Questions and recommedations for my first DIY Subwoofer @ 20hz

[chris661]

On the other hand, I had some problems with the subwoofer. Im thinking that maybe 8omhs wasn't a very good idea. Maybe I should change it for a 4ohm because it needs very much power from the amplifier so you can feel it (kicking/punching).

Did you bridge your amplifier?

There's a claimed 700w available there, should be enough to get everything out of that woofer.

The amp should have full instructions on how to do this, but if you get stuck feel free to ask

Chris

 

[head_unit]

Did you bridge your amplifier?

There's a claimed 700w available there, should be enough to get everything out of that woofer.

The amp should have full instructions on how to do this, but if you get stuck feel free to ask

Chris

That won't make any difference, presuming the current connection is one 4 ohm coil per channel. Bridging the amp and connecting the coils in series for 8 ohms is basically the same. And bridging to 2 ohms would be a BAD idea-probably blow up the amplifier, and certainly deliver LESS power.

Very very very few amplifiers really deliver much more real power into low impedances. Under static conditions they might show more power, but it is not much. This amp's 350W vs. 240W is only 1.6 dB, and it is quite possible that at stressful frequency/phase angle combinations it will clip earlier at 4 ohms than 8 ohms.

And certainly, driving lower impedances eats more current from the wall. Efficiency goes down. Therefore heat increases drastically.

 

[head_unit]

...Im thinking that maybe 8omhs wasn't a very good idea. Maybe I should change it for a 4ohm because it needs very much power from the amplifier so you can feel it (kicking/punching).

Actually upon re-reading I am confused. How exactly do you have the sub connected to the amp?

If you have the amp bridged and the coils in series, that is the same as if you connect each coil to a separate amp channel.

Er, you do have both coils connected, right?

By the way, the Thiele-Small parameters are the same whether you drive the coils in parallel or series. Yeah, the impedance changes, but the ratio of mass to magnetic power stays the same.

And, don't get too hung up about the parameters. There are many methods to measure the parameters, and guess what? They all give DIFFERENT yet VALID results.

 

[ofesad]

First, sorry for the delay on replying your comments guys! I have been on bed sick.

Hi ofesad,

Sounds like you build a nice subwoofer, you shouldn't be able to locate it.

Have you tried the method of placing the subwoofer in you normal listening position, and moving (crawling) around the room until you find the point where it sounds best, then placing the subwoofer there, and listening in your normal listening position?

Regards,

Well... honestly, I have not tried that method because the subwoofer+box weights over 70 kilos.
I tried moving it in angle; so far the new position is working. Still it could sound better.

I would bet $1000 that changing to 4 ohms would gain you at most 1 decibel more volume on peaks. Or maybe LESS peak volume. The amp you have looks like it would run much hotter at 4 ohms too.

It's not clear to me why you are unhappy with the sub-just volume? Car subs generally have a high moving mass, to get a low resonance in small boxes. This means they are power hungry!

So your amp is fine, way more power than commercial subwoofers.

I wonder though if you have some cancellation going on. What happens if you switch the polarity (phase)? What are your crossover settings? How about time delays? Actually, you should play a mono source and play 2 channels only at a time to be sure all the polarities are correct: L vs R, L vs C, R vs C, Lfront vs Lrear etc etc. Google "polarity test track"

And forgive if I missed it, but if you are running the sub as LFE you are missing a lot of the bass-are your main speakers set to "small"?

Crossover settings: None. Using LFE from the RVX673 directly to the power amp.
Polarity is 100% correct. I doubled and triple check'd.
The speakers (FL and FR) are set to LARGE, I will see how does it sound if I set'em to SMALL.

Thanks!

Did you bridge your amplifier?

There's a claimed 700w available there, should be enough to get everything out of that woofer.

The amp should have full instructions on how to do this, but if you get stuck feel free to ask

Chris

The amplifier has an extra output for BRIDGE mode, I could try it, but the idea is that in the near future to have 2 subwoofers powered by the power amp
Sadly the power amp has no instructions what so ever, I buy it used.
I email'd the "official" distributor and they never send me a PDF or something.

That won't make any difference, presuming the current connection is one 4 ohm coil per channel. Bridging the amp and connecting the coils in series for 8 ohms is basically the same. And bridging to 2 ohms would be a BAD idea-probably blow up the amplifier, and certainly deliver LESS power.

Very very very few amplifiers really deliver much more real power into low impedances. Under static conditions they might show more power, but it is not much. This amp's 350W vs. 240W is only 1.6 dB, and it is quite possible that at stressful frequency/phase angle combinations it will clip earlier at 4 ohms than 8 ohms.

And certainly, driving lower impedances eats more current from the wall. Efficiency goes down. Therefore heat increases drastically.

That's interasting! I know that I could run more power with a lower impedance, but I didn't think that the difference could be small.
So it will be better to stay with a 8ohm sub than a 4ohm. Got it!

Actually upon re-reading I am confused. How exactly do you have the sub connected to the amp?

If you have the amp bridged and the coils in series, that is the same as if you connect each coil to a separate amp channel.

Er, you do have both coils connected, right?

By the way, the Thiele-Small parameters are the same whether you drive the coils in parallel or series. Yeah, the impedance changes, but the ratio of mass to magnetic power stays the same.

