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Help me convert old speakers to actives

AlmaAtaKZ

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Hello, all!

Always wanted to have a go at building a pair of speakers and hopefully finally will try. Thinking to start with a simple project, so I can learn. I have no experience of speaker design or build but I have basic understanding of tech and feel capable of basic to moderate craft, so there should be some potential, I hope. I have very limited DIY facilities - no space (small flat...) and only the most basic tools.

I have these old Monitor Audio Monitor 3 speakers - slim 3-way (or maybe 2.5-way) floor-standers and I think converting them would eliminate/minimize the cabinet work and make it manageable in my nonexistent workshop.

I am thinking to use a hypex plate amp (or similar) as it is a very capable ready-made package (power supply, DSP, amps, protection, remote option) - this would allow me to still learn something while not having to deal with too much in the first project. FA123 is the smallest 3-way in their range.

https://www.diyclassd.com/products/fusion-amplifiers/fusionamp-fa123

Not sure if I should go for the 'low', 'mid' or 'high' performance target (given the steep learning curve ahead). Probably low to mid, as the existing cabinet will dictate some compromises which pretty much eliminates the possibility of 'high' performance. The time it will take is not important. The budget is flexible and will be mainly dictated by the chosen performance target, I suppose (cost of drivers, amps, measuring mic, any software, materials and potentially some tools).

If some ASR members would be kind enough to support me in this project by providing advice based on experience, pointing to some useful reading resources and helping not to get confused, I would really appreciate.

One rule I have set for myself is do not buy anything (e.g. drivers) until the design is fully complete and I know exactly what I need and how I will make it work.

The speakers look like this (internet pic):


The bottom quarter of the cabinet is a separate chamber (currently filled with sand).

MA Monitor 3.jpg
 
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AlmaAtaKZ

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The initial few things I am trying to figure out:
  1. Should I use the existing drivers or should I buy new
  2. Should I use it in 2-way or 3-way
  3. Should I add another driver (e.g. side firing woofer at the bottom)
and/or - should I be trying to figure out something else?
 

sergeauckland

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I did this some years ago with my B&W 801s. Still have them in daily use. Never regretted it.
To make life easier, I use a Behringer DCX2496 as the crossover, with a DEQ2496 as a fine equaliser, as I already had the DEQ, but as the DCX includes a parametric EQ it isn't necessary.

I posted the project on another forum at the time, I'll try and find a link.

Happy to help with any questions

S
 

sergeauckland

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The initial few things I am trying to figure out:
  1. Should I use the existing drivers or should I buy new
  2. Should I use it in 2-way or 3-way
  3. Should I add another driver (e.g. side firing woofer at the bottom)
If you buy new drivers, they are unlikely to fit the woodwork, so you'll need more cabinet work. I'd stick with the existing drivers.

3 way will give you a smoother result.

Good idea with side firing woofers. Should eliminate the need for subs.

S
 
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AlmaAtaKZ

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I did this some years ago with my B&W 801s. Still have them in daily use. Never regretted it.
To make life easier, I use a Behringer DCX2496 as the crossover, with a DEQ2496 as a fine equaliser, as I already had the DEQ, but as the DCX includes a parametric EQ it isn't necessary.

I posted the project on another forum at the time, I'll try and find a link.

Happy to help with any questions

S
Serge
I saw and heard your speakers at the Wam show and they are certainly part of the inspiration. Your help will be appreciated!
 
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AlmaAtaKZ

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If you buy new drivers, they are unlikely to fit the woodwork, so you'll need more cabinet work. I'd stick with the existing drivers.

3 way will give you a smoother result.

Good idea with side firing woofers. Should eliminate the need for subs.

S

Re keeping the drivers: how will I know their parameters to choose the crossover points? Impedance?

And do I just wire one of the mid drivers to mid and the other to the bass channel? And then measure and tweak?

And for the option with an additional woofer, do I combine the two midrange drivers to the mid channel? In series or parallel? Edit: This I think is a very interesting option - use all existing drivers and add a bass driver at bottom. But what puzzles me is the use of two mid range drivers as one. Does not feel 'normal', 'optimum'.
 
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AlmaAtaKZ

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Re new drivers: I was thinking of selecting drivers that would be slightly larger so they can still be installed somehow in or over the existing cutouts. I obviously need to investigate the cutouts.

Another option is to use the existing drivers initially and then add new drivers (or abandon the cabinet and make a new one, reusing the amp).
 
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AlmaAtaKZ

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I did this some years ago with my B&W 801s. Still have them in daily use. Never regretted it.
To make life easier, I use a Behringer DCX2496 as the crossover, with a DEQ2496 as a fine equaliser, as I already had the DEQ, but as the DCX includes a parametric EQ it isn't necessary.

I posted the project on another forum at the time, I'll try and find a link.

Happy to help with any questions

S
I thought about using external crossovers and amps but despite the convenience of easy access they would take too much space, so a non starter domestically speaking
 
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AlmaAtaKZ

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I feel like many of my questions will be on drier selection. I am a complete newbie here. I know that software/online calculators exist but I do not know specific ones and which ones to use for what. Example question: how do I know the cabinet volume the driver needs? and vice versa - if I know the volume of a chamber, how do I know if the driver is suitable for it without chamber modification?

