Some questions before I purchase ...

[carel1966]

I recently discovered REW while reading a review for the Velodyne SMS-1. Excellent software product is all I can say. This has led me on a discovery path including the BFD. Although my sub (Revel B15) and pre-amp (Anthem AVM50) gives me 4 parametric equalisers between them I realised that I definitely need some more correction and decided to purchase the FBQ2496.

As part of this exercise I would also like to replace my SPL meter with the ECM8000 and Xenyx 802.

Before I go this route I would like to get some opinions about 2 things:

1) Will it make sense to purchase 2 microphones to get readings from my ‘no 1’ and ‘no 2’ seating positions at the same time? This will allow me to correct to an average that should be acceptable across both positions. (It will also allow me to measure with 2 microphones more or less the same distance from each other as our ears in the ‘no 1’ listening position.)

2) I am currently getting an -5.5db to +5.9dB response in the 20-80Hz range. In order to achieve this I had to boost 2 frequencies by +6dB using a high Q (0.1C). (I know this is not recommended but with the equipment I got currently is the only way to get to within an acceptable response graph.) My question is if further correction will bring any real sonic benefits?

Thanks for any assistance.

Graph with no EQ and graph after EQ included.

[Otto]

Hi Carel, and welcome to the Shack!

carel1966 wrote:

1) Will it make sense to purchase 2 microphones to get readings from my ‘no 1’ and ‘no 2’ seating positions at the same time? This will allow me to correct to an average that should be acceptable across both positions. (It will also allow me to measure with 2 microphones more or less the same distance from each other as our ears in the ‘no 1’ listening position.)

Well, REW doesn't allow us to measure two inputs at the same time, although something like that could be possible for a future release (technically possible, I don't think it's really under consideration at this time). So you wouldn't be able to measure two things at exactly the same time, but you could measure them one right after the other, and having two mics set up would save you some time in relocating them around the room. It would also save you any concern that the mic might not be in precisely the same location. There are a few people around that have averaged their response for various measurement points throughout the room, and I think it's a totally valid idea.

2) I am currently getting an -5.5db to +5.9dB response in the 20-80Hz range. In order to achieve this I had to boost 2 frequencies by +6dB using a high Q (0.1C). (I know this is not recommended but with the equipment I got currently is the only way to get to within an acceptable response graph.) My question is if further correction will bring any real sonic benefits?

A few things.

You can plot multiple measurements (up to nine) on the same set of axes by using the "All Measured" tab in the graph area of REW. It makes it a lot easier to see what happened, but it's OK for this one. I don't necessarily see where you would have boosted with two 6 dB filters -- maybe around 70 -85 Hz?

Do you have your mains on? It looks like you're still getting response out to 200 Hz... If the mains are on, remeasure with sub only. It's quickest and easiest to do it on its own since that's the thing we're really going after. Of course, if you wish to use your preamps EQ for sub and mains, it's a bit of a different animal that applying the BFD directly to the sub, so it's up to you.

What's your crossover point between mains and sub?

What sub are you using.

Have you played with room placement? I'm thinking that that giant hump at 25 Hz must be coming from the room. I know how it is if you can't move the sub around the room, but you might be able to get some better responses right off the bat if you can change placement (sometimes even a little).

Do you have any idea for how much headroom your sub may have? Is it turned up half way at this point? More? Less? Do you use it to its limits?

To answer your question -- yes, I think you can get better results with a BFD. Your response is a little rocky, but you should be able to clean most of it up. There are still a lot of things to play with!

[brucek]

Will it make sense to purchase 2 microphones to get readings from my ‘no 1’ and ‘no 2’ seating positions at the same time? This will allow me to correct to an average that should be acceptable across both positions

As Otto points out, you can store up to eight readings in REW and then push the Average button and it creates a new average waveform in the next slot that you can apply your filters to etc.

Some people use this method by taking a measurement in every seating position and then hitting Average and set the filters for an even response from that plot. This gives everyone a decent response. Then you can do another measure from the sweet spot and store a single set of filters for critical listening in that position...

brucek

[carel1966]

Hi Otto, and thanks for the welcome and quick reply.

I do understand that REW only makes provision for one mic, but actually want to measure using 2 mic's to "acoustically" average the response. As far as REW is concerned this will still be one measurement. For now I have decided to stay with one mic (make the variables less).

The +6db boosts were applied at 32.9Hz and 44.9Hz. My cut filters are currently set at 23Hz and 72.9Hz, although I realise that the mains contribute a lot at his point as well.) I am using the standard 80Hz crossover on my processor (24dB to SUB/12dB to mains).

The 22Hz peak has forever been a problem in my room, and is definitely related to the size, which is 8m by 5m by 3m. My room is the typical shoebox shape.

