Help understanding graph

**jbarcelona4** · **06-05-06, 09:54 PM**

I have spent most of the weekend trying to get the best reading for my room as far as fq. is concerned. I have moved the sub. and tried lowering its volume. What I do not understand is with the 3 graphs I will show, the sub only graph is flatter, and when the fronts are added, they increase the peaks from 22 to 80 Hz. and my crossover is set at 80 in the preamp. I do not understand how the fronts effect the fq. from 22 to 40 Hz. I have Paradigm 100 speakers and a HSU Sub. The 1st graph is sub only, and the 2nd is fronts only, and 3rd is Sub. and Fronts. Thanks for the help.
Joe

**Wayne A. Pflughaupt** · **06-06-06, 08:45 PM**

Quote:

What I do not understand is with the 3 graphs I will show, the sub only graph is flatter, and when the fronts are added, they increase the peaks from 22 to 80 Hz.

Hmm – actually the combined graph looks flatter than the sub-only chart, although the combined graph does have higher SPL level in the lows.

Quote:

and my crossover is set at 80 in the preamp.

You might want to double-check your settings, because it sure doesn’t look like that, judging from the “Fronts only” chart. It’s showing your mains having substantial output all the way down to 22-25 Hz. If your crossover is set at 80 Hz, then your SPL reading at 40 Hz should be about 24 dB lower than 80 Hz, assuming your receiver has 24 dB/octave slopes like most do. Instead, your response actually rises more than 15 dB below 80 Hz.

Likewise, your sub’s readings should be about 24 dB down at 160 Hz (an octave above the crossover frequency). Instead, it’s down less than 10 dB.

This might explain why your combined readings show your lows to be several dB higher than the sub-only graph. Since your mains are somehow putting out lots of low end, your “both” plot actually is a combined reading.

Regards,
Wayne

**jbarcelona4** · **06-06-06, 10:50 PM**

Thanks Wayne,
I called Nad today and they said that in the stero mode the crossover is not effected and the Paradigms do go down to 22 Hz. I'm really not understanding all of this, but trying. I thought that if you have your speakers set to small and the crossover at 80 Hz. the sub would handle the bass to 80. Nad said that in stero it isn't so. So confused I stay. I have fooled around with this for the better part of 4 days and today I decided to move my sub. to the front from behind the sectional. It has given me a pretty good reading and eventhough it is a little in the walkway there, there it will stay. Hsu had told me the sub would be great in the corner behind the couch. I think the closeness of the wall has caused it problems. I will see if I can show you the resuly so far. I would like to get the Eq. used here, but I'm afraid I would only mess things up. Thanks for the reply. You all are great here.
Joe

**brucek** · **06-07-06, 07:39 AM**

Quote:

I'm really not understanding all of this, but trying

Many receivers/processors do their best at creating a stereo bypass situation for the purists who want the minimum manipulation of the source signal. This stereo mode can be anything from bypassing the tone control section or as elaborate as routing the signal untouched to the mains output. Some have a separate bypass and regular stereo modes and some simply invoke bypass in stereo mode.

One of the standard signal manipulations that is usually removed in stereo is the bypassing of the crossover so that the mains receive a full range signal. Some manufacturers then will shut off the sub output and others will continue to send the sub full range for those that want to cross the sub externally.

In multichannel (5.1) all the channels are back to operating with their crossovers and large/small settings.

Anyway, your response looks pretty good actually. It's not really that much different than the original signal you graphed while the sub was tucked away, although it does appear to extend a couple hertz lower. Do you really want to be tripping over your subwoofer? Sometimes small movements of the sub can have dramatic effect.

Original graph...........

