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Old 23rd April 2006, 12:33 PM   #1
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Default A different sub approach, will it work?

My general impression of most subs I have heard is not favourable, boomy, lacking control, able to be identified as far as position goes, basically just not very musical.

Now I need to build a sub, cheaply for my daughter to go with a pair of speakers I have built for her, the details don't matter too much but lets just say these speakers are very detailed and convey every nuance in the music sent to them. So the sub has to be tight, fast so to speak and accurate. Ground shaking bass is irrelevant, it will never be used for home theatre. Above all it needs to be pretty cheap.

Now I am able to get hold of several good quality 6.5 inch woofers, they are 92db efficeint, handle about 60watts each and go to 40Hz in a 30 litre box. Oh and I can get them for just $20.00 each Aus.

In addition to the sub she wants a coffee table.

Here is my idea, the speakers go down to about 50hz before serious tapering so the cross-over could be about 60hz or so I guess.

I could use 4 drivers in a coffee table type box, double lined with sand in the cavity and have the woofers down firing, with the ports on top but emerging under the top of the table which can be a large concrete plate, painted to look like marble.

Amplification can be provided via a pair of gainclone modules (3886s) that I have, and I can get a sub processor/equalizer kit from altronics in OZ for I think around $40.00.

I guess by using the timber I have on hand and the clones it will cost a bit under $180.00 which is within the budget.

The coffee sub would be placed between the speakers but well out from the wall, so it will get no boost from any corner/wall proximity.

What I am wondering is can such a sub be likely to give inferior or superior performance to the taditional 12inch boomer in a box that typically cost around the $200.00 mark, will it actually go low enough, (I am assuming the combined effect of 4 drivers will take it usefully below the normal 40Hz of the individual drivers). Is there a drawback in the down-firing arrangement, basically it would look better in this application, but will it work properly, (The base of the table would be elevated about 6in off the ground on chrome legs).

Previous speakers I have built have had very very heavy boxs and the bass was tight (with 6.5 in drivers) but this is in a different realm I think!

If I could get down to say 25Hz that would be enough, so those really low notes are not going to be missed too much.

Does anyone know of any subs builtin this manner?

Thanks to everyone in advance.
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Old 23rd April 2006, 02:17 PM   #2
mazurek is offline mazurek  United States
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Look at
http://www.partsexpress.com/projects...man/index.html

and
http://www.htguide.com/forum/showthread.php4?t=19416

I would prefer something like this:
http://yellow.mynethost.com/~bv12636...a0ac2a048c1a6e
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Old 23rd April 2006, 02:54 PM   #3
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Not knowing what is available down under I cannot give you alternatives, but I think that mazurek is on the right track with larger driver(s).

Two major factors influence the ability to locate the sub. Crossover frequency/slope and distortion products. Downfiring into a carpet will help reduce the distortion products but trying to get 25 Hz out of most 6" drivers at any significant SPL will cause lots of distortion.

If the drivers model at 40 Hz, you're going to need lots of EQ. Hopefully that model is sealed, so you won't run out of excursion too quickly. You'll still be better off getting the largest driver with the greatest displacement that you can into the coffee table. Since you sound like you'd prefer sealed, do that and use a linkwitz transform to achieve the extension you desire with low group delay.

Another downside of EQ is that it will dramatically increase the power requirement. You'll quickly run out of steam with an LM3886, causing distortion (making it easier to locate the sub) If you need more than a few db, consider one of the fairly inexpensive plate amps or go Bridge-parallel with the 3886s.

With conventional sub placement (near the mains) I have not been able to localize my subs as long as the crossover is 80 Hz or below, 4th order. However, since your sub is going to be closer to the listener, I'd suggest as crossing to it low as you can squeak by with the mains - try 50 Hz.

