My first project, need some tips

50AE · 21st September 2011, 05:45 PM

Hi, I am a beginner and I have my first project in mind. I want it to be a 3 way active system with active crossovers.

I have two Gamma La1231 speakers repaired and sent for measurements. I'm waiting for their frequency response to think if I should build a 2-way or 3 way.

I have some questions:

First of all, how to choose bracing pattern? What is the best bracing? The speaker box will be rectangular, using the golden ratio and its volume is calculated to be 130L closed box judging from the speaker measured parameters.
I want to use MDF, because it's avaible and cheap.
Also, how to know what thickness is correct?

Then, while the box is of the correct size, I heard the walls should be covered with a resonance reducing material. What is good and cheap in same time?

Then about the electronics.

I already have a discrete components amp for the bass, but I'm tempted to make chip amps for the mids and highs, mainly because of price. Let's take the LM3886 for example. The highs are 20-30 and the LM3886 will be driven to 60W, so there should not be much distortion. Are chip amps inferiour to discrete amps these days?

I also read from many people that IC opamps aren't good for audio and that I should use preamps with discrete elements. Can someone give arguments about this?

These are the questions I can think of now. Thank you.

joe58 · 21st September 2011, 07:09 PM

Most people will say 18mm.

You could use egg crates that you could collect while you build the cabinets? Although you will have to get other opinions on whether it will work, but is similar to I suppose to Acoustic Profile foam.

Also by building it the golden ratio I believe this in itself minimizes standing waves, which is why you would be be putting stuff on the cabinet walls.

Happy to stand corrected by more experienced people.

planet10 · 21st September 2011, 07:24 PM

Here is a good backgrounder to one methodology to build a good box.

Discussion on what materials to build speakers out of

Not a short read.

dave

Francec · 3rd October 2011, 10:19 AM

I've built active three ways using LM3886TF chip amps for all drivers and they work well even in bridge mode for the woofers. Unless your ears are superhuman, it is unlikely you will be able to tell and even then, it wouldn't be easy.

Op amps are fine. Again, if you can tell the difference, put on a cape, put your underpants on the outside and fly off to the moon. :0

Frank

50AE · 5th October 2011, 08:30 PM

My biggest PITA is budget and I'll be trying to squeeze the best price to performance ratio.
What I'm not sure, what opamps should I use for the active crossovers? Should the choice be the same as for preamp opamps or not? For example LM4562, 5532 or else? I love the sound of the LM4562, but haven't tried anything else.

sreten · 08:40 PM

Hi,

IME first time builders inevitably get active speakers totally wrong.

As do a lot of first time passive builders using stupid crossover calculators.

There are no shortcuts with either approach.

rgds, sreten.

http://sites.google.com/site/undefinition/diy (see FAQs)
Zaph|Audio
FRD Consortium tools guide
Designing Crossovers with Software Only
RJB Audio Projects
Jay's DIY Loudspeaker Projects
Speaker Design Works
HTGuide Forum - A Guide to HTguide.com Completed Speaker Designs.
DIY Loudspeaker Projects Troels Gravesen
Humble Homemade Hifi
Quarter Wavelength Loudspeaker Design
The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs
Linkwitz Lab - Loudspeaker Design
Music and Design

Great free SPICE Emulator : SPICE-Based Analog Simulation Program - TINA-TI - TI Tool Folder

Francec · 6th October 2011, 04:05 AM

If you can afford the 4562, use them or, if no cash, the 5532 will be good. Remember, there is a lot of distortion added after the op amps, most notably by the speakers themselves.

Active is an easier thing to do. So long as the speakers have a reasonably flat response and have enough FR then LR 24dB crossovers are OK. I used Rod Elliott's and haven't ever had a problem.

Frank

sreten · 6th October 2011, 05:06 AM

Quote:

Originally Posted by Francec

Active is an easier thing to do. So long as the speakers have a reasonably flat response and have
enough FR then LR 24dB crossovers are OK. I used Rod Elliott's and haven't ever had a problem.

Frank

Hi,

No they are not, at all. Baffle Step Compensation and EQ is ignored.
You will end up with something that works, but does not work well.

Active crossovers require the right transfer functions, which are never
classic filter functions, they apply to the actual acoustic response.

rgds, sreten.

Francec · 6th October 2011, 05:26 AM

BSC can be added after the speaker is running. EQ is done through the buffers on Rod's boards.

Strange but people who my speakers think they are great.

planet10 · 6th October 2011, 05:36 AM

Quote:

Originally Posted by 50AE

.
What I'm not sure, what opamps should I use for the active crossovers? Should the choice be the same as for preamp opamps or not?

