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-   -   Can someone comment on my hornresp simulations on the MCM8? (http://www.diyaudio.com/forums/subwoofers/177681-can-someone-comment-my-hornresp-simulations-mcm8.html)

blamus 22nd November 2010 04:08 AM

Can someone comment on my hornresp simulations on the MCM8?
 
2 Attachment(s)
Just started to learn how to use hornresp. can the TH experts give me some comments just for educational purposes? the aim is to get as high SPL as possible in as small an enclosure between 35-80Hz, in a vehicle powered by a 70W amp at 2 ohms.

best regards

MaVo 22nd November 2010 08:16 AM

Number 1 looks fine to me. Its interesting how you got that design to work by using such a long L12. I usually try to make L12 as short as possible, but here it seems to be better your way.
Number 2 has this deep notch directly above the passband. If the real box is just slightly off (which is very likely to happen - happened to me all the time), it could jump right into the passband.
Try to make your designs a little "safe" or "stable" concerning parameter variation, because what you build will never be a 100% representation of what you design.

All that said, i would go with no.1.

blamus 22nd November 2010 10:10 PM

I made some improvements - i think!
 
4 Attachment(s)
Thanks Mavo for the comments!

Thats a very valid point about the huge notch may get into the passband when built, I never even thought about it that way.

I made some adjustments/improvements - smaller and louder:

Now all my simulations are done in 2pi and 2.83v, so I can compare to other box programs such as winisd

3. Flat from 40-100Hz at 99db, at 75L - This is a variation from TH1 above, smaller, higher SPL, flatter.

4. 30-80Hz, 93-99db, rising response at about 6db/oct. 46L. This I think I like. I believe the response shape here is perfect for cabin gain. Larger than TH2 above, the notch is still there but at a higher freq, way above the low pass would be used.

displacement seems fine at 12V (70W@2ohms) if I high pass at 25Hz.

This time I have included both screenshots and the honresp export, so people can just look at it or import it if they want to play with it (please!)


What do people think? Are these designs worth pursuing? As in, can it be improved much more?

littlemike 22nd November 2010 10:31 PM

Compression (area of horn at throat entry vs Sd) looks a little high. I tend to aim for values lower than 4 with these drivers.

Brian Steele 22nd November 2010 10:50 PM

Quote:

Originally Posted by blamus (Post 2373988)
What do people think? Are these designs worth pursuing? As in, can it be improved much more?

Caution: I don't think HornResp includes losses in its modelling. What looks flat in the same might not end up being flat when you measure it. Rolloff might end up being higher and faster than predicted, for example. On the plus side, the response is likely to be smoother than predicted.

blamus 23rd November 2010 05:19 AM

Quote:

Originally Posted by littlemike (Post 2374011)
Compression (area of horn at throat entry vs Sd) looks a little high. I tend to aim for values lower than 4 with these drivers.

You mean the ratio hornresp shows when I put the mouse over S2? I have done a bit research there and apparently jbell has tried using a compression ratio up to 8:1 and its fine for these particular drivers. But I maybe wrong.


Quote:

Caution: I don't think HornResp includes losses in its modelling. What looks flat in the same might not end up being flat when you measure it. Rolloff might end up being higher and faster than predicted, for example. On the plus side, the response is likely to be smoother than predicted.
So do you think sim 3 would work better even with cabin gain? Which one do you think would work best in the average car? Or do you think none of them are any good? Am I doing the right thing/heading in the right direction? I really have no idea!

mwmkravchenko 24th November 2010 03:20 AM

Quote:

You mean the ratio hornresp shows when I put the mouse over S2? I have done a bit research there and apparently jbell has tried using a compression ratio up to 8:1 and its fine for these particular drivers. But I maybe wrong.
4 to 1 is usually safe. 8 to 1 is asking for some blown drivers if they are not tough enough. Remember that the ratio is describing the area of the cone to the area of the throat. That means that what ever pressure is being created by cone movement is being amplified by roughly eight times.

Mark

littlemike 29th November 2010 03:35 AM

Jim got away with high compression by using a compression chamber, something you don't have. Additionally, his is a front-loaded horn, not a tapped horn.

I've not taken these drivers much above 4:1 in tapped horns. I've not killed a driver yet, but I really have not tried.

jbell 29th November 2010 12:24 PM

yea, 8:1 with a compression chamber works great -- I've yet to rip a cone in that configuration -- and I've tried. 8:1 FLH with chamber is the most efficient config I've found. I've yet to find a TH config for the mcm that will beat the FLH's I've done.

I'm not sure why you are using 2.83 volts and 2pi with a pair of 4ohm drivers in parallel?

If you want a 1 watt reading @ 2 ohm, you need to be using 1.41volts.

MaVo 29th November 2010 07:32 PM

Have you ever tried the 8:1 without a compression chamber? And what size do you use?


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