I have some crossover (including Linkwitz transform) and power supply boards leftover from the group buy due to cancellations, but if the kit EQ meets your needs it will be less expensive.
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Old 23rd April 2006, 06:05 PM   #4
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its been said a million times, but hasnt been said once in the thread.

DRIVER SIZE HAS NOTHING TO DO WITH TRANSIENT RESPONSE FAST BASS OR TIGHTNESS!!!

most commercially deisgned subwofoers are designed for instant plug and play appeal, lots of boom, nto much real lows, and therefore TONNES of group delay and percieved sloppyness.

i would say, that a PROPERLY designed sealed 10" or 12" driver would reduce that 6.5" monstrosity to rubble in terms of sound quality and SPL

this is definately pushing the budget, but depending on how much you love your daughter, see if you can get a peerles 10" XLS

from what i recall they model well in small sealed boxes and i KNOW that they have VERY good sound quality for a 10" driver of its class. they are also readily available in austrailia.

but seriously, a music sub DOESNT need extension to 25hz, 35 should be adequate. id reccomend a sealed box for the lower group delay and shallow rolloff, which means that the low stuff is THERE its just not quite as prominent as it should be.

peerlees have many other good quality 10 and 12" sub drivers all of which are available almost worldwide.

about crossover point, see how loud your daughter lsitens to her stereo, and i mean the loudest, like if she has friends over or "its her favourite song!!!!", and see how youre doing excursion wise, if youre not comfortable with how much the drivers are moving, trust your intuition and play with crossovers.

as a 15 year old, i know the story, youre friends come over and the volume goes 3 fold, make sure she has adequate power on that sub(low end power runs out FAST) and make sure that the mains arent going to overexcurse themselves

have fun!
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Old 23rd April 2006, 08:56 PM   #5
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Sounds like you've heard or seen(Or heard) one too many spl car audio systems(And were not pleased)Which in truth have little or nothing to do with accurate low-frequency reproduction.That's just rubbish and spl bragging rights.But it seems you are associating big drivers and low frequencies below 50hz with it.When in actuality car audio is not intrested in low frequency just high spl at the frequencies that are just audible.Even music reproduction needs decent low frequency exension I would think.


xstephanx has a point about fast bass and tightness.And really it's fast midrange and tightness,bass is bass.Now boominess is different that's just one part of the subs frequecy being exaggerated.And I'd second his recommend about driver size for accurate bass a big woofer drives much easier then 4 small ones.A perfect driver would be like one 15" under that concrete slab or 2 10"s even.I'd think you would be hard pressed to get accurate bass below 65hz with 6.5" woofers no matter how many you used.Plus it would be mucher easier on your amps to drive a bigger more sensitive driver or drivers.
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Old 23rd April 2006, 09:23 PM   #6
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have you considered a folded horn?

P.S.

http://www.diyaudio.com/forums/showt...798#post899798

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Old 24th April 2006, 12:23 PM   #7
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Thanks for all the advice, it all makes good sense.

Although I think I will go down the 12inch route I still do wonder however if the 6.5s may work OK, mainly based on a few experiences I have had, some might like to comment on these.

First up, yes I have heard too many of those Car doof doof units.....utterly horrible.

I was given one by my brother with 2 12 inch bass drivers, someone gave it too him and he didn't need it, I think I can guess why. I tried it in my system and lets just say if it plays more than one note, Im not real sure which one it is. Sure its basic and I reckon I could probably make it better but really it didn't show much promise, lots of boom boom though!

Another thing I found was that a pair of speakers I built last year for my home theatre with 2 6 1/2 drivers in each box and really solid constuction actually produces about the best tightest most balanced bass I have heard, and thats the feeling of many many folk who have heard them, it wasn't I should add any reflection on my great or talented abilities as a speaker builder, rather just very good luck and putting into practice what I had gleaned from a few in the know.

And the third thing is that our previous home theatre system (panasonic) actually used a 6.5 sub/bass driver, probably more bass than sub, but it actually sounded very good bass wise, treble wasn't great however.

