may not be the highest quality.

Or you can buy / build a discrete active crossover. This is probably the most flexible option and the best sound quality.
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Old 23rd June 2006, 10:10 PM   #10
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Default Newbie system suggestions

System Composition:

"Firstly, I think my first DIY project will be a subwoofer. I will most likely incorporate a plate amp into the box. These have a built in crossover (active I believe). So does this mean that you use this amp to drive the sub plus the other speakers? Or is it simply to ensure that only the low freqís go to the sub? ..."

I attended a local flea market and copped a very old BSR subwoofer just to get the box. ... throwing out all the wiring, speaker, stuffing, crossover (if you could call it that) and have ordered one of those very interesting Hypex woofer amps and will pick up a healthy 15" locally as well. (Local purchase & pickup save big bucks on shipping partical board and big magnets = more to spend on components.)

"What Iím getting at is that I want to know how a standard system would fit together. Isnít a separate amp usually ..."

I'll leave this to other more expert than I ...

"A guy at work is going to give me an old 40W RMS/channel 2-channel amp that he designed and built a few years ago. The way I figure it, this shouldnít be too bad, provided itís only processing the top end? ..."

Try it before you condem or condone it ... some of the "old" stuff is very, very good. (Check out all the folks that mod and upgrade their big Mcintoshs.


"If my PC sound card has a subwoofer output (line level), does this mean that the crossover component has been done? ..."

Maybe, but probably not.

"If so, is there a software way to alter the crossover frequency? Or is it a better idea to not use this output, and take L/R signals and do your own processing before feeding amp(s)? ..."

Get the system going first, before you start experimenting with software equalization. Try to build toward a "reference" system, relatively flat, relatively good quality sound ... then start tweaking. (A basic setup can be tweaked with software (even iTunes' built in EQ works OK), then modified in hardware to clean up response, distrotion, etc.)

"For a home system, what are reasonable power values to be driving to speakers for good quality sound at decent levels (ie: party-proof)? ..."

:>) the question is always there = what's good, what's not, what won't die ... (I use automotive bass thumpers in some sub woofers, just to keep the party gangs from blowing up the good (expensive) stuff.)

"Also, what are decent crossover points for sub, mid, tweeter? Bearing in mind that (to an extent) I can design my system around these if needs be. ... "

:>) the question is always there = what's good, what's not, what won't die ...

" ... for as little cash as possible ..." :>) the question is always there = what's good, what's not, what won't die ... cheap.
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