The Bargain Hunter's subwoofer ...

[Fantastic]

Crossover filtering: Linkwitz-Riley, 18dB/Octave

The sub amp specs look OK though I don't understand the filter.
Can you switch between Linkwitz Riley and Butterworth(18dB/octave) ?

LR filters go in multiples of 2. Like 12dB/Oct , 24 dB/Oct etc. You will find LR filters to be 6dB down at the crossover frequency. Optimum Butterworth's are down 3dB at the crossover frequency. LR is preferable.
Everything is down to maths. Change a mathematical parameter and the curve changes. The ones with specific characteristics ( behaviour of the curve around crossover ) are named after the guys who first identified them. Like Butterworth, Linkwitz Riley, Bessel, Chebyshev.....in case you were wondering what all that was about ! Butterworth and LR are usually used more often in audio.

Damping factors don't always tell you how 'taut' the bass sounds ! A damping factor above 20 should generally be sufficient !
Don't be overawed by technical jargon. Once you understand it , you'd wonder why you ever thought it was 'sophisticated' ! Today with so much info available at your fingertips ( for free!), there is no excuse for not knowing ! So get cracking now ! Like cycling , everything is simple once you have understood it ! Enjoy the age of the Net !
I might add that you will also get to REALLY understand the saying " the more you know the less you know " ! Today , knowledge is like an Abyss . A bottomless pit ! You'd never get to the bottom of it ! As you go deeper the quantity of knowledge grows exponentially . Helps to down all those single malts around !

 

[mpw]

This is a non- selectable option on the Hypex DS4.0. The crossover filtering is at fixed 18 dB / octave - Linkwitz Riley.

OTOH, the Rythmik A370 PEQ has a 12dB or 24dB selectable option - i am not sure butterworth or Linkwitz Riley. They have described it quite nicely with all the graphs etc... on their website.

rgds

 

[Fantastic]

I see you are referring to a Hypex module. Well if Bruno made it, he wouldn't have made a mistake about LR and Butterworth(18dB). So I searched for your DS4.0 amp. The PDF user manual is here
https://www.solen.ca/documents/pdf/hypex/ds40.pdf

It doesn't say Linkwitz Riley anywhere. The person who supplied you with info must have made the mistake. Check the manual yourself. Should be a good amp.
Let us know how it works out.

 

[ShaQ.Blogs]

Dayton RSS26510 HF ( 4 ohm ) 10 inch driver + Hypex DS 4.0 plate amp

Dayton is from diyaudiocart

It is currently out of stock.
Did you get the Dayton drivers or is it yet to be purchased?

 

[mpw]

Hi ShaQ

I bought from Bibin at diyaudiocart

I must have got the last piece then.

Mpw

 

[keith_correa]

The damping is only used for a sub if required

It's a sealed sub. Are you saying that it should not be damped? AFAIK, it would always be required.

The simple explanation is that it makes the cabinet volume appear bigger ...up to a point.

You make it sound as if it were the only explanation. Increased perceived volume? The jury is still out on that. Damping smoothens out impedance peaks and resonances. That is primary!

 

[Fantastic]

It's a sealed sub. Are you saying that it should not be damped? AFAIK, it would always be required.

You make it sound as if it were the only explanation. Increased perceived volume? The jury is still out on that. Damping smoothens out impedance peaks and resonances. That is primary!

Yes, I'm saying that you 'may not' need a sound absorbent for a 'sub'. It depends on your design. The only frequencies involved are below 150 Hz. There are no resonances below 150 Hz in that sealed box apart from cone resonance. Cabinet vibration cannot be damped by the internal sound absorbent. Bitumen panels etc. are used and are a totally different thing. They aren't sound absorbers.
Sound absorbents don't increase spl. I don't know where you read about " Damping smoothens out impedance peaks and resonances. That is primary!".
Are you talking about frequencies above 150 Hz ? We are talking about subs and reasons for internal stuffing.

A quick search and I found this about sealed subs.

