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Old 28th December 2012, 09:15 PM   #1
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Default Please offer suggestions for small subwoofer (design, driver, amp)

Having been running a local cycling forum for ten years I quite hate the "please suggest a bike" questions. There are not too much such questions (gimme a solution) here, but I'm going to post one now. I prefer to be good at what I am and trust the specialists like myself. One just can't be a man of all trades. I've reached my personal limit.

Audio source is a decent PC equipped with BluRay drive, soundcard Creative Sound Blaster X-Fi 0460 with hacked/added optical SPDIF port. Optical cable ends up in a deommissionned Panasonic SA-HE200 AV receiver. When keeping it vented, it has enough power for any home use application. Speakers are two self-built uFonkens with Fostex FF85WK, located on the computer desk. Soundcard is set to 2/2.1.

The room itself is a tiny one of 3x3 meters, height 2,5 m. uFonkens about 0,8 m from listener. They can be either tilted upwards on desk or set on pedestals of correct listening height.

I think I need a subwoofer to support the uFonkens with the low end. Currently have thrown in a Creative Inspire 5.1 5300 active sub and the low end has improved a lot.. However, it's not what i'd like to live with too long. Here comes my simple request.

Please suggest:
- design (with dimensioned drawings or explained dimensions a mechanic could make correct judgements of)
- SW element(s)
- SW backplane amplifier

Budget around EUR (USD) 250 (as an indication, not the ultimate limit) for element and amplifier. If high quality dual elements design would be a serious option to consider, budget can be slightly increased.

My personal unqualified opinion has been suggesting 6.5, max 8 in element in a closed box.

Size matters, bigger is not better. Compact cube (closed design ) would be preferred, thin vented vertical design as an alternative. Room (floor space) is serious constraint.

European sources for element(s) and amp are a must. Freight from the US plus import taxes just do not make sense.

Webshops like
Strassacker: Lautsprecher - Boxen - Selbstbau
Hobbyhifiladen
are known good reliable sources.
Well-established ebay sellers have their chances.

TIA
Erik
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Old 28th December 2012, 10:52 PM   #2
DUG is online now DUG  Canada
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Find a source for small woofers that you might like to try.

Get their parameters and simulate what you might like to buy. (using WinISD or other)

Then purchase and build.

The same with amplifiers only here it gets more complicated.

Finding discrete parts may be easy but finding a design for any particular part may be a little more difficult.

Chip Amps make more sense in that there is usually a schematic in the data sheet.

Kits and pre-built plate amps are available but I am not familiar with the European suppliers.

Select, simulate, choose, purchase, build, enjoy (or redesign )
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Old 2nd January 2013, 11:35 PM   #3
DrNick is offline DrNick  United Kingdom
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I have just built a sealed sub using a 15" Dayton driver and a pre-built BK Electronics amp, which I have discussed in this thread. This was my first build, and I found out a lot on the way. I went for a sealed sub to make it possible to go as low as possible, and to vary the equalisation easily after building it using a miniDSP processor. This worked out to about 500 all in, 200 for the 15" driver, 120 for the amp and same again for the miniDSP.

If you want to stay small and use 6 to 8 inch drivers, I think you'll have to go for a vented design, I tried modelling all sorts of different drivers before deciding what to build, and it came down to either going for vented designs or very big sealed systems. I posted a few models in the thread linked to above, but I was shooting for 20 Hz or lower so the dimensions were daft.

If you go to Zaph|Audio and look at the Dayton RSS315HF-8 12" amp design, that has full plans in the zip file linked to. This driver unit is available from Strassacker: Speaker Building, Components for EU204. If you follow this route, you will have to find a plate amplifier to fit on the back. Those at www.lautsprechershop.de/ might be fine for this, or look at http://www.europe-audio.com/. You might be thinking of getting a separate amplifier, but for a sealed sub you will probably need (or may be just benefit from) something that has a bass boost filter to artificially raise the response at bery low frequencies, where a driver's natural response will start to fall off. Most seperate amlifiers' bass control will just amplify all of the range in which a sub works, whereas the filter built into a dedicated sub amp (like those at the two shops above) might match the requirement better. Hypex might be a bit more expensive but seem to have some great products, and their cheapest 120W class D sub amp is not much more expensive than the competition. Here is a link to a 10" bass reflex sub, although I do not know of the availability of that driver in Europe.

