[bassboy]

This is a drawing of my current audio room.  (You may or may not remember that I had big plans for a much bigger, better room but ultimately they didn't work out, so I'm stuck in this little room - at least I got started on making some diffusors.)  It measures 11.25 x 14 and 7.5 feet high.  The red line in the drawing is the doorway to the closet. The closet is pretty big at about 155 cubic feet total volume.  The blue line is the door to the hallway, the green lines are my dipole speakers and the brown circle is my head (and sometimes mic location since I've recently tried to do frequency response measurements.  The floor is carpeted.

This is a picture of my measured response from the listening spot.  I used arta (which I just started using a couple of days ago) on my laptop, using the mic built in to the laptop.  It's a low quality mic and it's embedded into the case and I have no idea how to calibrate it, so don't worry about the general downtilted response as frequency increases, since even outside measurements show the same downtilted response trend.  I'm only using this to try to graphically determine the general affected frequencies and severity of my very unpleasant bass boom problem.  When I rearrange the room mirror image, so that the listening spot faces the closet the response is a bit different but not any better.



I'm not sure how to approach this since I don't know if / how much the closet is contributing to this mess, and also not sure if I can fit enough treatment in the room to fix this since the issues I am worried about are all well below 100 hz.  I used software to calculate the room's and the closet's standing waves, and I also calculated the helmholtz resonance of the closet (with the sliding doors full open and mostly shut) and still have no idea where this huge problem is coming from.  So...

Which option below sounds best?

1.  Disregard the closet completely and treat the room extensively with broadband and low bass sealed panel traps.  (I don't think this will be very effective at 50 hz)
2.  Cover most or all of the closet opening with rigid fibreglass type absorbers and treat the room extensively.  (I don't think this will be very effective either)
3.  Completely seal the closet and turn it into a sealed panel trap and treat the room extensively.  (I think this might work but it's a drastic measure, since the room is fully and nicely finished and I'd have to frame in the existing doorway opening)
4.  Reduce the doorway opening size so that it's helmholtz resonance is tuned to ~60 hz and treat the room extensively.  (Again, pretty drastic, with the framing and such.)
5.  Completely seal the closet and throw a couple of 15 inch IB drivers in there and treat the room extensively.  (Can't see how this would help but I don't think it would hurt the situation)
6.  Other possibilities???
7.  Try to find a better room.

[Sonny]

ofcourse option #7 is best, but we know that's not possible.

I would, since I've had this problem before in a small room, build Jon Risch's bass traps (cynlinder) and place them in the corners (all 4 of them).  That's the only way to get rid of the boom, but they have to be some big traps (diameter wise, like 24" by 48") to absorb the 50-60hz bump you have.

Allt he others will actually be worse as the other stuff is not meant to capture the low frequencies that you have an issue with, thus will reduce the mid-range, which will exaggerate your boom even more!

T

[MaxCast]

Did you run the FR with the doors off the closet?
You could try stuffing the closet with rolled fiberglass in bags.  Keep your receipt.

[bpape]

Agree with Sonny to a point. In addition, I wouldn't make too many assumptions until you can measure with a reasonably accurate mic.  Those built-ins have horrible response on both extremes - not just the top end.  Also, It appears, if the drawing is to scale, that the seat is back a bit too far in the room - if the door to the closet is closed.

Bryan

[bassboy]

Thanks for your comments everyone.

Sorry, the drawing is not to scale, these were taken about 4.5 - 5 feet from the back wall (closet) at head height when seated.  The closet has sliding doors, so it's either full closed or half open.  They were half open for these measurements, but closing them makes very little difference.  And since they are sliding doors it will never be possible to seal them.  They rattle so I am going to remove them.

You could try stuffing the closet with rolled fiberglass in bags.  Keep your receipt.

That's a great idea, and sooner or later you always need a bunch of insultation.  It's a big closet though, and may require several hundred dollars worth of insulation.  BUT I just noticed that home depot only seems to carry roxul brand now, and the interior wall "safe'n'sound" type (25% denser than flexibatt - but still less than half as dense as 705 I think) is only a couple $ more than ordinary insulation.  http://www.homedepot.ca/webapp/wcs/stores/servlet/CatalogSearchResultView?D=972188&Ntt=972188&catalogId=10051&langId=-15&storeId=10051&Dx=mode+matchallpartial&Ntx=mode+matchall&recN=112022&N=0&Ntk=P_PartNumber

...they have to be some big traps (diameter wise, like 24" by 48") to absorb the 50-60hz bump you have.

