First Sub - Small and Cheap

[LightwaveDude]

Just wondering what everybody's thoughts are on these components:

Dayton SD270-88 10" Driver

Dayton SA25 25W Plate Amp

As soon as I save up a little more money I'm hoping to build one of these things (that is if my parents will allow me. They think my audio hobby is a waste of money )

I know that extreme SPL isn't really an option, but I'm not looking for hight output levels (though it's always a nice wow factor to impress thefriends )

I'm more interested in knowing how the quality is in on these components. If things go through, I'd like to build a 2.938 cu. ft ported enclosure for an f3 point of around 28 hz. This sounds very good to me since I'll mainly be using it for music in my room along with my stereo system.

Excursion should be good down to 20 hz with 25 watts of power, extension is good enough for music, and supposedly it will reach 102 db at full power (though I usually listen to music rather quietly, nobody else seems to appreciate it and I like my hearing).

The only thing that concerns me is the group delay. Down to 50 hz it's a slow climb up to 5.4 ms but from there it rises rather sharply to it's peak at 24 hz at 20.27 ms of delay.

What is an acceptable level of delay. I know lower is better, but just how high is acceptable for most music listening?

I've had a pair of borrowed TSW306C subs in a bandpass enclosure for a while and even though they pump out bass.... I just can't stand to listen to it becuase it sounds very sloppy and it sounds like it rings. Is this a problem with the subs? the fact that it's a bandpass box? or is that just a problem with cheap subs? My main goal is to avoid the way that they sound and instead create good quality subs for music for cheap.

I plan on building a 36.5 in tall x 14.5 in wide x 13 in deep box made of .75 in MDF. I haven't factored in bracing or stuffing yet since I'm not sure how much to use or how much of an effect it will have on the design. The size is pretty much set. The depth can vary a little since I'm designing these to go behind my S-G300B-K speakers next to my computer desk.

For the time being... I'm planning on only having one, but I'd like to make one for each channel side.

So, to sum everything up...

What do you think of the components? Is the driver good quality/low in distortion? Is the plate amp good for the full 25 watts of power and is it a clean source?

Is the group delay acceptable? What is generally and acceptable level for different bass frequencies?

How much of an improvement would having a second sub be besides adding more output?

 

[Volenti]

Re; group delay, as a rule of thumb, the lower you go the more GD you can get away with , 20ms at 24hz is fine, most music doesn't go that low anyway and the stuff that does is usually semi constant tones that aren't that critical timing wise.

regarding your experience with the bandpass box, it was probably just a shitty design, a box with low GD but with a peaky response can still sound sloppy and boomy, BP boxes have little use in the home IMHO and are better left for car use (which suits that style well)

I'd look at a bit more powerfull amp, say 80-100w, but that's just personal preference.

 

[LightwaveDude]

OK... I'm glad to hear that the delay is acceptable.

I just modeled the box so that the Dayton 70W amplifier would also work in the enclosure if I ever wanted to upgrade; all I had to do was decrease the size of the enclosure to 2.675 cu. ft to ensure I wouldn't exceed Xmax. I think I'll just save and spend the extra $13 if for nothing more than the extra headroom. I don't know if I'd spring for the larger amp seeing as how this is my first ever DIY project I've actually had a chance of accomplishing. I'd rather keep the cost of the this sub very low and save my money for a larger sub with more power and a more capable and higher quality driver.

Thanks for the advice.

Does anybody know how the DVC 10" sounds? I know that the charactoristics of the driver can make a sub perform a lot differently than what it is modeled to do.

Thanks for any more help in advance.

 

[ScottG]

For low a low cost driver my choice would be the Apex Jr. 8 inch sub at 40 bucks.

http://www.apexjr.com/speakerstuff.html

http://www.apexjr.com/SuperSub.htm

(Thorsten has commented favorably on these drivers - and he knows good sound.)

For a low cost plate amp check E-bay..

ex.:

http://cgi.ebay.com/KLIPSCH-KSW10-s...ryZ67786QQrdZ1QQcmdZViewItem#ebayphotohosting

http://cgi.ebay.com/NEW-CERWIN-150-...5852109387QQcategoryZ3280QQrdZ1QQcmdZViewItem

 

[LightwaveDude]

Well, I went looking around e-bay for more amplifier options, and I came across a Nikko Alpha 230 EXC Power amplifier. I'm just curious to know if anybody has info on the amp. Is it worth buying? It's listed at $24.95 at the moment. It's supposed to put out 120W/ch at 8 ohms and 130w/ch at 4 ohms. The very limited info on the net I could find about it said that it runs hot. Would running the amp at 4 ohms pose a problem with the heat generated?

