Cheap and FAST OB, Literally

[perceval]

and going active, it will be easy to add a bit of EQ down low to flatten and extend the lows a bit. Given the number of drivers used, they will be able to take the EQ and not add distortion.

 

[perceval]

talking about going active, I'm thinking I'd like to try it as soon as we get settled in the new place.

Keeping it simple, I'm thinking of doing the woofers and the mid active to blend them easily in my room, but passive for the switch between the mid and the tweet with cheaper components this higher up.
That way, I can use a single miniDSP 2x4 HD, and only 4 outputs, so 2 amps, instead of 3. Actually, I have a very good amp that has 8 outputs. That will do nicely, and still have channels for center, sub and two sides for movie nights!

 

[kazap]

that has just been my understanding of things

I dont want to derail this thread into hearing damage research, but I dont want you or others here going deaf. Also it may interest other SLOB builders that OB/SLOB bass may be less damaging then sealed subwoofers by not pressuring the room and lessening low frequency impact on the cochlea, but that's pure speculation on my part with no evidence.

The danger with loud bass and hearing damage is it doesnt hurt. The ear is sensitive at mid-freq and discomfort is a great reminder. We dont get that warning with bass. Its seems innocuous. This makes it potentially dangerous.

Id suggest being careful what advice you follow when looking at guidelines on the role of low frequencies in hearing loss. If you look at recommendations from reputable sites that outline dB x hours you might struggle to find anyone that states low frequencies are OK at ydB x zTime or whatever.

This is an area that needs more research but a recent paper concluded that ~60Hz band noise at 90dB for 6hrs damages hearing across higher frequencies with loss of the inner ear cilia hair cells. Once they are gone dont expect then to come back, despite imaginative claims by some.

 

[xrk971]

"Also depends on driver Fs and Qts. Lower Fs is better. If you go with the 4.5in drivers, the Fs might be higher. Ideally you want Fs down near 30Hz. We are at 75Hz with the GRS so we can reach deeper since Qts is high (weak magnet) so cone will be able to resonance below its Fs." -X

thanks, Bryguy.

@TubaV,

The 1354 is an excellent full range driver meant for the mid and top end. It’s kind of a shame to relegate it to slob bass duties.

My concern would be lack of Xmax. You want to be able to move air and that takes cone displacement.

 

[TubaV]

XRK, thanks for your reply. I just wanted to use what I had on hand but if you recommend against it, I'll look for another project. I'm currently using my Dayton RS225-8 for bass duties in a 42 liter cab.
Biamping to my sealed SB16/GRS planar tweeter cabs.

 

[jimk04]

Trying to understand dipole...Am I correct in saying that for example on the XSD with a 12" wide baffle, the dipole corner frequency is approximately 575hz for the midrange....at 6db/octave. (Using fd = 172.5/0.3(metres or 12") And we add an electrical filter to add more poles to make it 2nd or 3rd order if we wish.?

 

[xrk971]

I cross it at 475Hz to match the upper end of the woofer array which has a natural falloff there due to the slot depth.

 

[jimk04]

How do we cross at 475 when the midrange is rolling off already at 575 from dipole baffle loss.? Is it due to the wings, albeit tapering by now, are adding enough to the baffle width?
Thanks once again in helping me understand.!

 

[xrk971]

That’s not what I got with measurements. Maybe the partial extension of the wings on the side made a difference?

Here’s the crossover plot

 

[jimk04]

Sorry I was using a theoretical roll off, measurements are always better! I was trying to get my head around what baffle width for the mid I might be able to go down to whilst still reaching an LF to reach the woofers

 

[mayhem13]

Haven’t read all the posts in this massive thread but was wondering if this Goldwood GW8028 8“ woofer would be a good choice?

https://www.parts-express.com/Goldwood-GW-8028-8-Butyl-Surround-Woofer-8-Ohm-290-355

Qts is high and Fs is low. Xmax ain’t great but 6 of these exceed the Sd of 18” woofer.

 

[kazap]

wondering if this Goldwood GW8028 8“ woofer would be a good choice?

Vd is vital with an OB. Goldwood GW8028 Xmax=2.5mm is not promising. Vd p-p = 6 x 0.25 x2 x 219 = 0.657L cf AE Diploe 18"= 3.6L

Look at https://www.parts-express.com/GRS-8PT-8-8-Paper-Cone-Prosound-Woofer-8-Ohm-292-802

if you get 8, Vd p-p = 8 x 0.7 x 2 x 212 = 2.4L = promising

 

[xrk971]

It will work but note that the deeper chamber depth will mean the crossover frequency will be lower. The mid range might have a harder time crossing lower. You will also be on your own with the crossover development. However, if you were planning on an active crossover with DSP, all that is a non issue.

 

[mayhem13]

Vd is vital with an OB. Goldwood GW8028 Xmax=2.5mm is not promising. Vd p-p = 6 x 0.25 x2 x 219 = 0.657L cf AE Diploe 18"= 3.6L

Look at https://www.parts-express.com/GRS-8PT-8-8-Paper-Cone-Prosound-Woofer-8-Ohm-292-802

if you get 8, Vd p-p = 8 x 0.7 x 2 x 212 = 2.4L = promising

I peeked at that driver but an Fs of 60hz?………

 

[mayhem13]

It will work but note that the deeper chamber depth will mean the crossover frequency will be lower. The mid range might have a harder time crossing lower. You will also be on your own with the crossover development. However, if you were planning on an active crossover with DSP, all that is a non issue.

Hypex active for sure……..a self contained speaker system has always been appealing to me in it’s simplicity…..probably a bias of mine after years of active monitor use in the studios.

 

[kazap]

I peeked at that driver but an Fs of 60hz?………

What does the L in SLOB do?

 

[mayhem13]

It will work but note that the deeper chamber depth will mean the crossover frequency will be lower. The mid range might have a harder time crossing lower. You will also be on your own with the crossover development. However, if you were planning on an active crossover with DSP, all that is a non issue.

So the larger, deeper chamber will result in a higher amplitude resonance and change in its frequency?…….I would assume the resonance would be lower in frequency?

 

[xrk971]

Deeper chamber will have lower upper frequency. It’s the depth more than volume. Simple 1/4 wave cancellation of a 7in deep slot.

 

[sumotan]

Hi XRK,
Would an MTM Slob work just as well meaning 2 slot at the bottom with FR driver in the middle & another 2 slot above ?
Think I've found an 8 inch at my end that fits the bill to try cheap too. Lol

As always many thanks

 

[perceval]

Looking at the GRS for the slob, they have a Qts of about 1, and Fs of 75Hz.
I have a few offerings here in the 6.5" version, one that looks a little like that GRS!

Some have higher Qts, some have lower Fs. Puzzled as to which one might be the best in a slob here.
Care to take a quick look and help me decide? Thanks!