DIY Home theater sub project help (1 Viewer)

[VanillaRice]

After much hesistation back and forth, I've finally gone ahead and purchased a 2nd hand Behringer ep 2500 to run an 18" sub.

I live in New Zealand and my original plan was to buy a stereo integrity 18" sub and import it with their resonable shipping costs. But just this morning I came accross a blaupunkt VPW-460 18" sub for sale and I snapped it up for a good price. Now I'm trying to understand if this sub will be comparable to the SI 18". The first thing I noticed is that the Blaupunkt's power handling is much higher, some 1800w rms. I figure the ep2500 should drive this nicely bridged at 4ohms.

But when I look through the specs they are quite varied so can someone please shed some light on the sound characteristics of these speakers ? At a guess I'd say the Blaupunkt will have more punch but not reach as low ? I'm yet to fully understand what all the listed specs mean. My intended sound from this speaker is for low rumbling bass for explisions etc for movies. So I want it to play as low as possible. Punchy bass not a priority.

Blaupunkt VPW-460 18" - all I could come up with for this sub

Nominal power handling capacity 1800 wattsSensitivity 94 dB (2.83V/1m)Frequency response Hz 20 - 200 HzImpedance 2 x 2 OhmCone material Carbon/fibreglass

Thiele/Small parametersFres 37 HzQts 0.6Qes 0.71Qms 3.8Vas 36.7 lXmax + / - 15.0Enclosure recommendationBass reflex 60 litresTunnel Ø 2x 10 cmTunnel length 2x 80 cm

----------------------------------------------------------
Si 18" sub

18" D2Re: 3.5 OhmsFs: 17 HzQes: 0.41Qms: 5.8Qts: 0.38Le: 3.2 mHSd: 117841 mm^2Vas: 411.9 lBL: 19.7Mms: 416 gCms: 208.8Sensitivity (1W/1m): 88.7 dBXmax: 22.5mmRecommended enclosures: 18"Sealed = 4 ft^3Ported = 5-6 ft^3 tuned to 20 HzCutout: 16.7"OD: 18.5"Mounting depth: 9.5"Mounting flange to top of surround: 1.5"Displacement: 0.25 ft^3

 

[schan1269]

Message Robert_J directly. He's the resident guy here.

But...

Sealed is the way to go. Providing a port means the sub is "dead" below the port...unless you EQ it(which if you EQ it to make up for the port...why have one? However you could design a Transmission Line...that is a different animal)

Don't know if you'll get any good info here or not (can you even see the forum?)
http://ibsubwoofers.proboards.com/

Another...if you are allowed to see it...
http://www.diysubwoofers.org/

 

[schan1269]

According to the DIY subwoofer...the Blaupunkdt you bought lies outside what is recommended for Transmission Line, where the other one fits.

But...an 18" Transmission Line is HHHUUUUUGGGGGEEEEE anyway.

 

[schan1269]

Your 18" Trans Line would be bigger than this thing...

http://www.teresaudio.com/haven/subs/subs.html

 

[VanillaRice]

Interesting schan1269 but a Trans Line is to tall / crazy for what I was thinking hehe. I'd prefer a more conventional design. I know to satisfy the lower frequencies a ported enclosure is usually recommended. But if it means the enclosure is a little smaller than I can always go for sealed as long as my lower frequencies aren't sacrificed too much.

 

[schan1269]

Sealed plays lower(deeper) than ported.

Hence my comment..."dead below the port".

 

[VanillaRice]

ok if I can save space and go deeper at the same time.. then sealed it is oh and robertj has helped me in the past.. hope he can chime in at some stage

edit.. Are sealed enclosures usually smaller than ported ? Reading the manual of this sub tells me the opposite is true

 

[VanillaRice]

Found this online, a bit more info

 

[VanillaRice]

Ok the Sub is in my living room now. But does anyone know how to set the low pass filter on these sony a/v receivers ? The model is an strdn1020. I can hear the lower octaves of peoples voices when I'm watching movies. Will I need to install a crossover between the sony receiver and my behringer ep2500 ? I can't find any LPF settings on this thing. I've set my front speaker size to small by the way.