"The loudspeaker driver's moving mass and compliance (slackness or reciprocal stiffness of the suspension) determines the driver's resonant frequency. In combination with the damping properties of the system (both mechanical and electrical) all these factors affect the low-frequency response of sealed-box systems. Output falls below the system's resonant frequency (Fs), defined as the frequency of peak impedance. In a closed-box, the air inside the box acts as a spring, returning the cone to the 'zero' position in the absence of a signal. A significant increase in the effective volume of a sealed-box loudspeaker can be achieved by a filling of fibrous material, typically fiberglass, bonded acetate fiber (BAF) or long-fiber wool. The effective volume increase can be as much as 40% and is due primarily to a reduction in the speed of sound, and not to the popular misconception of a change in operating conditions from adiabatic to isothermal. The enclosure or driver must have a small leak so internal and external pressures can equalise over time, to compensate for barometric pressure or altitude; the porous nature of paper cones, or an imperfectly sealed enclosure, is normally sufficient to provide this slow pressure equalisation."

Taken from: http://en.wikipedia.org/wiki/Loudspeaker_enclosure
A good read for those who can add to their current knowledge. Note that at low frequencies the absorption coefficient of the usual 'sound absorbent' is very poor. Of no practical use. That's why for reduction of low frequencies in noisy areas they use very large wooden panels which act as absorbents rather than the 'stuffing' we use in boxes.

For those who are interested, I found another article on sound absorbents and how they effect the sound in different types of boxes.Not just theory but with actual measurements.Enjoy !
http://www.data-bass.com/data?page=content&id=79

Check here to see how absorption falls off rapidly as frequency declines.
http://www.paroc.com/knowhow/sound/sound-absorption

 

[keith_correa]

Thank you for "adding" to my knowledge by pointing to a link from Wikipedia. That statement was both condescending and patronizing and, I don't believe everything in Wikipedia! Sorry for going OT with this post! Carry on.

BTW, FM Fantastic is right when he says that you MAY not need to stuff the enclosure. If the enclosure is undersized (which yours is not), stuffing also lowers Q and Fb resulting in reducing a typical hump in frequency that appears in undersized boxes. I know of people who have built could correctly sized boxes but have then reduced volume by putting in wood/thermocole blocks in to reduce the volume and then stuff the box well. They prefer the bass from those enclosures. What can I say? It's to do with what you like, after all.

Like many others, I believe that there is a misconception about increased volume with stuffing. I let live and expect the same attitude towards me too.

 

[mpw]

please refer to the emotiva lounge link i put in earlier... the builder has used 1 bag polyfill per subwoofer and i think its the simplest thing to do.

maybe i may add 1 layer bitumen sheet as well.

Now that i think of it - i think i should decide fast on this as well any layering on the inside of the cabinet walls will have to be done after the sheet cutting and before assy.

BTW, the MDF used is "external" grade and is 1 inch thick with a 1.5 inch thick baffle.

regards

A note on weights :-

Dayton RSS 265-4 10 inch driver = 8 kg
Hypex DS 4.0 plate amp = 4.1 kg
Calculated weight of MDF at @ 4.3 pounds per sq foot for 1 inch thick
= 2304 sq inches = 16 sq ft = 16*4.3/2.2 = 31 Kg !!!

Therefore.. calculated total weight = 8+4.1+31 = approx 43 kg !!! + polyfill / damping etc.. + any bracing weight

i hope i have calculated right...

i need to get this up 12 floors !!

regards
mpw

 

[prem]

There's something called a lift

 

[mpw]

There's something called a lift

:

good to see you here prem...

i need to cross the watchman first

regards

 

[Hari Iyer]

Since your enclosure is slightly under damped due to little more Vb, this enclosure will do well with higher damping. You can work out the damping required if you are able to decide what kind of damping you are planning, under, critical or over damping. You then decide the damping coefficients and work that out based on the Vb, Vas, Qtc and Fs of the driver. You can start with critical damping then add more polyfill to under damp or remove polyfill to over damp.
BTW have you worked out the damping coefficients and the weight of the damping material required?
@ FantasticDaming does help to reduce the standing waves , but the enclosure tuning freq helps to reduce the driver resonance by getting tuned. The system Q helps to neutralize the drivers mechanical Q and needs to be in sync.

 

[prem]

On a more serious note, your Merlins are fast speakers. Which is what brings it alive. I don't understand technicalities but make sure your sub matches up to the speed of the Merlins. Else bass will sound separate.

