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Old 9th January 2008, 12:57 PM   #1
scottjr is offline scottjr  United Kingdom
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Default Small Sub Woofer

Before I made my Jordan Transmission Line speakers I had decided to make a sub-woofer to go along with my small BBC monitor speakers. The attempt was not at all successful. I will probably give up and use the unit as a full range speaker with my PC (without the crossovers) or throw them out but I would be interested to know whether there is anything I could do to give some improvement.
I had two Wharfdale speakers lying around in the workshop which I used. I made a box from 3cm thick elm with overal dimensions of 27cm by 27cm by 50cm high. I bought two crossovers for a car system (iron cored) and put the two speakers in the box. With the BBC monitors they give better low frequency response but they boom and make men's voices seem particularly loud. I have not put any lagging inside the cabinet.
Any ideas or do you agree I should throw them out. The wood cost £55 and the crossovers cost £25.
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Old 9th January 2008, 03:54 PM   #2
GM is online now GM  United States
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Greets!

With no driver specs, XO details, etc., don't have a clue, but at the very least I'd stuff the sub with ~1.5 lbs/ft^3 of R-19 fiberglass insulation to lower its Qt and just generally smooth it out. Try different room positions too since corner loading just increases any tendency to 'boom'.

GM
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Old 12th January 2008, 08:54 PM   #3
gfiandy is offline gfiandy  United Kingdom
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Hi,

From the description you have given it sounds like they are in a box that is too small for them and are peaking in the bass. If you can find the TS parameters for the speakers then you can simulate what this peak is. You could possably fix the problem using either a linkwitz transform if you are using an active crossover or it may be possible to come to a compromise solution by using a passive high pass or notch filter to tame the bass peak.

But first of all you need to find some information on the drive units.

Regards,
Andrew
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Old 13th January 2008, 05:44 PM   #4
scottjr is offline scottjr  United Kingdom
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Default sub woofer

You are right in that I really need information on the drivers. I don't have it other than they are 8 ohm nominally 8inch drivers with paper cones used in the Wharfedale Diamond speakers. I used a low pass filter with each described as 600w 1 Way Subwoofer Crossover with a Crossover frequency 120Hz and Damping factor of 12dB/oct with 8 Ohms impedance.
I agree the box is far too small so I will try putting some wadding in it. At present the box is sealed. I had considered including a vent but decided not to.
Thanks for your interest.
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Old 17th January 2008, 02:30 PM   #5
djk is offline djk
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Your box is about 0.65 cu ft net.

Two of these will work in that box:

http://www.partsexpress.com/pe/pshow...number=264-854

They need to be wired in series, and driven with this amp/crossover:

http://www.partsexpress.com/pe/showd...Number=300-805

The box will need a 30hz port out the back.

The box/driver/amp combination will go to 28hz or so.
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Old 18th January 2008, 03:36 PM   #6
gfiandy is offline gfiandy  United Kingdom
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Hi,

Since you don't have any information and I am guessing you don't want to spend out on new drive units here is a filthy bodge which might work.

Try putting a 470uF 100V bipolar cap in series with the input to the sub. (if you cant get a bipolar 2 x 1000uF 100V with the negatvie terminals connected together can be used) you can use a lower voltage if yo have a small amp on it 100V is good for upto about 100W.

I can't promise this will solve it and you may need a smaller or larger value but this should be in about the right ball park to tame a peak at arround 100Hz which is what I suspect you have.

Regards,
Andrew
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Old 18th January 2008, 03:45 PM   #7
herm is offline herm  United States
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Have you considered crossing over lower?

I don't like systems where the subs are doing anything but SUB-
woofing.

How is a system suppose to image well when you have voices
being produced at ear level (from the front speaker) and at floor
level (the sub)?

Don't give up yet! You may not get great performance, but you can
certainly get some bass augmentation from them without interfering
with the mains...

herm
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Old 18th January 2008, 04:05 PM   #8
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I'm guessing that you have a relatively high Fcb. (closed box frwquency.) If that is the case, find the ESP website, and check out the ELF subwoofer article. You can operate the sub below resonance and get really spectacular sounding bass.

I do this with multiple 6.5" drivers--the bass is incredibly articulate.

JJ
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Old 18th January 2008, 04:08 PM   #9
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