subwoofer dead spots

[kyle lovett]

this is my first thread and I hope you can help me with this problem I have!
I own two wharfedale 15b subwoofers http://www.wharfedalepro.com/Home/P...S/DELTASERIES/DELTA15B/tabid/418/Default.aspx
and I use with these a kam krx2000 amp rated at 670w@8 ohms
the problem I have is that wherever I place the subs there is almost always a dead spot in the middle of the room! when I place them together or stack them, either side of the subs Is brilliant bass but as soon as you move to the centre there is no audible bass, the ground shakes but you cant really hear any bass, I have a crossover and have reverted the phasing but is even worse when I do that, but my friend owns two of these subs aswell (the reason I got them because they sound so good) and his sound brilliant everywhere.. any ideas? any more info needed just ask, thankyou!

 

[Per Søvik]

Re: subwoofer dead spots

If it is a dead spot, it is probably due to reflections, and it's difficult to get rid off if the room is symmetric, but you can try with a asymmetric placement of the woofers. (moving the deadspot)
If you have an "inverse power alley" where it is dead down the middle, one of your subs is out of phase.

 

[kyle lovett]

Re: subwoofer dead spots

If it is a dead spot, it is probably due to reflections, and it's difficult to get rid off if the room is symmetric, but you can try with a asymmetric placement of the woofers. (moving the deadspot)
If you have an "inverse power alley" where it is dead down the middle, one of your subs is out of phase.

I have changed the phasing with my crossover but it makes the sound even more dead haha

 

[Ivan Beaver]

Re: subwoofer dead spots

I have changed the phasing with my crossover but it makes the sound even more dead haha

It is POLARITY-NOT PHASE!!!!!!!!!!!!!!!!!!!!!!!!!!! Your crossover does NOT have a phase adjustment-I am sure.

It could be that ONE of your cabinets is out of polarity with the other. But this seems weird that since you say when they are together the bass is fine.

You have to "divide and conquer". Put some pink noise (going through your crossover to low pass it) into one speaker. Then put the other speaker beside it and plug it in. Did the noise get louder or quieter? If it got louder-then the speakers are probably in POLARITY.

So that means the problem is elsewhere. Do your friends speakers sound fine in the SAME ROOM AND IN THE SAME POSITION? If you have not tried this-do so-it gives a reference.

It could be that you are some nasty room modes in the middle of the room.

 

[kyle lovett]

Re: subwoofer dead spots

It is POLARITY-NOT PHASE!!!!!!!!!!!!!!!!!!!!!!!!!!! Your crossover does NOT have a phase adjustment-I am sure.

It could be that ONE of your cabinets is out of polarity with the other. But this seems weird that since you say when they are together the bass is fine.

You have to "divide and conquer". Put some pink noise (going through your crossover to low pass it) into one speaker. Then put the other speaker beside it and plug it in. Did the noise get louder or quieter? If it got louder-then the speakers are probably in POLARITY.

So that means the problem is elsewhere. Do your friends speakers sound fine in the SAME ROOM AND IN THE SAME POSITION? If you have not tried this-do so-it gives a reference.

It could be that you are some nasty room modes in the middle of the room.

I did the pink noise thing with the subs side by side and it got louder, what are room modes?, may I point out that I only get dead spots in my kitchen and out house, my out house is square and 6x6m(brick) and my kitchen 8x8, both square and kitchen has cabinates all round, my friend has it in his out house and that 8x6 and sounds brilliant everywhere

 

[Art Welter]

Re: subwoofer dead spots

I did the pink noise thing with the subs side by side and it got louder, what are room modes?

Room modes are reflections from boundaries (walls, floor, ceiling) that result in peaks and dips in response at various frequencies determined by room dimensions and loudspeaker placement.
Here is a room mode calculator:

http://www.mcsquared.com/modecalc.htm

 

[Riley Casey]

Re: subwoofer dead spots

http://adn.harmanpro.com/product_at...hments/1398_1353359519/hi_fds360_original.jpg


Couldn't resist

It is POLARITY-NOT PHASE!!!!!!!!!!!!!!!!!!!!!!!!!!! Your crossover does NOT have a phase adjustment-I am sure.

