What mids for a baffle that already has its woofer?

[stf92]

Hi: I've got a three-way acoustic suspension baffle which is missing the mids. Also the crossover is lacking, so we have one variable less.

As I lack this mids characteristics, my problem is to select a mids for the set I described. The question is: how do I determine its parameters and then, everything's fine but, where do I buy it, if it even exists???


EDIT: I think I've got the answer. The mids must simply be good, that is, have the flatest possible response curve. If it reaches very high or very low frequencies, better off. That is why crossovers are built for.

[Loren42]

Originally Posted by stf92

Hi: I've got a three-way acoustic suspension baffle which is missing the mids. Also the crossover is lacking, so we have one variable less.

As I lack this mids characteristics, my problem is to select a mids for the set I described. The question is: how do I determine its parameters and then, everything's fine but, where do I buy it, if it even exists???


EDIT: I think I've got the answer. The mids must simply be good, that is, have the flatest possible response curve. If it reaches very high or very low frequencies, better off. That is why crossovers are built for.

You need to find the Thiele-Small parameters of the speakers you have. The best way to do this is to go through the trouble to measure them yourself.

The other way is to get them from the manufacture, but that may be difficult and the numbers may not be really right.

You should also measure the existing drivers for on-axis and off-axis response in the enclosure they are in now. You may, at the minimum, need to temporarily plug the hole of the mid if it is open to the woofer.

Once you have the other driver's characteristics you can search for a mid that will fill in.

Then you need to design a crossover network that works with the system.

All this is a lot of work. This will be a project, which is okay if you want to take the time, effort, and money to do it. However, there is no assurance that will find what you need. Any way you can simply find the OEM midrange?

Depending on what you have now, it may be faster, better, and cheaper to simply buy a new set of speakers.

There will need to be test software, microphone, and other equipment just to do all this. It can be quite the investment in tools and then you need to learn what you are doing.

Simply filling the hole with a speaker that fits will yield an unpleasant results.

[PeteMcK]

I'd determine a suitable crossover freq for the woofer, and find a mid to match, preferably with sensitivity to match the woofer, less any baffle step.

[stf92]

Thanks for your kind replies. Loren42, I am terribly sorry not having been more precise. You'll see,
I simplified my case in order to make the exposition clearer. It was a mistake, I now see. The whole picture is this: the only OEM elements in the baffle are the woofer, the midrange and the crossover (sic). Besides, this is actually a four-way speaker system (= baffle). I had said three-way, I know. But of the two mids only one survives and the baffle is too old to get identical mids.

Having said this, I must add that, having in my power a pair of Yamaha tweeters (soft dome) I want to use them to make a three-way out of the old four-way. The scenario is a little confusing, you see? So,

woofer: OEM.
mids: lacking.
tweeter: not OEM but a fix element of in design.
crossover: has to be modified.

This are not so desperate, because I know what the frequency bands of the old crossover are, namely

30-500
500-5000
5000-10000
10000-22000

Additional data for the old baffle:
System: acoustic suspension.
Power: 50w
Impedance: 8 ohms

This makes the woofer go up to past 500Hz, I mean they should have picked that range. This is the only datum the crossover can give me. So my new midrange must go below 500Hz. This is clear to me.

On the other hand, the crossover two upper bands filters are made with resistors and capacitors alone. So, somebody told me it would be easy to make the crossover three-way. As to the rest,

Originally Posted by Loren42

Any way you can simply find the OEM midrange?

Unfortunately the answer is categorically no, given the age of this midrange. It has been discontinuated long ago.

Originally Posted by Loren42

Depending on what you have now, it may be faster, better, and cheaper to simply buy a new set of speakers.

Do you mean a set of baffles?

Originally Posted by Loren42

There will need to be test software, microphone, and other equipment just to do all this. It can be quite the investment in tools and then you need to learn what you are doing.

I have a desktop computer, a Yamaha OPL3-SA sound board which optionally inserts a power amplifier in the signal path, I could get the software and, about the microphone, I always wanted to have one. Plus, I have some theoretical knowledge in electricity, from the university environment. I am now rereading the chapter Frequency Response from a book on circuit theory.

Originally Posted by PeteMcK

I'd determine a suitable crossover freq for the woofer, and find a mid to match,

Well, according to what I said above, but HAD omitted before, that freq would be 500Hz. I trust the baffle manufacturer and know, except unit-to-unit variations, the woofer must reach past 500Hz.

Originally Posted by PeteMcK

preferably with sensitivity to match the woofer,

They spoke to me about the efficiency of the mid having to be in accordance with that of the woffer. But if so, what do I try to match, sensitivity or efficiency?

Originally Posted by PeteMcK

less any baffle step.

What is a baffle step? Would you mind expanding?

Thanks again and regards.

