2nd time around..measurements

[Mattlock]

JohnM wrote:

Just lower volume - was the sub playing particualrly loud when generating that impulse response? Otherwise might just be the nature of the drive unit.

Actually it wasnt playing that loud. Another thought....could it be possible leakage around the top and bottom endcaps? I havent sealed it yet but to be honest they are very tight anyway..had to hammer down.... Another thought...my doors in my room rattle pretty loudly but this is probably a higher hz anyway....

thanks John for the thoughts
Matt

[Mattlock]

Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....

Question: I realize gains have to be used with caution but at what point (ie amount) is the gain considered "pushing the boundary of reasonableness"?

thanks
Matt

[MakeFlat]

Mattlock wrote:

Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....

Question: I realize gains have to be used with caution but at what point (ie amount) is the gain considered "pushing the boundary of reasonableness"?

thanks
Matt

That depends on the sub's power.

You can push the gain as long as you have the headroom. For the sake of explanation, let's just say that you have 6 dB headroom for the sub, like your loudest movie is 6dB below the power reserve of the sub. Then you can push 3dB and still maintain a 3dB headroom for the sub, just in case you happen to crank the avr volume control a little higher than normal.

A little boost is not going to cause an issue. If however, the boost does practically nothing, you may as well not apply the boost. That 49Hz dip is likely much deeper than visible on the graph, so it's not going to budge. The value of adding 6dB to a 16dB dip is questionable.

[Jman]

Mattlock wrote:

Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....

Question: I realize gains have to be used with caution but at what point (ie amount) is the gain considered "pushing the boundary of reasonableness"?

thanks
Matt

Earlier I asked if you had room for bass traps. They'll reduce those deep/narrow nodes that you're getting. The problem with trying to fix deep notches with EQ is that it usually does little or nothing. That's the nature of room nodes. The traps reduce the room interaction, which are what cause them in the first place.

The front left and right corners would be a great place for 2 traps. Is that door at the front right used? You could also put one at the back where the sonosub is. The traps would need to be 2' wide and mounted at 45 degree angle at 2 boundaries like 2 walls, wall/ceiling, wall/floor.

[DrWho]

It also looks like your sub is tuned too low, and the ports aren't being loaded fully. It's hard to tell from the pics, but the measurements indicate that the sub is about 6 feet tall? (on the inside) What's the internals of the sub look like?

Also, is your mic moving inbetween measurements? If you think about it, it doesn't make sense for your dips to move around in frequency (unless of course you move the mic around).

[tnargs]

Mattlock wrote:

....Does it make any sense for me to consider a 2nd sub up front if indeed I cannot get the peak/dip range shortened?

It certainly makes sense. Research has shown that multiple subs, up to 4 or 5, increases the listening area that gets good (smooth) bass.

Arg
http://tnargs.googlepages.com/tnargsound

[Mattlock]

tnargs wrote:

It certainly makes sense. Research has shown that multiple subs, up to 4 or 5, increases the listening area that gets good (smooth) bass.

Arg
http://tnargs.googlepages.com/tnargsound

I assume a 2nd sub would need to have the same tuning as my first? REad that somewhere....Obviously my original sub SVS PB12 isnt as low as my DIY (13hz) so I had planned on selling that and possible building a 2nd tuned to 13hz

[Mattlock]

DrWho wrote:

It also looks like your sub is tuned too low, and the ports aren't being loaded fully. It's hard to tell from the pics, but the measurements indicate that the sub is about 6 feet tall? (on the inside) What's the internals of the sub look like?

Also, is your mic moving inbetween measurements? If you think about it, it doesn't make sense for your dips to move around in frequency (unless of course you move the mic around).

Yes Sub is about 6 feet tall. The inside has a about 3 layers of 1/4 inch polyfill around the tube with more polyfill on the Top Endcap (opposite the driver) and also about 2-3 inches wrapped around the port.

My mic has not moving during the testing.

What suggestions do you have based on this info? I have not sealed by endcaps so I can get back inside fairly easily if I need to.

thanks for the advice....as I am still learning

[Mattlock]

Jman wrote:

Earlier I asked if you had room for bass traps. They'll reduce those deep/narrow nodes that you're getting. The problem with trying to fix deep notches with EQ is that it usually does little or nothing. That's the nature of room nodes. The traps reduce the room interaction, which are what cause them in the first place.

