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DIY Budget subwoofer design
DIY Budget subwoofer design
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Old 16th September 2018, 10:31 AM   #1
hagarth is offline hagarth
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Default DIY Budget subwoofer design

I have access (~25 euro) to a Fenton 902.426 driver (8" Woofer with Kevlar cone | Tronios) and I'm considering building a vented box around it. I have modeled a 41L box (300x400x500) in speakerboxlite, for a vented enclosure with a port tuned around 28-30Hz, built using 18mm MDF. My plan is to do a bottom firing or side firing, with the port in the front. I will match this with a yet to be defined class D amp.

As far as I can tell I will get a inefficient, but usable, subwoofer, with an F3 around 28Hz, and a almost flat response (some EQ/XO will be required). The max SPL will not be that high, but I think it is adequate for the scenario.

The subwoofer will be used to complement other speakers (dual drivers with a port) in a HT scenario, which go down to 80Hz. These are 50W speakers, but due to neighbors and kids, the volume never goes that high. I'm looking for extending the frequency range and some stronger and deeper bass.

Although I'm a long time lurker of this forum, this will be my first attempt at the DYI aspect of subwoofers. I'm a bit uncertain, and would like to have your opinion on this build. Can you help?

Thanks in advance!

Edit: Link to speakerbox calculations: Project short info

Last edited by hagarth; 16th September 2018 at 10:37 AM. Reason: Added link to calculations
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Old 18th September 2018, 12:31 AM   #2
hollowboy is offline hollowboy  Australia
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Originally Posted by hagarth View Post
I have access (~25 euro) to a Fenton 902.426 driver [...] I have modeled a 41L box [...] My plan is to do a bottom firing or side firing, with the port in the front. I will match this with a yet to be defined class D amp.
The Fenton range is of unknown quality*. I'd suggest treating the specs with caution: have a plan B in case the (already quite high) Qts is higher than advertised.

I'd also go with side firing unless there's something that really compels a down firing layout (like a woofer-destroying puppy in your home).

The low sensitivity is not strictly bad news. A cheap amplifier that would be unacceptable for hiss / high noise level in an efficient system might be fine when driving an 85dB woofer.





*I'd like them to be good, cos a local store has them at decent prices.
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Old 18th September 2018, 10:45 AM   #3
hagarth is offline hagarth
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Fenton seems to be the same as tronios, QTX, Skytronic, which places the brand in the budget segment. I have seen "good enough" reviews for the brand: it works but will not meet audiophile standards

With VAS at 23.6L, QTS of 0.482 and actual volume of 40L I think i'm already giving some slack for higher QTS. Additional stuffing can also help.

The only backup plan will be to select a speaker from a catalog. However, the price will skyrocket. I miss parts-express in western europe....
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Old 19th September 2018, 05:15 AM   #4
hollowboy is offline hollowboy  Australia
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The only backup plan will be to select a speaker from a catalog. However, the price will skyrocket.
If it is high Q and boomy, the backup plan could be to plug or stuff the port, and / or apply eq.
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Old 19th September 2018, 07:44 AM   #5
hagarth is offline hagarth
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I doubt that no EQ will be needed in order to make the subwoofer coexist with the other speakers.

Is there a way to simulate/calculate the effect of stuffing the interior?
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Old 19th September 2018, 04:18 PM   #6
bjorno is offline bjorno  Sweden
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Hi All,

FYI:

b
Attached Images
File Type: jpg Fenton 8inch_SKU 902.426.JPG (794.5 KB, 334 views)
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Old 19th September 2018, 11:04 PM   #7
GM is offline GM  United States
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Originally Posted by hagarth View Post
With VAS at 23.6L, QTS of 0.482 and actual volume of 40L I think i'm already giving some slack for higher QTS. Additional stuffing can also help.
Close! FWIW, Vb = 20*23.6*0.482^3.3 = ~42.46 L

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Old 21st September 2018, 03:32 AM   #8
hollowboy is offline hollowboy  Australia
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Is there a way to simulate/calculate the effect of stuffing the interior?
Some real tests, arguably better than a simulation:
Data-Bass

Bjorno's calculations look good. I had to zoom in to make them legible

If eq is a given, you might consider using 2 drivers in sealed configuration.

When I sim two drivers in 40 litres (sealed), it appears to have the same excursion limited SPL (in the 30-80Hz range) as the 40 litre ported option.

Pros (2 drivers sealed)
-ability to mount them on opposing walls (for vibration cancelling)
-less harmed by TS parameters being off

Cons
-greater cost
-less heat dissipation
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Old 21st September 2018, 09:00 AM   #9
hagarth is offline hagarth
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Awesome. Thanks bjorno, hollowboy.

I will try the ported approach to keep the design simpler and because I may be optimizing an non-existing problem (according to my ears and living room). Also, I can get a MDF board cut to my specification with no extra cost, which reduces the burden of changing the enclosure.

The simulation provided by bjorno states the driver dimensions are actually off, is this correct?
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Old 29th September 2018, 01:59 AM   #10
academia50 is offline academia50  Argentina
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Originally Posted by hagarth View Post
............

The simulation provided by bjorno states the driver dimensions are actually off, is this correct?
Bjorno is an entity, he will not answer you.

You must direct the question the rest of the forum.
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