15" Crossover Question *PIC*

[zinger084]

http://www.partsexpress.com/images/295-560m.jpg

Provided Link: 15" Sub (http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=295-560)


I finally finished the construction on my 15" project but I have a few questions.

1st
Where should I set my crossover at? I peak around 70-75Hz, but I really don't know how high to go with a 15"? Im assuming somewhere around 80-90Hz would be max?

2nd
This box has 2 4" ports and is tuned to 21Hz. It is centerered directly in the middle back of my room with the ports facing towards the center of the room. Although in some spots of the room it is loud and audible, in other parts, it sounds like it is almost dead and inaudible. I am guessing it is because of the limited placement area i had for it being placed in the middle back, but im not sure. POssibly because it is tuned so low? too small of room (11'x13')?....

3rd
I thought that this sub could handle 300rms but with the dayton plate amp rated at 250rms (272measured), and the level not even half way up, this beast is almost hitting Xmax. Any ideas?
Any help on either issue would be appreciated.

[ccochran]

> 1st
> Where should I set my crossover at? I peak
> around 70-75Hz, but I really don't know how
> high to go with a 15"? Im assuming
> somewhere around 80-90Hz would be max?

The answer depends on what you are crossing it over to. If you have some very small mains, you will need the subwoofer to fill in a little higher.
However, if you are having some "peaks" in your response around 70-75Hz, you could try lowering the crossover frequency below this and help carve off that peak.

> 2nd
> This box has 2 4" ports and is tuned to
> 21Hz. It is centerered directly in the
> middle back of my room with the ports facing
> towards the center of the room. Although in
> some spots of the room it is loud and
> audible, in other parts, it sounds like it
> is almost dead and inaudible. I am guessing
> it is because of the limited placement area
> i had for it being placed in the middle
> back, but im not sure. POssibly because it
> is tuned so low? too small of room
> (11'x13')?....

Room placement is the problem. The problem will exist no matter where you put it, its just that some places will be worse than others. The small room should actually help with the lower bass.
The dimensions of the room do effect the response. It all depends on how far the sound wave has to go to bounce off a wall and return back to you. THere is an Excel calculator that attempts to predict the room response based on the dimensions and placement. I'm not sure its highly accurate given the other variables that play a roll (furniture, carpeting, doorways to other rooms, etc.)

> 3rd
> I thought that this sub could handle 300rms
> but with the dayton plate amp rated at
> 250rms (272measured), and the level not even
> half way up, this beast is almost hitting
> Xmax. Any ideas?
> Any help on either issue would be
> appreciated.

The power rating on most all subwoofers is the thermal rating - how much it can handle before burning up. I'm going to guess your box volume is around 8Cu.Ft. if you have it tuned to 21Hz with a pair of 4" ports. Using Unibox, I'd say you will have to limit it to about 150Watts.
Also keep in mind the output power of the amp depends on the signal being sent to it. If the source signal is relatively strong, then you will not need to have the gain on the amp up all the way to get the full power out of it.

[bogie]

> I finally finished the construction on my
> 15" project but I have a few questions.

> 1st
> Where should I set my crossover at? I peak
> around 70-75Hz, but I really don't know how
> high to go with a 15"? Im assuming
> somewhere around 80-90Hz would be max?

I've got the crossovers my 240 watt amps turned up to 160, and I just let the AVR handle it - I also like a little extra thumpage... The Denon 2803 AVR's LFE crossover is usually set at 60hz, but I'll run it up to 125 for movies that I suspect will be Really Loud.

> 2nd
> This box has 2 4" ports and is tuned to
> 21Hz. It is centerered directly in the
> middle back of my room with the ports facing
> towards the center of the room. Although in
> some spots of the room it is loud and
> audible, in other parts, it sounds like it
> is almost dead and inaudible. I am guessing
> it is because of the limited placement area
> i had for it being placed in the middle
> back, but im not sure. POssibly because it
> is tuned so low? too small of room
> (11'x13')?....

Put it in the listening spot, and crawl around until it sounds nice. Rearrange the furniture.

> 3rd
> I thought that this sub could handle 300rms
> but with the dayton plate amp rated at
> 250rms (272measured), and the level not even
> half way up, this beast is almost hitting
> Xmax. Any ideas?

What size box are you using? How long are those 4" ports? Thus far the only time I've xmaxed my twin Q15s (17x34 room) was in Sin City...

> Any help on either issue would be
> appreciated.

[bogie]

> Also keep in mind the output power of the
> amp depends on the signal being sent to it.
> If the source signal is relatively strong,
> then you will not need to have the gain on
> the amp up all the way to get the full power
> out of it.

True - I can change the "strength" of my LFE signal both via my AVR's setup, and via my Behringer Feedback Destroyer. I've got my AVR set to -9 for the subs, so that I can punch 'em a little if I feel like it.

[scottanderson]

> 3rd
> I thought that this sub could handle 300rms
> but with the dayton plate amp rated at
> 250rms (272measured), and the level not even
> half way up, this beast is almost hitting
> Xmax. Any ideas?
> Any help on either issue would be
> appreciated.

