Engineering help - selecting midrange driver

[dhomer]

In the process of modeling some possible projects for a 30 watt Ampeg B15. Pretty much set on the LF component, either the Dayton Pro 12, or its 15" cousin.. I am leaning towards the 15 because of better displacement, and the cab could better house a mid driver. Finding a relatively low cost mid is beginning to be a hassle...lol... I found some candidates (Faital Pro 4FE30/3FE20, Dayton PK165-8), but there's a huge SPL dropoff (6-9dB) from the woofer modeling 'em on the ol' ISD.. (Making the assumption the woofer gets about 20 watts of the power and the mid gets 5-6) Even the Alpha 6 looked weak..

However, I also know the Alpha 6 is recommended for the fEARful 12/6, and that 3012LF ain't very quiet..

My question is, How important is sensitvity as it applies to matching up a woofer w/a midrange? I could see a mid being 2-4dB less sensitive than its woofer and sound OK, but what would be a practical limit? Would I have to use two mid drivers to match up better?

[JimmyM]

Bumping this because I'm a little curious, too.

[Bassmec]

You should horn load the mid they make a cool glass fiber horn that gets a few more dBs out of the six inch, it sets the mid driver into the cab enough to help time/phase alignment too.
Failing that doubling up on midrange units is going to get you there too.

[1n3]

Originally Posted by Bassmec

... they make a cool glass fiber horn that gets a few more dBs out of the six inch

Reference, please.

[Bassmec]

Originally Posted by 1n3

Reference, please.

Ask Greenboy it looks to me very like a knock off of the JBL unit:

[MuzikMan]

You shouldn't rely on WinISD for anything above 200 hz. Use spl charts to match drivers when crossing over in the midrange area. It makes no sense to me that you are trying to match drivers by plugging in 20 watts for the woofer and comparing it to 5 watts into a midrange driver. In order to match them up you need to compare their output with the same input. I think you will find that many midrange drivers are MORE sensitive than typical low frequency drivers across their intended bandwidth.

[billfitzmaurice]

Originally Posted by MuzikMan

You shouldn't rely on WinISD for anything above 200 hz. Use spl charts to match drivers when crossing over in the midrange area. It makes no sense to me that you are trying to match drivers by plugging in 20 watts for the woofer and comparing it to 5 watts into a midrange driver. .

+1. You don't model a midrange driver, just use the data sheet SPL chart.

[dhomer]

Ok, I figured I was overthinking this a bit.. just want to make sure when I cook the recipe, the result's worth serving... More stuff to look at, methinks the solution will come.. Thanks again for the help, I'll report back on what we come up with..

[Passinwind]

Originally Posted by Bassmec

You should horn load the mid they make a cool glass fiber horn that gets a few more dBs out of the six inch, it sets the mid driver into the cab enough to help time/phase alignment too.

This JBL mid horn piece from the PRX 635 cab that greenboy found in the JBL spare parts stores was under $20 when I bought mine a year or three ago:



It's molded plastic, and not glass filled IIRC, but in my experience it works quite well if you add some constrained layer damping to the backside of
it. Be prepared for some DIY dweebing to make the driver mounting work though...

There is at least one variant with a nice phase plug too, but it costs quote a bit more dearly, and JBL may or may not even feel like selling you one.

[billfitzmaurice]

Originally Posted by Passinwind

There is at least one variant with a nice phase plug too, but it costs quote a bit more dearly, and JBL may or may not even feel like selling you one.

Without a phase plug the best you can hope for in HF extension is 3kHz. Even with one maybe 4kHz. Horns are low-pass devices, and you can't just slap a driver onto a horn and get a predictable result.

[Passinwind]

Originally Posted by billfitzmaurice

Without a phase plug the best you can hope for in HF extension is 3kHz. Even with one maybe 4kHz. Horns are low-pass devices, and you can't just slap a driver onto a horn and get a predictable result.

Spot on. I'm crossing at 3K, more or less where JBL does in the 635 IIRC. I slightly prefer the sound to a simple baffle mounted 6.5, but it's probably not worth the hassle for many people. To my ears it sounds pretty nice even without a tweeter too -- this with the 18Sound 6ND410 driver, FWIW.

[will33]

Hmm....what kind of modeling results are you getting with that woofer? That 98+db spec has a huge spike in the top end averaged in. Looking at the chart it runs 94-95db up to where you'd cross to the mid, that makes the Alpha 6 a good match for it but there's a big but coming here.....

fs of 28hz is super low, that's a heavy cone. Bass cabs with a real f3 in the 50's sound deep already, no need to venture into subwoofer territory. Commercial offerings that claim deep bass really start trailing off around 80-100hz. You're working with 30 watts. If it were me I'd give up that 28-56hz octave in exchange for more sensitivity. Try modeling it against a emi. Delta15 (non-LF) and see what you think. Then look at mids that can do at least 97db or so above 1kz. Having the mid a little less than the woofer still has plenty of clarity and presence, how much lower you can go depends on your ear. If you're crossing to a mid, ignore what going on above 1kz when looking at woofers, 800hz or so is a good place to cross a 15. Gaining 4-5db sensitivity where you need it has the same result as getting 3 to 4 times the amp power.

Edit: Delta Pro 15 or Kappa Pro 15 will get you even more.....just model the lowend in each in your box to find an acceptable midbass hump (or lack of).