First REW graphs - Advice pls

[Ninj]

Hi guys,

Posted the first of the graphs over on AVForums, but pointed to the REW forum here for more advice.

The blue line is the in phase graph, the green is 180 phase. I was reasonably happy with the in phase but needed to sort the dip at 62Hz and the peak at 45Hz.

In an attempt to move the 62Hz dip, I tried inverting the phase which has introduced a more unstable curve, but its moved the deep dip nearer to the 80Hz crossover. The 45Hz peak is stil there, but I think that is a room issue??

I have a BFD sitting here awaiting cables so Im sure I can help iron out those problems, but any advice or suggestions most appreciated.

Thanks in advance

Richie

[Otto]

Hi Richie,

What's your crossover point? 60Hz? Are these measurements with the mains on? If so, take measurements again with them off and let's see how that looks.

Both curves look a little rough. Can you play with sub placement and delays? Where's the sub located now?

You should be able to get it looking better than it is now -- one way or another!

[brucek]

You're not getting a lot of extension below 40Hz. What type of subwoofer are you using? Are you using a Radio Shack meter with the calibration file in REW?

You can also use speaker time delay settings to modify the phase between the sub and mains in a smaller increment than would be achieved with a 0deg vs. 180deg change of the phase switch.

brucek

otto...quickest draw in the west.. beat me

[Ninj]

Hi guys, thanks for the replies.

Yep, using the new cal file for the RS 4050 SPL. The sub is pretty new so could explain why its not going down too low yet. Only has about 20 hours on it tops.

The sub is in a corner (out from the corner by about 4"), although it has a couch on one side. Im kinda stuck with that rough placement for now.
i have the amp crossover set to 80Hz at the moment, although I have adjustment between 40 and 200 Hz. Is it worth moving the crossover?
The sub has a frequency adjustment on it between 0 and 200Hz and although it shipped set to 200, Im not entirely sure what effect it is having. The sub is a Mordaunt Short 309i.

Those graphs are with mains on, Ill try another if I can see how to isolate the mains and just use the sub, if not Ill just unplug them.

Thanks again

Richie

[Ninj]

Ok guys this is the sub only. Green = 180, red = in phase.

Youll see theyre virtually identical. Surely something is wrong there? I would have expected them to be completely different??

I think my next step is to adjust the sub distance in the amp menu to try and move the 69Hz dip up nearer to the crossover?
Thanks

Rich

[Otto]

Hi guys,

I think 80 Hz is OK for now. Be sure the one on the sub itself is set to its max (200 Hz). Setting it to its max will effectively remove that crossover from sub's signal path. You're letting the receiver do the bass management, which is most likely the way to go.

Unfortunately, I doubt you will gain much more low-end extension just by allowing a break in period. If possible, I might move it a little more out of the corner. 4" might be a little tight. I know how it is with placement sometimes, though, so if you can't it's OK.

[Otto]

Ninj wrote:

Ok guys this is the sub only. Green = 180, red = in phase.

Youll see theyre virtually identical. Surely something is wrong there? I would have expected them to be completely different??

I think my next step is to adjust the sub distance in the amp menu to try and move the 69Hz dip up nearer to the crossover?
Thanks

Rich

Well, without the mians involved, there's no point of reference for any phase difference, so I wouldn't expect much of a difference (you probably know by now, but there were no graphs attached).

Are you running the mains as "large" or "small"?

[brucek]

You'll see they're virtually identical. Surely something is wrong there? I would have expected them to be completely different??

I think my next step is to adjust the sub distance in the amp menu to try and move the 69Hz dip up nearer to the crossover?

Phase and distance are not perceivable with a single speaker. They are meaningless by themselves.

brucek

[Ninj]

Otto wrote:

Hi guys,

I think 80 Hz is OK for now. Be sure the one on the sub itself is set to its max (200 Hz). Setting it to its max will effectively remove that crossover from sub's signal path. You're letting the receiver do the bass management, which is most likely the way to go.

Unfortunately, I doubt you will gain much more low-end extension just by allowing a break in period. If possible, I might move it a little more out of the corner. 4" might be a little tight. I know how it is with placement sometimes, though, so if you can't it's OK.

Thanks Otto, I have the subs freq set to 200, understand how that works now.

Its actually about 6" from the corner, but its a dog leg corner if that makes sense.

Rich

[Ninj]

Otto wrote:

Well, without the mians involved, there's no point of reference for any phase difference, so I wouldn't expect much of a difference (you probably know by now, but there were no graphs attached).

Are you running the mains as "large" or "small"?

Mains set to small.

Ah I understand that now about phase. So its with reference to the mains. I get it thanks. If I was to plug the mains back in, Id see the difference again.

Rich

ps the graph should be there at post #5?

[brucek]

Did you tell us the model of the sub?

[Ninj]

Sure did, its a Mordaunt Short 309i.

link

[brucek]

OK, the response is consistent with the specs of the sub, which is ~-3dB down at 35Hz.

You will have to use a BFD filter or two in the 40Hz to 60Hz range to reduce the peak you have there. That will bring out the lower frequencies much better. You may be able to reduce the mains added effect at 80hz with a sub filter there also, but you'll have to see how that goes...

brucek

[Ninj]

Thanks Brucek.

Do you think theres any point in using the subs own notch filters?

Thanks again, all help much appreciated

[Otto]

Ninj wrote:

Do you think theres any point in using the subs own notch filters?

How are they implemented? i.e., what controls are there? I'll have a look for the manual on the web, time permitting.

[Otto]

Got it. Looks like a gain and frequency are selectable, bandwidth is not. It might be an interesting experiment to try to address that peak at ~45 Hz. However, since you already have a BFD, you will find that it's much more powerful.

[Ninj]

Yeh I suspected the BFD would have the edge. Ill give it a go and report back once Ive put some filters on.

Am I right in thinking, in basic terms, rca from amps low level subwoofer socket to 1/4" jack plug into the BFD. Then 1/4" out from BFD to RCA into the sub?

Just had a quick look at the BFD manual and couldnt find a real easy connection diagram.

Thanks

Rich

[Otto]

In general, that's right. You'll want to use a mono TS 1/4" plug. There are also adapters available at RS if you're in a hurry. So, that'll inset the BFD into the signa path.

It looks like you've already got REW working, and that's an excellent start!

[Ninj]

Thanks

And I assume I can use XLR to rca instead of 1/4"? Are XLR stereo/mono

[Otto]

The XLR out will be balanced, so you will only use one of the "hot" legs. I'm not sure of the exact orientation of the pins on the XLR, but I'm pretty sure it's available in the various manuals and the web. brucek will probably know more about creating one. While I like the look and feel of the XLR, there's no reason to go away from the 1/4" mono plug. I think it will be easier to deal with in a DIY cable, and will be more readily available at RS, PartsExpress, etc.

[Wayne A. Pflughaupt]

The XLR will be Pin 2 (+), Pin 3 (-), Pin 1 shield. The Pin 2 lead will go to the RCA’s tip, with Pins 3 lead and the shield will be tied together to the RCA’s sleeve. If you’re using single-conductor cable, install a jumper between pins 1&3 at the XLR.

No good reason to use XLRs over 1/4” mono, although some people seem to prefer them.

Regards,
Wayne

[Ninj]

Thanks,

Ill just stick with the 1/4 to save any confusion.

Rgds

Richie