First DIY Project Subwoofer

[ozynigma]

Hi All,

Found this site by accident and am very impressed with the level of knowledge and enthusiasm shown.

I am about to start my first DIY project. I am looking to replace a JBL Digital 10 Subwoofer in my HT system. The JBL only goes down to about 34Hz which is only 8Hz below my main speakers.

Before I start designing the enclosure (which I will also need some help with) I would like some advice on placement.

Currently I have the forward firing ported subwoofer IN the cabinet. It fits neatly and I cannot detect any significant change in performance from having it in the corner of the room.

The attached image shows where the current subwoofer is located and you can see that the main speakers fit nicely into the corners of the room.

1) So should I make my new enclosure to also fit into the cabinet or should I make it freestanding and rearrange the living room? (Note room is 4.8m W x 6m D x 3m H.)

2) High sound levels are not very important to me as the neighbours (and wife) are already complaining. Can a single 12 inch 100 W sub in a sealed enclosure get down to 20Hz and improve my HT setup?

I am currently sourcing a driver and amp and will advise specs when I have them.

Thanks
Ozynigma

 

[busterno1]

The answers to your question will depend on which driver you get .

It will tell what sort & size of box you need to use .

Yes some 12 "sub drivers will go down to 20hz .

Some of It will depend on your choice of driver

do you have a budget in mind . I am sure there a aussies here which gladly offer advice on what drivers are available

 

[ozynigma]

Hmmm budget....

Well initially I am treating this first project as a bit of an experiment so keeping the costs down. Looks like I can get the amp for under $200AU. I might be able to get a slightly used Peerless driver under $100AU. However I would probably be prepared to pay $150-300AU for a new driver if necessary.

I noticed that SkinnyBoy had two 8" Peerless drivers for sale on the trading post of this site........

Ozynigma

 

[moving_electron]

Given the moderate SPL and small cabinet size benefit, Linkwitz transformed sealed sub might make a lot of sense. Could make a nice low Q sub crossing in at 60 or so.

It would be interesting to calculate what could be done utilizing your existing sub by sealing the port and utilizing a LT. A new 12 inch would give you more SPL, but you may be able to take the existing JBL very low and give you very tight base for music.

 

[ozynigma]

I have been looking at the Linkwitz site and conceptually I think his Thor design of a 12" driver in a 50 litre sealed enclosure could be the way to go for this beginner with only moderate expectations for SPL.

Yeah I could try modding the JBL but I am thinking of using it as is with my PC and some self powered satellites (my next project???). I think I would need to learn a lot more and probably need some test equipment to go down the route of modifying the JBL.

Also it seems strange that JBL would not have optimised the subwoofer to deliver deep bass. Perhaps they ported it to maximise SPL at the expense of frequency range?

Ozynigma

 

[michael]

A ported enclosure will always go lower than a sealed one and it will with the same driver be a larger optimum enclosure.
I suggest you look at the Adire DPL and the Shiva, both of which at 12"ers with rave reviews and high SPL capabilities. Both will cost you about 300.
A driver between these two would be the Eminence Lab12 at the same price it is better built than the shiva and has higher efficiency than the DPL.

what size is that other sub that you have and how deep can we put it in the rack. That way we can see how much space there is to work with. And i think that you want a ported as sealed would not go as low as the JBL there.

 

[BAM]

It's my understanding that the DPL12 likes smaller sealed boxes.

 

[michael]

It's my understanding that the DPL12 likes smaller sealed boxes.

To a degree, it performs better than most in sealed boxes, though those sealed boxes are around the 60L mark.
Its F3 will be about 10hz lower than the shiva in the same box.
But i would turn him away from the DPL due to its low efficiency of 84db, this with his desired 100w would make a rather low spl subwoofer.

 

[ozynigma]

The rack is 400mm deep.

So I can go a box size 400mm D x 450mm W x 345mm H.

With 20mm thick material that would give internal volume of 47 litres, less the internals.

If necessary I can go taller on the H dimension up to say 450mm.

I am currently attempting to source a cheap Peerless 12" Bass Driver 831857, specs are here ;
http://www.d-s-t.com/peerless/dataover/wo_class.htm

This and a 110W amp are my starting point.

Any advice on box size and porting alternatives and their effectiveness would be appreciated.

Ozynigma

 

[michael]

The peerless 831857 requires at least 140L to work, i recomend that with that 47L to play with that you push your budget up and go for the adire DPL12, put it in the 47L box, heavily stuff it with polyfil and throw about 200w at it, wes components sell a 200w plate amp for 300 that is very good (have it myself).
This will give you 103db of output at 30hz with an f3 at the same point. you will also have the headroom of the large excurtion.
All in all would cost about $600 for the parts then more for the box.

 

[ozynigma]

To a degree, it performs better than most in sealed boxes, though those sealed boxes are around the 60L mark.
Its F3 will be about 10hz lower than the shiva in the same box.
But i would turn him away from the DPL due to its low efficiency of 84db, this with his desired 100w would make a rather low spl subwoofer.