 

[Robert_J]

Mentioned twice in 1 thread.

Comparing the Theile/Small parameters of the two subs. The Blau has a Qts of .6 while the SI has a .38. The higher the Qts, the steeper the roll-off down low. Supposedly, a Qtc (that's the roll-off measure when the sub is in a box) of .707 is perfect. But the Qtc always goes up when a sub is put in a box. It can never be lower than the Qts of the driver. I like a final Qtc around .5 so I get subs with a low Qts.

The resonant frequency (Fs) is a full octave lower on the SI sub. 37hz vs 17hz. The SI will play the low notes easier.

The xmax (maximum linear travel) is 50% higher on the SI sub. Bass is about moving air and the SI sub will move more air.

So is the SI sub a Ferrari and the Blau a Yugo? (If you aren't old enough to know about the Yugo cars, Google it) No. It's more like a Ferrari compared to a Corvette ZR1. They are both high performance subs but the SI will edge out the Blau in most (not all) cases.

Build a sealed box as large as you can build.

 

[Robert_J]

The first thing I noticed is that the Blaupunkt's power handling is much higher, some 1800w rms. I figure the ep2500 should drive this nicely bridged at 4ohms.

Power handling is the most misunderstood parameter in the audio world. That 1800w could be at 1,000hz. Basically, they run power through the sub until some parts fails from thermal overload. Basically, the glue melts off the voice coil and it unwinds.

In the world of home theater subs, most of the time we hit xmax (max linear excursion) long before we hit the thermal limits of a sub. Push a sub past xmax and bad things happen. It could be as simple as distortion assuming xmax is less than xlim (max physical movement of the cone). Push it to xlim and tinsel leads snap, spiders tear and worst of all - the voice coil slams into the back plate of the magnet. When that happens enough, it is like someone stomping an aluminum can. The coil deforms and touches the magnet. You get a scraping noise. If the coil wire rubs, then the laquer insulation will wear through and there will be a short. You may lose the sub and you may lose your amp.

In the video below, you can hear the clank clank of the coil tapping the back of the motor (magnet). It wasn't hard so no harm done. Not my video but that was a sub I built from spare parts.

 

[Robert_J]

Providing a port means the sub is "dead" below the port...unless you EQ it(which if you EQ it to make up for the port...why have one?

One of the rare times you have ever given incorrect information. You should never feed any signal to the sub that is below the box's tuning frequency. If your ported box is tuned to 22hz, then a subsonic filter should be set at approximately 20hz. I always go 2 to 3 hz below tuning. Below tuning, there is no spring support from the air in the box. It's as if the sub is playing free air (see vid above) and it only takes a percentage of the power to push it to its physical limits. EQing below the tuning frequnecy isn't advised.

The EP line of amps has a built in subsonic filter but it is designed for pro audio use and 100% useless in the home environment. Make sure it is bypassed. Sealed is the only way to go with an EP amp. The iNuke DSP amps have an SSF at 20hz and it can be tweaked to 17hz. Those amps work well with both ported and sealed designs.

 

[schan1269]

I knew about the lack of spring support...forgot that you have to have a SSF.I haven't had a chance to look up the Sony owners manual.But in speaker setup should be the crossover. Have absolutely no idea how you would ever hear voices from anything out of the .1 on any AVR. Even if set up absolutely wrong.The most wrong crossover is 200hz.

 

[VanillaRice]

Thanks Robert and schan for your input.

Wow had an interesting day today testing out my setup. I have many topics to cover.

First off, I had a different amp to try my sub with. Now this is funny, my dad was kind enough to loan me his old Sansui class A amplifier from 1978! Its only 100w per channel but it has a nice EQ setup which is fully adjustable. I decided to try my 18" sub with this and to be honest it actually sounded really good and doesn't get hot. I'm actually having second thoughts about even needing my ep2500. It's true that power ratings are a misunderstood parameter of audio systems. Do I run the risk of damaging the amplifier with this sub considering the power ratings are so different? If temperature is anything to go by I'm guessing not.

