Good sub

[kipman725]

hello I am in the initial stages of designing my first speaker which shall be a nice 8ohm powered sub with a filter to extend the bass response (I think this is called a Linkwitz circuit in the speaker world). Anyway I was thinking about this driver:
http://www.rapidonline.com/netalogue/specs/35-2932.pdf

For an enclosure I was planning on a closed cubic aprox (haven't calculated anything yet) 35L box made of 18mm MDF with box joints and some sort of internal bracing structure.

the driver has a lf cuttoff of about 40Hz and -12dB/octave slope below this turning point. Therefore is aiming for response down to 20Hz realistic? (for flat program matirial this seems to limit me to 7W peaks...). Could I overcome this by using more drivers (and suitibly monster amp), or is there a more elegent solution.

I would like the extended bass response however as I like Albinoni's Adagio in G minor alot.

 

[Moondog55]

That woofer works in an Open Baffle but i don't think you can get down anywhere close to 30Hz using it, the advice given to me when I started was that OB speakers do not have much below 40Hz.

One of my favourite pieces of music, needs good clean bass reproduction to do well.

How big is your room??

 

[kipman725]

room will be typical living room, haven't sorted out house for next year yet so can't be more specific. I'm not sure if open baffle is suitible as this is a student house and durability is an issue.

 

[Moondog55]

Its big advantage is its price, one of Visatons cheapest woofers, when you say durability do you mean from the power handling or furniture sense?? OB speakers can't handle too much power but as furniture no better or worse that your skills as a chippie will make it

 

[chris661]

I have done a similar project to this, but with 2x 8" Dual Voice Coil woofers from Dayton, with a Linkwitz circuit. -3db at 28Hz. And still enough headroom for a reasonable all-house party (not a particularly big house - 10m by 10m)

I could get you a schematic of that if you are interested.
http://www.diyaudio.com/forums/showthread.php?threadid=140927&highlight= is the thread,
If you want to keep it as your own work, I recommed this driver. You can order them from CPC, but this site has the tech specs.

http://cpc.farnell.com/LS00415/audi...branded-55-1455

http://mcmelectronics.com/product/55-1455 - that has the specs and reviews.

Gotta go - school soon.

 

[kipman725]

thanks for the replies. I am now not sure if this driver is suitible as using the spreadsheet here:
http://www.diysubwoofers.org/sld/

It apears I ethier have a huge box (1m^3) or rubbish freq response. The problem apears to be its high Fs and high Qts.

*I think I misunderstood open baffle is this what is ment:
http://www.linkwitzlab.com/proto.htm#PW1

If I could obtain the bass exstension from this configuration it would be ideal as the actual sub would be small in volume (It has to fit in a car boot for transportation).

 

[Moondog55]

High Qts usually means very big box, the Linkwitz page shows a top-of-the-line OB woofer arrangement, you could copy that sort of backless box.

But they will be woofers not sub-woofers ( they won't reproduce infrasonic sound)

 

[kipman725]

Thanks for the replies, I think this driver may be more suitible with its F0= 33.5Hz and Qts = 0.52.

http://www.rapidonline.com/netalogue/specs/35-1415.pdf

(It also seems to have quite good results with only a 35L box according to the datasheet).

 

[tinitus]

With no specs on Xmax, means it could be anything and wild a shot in the dark
But high Fs, high Qts, low SPL
Hard to say what driver that is without knowing more

 

[kipman725]

hmm but Xmax only effects the maximum SPL? I am not too bothered about this due to not having huge rooms (and curently upgrading from water damaged mission audio "monitors" from the 80's). (which have a very low max SPL)

I tried to find what brand the sub is but apears to be some OEM job that just gets rebranded everwhere, it's cheap though.

I checked the freq response graph they give and it seems realistic for a 35L closed box, I will have to apply a fair bit of equalisation but this is fine as I the eventual system will use an FPGA based equaliser that samples the actual frequancy response at the listening position and adjusts itself and has a GUI etc for creating a custom frequancy response (FPGA's are fun). Before I do that I guess I will use a passive network for equalisation

 

[kipman725]

Well I got the subs and managed to get almost full t/s parameters. Using bassbox:

File: skytronic.bb6
-----------------------------------------
Driver Properties
Name: 902.163
Type: Standard one-way driver
Company: SKYTRONIC
Serial No: 902.163
No. of Drivers = 1
Fs = 33.5 Hz
Qms = 2.51
Vas = 66 liters
Cms = 0.404 mm/N
Mms = 56 g
Rms = 4.685 kg/s
Xmax = 6 mm
Xmech = 9 mm
P-Dia = 207.8 mm
Sd = 339 sq.cm
P-Vd = 0.203 liters
Qes = 0.67
Re = 7 ohms
Z = 8.4 ohms
BL = 11 Tm
Pe = 150 watts
Qts = 0.53
no = 0.358 %
1-W SPL = 87.5 dB
2.83-V SPL = 88.27 dB
-----------------------------------------
Box Properties
Name:
Type: Closed Box
Shape: Prism, square (optimum)
Vb = 52.83 liters
Qtc = 0.707
QL = 6.831
F3 = 49.77 Hz
Fill = none


not sure about the fill, having non apears to give me slightly more LF exstension. Maximum output is 110dB per sub @ 150W input. With two subs I think this means I get 116dB (6dB boost). However by using a linkwitz transform filter I will be cutting my power handling by upto 12dB in the 25 -50Hz range. I will use a very steep cuttoff filter (-24dB/octave) at 25Hz as they don't have any usefull power handeling. Seems pretty respectable for such low cost stuff.

 

[bjorno]

.. With two subs I think this means I get 116dB (6dB boost)..

Hi kipman,

In the mid bass at 80 Hz you'll get about 113 dB max. but not at 25 Hz. I vote for the use of 3 or 4 closed boxes. See picture 1(1)

b

1(1)

 

[kipman725]

Problem is the entire sound system has to fit in the car along with everything else for a year at uni so unless I build the stuff down in London I am very restricted for space. I already have two 0.89m x 0.3m x 0.3m open baffles to take. 93dB is quite low I could use a triode (or simlar solid state circuit) to soft clip any transiants that would cause damage to the sub?

 

[bjorno]

93dB is quite low I could use a triode (or simlar solid state circuit) to soft clip any transiants that would cause damage to the sub?

Hi kipman

I wouldn't worry.In my listening room things starts already to rattle around 90 dB SPL for frequency's below about 30 Hz.

Two of your sub drivers will produce above 102 dB at 42 Hz where the mid-bass octave ends and for listening music at this possible level is IMO loud enough.

I don't think you should include any transient protection for over excursion, its quite adequate if your sub amp is equipped with a 12 dB HP filter at about 20 Hz even if you are using a LT circuit too.

b

 

[kipman725]

well I now have one of the subs built in a 400x410x300mm box constructed out of MDF and even from a 30W amp and without equalisation, stuffing or even proper box seal this thing is monsterous. Will get it stuffed and sealed tonight and hopefully get some mesurments in.

 

[kipman725]

Freq response, done with crappy pc mic due to running over my test mic with my stupid weeley chair. F3 slightly lower than simulated, interesting cancelation at 350Hz not sure what thats about but outside of operating range so no big deal.

 

[kipman725]

2nd sub done. More than powerfull enough for my needs with two of them. Used old carpet glued to the insides as stuffing it seems to be quite good at attenuating >500Hz.

 

[GM]

..........the advice given to me when I started was that OB speakers do not have much below 40Hz.

FYI, 30 Hz dipole woofer array: http://www.stereophile.com/floorloudspeakers/290carver/index5.html

GM