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Tempest In-room Frequency Response - Needs BFD ?


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#1 of 56 OFFLINE   Joe Mihok

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Posted October 04 2004 - 01:41 PM

So most of you know the story. I have a 194L SBB4 Tempest and finally broke down and got a Ratshack Analog SPL Meter. Anyways, I took the readings three times and got the exact same reading every time. This is the frequency response with both mains hooked up and crossed over to 80 hz with my sub. Is this normally how one tests for in-room frequency response ? Or do I unplug my mains ?

Here's what I get so far:

Posted Image

Is this a decent response ? Can a BFD flatten this out ? And if it could, would it be a drastic change ? During some movies the bass can get a little boomy and I'm not sure if it's the rooms response or just a poorly mastered movie ....

Hope you guys can give me some input. Thanks Posted Image

#2 of 56 OFFLINE   GrahamT

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Posted October 04 2004 - 02:06 PM

Not pretty, but not unusual. Yes, a bfd would certainly help. You have about a 10 dB hump at 45 Hz, and another at 80 Hz. The BFD can take them down easy. You have a 5 dB depression at around 60 which may be a null. It is possible the BFD could help that, but you wont know till you try.

I run a FR sweep with only the sub, then only the mains, then both together to try to guess what the problems are.

#3 of 56 OFFLINE   Joe Mihok

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Posted October 04 2004 - 02:56 PM

GrahamT to the rescue again Posted Image. I guess my next purchase will have to be a BFD.

Today I calibrated my sub with the rest of the speakers using AVIA. I was a bit thrown off during the subwoofer calibration because the sub uses a tone comparison for each channel in a 5.1 setup. I had different low frequency readings for each speaker. Here is what I had gottten from Avia:

Front left (which is where the sub is) - 71 DB
Centre - 72 DB
Front right - 75 DB
Rear left - 68 DB
Rear right - 68 DB

So what setting does one use ? I just took the setting from the left speaker comparison and made it flat with the subwoofer. This was done NOT using the corrected RatShack numbers (So I assume it's about +3db hot which is fine with me).

EDIT: I edited the Rear Left and Rear Right levels from 86 to 68. Too much bass tones affecting my brain Posted Image.

#4 of 56 OFFLINE   GrahamT

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Posted October 04 2004 - 03:08 PM

Glad to help you Joe,
You can find the BFD at any local music supply store. You will need some 1/4" male to RCA female adapters. I think the BFD will make a big difference by just knocking down the two humps. no problem for 2 to 4 filters.

I use the S&V disc which might be similar. I set all the speakers to 85, master volume at 0 and then the sub to 85 dB uncorrected as well, a little hot. If you do some searches for avia, calibration etc, EdwardJM has made a lot of detailed posts on using the various calibration discs.

#5 of 56 OFFLINE   Joe Mihok

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Posted October 04 2004 - 04:18 PM

I answered my own question with AVIA by looking here:

http://www.hometheat....AVIA SUBWOOFER

Lots of great info in that thread Posted Image. Should have done a "slow search" from the start.

#6 of 56 OFFLINE   MikeDuke

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Posted October 05 2004 - 02:12 AM

That response is incredibly close to what my sub was doing. But I have the krell showcase and it has a parametric eq built in. After I played with it I got a very flat response except for 63HZ down to about 25HZ. It just looked so freaky close to what mine was doing I had to say something.
I know what I like when I hear it

#7 of 56 OFFLINE   Joe Mihok

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Posted October 05 2004 - 02:27 AM

Well, it's reassuring you fixed your peaks ... it gives me some hope Posted Image. I know every room is different, so I'll have to wait and see. Like Graham mentioned, I only have to calibrate a few frequencies and it should be fairly easy to do (or so I hope). The cost of a BFD here in town after local taxes will be around the $200 mark. That's fine and all. I've spent alot more on some HT gear, but it's just bad timing. If things work out and my car has no more problems, I'll be able to buy the BFD at the end of the month.

#8 of 56 OFFLINE   MikeDuke

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Posted October 05 2004 - 02:43 AM

"I only have to calibrate a few frequencies"
Agreed. I only did it on 4 frequencies.
I know what I like when I hear it

#9 of 56 OFFLINE   TonyWright

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Posted October 05 2004 - 05:38 AM

What software are you using to do these frequency sweeps?

