Question Help with building non-cube shaped subs and other questions

[Starmax]

Hello all,

After posting in the subwoofer forum I have ended up here because I am hoping that by going DIY I can get more bass without reducing the size of the floor area in my home cinema room.

I want to replace my 2x Tannoy SFX ported subs with 2x new non-ported subs, with 15" drivers. I know that the move from my current 8" subs to 15" will give me deeper bass, but with my current setup will I be leaving a noticeable hole in the bass response between the subs and my Wharfedale speakers?

Looking at turn-key subwoofers they are mostly cubed shaped. By going bigger on the driver front gives me a bigger cube. I'm hoping that by going rectangle-cube I can keep the volume the same but the depth to 300mm.

In my DIY search I found the self-build IPL SW6 Mk2. Specs are 445 by 445 by 440mm, 60 litre 25mm MDF. If I were to go 300mm deep and H&W of roughly 545mm and using the same 25mm MDF, I have roughly the same volume.

Is there anything else I should be considering? Does the rectangle shape alter bass dynamics over the cube design? I am already thinking that this design will make the box more unstable so I would secure it to the wall behind to stop movement.

Having built other simple speaker enclosures and furniture for my HC I am willing to give this a go, although with the much higher forces involved with moving more air then I would welcome suggestions or links to websites about building methods. At the moment I have only been using a jigsaw and getting B&Q to cut MDF to the straight line shapes I need. If fancy cabinet joins are better then perhaps there are people out there that will build custom size sub enclosures?

Once confirmed that I can go down this route then it will be a quest for drivers and an amp. Seeing other posts on here I'm already liking the idea of a Behringer amp.

Please see below for more information on my HC room.

Thanks!


Detailed Overview:
In January this year I embarked on upgrading my dedicated home cinema room. I would prefer to have a room 3 times the size but I feel fortunate enough to actually have a room that I can use purely for this one hobby and also one that I don't really have to worry about high sound levels being as the house is detached.
The size and shape of the room has meant I have had to make compromises, but I feel I've managed to make the best of the situation.
Compromise 1: Seating - against back wall - would rather have in the middle of a much larger room for surround sound distance.

The room has a cottage style window (shown on the right of my simple plan). This also means a stepped down ceiling which also slopes down. It was easier and cheaper for the house builders to box in that part of room. I used that wasted space to fit MDF cubes (shown in orange) to house the AV kit, PC and gaming consoles etc. Ceiling height in the tallest part of the room is 2.3m. As I mentioned previously, the ceiling steps down and also slopes so it is difficult to calculate the exact volume of the room.

I've managed to install 4 ceiling and 4 surround speakers, so giving me a Dolby Atmos 7.2.4 configuration.

Equipment:
Denon AVR-X3600
BenQ W2700 Projector
Pro-Ject Amp Box S2 Stereo Power Amplifier (to drive those extra 2 channels)
Tannoy SFX Subs
Wharfedale speakers (Surrounds are in-wall WCM-65's)

I've built custom furniture in order to house in-wall speakers & lighting and provide sound absorption. They are as follows:
1.5m x 1.2m x 10cm box - attached to ceiling
Box for centre speaker to sit on
Wall mounted shelving and box providing housing for in-wall surround speaker (shown in brown on plan)

The sound absorption I have used is rockwool and the outer covering is sound transparent material to allow sound to pass through. As I created and installed each piece of furniture it was amazing to hear the difference the absorption made to the sound in the room. The room originally had a wooden floor and there was quite a bit of bass boom and echo with voices - the sound absorption in the furniture pretty much eliminated this - to my amateur ears anyway!

The flooring is now carpet with 11mm Cloud 9 underlay. I was expecting the carpet to absorb some of the bass from the Tannoy's and it certainly has done that. Better performing subs have always been on my radar and now is the time that I am wanting to upgrade.

Not to scale

Key:
Red - Wharfedale Diamond 230 Floor Standing Speaker
Green - Wharfedale Diamond 11.CS Centre Speaker sat on home-made box stand incorporating sound absorption material
Yellow - Tannoy SFX Subwoofer
Pink - 90" Screen
Orange - AV equipment housed in home-made boxed enclosure recessed in wall
Brown - homemade shelving also housing surround speaker and sound absorption material.
Blue - Main listening position (projector mounted above this position)

 

[noiseboy72]

In terms of a "hole" in your frequency response, I would suggest you choose a plate amplifier or external amp that enables you to adjust the roll off. If you go down the PA power amp route, consider one with built in DSP to accomplish this. The bass driver will certainly go high enough to cover the hole and sealed drivers tend not to have that boominess in the lower registers that can otherwise overpower a well balanced system.

I would go to a wood yard rather than B&Q and get them to accurately cut all the wood. You can use a jigsaw for the drivers, but trying to cut straight edges takes practice and a substantial straight edge to cut against. 18mm MDF or ply are both good materials. MDF is easier to work with, but can chuck the screws out over time. Most home builders and domestic subs use MDF and big professional subs ply, but glue and screw all joints and seal all joints as well as you can whatever you use. No issues with the shape of the cabinet so long as the volume is similar. Put in lots of bracing to reduce cabinet resonance on long sides and a foam lined "cradle" to rest the back of the magnet into reduces stress on the basket and can help to improve the longevity of the speaker. I wouldn't worry about fancy joints, just use corner bracing and lots of PVA!

I doubt the carpet will absorb much of the low bass energy. It will attenuate the higher frequencies to some extent and the thicker underlay will slightly reduce transmission through the floor. This will reduce reflection and coloration which is probably what you were hearing.

I would suggest it's worth investing in REW (Which is actually free) plus a good measurement mic so that you can continue on your acoustic and sub building journey. This will provide empirical results to your efforts and help you to experiment and tweak your builds to optimise the listening environment.