 

[Bennett Prescott]

Re: subwoofer dead spots

http://adn.harmanpro.com/product_at...hments/1398_1353359519/hi_fds360_original.jpg

I measured the response of an Omnidrive that had the same Phase control a few years ago. At the XO point it did exactly what it said. Outside the XO point, though, it gave me a lot of headaches. Listening tests proved that using delay and a different XO slope produced a way more listenable result.

 

[Riley Casey]

Re: subwoofer dead spots

Twas not a post to tout the merits ( or lack thereof ) of the feature, just a never say never admonition.

I measured the response of an Omnidrive that had the same Phase control a few years ago. At the XO point it did exactly what it said. Outside the XO point, though, it gave me a lot of headaches. Listening tests proved that using delay and a different XO slope produced a way more listenable result.

View attachment 10701

 

[Max Warasila]

Re: subwoofer dead spots

I did the pink noise thing with the subs side by side and it got louder, what are room modes?, may I point out that I only get dead spots in my kitchen and out house, my out house is square and 6x6m(brick) and my kitchen 8x8, both square and kitchen has cabinates all round, my friend has it in his out house and that 8x6 and sounds brilliant everywhere

Judging by the fact that the rooms are square, I'd definitely look into the room modes.

 

[Ivan Beaver]

Re: subwoofer dead spots

http://adn.harmanpro.com/product_at...hments/1398_1353359519/hi_fds360_original.jpg


Couldn't resist

My "assumption" was that with the other equipment listed-the crossover used (not listed) would not be of the "higher quality".

While those old 360s sounded great (I used to have several) I hated the way the freq/filter selection was (having to change out resistors and caps to change filter types and freq). You needed to be sure before you started-but back then we didn't have the measurement systems we do today-so it was basically guess work and a lot of experimentation

But of course-having less variables (pots) added to the quality.

 

[kyle lovett]

Re: subwoofer dead spots

My "assumption" was that with the other equipment listed-the crossover used (not listed) would not be of the "higher quality".

While those old 360s sounded great (I used to have several) I hated the way the freq/filter selection was (having to change out resistors and caps to change filter types and freq). You needed to be sure before you started-but back then we didn't have the measurement systems we do today-so it was basically guess work and a lot of experimentation

But of course-having less variables (pots) added to the quality.

May i ask have you had any experience with the delta series? They are 400 quid a pop, with these i also have the klx2000 again powering two delta 215 which are 549 each, so the "quality " is fine thats an output of 4kw as for crossover i use the dbx 234xs which i would not call shabby at all, as for eq i use the dbx 2215 hope that cleared things up for you you patronising little man... I have spent alot of money on my set up only for you to say "lesser quality" which may i point out... It isnt! This system isnt made for your anal ear for sound quality its made to blow the b**tard roof off... That is all...

 

[Tim McCulloch]

Re: subwoofer dead spots

May i ask have you had any experience with the delta series? They are 400 quid a pop, with these i also have the klx2000 again powering two delta 215 which are 549 each, so the "quality " is fine thats an output of 4kw as for crossover i use the dbx 234xs which i would not call shabby at all, as for eq i use the dbx 2215 hope that cleared things up for you you patronising little man... I have spent alot of money on my set up only for you to say "lesser quality" which may i point out... It isnt! This system isnt made for your anal ear for sound quality its made to blow the b**tard roof off... That is all...

Now now, Kyle. Don't turn into a prick because you got your kinickers all bunched up.

Ivan made 2 points in his first post, the first of which regards the proper (and often improper) use of the word "phase" when the actual change of condition is "polarity." He also postulated that your crossover probably didn't have a "phase" control (and hence his correction with Polarity). Riley responded with his picture of a retired BSS piece that has actual phase adjustment as well as the more conventional Polarity. Riley's response and Ivan's reply to him basically does not involve you.

Now, regarding the relative "quality" of the BSS piece to your then-unnamed dbx - it's not close. No, not even. Not being a snob here, but they really are in different classes. Note that the dbx is still available as new stock as BSS have put their eggs in the digital processing basket and discontinued analogue products.

As for the rest all I can say is you're digging yourself a hole; you'd do best to put aside the shovel. The folks that so far have offered comments, general knowledge and advice collectively have decades - maybe a century - of professional audio experience between them. They started back when speakers were made of stone and microphones were sea shells (except for Bennett and Max, they're still new kids). They've used it all, and at least 2 of them are actively involved in building professional speaker systems that would probably blow your mind. Unbunch your knickers, take a deep breath and go back and read Art Welter's reply and use the mode calculator he linked to. Notice that the center frequency of nodes vary with dimension (as wavelengths have a physical size). The only things you can do to alter how nodes behave is by moving the subs relative to boundary surfaces (walls), but the fundamental limitation is whatever permanent architectural boundaries exist. As Max pointed out, that the rooms are square means you will have more issues that rooms that are rectangular.