This is what I figured, no matter what type of traps I use they are going to have to be pretty big.

Those built-ins have horrible response on both extremes - not just the top end.

What mic (and preamp if necessary) do you recommend (are there any inexpensive ones)

[bpape]

You can use a Radio Shack meter.  Mic isn't great but a lot of measurement programs have calibration files to compensate.  A good program to run is Room EQ Wizard.  It's a free download available at www.hometheatershack.com  There is a .cal file there for the meter also.

REW will not only give you frequency response, but also decay time, waterfalls, and impulse response as well as an RTA function to help see what happens in real time as you move the mic/speakers/etc.

As for seat placment - if you were 4.5' from the closet (open) and the closet is approx 2.5' deep, you're basically dead center in the room length wise which isn't a good place.  I think taking off the doors is a good idea.  If you want to do some temporary playing with bass control, buy some rolls of insulation and leave them in the bag and play with them in your room.  They can always bee returned.

Bryan

[bassboy]

Thanks Bryan.  REW was going to be my next download if arta proved tricky.  I'll get that and play with it too.

In the meantime, just for the sake of interest, this is the ambient noise floor a few meters outside my house, out in the country, on the lawn at midnight.  It was pretty quiet, by far the noisiest thing was the laptop hard drive spinning, and it's a quiet machine.  There might be a bit of low frequency noise from the highway 10 kilometers away but overall very quiet.



Useless info, but interesting nonetheless.

[bpape]

There must be some built-in EQ at work in your machine.

Bryan

[Scottdazzle]

Bassboy,

I have an almost identical listening room.  I removed the closet doors (they now live in the garage) and got a large improvement.

[Brian Cheney]

Since your room is small bass problems tend to be exaggerated.  Bass traps are a good idea but won't solve the problem by themselves.

You might try applying a bass cut via parametric EQ at 75 Hz, the floor-to-ceiling room mode for a 7.5ft ceiling.  About 4dB reduction should be fine, with a Q around .25.  Several prosound manufacturers offer such machines at low cost. less than $300. 

This should tame just about all your remaining problems.

[bassboy]

Bryan - not sure what's up with the laptop, maybe it is eq'ed internally (not sure why they would do that though, since it's obviously not eq'ed flat), maybe it's incredibly sensitive to it's own very low level noise, maybe the whole mic system is just junk in general.  It's a newish (few months old) hp pavillion 6000 series, one of the black shiny ones - quite quiet until the fan turns on.  I knew before I started that it would be somewhat (or maybe completely) inaccurate, but I figured for the time being, if I did pink noise measurements outside and inside I could just subtract the difference as a cheap and dirty calibration method.  Obviously I'd have to drag the stereo outside to get my outside pink noise measurements, so that probably won't ever happen anyway since I'll just get a better mic sooner or later.

Scotthobby - that's great news and just what I wanted to hear.  I'll try it asap, fingers crossed.

Brian - this is exactly what I was fearing - that no amount of treatment will really be as effective as a better room.  Thanks for confirming my continuing nightmare.

So it looks like -

- $500 for 12 bats (bags/bales) of insulation to distribute throughout the room and closet
- $300??? for parametric eq (probably more with shipping), might as well get the DEQ2496
- $100??? for a mic, might as well get the one that goes with the 2496
- $200??? for the treatments to cover the rest of the frequency spectrum

At this point I'm going to have to do some serious thinking about whether I want to try to wrestle with this room or begin building a dedicated room from scratch - either within an outbuilding or a completely separate structure (since compromise is too hard to come by inside the house and there's no more available rooms inside).  It's within grasp financially RIGHT NOW and I've been planning for it but I wanted to learn a whole lot more about that type of project before wasting thousands of $ on stupid mistakes.

[bpape]

If you can build a dedicated space from scratch specifically designed for audio, that's almost always a preferable solution.  Just understand that even in there, some treatment and potentially some bass EQ is still going to be required.  NO room is perfect and EQ won't deal with the time domain. 

If you play your cards carefully, you can have both and not waste any money.  Use the insulation now for treatment and reuse when you build the space.  Keep in-room treatments to the basics (corner treatment and early reflections) so they'll be reusable in the next room.