The front left and right corners would be a great place for 2 traps. Is that door at the front right used? You could also put one at the back where the sonosub is. The traps would need to be 2' wide and mounted at 45 degree angle at 2 boundaries like 2 walls, wall/ceiling, wall/floor.

The door is used but I can look around and see about possibly adding some traps..Do you have any websites or pics of traps installed so I can get a feel for what you are describing?

I did a little searching around and several websites had the traps mounted vertically on walls or on the ceiling...I can certainly do that all over my theater...the 45 degree angle might be tough though....

Question: Would traps also help reduce the "Den shaking" that goes on right above my theater room which is in the basement?. Last night I had WOTW cranking and my lovely wife informed me that the effects upstairs were "ridiculous" her.... me




thanks
Matt

[Jman]

The traps won't lessen transmission to other rooms. The reason for the 45 degree angle is to maximize the depth from boundary corner to the edge of trap. With a 2' wide trap, that gives you about an 18" depth. As you lessen the angle you get closer to what is just the thickness of the trap itself - i.e when you reach 0 degrees, your 3" thick trap only has a depth of 3" so now you're only absorbing down to ~200hz. With a depth of 18" you can get full absorption down to 100hz and still good performance below that.

[clubfoot]

Mattlock wrote:

Question: Would traps also help reduce the "Den shaking" that goes on right above my theater room which is in the basement?. Last night I had WOTW cranking and my lovely wife informed me that the effects upstairs were "ridiculous" her.... me

thanks
Matt

You would need to at the very least, isolate the ceiling sheet rock from the floor above using something like sheet rock Z channels, and insulation between the ceiling joists. Of course if you secured the walls directly to the ceiling joists,...it's not going to make your wife very happy upstairs in WOTW

[tnargs]

Mattlock wrote:

I assume a 2nd sub would need to have the same tuning as my first? Read that somewhere....Obviously my original sub SVS PB12 isn't as low as my DIY (13hz) so I had planned on selling that and possible building a 2nd tuned to 13hz

Not necessarily needing the same tuning... after all, two different subs might even out the irregularities of each other.

Recommended positioning for a 2-sub system is one centre front and the other centre rear, or one on the midpoint of each side wall.

[Wayne A. Pflughaupt]

Mattlock wrote:

Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....

Hmm... Doesn’t look much different than the others. I take it you haven’t moved it? You might want to take a look at these two threads, where people with highly problematic response, due to unusual placement, realized instant improvement just by re-locating the sub to a good corner. Good chance it’ll eliminate your 49 Hz problem as well.

http://www.hometheatershack.com/foru...html#post70673

http://www.hometheatershack.com/foru...get-curve.html

Regards,
Wayne

[DrWho]

Mattlock wrote:

Yes Sub is about 6 feet tall. The inside has a about 3 layers of 1/4 inch polyfill around the tube with more polyfill on the Top Endcap (opposite the driver) and also about 2-3 inches wrapped around the port.

My mic has not moving during the testing.

What suggestions do you have based on this info? I have not sealed by endcaps so I can get back inside fairly easily if I need to.

thanks for the advice....as I am still learning

What are the dimensions on your port and where is the driver and port located in the enclosure?

The 6 feet height of your cabinet is going to give you standing waves inside your enclosure. At 1/2 wavelength you're going to get the first null, which happens at ~95Hz...looks to be exactly around 98Hz or so from your measurements.

Anyways, you're going to end up with a response that looks like this:

This should also be showing port resonances too, but I'm not sure exactly what size and tuning you have for your ports so it will probably be different. Heck, it's a different driver too...only intended to demonstrate the effects of the cabinet and ports being "too large".

You probably won't be able to address the ports, but you could try to break up the standing waves inside the cabinet. The ~3" of absorption you have right now will only be good down to about 1kHz. You would need 3ft to be effective down to 90Hz (yikes). You wouldn't want to go that low anyway since it will effect the Q of the enclosure too.

[Mattlock]

DrWho wrote:

What are the dimensions on your port and where is the driver and port located in the enclosure?

The 6 feet height of your cabinet is going to give you standing waves inside your enclosure. At 1/2 wavelength you're going to get the first null, which happens at ~95Hz...looks to be exactly around 98Hz or so from your measurements.

Anyways, you're going to end up with a response that looks like this:

This should also be showing port resonances too, but I'm not sure exactly what size and tuning you have for your ports so it will probably be different. Heck, it's a different driver too...only intended to demonstrate the effects of the cabinet and ports being "too large".