 

[Starmax]

In terms of a... ...listening environment.

Noiseboy72 - thank you so much for your reply. You pretty much answered all my questions and then some!

I'm feeling pretty excited about this build! As I have now mentally built the cabinets the next step is to choose the drivers and amp. I'll take a look back through the forum to see what is recommended. With a brief look, and a suggestion by another forum member on another post of mine, I'm currently short-listing a Behringer NX3000D or NX6000D amp. If anyone has any recommendation of drivers that would suit these amps and sealed cabinets then please let me know.

Cheers

 

[Liammonty123]

Welcome to the world of DIY, I can almost guarantee you will never return to normality now. I see your post mentioned 15’s. If you could even fit two Dayton Ultimax 18s in 2 sealed cans (4cuft) and one NX6000d that should be a great set up for movies.

 

[Starmax]

Welcome to the world of DIY, I can almost guarantee you will never return to normality now. I see your post mentioned 15’s. If you could even fit two Dayton Ultimax 18s in 2 sealed cans (4cuft) and one NX6000d that should be a great set up for movies.

Haha - when processing all my options the idea of 18s did occur to me. I think 4cuft works out to be 113 litres. I could just about fit that into the space available. The magnet on that Dayton driver would be nearly touching the back of the cabinet. Would that be an issue? If not, then it would help in building in a support for the magnet/basket.

Even though it took me many hours/days/weeks to build the furniture and cabinets in my cinema room I did quite enjoy the experience. Would have been quicker with the right tools and not just a jigsaw.

Thanks.

 

[Liammonty123]

What’s the max cab size you can fit, dimensions wise?

Also I would use regular 18mm MDF and brace well, 25mm is likely to add a lot of weight but not significantly more strength.

 

[Starmax]

What’s the max cab size you can fit, dimensions wise?

Also I would use regular 18mm MDF and brace well, 25mm is likely to add a lot of weight but not significantly more strength.

I'll have to confirm the maximum height and width dimensions when I am back at home, but I know that I wanted to keep the external depth of the cabinet to 300mm. Could go to 350mm at a pinch but 300mm will match the depth of my centre speaker stand.

Interesting to note your views on the 18 v 25mm MDF. I built my furniture out of 18mm and noticed that there was some flex on the longer pieces that I used. I was going on the idea that rigidity would be king in a sub build hence wanting to choose 25mm. Maybe as internal bracing will eat up my volume I might be better to choose 25mm for the cabinet and minimal bracing?

 

[Liammonty123]

25mm won’t add much rigidity vs 18mm, bracing is much more effective at making panels rigid and shifting any resonances out the passband. I like to use window braces, as I find them easiest to install and very rigid, although they do use more wood. Stick bracing from opposing panels is usually fine.

 

[Starmax]

What’s the max cab size you can fit, dimensions wise?

Okay. Maximum box size is 300D x 580H x 750W (mm). If my sums are right, and by using 18mm MDF, that gives me a volume of 102.5 litres - before subtracting the driver and internal bracing. Not enough for the Dayton Ultimax 18s you mention.

I've just been researching how to calculate box volume using speaker specs and after a brief comparison with another 18" driver I don't think I've got the volume. Back to 15" I guess?

 

[Liammonty123]

Your calculations are correct re box size. Although I can’t see this being much of an issue. A smaller sealed box just requires slightly more power to reach XMAX than a larger one. If you can physically fit the driver you should be good to go!

 

[Starmax]

Your calculations are correct re box size. Although I can’t see this being much of an issue. A smaller sealed box just requires slightly more power to reach XMAX than a larger one. If you can physically fit the driver you should be good to go!

Thanks for that information. After some more research on what drivers to choose it would seem that BMS 18N862's could be a good choice. They are a bit over budget but I am continuing my research...

 

[Liammonty123]

They are a better all rounder than the UM18s. Would think defo best for music due to the low mms high sensitivity nature of them. Plenty of XMAX also!

 

[Starmax]

They are a better all rounder than the UM18s. Would think defo best for music due to the low mms high sensitivity nature of them. Plenty of XMAX also!

Ah yes, the UM18s. I understand that they would be better than the BMS for the very low frequencies in HC. I am more HC than music, but maybe I'd love the all-roundness of the 18N862's . It is a difficult one to call with my lack of experience so I'll just keep researching and, of course, listening to your sage advice!

I'm a little put off the Dayton's as I understand there isn't a UK distributor, but if they are really the one's to go for then I might just have to take the plunge.

Cheers

 

[neo_2009]

On UK, you also have the Fi HT3, for £529.

 

[12harry]

Have a look at Tympany/Peerless drivers... for example the 10"XLS has a very low resonant freq. and a double-magnet system. Peerless suggest a sealed box of very few litres . . . but then you have to compensate for the LF fall-off with a steep pass filter, like 24dB/octave which isn't easy. Whilst BK( Essex, UK) can/could supply the drivers, in several sizes it's my understanding that the larger speakers will be louder ( with more input), but with less Sub-bass, since having a resonant freq often above 30Hz.
Sadly Tympany do not yet provide any filter suggestions....

If "loud" is what you want bear in mind that sub-freq are felt more than heard and high op can damage hearing. You could fit a "Shaker" driver to your sofa . . . and you'll probably only "feel" that - and it can be driven by a modest quality amplifier + Filters.
Snag is you need one shaker per person!
Having a shaker fitted to a sofa needs some care in installation to avoid losing the movement, which is quite small and not (usually) exactly HiFi - but it's a "different" experience that is almost impossible to achieve other than by leaning against big drums.

Cheers.

Good Luck.