[stf92]

Hi: I attach the circuit of the crossover spoken of in post #4. Regards.

[PeteMcK]

Baffle Step Compensation

STF, you aren't making it easy for us,it would be a good idea to keep all your questions about this project in one thread...

[jerome69]

Yes one thread is better.

Originally Posted by stf92

Thanks for your kind replies. Loren42, I am terribly sorry not having been more precise. ...

Yes give the right information is better.

What is the diameter of the woofer ?
What is the sensitivity of your speaker ?
Do you have the values of the components in the crossover ?
A photo of the front of the speaker can help.

I see you have a 45mm~1.8" dome, it is not a tweeter but a upper midrange. You will need a 1" or 3/4" tweeter

Go to a 3 way, you can keep the old crossover and add a tweeter, suppress the part 10k-20kHz.
The crossover frequency could be :
30-500 : woofer 200mm or 250mm ?
500-5000 : 45mm upper mid
5000-20000 : 25mm or 19mm

[stf92]

CROSSOVER04.gifYes, a good mess is what I have done here, scattering information over several threads.

There is an important limiting factor: the OEM midrange was 8" and the hole on the box was made for a driver this diameter.

Any possibility to use the 4-ohms Yamaha tweeters? The model is JA-0510A, used by Yamaha in their speaker models NS-470/625/645. The 625/645 were two-way baffles with a crossover frequency of 2000Hz and extending up to 20000Hz according to the manufacturer specs. Some non-numerical data on JA-0510A are here. As for the data you asked for:

OEM woofer diameter: 12"
OEM midrange diameter: 8"
speaker sensitivity: most unfortunately, I lack this datum.
crossover components: I list here the values, except inductance. The letters refer to the circuit, which I'm sending you.

R1 + R2 = 23 ohms
R2 >= 12 ohms
R3 <= 10.9 ohms
R1, R2 and a one-pole 5-throw switch make an L-pad, I think.
Instead, R3 has a one-pole 5-throw switch which merely acts a an attenuator.

C1 = 50uF
C2 = 5 uF
C3 = 2.2uF
L1 = ?
L2 = ?

I've never seen practical methods to measure inductance but, applying a step function to the inductor, I could measure the time constant and, hence, L. Better yet, a square wave and measure the resultant excursion.

So, the values of L1, L2 together with a photo will follow soon. Finally, as you say the Yamaha tweeter is a 45mm upper midrange, does the following imply to use it to cover the 500-5000 range?

The crossover frequency could be :
30-500 : woofer 200mm or 250mm ?
500-5000 : 45mm upper mid
5000-20000 : 25mm or 19mm

But look above at the third paragraph. Is it a typo?

Thank you for your kind interest in this project and regards.

[jerome69]

Originally Posted by stf92

Finally, as you say the Yamaha tweeter is a 45mm upper midrange, does the following imply to use it to cover the 500-5000 range?

yes, due to its size but a measurement of impedance should be done.

Originally Posted by stf92

But look above at the third paragraph. Is it a typo?

??? no.

Thanks, we can have a better vision of your speaker.
12"+8"+2"+1" ? but not enough. Do you have its company, model, reference ?

The sensitivity of this speaker should be high at least 90dB.

If you know wood working, you can redo the front panel. The 8" midrange hole will be not a problem.
The value of the crossover are compatible with the crossover frequencies. I think L1 and L2 should be near 4.7mH and 0.33mH.
To measure impedance, T/S parameter, that will be very usefull, see my tuto. (in french)
Mesure d'impédance et de paramètres T/S grâce à son PC
You need a sound card with line input.

It is very bizarre to use a 8" starting at 500Hz till 5000Hz ?
Without SPL measurements because we don't have specifications of the drivers, it could be difficult to do something.
The sensitivity of the drivers must be known.
I can't give you a response if you can use your "tweeter", estimate to 89-92dB/2.83V. The sensitivity of the wooofer is missing.
There is a strong probability.

You have the possibility to do a 2 ways, just add a 2" compression tweeter to your 12". No problem with the sensitivity, a L_PAD is sufficient.

To summarize, your crossover schema could be used but the sensitivity of the 12" is missing. You need a 8 ohms mid and a 8 ohms tweeter.
Your "tweeter" perhaps is a 4 ohms (measure it) , we can't say if it could be used. The mid used 500-5000Hz, the sensitivity ?

[stf92]

Thanks for you estimate of the inductances to two figures. The presence of an 8" mid is due, I think, to the fact the baffle was manufactured during the 1980's, in a time when bigger drivers were used, but this is merely speculative. The firm was of only local prestige and has long ago disappeared.

I will begin with the measurements but, due to my lack of experience, I anticipate this thread will be dead by the time I will have gathered the data. Never mind, I'll start a new one. I'll try to read the tutorial with the help of my sister. Thanks a lot and au revoir.