Also make sure the bass texture of your sub and your Merlins match. I think the texture will be a function of the cone material and the magnet but I may be wrong. The experts can chime in

 

[mpw]

Since your enclosure is slightly under damped due to little more Vb, this enclosure will do well with higher damping. You can work out the damping required if you are able to decide what kind of damping you are planning, under, critical or over damping. You then decide the damping coefficients and work that out based on the Vb, Vas, Qtc and Fs of the driver. You can start with critical damping then add more polyfill to under damp or remove polyfill to over damp.
BTW have you worked out the damping coefficients and the weight of the damping material required?
@ FantasticDaming does help to reduce the standing waves , but the enclosure tuning freq helps to reduce the driver resonance by getting tuned. The system Q helps to neutralize the drivers mechanical Q and needs to be in sync.

haribhai,

have ordered

bitumen sheets
3 mm felt

polyfill - i will manage locally - if i need.

In short - i havent done any calculations.... will go by an approximation and by the ear.

Many things are confusing to me if i were to totally go by calculations alone. This is a 1 off build or maybe another one if this succeeds.

I dont have any ports to play with as well.

What i would not want is to overfill or overdamp the cabinet to completely deaden the sound at the cost of pace.

Would prefer a fast and furious notes to hammerblows.

Also make sure the bass texture of your sub and your Merlins match. I think the texture will be a function of the cone material and the magnet but I may be wrong. The experts can chime in

prem,

i am concerned about it as well and this was one of the consideration ( Aluminium cone ) on the Seas L26 ROY but since that will not be available till July 2015 atleast ( i am told )... we went in for the next best option Dayton RSS265HF-4 which is also same cone material and spec wise more than 90% of the Seas L26 ROY.

I am drawing information from Kapvin and i understand he has worked with the MW164 Merlin driver before. I have been to his place and like the DiY stuff he does...very well thought out, articulated and executed.

He has been home and has heard the Merlins as well.

All the advise and knowledge are with serious and good intentions and i hope the build will reflect that.

However - we will know when the sub is ready for a shake and keep the vada pavs and beer ready as well..

fingers crossed...

regards
mpw

 

[prem]

After a few drinks everything starts sounding good. So that's always an option

 

[Hari Iyer]

What i would not want is to overfill or overdamp the cabinet to completely deaden the sound at the cost of pace.

regards

Ok. To overfill means under damping and to under fill means over damping in speaker terminology.

Under damping will help to reduce the Q of your system which will in turn help to reduce the resonance peak. The harmonics of the standing waves will also be better controlled with under damping. If you over damp the cone excrusion can be high (12.5mm for the Dayton) that can hamper with the low frequency reproduction and can be too fast than needed. Under damping will also work well with the cone stiffness and offer better compliance and give more tight bass based on your enclosure volume.

If you have not calculated the damping weight required and want to calculated based on the published parameter do let me know.

 

[arj]

After a few drinks everything starts sounding good. So that's always an option

hyeah:
2 drinks and you dont need a sub
3 drinks all systems sound the same
5 drinks and you become rafi/bono/cliff richards all rolled into one..so who needs a music system

 

[mpw]

If you have not calculated the damping weight required and want to calculated based on the published parameter do let me know.

I have ordered some that i dont think would be available easily close to me. If anything else is required ...maybe i will raid a few fluffy pillows

you may post it here.

thanks.

 

[Hari Iyer]

maybe i will raid a few fluffy pillows

you may post it here.

thanks.

Looks like a casual approach towards damping with not much importance given to damping density, the polyester fiber damping density is equally important. For a sealed enclosure you can still get away with a little higher density but not with other designs. If you mix polyfill with two separate density materials it will then be even more difficult to predict.

Btw when is your box expected to be ready? I am considering net internal volume of 52 liters for the calculation - correct me if I am wrong.

 

[Fantastic]

That statement was both condescending and patronizing

Thank you.
Actually my reasons for posting information is to keep FM's updated on some topics. Not everyone has time to look up for info. If it looks 'condescending and patronizing' it's unfortunate as it wasn't meant that way. I do hope that now some guys would understand some things better .
Increasing ones knowledge only helps to improve one's perspective on various issues. Everyone learns from what the other have learned and they from others....and so on ! Knowledge doesn't belong to anyone. It's just passed on !
And the following old saying always applies:
" The more you know the less you know" !
That should have a very high damping coefficient !