For example - there is an existing bottom chamber and I could fit a bass driver in it. How do I ensure the driver will work properly with that volume?
 

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First: basically You will need some fundamental knowledge of crossover design and a Mic.

Then You should begin with one modification and complete this before proceeding to the next step.

So let's assume activation is step #1: bridge or extract the passive xover and connect every driver to a post, if you have the plate amp in an external housing, or connect directly to PA, if this is built in to the speaker. Both versions need some DIY woodworking and soldering.
Then you need the mic to measure FR of every driver solely to then calculate the xover, for what you need some basic technological knowledge.

After this you may step further to driver and/or cabinet modification.
 
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AlmaAtaKZ

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First: basically You will need some fundamental knowledge of crossover design and a Mic.

Then You should begin with one modification and complete this before proceeding to the next step.

So let's assume activation is step #1: bridge or extract the passive xover and connect every driver to a post, if you have the plate amp in an external housing, or connect directly to PA, if this is built in to the speaker. Both versions need some DIY woodworking and soldering.
Then you need the mic to measure FR of every driver solely to then calculate the xover, for what you need some basic technological knowledge.

After this you may step further to driver and/or cabinet modification.
Yes, this is what I understand, but not much beyond that.
 

Purité Audio

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Can’t you use the existing passive crossover points/slopes as guides?
Keith
 

Purité Audio

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Old reviews?
You know when they actually contained information.
Keith
 

sergeauckland

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My view about crossover frequencies is to start with whatever Monitor Audio used, as at least they should know! Slopes and type of crossover are secondary, albeit important. I decided to use 48dB/Octave L-R as that's the most my DCX does, and I can't think of any reason to use less.

Your current 'speakers I think will be 2 1/2 ways, i.e. at LF both drivers operate. At MF only the upper driver operates, and at HF, clearly only the tweeter operates. Meridian did the same with their 5000 series and is one way of avoiding the 'speaker box being too wide, whilst getting enough driving area in the bass.

As to space, there's no reason not to use a plate amp attached to the 'speaker box, but you'll need an external crossover, either on a PC, using a multichannel sound card, or in a 1U box, such as the DCX. I don't know of any smaller DSP-based crossover you can attach to the 'speaker box.

I'm assuming you're thinking of a DSP-based crossover, not an analogue crossover made with op-amps. The benefits of a fully adjustable DSP-based crossover are just too great to contemplate analogue.

By the way, here's a link to the write-up I did on Audio-Forums, which also went on the now defunct 'Wam.

S.
 

sergeauckland

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If only I knew these!
If you can't find these from reviews as Keith suggested, you'll have to measure them. That's not difficult but you'll need some instrumentation, even if it's only a signal generator and meter, which you can get for free using REW and a PC sound card with a line input. You'll need to make some sort of attenuator interface for the sound card, or use something like a recording USB interface.

S.
 

Salt

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My view about crossover frequencies is to start with whatever Monitor Audio used, as at least they should know! Slopes and type of crossover are secondary, albeit important. I decided to use 48dB/Octave L-R as that's the most my DCX does, and I can't think of any reason to use less.

Your current 'speakers I think will be 2 1/2 ways, i.e. at LF both drivers operate. At MF only the upper driver operates, and at HF, clearly only the tweeter operates. Meridian did the same with their 5000 series and is one way of avoiding the 'speaker box being too wide, whilst getting enough driving area in the bass.

As to space, there's no reason not to use a plate amp attached to the 'speaker box, but you'll need an external crossover, either on a PC, using a multichannel sound card, or in a 1U box, such as the DCX. I don't know of any smaller DSP-based crossover you can attach to the 'speaker box.

I'm assuming you're thinking of a DSP-based crossover, not an analogue crossover made with op-amps. The benefits of a fully adjustable DSP-based crossover are just too great to contemplate analogue.

By the way, here's a link to the write-up I did on Audio-Forums, which also went on the now defunct 'Wam.

S.
Hypex PA have DSP included.
 
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AlmaAtaKZ

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My view about crossover frequencies is to start with whatever Monitor Audio used, as at least they should know! Slopes and type of crossover are secondary, albeit important. I decided to use 48dB/Octave L-R as that's the most my DCX does, and I can't think of any reason to use less.

Your current 'speakers I think will be 2 1/2 ways, i.e. at LF both drivers operate. At MF only the upper driver operates, and at HF, clearly only the tweeter operates. Meridian did the same with their 5000 series and is one way of avoiding the 'speaker box being too wide, whilst getting enough driving area in the bass.

As to space, there's no reason not to use a plate amp attached to the 'speaker box, but you'll need an external crossover, either on a PC, using a multichannel sound card, or in a 1U box, such as the DCX. I don't know of any smaller DSP-based crossover you can attach to the 'speaker box.

I'm assuming you're thinking of a DSP-based crossover, not an analogue crossover made with op-amps. The benefits of a fully adjustable DSP-based crossover are just too great to contemplate analogue.

By the way, here's a link to the write-up I did on Audio-Forums, which also went on the now defunct 'Wam.

S.
The hypex amp has built in DSP including crossover, filters and I think equalisation
 
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