I also have built a makeshift line arrays and I noticed that in this formation bass was much improved despite the fact the individual drivers had resonant frequency of only 120hz, so I guess you can see where I was coming from.

So a few more Qs then.

I can get some cheapish 12 inch drivers that will be within budget, but I imagine they are not going to brilliant, are there mods that can be applied to drivers to improve performance, I have had considerable success with modded small full range drivers, PVA glue on cones, padding in the basket etc, do 12 inch drivers respond to these things as well.

I also wonder would a high efficiency driver be more likely to give good transient response, I have found this is certainly the case with full range drivers, however with full range drivers it tends to lead to more pronounced midrange/treble which needs dealing with. Are there any such trade-offs with 12 inch drivers.

The idea of the sealed enclosure sounds good, somehow it just seems right, but if I went sealed how much more power is usually required for similar results to a vented unit

Once again many thanks to all who posted.
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Old 24th April 2006, 01:13 PM   #8
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Do you have the Thiele-Small parameters for the drivers you are considering?

As for mods, the drivers will respond, but perhaps not as you expect. As xstephanx pointed out, the transient response of a subwoofer crossed over 4 order at 60 Hz. is nonexistent. You might be able to hear something from it up to 120 Hz, but after that you aren't going to get much (unless it is distortion products). The attack of a kick drum is actually reproduced mainly by the midrange driver.

A well designed ported subwoofer can be very satisfying. Trying to get too much extension out of it or squeeze it into too small a box is usually what causes the one note or loose bass issues.

You might be able to lower the resonant frequency by adding PVA or someting else to the cone, which will require you to measure the rest of the T-S parameters again. Added cone mass also will affect the driver's susceptibility to sag when mounted face down.

How much additional power for sealed is required depends on your driver and how low you are trying to make it go in what size box. For example my 8 cubic foot JBL2245H subs need 180W each at 15Hz to keep up with 5W at 60 Hz. This gets me 100+ dB to 15 Hz out of a 94 dB/2.83V driver. It's an 18" driver with 9 mm of xmax.

Download one of the Linkwitz Transform calculators to see what you can do with your driver. You should also model it in WinISD, to ensure that you can get the extension and SPL you desire without exceeding the driver's excursion or power handling capability.

With your line array you may have ended up in the nearfield - sort of the same way dinky computer speakers can seem to have decent extension with 2" drivers. The other possibilities are that you were hearing harmonics that you mistook for low fundamentals or that you happened to find a room mode that reduced your excitation requirements.

On factor not considered is room size. Smaller rooms get earlier room lift so sometimes a small driver can have quite good extension. In my bedroom a pair of RS150s sound quite good full range, as long as I don't want to get too loud.
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Old 24th April 2006, 01:52 PM   #9
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Thanks Bob

That is really helpful and goes a long way to explaining a few things I was wondering about.

I have looked a Elliot Sound Products site her in OZ and read about the linkwitz transform circuits etc, I can see this needs a lot more investigation on my part, and I'm sure its worth it too, I'd really like to get something that sounds good first up.

There are some drivers available in OZ under the response name from jaycar, they apparently rate very highly and ESP used one in the sub they built with the linkwitz tranform circuit. A couple of these drivers are going cheap on ebay this week, never used apparently.

It seems that driver choice is crucial where subs are concerned, bit different to tweeters and mids where you seem to get away with all sorts of things.
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Old 24th April 2006, 02:05 PM   #10
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I wouldn't go as far as saying you can just grab a mid and tweeter and go for it, but you generally look at the interplay of a sub's extension, xmax, power handling and excursion more often.

Tweeter excursion becomes a factor if you want high SPL and a low crossover. It takes a heck of a tweeter to be able to cross over at 1,000 Hz and still play over 100 dB cleanly.

That's also why the pro audio guys will often use 12" midranges.

Good luck winning those drivers on Ebay.
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