The peerless 831857 requires at least 140L to work, i recomend that with that 47L to play with that you push your budget up and go for the adire DPL12, put it in the 47L box, heavily stuff it with polyfil and throw about 200w at it, wes components sell a 200w plate amp for 300 that is very good (have it myself).
This will give you 103db of output at 30hz with an f3 at the same point. you will also have the headroom of the large excurtion.
All in all would cost about $600 for the parts then more for the box.

Michael,

Thanks for your advice, I will forget the 831857, even though it is very cheap as it is obviously the wrong driver for my application.

As you stated earlier I think the Shiva might be my best choice rather than the DPL12 due to its higher efficiency, also I have ordered the 110W amp from another DIYAudio member so that is a limiting factor.

Enclosure wise I can go up to about 73 litres by making the unit taller. I am still leaning towards a sealed enclosure for simplicity of design and construction.

I have been using the closed-box.xls spreadsheet from linkwitzlabs.com to do some basic modelling of the sealed enclosure. It seems the bigger the enclosure the easier it for the amp to drive.

Are there any other or better public domain modelling tools I could use to evaluate my proposed design?

Ozynigma

 

[michael]

Go and get yourself a program called winisd, its very easy to use.
73L is a decent volume, sealed shiva would work well in it, a port could be used and would give more output below 40Hz but it would be very long and difficult to implement. Besides you can always do it later on.

 

[ozynigma]

Given the moderate SPL and small cabinet size benefit, Linkwitz transformed sealed sub might make a lot of sense. Could make a nice low Q sub crossing in at 60 or so.

It would be interesting to calculate what could be done utilizing your existing sub by sealing the port and utilizing a LT. A new 12 inch would give you more SPL, but you may be able to take the existing JBL very low and give you very tight base for music.

moving_electron,

I am leaning toward the LT and a small enclosure with a suitable 12" or even 15" driver (like Project 48). However I have just purchased a 110W@8Ohm amp. Is this going to be sufficient for moderate volume levels at very low frequencies?

Also I would normally be getting a mono input signal for the subwoofer out of my HT amp (for both HT and music). Where does the LT circuit go in relation to sub amp? Note my mains have a 3db point of 42Hz.

ozynigma

 

[michael]

Forget about an LT. It would use up far too much power, stick to a shiva in that 73l box sealed. Anything else will be diffcult to do and be inneficient for your application.

Sealing your JBL would be a WASTE OF TIME, sorry but it would harshly reduce the SPL limits of the sub, basically taking your HT a step backwards in terms of SPL.
Just to let you know the LT would be placed inbetween the "subout" and the line level in on the plate amp.

Once you have the shiva in its sealed box you can always port it to gain some deep bass efficiency and punch. a 75mm port 320mm long would give you a 22hz tuning point and an f3 of 27hz instead of the 40hz of the sealed.

 

[moving_electron]

moving_electron,

I am leaning toward the LT and a small enclosure with a suitable 12" or even 15" driver (like Project 48). However I have just purchased a 110W@8Ohm amp. Is this going to be sufficient for moderate volume levels at very low frequencies?

Forget about an LT. It would use up far too much power, stick to a shiva in that 73l box sealed. Anything else will be diffcult to do and be inneficient for your application.

.....

Once you have the Shiva in its sealed box you can always port it to gain some deep bass efficiency and punch. a 75mm port 320mm long would give you a 22hz tuning point and an f3 of 27hz instead of the 40hz of the sealed.

While the 110W@8Ohm amp is "not that big" it actually could produce some good results for you. I think it depends on your goals in terms of SPL. It actually is quite a bit of power when you consider the number of decibles you get from the first 10 watts.

If you have the room for the 73l box or larger (see the Adire site for recommended sealed plans) then it certainly may make sence to go that big. Adding a port as suggested sometime for HT is a relatively easy change. Most of the group delay issues etc. occure low enough in this case that they would not really be an issue for most music etc. The disadvantage is you don't really have very much control over the rolloff and matching to the room. If you tune the port low you may actually get a pretty good rise when combined with the room effect. It you tune it higher you will get a hump near the tuning frequency and will also loose some of the lowend frequencies.

On the otherhand the Linkwitz transform does have the disadvantage that you have to build the electronics to do it. So it really depends on whether you would get enjoyment from doing so. It really is a good project because in can be done in such a way that you do not have to work with any lethal voltages (only 16v AC and +-15v DC), and so is a good early project.

But you have some nice advantages if you want to really match your system to the room. You can measure the frequency response of your sealed subwoofer in the room and then determine what transform slope would bring it up to flat down in the lower frequencies. Or you could build in a bit of a rise (with room gain). Or you can switch in the HT setting as needed.

Although a larger amp would be better since the Shiva can really handle a lot there is quite a bit you can do with this one.

Lets say your 110 W into 8 Ohm amp is maybe 130 watts into 4 ohm (Shiva has two 8 Ohm voice coils that can be put in parallel) then you can do the following with the amp per calculations in linktranadv29.13.xls:

With a Linkwitz transformed 73L sealed box with Shiva you can get: An F3 of 24 and a SPL of 102 dB via the transform. The maximum correction is about +6 dB ( amp must supply 4 times the power at ~24 dB as it does to product the same SPL at say 80Hz).