Would it be suitable to use as a sub amp? I can output the subwoofer pre-out from my VSX-515 to the amp if I were to buy it. Would that crossover be sufficient?

Also... even though the price of the Apex Junior looks tempting... It just doesn't seem to have the output or extension that I'm looking for. I have a pair of S-G300B-K Pioneer mains with 12" woofers that output down to 50 hz. A sub with an fs in the upper 40 htz range just doesn't seem like it would do it. I'm not looking for anything amazing... but I think I'm still leaning toward the 10" driver.

 

[ScottG]

Well, I went looking around e-bay for more amplifier options, and I came across a Nikko Alpha 230 EXC Power amplifier. I'm just curious to know if anybody has info on the amp. Is it worth buying? It's listed at $24.95 at the moment. It's supposed to put out 120W/ch at 8 ohms and 130w/ch at 4 ohms. The very limited info on the net I could find about it said that it runs hot. Would running the amp at 4 ohms pose a problem with the heat generated?

Would it be suitable to use as a sub amp? I can output the subwoofer pre-out from my VSX-515 to the amp if I were to buy it. Would that crossover be sufficient?

Also... even though the price of the Apex Junior looks tempting... It just doesn't seem to have the output or extension that I'm looking for. I have a pair of S-G300B-K Pioneer mains with 12" woofers that output down to 50 hz. A sub with an fs in the upper 40 htz range just doesn't seem like it would do it. I'm not looking for anything amazing... but I think I'm still leaning toward the 10" driver.

You need to try modeling the driver - just going by driver fs is pointless. (its really a shame that none of the cheap drivers have THD vs freq..) there are plenty of free modeling programs for this (try googling the FRD consortium). I typically use BoxPlot for quick enclosure modeling. Of course your original suggestion may appear to perform better (when modeled) - it doesn't mean though that it will sound better. Then again it may sound better as well. (..yup, DIY is something of a "hit-and-miss" affair.)

You'll PROBABLY need a low pass crossover and a VARIABLE one at that. Additionally, you would be better of with a least a phase switch (but it would be better to have a variable phase adjustment - prob. to expensive though). You'll definitly need a VARIABLE gain adjustment. IF you have all this taken care of from other sources then a basic amplifer would be fine, otherwise stick to the subwoofer plate amplifer group.

I just did a quick boxplot model (bass reflex aka ported) with the Apex Jr. 8 inch and the following box parameters: Alpha .3, H .4, Ql .7 with a coresponding internal volume (not including stuffing gains or bracing losses) of 1.27 cubic feet which gives -7 db point at around 18 Hz with power handeling at 18 Hz up to around 100 db (without factoring room gain). This -7db point also coresponds fairly well with room gain so that the average in-room response should be close to flat at 18 Hz without eq. (depending on the size of the room). All this from a driver that has a reputation for sounding good. Provided you can live with the size of the enclosure (which isn't that big), I'd say at this price its a "no-brainer".

 

[LightwaveDude]

Sorry if I made it sound like I hadn't modeled it and I just guessed... I do have WinISD which I use to model. I'll clearify myself now: When I saw the 47 htz Fs... I just seemed like a long way to push I driver down to low 20 htz region. I've read that pushing a driver below resonant frequency quickly increases distortion. Does this only apply to a box tuning? If so, the Apex Junior does look like a good deal.

 

[LightwaveDude]

OK, Doing my best here to follow your example, however, the best response I can get for -3 db is around 3 htz.... 18 hz, the way I've modeled it at least, is down almost 20 db...

I assume that Ql is the parameter in WinISD that defaults to 7.00. However, you have put a value of .7. How do you determine the Ql (Q? I think it's the dampening, correct?) of the box? How do I change the value when building the box? I don't think I can just say it's a Ql of 10, and it is like it allows me to. Anybody want to explain this to me?

Next. What are the Alpha and H values? I don't see anything that corrosponds to that in WinISD (as far as I can tell)

Lastly... just how much (on average... I know it's only an estimate...) does room gain boost lower frequencies? I have a small room (13 ft x 9 ft x 7 ft) since I know that comes to play in there somehow (something about quarterlengths?)

