Making a compact Sub without the info (cheap!)

Surtsey

Member
2019-09-21 4:51 pm
I was given a Bush subwoofer from S21192. The unit had a 5" driver in a cabinet measuring 20cm x 20cm x 25cm. I replaced the driver with a 6.5" unit from an Acoustic Solutions AV-120.

Unfortunately, I do have the specifications for either drive unit other than the Acoustic Solutions AV-120 bottoms out at 48hz in a floor-standing cabinet.

The results are okay but the bass ain't going to trouble the neighbours. Because the cabinet is so small would I be better off removing the port and converting a sealed enclosure?

Or should I discard the port in favour of 2 x 4" passive radiators?
 
Usually your passive radiators will be larger and heavier than the units driving them. You have no parameters to work off of to find suitable PR's unless you purchase new drivers as well. Obtaining the T/S parameters of the speakers isn't too hard if you want to learn. Also, if you can give me some info off the speaker itself, I have some resources that may be able to provide more info about them. I didn't find much on a quick search of the web but I will be glad to assist if I can.

-LL
 

Chompy

Member
2016-08-26 5:11 pm
Oregon
To help with the undersized cabinet, you could move the port to the outside and experiment with different lengths. For example, 5cm diameter by 20cm for 50hz tuning; up to 60cm length for roughly 30hz tuning. If you like a result, you could buy elbows and wrap it around the box like this: Sidewinder Subwoofer

Port length calculator used (imperial units; I used 0.34 ft3): Port Length Calculator
 

Surtsey

Member
2019-09-21 4:51 pm
Thanks for all your help. This is just a silly project to help me advance my learning and keep me out of the pub. I realise that attempting to get any real sub-bass out of a 6.5" driver in such a ridiculously small cabinet is futile.

The current set-up produces interesting results: good 'kick' without having any real 'thump' or 'growl'. At this point I suspect the biggest weakness is the driver itself.

The good news is that have a great resource for used components. I have obtained a driver from a Yamaha SW-P130. I have also obtained another identical cabinet. In line with Chompy's suggestion I will extend the port length by 50mm externally.
 
I found some specs from the original speakers which held 2 of these woofers:
2-Way Peak Power Handling 190 watt Nominal Power 130 watt
Frequency Response 48 Hz - 20 kHz
Impedance 8 ohm
Sensitivity 88 dB
Dimensions
Width 22 cm (8.66 in.)
Depth 23.5 cm (9.25 in.)
Height 78.99 cm (31.1 in.)
And the AV-120 was ported and stuffed. (Using super thick wires like in the last video makes no sense especially not for the tweeter.)

internal volume is about 1.9x2.0x7.5= 28.5 liter

That is about 14 liter for 1 woofer in the original speaker.

Play a frequency sweep (20-100hz) through the ported speaker and see where excursion is minimal; that is the current tuning frequency. If make the port longer tuning goes down, shorter goes up.
 
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Good find, @Think.

Most of the reviews I read on them were favorable. I like chompy's idea about the external ports.

Surtsey, keep us updated on how you get on with the setup and config. Oh and dont underestimate the potential based on size. Some of those 6.5's make great bass in some of the mildly exotic cabinets. Good luck!
 

Chompy

Member
2016-08-26 5:11 pm
Oregon
In line with Chompy's suggestion I will extend the port length by 50mm externally.
BTW there was sort of an implied two parts to that suggestion which I'm not sure if I made clearly; one would be to extend the current port with an external one, two would be to remove the current port and use a new one with all (or most) of it outside the box. The idea being to create more volume inside the box without rebuilding it. (Port tubes inside the box subtract their own volume from the box, so if you don't care about looks you can move it all outside! Though I think you want to bring it inside by at least 1 diameter for airflow reasons, rather than perfectly flush) 20-60cm is total length at 5cm. Sorry if I'm being pedantic, I want you to have fun and good results! :)
 

Surtsey

Member
2019-09-21 4:51 pm
BTW there was sort of an implied two parts to that suggestion which I'm not sure if I made clearly; one would be to extend the current port with an external one, two would be to remove the current port and use a new one with all (or most) of it outside the box. The idea being to create more volume inside the box without rebuilding it. (Port tubes inside the box subtract their own volume from the box, so if you don't care about looks you can move it all outside! Though I think you want to bring it inside by at least 1 diameter for airflow reasons, rather than perfectly flush) 20-60cm is total length at 5cm. Sorry if I'm being pedantic, I want you to have fun and good results! :)

I don't mind giving the subwoofer a wart or a pimple but a colostomy bag is a step too far.

In the original cabinet I have extended the port by 50mm externally and removed 25 mm internally. I am resigned to notion that the driver is problematic but my pragmatic nature is, perhaps, taking me in a different direction: I'm never going to get any sub-bass out of this unit but it is proving excellent for reproducing one of my preferred genres: 70s / 80s Jazz Funk sounds superb. However, anything more modern with programmed sub-bass, 808's and the like - it downs tools.

In other news . . . I have acquired an identical cabinet and fitted the driver from a Yamaha YST-SW60. This comes with its own set of problems. The driver is a genuine sub. I've got better sub-bass at low volumes but reduced bass. The port blows a gale. I could power a wind farm from the port.


I'll continue to tinker.
 

Surtsey

Member
2019-09-21 4:51 pm
I'm getting a handle on this now. The Yamaha driver in same cabinet produces better results, although I'm still getting a a 90s Volvo sound (boxy but good). The Yamaha driver in its original cabinet responds down to 25hz. Reverse calculations reveal that the port is currently tuned to to around 60hz. Ergo, I need a longer port (which there no room for).

My next move may be negative. I plan to reduce the port diameter from 40mm to 30mm in order to reduce the length requirements.
 

Surtsey

Member
2019-09-21 4:51 pm
Unfortunately this project came to a sorry end. I found a rare 7" driver. It sounded awesome for a couple of days before a worrying rattling set in. Turns out the new sub totally destroyed the cabinet. At some point I'll try to re-assemble it, albeit with some serious bracing.

I'm new to all of this but there are obvious parallels. If you try to put a V8 engine in a Toyota Corolla - how long do expect the brakes and transmission will last.

C'est la vie.