Finally, here is a link to a useful page which has a few other onward links to projects people have built. Best wishes for building your sub!

Nick.
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Old 3rd January 2013, 11:30 AM   #4
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SAM-100D - Subwoofer active module 100W - Europe Audio

plus

SD215A-88 - Dayton 8 inch DVC Shielded Series Subwoofer - Europe Audio

Build the box as big as you can, keep it sealed. Apply LF eq to taste. Playing with the "cutoff frequency" dial might help.

Chris
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Old 3rd January 2013, 05:24 PM   #5
DrNick is offline DrNick  United Kingdom
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I'm just going to post some stuff to try to persuade you that a 10" or 12" driver might be better, and not necessarily need a bigger box.

The limit for the volume of sound that a speaker can produce, for woofers at least is proportional to the surface area (Sd) and the distance the cone can move backwards and forwards (Xmax). The product of these is the volume of air displaced when the speaker is moving. Bigger speakers do not just have bigger areas, they also usually can move further, so are more efficient. As the distance a speaker must move forwards and backwards goes up to produce a given power as you lower the frequency, it is practical to set some minimum frequency that you want to have the speaker handle and filter out the frequencies below this. As an example, if the figure below I have modelled the Dayton drivers

15" RSS390HF-4
12" RSS315HF-4
10" RSS265HF-4
10" SD270-88
8" SD215-88
8" RSS210HF-4

The figure shows the cone excursion in mm on the y axis for the frequency on the x axis.

Click the image to open in full size.

You will notice that the power applied to each speaker is different. I have selected the maximum level for each speaker that will not exceed the limit of how far the speaker can move at 10 Hz. The figure above shows the cone excursion continuing to rise below 10 Hz, so I have also plotted the excursions once the speakers are protected with a filter at 10 Hz.

If the speaker is driven beyond Xmax it will start to distort the sound, and if overdriven too far, may damage itself. If you end up getting a really cheap amp, it may not have a low frequency filter, and so if you set things up to deliver maximum power at 20-30 Hz, a large burst at 5 Hz could damage the speaker.

Click the image to open in full size.

In this figure each speaker will hit it's maximum cone excursion just below 20 Hz before the filter starts to reduce the input signal. In the data boxes the box size to achieve an optimally flat frequency response is also shown (except the 15", where the box at 137 is just below the optimal size of 160 litres). The box sizes as plotted are

15" RSS390HF-4 137 litres
12" RSS315HF-4 84 litres
10" RSS265HF-4 31 litres
10" SD270-88 77 litres
8" SD215-88 27 litres
8" RSS210HF-4 41 litres

The final thing to look at is the sound pressure pressure produced by each speaker when it is working at its maximum excursion.

Click the image to open in full size.

So, for my money, the 10" RSS265HF-4 looks great. Way more usable bass than the other 10" or either of the 8" speakers, and in a 31 litre box.

The efficiency of the SD270-88 with its lighter paper cone is very high, so you can drive it to its limit at 20 Hz with just 21 W of power, so you could get a really cheap class D amp (like this one) which will have no output below 20 Hz and need a 12V power supply but cost you something like EU20 delivered, or this which looks a bit better presented and more powerful.

Hope this is useful!

Nick.
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Old 3rd January 2013, 09:49 PM   #6
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Nick, not messing around or anything, but did you read the first post?

The OP asks for a small subwoofer, to integrate with a pair of 3" satellites in a PC system.

There's also a 250 euro budget. The more expensive 8" driver is a sane option, but the rest of the ones you present are, I suspect (prepared to be argued with here), out of the question.

Nice find on the 2nd amplifier, though. Worth a look if the OP is prepared to have an external amp.