Sounds like a problem with your box size/tuning/loss not loading the cone right. I have 2 of these drivers and I'd have glass on the ground outside before they clipped. We're talking like 116-120db here without clip. Give your box specs and maybe we can find a fix.

[zinger084]

Scott,

Let me know what type of parameters you are asking me for and i can let you know. To start:

Vb=8854.5 in^3
Ports: 2 @ 4"dia x 25.96 inches long
Tuned to 21.01 Hz.

All using WinISD Pro which I have used for about 4 years now...

> Sounds like a problem with your box
> size/tuning/loss not loading the cone right.
> I have 2 of these drivers and I'd have glass
> on the ground outside before they clipped.
> We're talking like 116-120db here without
> clip. Give your box specs and maybe we can
> find a fix.

[Some Guy]

> I finally finished the construction on my
> 15" project but I have a few questions.

> 1st
> Where should I set my crossover at?

Dunno. What are you crossing over to?

> I peak
> around 70-75Hz, but I really don't know how
> high to go with a 15"? Im assuming
> somewhere around 80-90Hz would be max?

You can go higher. You can go lower. It all just depends.

> 2nd
> This box has 2 4" ports and is tuned to
> 21Hz. It is centerered directly in the
> middle back of my room with the ports facing
> towards the center of the room. Although in
> some spots of the room it is loud and
> audible, in other parts, it sounds like it
> is almost dead and inaudible.

Standing waves. Cancelation from reflections in your 11x13 room.

> I am guessing
> it is because of the limited placement area
> i had for it being placed in the middle
> back, but im not sure.

You're going to have variation in output no matter where you put it.

> POssibly because it
> is tuned so low? too small of room
> (11'x13')?....

See above.

> 3rd
> I thought that this sub could handle 300rms
> but with the dayton plate amp rated at
> 250rms (272measured), and the level not even
> half way up,

What do you mean "half way up"? The position of the volume control, especially with a logarithmic "audio taper", doesn't really have a direct relation to output. "Half way up" could well be full output depending on the signal.

> with this beast is almost hitting
> Xmax.

Well, how loud is it? How does it sound? What is the input source? Is the cone flapping around at infrasonic frequencies below port tuning?

If you're getting uncontrolled cone excursion it would be a good idea to look at factors that affect box loss (QL) like air leaks and cabinet flex. If everything is right and your woofer is anywhere close to spec, you should be able to drive the full 240 watts through it without exceeding x-max all the way down to around 18 Hz. But again, the position of the volume control at "half way up" doesn't mean that you aren't already driving close to the full 240 watts so maybe everything is exactly as it should be.

[zinger084]

http://www.covertofcanton.com/insidepages/images/gallerypics/Misc/DSC01076small.jpg


> Standing waves. Cancelation from reflections
> in your 11x13 room.
I figured that standing waves might be the problem, but then again, my room is filled with plenty, and I mean PLENTY of furniture, tables, bed, and other stuff for the waves to bounce of of not at 90 or 180 to cancel. So I really don't know...

> What do you mean "half way up"?
> The position of the volume control,
> especially with a logarithmic "audio
> taper", doesn't really have a direct
> relation to output. "Half way up"
> could well be full output depending on the
> signal.
The gain on the amp is about 1/3 of the way up and the Yamaha HTR-5840 that has volume from 80db down to 0db is around 25db.

To set the gain right, i should play the speakers until they distort, and then play sub and adjust the sub until it distorts. I want to make sure I don't blow the sub, so is it very obvious (loud) where the sub will start to distort?

> Well, how loud is it?
Don't get me wrong, this thing is loud,but i figured that a 15" with a measured output of 272watt amp feeding it would seriously blow my windows out. The problem is though that where i sit right now, its very loud, but if you go somewhere else in the room, thats not a closet or a corner, it's almost inaudible.

Also, upon leaving the room, you can barely hear the sound coming from my 15". This is not the case with my dad's sony 12" with 120rms. That is very audible anywhere in the house. Possibly because his is in the corner? I just dont't know why mine doesnt seem to me loud everywhere in the house.

*Is there a free program out there that measures sound output (SPL)?

> How does it sound?
It's very clean and all but I am afraid to turn the xover up to the F3 of the fronts (2 6.5's in each front) in fear of pushing too high of Hz through the 15"

> What is the input source?
eh... Yamaha HTR-5840 with AR Pro 25ft subwoofer cable running directly to it (yes, the direction is balanced and it is running the right way).

> Is the cone flapping around at infrasonic frequencies below port tuning?
No, not from what I can see at all. To me, this sub does not look like it can take an Xmax of 20mm... more like 15mm or 10mm. Maybe I'm just not pushing it to it's limits?

> If you're getting uncontrolled cone
> excursion it would be a good idea to look at
> factors that affect box loss (QL) like air
> leaks and cabinet flex.
If its one thing I do know, it's how to build boxes. This beast is double layer 3/4" MDF with overlapping corners and internal bracing. It weights about 175-200lbs with everything in it.

