Some help: 18" selection for replacement

[djkib]

To all,

Last night, we had some issues with one of our Peavey 18" subs (as seen here... http://www.peavey.com/assets/literat...s/80304858.pdf ).

Long story short, we are looking to stock a replacement driver for this cabinet. external dimensions are 32.5" x 20.75" x 30", and assuming 3/4" material, internal volume would be 9.524 ft3, or 270 liters. There is also an 8" diameter port, about 3"-4" long (guessing - didn't have a ruler or tape measure).

We are not thrilled with the quality of the Peavey drivers, as this is the 7th driver we have had issues with. Additionally, we are probably under driving this a little, providing probably 200-400 watts, rather than the 600-1200 this thing handles. Our volume levels are such that we never come close to clipping on the amps.

Do you have any suggestions for replacement drivers, other than the Peavey BWX that are supposed to be in these? Are there any 15" drivers of decent quality that would fill these cabinets?

We are kind of married to these cabinets, as they are mounted in our sanctuary...

Oh, did I mention that these are supposedly rated at 16 ohms?

A BIG thanks to all that contribute to this forum - there's lots of good info here!

Peace,
Keith

[jbell]

American Music*|*Live Sound*|*Speaker Parts*|*Peavey 1808-8 SPS BWX 18" 8 Ohm Low Frequency Speaker Driver

4.6mm xmax? wow....

I would not replace this with the original 1808-8sps driver. Even the low rider would be better.

Who cares if you can handle 1000 watts, if you go over xmax at 150 watts? What is your high pass set to? If it's not 40hz@48db/oct, that is probably why you are killing drivers.

Here's what you get assuming a 4" long port in your cabinet at 150. That's all I'd put into it, 150.... no more.

[Rademakers]

We are not thrilled with the quality of the Peavey drivers, as this is the 7th driver we have had issues with.

What kind of issue's?

Are there any 15" drivers of decent quality that would fill these cabinets?

the 250-270 ltr internal is al ready quite large for 18" drivers. For a 15" driv3r it would be relly big, probably to big.

Oh, did I mention that these are supposedly rated at 16 ohms?

Supposebly? As in, you don't know? You could measure Re as a quick answer. Do the replacements need to be 16 ohms or would 8 ohm do aswell?

Best regards Johan

[jbell]

Parts-Express.com:Peavey 18" Low Rider Subwoofer | low rider subwoofer 18" subwoofer peavey pa subwoofer high xmax

peavey Lowrider, definately.

Here's it's output at 600watts, assuming a 40hz high pass, it's good to go.

10 to 1 better choice of driver for that cabinet, and your needs.

It's lower, louder, and won't trash itself at 150watts.
In fact, you could have more bass with half the cabinets using the lowrider driver.

[djkib]

Thanks for the speedy responses...

To JBell:
I looked at that and was wondering if it would work... i don't know how to "back in to" an appropriate driver, given a cabinet... there isn't a huge selection of 18" drivers out there anymore...

Regarding the cross point and rolloff... I will double-check the settings on the crossover Tuesday night when I'm back in the hall...

To Rademakers:
1. Mostly quality issues. we have 6 15" cabinets hanging, and have had issues with the 15" woofers, random unexplained failures - one second working ok the next not... when they are opened up it is mostly cold solders as the problem. This is the first 18" that has failed like this...

I'm wondering (and pardon my ignorance...) - if the amp does go into clipping, will it cause significant heat in the speaker? Could that effect the solder connections at the voice coil?

2. Ok... thanks - just trying to think outside the box...

3. Yes, they are 16 ohm... the original intent was to run two of these in parallel, which would present 8 ohm to the amp... I would have run two at 8 ohm to present 4 ohm to the amp, but that's just me...

[davygrvy]

Originally Posted by djkib

I'm wondering (and pardon my ignorance...) - if the amp does go into clipping, will it cause significant heat in the speaker? Could that effect the solder connections at the voice coil?

A clipping amp most definitely will cause overheating of the VC. This is the biggest cause of driver failure. The usual method (for live sound) to choose an amplifier is to double (or more) the RMS power rating of the driver and use the limiting feature of the electronic crossover to prevent an input signal that would ever cause clipping.

For tweeters, the failure mode for overheating is an immediate loss of output; like a fuse. LF drivers can behave differently. When they get too hot, they lose output level, called power compression. The person at the mixer usually compensates and pushes them harder. To which they get hotter and the fight begins. Good drivers just act like a brick wall and don't fail, nor do they get louder. The "bad" drivers fall off the cliff and keep getting quieter as they get hotter because they can't dissipate the heat. The "awful" drivers burn up without indication they're having a problem; like a fuse.

Overexcursion is damage when the driver moves too far and the spider gets stressed and leads to a rubbing sound and general distortion. Or may go so far the VC comes out of the gap and gets stuck or smashes itself.

If I was to come in and check to see if your amps are clipping, I'd use a scope and monitor both amp input and output. I'd subtract the two signals and monitor the difference thus leaving a flat line when the gains are matched. On any peak that clips the amp, a large jump in the trace would be shown.

[NEO Dan]

While Peavey spec sheets are very accurate for some models, the low Rider 18 is not one of them.

Actual measured TSP's for Low Rider 18"

FS:
37.45

QMS:
8.614

VAS: L
237.8

CMS: um/N
110.6

MMS: g
163.3

SD: sq.cm
1237

QES:
.556

RE: ohms
5.873

LE: mH
1.958

BL: Tm
20.15

QTS:
.522

[freddi]

hi Dan - that qes sux

Peavey 1808-8 spec I measured - by accident makes an ok open baffle woofer - IIRC after beating it hard with sine for a few days
fs dropped a bit

Revc = 6.1118 ohms
Fs = 50.1638 Hz
Zmax = 63.7015 ohms
Qes = 0.8988
Qms = 8.4693
Qts = 0.8126
Le = 0.8464 mH (at 1 kHz)
Diam = 412.7500 mm ( 16.2500 in )
ConeArea =133802.4437 mm^2(207.3942 in^2)
Vas = 219.2645 L ( 7.7433 ft^3)
BL = 15.7291 N/A
Mms = 115.4353 g
Cms = 87.2007 uM/N
Kms =11467.7949 N/M
Rms = 4.2960 R mechanical
Efficiency = 2.9686 %
Sensitivity= 96.7255 dB @1W/1m
Sensitivity= 97.8947 dB @2.83Vrms/1m

[Andrew Eckhardt]

Originally Posted by NEO Dan

While Peavey spec sheets are very accurate for some models, the low Rider 18 is not one of them.

Actual measured TSP's for Low Rider 18"

FS:
37.45

QMS:
8.614

VAS: L
237.8

CMS: um/N
110.6

MMS: g
163.3

SD: sq.cm
1237

QES:
.556

RE: ohms
5.873

LE: mH
1.958

BL: Tm
20.15

QTS:
.522

How is it that subsequently measured T/S parameters always yield such instantly believable numbers when the published ones are considered "inaccurate"?

Someone should type up a T/S paramter lie-O-meter in javascript. For a complete set of measurements it would be easy to show by what factor the overall performance deviates from possible.

[NEO Dan]

Oddly enough the program that get's little respect Bass Box Pro has just such a "Lie O' Meter", I love this feature. But it only points out when the params don't jive. A smart liar would use it to construct a whole fake TSP set.