My diy Subwoofer – I didn’t see (hear) anything worse

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This is my first subwoofer and it is very unsuccessful! It’s no wonder because I did it without any rules or calculations, and the results are very sad. Can you tell me what to do my case? Is it possible to reform the situation or should I forget this box?
Some facts:
The driver is very good! I heard it in right box, sounds impressive (not audiophile is more industrial :) ).
The box is sealed.
I’m sure that I hear sub harmonics described in page http://www.arcavia.com/kyle/Equations/Beats&SubHarm.html
Or it can be standing waves.
So is it possible to make it sound better?
Is it possible to avoid standing waves and subharmonics?
 
Telling us something about the construction of the box and implementation would be useful...

There will not be any standing waves unless your box is has extremely strange dimensions, or your low-pass filter is rubbish. Harmonics indicate a very nasty drive unit or driving the unit into over-excursion or with an underpowered amplifier.

I would say that as it's a sealed box there is nothing much you can do that will change sound substantially, so time for a new design. If you put up the Thiele-Small parameters of the driver then people can help you.
 
Thank you, richie00boy, for your advices. I forgot the picture of my subwoofer. Some parameters of box: internal volume v=142.2 litres or 5.02 kub. Ft3; with foam rubber inside.

Driver’s parameters: Power handling: 600 watts RMS; voice coil diameter: 4"; nominal impedance: 8 ohms; frequency range: 45-1,200 Hz; magnet assembly weight: 15 lbs. Fs=52 Hz; SPL: 92 dB 1W/1m; Vas= 2.2 Ft3; Qms= 4.5; Qes= 0.34; Qts= 0.32; Xmax= 7.5 mm; dimensions - overall diameter = 12-1/4", cutout diameter: 11", mounting depth= 5". Effective moving mass 65 grammes. That’s all I found.

I don’t use any filters inside, I just connect an amp throughout the low pass crossover and the sound is not musical at all… it’s like bellow or bump I don’t know even how to describe it… By my opinion it is low subharmonics. One more moment, if I will make this box vented, is it possible to improve the sound?
I would like to ask some more questions:
Can you tell me is it mater what kind of shape is box, or the main thing is to hold the volume of subwoofer? (I mean right calculated volume, not my case:cool: )?
And how much percentage deflection in volume is tolerated?
Is it true, that I can compensate the volume with special foam?
 

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OK those details make things a lot clearer. I can tell you straightaway that is never going to be much of a subwoofer as Fs is far too high.

As it is at the moment, your box is far, far too big. The good news is that you can add a vent to that box and it will improve matters, but it's still far too big. Half that size would be in the right ballpark although still a little on the large size.

I think the bad sound you are getting at the moment is because you are expecting bass out of a poor woofer, and the box is far too big so you're overdriving it at some frequencies. I also suspect your low-pass filter is too shallow slope.

Box shape is of little importance for subwoofers, but at the moment yours is so big it might have a small influence.

Depending on the density of the foam rubber you have used, it may be good or bad to have inside.

My personal opinion is that you should write the project off as a learning experience and start again with a more suitable drive unit. I appreciate that this might be difficult for you in your country or with how much money you have, but you will only ever have a mediocre result if you continue with what you have. Trust me, I have been there and learnt already.
 
Hey, the box might not be a throw-away article. There's plenty of subs out theere looking for about 140-150 litre sealed boxes, so getting a new driver might be an option as well (depending on your budget, of course).

There's a couple of woofers at Zalytron that would fit the bill at under $100US (Vas over 200l) - but I'm not sure what you've got available locally.
 
mashaffer said:
At first blush it looks like it might do very nicely as a TL or horn sub.

mike

I have to disagree, with Fs as high as it is, it will never produce anything other than not-really-very-deep bass.

For all the time and effort and materials expended building a TL or horn, it will get slaughtered by a simpler, smaller vented box with a better drive unit.
 
Thank you proDiy’rs, for advices. And what can I say – I am very surprised with Notax’s calculations! I did calculations yesterday and get approximately the same results. Vbox=62-57Litres (depending on filling the box with foam or smthg). Only tube I took smaller and got it shorter…
Please take me on the right way and correct were me thinking is wrong…

I found that mainly volume of the box depends on:
Qts – total Q factor;
Vas – Equivalent volume;
Fs – Resonance frequency;

And the length of tube mainly depends on:
Xmax – displacement of cone (As I understand)
Sd – piston surface area.

