| Gorbee |
I am a DIY speaker amateur so sorry if its a simple question :smash: .
I am hoping to build a home cinema system with some low powered speakers that i picked up (it is in the bedroom of a terraced house so can't be too loud!) I am going to be using an old Goodmans 12" at 50w as it is the one I was given. It is going to be in a small as possible box (will be experiment the size at some point). Now, I have seen people fire their subs downwards, upwards, sideways, inside out. What difference does this actually make and what would be best? Also, would I need a vented or sealed box design? Thanks :up: |
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| badman |
The size of the box will be determined by the Thiele Small parameters, which we'd need to advise you. This driver likely doesn't have the Xmax to do a down or upfiring. Dan Wiggins of Adire Audio has some guideline for which subs can be used down or upfiring. Small boxes are not ideal for subs as a rule- build the biggest box you can live with and, if you vent it, vent it LOW even if it doesn't model flat.
There are many free programs to model driver response in various boxes. WinISD, Bassbox, others.
This is all very rudimentary- the specifics of the driver determine what it wants to have for an enclosure. |
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| zenmasterbrian |
| This best firing direction is also of interest to me. I think it a very practical question. |
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| richie00boy |
Basically point your drive unit down and see how far the cone sags compared to vertical. If it's like 5% of total normal Xmax then maybe not a problem.
'Best' is dependent on where you put the sub and what you want from it. Downfiring will excite the floor more, but be hidden from view. Side firing could be better if you can't fit much space for the driver to 'breathe' in downfiring position. |
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| zenmasterbrian |
I agree. I think most store bought subs lack because they aren't designed for you situation. So they just take up space.
Imagine a subwoofer that is designed as a coffee table, part of a desk, the lower part of a book case, or a stool to sit on.
Think about that, then consider firing direction.
I think there is complexity in down firing, but it protects the driver more. |
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| nunayafb |
General rule of safety is to always fire your sub in a safe direction and beware of you back drop.:rofl:
No, I dont know why I thought that was funny, maybe because with enough excess power it applies.
Seriously, at sub freqencies sound radiates omnidirectionally so you can face it any direction you want. As far as downward, with the duplex situation I would avoid it, your goal should be to decouple the sub from the floor and downfiring will send the shockwave there first. |
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| noodle_snacks |
| For subwoofers i don't believe it matters that much, however downfiring i think is a bad idea (having had a downfiring adire tempest before). Even with a very heavy cabinet the tempest was able to shake it around when down firing and make a noise on my wooden floors, and be a pain basically. |
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| zenmasterbrian |
If you downfire, you can have a base plate.
But you have to be concerned about driver sag.
Also, I have never seen an analysis of how long the legs need to be on a down firing system. You need to be concerned about asymetrical driver loading.
AISI, down firing was more popular 15 years ago.
This is non-trivial. Loading of subwoofers with floor, walls, and corners does effect how they behave.
I would like to see a text where all the issues are analyzed.
Down firing is attractive because it can protect the sub better.
But it is less popular today, IMO. Driver sag? I don't know. |
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| RobWells |
| quote: | Originally posted by zenmasterbrian
-snip-
AISI, down firing was more popular 15 years ago.
-snip-
But it is less popular today, IMO. Driver sag? I don't know. |
Don't let SVS hear you saying that!
Rob. |
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| zenmasterbrian |
| Please elaborate, who is SVS? |
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| RobWells |
LOL:D
google is your friend. |
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| AndrewT |
Hi,
downfiring will cause some sag in the suspension.
I have seen the 5% figure quoted elsewhere.
If you can see/measure any sag difference between upfireing and downfiring, you have probably already exceeded the 5% limit on a low Xmax driver.
Stick with side firing except for a driver specially developed for vertical mounting. |
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| zenmasterbrian |
I've seen the 5% number too. But I don't know how it is derived.
It seems like it would be different for different drivers.
I have never before heard of drivers specially designed for vertical firing. That sound intriging.
