Help me convert old speakers to actives

[sergeauckland]

I think they are indeed 2.5-way. But does it matter for conversion to actives?

There are two options:
1. with adding a larger bass driver (side firing) - I then use both current drivers as the mid channel. Is it a good implementation? How do I wire them - parallel or series?
2. drivers as is - I assume I connect the mid channel to one and the bass channel to the other.

I could start with option 2. and add a larger bass driver later.

I would start by using one bass unit for bass and the second (upper) one for mid-range. Better, I think, would be to blank off the lower bass unit, and fit a larger side-mounted bass unit, or better still, two side mounted bass units, so their 'equal and opposite' reactions cancel. A further refinement might be to change the mid-range for a smaller one, as that's likely to improve the dispersion characteristics of the system.

How far you want to go with this depends on your motivation.

S.

 

[AlmaAtaKZ]

Second one.
Coming from analogue design where trial and error is the main approach and simulation can provide just a frame, it now is a relief with DSP. Instead of hours of switching every part and remeasure again you now switch frequency and mode within seconds and see results instantly. It has a high educational aspect and with overlays every step can be compared to other.
How to find the correct crossover frequency?
First approach could be measuring the speaker as is (every single driver) so you can estimate what the constructors idea was, and then try to imitate this after extraction of the passiv xover.

Second approach could be measuring single drivers directly without xover and decide with given FR and distortions and radiation pattern where to cross.

For the crossover most use LR 24 dB, so that would be a good beginning.

Concerning the electrical part in the project I see no problems ahead.
Problems may pop up if one or more of the drivers are bit worn out. But even if so, when you should arrive at this point you have learned a lot and had a lot of fun.

The second approach I got a better feel for

 

[AlmaAtaKZ]

That is a good start.

Also, you may want to measure the off-axis frequency response, e.g., at 15 degrees, 30 degrees, 45 degrees and at 60 degrees. If possible, it is good to have about the same dispersion from the tweeter and the midrange at the crossover frequency. However, given the tweeter is flush mounted and not in a waveguide, it may not be optimal. Nonetheless, you can play with the crossover to try to get a good balance.

Ok, makes sense. The objective of smooth transition also applies to directivity. Learned something!

 

[AlmaAtaKZ]

I would start by using one bass unit for bass and the second (upper) one for mid-range. Better, I think, would be to blank off the lower bass unit, and fit a larger side-mounted bass unit, or better still, two side mounted bass units, so their 'equal and opposite' reactions cancel. A further refinement might be to change the mid-range for a smaller one, as that's likely to improve the dispersion characteristics of the system.

How far you want to go with this depends on your motivation.

S.

So, do I feel correctly that it is not a good idea to have the two drivers working on a single MF channel? Why would d’appolito layout exist, if so?

Re adding two opposing woofers - I do think about it but the depth of the cabinet is only about 13cm. Impossible to fit two unless offset. Then the cancellation is partly/mostly lost.

 

[terryforsythe]

So, do I feel correctly that it is not a good idea to have the two drivers working on a single MF channel? Why would d’appolito layout exist, if so?

In a narrow cabinet, the bass response rolls off at about -6dB/octave due to baffle step loss. Two ways commonly used to address this are concepts 1 and 2 below. Concept 3 is another possible solution:

1. If using a single woofer, use the crossover to lower the output of the woofer in the upper frequencies to match the output at the lower frequency. The downside to this is that this results in a lower efficiency.

2. Add another woofer to fill in the lower frequencies, which appears to be the design for your speakers. The downside to this is that there may be some phase differences between the two woofers in the frequency range where the stop band for the lower woofer begins and the upper woofer still is in the pass band.

3. You could try running both woofers over the same frequency range, and use the crossover to lower the output of both woofers in the upper frequencies. The downside to this is that it will negatively affect vertical dispersion due to the different spacing between the tweeter and the two different woofers. That is why this type of setup usually is used on WTW (woofer-tweeter-woofer) configurations rather than TWW (tweeter-woofer-woofer) configurations.

Given that your speakers have a TWW configuration, I believe that concept 2 probably will give you the best overall performance. If the speakers came from the manufacturer with that type of crossover, that probably is why the designer chose that design.

As a side note, I have designed speakers using each of these concepts. For single woofer configurations I designed the speakers per concept 1. For TWW configurations I designed the speakers per concept 2. For WTW configurations I designed the speakers per concept 3.

 

[Salt]

Agree with concept 2.
Tried to find out some specs of the speaker but there's nothing to dig. Maybe at net-archives.
But what I found is that Monitor Audio focused on high sensitivity and in respect of this 2 1/2 way makes much sense.
The hints to this would be
- a unique path to each woofer on xcover
- no unique séparée for each woofer (if, then it would be three-way)

 

[AlmaAtaKZ]

In a narrow cabinet, the bass response rolls off at about -6dB/octave due to baffle step loss. Two ways commonly used to address this are concepts 1 and 2 below. Concept 3 is another possible solution:

1. If using a single woofer, use the crossover to lower the output of the woofer in the upper frequencies to match the output at the lower frequency. The downside to this is that this results in a lower efficiency.

2. Add another woofer to fill in the lower frequencies, which appears to be the design for your speakers. The downside to this is that there may be some phase differences between the two woofers in the frequency range where the stop band for the lower woofer begins and the upper woofer still is in the pass band.

3. You could try running both woofers over the same frequency range, and use the crossover to lower the output of both woofers in the upper frequencies. The downside to this is that it will negatively affect vertical dispersion due to the different spacing between the tweeter and the two different woofers. That is why this type of setup usually is used on WTW (woofer-tweeter-woofer) configurations rather than TWW (tweeter-woofer-woofer) configurations.

