Rear located IB

**collo** · **02-15-07, 10:35 PM**

Quote:

Chrisbee wrote:

I've been getting away with a 20Hz + 16dB 120/60 BFD boost for ages now.

I'll file that away for when the BFD turns up

**htnut12** · **03-06-07, 12:52 PM**

I have a rear IB to which a front IB will be added in the next few weeks. I have boosted at 8 hz using a Rane and got flat from 10 to 50 hz. I cross over at 40 to the mains.

**collo** · **03-06-07, 04:40 PM**

Quote:

htnut12 wrote:

I have boosted at 8 hz ....

Do you have any excursion problems with DVDs containing Ultra-low content, such as WOTW or Black Hawk Down?

**htnut12** · **03-06-07, 07:32 PM**

Don't have those DVDs but I have had no problems with HD DVDs with plenty of low content, Serenity, Terminator 3, Doom, etc. And no problems while doing the tuning and running sine waves through the system.

**collo** · **03-06-07, 10:20 PM**

All good info. You'll have to give us an update when you add your 2nd IB - maybe even an REW plot.

**htnut12** · **03-06-07, 10:40 PM**

Sorry I don't do the REW. Just hold my trusty Rat Shack meter and dial and tweak. If I plot my measurements it is a flat line, because I dialed and tweaked until the measurements fit a flat line.

I found a nice room mode calculator and found a good place for the front IB. Will work out really great because it will put the drivers in an area of the attic we do not use for storage, or for my heat duct runs. Both my seat and my lovely wifes seat will be relatively smooth response once the front IB is in. Now if I can just convince her that I need to poke a hole in the ceiling.

**Sonnie** · **03-07-07, 08:59 AM**

Quote:

Just hold my trusty Rat Shack meter and dial and tweak. If I plot my measurements it is a flat line, because I dialed and tweaked until the measurements fit a flat line.

I assume you are at least using correction values with that RS meter and some test tones along with a BFD, otherwise I highly doubt you would plot a flat line. If you did you'd be the first person I've ever known on planet earth to do it...

**htnut12** · **03-07-07, 11:30 AM**

Sonnie,

I start out with the trusty Rat Shack and a signal generator to be sure that the various and sundry parts in between are at least giving me a chance to succeed. Then I switch to test tones played through my system. I do a quick compare without any EQ to see that there is at least some correlation to the signal generator into the amp. If I am sure that the system isn't mucking up the measurements. I use the Rat Shack and my table of what the Rat Shack has to read to give me flat. i.e. desired measurement at a given frequency minus the correction factor. I then start setting filters (Thomas W. on the Cult gave me the idea of using two of the Rane bands to get a really low, 8hz, filter). Then comes the play adjust play adjust play adjust play adjust all up and down the frequency regime of interest until I get the desired Rat Shack reading at each frequency. Took a bit over a half hour for me.

Because I get the flat reading dialed in with the EQ of course a plot is going to come out flat. As an engineer I know it is not flat. The measurements certainly have a band of uncertainty. And I never ignore the MKV earball. If it measures "good" and sounds "bad" what's the use of keeping it that way. I guess we could call it a Chez HTNut curve.

**Chrisbee** · **03-07-07, 01:15 PM**

Somebody has to ask (so it may as well be me): Why don't you use REW?

Edited by moderator: Please see this thread for answer and the topic concerning BFD hum.

**collo** · **03-19-07, 05:54 PM**

The BFD and EP2500 are now installed.

I must say that I was impressed that the REW predicted response with filters engaged exactly matched the new measured response.

Here's what I'm running (before EQ in grey, after in red)

The filters...

The loudest part of the crash sequence in Flight of the Phoenix gave 115dB (RS meter uncorrected) at the seating position. I think the peak is around 30hz, so adding 5db correction would give approx. 120dB

It was really loud - dust came down from the ceiling....

**WillyD** · **03-19-07, 05:59 PM**

Real nice, Collo!

**terry j** · **03-19-07, 09:24 PM**

woo hoo, a trip to Newcastle is getting closer and closer!!

I too have found the filters suggested by REW to be very accurate, certainly gives faith in the whole shebang.