I have also never seen anything in print which analyzes how long the legs need to be, and the effect of the design of being so close to the floor. |
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| Ap |
I think if the box is sealed, then sag would be minimal as the driver effectivley is held by the air pressure of the box - does that make sense?
Anyway I quite like the look of SVS subwoofers.
http://www.svsound.com/ |
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| AndrewT |
Hi,| quote: | | if the box is sealed, then sag would be minimal as the driver effectivley is held by the air pressure of the box |
sorry, Rubbish. |
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| Ap |
Why is that rubbish?
The only way the driver can move is if the volume of air in the box increases, this can only happen if it is not properly sealed.
Of course the other way the driver moves is by the force applied to it from a signal applied to the voice coil, in this instance the air inside the box is being compressed - that is why a sealed box is often referred to as working like a spring. |
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| SY |
| quote: | | The only way the driver can move is if the volume of air in the box increases, this can only happen if it is not properly sealed. |
That's not correct; the volume can (and does) increase with varying energy inputs. In the case of cone-down, the driver gives up an energy 1/2kx2, balanced against the change in energy from expansion of the volume PdV. It's no different than any other mass-on-a-spring: if you exert a force mg, you'll get a response kx.
Now, you can argue that eventually, the box's pressure will equalize (no box is totally impermeable). And that's a correct argument. But it really means that the cone sag increases with time until that equilibration occurs. |
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| AndrewT |
| and what if the air temperature in the box changes? |
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| Ap |
Hey good point - I haden thought of that!
(BTW I think Im completely wrong about sag).
I guess the trend nowadays is to go for forward firing because more drivers have very large soft surrounds & high xmax - maybe something to do with the low Q, low efficiency, low Fs woofers and therefore low Vb. |
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| AndrewT |
Hi,
you're allowed ONE. what is the sanction for a second? ;) |
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| Ap |
| Gee only one! Surely there has to be a time limit, maybe one a year? |
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| owdi |
| quote: | Originally posted by nunayafb
Seriously, at sub freqencies sound radiates omnidirectionally so you can face it any direction you want. As far as downward, with the duplex situation I would avoid it, your goal should be to decouple the sub from the floor and downfiring will send the shockwave there first. |
While low frequencies are omnidirectional, high order harmonics can be very directional. Pointing the driver away from the listener, and at some material that will absorb the harmonics, will make the sub more difficult to locate in the room.
Dan |
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| nunayafb |
Owdi, which harmonic frequencies are you talking about?
Most subwoofers have very low distortion in their upper range, distortion usually climbs as f goes down.
So the 3rd and 4th harmonics of a 20 or 30hz signal will still be low in frequency and hard to locate. In addition the only thing that can absorb these low freq. harmonics is bass traps or thick wall treatments, so now the harmonics will be reflected and time delayed.
This brings us right back to what everyone is saying, cross the woofer over low. |
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| Ap |
Exactly. In my setup I have achieved excellent results with subs poitning away from the main speakers on a side wall - not towards me.
It all depends on your room & your setup there is no one single best theory. |
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| mike.e |
| quote: | Originally posted by zenmasterbrian
If you downfire, you can have a base plate.
But you have to be concerned about driver sag.
Also, I have never seen an analysis of how long the legs need to be on a down firing system. You need to be concerned about asymetrical driver loading.
AISI, down firing was more popular 15 years ago.
This is non-trivial. Loading of subwoofers with floor, walls, and corners does effect how they behave.
I would like to see a text where all the issues are analyzed.
Down firing is attractive because it can protect the sub better.
But it is less popular today, IMO. Driver sag? I don't know. |
Asymmetrical loading : I need to be concerned,so where are your papers? If i was concerned about everything that wasnt proven,id be rather worried.All you need is enough area to radiate the sound,without any compression.
Adire has the sag paper.Its all based on the driver CMS.
Down firing seems popular with those all in one mini subs like wharfedale offer.
Losing 5% of your Xmax due to down firing means how much less SPL :rolleyes: |
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