And, don't get too hung up about the parameters. There are many methods to measure the parameters, and guess what? They all give DIFFERENT yet VALID results.

Let me put it more easy:
[RVX673] LFE--- RCA Cable + Audio Plug Adapter--->[PAX700 Power AMP] Channel A---Speakon--->Subwoofer.
The Sub coils are wired in series to get 8omhs, of course.
Also tested and checked that the impedance it's around 8 with a Tester.


Now Im a little concerned about the cable/connection. Im using a SpeakOn connector (+1 and -1) from the power amp to the subwoofer....
Could the problem be thatt Im not using the +2 and -2? As I said earlier, I dont have the Power Amp manual to check
Sorry if the question sound stupid, It was my first time dealing with speakon connectors.


Thanks all of you who commented!

 

[head_unit]

I tried moving it in angle; so far the new position is working. Still it could sound better.

The classic way to find a good subwoofer position is to put the subwoofer where your head would listen, and put your head at possible subwoofer positions. By the principle of reciprocity, the sound should be equivalent (or pretty much).
Since your sub is so huge, maybe you could borrow another sub for this purpose.
The main thing is, each position gives the subwoofer a different acoustic loading, different interaction with room resonance modes, and different interaction and phasing to the main speakers. So where the subwoofer sits can make a big difference. I've moved a sub several inches and notices a difference-not a big difference, but noticeable. Probably an artifact of upper bass blending with the satellites, or reflection, or ????

Crossover settings: None. Using LFE from the RVX673 directly to the power amp.
Polarity is 100% correct. I doubled and triple check'd.
The speakers (FL and FR) are set to LARGE, I will see how does it sound if I set'em to SMALL.

NOOOOOOOOOOO!!!!!!!!!!!!!!!!

This means your bass is not actually going to your subwoofer at all. You are only getting bass which was mixed into the Low Frequency Effects channel, a kind of extra channel which may not always be used. Your "real" bass is being sent to your main speakers, instead of to your subwoofer. Yeah, you need to be at SMALL.

I'll leave it to others to look at your Yamaha manual and comment how you should set the crossovers there and on your sub amp.

The amplifier has an extra output for BRIDGE mode, I could try it, but the idea is that in the near future to have 2 subwoofers powered by the power amp
Let me put it more easy:
[RVX673] LFE--- RCA Cable + Audio Plug Adapter--->[PAX700 Power AMP] Channel A---Speakon--->Subwoofer.
The Sub coils are wired in series to get 8omhs, of course.
Also tested and checked that the impedance it's around 8 with a Tester.
Now Im a little concerned about the cable/connection. Im using a SpeakOn connector (+1 and -1) from the power amp to the subwoofer....
Could the problem be thatt Im not using the +2 and -2? As I said earlier, I dont have the Power Amp manual to check
Sorry if the question sound stupid, It was my first time dealing with speakon connectors.
Thanks all of you who commented!

Right now it appears your 8 ohm sub is connected to only one channel of the power amp, putting out supposedly 240 watts. If you move the Speakon connector to BRIDGE, both channels are hooked in series across the speaker. The bridged connection is rather like each channel seeing 4 ohms from the 8 ohm sub, and the speaker would get supposedly 2x350 = 700 watts. When you make another 8 ohm sub, connect each to A and to B. Now each will get 240 watts, =480W total. In real dynamic music from an inexpensive amp, you'll actually have as much power as the "700W" bridging your 8 ohm speaker. Plus you will gain 6 dB from the 2 subs loading each other, for more total output.

 

[ßart West-VL.]

My receiver puts out bass to the sub an both channels when in stereo.
L + R + SW
When I watch a DVD, it switches to:
L + R + LFE
very different and only when LFE is on, the L and R are at small.
Otherwise it's full range.

The classic way to find a good subwoofer position is to put the subwoofer where your head would listen, and put your head at possible subwoofer positions. By the principle of reciprocity, the sound should be equivalent (or pretty much).
Since your sub is so huge, maybe you could borrow another sub for this purpose.
The main thing is, each position gives the subwoofer a different acoustic loading, different interaction with room resonance modes, and different interaction and phasing to the main speakers. So where the subwoofer sits can make a big difference. I've moved a sub several inches and notices a difference-not a big difference, but noticeable. Probably an artifact of upper bass blending with the satellites, or reflection, or ????





NOOOOOOOOOOO!!!!!!!!!!!!!!!!

This means your bass is not actually going to your subwoofer at all. You are only getting bass which was mixed into the Low Frequency Effects channel, a kind of extra channel which may not always be used. Your "real" bass is being sent to your main speakers, instead of to your subwoofer. Yeah, you need to be at SMALL.

I'll leave it to others to look at your Yamaha manual and comment how you should set the crossovers there and on your sub amp.




Right now it appears your 8 ohm sub is connected to only one channel of the power amp, putting out supposedly 240 watts. If you move the Speakon connector to BRIDGE, both channels are hooked in series across the speaker. The bridged connection is rather like each channel seeing 4 ohms from the 8 ohm sub, and the speaker would get supposedly 2x350 = 700 watts. When you make another 8 ohm sub, connect each to A and to B. Now each will get 240 watts, =480W total. In real dynamic music from an inexpensive amp, you'll actually have as much power as the "700W" bridging your 8 ohm speaker. Plus you will gain 6 dB from the 2 subs loading each other, for more total output.