I am interested in trying this out in my setup.


Thanks.

Tony

#10 of 56 OFFLINE   MikeDuke

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Posted October 05 2004 - 05:52 AM

I am not that high tech. I only used my radioshack SPL meter and the avia disk. But after a few hours I got it down.
I know what I like when I hear it

#11 of 56 OFFLINE   Brian L

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Posted October 05 2004 - 06:44 AM

In case you have not seen it yet, here is a fabulous web site devoted to the BFD:

http://www.snapbug.ws/bfd.htm

FYI, the key to getting decent measurements (without resorting to PC based measurement software) that can be used to tweak a BFD is to use Sin waves, and make sure you adjust the readings per the RS correction factors.

The BFD site has a downloadable spread sheet that has the correction factors built in.

BGL

#12 of 56 OFFLINE   Joe Mihok

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Posted October 05 2004 - 07:17 AM

Yeah, I downloaded the needed sine waves and the corrected spreadsheet from that site yesterday. It's so simple. Those tones can get real annoying after a while tho. I had to take a break after the third round of measurments. Is it just me or do other people have a hard time playing sixty low fequency sine waves one after another ?

#13 of 56 OFFLINE   Brian L

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Posted October 05 2004 - 07:40 AM

Quote:
Is it just me or do other people have a hard time playing sixty low fequency sine waves one after another ?


I actually think its kind of funPosted Image

Seriously, I don't know that you need to run 60 test tones. I only ran about 12, all below the 80 Hz sub crossover, and to match up with frequency centers that the BFD was capable of acting upon.

Since the BFD will not work exactly on the 1/6 octave centers, and my test tones are in 1/2 hertz increments, I went through the fine adjustment chart of the BFD, and picked frequencies that were in whole or 1/2 hertz increments to match my test tones (Bass Mekanix CD), but still fairly close to the 1/6 Octave frequencies.

I did all my measurements based on those, and then adjusted accordingly.

One thing I did which is probably a BFD Noob kind of thing is that I programmed 12 filters and made adjustments to each one at 1/60th bandwidth, even though I could likely have used fewer filters at wider bandwidth....I just did not want to have to think too hard about getting the correct bandwidth for a given peak.

From 25 to 80 Hz, I have absolutely flat in room response(subject to interpolating the RS correction factors for my test frequencies, and all the other vagueness that using a hand held SPL meter introduce).

Now I need to copy my preset, and dial in a house curve for giggles and shits.....boys and their toys as they say!

BGL

#14 of 56 OFFLINE   MikeDuke

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Posted October 05 2004 - 07:55 AM

It was definatly a pain listening to those Avia tones by my self and loging the info. But it was cool at the same time. Check out my SW900 review and see my final chart. I think it looks pretty good for such a small room and only using basic measurements. Like I said before, can't do anything about that dip at 63 Posted Image.
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#15 of 56 OFFLINE   Joe Mihok

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Posted October 05 2004 - 08:17 AM

Quote:
Seriously, I don't know that you need to run 60 test tones. I only ran about 12, all below the 80 Hz sub crossover, and to match up with frequency centers that the BFD was capable of acting upon.

I haven't really done this before .... so I just downloaded the spreadsheet and the sine waves for the frequencies that are listed listed in it. I measured the readings of all the frequencies three times just to make sure I had done everything accurately.

I'm gonna try again tonight with my mains unplugged. Maybe I am getting some cancellation with my mains and my sub ? I dunno, like I said, I'm new to this Posted Image.

#16 of 56 OFFLINE   Wayne A. Pflughaupt

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Posted October 06 2004 - 04:41 AM

Joe,

About the changeover from RCA to 1/4 “ Graham mentioned:
Quote:
You will need some 1/4" male to RCA female adapters.
Don’t fool with those cheesy adapters from Radio Shack. Pick up a couple pairs of these:


Posted Image


The store you buy the BFD from will have them.

Regards,
Wayne A. Pflughaupt

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#17 of 56 OFFLINE   Brian L

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Posted October 06 2004 - 05:06 AM

Quote:
Don’t fool with those cheesy adapters from Radio Shack.

