DIY 250W combo .

[agedhorse]

My calculations show that with 25 degrees C ambient, a 31cm x 31cm x 31cm wood box with nominal 12mm thickness, the final temperature after "forever" (called the asymptotic limit) will be 33 degrees C with an 8 degrees C total temperature rise. This is about what I would expect worst case, pretty much trivial.

 

Here's one handy enclosure calculator, there are several. These sorts of formulas are also used in the heating and air conditioning industry too, the walls will have a thermal resistance, and if playing in the sun there will also be heat gain due to radiation.

 

https://www.powerstream.com/temperature-rise-in-an-electronics-enclosure.htm

[agedhorse]

9 hours ago, Matt P said:

@Downunderwonder your maths looks right to me (although it is nearly 20 years since my thermodynamics lectures at uni)

 

the TC Electronic combo that is shown above might have a side mounted vent/fan but it also has an air gap all round the head in that enclosure so there is some ventilation for the amp (and i'm not going to mention the actual rating of that particular amp being much lower than the quoted value)

 

I think this little 250w head is going to get rather warm and possibly shut down (assuming it has a thermal cut-out)

As there is an insulating layer of wood between the amp casing and the outside world it will be difficult to keep track of how hot the amp itself is getting. 

 

Matt

Yes, the air gap will reduce the enclosure heating effects somewhat which is why I keep mentioning worst case.

[Downunderwonder]

20 minutes ago, agedhorse said:

My calculations show that with 25 degrees C ambient, a 31cm x 31cm x 31cm wood box with nominal 12mm thickness, the final temperature after "forever" (called the asymptotic limit) will be 33 degrees C with an 8 degrees C total temperature rise. This is about what I would expect worst case, pretty much trivial.

 

Here's one handy enclosure calculator, there are several. These sorts of formulas are also used in the heating and air conditioning industry too, the walls will have a thermal resistance, and if playing in the sun there will also be heat gain due to radiation.

 

https://www.powerstream.com/temperature-rise-in-an-electronics-enclosure.htm

Thanks for that.

 

The opening line is so apt:

"I find that there are far too many fins, louvers and holes in this world."

 

A furry carpet coating not accounted for and a sunny day outside might add up to a few more degrees inside but not enough to trip the overheating breaker methinks. Gut instinct overridden by actual numbers.

 

Next question. What's the actual surface temp of a furry cab in the summer sun?

 

I would run it sideways just because everything likes running cooler rather than hotter.

[Downunderwonder]

25 minutes ago, agedhorse said:

air gap

Not seeing it.

[JohnH89]

'My calculations show that with 25 degrees C ambient, a 31cm x 31cm x 31cm wood box with nominal 12mm thickness, the final temperature after "forever" (called the asymptotic limit) will be 33 degrees C with an 8 degrees C total temperature rise. This is about what I would expect worst case, pretty much trivial.

 

Here's one handy enclosure calculator, there are several. These sorts of formulas are also used in the heating and air conditioning industry too, the walls will have a thermal resistance, and if playing in the sun there will also be heat gain due to radiation.'

 

Cheers for that . Way beyond my comprehension but I have confidence in the design . For info , cabinet measures 395mm on each side of the cube (internal measurement ) . 2 x 75mm ports in the lower part of the rear plate . Cabinet is built from 9mm ply , laminated to 18mm across approx 65% of surface area . Baffle and rear panel from 18mm MDF . 

I will really try and destruction test it tomorrow . If it survives ( it will ) I will buy myself a beer . And those that have helped can have one on me .  😀

#downunderwonder . Just what is your obsession with the sideways thing ? I said I would do it just to please you . Just wait for some empirical evidence . Not long now .......

Edited November 10, 2022 by Wally Gogg

[Downunderwonder]

I make it an average 15mm thick. The bigger size 41cm nets 5.7°C rise.

[JohnH89]

A quick update for you who may be interested . Played my Yamaha BB734 through the amp for 2 hours at a rehersal tonight . Sounded great to me and compliments from other band members . Had it up way too loud and made the point it was to stress test the amp . It coped with the above plus 20 minutes or so idling between songs . A couple of quieter tunes to give the ears a rest and finished up with a full on hammering . Now here is the thing ......

No noticeable heat at all . Played with it on its side for a couple of minutes at the end , and no noticeable heat from the upper reflex port . Not even detectable above ambient temperature . I couldn't tell you if the fan even ran as it would be impossible to hear unless cabinet was dismantled . The rehersal space is centrally heated to 21 degrees (70 F) . 

Very pleased all round , the only possible casualties are the windows which got rattled a bit .

Thank you all for your help , assistance and ideas . Any further reports or problems in the future I will post it here .

[agedhorse]

Yup, insignificant heating issues.

[LarsTimm]

Good to hear, thanks 👍

Love these diy builds 😀

[JohnH89]

12 hours ago, agedhorse said:

Yup, insignificant heating issues.

I think we knew that . Well , you did and I believed you . Cheers Mon Ami .