Adding Second Midrange!

[ynot311]

Hello, been a while since I have been doing any projects. I've had a search on what I THINK is a fairly simple mod... I have a 3 way crossover and wanted to add a second midrange? I am not too sure how to do it and I was hoping for some guidance? Attached is an image of the crossover.

Any advice would be appreciated.... Thank you. Tony

 

[DVDdoug]

I'd advise against it...

In parallel, you'll halve the impedance (double the power = +3dB) and in parallel you'll double impedance (half the power = -3dB). And either way you are fouling-up the crossover frequencies.* To do it properly you'd have to re-design the crossover and assuming parallel your speaker would go from being an 8-Ohm speaker to being a 4-Ohm speaker (or from 4 to 2-Ohms, etc.).

You CAN wire 4 speakers in series-parallel so the overall impedance doesn't change.

If the new midrange is different it's output may be higher or lower.

You can get soundwave interference depending on how they are positioned/oriented and your listening position. 4 midranges could possibly be worse.



* It might foul-up the slopes too, but it's been too long since I've studied filters so I'm not sure...

 

[LTig]

Hello, been a while since I have been doing any projects. I've had a search on what I THINK is a fairly simple mod... I have a 3 way crossover and wanted to add a second midrange? I am not too sure how to do it and I was hoping for some guidance? Attached is an image of the crossover.

Any advice would be appreciated.... Thank you. Tony

I don't think this is a good idea. You have to adapt the crossover, the impedance will be halved in the midrange and the directivity (horizonal or vertical, depending on how you mount them) will suffer.

 

[ynot311]

I don't think this is a good idea. You have to adapt the crossover, the impedance will be halved in the midrange and the directivity (horizonal or vertical, depending on how you mount them) will suffer.

Ok, So I would be better off finding or building a 4 way crossover with the speakers in mind?

 

[LTig]

Ok, So I would be better off finding or building a 4 way crossover with the speakers in mind?

A typical 4-way uses 4 different drivers (low, low mid, high mid, highs), not 2 mids.

 

[restorer-john]

@ynot311 I rarely bother with ASR these days, as it is generally a waste of my time, but I happened to see your post and recognized the schematic immediately. You would be correct in the case of these loudspeakers in feeling the need for lifting what is a somewhat recessed and, at times, "tubular" sounding midrange.

Most people on ASR not only don't know the speakers, the designer, the components, or when they were made, so take any "advice" they give you an enormous grain of salt.

For the technically ignorant, they are a David Tillbrook design (series 4000/2), published June 1980 in Electronics Today and the driver concerned is a notorious Philips ADO2161 (8) or ADO2160. At 45 years of age, I would be dismantling the midrange and treating the material to make it more pliable. Test with one and see what happens- then compare and/or treat the other. The roll surround becomes hard over time and the output diminishes significantly.

 

[ynot311]

@ynot311 I rarely bother with ASR these days, as it is generally a waste of my time, but I happened to see your post and recognized the schematic immediately. You would be correct in the case of these loudspeakers in feeling the need for lifting what is a somewhat recessed and, at times, "tubular" sounding midrange.

Most people on ASR not only don't know the speakers, the designer, the components, or when they were made, so take any "advice" they give you an enormous grain of salt.

For the technically ignorant, they are a David Tillbrook design (series 4000/2), published June 1980 in Electronics Today and the driver concerned is a notorious Philips ADO2161 (8) or ADO2160. At 45 years of age, I would be dismantling the midrange and treating the material to make it more pliable. Test with one and see what happens- then compare and/or treat the other. The roll surround becomes hard over time and the output diminishes significantly.

Thank you, Just what I was looking for. I knew it was an ETI kit from 1980. I have managed to download the actual Volume it was featured in. I vagally remember it. I was about 20 at the time. I have just bought a pair for 100 bucks and they appear to be in reasonable condition. So looking at enhancing them in any way I can. The boxes I can fix up. Its just the crossover and drivers.
Any info. you have on the midrange treatment? I would be very interested. They still sound quite good.

