Sub levels & fun with spreadsheets...

[brad1138]

I just spent some time with a test tone cd and SPL meter. I also found it very easy to make a graph with Open Office SpreadSheets (I run Linux-Ubuntu). I ran the test from 20 to 90 Hz on Both My Velodyne and Polk Subs. My Yamaha rec crosses over at 90 so I didn't bother going above that, also the Velo has a built in, unchangeable, crossover at 85Hz. I set them to match at about 60 Hz, but it is all relative so I didn't try that hard. I think from 40 on up they were quite close.

I was surprised how easy and fun it is to do this. When I have more time I may do my spks from 20-10k (SPL meter only goes that high) The point in this is to see if I could use an Audio Control EQ I have laying around to flatten the response. There is an obvious hump at 50-60, but with the Velo I am very happy at the overall flatness of the the results. The Polk on the other hand is all over the place especially below 40Hz. The EQ I have has +-12db adjustments at 36 & 60 & 120 Hz. The 36 is perfectly placed for boosting that dip in the Polk, but being 20-25 db down in that range, I am not sure it could handle boosting it 12 db at 36, and it would only be about half way back. I could use the 60 Hz adj to lower the hump, but it should be lowered at 55 and I am not sure if it would help or not.

Also the room is large, 20+' x 25+'. I use the Polk to supplement the Velo, and it works well.

Brad

 

[brad1138]

Here is a link to pictures of the room, the Velo is on the right in the corner and the Polk is on the left next to the rack.

 

[TLS Guy]

I just spent some time with a test tone cd and SPL meter. I also found it very easy to make a graph with Open Office SpreadSheets (I run Linux-Ubuntu). I ran the test from 20 to 90 Hz on Both My Velodyne and Polk Subs. My Yamaha rec crosses over at 90 so I didn't bother going above that, also the Velo has a built in, unchangeable, crossover at 85Hz. I set them to match at about 60 Hz, but it is all relative so I didn't try that hard. I think from 40 on up they were quite close.

I was surprised how easy and fun it is to do this. When I have more time I may do my spks from 20-10k (SPL meter only goes that high) The point in this is to see if I could use an Audio Control EQ I have laying around to flatten the response. There is an obvious hump at 50-60, but with the Velo I am very happy at the overall flatness of the the results. The Polk on the other hand is all over the place especially below 40Hz. The EQ I have has +-12db adjustments at 36 & 60 & 120 Hz. The 36 is perfectly placed for boosting that dip in the Polk, but being 20-25 db down in that range, I am not sure it could handle boosting it 12 db at 36, and it would only be about half way back. I could use the 60 Hz adj to lower the hump, but it should be lowered at 55 and I am not sure if it would help or not.

Also the room is large, 20+' x 25+'. I use the Polk to supplement the Velo, and it works well.

Brad

That is the classic problem of what is basically wrong with the system of subs and receiver crossovers. This is a crossover gain problem. The sub crossover needs to be lowered. Try leaving the receiver crossover were it is and also engaging the sub crossover at around 40 Hz and increasing the level.

 

[brad1138]

That is the classic problem of what is basically wrong with the system of subs and receiver crossovers. This is a crossover gain problem. The sub crossover needs to be lowered. Try leaving the receiver crossover were it is and also engaging the sub crossover at around 40 Hz and increasing the level.

Thanks, my worry there is the freqs. below 40 are very hard for even subs to recreate. By doing what you are saying I am boosting the relative output of the difficult freqs by ~20db, I think the sub would fry if I tried that. I am going to try moving it around the room a bit, see what that does.

For the heck of it I tested me M3SIs, Yikes! There is a HUGH hole at 55 hz, you see a bit of it with the Polk. I don't think there is anything I can do about it, it is definitely the room. I may move them a bit farther apart, I just did that a few days ago and the bass improved a bit.

 

[brad1138]

One thing I didn't mention is that these reading were taken from the main/center listening position. Most, if not all of the dips disappear in different areas of the room. I am getting a new, more versatile preamp soon (UPS should be here any minute) that will allow me to experiment with using the subs (Velo anyway) with the M3SIs, I may be able to get a much smoother bottom end that way. I think part of the reason that the Velo is so much flatter is that it is the only Sub/spk in a corner.

 

[moreira85]

I know you have the Xover set at 90 but when you did the test did you do sub only or did you have the mains running during the test as well. Just curious.

 

[lsiberian]

Thanks, my worry there is the freqs. below 40 are very hard for even subs to recreate. By doing what you are saying I am boosting the relative output of the difficult freqs by ~20db, I think the sub would fry if I tried that. I am going to try moving it around the room a bit, see what that does.

For the heck of it I tested me M3SIs, Yikes! There is a HUGH hole at 55 hz, you see a bit of it with the Polk. I don't think there is anything I can do about it, it is definitely the room. I may move them a bit farther apart, I just did that a few days ago and the bass improved a bit.

You know with a sound card you could automate the process using the Room EQ wizard.

 

[brad1138]

I know you have the Xover set at 90 but when you did the test did you do sub only or did you have the mains running during the test as well. Just curious.

It was each sub or spk only.

You know with a sound card you could automate the process using the Room EQ wizard

Well... I don't have a pc at all involved in this system, but even if I did I don't think it is practical to try to use an EQ to fix 20+db fluctuations. It would cause quite a strain on the subs/spks. Also if I move 5-8' to the right of center the dip @ 55Hz in the M3SIs goes away. So if I have them boosted 20+db for the center listening position, it would be 20+db to high elsewhere.

I just got in a new (to me) preamp, a Lexicon DC-2. It is much more versatile that the Yamaha I was using. With it I cross over at 80Hz. I did some testing using the Velo in stereo mode handling the bass for the M3SIs. It didn't sound better, if anything it was worse, I guess a flat response isn't everything.

 

[brad1138]

Never mind on the room EQ wizard thing, I thought you meant a computerized EQ adjustment, I get what you meant now. Yes I could, but this was kind of fun.

Brad