What you are experiencing is not a deficiency of equipment, but enforcement of the Laws of Physics. Officer Einstein will be along to cite you...

 

[Mark DeArman]

Re: subwoofer dead spots

Now now, Kyle.

The cool head comes in to diffuse the situation ;-)

 

[Mark DeArman]

Re: subwoofer dead spots

There was a bar here in town, about five miles from our factory, that had come across two of our older double 18” cabs for their dance floor somehow. They called up one day and ordered two sets of replacement baskets, and then they ordered another set about three months later. So I decided I would go over and see what was going on. Long story short, a null right on the dance floor and mix position; this is a pretty small room. Tried to get the house DJ/FOH/Sound guy to move the subs… Nope. I was told the subs just sucked.

 

[Ivan Beaver]

Re: subwoofer dead spots

There was a bar here in town, about five miles from our factory, that had come across two of our older double 18” cabs for their dance floor somehow. They called up one day and ordered two sets of replacement baskets, and then they ordered another set about three months later. So I decided I would go over and see what was going on. Long story short, a null right on the dance floor and mix position; this is a pretty small room. Tried to get the house DJ/FOH/Sound guy to move the subs… Nope. I was told the subs just sucked.

Did you tell them it was the ROOM that was SUCKING the subs? at that spot? Not the other way around?

I wonder how many subs they went through before they realized what you were telling them? But of course they will no come back to you-because of realizing they were wrong----------

 

[Chris Hindle]

Re: subwoofer dead spots

http://adn.harmanpro.com/product_at...hments/1398_1353359519/hi_fds360_original.jpg


Couldn't resist

Don't remind me of those fucking 360's.
Last century we had an Adamson rig processed with 2 of those (custom cards installed). 1 was always "back at mothership" for one problem or another. In 2 years, I think I actually mixed 3 shows stereo.

 

[Riley Casey]

Re: subwoofer dead spots

Nothing wrong with those 360s that soldering jumpers across the output relays wouldn't fix. Yea not having the mutes work was a nuisance but much less of a nuisance than say having the low band disappear.

To the original poster - yes, my post with a picture of a crossover that was popular 25 years ago and discontinued ten years ago was of no use to you. It was entirely an old geezer sound guy joke meant to sail directly over your head to the other old geezers in the thread. Even Bennett got suckered in. Sorry to abuse your good faith in the answers to be had here on the forum but once you do get a good faith answer run with it, don't bite the hand that informs you. Its genuinely valuable to be able to come here for knowledge and insight, don't toss that opportunity aside out of pique.

Don't remind me of those fucking 360's.
Last century we had an Adamson rig processed with 2 of those (custom cards installed). 1 was always "back at mothership" for one problem or another. In 2 years, I think I actually mixed 3 shows stereo.

 

[Greg Cameron]

Re: subwoofer dead spots

Nothing wrong with those 360s that soldering jumpers across the output relays wouldn't fix. Yea not having the mutes work was a nuisance but much less of a nuisance than say having the low band disappear.

Ye old Klark Teknik DN800 was another analog crossover with phase adjustments on the band passes. It too used hard wired crossover cards. Solid unit though. I still have one which was a backup for my Rat Traps. Before digital, it was the standard Rat Trap 5 processor. Hasn't been out of the box in over 10 years though as I have a backup Xilica processor for my XTA As for the phase adjustments, Dave Rat said they never used them because they "did funny things."

 

[Josh Millward]

Re: subwoofer dead spots

There was a bar here in town, about five miles from our factory,

This is problem number one. You are not an expert because you live there. You did not come in from at least 60 miles away.

Tried to get the house DJ/FOH/Sound guy to move the subs… Nope. I was told the subs just sucked.

Of course they suck, they are from your local factory, not some whiz bang outfit from some distance away.

In the end, remember that your advice is worth exactly what the people who you are giving it to are paying for it. If it is free, they will discount it as worthless. However, in this situation, getting them to pay for it won't happen anyway, so you just have to learn not to take it personally. They will eventually figure out that you were exactly right.