I'm very interested to know how you could push the driver down to 18 hz.... If I've been missing something critical here all this time maybe I would have been able to pick out a lot of other drivers I've dismissed becuase I couldn't get them to model low enough.

 

[ScottG]

OK, Doing my best here to follow your example, however, the best response I can get for -3 db is around 3 htz.... 18 hz, the way I've modeled it at least, is down almost 20 db...

I assume that Ql is the parameter in WinISD that defaults to 7.00. However, you have put a value of .7. How do you determine the Ql (Q? I think it's the dampening, correct?) of the box? How do I change the value when building the box? I don't think I can just say it's a Ql of 10, and it is like it allows me to. Anybody want to explain this to me?

Next. What are the Alpha and H values? I don't see anything that corrosponds to that in WinISD (as far as I can tell)

Lastly... just how much (on average... I know it's only an estimate...) does room gain boost lower frequencies? I have a small room (13 ft x 9 ft x 7 ft) since I know that comes to play in there somehow (something about quarterlengths?)

I'm very interested to know how you could push the driver down to 18 hz.... If I've been missing something critical here all this time maybe I would have been able to pick out a lot of other drivers I've dismissed becuase I couldn't get them to model low enough.

Alpha=Vas/Vb (Vb is box volume)
H=fs/fsb (fs is driver resonance and fsb is port resonance)
Ql=air leakage (7 is standardized, sorry about that it was supposed to be 7 not .7)

Its the port that is effectively "pushing" the driver so low - this is not an "aligned" port (meaning the port's bandpass does not create a flat response when combined with driver's output, rather it trades a flat response for extension - though at a lower spl).

http://www.musicanddesign.com/roomgain.html

the Martin Colloms room gain curve(s):

http://www.speakerbuilding.com/content/1020/rge.gif

baffle loading (non IB) effects on room gain (..or the effect of not having baffle loss compensation):

http://www.speakerbuilding.com/content/1020/rge-bafl.gif

 

[Volenti]

I'll clearify myself now: When I saw the 47 htz Fs... I just seemed like a long way to push I driver down to low 20 htz region. I've read that pushing a driver below resonant frequency quickly increases distortion. Does this only apply to a box tuning?

It depends greatly on box tuning and the type of enclosure it's self, for example; I'm currently using a cheap 12'' sub in a TL (transmission line) for the bass in my computer room, it's free air Fs is 42hz, in the TL it's almost half that (23hz) and due to the small size of the room I actually get a rising response down to ~18hz from room gain.

 

[ScottG]

Sorry if I made it sound like I hadn't modeled it and I just guessed... I do have WinISD which I use to model. I'll clearify myself now: When I saw the 47 htz Fs... I just seemed like a long way to push I driver down to low 20 htz region. I've read that pushing a driver below resonant frequency quickly increases distortion. Does this only apply to a box tuning? If so, the Apex Junior does look like a good deal.

Pushing a driver below fs is simply a generality. "Pushing" generally means that the driver is required to greatly increase its excursion below fs - therefor increasing distortion. This however presumes that you are in fact causing an increase in excursion. A bass reflex design however "effectivly" DECREASES driver excursion within the port's bandpass (which is below the driver's fs in-box). (..or said differently the port causes an increase in spl below the driver's in-box fs.)

Most drivers become increasingly non-linear near their fs - though that often depends on the amount of excursion. HOWEVER, below their fs they often start becoming more linear again (effectivly when impeadance starts "droping" back to a normal low level - say "around" 8 ohms for an 8 ohm driver). With the Apex Jr. we have a driver (as modeled in the box I suggested), that is normally non-linear 60-90 Hz (its in-box fs - i.e. the box is pushing the impeadance "bump" of fs up in freq.), while being more linear below 50 Hz to our vent tunning around 22 Hz (where between 18 Hz and 22 Hz its again non-linear). Exactly how linear or non-linear the driver is for a given freq. is anyones guessing game (unless they have used it similarly and measured it) - but again, the driver has a good rep. so that at least tells you something.

At 40 bucks - *I* think its a good deal at this price point IF used properly (i.e. with a design similar to what I proposed). In truth though I really don't know. All I can tell you is what I've modeled and that others who are both knowlegable and trustworthy have favorably commented upon the driver.