Latest graph...........

brucek

**jbarcelona4** · **06-07-06, 10:30 AM**

brucek,
Thanks for the help you and others have given me. From what I have shown, do you think it is worth the move. As you can tell, I really don't know much about this. I thought that the chart reading with the sub at the front of the room was a good bit better and this was with the fronts on. That was one of the problems with the sub behind the couch. It seems that when the fronts were on it caused problems rather than smoothing out the response. If there is anything else I can do to get a better sound stage, please advise. I know this is very difficult when you are dealing with someone like me and can't be on the site.
By the way, how do you get the charts to the site as you did? Don't know much about computers either. It would be nice to get a full graph and line them up for comparison, as you have shown here.
Thanks again,
Joe

**brucek** · **06-07-06, 11:44 AM**

Quote:

From what I have shown, do you think it is worth the move.

Not really. I doubt you'll notice the difference. If you do think one sounds better than the other, then you'll have to make the decision based on that.

Quote:

It seems that when the fronts were on it caused problems rather than smoothing out the response.

You haven't said whether you are invoking your crossovers when using the sub and mains that are only effective (as you've noted) in non-stereo modes? This is a huge point. If indeed there is no crossover utilized when in stereo mode, and in that mode both mains and sub are receiving a full range signal (appears true from your original set of graphs and backed up by your call to NAD), then you've got a problem to solve. It will sound terrible without some bass management or alternatively simply turn off the sub in stereo mode.

You can't feed a sub and mains a full range signal without at least using a low pass filter for the sub. Most subs come with an internal low pass filter that you can dial down to its lowest CCW position and it will provide a small amount of very low frequency passed signal to supplement the full range mains.

Can you explain your situation more with regard to using 5.1 and stereo modes and whether you want a sub for both situations?

Quote:

By the way, how do you get the charts to the site as you did

See here

brucek

**jbarcelona4** · **06-09-06, 08:58 AM**

brucek,
I would like to have a sub for music listening also. It is my understanding, from Nad, that in all other modes except stereo, the crossover is inplace. In stereo, the sub and mains are at full range. I would assume that I need a high pass filter for the mains or a low pass for the sub. I guess this is why the listening sounded muddy to me in the stereo mode. I am still not understanding all of this, but I did talk with Dr. Hsu, who produced the sub I use, a Hsu VTF3-Mk2 and he still suggest rear placement behind the couch for my sub, eventhough it is tucked in at close quarters, and the high pass filter.
burcek, when doing a graph, say at 70db for the sub, and the readings are high, to the 100's. Is it proper to say that the sub level on the graph has to be brought down by lowering the output of the sub to get the proper reading. If I do this the sub will be playing much lower than the test tones are for all speakers. Sub was say at 0 when all speakers were at 70 db. To get the graph to the projected line, I had to drop the sub's level to -9. Am I doing this properly.
Ex. With 70db as reference. Mains read -5, sub reads 0. To get the subs level close to reference on the graph, I will have to drop the sub to -9 to see where it's at, and it should be played at -9. Is this correct.
Thanks,
Joe

**brucek** · **06-09-06, 10:17 AM**

Quote:

I would assume that I need a high pass filter for the mains or a low pass for the sub.

Well, for two channel listening I would go for the mains receiving full range and a low pass for the sub. You would adjust the low pass to provide just enough bass at the lower frequencies to complement the low end roll off of the mains. Most subs come equipped with an adjustable low pass filter (that can be switched out or dialed high when using regular processor bass management). If you had capable mains, you might only need the subs low pass crossed at 35Hz or 45Hz, just to boost that very low end stuff leaving the rest of the duties to your mains.

Quote:

will have to drop the sub to -9 to see where it's at, and it should be played at -9. Is this correct.

You're making it a bit too complicated. First set up the sub and speaker trim levels so they sound balanced to you when playing a movie or music - then don't touch them or your subs amplifier level.
Then adjust the overall master volume of the processor/receiver to set the level you like for frequency response measurements - whatever that is.