 

[Arindal]

I THINK is a fairly simple mod... I have a 3 way crossover and wanted to add a second midrange

As mentioned, the midrange crossover will be useless and not work as intended, if you change the impedance of the load it sees.

In some rare cases it might work, if you replace a 4Ohm midrange driver by two units of identical 8Ohm units in parallel. Directivity and lobing problems will persist, though, particularly with bigger midrange drivers and higher crossover frequency between midrange and tweeter.

 

[JayGilb]

@ynot311 I rarely bother with ASR these days, as it is generally a waste of my time, but I happened to see your post and recognized the schematic immediately. You would be correct in the case of these loudspeakers in feeling the need for lifting what is a somewhat recessed and, at times, "tubular" sounding midrange.

Most people on ASR not only don't know the speakers, the designer, the components, or when they were made, so take any "advice" they give you an enormous grain of salt.

For the technically ignorant, they are a David Tillbrook design (series 4000/2), published June 1980 in Electronics Today and the driver concerned is a notorious Philips ADO2161 (8) or ADO2160. At 45 years of age, I would be dismantling the midrange and treating the material to make it more pliable. Test with one and see what happens- then compare and/or treat the other. The roll surround becomes hard over time and the output diminishes significantly.

Miss seeing you around here, but I understand.

 

[MaxwellsEq]

I rarely bother with ASR these days, as it is generally a waste of my time

Nice to see you post again. I'm sorry you are not as involved as previously.

 

[voodooless]

Most people on ASR not only don't know the speakers, the designer, the components, or when they were made, so take any "advice" they give you an enormous grain of salt.

What bad advice was given? I don’t need to know the speaker, the designer or the components to know that adding a second midrange has all kinds of adverse effects.

Meanwhile, nobody bothers asking the OP why the wants to add a second midrange? What’s the goal here? This is the real ASR sin..

 

[Flaesh]

I just read the thread. It might be impolite to ask about the purpose. Or maybe it's secret, strange, or absurd.

nobody bothers asking the OP why the wants to add a second midrange?

Okay, I'll ask: why do this?
Here are three graphs: one driver, two drivers with a resistor, and two drivers with a resistor:

With real impedance it will not be quite like that, of course.

 

[Francis Vaughan]

Gosh. I remember those speakers. I remember listening to a pair in a shop back in the day and being, well, underwhelmed. But a huge part of that was the poor conditions they were being demoed in. I later met Tillbrook, and he was perfectly nice guy. He was demoing his big series 6000 power amplifier through a pair of the speakers in another shop. They did sound pretty reasonable that time. He did have a peculiarly high regard for that mid-range, claiming it to be one of the best ever drivers. It did see service in all manner of speakers. At the time it was considered a pretty high end device.

As noted above. Messing with any speaker to add another mid range is just not going to work in any useful manner. It is one of those trick questions where you need to stand back and count how many different ways the idea is wrong.

If the mid-range is not functional, it needs replacing or repairing, not augmenting. It is very old, but well constructed. @restorer-john makes a very good point about the likely ravages of time and how to address them. It could make for an interesting project, and may pay real dividends. Although some basic test equipment would be a good idea. Measuring a full impedance sweep, and obtaining the various Q parameters will likely reveal a lot straight away. An ultra stiff suspension will show up instantly. Done periodically whilst proceeding could provide a good way of obtaining quantitative measures of how attempts at resuscitation are affecting its behaviour. Whether it can be restored to full specification is harder. Speaker design has progressed a lot since then, but these were not cheap or low quality designs.

 

[restorer-john]

I later met Tillbrook, and he was perfectly nice guy.

I've tried unsuccessfully to track him down. Perhaps he is older than I think and may have left us? There is a published relatively simple circuit he developed which I would like to modify/improve and bring to market in a product (potentially).