Sub woofer questions

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Hi,

So about 1x1.5x2?
No, not quite, lol. The idea is that the numbers are not multiples of one another!

The reason it's important for room acoustics is to avoid 'room modes' building up on top of each other. You must consider harmonics of the fundamental frequency. It's most easily explained with an example:

Room = h5xw15xl20m (your number ratio)
Speed of sound in air = 330m/s

Frequencies whose half-wavelength is equal to a room(or speaker cabinet side wall) dimension will be 'amplified'. Then multiples of this will be equally. So, back to our example..:

Room height = 5m > 330/10 (5x2) = 33hz(fundamental), 66hz (F2/2nd harmonic), 99hz, 132hz etc. etc.

Fine so far, but then these are added to our width modes:
15m > 330/30 = 11hz (yum yum), 22hz, 33hz, 44hz, 55hz, 66hz, 77hz, 88hz, 99hz, 110hz, 121hz, 132hz, etc. etc.

Already, without doing the same for length it's easy to see the problem: 33hz, 66hz, 99hz, 132hz etc. will directly pile up and combine to make the bass very, very lumpy.

Apparently it's possible to have variations of up to 30db from this effect in a room!!!

Golden ratios aim to have little overlap of these numbers - they should be spaced apart from each other.

I hope this makes sense to you, I know my explanations aren't all that good!


-Simon
 
SimontY said:
Hi,


No, not quite, lol. The idea is that the numbers are not multiples of one another!

The reason it's important for room acoustics is to avoid 'room modes' building up on top of each other. You must consider harmonics of the fundamental frequency. It's most easily explained with an example:

Room = h5xw15xl20m (your number ratio)
Speed of sound in air = 330m/s

Frequencies whose half-wavelength is equal to a room(or speaker cabinet side wall) dimension will be 'amplified'. Then multiples of this will be equally. So, back to our example..:

Room height = 5m > 330/10 (5x2) = 33hz(fundamental), 66hz (F2/2nd harmonic), 99hz, 132hz etc. etc.

Fine so far, but then these are added to our width modes:
15m > 330/30 = 11hz (yum yum), 22hz, 33hz, 44hz, 55hz, 66hz, 77hz, 88hz, 99hz, 110hz, 121hz, 132hz, etc. etc.

Already, without doing the same for length it's easy to see the problem: 33hz, 66hz, 99hz, 132hz etc. will directly pile up and combine to make the bass very, very lumpy.

Apparently it's possible to have variations of up to 30db from this effect in a room!!!

Golden ratios aim to have little overlap of these numbers - they should be spaced apart from each other.

I hope this makes sense to you, I know my explanations aren't all that good!


-Simon

ah, now i understand. the problem with learning from forums is, people never explain things when the person they are talking to knows what they are talking about. so my understanding of audio etc. is a bit patchy.
 
Having now finished my subwoofer and listened to it for a while, I am thinking of improving it.

As documented in different thread, I am building a Linkwitz Transform circuit, to equalise the output. This will be the only change for a while, as this is costing about £10, and I can’t afford more than this, ruling out more expensive upgrades.

The next development will be a new, better driver. I had previously assumed that I would get an Adire Tempest, as they seem to be a very popular driver. I then tried some of the other drivers by Adire in WinISD, and some look good. The main two were the tumult and DPL 12. In comparison to the tempest, the DPL 12 is amazing (see attached graph). Looking at the prices, the DPL 12 is the same as a tempest, and over three times cheaper than the tumult. I have read the DPL 12 is good for dipoles, and it says this one the page, but I don’t know if this meant it is useless for standard boxes.

My question is, is the DPL 12 ok for use in standard boxes? Most importantly, my 93L sealed box, which it would go into. If I can’t use the driver, which driver should I consider buying? I can’t afford $500 for a driver like the tumult, but possibly $300.
 

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>My question is, is the DPL 12 ok for use in standard boxes? Most importantly, my 93L sealed box, which it would go into.
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Of course!
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>Anyway, I also wish to mention that I want to try to build a horn (probably similar – size wise – to the LABSUB) using this new driver, so I would like to get one that was quite suitable for this use.
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Then I recommend you buy the Labhorn driver since the DPL12 isn't all that suitable for compression horn loading IMO, the compression ratio would be too high, potentially causing non-linear performance due to overheating and its surround deforming. Looks ideal for a large backhorn or TL though.

GM
 
Matttcattt said:
My question is, is the DPL 12 ok for use in standard boxes? Most importantly, my 93L sealed box, which it would go into. If I can’t use the driver, which driver should I consider buying? I can’t afford $500 for a driver like the tumult, but possibly $300.
Matttcattt said:
Hmm, can’t edit my post...

Anyway, I also wish to mention that I want to try to build a horn (probably similar – size wise – to the LABSUB) using this new driver, so I would like to get one that was quite suitable for this use.


Considering the above points would it not be wise to just buy 2 eminence lab12's? With these 2 in your 93l sealed box you get an f3 about 40hz. If you can't afford 2 get 1 and port your 93l for an f3 about 25hz. Then if you do go on to build a LABSUB you'll have the 2 lab12's required. LAB12's cost about £120 from bk electrics.

hope this helps
 
Well, the Shiva has specs very close to the Labhorn driver and I believe the Labhorn prototype used them, but if you plan to build a cab of ~the Labhorn's size, odds are pretty good you can't improve on its performance, so it seems reasonable to me that eventually building it is a no-brainer.

Even if you don't, the Labhorn driver is still the obvious choice.

GM
 
mikee12345 said:
see my site.

I wouldve liked to have used a dpl12 or similar cos its cheaper and models as well..but again i dont trust any woofer with 2.5:1 compression ratio.

im gona have to buy a single lab12 for my little horn

i have seen your site. you look like a horn expert. :d or one in the making. :p

would the lab12 work well in a lower frequency horn than the LABSUB (25Hz instead of 35Hz)?

i am trying to learn to use hornresp, so i will post any questions i have in this thread, and hopefully you (mikee12345) will see them. :)
 
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