THink of an active XO as a pre-amp with more parts. Execution is every bit as important as in a preamp.

dave

21st September 2011, 05:45 PM	#1
50AE diyAudio Member Join Date: Jul 2011 Location: Sofia, Bulgaria	My first project, need some tips Hi, I am a beginner and I have my first project in mind. I want it to be a 3 way active system with active crossovers. I have two Gamma La1231 speakers repaired and sent for measurements. I'm waiting for their frequency response to think if I should build a 2-way or 3 way. I have some questions: First of all, how to choose bracing pattern? What is the best bracing? The speaker box will be rectangular, using the golden ratio and its volume is calculated to be 130L closed box judging from the speaker measured parameters. I want to use MDF, because it's avaible and cheap. Also, how to know what thickness is correct? Then, while the box is of the correct size, I heard the walls should be covered with a resonance reducing material. What is good and cheap in same time? Then about the electronics. I already have a discrete components amp for the bass, but I'm tempted to make chip amps for the mids and highs, mainly because of price. Let's take the LM3886 for example. The highs are 20-30 and the LM3886 will be driven to 60W, so there should not be much distortion. Are chip amps inferiour to discrete amps these days? I also read from many people that IC opamps aren't good for audio and that I should use preamps with discrete elements. Can someone give arguments about this? These are the questions I can think of now. Thank you.

21st September 2011, 07:24 PM	#3
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	Here is a good backgrounder to one methodology to build a good box. Discussion on what materials to build speakers out of Not a short read. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

5th October 2011, 08:37 PM	#6
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, IME first time builders inevitably get active speakers totally wrong. As do a lot of first time passive builders using stupid crossover calculators. There are no shortcuts with either approach. rgds, sreten. http://sites.google.com/site/undefinition/diy (see FAQs) Zaph\|Audio FRD Consortium tools guide Designing Crossovers with Software Only RJB Audio Projects Jay's DIY Loudspeaker Projects Speaker Design Works HTGuide Forum - A Guide to HTguide.com Completed Speaker Designs. DIY Loudspeaker Projects Troels Gravesen Humble Homemade Hifi Quarter Wavelength Loudspeaker Design The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs Linkwitz Lab - Loudspeaker Design Music and Design Great free SPICE Emulator : SPICE-Based Analog Simulation Program - TINA-TI - TI Tool Folder __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow Last edited by sreten; 5th October 2011 at 08:40 PM.

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21st September 2011, 07:09 PM	#2
joe58 diyAudio Member Join Date: Dec 2009 Location: England	Most people will say 18mm. You could use egg crates that you could collect while you build the cabinets? Although you will have to get other opinions on whether it will work, but is similar to I suppose to Acoustic Profile foam. Also by building it the golden ratio I believe this in itself minimizes standing waves, which is why you would be be putting stuff on the cabinet walls. Happy to stand corrected by more experienced people.

3rd October 2011, 10:19 AM	#4
Francec Banned Join Date: Jul 2006 Location: Port Melbourne, Australia	I've built active three ways using LM3886TF chip amps for all drivers and they work well even in bridge mode for the woofers. Unless your ears are superhuman, it is unlikely you will be able to tell and even then, it wouldn't be easy. Op amps are fine. Again, if you can tell the difference, put on a cape, put your underpants on the outside and fly off to the moon. :0 Frank

5th October 2011, 08:30 PM	#5
50AE diyAudio Member Join Date: Jul 2011 Location: Sofia, Bulgaria	My biggest PITA is budget and I'll be trying to squeeze the best price to performance ratio. What I'm not sure, what opamps should I use for the active crossovers? Should the choice be the same as for preamp opamps or not? For example LM4562, 5532 or else? I love the sound of the LM4562, but haven't tried anything else.

6th October 2011, 04:05 AM	#7
Francec Banned Join Date: Jul 2006 Location: Port Melbourne, Australia	If you can afford the 4562, use them or, if no cash, the 5532 will be good. Remember, there is a lot of distortion added after the op amps, most notably by the speakers themselves. Active is an easier thing to do. So long as the speakers have a reasonably flat response and have enough FR then LR 24dB crossovers are OK. I used Rod Elliott's and haven't ever had a problem. Frank

6th October 2011, 05:26 AM	#9
Francec Banned Join Date: Jul 2006 Location: Port Melbourne, Australia	BSC can be added after the speaker is running. EQ is done through the buffers on Rod's boards. Strange but people who my speakers think they are great.

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