**Sonnie** · **03-19-07, 10:19 PM**

Very good looking response! I'm assuming you increased the volume on the corrected measurement since I don't see any boosting anywhere.

What does it look like below 15Hz... say down to 10Hz? Did you graph it to there?

Quote:

It was really loud - dust came down from the ceiling....

You mean you don't dust your ceiling...

Btw: If anyone gets to wondering, I moved the BFD hum discussion to the BFD Forum BFD and hum, since it was getting way off topic and taking up Collo's valuable real estate.

**collo** · **03-20-07, 04:35 AM**

Terry - you'll be welcome whenever you make it up this way!

Sonnie - The corrected graph was just moved up using the trace offset feature in REW.

The actual calibration worked out quite well.
Here's what I posted on my IB page.....

The BFD has a bar graph showing input level, including yellow warning and red clipping indicators.

I found that adjusting the subwoofer output of the AV receiver downward by -6dB allows me to use my existing "subwoofer safe" stickers, as detailed on the SPL Levels page

The resulting output of the BFD will drive the EP2500 to pretty much the required level when the EP2500 attenuators are set to maximum. This is a good thing, as it means the volume can't be turned up too high for the drivers to handle

I've since added a resistive divider (5k pot) between the AV receiver and the BFD, which allows me to use the same AV settings as I used in the past.

The dust came through the ceiling.....

**collo** · **03-20-07, 04:52 AM**

Heres the 10hz graph...

(RS SPL meter with corrections applied)

**norpus** · **03-20-07, 06:40 AM**

Love your work Collo

I'll hitch a ride with terry

after bathurst

**terry j** · **03-20-07, 07:19 AM**

collo better be careful, could be a whole minibus of melbournites making the assult on Newcastle aftre the races!!

Hhhmmmm, thats not a bad idea.

**collo** · **03-20-07, 02:55 PM**

Norpus, you'll be welcome too.

hmm .. Infinitely time two or three...

I guess that would make us "Baffled beyond measure"....

**collo** · **04-11-07, 04:02 AM**

I've been following Rodny's conversion from IB to LLT.

I don't know if it is for me, but a quick look with WinISD suggests that a few 10inch flared ports would come in handy.

As it happens, I've been developing some for a guy in the UK who's into SPL competitions. This pair have 40mm flares, although the next set will have 45mm flares on the outside.

Does anyone think that there's a market for this sort of tomfoolery?

**Chrisbee** · **04-11-07, 04:14 AM**

Very neat. They'd make ideal neck braces after fighting with an IB up in the roof space.

**Sonnie** · **04-11-07, 09:51 AM**

I think there would definitely be a market... although I wonder how you would install them. Of course I don't want to bog your thread down discussing it, but they do look very interesting and something I'm sure a lot of people would be interested in.

**SteveCallas** · **04-11-07, 11:26 AM**

NICE

I'd measure the IB response at the seat down to 3hz or so just to be sure the rolloff at 14hz is in fact the start of the rolloff and not a null. If it is, a 7-8hz tuning would make your system something of legend and folklore

**collo** · **04-11-07, 05:21 PM**

Quote:

Sonnie wrote:

... although I wonder how you would install them. Of course I don't want to bog your thread down discussing it, but .......

They would need to be glued in. It doesn't matter too much if the thread moves around a bit - the IB has been fairly well covered now.

Most DIY'ers make do with a routed rollover, but for those that wanted something a little larger, or smarter, these would fit the bill. I'm expecting to be able to drop these at your doorstep in the US for around $90US (plus any fees on Bank cheque)

Quote:

SteveCallas wrote:

...If it is, a 7-8hz tuning ............

I don't want any more output down real low - the house actually moves sideways ( feel the wooden floor move, windows moving, TV moving so much you can't focus on the screen) Probably not a good idea to go any further.

I would probably tune a bit higher to see if there is any more "punch" as has been suggested in Rodny's thread and elsewhere.

I've still got some more thinking to do on this....

**SteveCallas** · **04-11-07, 05:26 PM**

That's gotta be the first time I've heard someone say they don't want to extend lower

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