Peavey 115 BW and a JBL

[jackietreehorn]

A small magnet 15" speaker would displace about 2 liters
and very large magnet speakers like a K140 would be about 4 liters

Also a 6" port with a length of 5" would displace 2.3 liters

So assuming 91.67 liters and subtracting 6.3 liters for the speaker and port

83.37 liters or 2.944 cubic feet

Depending upon end factor correction a single 6" x 5" length round port would yield a tune of around 52 to 54 Hz

If you wanted lower tuning around 42 to 45 hz you would want that port to be around 9 to 9.5 inches length

Right now there is no padding or dampening material in there. Should I dampen it? Would the volume of the dampening material reduce the volume?

 

[808State]

Right now there is no padding or dampening material in there. Should I dampen it? Would the volume of the dampening material reduce the volume?

Dampening or absorption material will remove the overall box like reflective tone.
And is recommended for a better sound.

It will help improve response peaks in the midrange.

Poly fiber sheets wont reduce the volume.
Fabric stores or super walmarts with fabric sections will have white poly fiber batting.
Its a poly fiber sheet usually used for quilt blankets or comforters.
I usually buy the thickest material they have.

Likely a small roll for a twin or double blanket will line the cabinet.
I use 77 spray adhesive to stick it to the sides. But temperature changes
over time will make the glue loosen. So you use very few stables to hold it in place as well.
Sometimes I double line the rear of the cabinet. Basically where most the sound pressure hits.

Electro Voice tuned 15" cabinets to 40Hz like JBL and used 55 Hz for PA use. Overall your 3 to 3.2 cubic foot cabinet will work well for many speakers. Tuning is somewhat high for a 30 Hz speaker. You can experiment by adding length to the port. Assuming your cabinet is 9.75 to 10" in depth. You can add length but might want at least .5 to .75 inches away from the rear baffle. So you can barely get the cabinet in 42 / 45Hz with 9 to 9.5 inches of port length. You could experiment by wrapping cardboard temporarily to extend the port using tape.

 

[agedhorse]

@agedhorse just out of curiousity, how do you asses the mechanical power handling? I didn’t find the k140 spec’s in my winisd, and was to lazy to put them in. So I did not replicate your calculation. But my interest is in the general approach. Do you simply set the maximum at where the cone excursion graph exceeds x-max at a certain wattage for the input signal? Or do you allow some extra room for the fact that the actual input power will never be concentrated on one frequency? I myself allow some room for real world handling, but that’s for me diy-ing where I bear all the risk myself.

It’s the combination of several factors, including Xmax, power density at low frequencies, and how the driver unloads in the enclosure.

 

[Matthijs]

It’s the combination of several factors, including Xmax, power density at low frequencies, and how the driver unloads in the enclosure.

Thank you. It might be my english but I’m not familiar with the term power density. Do you mean how the power is divided over the lower frequencies?

 

[808State]

K140 Xmax is based on older calculations based on coil and gap height.

It was known practice that a cone can only travel so far before the magnet can maintain enough control
before 10% distortion is reached.

K140 is .22 inches or 5.5 mm
Its likely with modern laser measurements actual 10% distortion could be Further around 6 mm
Gap tolerance was very tight with JBL. A risky but innovative feature. Many modern manufactures dont
come close to those tolerances for multiple reasons.

Either way with typical suspension of a pro audio driver expect a real world 100 to 150 watts of power handling
with a 5mm to 6mm driver below 100 Hz

Of course that is very generalized and cabinet volume, and unloading below cabinet tuning plays a big roll.
After real world experience and modeling hundreds or drivers. You learn quickly what to expect.

5.5mm was a very big deal and powerful speaker at the time. Since it was almost double the typical 1 to 3mm drivers to achieve same high efficiency of around 98/99 dB Average

 

[tvbop]

I blew a K140 once in an old Fender bass man cab. Their not really very robust speakers..loud yes and sensitive yes...but not what I would call bomb proof....take it easy.

 

[808State]

LOL nothing is bomb proof in audio
Especially Musical instrument audio.

Except 5 to 6mm was the end of the road for a long time.
And anyone that touched it probably learned how do it from JBL

The tolerance was amazing really at the time.
The risk was mainly from the thermal capability of older glue
and voice coil material.

 

[agedhorse]

Thank you. It might be my english but I’m not familiar with the term power density. Do you mean how the power is divided over the lower frequencies?

Yes.

 

[jackietreehorn]

I blew a K140 once in an old Fender bass man cab. Their not really very robust speakers..loud yes and sensitive yes...but not what I would call bomb proof....take it easy.

I usually run my power amp bridged, but if I run just one side at 8 ohms, it maxes out at 215 watts. So I figure I’ll fun it like that... and not crank it.

 

[808State]

Good Idea, Thermally heat wise I believe the K series was around 150 watts and the E series was 200 watts.

Usually with most speakers you will reach mechanical distortion way before you worry about thermal destruction of a speaker.

Say a " 300" watt speaker can usually start to fart out around 130 to 150 watts below 100 Hz

Again the K series was pushing 5.5mm xmax way back in the day.
So it basically didn't reach mechanical distortion until you were riding it way up into its thermal limits.

Plenty of modern speakers that still only do 5mm xmax and reach distortion at the same old 150 watts.
Except modern glues and coil formers are actually thermally stable up to 300 to 450 watts.

 

[JW56789]

@jwilson



Brad Sarno is small, independent builder in St. Louis. He builds products, from what I can tell, that mostly hit two main categories - pedal steel players and guitar players who are chasing the Jerry Garcia sound. So everything he builds is designed to be clean and have a lot of head room.

I think his pre does what it’s supposed to. It gets that classic Fender sound, clearly, with no distortion. Plus it’s quiet. The whole unit is a 1u rack too.

I’ve never played an F2B, so I can’t compare them, but TB member, @edwinhurwitz is the one who turned me into this unit, and he probably has compared the two.

Brad is also a really nice and helpful person. When I’ve asked him questions, his response isn’t a sales pitch, which is refreshing. I also purchased his Earth Drive, because while the classic pre is super clean, which I want most of the time, sometimes I want that dirtier sound - like a bunch of sunn cabs being pushed to the brink, and the Earth Drive can do that.

So I recommend it, but I can’t fairly give it a comparison to the other “Fender style” preamps out there.

Thanks, Jackie. I've been intrigued by his products (more that a few guys use them here in Nashville), but never knew anyone who tried them for bass.

A link to the SMS Preamp:

[Invalid or Expired Link Removed]