GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.

Post Subject: Sarcophagusing the driver…Posted by Romy the Cat on: 9/17/2010

oxric wrote:

Hi Romy:

I have been following your mid-bass horn project with a mixture of fascination and horror for a little while and am awed by the remarkable amount of creative thinking that has gone into it.

I am sure there is no need to worry but I would hate for you to do some really serious damage to the drivers you are using. The 'vents' at the back of the Vitavox drivers are presumably there to ensure there is some amount of convection present to cool down the coil as 95% of the power used by the driver tends to be transformed to heat. I may be talking out of ignorance but I would be concerned with the 'sarcophagus' method you have employed to reduce rear chamber volume to virtually nil.

Also, when cooling by convection cannot take place, the heat will be transferred to the rest of the unit by conduction so that that chassis temperature
might rise considerably and I do not know enough to comment on the effect of high temperatures on the fabric and masking tape you are using.

In any case, operation of the coils at high temperatures, if present may well adversely affect the performance of the drivers when they are called into use for extended durations depending on volume and musical content.

Good luck (you may need it)
Rakesh

Rakesh, I never thought about it, good thinking. You might be right, in fact it might explains why some bass horns might sound soft. If the back chamber is sealed and the horn used as a compression driver then presumably the temperature of the VC would rise and raise the temperature of the magnet. If you remember in the thread about electromagnets a guy from Belgium I believe told that he have evidences (and I believe him) that as filed coil warms up the driver the temperature make the driver to sound soft. Do you see a possible connection?

I agree that sarcophagusing the driver into the foam cocoon I reduced the capacity of the driver to dissipate heat. I would not say that I did it deliberately –I just did not think about it and it was the only way to do the back chamber within the time frame. Still, analyzing the problem now I would bring to the table the following arguments.

1) Putting the driver into foam reduced or eliminate the exposure of the driver to attic heat (very hot on summer) and cold

2) Considering the very high efficiently of the channel the driver will use very low power (probably no more than 3W) and with this power the heating up of the VC will not be a subject at all.

3) The horn has a large front chamber that will be able to cool down the driver

4) The Vitavox driver use Alnicko magnet that has higher temperature resistance then other magnets

(table 5.2 at http://www.magnetsales.com/Design/DesignG_frames/DesignG_2.htm)

So, I think, or more precisely to say hope, that the het from VC would not be a problem. On summer the attic is so hot that you can cook pizza in there. The VC would generate this heat long after the VC will be melted. So not forget that this is very rare and very low power driver with no cone excursion. The driver has name Vitavox 15/40, 15 is impedance, 40 is max power that the driver can handle. So, considering very low power that I will feed the driver I think the VC’s hear will not be a subject.

Anyhow, thanks for warning, I did not think about it and in case the driver handle 300W-400W then the CV venting would be certainly an issue.

The Cat

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