Diy Question thread

Johnny: Parenthesis are fortunately not a limited resource, we can use as many as we like without fear of running out. Good work on the GCSE maths there though, what grade are you aiming for?
This link should clear up the equation problems for you http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html#c2 though I'm suprised you didn't recognise it straight away given your previous input to this thread.

Just for the record, you didn't specify what R, I and V are. Furthermore, your use of a space before a questionmark is unjustified etc. etc. etc. You also don't need a comma after 'that' in the statement 'your use of the parenthesis is unjustified given that,
multiplication is commutative in the field R'.

 

Are you for real?
You have no understanding of ohms law, you make that obvious.
Of course the length is a factor if using a single piece of wire.

If a wire has a resistance of 1 ohm per meter......you do the maths.

 

Johnny old fruit. One should always remember to start with a capital letter at the start of both sentences and paragraphs. Proper nouns need should also be spelt with a capital letter.
Technically the comma Anex mentioned should have been a colon.
However please continue, it is always entertaining watching someone make an ass of themselves.

 

I'd have thought you could just leave it as a statement, 'given that the use...' but I agree, Colon sums him up nicely

 

Having just moved my open baffle test speakers into my main listening room I found they exhibited some of that same confusion I heard in Thorstens system. Having put some absorption behind them to absorb the back-wave they have cleared right up. I think this is what I hear in your system T, as well as the amps and slightly lower SPL ability than the 12" Mags I am using on your recommendation.

My feeling then, is that open baffles (when designed for accuracy in the choice of drivers ect..) have a severe disadvantage in (IMO) NEEDING room treatment to deal with their rear output. Absorption in small rooms and diffusion (which works to a low frequency) in larger ones. However, once that handicap is dealt with, they take on a higher degree of accuracy than I have heard from any box speaker. The dynamics and imaging I am getting right now, even with these things I knocked up in 1 day and another playing with the Xover, is absolutely gob-smacking.

Of course box speakers need treatment too, but they aint so bad in the midrange as OB’s when they don’t have it.

So, I would suggest that you could SERIOUSLY benefit from some absorption behind those speakers T. You have some record storage at the moment don't you?

 

Obviously a fearsome intellect such as yourself would already know that in the context of our discussion those variables are defined. However, I shall humour you.

rho = resistivity
L = length
A = cross sectional area
R = resistance

Just as meaningless as your V/I=R was without similar definition. However, somehow through context I managed to know what you were talking about. Must be luck.

When it comes to forums, some are more equal than others.

 

Hi,

I had hoped I had enough absorbtion, but I had a somewhat abortive idea which I might dig back out.... Got any good commercial source for Basotect?

Ciao T

 

I don't think that would work in your room. I think you'd want to look at absorption at lower frequencies than you'd get from Basotect in the (limited) space behind your speakers, at least as long as they are positioned as I saw them.

 

Indeed, basotect’s absorption falls off sharply below about 400Hz due to its light weight. But yes I have some good sources for it.

What I would suggest is simply rockwool. I have some more of the things I am using if you want to give me a few bob for a pair (£50 each?). These are the prototypes I bought back from my distributor recently and mentioned in my PMC advert.

Here is a picture of one. The fabric needs re-doing but thats no problem.

 

Markus,

Right now they are stored away, I think before they come out again the whole room will have changed quite a lot.... (my wife has been endlessly nagging about doing it up).

And actually, I only want to absorb above around 250...500Hz anyway, below I do NOT want to absorb sound, hence BasoTect.

Anyway, I'll return to that subject in time.

Ciao T

 

Probably better to use a denser material in a thinner amount to control the frequency at which it becomes less effective. 250Hz is really more than you can expect from Basotect. Anyway if you need any help when you get round to it let me know.

and your wife is right, wallpaper is so 'old people'

 

Nice traps Simon.

Didn't realise you were into that sort of thing.

What's the effective operating range of those? I'm using some 3ft x 1ft x 1ft corner traps along with 2" tiles + eggbox tiles. I've found the wall treatments are effective above 800hz but the bass traps are somewhat dissappointing in performance and given their bulk and imposing nature I'm considering ditching them altogether and just settle for a little more EQ in the 80-200hz. I'd have a hard time bettering the measured performance above 200hz but have some serious problems in this region with a huge 13dB broad peak at ~115hz. That makes things sound terrible with a slow and plodding nature without some excessive EQ, the bass traps only seem to improve this by a few db's at best and towards the upper end(200hz). Below 100hz and they are useless of course.