Given that your speakers have a TWW configuration, I believe that concept 2 probably will give you the best overall performance. If the speakers came from the manufacturer with that type of crossover, that probably is why the designer chose that design.

As a side note, I have designed speakers using each of these concepts. For single woofer configurations I designed the speakers per concept 1. For TWW configurations I designed the speakers per concept 2. For WTW configurations I designed the speakers per concept 3.

This tww/wtw on narrow baffle starts to look overly compromised as a concept. Thinking now of Serge’s recommendation to blank one woofer off, use the remaining one as a single mid and add a proper woofer or two, side firing, at the bottom.

 

[terryforsythe]

This tww/wtw on narrow baffle starts to look overly compromised as a concept. Thinking now of Serge’s recommendation to blank one woofer off, use the remaining one as a single mid and add a proper woofer or two, side firing, at the bottom.

I would not add a different woofer.

If you do, the proper way would be to build an sub-enclosure inside your cabinet for your midrange to keep it isolated from the new woofer. Also, you would need to find a woofer that will perform well in the space you have left. You calculate the appropriate box volume from the woofer's Thiel-Small parameters, or you can put those parameters into a bass simulator (I think there are some on the internet). Anyway you proceed, though, modifying the box will be much more complicated than working with the cabinets and drivers that you have.

Also, keep in mind that you will have DSP for the crossovers, which makes tuning very easy - certainly much, much easier than making all of the cabinet modifications you would need to make in order to avoid making the speakers worse than in their original form.

 

[Salt]

This tww/wtw on narrow baffle starts to look overly compromised as a concept. Thinking now of Serge’s recommendation to blank one woofer off, use the remaining one as a single mid and add a proper woofer or two, side firing, at the bottom.

It's an approved and well documented concept supposed it's 2 1/2 way.
And I completely agree @terryforsythe not to change anything in hardware except applying plateamp instead of passive xover.

Anything beyond this can be overthought then.

 

[terryforsythe]

This tww/wtw on narrow baffle starts to look overly compromised as a concept. Thinking now of Serge’s recommendation to blank one woofer off, use the remaining one as a single mid and add a proper woofer or two, side firing, at the bottom.

Please keep in mind that your cabinets and ports were designed around your woofers. If you just add some other woofer for which the cabinets are not designed, you likely will mess up the bass response.

 

[AlmaAtaKZ]

Please keep in mind that your cabinets and ports were designed around your woofers. If you just add some other woofer for which the cabinets are not designed, you likely will mess up the bass response.

Yes, I do realise that I would have to modify the partitions to suit any new driver arrangement. And I take your (and Salt’s) point above that cabinet mods will be much more difficult than toggling software settings, especially so given my lack of workshop/tools.

 

[AlmaAtaKZ]

But! Just adding the plate amp does seem to diminish the learning challenge. No driver selection, no box design.

 

[Salt]

To prevent unnecessary thread inflation, please give us an image of the crossover and information about the cabinet's internal separations to come to an end with speculations.

 

[Sokel]

Now comes the unpopular opinion.
Let's assume you did everything that the friends above suggested and you did them right.

The hard part is that you'll have to measure the outcome in anechoic conditions both on and off-axis.
You can (short of) do that with gated measurements too above a frequency but you'll have to have a turntable of shorts.
And then you'll have to interpret the results and make the changes you'll need IF they are doable.

I suggest you start with modeling to see what it needs,VirtuixCad for example is brilliant.
Look at the existing x-over,copy the values there along with all the data you can gather and measure.

That if you don't want to throw money to something that will be questionable.

 

[AlmaAtaKZ]

To prevent unnecessary thread inflation, please give us an image of the crossover and information about the cabinet's internal separations to come to an end with speculations.

Ok, will do a comprehensive ‘survey’ of the speakers this weekend.

 

[AlmaAtaKZ]

Now comes the unpopular opinion.
Let's assume you did everything that the friends above suggested and you did them right.

The hard part is that you'll have to measure the outcome in anechoic conditions both on and off-axis.
You can (short of) do that with gated measurements too above a frequency but you'll have to have a turntable of shorts.
And then you'll have to interpret the results and make the changes you'll need IF they are doable.

I suggest you start with modeling to see what it needs,VirtuixCad for example is brilliant.
Look at the existing x-over,copy the values there along with all the data you can gather and measure.

That if you don't want to throw money to something that will be questionable.

That would be modelling what? The whole system amp-driver-cabinet-room?

 

[terryforsythe]

But! Just adding the plate amp does seem to diminish the learning challenge. No driver selection, no box design.

If you want a learning challenge, I would start fresh. Choose initial components, create a model in VituixCAD, change components as necessary, etc.

But, you would need access to wood working tools to build the cabinets. Some places sell flat packs for enclosures with the pieces pre-cut, but you still need to glue them together and route out the openings for the drivers.

 

[Sokel]

That would be modelling what? The whole system amp-driver-cabinet-room?

It would be modeling the speaker (enclosure+drivers+x-over,etc)
It's a steep learning curve but it's all there and you can decide if it'll worth it.

 

[terryforsythe]

That would be modelling what? The whole system amp-driver-cabinet-room?

As a first speaker project, I think your initial idea of removing the passive crossovers and adding plate amplifiers is a fun project. That will keep things from getting overly complicated right away, letting you tip your toe in the water so to speak. Indeed, my latest speaker project was doing something very similar, though with external amplifiers: https://www.audiosciencereview.com/...-fi-reference-ubr62-bookshelf-speakers.51780/

 

[AlmaAtaKZ]

I understand why one would model the box, drivers and crossover when designing a passive speaker from zero. But if theres is almost any crossover available in the dsp amp what would still be the purpose of modelling? And if, as in my case,I have the drivers and the box as a given, and any crossover available in dsp, what and why would I still model then?