Yes, sorry, my mains are on. I actually wanted to see the full response and integration between sub, a Revel B15, and mains, B&W N802's. I have tried a lot of room placements but in order to minimise dips in the response I always end up in the front corner, a couple of inches from the front wall. Although this creates significant peaks the dips are a lot less in this position.

The volume of the SUB is set at 70% at this stage, but this is mainly to prevent my processor from clipping. I do not hear any stress from the subwoofer, and listening to stereo music it actually blends in quite well (transparent) with the main speakers.

Again, thanks for the advice; I will confirm the order for my BFD now!

[carel1966]

Hi,

Got the "kit" and played a bit this weekend. This is my best result after making use of all 20 filters on the BFQ2496.

I obviously got serious problems in my room. Crossover at 80Hz. Thinking of upping crossover to 100Hz to see if I can tame some of the peaks and dips in 100-200Hz area, but not sure if this will help.

Any suggestions on where to start with correction will be appreciated.

Thanks.

[Otto]

Hey there,

Things look pretty good, really. What does the sub response look like without the mains on? I would probably not increase crossover frequency, but I'm always trying to keep it as low as possible.

[carel1966]

Hi,

I have actually not saved a plot with the subwoofer only, but will do that soon.

What I did do was to get the subwoofer plot as smooth as possible, then add the mains, and tweak some of the filters to help where the mains with the sub created new problems.

I have always used a 50Hz crossover, until about 2 years ago. The better dynamics I got out of my mains by upping the crossover frequency to 80Hz was quite astonishing.

I will make sure that there is no localisation of the bass when I try 100Hz. As faithful music reproduction is (still) my no. 1 priority this is very important to me.

[brucek]

I will make sure that there is no localisation of the bass when I try 100Hz. As faithful music reproduction is (still) my no. 1 priority this is very important to me.

Yeah, in addition to localisation as a problem with the higher crossover will come a weakening of the soundstage since you've passed the freqencies up to 100Hz to the mono subwoofer.

You might also take a look at the sub with each main individually to get a feel if perhaps moving the mains a bit might help the small problem around 100Hz.

You might also consider turning your sub up a wee bit and see how it sounds.

Anyway, your response is still quite good......

brucek

[Wayne A. Pflughaupt]

carel1966 wrote:

This is my best result after making use of all 20 filters on the BFQ2496.

Say what?????

There’s no way you should have needed even half that number of filters, judging from the unequalized graph in your first post.

Regards,
Wayne

[Chrisbee]

Don't use narrow filters as they affect the Q of the subwoofer.

Paint with a broad brush.

I'd turn up the subwoofer by 3-6dB (to taste) and add a gentle house curve for more bass impact.

[carel1966]

Hi all,
Thanks for the advice.
I agree on the number of filters used being overkill. If we consider that my first equalised plot was actually using only 4 filters then I should get a smoother response with only a couple of additional filters added.
The other question I am unsure of is what is considered good, as in +/- 3dB, 6dB or even something like +/-2dB.
I think I should redo this and concentrate on getting a smoothed, let’s say 1/3 octave response, instead of worrying about very specific frequencies where the problem is in a very small bandwidth.
One thing I can mention is that the overall affect of the equalisation is that I now got more “discernable” bass, which is probably correct, as the bass level was previously set including peaks, i.e. still leaving all the dips.
I will play around this weekend using less narrow band filters and see what I can achieve, will post the separated plots afterwards.

[carel1966]

Hi all,

Attached the graphs after my final sub equalization attempt this weekend. I attached both graphs for the sub only and the mains and sub together.

Couple of things I learned during this exercise:

• Don’t be afraid to do manual tweaking. The software is great but sometimes just changing the filter frequency one way or the other makes a huge difference.
• Put enough time aside. This whole process took me a couple of days trying the speakers in different positions etc, but this is the best so far and will leave it there in order to allow me to enjoy my music a bit.
• DO NOT equalize the sub and mains together if you listen to 5.1 source material. As the sub have to make up for both peaks and dips in the mains it sounds awful on its own with a dedicated LFE soundtrack. (I took the forums advice and EQ’d the sub first, and was lucky that it integrated well with the mains).
• Do not use 2 mic’s at the same time, the difference (and associated frequency wavelengths) between them create great anomaly’s in the measurements. I ended up calibrating both mikes to exactly the same level and then averaging the results to make adjustments off the average measurement. This also allowed me to give my seat just a little bit more emphasis by measuring it twice.

Again – thanks for everyone’s advice and like before this just shows me that I will seriously have to consider room treatment to get a more natural flat response.

For now I will enjoy the music, stereo first but also surround sound concerts etc.

Have fun,
Carel