Chris
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Old 3rd January 2013, 11:05 PM   #7
DrNick is offline DrNick  United Kingdom
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Quote:
Originally Posted by chris661 View Post
Nick, not messing around or anything, but did you read the first post?

The OP asks for a small subwoofer, to integrate with a pair of 3" satellites in a PC system.
The sims in the figure I posted shows that the driver you suggested will need 27.9 litres and the one I suggested will need 31 litres of cabinet volume, to get the same Qtc. Not enough of a difference to be significant, I wouldn't have thought.

Quote:
Originally Posted by chris661 View Post
There's also a 250 euro budget. The more expensive 8" driver is a sane option, but the rest of the ones you present are, I suspect (prepared to be argued with here), out of the question.

Nice find on the 2nd amplifier, though. Worth a look if the OP is prepared to have an external amp.

Chris
Chris, sorry if I was not clear, I wasn't suggesting he should consider all of the ones I put in the graph, they are just there to make the point that the low end is very sensitive to driver size, and also to show that smaller drivers do not automatically work in smaller boxes. You should find out what volume suits a given driver unit. TheRSS265HF-4 is EU 161 at Strassacker: Lautsprecher - Boxen - Selbstbau, so could be within budget, if you go with a cheaper amp.

The class D amps are so small and cheap, I've been waiting for them to bring out more powerful chips for years. I've read a lot of reviews over the years, and of course there are some nice threads about modding them to improve them. Here's a guy running huge Klipsch horns off one, and he's modded it to get great bass out of a 20W per channel unit. There are also some cool headphone amps out there using these Tripath (now made by Cirrus Logic) chips. They use these chips in iPhones too, the technology is totally proven, it's just a questions of finding one at a good price, with a power supply and analogue circuit components that are up to spec and don't degrade the sound.

All the best,

Nick.
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Old 4th January 2013, 08:55 AM   #8
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Thanks for the replies and suggestions. I appreciate your support.

Meanwhile I did a lot of trawling and ended up with CSS SDX7 from spectrumaudio.de. Also they were friendly to offer a Monacor SAM-1 plate amp.
Parts just fitted my budget, freight cost was fair. My package will ship on Monday.

I'll start off with the top right design from Planet10. Suits best with my uFonkens designwise and is most compact spacewise. My decision has been to
use a design from a qualified source.

The remark on drawing says the designed volume of the box has been considering also the brace to support the driver and overall rigidity.
My question here is - should I increase the volume equal to the volume of the plate amp major parts? Seems safest to increase the height.

Found also an encouraging build from SDX-7 cabinet for the 2+1 system | Stereo Clarity
Seems proportionally only slightly different.

For material I'm going for either 19 or 22 mm MDF, depends on a parallel ongoing small furniture project.
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Old 4th January 2013, 11:07 AM   #9
DrNick is offline DrNick  United Kingdom
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Quote:
Originally Posted by crossride View Post
Thanks for the replies and suggestions. I appreciate your support.

Meanwhile I did a lot of trawling and ended up with CSS SDX7 from spectrumaudio.de. Also they were friendly to offer a Monacor SAM-1 plate amp.
Parts just fitted my budget, freight cost was fair. My package will ship on Monday.

I'll start off with the top right design from Planet10. Suits best with my uFonkens designwise and is most compact spacewise. My decision has been to
use a design from a qualified source.

The remark on drawing says the designed volume of the box has been considering also the brace to support the driver and overall rigidity.
My question here is - should I increase the volume equal to the volume of the plate amp major parts? Seems safest to increase the height.

Found also an encouraging build from SDX-7 cabinet for the 2+1 system | Stereo Clarity
Seems proportionally only slightly different.

For material I'm going for either 19 or 22 mm MDF, depends on a parallel ongoing small furniture project.
That driver does look pretty cool with the copper phase plug. The Planet 10 site is a great source, so I'm sure if you follow one of their designs the volume will work well for the driver. The volume should just be the air volume, so if the amp intrudes more in your build, you should compensate by adding volume. The exact dimensions should not be so important, as long as the total volume is right, so adding height should be fine. Please post some photos up to let us know how it goes!
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