Low end resonance, Boston Pro60's

[Kickerkitty 10+ year member]

Maybe someone can help, I have Boston Pro60 6.5's in my doors, the doors are dynamated twice over, and the door behind the speakers is dynamatted with two layers, the speakers are sealed in foam baffles like from crutchfield. When I play something with somewhat low frequencies, like 90-120 hz, I get a bit of resonance from the speaker area. I am giving them around 400 watts each from a PRS-X720, but will probably drop that to around 200 each soon.

Any suggestions?

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[FoxPro5 5,000+ posts]

Maybe someone can help, I have Boston Pro60 6.5's in my doors, the doors are dynamated twice over, and the door behind the speakers is dynamatted with two layers, the speakers are sealed in foam baffles like from crutchfield. When I play something with somewhat low frequencies, like 90-120 hz, I get a bit of resonance from the speaker area. I am giving them around 400 watts each from a PRS-X720, but will probably drop that to around 200 each soon.
Any suggestions?

Do you have anything behind the seaker that would help absorb/defelect back waves from bouncing back to hit the driver??

Another thing that might help would be to pack some non-hardening modeling clay or equivalent around the baffle to prevent it from resonating also.

If you have an EQ, maybe try cutting that region and see what happens.

 

[Kickerkitty 10+ year member]

Do you have anything behind the seaker that would help absorb/defelect back waves from bouncing back to hit the driver??
Another thing that might help would be to pack some non-hardening modeling clay or equivalent around the baffle to prevent it from resonating also.

If you have an EQ, maybe try cutting that region and see what happens.

Yea I am running the Premier 880PRS so I am pretty much able to isolate the resonance. It pretty much disappears above the 120 hz range. Behind each speaker is the foam baffle and two layers of dynamat. The resonance seems to be an effect of the airspace, but perhaps it is the area around the speaker. I have two layers on both door skins, inner and outer. Don't know if that's enough though. Next week comes an amp that will be giving it 150-200 watts per channel, this might make a difference over before.

 

[Kickerkitty 10+ year member]

Solved it by doubling the deadedning and lowering the power to 175 watts per side, sounds great now.

 

[Starky 10+ year member]

checked out that amp...and it doesnt do 400x2...it does 200x2 at 2 ohms

here are the Specifications I got from Pioneers Website

* Continuous Power (20Hz-20kHz, 0.04% THD)

o 2 ch: (4 Ohm) 100Wx2

o 2 ch: (2 Ohm) 200Wx2

o 1 ch: (4 Ohm) 400Wx1

* Maximum Power (EIAJ)

o 2 ch: (4 Ohm) 250Wx2

o 1 ch: (4 Ohm) 750Wx1

* Frequency Response: 10Hz - 50kHz (0,-1dB)

* Total Harmonic Distortion:

* Signal-to-Noise Ratio: >105dB (IHF-A Weighted, at 1kHz)

* Dimensions: 10-3/8" x 2-1/2" x 13-5/8"

link to it

 

[khail19 10+ year member]

From what I've heard, those PRS amps were waaaaay underrated though.

 

[Starky 10+ year member]

I doubt they're THAT undertated....to put out double of what they're actually rated

 

[khail19 10+ year member]

I doubt they're THAT undertated....to put out double of what they're actually rated

Actually...they are.

From Mr. Marv on ECA...

The X720 is rated 100x2 or 400x1 @ 4 ohms (my first clue they were under rated was the 90 amps worth of fuses ). I don't have the birth sheet for this actual amp but the birth sheet I have for another one I sold to a friend shows 200+x2 or 717x1 rms @ 4 ohms (13.8 volts I believe). I have used and sold many of these amps and most of them had birth sheets at least twice their rated power. They feature a 12 db HP/LP crossover, 18db bass boost, rca outputs, accept up to 6.5 volts input and are 1 ohm stereo/2 ohm BRIDGED MONO STABLE. Not that it matters much, but I hit 129.4 (single JL 10W7 in a sealed enclosure) with the gains all the way down for SQ .

Something most don't know about the PRS amps is that they are extemely under rated and are 2 ohm mono stable. (my 10W7 is 3 ohm SVC) The X320 is rated at 50x2 or 200x1 but the birth sheet on one of mine is 127x2 rms and it has 2 30 amp fuses on it . I am looking for a PRS-X720 for the sub and then I am going to bi-amp my Dynaudios with the 2 X320's. The last PRS-X720 (rated 400x1) I installed in a friends car had a birth sheet of 717x1 rms!

Another ECA member...

i had a prs-x220. it was rated at 30x2@4 and 120x1@4. surprisingly, it tested at 67x2 and 232x1. that little amp kicked ass. was a good buy for the price, very solid, never had a problem in 2 years of using it.

 

[Starky 10+ year member]

But still 200 wrms, is no where near the 400 watts rms that kickerkitty said it did

 

[khail19 10+ year member]

True, I was thinking 400w for the set is possible. Then I read where he said he was dropping to 200w per side, so it seems like he means he's at 400w per side. No way, unless he's running each side on a separate amp. I think those foam baffles are the problem, you need to cut the back out of those for the mids to have more airspace.

 

[Kickerkitty 10+ year member]

You sir are correct, the PRS amps are monstrously under-rated. I personally only use two at the moment but have owned many others. The Pro60's were being run off of one amp. You will better understand when I say that the PRS-X720 actually behaves like it's OPTIMIZED for 2 ohm mono loads. The PRS amps I have kept are some of the better performing models. It's not unusual for a PRS-X720 to put out 850 watts at 4 ohms mono. Drop it to 2 ohms mono and they will give you upwards of 1200 rms all day long. Point being they are often even %120 under-rated. Now 400 watts per side is more than the speakers would be seeing true. Even at 3 ohms, they won't be receiving that much constantly. Probably more like 300, but it was simply a hasty number.

Regardless, now they are powered by a PRS-X320. Receiving around 150 rms per side, and with the addition of four more layers of deadening, they now sound superb.

True, I was thinking 400w for the set is possible. Then I read where he said he was dropping to 200w per side, so it seems like he means he's at 400w per side. No way, unless he's running each side on a separate amp. I think those foam baffles are the problem, you need to cut the back out of those for the mids to have more airspace.

 

[khail19 10+ year member]

I forgot that those Bostons were 3 ohm speakers, so you were probably over 300w per side. Glad you got the problem solved though. Aside from the resonance, do the speakers still sound as good with less power?

 

[Kickerkitty 10+ year member]

I forgot that those Bostons were 3 ohm speakers, so you were probably over 300w per side. Glad you got the problem solved though. Aside from the resonance, do the speakers still sound as good with less power?

Yes, the drop in power resulted in great sound after I tuned it all. If I had my way I might add another 50 watts for the heck of it, but they sound great , loud and very clear with what they have now. Definately one of the best speakers I have ever heard at any price range. From what I have seen 200+ watts is a sweet spot for them.

With 300 watts they were beating my doors apart (in a very heavy built car), with 175 or so they only make a ruckus.