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Reduce MT-130 horn

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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Topic: Reduce MT-130 horn
    Posted: 25 November 2014 at 10:48am
Hi!

I´m planing to build some MT-130 with limmer 042 over it.

The question is that I´ll like to reduce the lenght of the horn in 10cm to make the speaker thinner to fit better the limmer horn. How will this afect to the speaker response?



Regards!


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DMorison View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 25 November 2014 at 12:12pm
It won't provide its acoustic loading down to as low a frequency, and will exhibit a wider coverage pattern towards the bottom of its range, therefore will need crossed over higher than the original.
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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Posted: 25 November 2014 at 12:21pm
Thanks DMorison.

And you think it will get low enough to meet the ES18BPH under it?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote nickyburnell Quote  Post ReplyReply Direct Link To This Post Posted: 25 November 2014 at 5:53pm
I forgot I built these once!  Long distance cab, used them on a farm, up close seemed like they wern't on, but at a distance were mad loud.
It's everything, not everythink!
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DMorison View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2014 at 1:52pm
Originally posted by vicenturi vicenturi wrote:

Thanks DMorison.

And you think it will get low enough to meet the ES18BPH under it?
 
Wouldn't know without modelling it, sorry.
Also haven't used that bass bin so I wouldn't know what upper cutoff it can use and still sound good. If it's really OK up to 250 per the plan then you might be OK.

HTH,
David.

Edit - corrected typos, added reference to nominal cutoff of ES18.


Edited by DMorison - 26 November 2014 at 7:19pm
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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Posted: 28 November 2014 at 1:34pm
Someone can help me to sim this modified mt-130?

I´m planning to build one model to test it with measuremen equipment but will like to see what hornresp or similar program tells.

The possible drivers that I will mount are the pd121 or the rcf 12 p110k.

I´ll like it to work between 200-550 Hz.
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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2014 at 11:54am
I´m trying to sim my mod. mt130 in hornresp but I´m new in this and don´t know if I´m doing it good.

Someone can show me a screen capture of the input parameters of a normal mt130?

Thanks!
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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Posted: 04 December 2014 at 11:31am
Trying to sim the speaker in hornresp, in the schematic diagram window i see that apears a conical flare adaptor that I think that is not suposted to be there in this speaker.

Anyone can help me with the input parameters?

There is a screenshot of what I´ve introduced, and the diagram with the conical flare marked.



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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2014 at 10:15am
Anyone?
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DMorison View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2014 at 12:56pm
Am not a Hornresp expert but as far as I can see I'd model it a bit differently:
1: Rear chamber calculates out to 15l max so will be about 12-13l net by the time you account for the driver in it.
2: Front chamber includes the space in the cone of the driver plus the 28cm disc in the first, 10mm baffle - that disc alone is over 600cm^3 so I've estimated 2l total.
3: S1 & S2 are the 27.3*6.8cm aperture in the second, 18mm baffle.
4: I put a very short section (S2 - S3)  to account for the change in height from that second baffle to the full horn height.
5: As all the sections are straight sided I used conical rather than exponential flares.
6: Your two sections (with corrected areas)  then become sections 3 and 4.
7: There's no port from the chamber to the horn, so I used standard driver alignment (I think you used "Compound") and didn't put anything in Ap(1) and Lp(t).
8: Midranges should be modelled in 4Pi (full space) rather than 2Pi.
 
 
Black is your shortened version, grey is as close as I can get to the original.
You should still get down to around 200Hz if this is accurate, but you also may have more dips further up in the midrange (600Hz) which I didn't expect.
I know Hornresp always shows more rolloff at the upper end of a horn's response than people report in real life, so I don't know how much of an effect that will have.
 
Cheers,
David.


Edited by DMorison - 05 December 2014 at 1:01pm
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vicenturi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vicenturi Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2014 at 9:57pm
Thanks for your help DMorison, very usefull!

The diferences in the area sections are because I´ve modeled the speaker in CAD program with small diferences in pieces (for easyer build) and the dimensions are directly measured in the model.

This are my revised input parameters and the results.



How does this look to you?

I get this message in the calculation proces, is it normal?



Kind regards!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2014 at 9:47am
That looks pretty realistic to me now, that popup warning comes form having the very short section in to account for the step from the baffle to the full height of the horn - you could try modelling without that to see if it makes any difference, but I prefer to be as accurate as possible in case there is some unexpected effect I'd otherwise overlooked.
Your curve looks very similar to mine, the dip in the mids is pushed up to a slightly higher frequency which may even be a good thing.

Edit - just tried modelling a smoothed out version without accounting for the step and the difference is so small as not to be worth it.


Edited by DMorison - 06 December 2014 at 12:31pm
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