I've tried a couple of traps now from Auralex (LENRD's) and the cheap ebay ones(3ftx1ftx1ft). I'm guessing that I'm using inferior traps with exagerated specs and naff performance in the range I'm looking at. I've been looking at RPG and Auralex Venus but these traps are huge with a price tag to match.

I was wondering if you could make a more informed suggestion. Other than that I'll have to leave with the EQ and ineffectual traps.

 

Paint the room various shades of grey You'll feel like killing yourself after a few hours spent in the room.

I wish I'd gone with something a little more 'upbeat' now but the projector dictates much regarding light control. If I'd only got hifi to worry about I'd have a much prettier install:





I particularly like the discrete wall mount absorbers and diffusor panels with maybe some soft lighting behind them. If and when I get round to doing the room again I'll probably try to make it look a little better. It gets depressing after a while in there.

 

The performance of the ones pictures is equivalent to the Auralex ones, but made to look nicer for WAF. I intend these 'Essence' traps more for midrange and upper-bass. ...when I bring them out, for now funds only allow me to launch the other 2 products.

What ya need is a decent bass trap like the RPG Modex. My version is the 'Confidence' as on my website. They are just less than 4ft tall so you can stack them. Compared to foam type bass traps they are vastly superior, but performance drops above 110Hz as they work on pressure, not incidental sound. They work down to about 50Hz (like the RPG's). Contrary to Auralex’s claims their foam traps will only work reasonably well down to about 80Hz.

I have a pair you can take for a test drive in a few weeks if you like, either pick them up for pay postage. I have to keep them at the moment though so I can check packaging samples fit when they EVENTUALLY arrive!

On the other hand you could wait a month or two and demo a pair or even better a quad from Sounds of Music.

 

Shin, Johnny has made away with your mid-range's!

 

I'm sure he'll refute that claim using a combination of prowess in physics and electronics.

 

I'd definitely be interested in that, its the biggest complaint that I have at the moment, well that and lack of bass below 35hz.

Can you reveal anything about the construction of the Confidence (PM if you like). I've found that most of my bass problems are related to the position of my speakers relative to the rear wall. If I move them a foot into the room then things are improved in the problematic region I was talking about. I've tried piling up the corner traps I have now behind the speakers but this was less effective than fixing the traps into the corners of the room and between the wall/ceiling.

From my meagre experience I've found it very easy to fix my region above 200hz - I played with placements and settled on what you'd expect from conventional wisdom, all in all it was much less critical than the 80-200hz bass range which is a law unto itself.

Where do you think these Confidence traps of yours will work best? I mentioned the real wall-loudspeaker distance as improving matters, would the trap work well directly behind the speakers? Like I said, I've tried this with the existing traps and it measured and sounded worse than with the corner placements.

I agree with Thorsten that dipole bass is superior to monopole for exactly the reasons I'm talking about.

 

You need to place the Confidence in the corners. It works on pressure changes and the corners are (as T said) where pressure is at a maximum.

The foam type of traps are kind of a contradiction, they work by absorption of particle vibration yet particle velocity is lowest near a boundary (where bass builds up!).

You might get some more out of what you have by placing them in the corners of the room but spaced 5-20cm or so off the wall.

I'll send you a PM.

 

I asked you if I need to specify the length to know the resistance of a component, say a resistor.

and you replied : '' If you were making a resistor out of a single piece of wire, yes you would. The question was asked in the context of a cable so yes. ''

''You would only need to specify those things in order to know resistance''

''Resistivity is a property of a material. It is not dependant on the dimensions. Resistance is. ''


So here we have three quotes all highlighted in red for the convenience of the forum members, which are false and/or demonstrative of his incompetence.

The first/second statement is false, since as I have already explained, ohms law gives a simple relationship which does not include length as a factor, but enables one to determine the resistance of a component based on the time derivative of charge for a given volatge v.

The third, and rather vague statement merely exemplifies his lack of knowledge in electronics.

Would you care to explain what you mean by '' resistivity is a property of a material '' ? What sort of property ?

Please also explain to us, what you mean by '' It is not dependant on the dimensions ''.

What do you mean by dependant ?



Johnny.

 

Isaac you’re so incompetent!

Johnny: Seriously, you’re a spanner. You have just proven to the whole forum you have no grasp of the most basic physics/electronics principles. I'd expect any AS level physics student to be able to answer those questions. You clearly have no idea about Ohms Law and didn't explain anything with it.
Can I suggest you get yourself a science book from the library, one of those nice ones with lots of pictures, and perhaps a dictionary to look up the definition of dependant.