Can someone comment on my hornresp simulations on the MCM8?

[jbell]

Originally Posted by MaVo

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

The compression chamber is THE KEY to flat response with the mcm and FLH design. Depending on the design -- anywhere from 4-20 liters. It's amazing how changing the compression chamber size really affects response. One of my test cabinets, I intentionally left the chamber too big, and played with closed cell polystyrene foam to test/measure the response differences. That was a real learning experience.

One thing I did find out, that at 8:1 compression ratio, a more 'square' aspect throat sounds better than a high aspect ratio throat -- aka, 2x2 sounds better than 0.5 x 8. That I don't have a real good explanation for....

[tb46]

Hi blamus,

I just tried to import your thdual4.txt, and it imports fine, but there seem to be some version problems. What version of Hornresp did you use? I'm using Version 28.10 (2810-101129).

To make the woofers fit you have to either add a chamber between the woofers and the horn, or provide at least one woofer diameter as L12, the same hold true for L34. Ap1 and Lpt are the port dimensions from a throat chamber (Vtc / Atc) to the horn at S2, you don't need them unless you add a throat chamber.

Regards,

[MaVo]

Thanks jbell

[jbell]

Here's a case in point mavo... play around with this one, run the chamber size down to 1 liter, then up to 10 liters.... 4.5 liters appears to be 'just right'

If I remember right, this is the sim for the dual mcm flh thread cabinet. Dual MCM FLH

[blamus]

Hi guys,

Thank you very much for your responses.

tb46:

I have increased L12 and L34 to 25cm (about 9") and tweaked the model. See attached. Good that you pointed that out. I really didnt even think "physically" in real life space when I was playing with the sliders. The numbers in AP1 and lpt are just copied from another hornresp record.

I have now removed it.

Turns out I am using version 28.00 I hope there isn't much that would change my simulations in the different version. I shall update soon.

Jbell:

Thanks for the heads up about the compression ratio significance between THs and FLHs and compression chambers. I honestly didn't know the differences until now.

I used 2.83V and 2pi for all my simulations just for comparison. I started with just one MCM driver so thats why it was 2.83V. All that matters is that I know I will have 12V (70W@2ohms) in 0.5pi (in car) at the end of the day. It doesn't matter as long as I make sure I have the same input voltage for all my simulations right?

Mark:

you have mail and thanks again for all your patience!

I have my MCM woofers in the mail. No turning back now!

Best regards

Bern

[mwmkravchenko]

Happy to help.

Mark

[blamus]

I do have some other queries.

1. In some designs an inductor is used to tame the response. If I do that, do I just add the inductance of the coil to the Le of the driver specs in hornresp? Because that does seem to affect the response alot.

2. When EQ is used on bass horns, be it TH or FLH, is the effect of the EQ altered by the horn as well? For example, if I have a 3db dip at 60Hz, and I "EQ-up" at 60Hz 3db, would that actually work? Or would that boost also affect other freq in strange ways and at different levels (e.g boost 6db instead)?

[mwmkravchenko]

Bern Driver.JPG

In the Horn Wizard there is a drop down menu on the bottom right. One of the things on the list is the driver. In the driver parameters you can add in inductance. This will create a lowpass filter effect.

As for EQ you can shape the response of a horn in it's designed passband. If you try boosting it below it's passband you will have to buy drivers fairly regularly. The effects on the EQ on the adjacent areas of the frequency response depend on the Q of the filter used. High Q means a narrow filter width. Low Q a broader filter width.

In a car sometimes the best thing to do is move the sub around a bit. It will change the response quite dramatically. Same goes for a house actually.

Trying to tame low frequencies any other way gets increasingly complex and ineffective. Location and number of points being excited in the room are the most important points to work with.

Mark

[tb46]

Hi blamus,

I may be worthwile noting, that when you add a series inductor you are also adding a series resistor. As a rule of thumb .05 Ohm / 1 mH. The resistance is added under Rg, and the inductance added to Le.

Regards,

[blamus]

ok cool, so eq works just the same way as with sealed boxes. And when I add a coil, I'd also have to add the resistance.

Now that brings me to wonder, if I was to use a passive high pass filter - as with most of these bass horns a HP is needed - at say, 30Hz, would the caps and coils do anything unexpected to the response? Or would it just apply the designed high pass effect just the same way as it would if used on a sealed box?

That might be a stupid question with a simple answer, but I have to ask, since horns are sooooo different than a sealed box, and I have never used a horn before.