Love those sideways graphs - doh, I think I hurt my neck.....

brucek

**jbarcelona4** · **06-09-06, 12:23 PM**

I don't know, I guess this is just pass me. I did balance the speaker levels at 75db with the test tones. As such, with the volume set at -15 on the preamp with the sub at +3 the, which is where it matched the other speakers, the reading for the sub was off the chart. That's why I lowered the sub to -12. Should I just lower the volume level, say to -25, but that would be too low of a volume for listening. Sorry, I'm so mixed up. Oh, still don't get the maps. The last 2, I scanned, resized, rotated, and then uploaded. Man.
Thanks,
Joe

**brucek** · **06-09-06, 02:31 PM**

Quote:

I did balance the speaker levels at 75db with the test tones. As such, with the volume set at -15 on the preamp with the sub at +3 the, which is where it matched the other speakers.

OK, at this point you have the balance between the speakers (including the sub) finished. Now the only control you will touch will be the Master volume control on the receiver/processor, just as you would balance the front & rear speakers in your car first, then after that you would only touch the master volume.

When you want to do a frequency response test and make a graph, play a tone of say 50Hz and set the master volume control of your receiver to ~80dbSPL. Once that's accomplished, do the frequency response test without altering the master volume through the entire sweep. We're only doing frequency response tests to get a look at how the speakers react in a room over a certain frequency range so we can make appropriate changes if neccessary. Changes such as equalization or speaker movement.

brucek

**jbarcelona4** · **06-09-06, 08:04 PM**

That is exactly how I did the test, but with my levels reading so high on the chart; I tried to get the chart more in line by decreasing the subs level because it was so high. If the chart looked better, I was thinking just to play the sub at that level. To get the chart more to reference, if it is all high, I could do a reading with only the master volume lower, sub and fronts with same settings. The lower master volume would bring the graph into a better perspective with the reference line I'm tring to attain, pink line on the chart. Thanks again.
Joe

**brucek** · **06-09-06, 10:06 PM**

Quote:

That is exactly how I did the test, but with my levels reading so high on the chart; I tried to get the chart more in line by decreasing the subs level because it was so high

That was a mistake decreasing the sub level. To get the readings lower, simply turn down your master volume before doing the test for the chart.

Quote:

the reference line I'm tring to attain, pink line on the chart

The pink line is not a reference line. That column in the excel sheet of 75db entries is only there to show you where to enter values when you take readings when you have a BFD. You're suppose to delete those entries if you're not using that column and the pink line will go away.

There is no reference. We usually suggest 80dB at 50Hz as a good level to set with the master volume before you begin your testing, since that should normally center the graph vertically. You can use a slightly higher or lower reference and it doesn't really matter. 75dB to 85dB is fairly common.

brucek

**jbarcelona4** · **06-09-06, 10:19 PM**

brucek,

Thanks again for the advice. Today Nad was able to tell me that because I had the CD connected with analog cables, is the reason my mains are playing full eventhough set to small in stereo mode. I will get a digital coax cable and see if it will work properly in the stero mode.

Dr. Hsu said that if I play the sub in the IN position with the crossover set to 90, the sub would not play after the crossover. I think that these maps will show he is right.

I wish they had a bigger one of these, thanks bru. Now to get the graph looking better, and maybe better sound.

Joe

**brucek** · **06-10-06, 07:17 AM**

Quote:

I will get a digital coax cable and see if it will work properly in the stero mode.

Any RCA video cable you have will substitute for what the industry likes to call a "digital" cable. They are the same.

Quote:

I think that these maps will show he is right

Yep.

brucek

**jbarcelona4** · **06-10-06, 10:30 AM**

Do you mean any yellow rca cable? If so will it give the same quality? I'm not familiar with RCS cables.
Joe

**brucek** · **06-10-06, 10:31 AM**

Quote:

Do you mean any yellow rca cable?

Yep.

I edited my spelling mistake above - I meant to type RCA

brucek

**jbarcelona4** · **06-10-06, 09:12 PM**

Thanks brucek,

And you told me this BFD stuff was easy. I didn't realize when you said this that you wrote the review on it. Quite a job, but really over my head. I'm still reading it though, maybe something will connect. It's certainly not like a history lesson, but is very interesting. Again, I thank you for giving me the time and help; it has been fun. Didn't think I would ever get the maps. lol

Joe

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