15/6 Bass Cab Design

[GordB]

Hi. I'm new here and new to speaker design. I originally posted this over in software but didn't receive many replies. My apologies if I've broken any rules.

At this time I have on hand two Eminence 3015 drivers which, while being very efficient, having good xmax, and good power handling have a large spike above 1100 Hz that makes them very hard to eq, and they also have a strong tendency to beam which makes them hard to use as a stand alone speaker in a live band situation.

I have decided to build a cab with a 6" midrange to improve dispersion and smooth out the spikes. I recently purchased an Eminence Alpha 6a for this task. My intent is to build two cabs with a woofer and mid in each. Mid will be housed in a .14 cubic foot sealed chamber within the 2.87 cubic foot bass reflex cabinet. Cabinet will be tuned to 47 Hz.

Amplifier is a Mesa D800+ which is rated at 800 watts for 4 or 2 ohm operation, and 400 watts for 8 ohm operation. This amplifier comes with a 2 pole 22 Hz high pass filter plus a variable 2 pole high pass filter up to 150 Hz.

I am using Vituixcad2 to help design the crossover for this. Below are some graphs for an early design. I realize that I will have to measure the drivers in cab at some point to fine tune the crossover, but I have to start somewhere.

Please let me know if you see any problems. I'm concerned about impedance issues.

Thanks in advance for any help or advice.

[tmuikku]

Hi,
without measurements it is shooting from the hip Altough, instrument use is different than hifi so you don't have to show your measurements (or lack of) to anyone so you could try to fine tune it by ear. It is your sound as a bassist.

Seems close enough to work. I'm no expert so cannot give further advice than check out what others do and try to find out why, for example fEARful passive crossovers by greenboy

[GordB]

Thanks for your reply. I've crawled through those Greenboy pages a lot. He really put a lot of effort into those designs.

My set up is different though. I'm using the 3015 standard, whereas he uses the 3015 LF which is more like a sub. He also uses the 18sound 6" as opposed to mine which uses the Alpha 6a.

I bought the 2 3015 drivers and built a cab with no mids or tweeters based on the recommendations of others, but it doesn't sound all that great as is. Sure, it's loud. But it honks like a goose.

So now I'm stuck with them and have to build around what I have.

[tmuikku]

Ah, alright, might be baffle step? I mean ain't honkin around 400- 1000 hz region, which is still under the crossover to 6" you are planning, and possibly above bafflestep frequency. Not knowing your box of course.

edit1: I've been playing el. bass over 20 years but never done a DIY cab or amp so haven't checked whats the fuzz Happy ampeg user.
edit2: your cabinet might be resonating making it honk, how is your construction? any pictures / drawings? I mean something must be wrong in the implementation since there is millions of 15" cabs out there doing their thing since original Fender Precision.
edit3: now thinking about it it is not probably bafflestep either, because of the million small and large 15" cabs working just fine. It is either the box emitting sound and / or mids leaking out from the possible reflex port(s).

[GordB]

Ampeg. The gold standard. The sound on pretty much every hit record over the past 40 years.

Thing is, with the 215, the amp, the pedal board and two basses, it's a one trip load in. The cab in it's current state is built of heavily braced 12mm ply and weighs 66 pounds. It's on wheels and fits in the back seat of a Mazda 3.

It's not a bad situation, but it could sound way better.

[tmuikku]

Yes You could try the cabinet with reflex ports blocked, try to listen if it changes the honking. Also, do you have any linings on the walls / fillings inside the cabinet? Too much filling could be detrimental the low end response of a reflex cab, making it midrangy sounding. On the other hand, some filling / lining along the walls could remove some of the resonances inside the box, which will leak out from the ports (might be audible).

You could also borrow an EQ pedal if you don't own one and play with it if you can spot the problem frequencies. You would hear if it some kind of resonance that could be fixed or is it just that the drivers / cabinet is something that just doesn't fit your personal taste. You can always sell the drivers and buy something else, like Ampeg or Mesa cab

Good luck!

edit: yes it could be that your box is fine and the 15" are beaming too much for your taste. In that case addition of a 6" mid would help

[GordB]

These drivers don't do well in a sealed box. No bass whatsoever. I haven't tried it personally but others have and reportedly its pretty weak. And, the manufacturer recommends bass reflex.

The box is lined with 1 1/2" foam mattress topper. Everywhere except the back wall at the port.

This amp has a two band semi parametric eq with lots of frequency range. The peak extends from 1100 Hz to about 2500 Hz and is about 4 db. On the one hand, I can kill the honking but it then sounds pretty lifeless.

For pedals I have a tuner, Diamond compressor, OCD overdrive and Chorus. The Diamond has a feature called a tilt eq. Switchable from 700 to 250 Hz. Clockwise boosts everything above the frequency point while cutting everything below, and counter clockwise the reverse is true. What makes it sound pretty good is boosting everything below 250 and cutting everything above 250. Just a little bit.

I don't think I could sell the drivers unless I take a pretty significant loss. Until very recently there was nothing like this 215 cab on the market for power handling, volume and portability. Now some of the manufacturers are building something similar. I could just go buy cabs but where's the fun in that?

I have to go forward.

[GordB]

Prime areas of concern are impedance load, relative power handling and the difference in sensitivities between the two drivers.

The graph indicates 5.9 ohms minimum with the current crossover configuration. Is this too low? Should I consider it a 4 ohm cab or an 8 ohm cab as is? (The amp is capable of 2 ohm operation.)

As to efficiency, the 6 is rated at 93.6 db while the 15 is rated at 100 db. I do want the top end to be subdued but will this be too much?

Also, the 15 is rated at 450 watts while the 6 is rated at 100 watts. Should the mid be upgraded?

[tmuikku]

Ok, as per your description it might very well be the baffle step issue after all

You could try that first, an inductor and a resistor, you'll find calculators online. Hopefully someone more knowledgeable has tips regarding this since it is relatively high power application and puts some requirements on the components.

Baffle Step Compensation

[leadbelly]

Wrong forum. You're overthinking it. MI speakers not designed with flat FR as important criteria. Forget baffle step. Bass cabs typically tuned a little HIGHER than flat bass extension.