Robert regarding your advice to choose an enclosure which is as large as possible, my enclosure is 8.8cu ft (outside dimentions) the guy threw it in for free with the sub and it sure saved buildling one myself. So if I'm not mistaken my ported enclosure means I get slightly more SPL but wont reach as low as a sealed enclosure correct ?

Here are some pics of the sub, enclosure and amp I have just aquired.

 

[Type A]

This is a killer little project Tim, thanks for sharing.

 

[VanillaRice]

No problem type A. I'm considering purchasing a decibel meter to graph frequency response. What I'd like to see is how these two amplifiers compare when driving my 18" sub. For the ep2500, the Sansui will be used as a pre-amp so EQ settings will remain the same.

 

[Robert_J]

my dad was kind enough to loan me his old Sansui class A amplifier from 1978! Its only 100w per channel but it has a nice EQ setup which is fully adjustable.

If it is only a graphic EQ, then it is not fully adjustable. The Q portion (width of the filter) is standard and filters are centered on a frequency. A parametric EQ allows you to change both the frequenc and width of the filter.

I'm actually having second thoughts about even needing my ep2500. It's true that power ratings are a misunderstood parameter of audio systems.

An EP2500 will push 800w RMS per channel into 2 ohms before clipping. I've never heard of anyone saying they had too much power. Having headroom lowers distortion. Would you rather drive a 4 cylinder sedan at 120mph all day long or a Ferrari? A little 4 banger is working at near it's max and will soon give up. A super sports car is working at 50 to 60% power and in no danger of reaching its limits.

Robert regarding your advice to choose an enclosure which is as large as possible, my enclosure is 8.8cu ft (outside dimentions) the guy threw it in for free with the sub and it sure saved buildling one myself. So if I'm not mistaken my ported enclosure means I get slightly more SPL but wont reach as low as a sealed enclosure correct ?

It depends on what your enclosure is tuned to. You really need to determine that. What is the thickness of the wood? What are the port dimensions? Height, width and depth.

 

[VanillaRice]

If it is only a graphic EQ, then it is not fully adjustable. The Q portion (width of the filter) is standard and filters are centered on a frequency. A parametric EQ allows you to change both the frequenc and width of the filter.

An EP2500 will push 800w RMS per channel into 2 ohms before clipping. I've never heard of anyone saying they had too much power. Having headroom lowers distortion. Would you rather drive a 4 cylinder sedan at 120mph all day long or a Ferrari? A little 4 banger is working at near it's max and will soon give up. A super sports car is working at 50 to 60% power and in no danger of reaching its limits.

It depends on what your enclosure is tuned to. You really need to determine that. What is the thickness of the wood? What are the port dimensions? Height, width and depth.

You raise some interesting points Robert. I suppose it is only a graphic EQ after all. I will consider a parametic EQ when funding allows.

At present my ep2500 is sitting in my cabinet disconnected because running the sub off this little amplifier seems to be doing the job. I'm confused as to why the amp doesn't get very hot, much less heat than the ep2500. I don't believe I've heard it distort yet either. I suppose I am not turning it up high enough Even though I'm shaking panels in my house, I look at the driver and its barely moving.. it's great ! In the mean time I can re-connect my ep2500 if you think I am stressing my little amp too much. I will continue to use the Sansui as a pre amp as I have no other way to EQ it.

The enclosure is 95cm x 60cm x 44cm and the MDF is approx 15mm thick. I will measure the port dimensions when I am home from work. There is no internal bracing, basically a big open space inside but feels structurally solid and has no polyfill etc.

 

[VanillaRice]

Here are the dimensions of my enclosure. The MDF is actually 20mm thick, not 15mm. Can you approximate what the enclosure is tuned to given these dimensions ?

 

[Robert_J]

Based on your dimensions, I calcualted that your enclosure is tuned to 41.5 hz. Give or take 1/10hz.

That is way, way, way too high unless you are listening to 80's rock (they didn't record any bass in it). For that sub, you need to tune 25hz or lower.