I resemble that remark, and now I suffer from connector envy!Posted Image

BGL

#18 of 56 OFFLINE   Joe Mihok

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Posted October 07 2004 - 02:23 AM

LoL, too late. I picked up the BFD yesterday and got some adapters from the music store as well. At first I got an annoying hum. Then I got rid of the ground on the A/C chord and now all is well. At first the BFD was a bit confusing, but after about an hour, it's a peice of cake. On to adding the filtered frequency's and gain ......

First of all, I wanted more "earth moving" bass from the sub, so I managed to increase the low end (20hz 1/3) by +5 and decreased my 45hz and 80hz peaks by -7 Db's. I couldn't really get rid of the null at 63hz so I assume my room is to blame for this (oh well, maybe I'll experiment with positioning at a later date)). After placing the new mesurments in the excel spreadsheet, the resulting frequency curve is not flat, it starts off strong at the low end, and then gradually lowers until about 65hz, then climbs again into the 80hz region. I'll have to post the chart when I get home. As a result of the peaks being reduced, I had to turn my sub volume up +10 (the actual volume knob on my tempests power amp) to match with the main speakers using AVIA. I found it hard to believe I had to bump my volume that high but I did it anyways because I trust AVIA. The first thing I did was throw in some music, and the bass sounded a bit lacking but I figured I would let my ears get used to it. Sure enough, the bass seemed more detailed and less "in your face". I could pick out different bass fequencies that I've never heard before. Sure I kinda miss the "punch" I had before, but I'll wait and see how I adjust with this new curve.

Next in line was Finding Nemo, I quickly skipped over to the "Whale" scene ...... OMFG!!!!!!! I could not believe what just happened. My entire house felt like it was going to fall apart. Whenever I played that scene in the past, while impressive, I always heard alot of bass, but never felt it like this. It's hard to describe. I guess it felt like the ground under my house was caving in. The biggest thing that tickled me is that I could not hear any bass at all ....

Then I proceeded to Star Wars EP1 .... speechless. Even my wife was amazed that this black box I built could knock her mirror off the wall in the bathroom downstairs. All I can say is the BDF did AMAZING things to the frequency response in my room. Even if it is not perfectly flat, I prefer the curve I have going right now. Anyways, another big thanks to GrahamT and everyone who pointed me in the right direction. The BFD and Tempest are THE most important thing in my HT. If there are any n00bs (like me) out there that wanna know what to buy first for your HT (and on a budget of course), start off with good mains and a good sub with a BFD. Posted Image

#19 of 56 OFFLINE   Brian L

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Posted October 07 2004 - 02:44 AM

Great results can be had with a BFD, eh Joe????

I have been doing a lot of experimenting lately, moving my sub from a front corner to behind my couch (its a HSU 1225). I also tried a 2nd sub back up in the front corner, and of course, added a BFD into the mix. I was using EQ before (AudioControl Bijou), but just could not resist the call of the BFD at $120.

Currently configuration is just the HSU, behind the couch, EQ'd via the BFD. May I quote you??

OMFG!!!!!

If you have it, try the very opening scenes of SW Attack or the Clones. The senators transport sounds like a B29, and as you say, quite literally shakes the room. And then when it is blown up, the initial ka-boom is stunning, but the residual rumble immediately thereafter is incredible.

The combo of moving the sub and improving the EQ has finally delivered the proverbial "room shaking bass". My room has concrete floors, and while I could always hear the bass, it was never really felt. But with the sub in close proximity to the couch, I think I now have a good idea what a "bass shaker" feels like.

BTW, I too needed to lift the ground...not uncommon in my experience with subs.

BGL

#20 of 56 OFFLINE   Mark Seaton

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Posted October 07 2004 - 02:50 AM

Hi Joe,

Quick suggestion... take the boost for the low end and cut at ~45Hz & 80Hz about 1-2dB less than you have now. Now re-calibrate and set your sub 1-3dB hotter. The hotter you calibrate the sub, the more you might want to keep the full -7dB near 80Hz. That might yeild a nice balance between the two qualities you described before. If putting a lift to the low end, the range you want as the peak is roughly 25-35Hz.

Enjoy...
Mark Seaton
Seaton Sound, Inc.


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