> If everything is right and your woofer is anywhere close to spec, you should be able to drive the full 240 watts through it without exceeding x-max all the way down to around 18 Hz. But again, the position of the volume control at "half way up" doesn't mean that you aren't already driving close to the full 240 watts so maybe everything is exactly as it should be.
It could possibly be right, I just guess I will have to listen to it more and adjust accordingly, but in a room this small, I think its completely placement.

[scottanderson]

> Scott,

> Let me know what type of parameters you are
> asking me for and i can let you know. To
> start:

> Vb=8854.5 in^3
> Ports: 2 @ 4"dia x 25.96 inches long
> Tuned to 21.01 Hz.

> All using WinISD Pro which I have used for
> about 4 years now...

Everything looks right...is your box tight, well sealed / braced?

What sorce material are you driving it with? At what lvl? Is it being pushed in full range or just at a narrow band near fs?

Did you use any stuffing in the box?

How loud is it when it starts to clip? You may very well be pulling full amp power. RMS is not a full 300 from 20-50hz but more like 150. 300 would be at like 50-100hz. Max SPL for one driver at 20 hz should be about 114-116 db

[bogie]

The box is a little undersized for a Q15, but not too bad... You shouldn't have any xmax problems. May be something else - leads, or something's broken.

> Scott,

> Let me know what type of parameters you are
> asking me for and i can let you know. To
> start:

> Vb=8854.5 in^3
> Ports: 2 @ 4"dia x 25.96 inches long
> Tuned to 21.01 Hz.

> All using WinISD Pro which I have used for
> about 4 years now...

[bogie]

Darn nice looking...

One thing to consider... You're talking LONG wavelengths... I disrecall... Did you say that you used much stuffage? I'd add some.

Also, I set my twin Q15s using a ratshack SPL meter... I found that if I did it "listening," I'd run 'em too high. As it is, I have them about 6db hotter than the mains, but then they're mostly for HT and rock and roll. Setting 'em so you hear the "thump," you'll end up running 'em 10-15db hot... May work for some folks, but it makes my brain hurt after a while.

Oh yeah... Try stuffin' a Nerf football in each of the ports, and see how you like it in a sealed oversize box for music... Don't feed it anything under 30hzish or so at high volume tho... or try plugging just one port (4" should actually be enough for a Q15), and see how you like it tuned at 15hzish...

> I figured that standing waves might be the
> problem, but then again, my room is filled
> with plenty, and I mean PLENTY of furniture,
> tables, bed, and other stuff for the waves
> to bounce of of not at 90 or 180 to cancel.
> So I really don't know...
> The gain on the amp is about 1/3 of the way
> up and the Yamaha HTR-5840 that has volume
> from 80db down to 0db is around 25db.

> To set the gain right, i should play the
> speakers until they distort, and then play
> sub and adjust the sub until it distorts. I
> want to make sure I don't blow the sub, so
> is it very obvious (loud) where the sub will
> start to distort?
> Don't get me wrong, this thing is loud,but i
> figured that a 15" with a measured
> output of 272watt amp feeding it would
> seriously blow my windows out. The problem
> is though that where i sit right now, its
> very loud, but if you go somewhere else in
> the room, thats not a closet or a corner,
> it's almost inaudible.

> Also, upon leaving the room, you can barely
> hear the sound coming from my 15". This
> is not the case with my dad's sony 12"
> with 120rms. That is very audible anywhere
> in the house. Possibly because his is in the
> corner? I just dont't know why mine doesnt
> seem to me loud everywhere in the house.

> *Is there a free program out there that
> measures sound output (SPL)?
> It's very clean and all but I am afraid to
> turn the xover up to the F3 of the fronts (2
> 6.5's in each front) in fear of pushing too
> high of Hz through the 15"
> eh... Yamaha HTR-5840 with AR Pro 25ft
> subwoofer cable running directly to it (yes,
> the direction is balanced and it is running
> the right way).
> No, not from what I can see at all. To me,
> this sub does not look like it can take an
> Xmax of 20mm... more like 15mm or 10mm.
> Maybe I'm just not pushing it to it's
> limits?
> If its one thing I do know, it's how to
> build boxes. This beast is double layer
> 3/4" MDF with overlapping corners and
> internal bracing. It weights about
> 175-200lbs with everything in it.
> It could possibly be right, I just guess I
> will have to listen to it more and adjust
> accordingly, but in a room this small, I
> think its completely placement.

[Paul O]

Your problem is speaker location, Period. Cross it no higher than 80hz and face the driver into a corner, leaving a couple inches between the enclosure and the walls. Try it.. I dare ya!!!

[scottanderson]

> Your problem is speaker location, Period.
> Cross it no higher than 80hz and face the
> driver into a corner, leaving a couple
> inches between the enclosure and the walls.
> Try it.. I dare ya!!!

A corner horn is born.