One more moment. Can you tell me something about parameters Fb – the resonant frequency of vented box and F3 – the half power (-3dB) frequency of driver. Should they be close to each other? What I will if the difference is huge, and what if they are almost the same?
 
Yes you're right. It’s not subwoofer now I understand that it was my mistake. And few minutes ago I found, that Fs – drivers resonance frequency do not influence to the box size… Now I’m playing with JBL Speaker shop program, and it gives me that vented box for my driver must be Vb=24.17 liters, with vent tube Dv=16.7cm and length Dl=62.9cm

Deep – Dark forest :)

So, that mainly volume of the box depends on:
Qts – total Q factor;
Vas – Equivalent volume;
Any else parameters???

Thanx in anticipation!
 

AKN

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vytas said:

The driver is very good! I heard it in right box, sounds impressive (not audiophile is more industrial :) ).

I think this is a very important statement made from vytas.
If he had heard this woofer in an another box and was satified with sound it must be some aligment that could be right for him.

Maybe he want punchy not so low freq bass. For bass over 50Hz this woofer is perfect in a smaller ported box. Big voice coil for low thermal compression as i can see and just everything else just right for not so low freq bass.

A simple question, what box was it that sounded ok for you?

My guess, a smaller ported box.

If you want to use your existing box and decrease volume, put a smaller box in existing box and subtract the small box volume with should be the size of volume you want to subtract.

Can you dig out some more parameters as SD and Le?
What brand and size is your woofer?
 
vytas said:
Thank you proDiy’rs, for advices. And what can I say – I am very surprised with Notax’s calculations! I did calculations yesterday and get approximately the same results. Vbox=62-57Litres (depending on filling the box with foam or smthg). Only tube I took smaller and got it shorter…
Please take me on the right way and correct were me thinking is wrong…

I found that mainly volume of the box depends on:
Qts – total Q factor;
Vas – Equivalent volume;
Fs – Resonance frequency;

And the length of tube mainly depends on:
Xmax – displacement of cone (As I understand)
Sd – piston surface area.

One more moment. Can you tell me something about parameters Fb – the resonant frequency of vented box and F3 – the half power (-3dB) frequency of driver. Should they be close to each other? What I will if the difference is huge, and what if they are almost the same?


Tube diameter depend od Xmax, Sd and SPL. But not physical Xmax, but one you get at nominal power at low frequencies. Real excursion.
Than, its Dt=sqr(Fb*Sd*Xp) where Xp is peak excursion at nominal power.
Real excursion at nom. power you can got at some simulations as BassBox Pro6.

When you put tube with small diameter, at higher volume air flow in tube becomes turbulent, which is not good. More distorsion. Big tube diameter is not good, too.

Calculations in simulations are not so exact. There is gap between results by simulations and what is best in real. In this case, you must go with larger box that you got from Vas, Qts, and some lower Fb.

Very often, Fb and F3 are very close. When F3 is much higher than Fb its in the case of higher Qts and it is not so good calculated box. When Fb is higher then F3, there is too big bulb (too loud bass) above that frequency.
 
vytas said:
Yes you're right. It’s not subwoofer now I understand that it was my mistake. And few minutes ago I found, that Fs – drivers resonance frequency do not influence to the box size… Now I’m playing with JBL Speaker shop program, and it gives me that vented box for my driver must be Vb=24.17 liters, with vent tube Dv=16.7cm and length Dl=62.9cm

Deep – Dark forest :)

So, that mainly volume of the box depends on:
Qts – total Q factor;
Vas – Equivalent volume;
Any else parameters???

Thanx in anticipation!

My own preference for box design is that the JBL program is suggesting a box that is too small. Maybe it's geared towards making a bulletproof speaker for PA. I think more around 45 litres would be better.
 
Still deep dark forest…
I’ll take a photo of the correct made box and drop it in forum… But it was smaller, and ported for sure. :)
As Anders asked I found Sd=615 sqr.cm and Le=3.4mH. the brand is JLS. I had newer heard it before. Didn’t find it on net… and it is 12’ diameter.
I made experiments with some solids inside, but nothing positive. I think on weekend I’ll install the port and try my box again with some solids…

Notax, can you clarify the situation with Dt?

Sd – area of piston (615-635cm);
Xp - is peak excursion at nominal power in (cm) measured about 0.6-0.7cm;
Fb – the resonant frequency of vented box in (Hz);
Dt=sqr(Fb*Sd*Xp)=sqr(54*615*0.7)=152 (cm) (mm)?

As far as I understand you prefer calculations by manual, not software… I would like to make such calculations, but I’m not sure I can do this right…
 
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