manually plotting response

[DerekCV]

Hi all,

I’m new to this home theater thing, I have been reasearching for a long time and finally went out and built up my 5.1 system with HTD level 3 speakers all around and a SVS PB12-plus2 for my sub. I’m not as happy with the sub as I thought, my general issue being that I can hear the sub vibrating the walls and the light fixtures, I just can’t FEEL the bass, which is half of the reason I bought such a monster sub. I assume that the issue, in part, due to the sub location. I don’t have a lot of places to move my sub, but I’m going to try. I do have the PEQ on my sub that I’m not sure how to use….

I also want to try and measure the frequency of my sub. The problem is I don’t have a working computer at home, only my work laptop, so I can’t download programs. So it looks like I will just do it the old fashioned way and run SIN waves and read the dB off my radio shack meter and then plot it in excel. Do I do this with only the sub, or do I include the other speakers as well? Any other pointer you can give me?

[Wayne A. Pflughaupt]

Do it with just the sub. You can use the Excel worksheet on the Downloads page, and post a graph here. We have folks here who can help you evaluate the readings.

Regards,
Wayne

[DerekCV]

I attached the graph that i created, I sent the output with a Pink noise until it read 75dB and went from there.

My meter didn't pick up any thing until 15Hz and in the 190Hz and over it was hard to tell because the meter would range between LO-52dB, I think some of it being ambinet noise at times. Please let me know what you think, I would think that i'm low in the mid 40Hz region and too high in the 20Hz region. Please help and any advice on utilizing my PEQ would be great. Thanks

[Wayne A. Pflughaupt]

That dip at 44 Hz is probably your culprit as to why things sound weak. That’s a key area for the “feel” you’re lacking. Probably not much you can do about it with the subwoofer’s built-in PEQ, though. Typically they are “cut only” filters.

As to the sub vibrating the walls and lights, that would be because of the high output in the 22 - 31.5Hz range.

Also, the 25 dB drop above 63 Hz is way too severe. What do you have your crossover set at? This is going to make mid-bass notes weak, unless your mains are making up the difference.

Recommendation: Get a BFD.

Regards,
Wayne

[DerekCV]

I had a feeling that you would say that... I was shopping around on ebay for them to get a feel of the cost. What is a good one that will fit my needs? I see a few DSP-1100 and DSP1124P that seem pretty inexpensive... will one of those work?

oh and my crossover is set at 80Hz, I was thinking about maybe bring in down to 50Hz and also running my mains as large, i did that before i had the sub and they sounded nice.

[Otto]

DerekCV wrote:

I had a feeling that you would say that... I was shopping around on ebay for them to get a feel of the cost. What is a good one that will fit my needs? I see a few DSP-1100 and DSP1124P that seem pretty inexpensive... will one of those work?

The 1124P is the one you want.

oh and my crossover is set at 80Hz, I was thinking about maybe bring in down to 50Hz and also running my mains as large, i did that before i had the sub and they sounded nice.

Yeah, I go back and forth with those types of settings myself. Just did it yesterday... If you have a PC and REW you can easily test and measure that stuff, even without a BFD.

[tdamocles]

DerekCV wrote:

I was thinking about maybe bring in down to 50Hz and also running my mains as large, i did that before i had the sub and they sounded nice.

Not sure if you really want to set it to large. The mains may not like the dynamic LFE in movie use. They may bottom out if set to large.

[Wayne A. Pflughaupt]

If you want to run your mains as large with movies, it takes more than them having good extension. They also have to have high power capability. Otherwise, you’ll find that action movies played at high volumes will bottom out their woofers.

There are other issues as well. For instance, your sub is good down to about 22 Hz. Unless your mains also go that low, you’re going to have greater output at the frequencies where the mains double with the sub, but reduced output below that point.

And, you won’t be able to do any equalizing in that range where the subs and mains are doubled. If there is a peak in response at a certain frequency, for instance, it won’t do any good to equalize it out in the sub, because it will still be there with the mains.

And, you won’t be able to equalize anything above 50 Hz at all (if that’s where you set your sub’s crossover).

Bottom line, running the mains as large and crossing the sub low can give a lot of low frequency response problems. Not to say it can’t be done, because it has been. You just have to do a lot of measuring to make sure it’s working well.

Regards,
Wayne

[DerekCV]

I left everything the same and I adjusted my PEQ per another memeber recommendations and it produced the following response. still think I need a BFD to boost the 40Hz area?

[MakeFlat]

You can try it. However, room acoustics is such that a +/-5dB generally does not mean that much. A mere 6" change in seating position may result in a different response. A boost in the 40-45Hz area may solve the problem at a fixed listening position. What about other listening positions? I have made measurements at 3 listening positions and found that some peaks/dips are fairly consistent across all but there are times when only two out of three positions show the peak/dip at a particular frequency.

Anyway, if you try a 5 dB boost, check other listening positions for consistency in response.

[DerekCV]

I did another run though my sweeps after adjusting my PEQ slightly, tunning my sub to 20Hz, and bumped my crossover on my reciever up from 80 to 100Hz in an attempt to shift the drop off after 50-60Hz range. The new plot is in magenta and my previous PEQ adjustment is in blue. Any advise on this sub only plot? Were should i look to improve? Other then the 40Hz dip i still have I think it looks pretty flat from 20Hz to 60Hz. Thanks for the advice again!