Bryan

[Bob in St. Louis]

- $300??? for parametric eq (probably more with shipping), might as well get the DEQ2496
- $100??? for a mic, might as well get the one that goes with the 2496

To help save you some cash, how 'bout this:

Would this work for the EQ  ($100): http://cgi.ebay.ca/Behringer-Feedback-Destroyer-Pro-DSP-1124P_W0QQitemZ320240102796QQihZ011QQcategoryZ23790QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247
I tried to find one on ebay Canada to save you shipping/tarif/duties, but the shipper is from the US anyway. 

Regarding the meter, to save $50 you could get the Ratshack meter and download the calibration file. I assume ALL meters are going to have a certain amount of a software calibration adjustment needed anyway?? So you may as well get one that's halfway decent and save a few dollars. Just a thought.

By the way, looking at your outdoor FR graph, you must have some badass crickets to make chirping noises at frequencies THAT low. 
Must be a Canadian thing. 

Bob

[bassboy]

Hey Bob, thanks for stopping by.  I haven't studied the behringer products indepth and in fact I don't even know what most of the features on these things are for.  But from what little I have absorbed on the subject, here's what I think I know.

The feedback destroyer products (and I think there are more than 1 of them) do indeed have parametric eq, and can apply it to 2 channels.

The deq2496 is actually a 4 way crossover first and foremost I think (which is INCREDIBLY valuable and means I could let my 10 year old car audio xo out to pasture) and as such it can apply it's parametric eq to 8 channels.  It's packed with other features too as far as I can tell and just way more flexible and usefull than a feedback destroyer type unit.

The behringer measurement mic is incredibly accurate down to 15 hz as per advertisements, so I assume it needs no calibration.  It does however need a preamp, and the behringer preamp is also packed with features you don't usually get with a regular preamp.

I looked up these items on ebay just for an idea of cost and it's not quite as bad as I thought.
$250 - deq2496, comes with 2 free optical cables and free shipping (US only)
$49 - behringer measurement mic
$39 - behringer mic preamp
$??? - shipping cost (to canada) is probably not too bad if all 3 items are shipped together

I'm not really sure what I'd do with free optical cables, what I really need is a bunch of rca / balanced cables, and that's probably not going to be cheap.

The only reason I don't already have a deq2496 (for the crossover abilities alone) is because I haven't decided whether to do my crossover with software (thuneau software) or hardware (behringer).  I'm not sure if the software has built in parametric eq or auto eq features, since it's just crossover software, but it might, and it's cheaper than the equivalent hardware crossover and doesn't need special balanced cables.  Still need a better mic though regardless of whether I choose hardware or software eq.

I'll check if the thuneau software has parametric eq, if not the behringer is the obvious choice.

[mgalusha]

Actually the DEQ2496 is an equalizer/DSP and not a crossover. Behringer does make several XO's such as the DCX2496, which is the same one that is used with the Emerald Physics CS2's. The DCX2496 does have some parametric EQ capability but not on the level of the DEQ2496. I've been using a DCX2496 for quite some time and it works very well though my unit is far from stock.

Since both Behringer products are pro audio gear, the levels are quite a bit higher than consumer gear. It may not be a problem but is something to be aware of.

mike

[bassboy]

Thanks for correcting that for me.  One thing I did notice when searching ebay is that a LOT of the behringer products have parametric eq, so I guess it's just a matter of finding one that has other attractive features at a decent price.

Since both Behringer products are pro audio gear, the levels are quite a bit higher than consumer gear. It may not be a problem but is something to be aware of.

The levels of what? 

Do you find the sq mods on these behringer products necessary when used with a (very) modestly priced system or is it only an issue with really high end systems?

[mgalusha]

The levels of what? 

Do you find the sq mods on these behringer products necessary when used with a (very) modestly priced system or is it only an issue with really high end systems?

The level of the analog output's. Most pro gear runs about 14dB higher levels than consumer gear. This has the potential to overload whatever is being driven by the pro gear. Sometimes folks build a voltage divider to cut this down to consumer levels, sometimes as part of a balanced to unbalanced converter.

As for the mods, I can't say if it's an issue, I had the opportunity to compare a stock vs modified unit side by side and for me the differences were enough that I couldn't live with the stock solution.

Mike