With a Linkwitz transformed 54L box per Adire small enclosure (13.5" cube) you can get an SPL of over 100 dB. The correction is about 8 dB at the highest point (something on the order of 6-7 times the power).

For comparison standing next to a loud lawnmower or in a factory would be in the 90 dB range. A woodworking shop is in the range of 100dB.

For various reasons you will normally not push it this hard. But it does show that for quite useful sound levels you can do quite a bit to enhance the lows and match to a room with a Linkwitz transform and moderate size subwoofer amp. Remember when 100 watts was a lot?

I am running smaller less capable subs on similar wattage with this kind of EQ and the increase on the low end was quite an improvement and the SPL is plenty much for a 12x24x8 room.

If is ever insufficient to irritate the neighbors, you could upgrade the amp at some point down the road. With 300 watts you could more than double the SPL. It would be very loud indeed.

 

[moving_electron]

I am leaning toward the LT and a small enclosure with a suitable 12" or even 15" driver (like Project 48).
ozynigma

Project 48 could work but is pretty fixed. It basically compensates for a 12 dB/octave rolloff. There are no other choices. Could be used with different enclosures that had a 12db/octave over time though. 12dB might not be what you are experiencing in your room and box. Project 71 is much more flexible for room matching since you can pick f and q. More calculation upfront but not much different from a project point of view.

Sealing your JBL would be a WASTE OF TIME, sorry but it would harshly reduce the SPL limits of the sub, basically taking your HT a step backwards in terms of SPL.

Agreed, but in his requirements highest possible SPL is not a need. It does seem though like sealing the JBL and using it would a real lost opportunity to get more drivers and boxes into the house. Sorry for suggesting that option.

 

[moving_electron]

With 300 watts you could more than double the SPL.

To clarify: the actual pressure is more than doubled which would be a 3 dB increase on the dB log scale. Obviously if sound pressure was doubled in dB to 200 dB you would be dead and needed electrical power would have set your house on fire. I believe the increase from 100dB to 200dB would be something like ten billions times more power (~2^^33.3) than that used to product the 100dB.

 

[ozynigma]

moving electron

Thanks for all the time you have spent calculating the numbers above. It is all starting to make sense now.

Current plan is to go the 15" Adire Tempest driver in a 55 litre enclosure with the 110W amp and LT.

I have contaced ESP regarding purchasing Project 71 and have used the spreadsheet to calculate component values based on the driver / box combination. I have just spent all afternoon drafting up the enclosure design to fit the available space.

I am going 15" driver for only an extra A$90. I only want to buy one driver and I think I would regret it if I bought the 12" then wanted more performance later. The 110W amp has been purchased opportunistically (and perhaps prematurely) second hand and if it proves inadequate I will upgrade it.

I am looking for depth of bass more so than volume. Neither the wife nor the closest neighbour like the system to be too loud. If I want more volume I can just plug the JBL back in as well and get heaps of bass reinforcement from 30 Hz up.

My main speakers have an F3 of around 42Hz so I really want the sub to be true sub only and roll off from 40Hz up.

I ran test tones through the JBL today and I got virtually no output below 30 Hz as I suspected. However without modification it will work well enough as part of a planned multimedia setup in my computer room. Next project will be to build some satelite speakers to replace the junk that comes with a PC.

I will post the results up when the subwoofer project is completed in a few weeks time.

Michael,

Thanks also for your advice. I have considered it and been modelling different drivers, enclosures and vents. But nothing within my size limits was bringing F3 down around 20-22Hz where I wanted it. I am also really interested to see if the LT works so I am going to give it a try and see what happens. If it doesn't work I can always build a new cabinet (the cheapest part) and I will have an excellent driver to start with.

Ozynigma

 

[MikeB]

Another alternative ?

Hi !

If you are looking for a small subwoofer with extreme depth,
(Tests say down to 11hz) maybe you should have a look
at the peerless XLS-10, (830452). It's not that expensive,
and requires only 30Liters, using a passive slave.
I'm thinking about trying these...

check these links:

http://www.lautsprechershop.de/hifi/peersub.htm
http://www.lautsprechershop.de/hifi/bau_xa10.htm

(Sorry, these are german)

What do you think ?

Michael

 

[moving_electron]

A couple of quick thoughts.

1)I assume your new sub will go in place of the other one. In the picture it looks like it will be placed in the shelving unit with the closed back so air flow behind the sub box will be ver limited.

Rather than bolt the sub amp into the back of the subwoofer box as is traditional you might want to keep it separate and run just the output wire to the subwoofer box. From the picture, it looks like the shelving unit is closed on the back and a lot of heat will be trapped if the amp was mounted on the back of the sub box.

2) If you feel you are pushing the amp hard and want to keep the output transisors running cool, one of the new quiet PC fans aimed at the heatsink fins will reduce the temperature tremendously. They run fine on DC transformers. You have to get really close to hear these in a quiet room. It will be inaudible more than about a foot away. For a main amp I have I just run it as needed via a switch but I intend to implement Project 42 in Misc. It is a simple temperature sensing auto turn circuit that runs on the 12v DC.

Good luck on your build. Let us know your experiences.