You probably won't be able to address the ports, but you could try to break up the standing waves inside the cabinet. The ~3" of absorption you have right now will only be good down to about 1kHz. You would need 3ft to be effective down to 90Hz (yikes). You wouldn't want to go that low anyway since it will effect the Q of the enclosure too.

the port is an 8x26.75. The port (top) is exactly opposite the driver(bottom), ie sonosub design. My crossover is set at 80hz so my focus has been below 80hz.

[DrWho]

Mattlock wrote:

the port is an 8x26.75. The port (top) is exactly opposite the driver(bottom), ie sonosub design. My crossover is set at 80hz so my focus has been below 80hz.

That doesn't mean it's not going to be an issue...

Harmonic distortion will trigger the resonances, not to mention the crossover isn't instantaneous so you've still got the driver itself triggering them too. It's probably why your distortion measures so high.

[Mattlock]

Since my sub is too big to re-locate we moved my sitting area forward 3 feet, ran REW and applied some filters. My target needs to be raised but my curve is improving.

I give credit to "Kbgl" who has been coming over and helping me out. He guessed that moving forward 3 feet would help based on his measurements and sure enough he was right. We tested it out with WOTW and I could definitely tell an improvement with the sounds in the lower range...I'm no audiophile with trained ears but I could tell the difference in the lower end stuff

Now I am dealing with the tempation to put a matching 2nd sonosub beside my current one...twins.... 1400 liters total... me wife


The first graph is with the sitting area moved forward 3 feet.
The second is with sitting area in the original position (back 3 feet)

I am also wondering if I can get any benefit in the lower end (<80hz) with adding bass traps. Any thoughts on that? For budget reasons I may have to go with some DIY traps especially if I am remotely considering a 2nd sonosub Got to spend my $$$ wisely. Of course I am now thinking with results I ought to focus on possibly a 2nd sub vs. traps....but I dont pretend to know all the advantages of traps.


Matt

[Jerm357]

Now that looks much better. Are these new graphs raw or do you have Eq already applied to them?

[Mattlock]

Jerm357 wrote:

Now that looks much better. Are these new graphs raw or do you have Eq already applied to them?

EQ is applied on both...2nd one doesnt make much sense because the filter settings for the +3 feet position were left on and the couch was moved but it is very similar the curve.

[SteveCallas]

HUGE improvement! If you can't move the sub, move your seat = brilliant I came across this thread late, but I want to comment on a few things I read.

DrWho wrote:

It also looks like your sub is tuned too low, and the ports aren't being loaded fully.

Not at all. With the driver being used, the enclosure volume and tuning were chosen to yield a gently sloping low end that would mesh well with a bit of room gain. The valley in response in the low end was clearly a room effect, not subwoofer response related, as can be seen from his new measurement with the seat moved. The new measurement is a great example of how extended and powerful the in room low end will be with a LLT design. Mattlock is either using filters to go for a house curve or he is benefitting from strong low end gain to achieve that rising low end - either way, in nearly every case, the result is deep, flat, in room response.

The 6 feet height of your cabinet is going to give you standing waves inside your enclosure. At 1/2 wavelength you're going to get the first null, which happens at ~95Hz...looks to be exactly around 98Hz or so from your measurements.

Again, not the case, that dip is merely another room related or phase issue. If you take a look at Ilkka's testing of a large and low tuned sub, you'll see that the FR is not affected in the least by any type of standing wave created inside a large enclosure. You do benefit from decreased harmonic distortion at that frequency, but it doesn't affect FR.

This should also be showing port resonances too, but I'm not sure exactly what size and tuning you have for your ports so it will probably be different.

Port resonances will show up as a blip in the FR, but with his first resonance being ~250hz and a 24db/octave 80hz crossover in play, it's a non issue.

It's probably why your distortion measures so high

Nah. Though a different driver is being used (Fi Q18 vs TC2k 15), you can see again from Ilkka's measurements that that type of a design will keep distortion very low throughout the subwoofer range. These high excursion drivers sometimes have high inductance which can result in increased distortion as frequency rises, but with the 80hz crossover, distortion should be quite good at even spirited levels.



Mattlock, are you using filters to achieve that rising low end?

[kbgl]

We tilted the response a bit using a very wide bandwidth filter out around 600 Hz. (Possibly more than necessary.) Also added a little boost to flatten it out a little between 10 and 20 hz. We only had about an hour to play with it, and we were both learning how to use the REW software. We made all the filter settings manually. This was the first measurement after we entered the eq filters.