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Multi-Way Conventional loudspeakers with crossovers

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Old 10th June 2013, 05:40 PM   #61
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I'd reckon the 600Hz to be a cabinet issue: standing waves or similar. Its the right sort of order of magnitude. Any of the box dimensions around 30cm (or multiples)?
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Old 11th June 2013, 08:23 PM   #62
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Hi there Wintermute,

Woofer measurements attached, in box.

Thanks!
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Old 11th June 2013, 08:30 PM   #63
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And tweeter in box, in case it makes a significant difference...

Thanks!
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Old 12th June 2013, 03:06 AM   #64
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the woofer measurement looks much more like what I would have expected

There is something odd with the tweeter measurement though... The impedance peak and the other irregularities in the impedance plot seem to have shifted up by about 1Khz. I wouldn't have thought that mounting it in the box should have had this effect...

could you do the tweeter one again just as a sanity check?

edit: Just out of interest, I've posted a comparison between a textbook 2nd order L/R at 3Khz with a textbook lpad (with 8db cut target) and what I had so far come up with. I think this is a good example of how poorly an off the shelf text book crossover can perform. text book is the black curve. Note this one has not got full bsc, as per Chris' comments. I'm not sure yet if it is as good or not. using full BSC gives a bit more room for manipulation

Tony.
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Last edited by wintermute; 12th June 2013 at 03:26 AM. Reason: add comparison of text book and custom crossover.
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Old 16th June 2013, 09:56 AM   #65
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Hi Shaolin. I decided that as a sanity check I should check how much it would cost for the crossover components in the crossover I was modelling. The bad news is that it came to almost $100 (and that is not using anything expensive). Just off the shelf parts from parts express. I'm guessing that is many times the cost of the actual drivers, so may not make a lot of sense to persue.

I think you said originally you had some off the shelf crossovers?? Could you post what they actually are, ie rated ohms, and whether they are 2nd order 4th order and what the crossover frequency is?

Also if you could the values of the caps used in them....

It may be more economically sensible to approach it from a improve what you have got rather than start from scratch angle.

A large part of the cost was inductors. There were 4 and they were biggish values. three of them were 1mH or bigger.

I can post what I came up with but I'm just not sure it makes economic sense

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Old 17th June 2013, 02:39 PM   #66
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Hi there,

This is the crossover:

Q-components

Thanks!
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Old 17th June 2013, 11:14 PM   #67
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And here is a photo of the crossover in detail - it's a 10uf cap.

Thanks!
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Old 18th June 2013, 03:14 AM   #68
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thanks my next question after looking at the crossover was is it a 10uF cap looks like textbook 1st order. so coil will be around 0.63mH (I'll guess the closest standard value).

I put this into speaker workshop this morning and it was surprisingly not too bad (better than the 2nd order 3Khz I modeled before).

I accidentally shut down my main machine (rather than the VM) and it is looking like the speaker workshop project I had for this has been corrupted running a checkdisk now hoping it will come back.

2Khz is a very low crossover point but I think that it should be possible to improve on your basic XO mainly concetrating on the peak from the woofer.

I think you said you had an LPAD. Is it one made from two resistors or one of the infinitely variable types. If two resistors, what value for the series and parallel ones..

Tony.
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Old 19th June 2013, 12:10 AM   #69
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Heya,

Here's the L-pad detail. It's an AT-50H, similar to this but the stereo variant:

L-Pad 50W Mono 1" Shaft 8 Ohm 260-255

At this point if the box isn't salvageable, I'm thinking of possibly building something like this with the dayton ND91:

The Sprite - self-contained ND90 boombox

I probably should have started with a kit in the first place

Thanks!
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Old 19th June 2013, 11:18 AM   #70
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Hi Shaolin,

Below are the results of tweaking the off the shelf crossover circuit. The first is the actual modifications to the circuit.

2nd is the simulated spl compared to the (blue) simulation of the off the shelf crossover with just an lpad. There isn't a huge difference, but I think the removal of the peak between 4 and 5Khz should make quite a difference to the sound balance.

3rd is the simulation with the tweeter phase reversed (note that it should be connected in reverse polarity in this crossover). The null is not too bad and shows reasonable phase tracking in the crossover region. The off the shelf doesn't do as well.

4th is the impedance plot to show that there are no nasty dips.

The crossover is actually 2nd order bessel acoustically at around 2Khz. This is rather low for this tweeter, but provided the speakers are not pushed too hard it will probably be ok.

The bass response was using the model for the bass reflex tuning of 53Hz in your existing enclosure. I'll see if I can do a sealed for comparison.

Note that this still needs some baffle step compensation. I'd suggest doing this as passive line level as Chris posted earlier. It should be much cheaper and easier and easier on your amp. Rod Elliot covers it here --> Baffle Step Compensation

I haven't tallied up the cost for this variation, but I think the coils will be the most expensive and I simmed using these ones Jantzen 0.50mH 20 AWG Air Core Inductor 255-036 which are only $4.59 each. In total it probably won't be much over $20.

So I guess the question is whether you want to spend a bit more to see what improvments you can make or start from scratch with a proven design. I guess the most important thing is to have learned something from this one

Tony.
Attached Images
File Type: png tweaked.png (8.9 KB, 15 views)
File Type: png teaked_spl.png (25.5 KB, 15 views)
File Type: png tweaked_null.png (27.9 KB, 4 views)
File Type: png tweaked_impedance.png (17.0 KB, 3 views)
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