The H-frame makes great bass. Thanks to MJK’s wonderful H-frame design I’ve been able to enjoy open baffle bass in my home. It also makes a great speaker stand. I’ve placed small sealed and ported speakers on top (and enjoyed the sound) but decided to try open baffle with my growing collection of full range drivers.
I enjoy full range drivers for their coherent, crossover-less sound. I was pleasantly surprised how good they sounded on a simple open baffle. This has been my setup for the past few years and its provided a very enjoyable listening experience.
Following the basic formula MJK outlined in his H-frame + Jordan project with just a few modifications proved successful. While MJK chooses to administer crossovers on the woofers I take an easier approach using a typical subwoofer amp to dial in the bass. MJK incorporates a cutoff frequency on the full range driver where I simply run them without filters. With my approach the baffle size (18″ x 18″) naturally rolls off the full range driver of your choice somewhere around 250Hz. Feel free to include circuits for an even steeper bass rolloff and additional protection. An inexpensive option is to use a single 200mf capacitor wired to the positive terminal of the full range driver. This will reduce bass frequencies another 6db per octave from about 150Hz and below. Although I understand the benefits of filtering out bass I’ve yet to blow a driver and do not hear any distortion. In fact, the driver barely moves in my setup. Additionally, the idea of running the wire directly from the amp to the driver is appealing. Steeper filters consisting of caps and coils can be used but require more expensive components that cost more than many full range drivers.
Sample of 3″ drivers naturally rolling off on an 18″ x 18″ baffle. Larger diameter drivers will roll off at approximately the same frequency.
Once you’ve built your H-frames position them where you like and listen. Modify the placement if necessary and mark your spot. Although many suggest two to three feet of space from rear and side walls sounds best I found that just a foot or foot and a half works good too.
In this chart I’ve included the Eminence Alpha 15 response on open baffle (pink line). As you can see the Alpha 15 is much more efficient than the 3″ drivers. I’ve taken the liberty to show what I believe is happening once the Alpha 15 is connected to a subwoofer amp with Gain and Frequency controls. Using Photoshop, I created the adjusted curve (blue line).
Since I enjoy rolling drivers a way to swap different baffles was necessary. I devised a handy stand. A wooden lip in front and a cinder block in back enable easy angling for best sound.
The baffle is simply a 19″ x 19″ square with a hole in the middle. Offset the hole if you feel it will sound better. Personally, there are so many room variables that I don’t think offsetting the driver will sound much different – for better or worse. But feel free to experiment and do what you feel comfortable with as a DIY speakerbuilder. In addition, there’s no need to concern yourself with driver specifications (for example, Qts, Qms, Vas, etc.) as needed for sealed, ported or back horn designs. Just screw your favorite full range driver onto the baffle and you’re good to go.
So how does it sound? Excellent! Fortunately, all the calculations and math have been done for us thanks to the mindshare on the internet. The H-frame is a brilliant design that maximizes bass quality and quantity. Its size vs performance ratio is better than anything I’ve heard. Large bass bins or back horns don’t need to live in your home – unless you want them there (they do have their own advantages of efficiency and dynamics that are tough to beat). The H-frame does require a good amount of floor space so this is an admittedly large speaker. But the sound is beyond reproach and very musical, in my opinion. Mini monitors plus powered boxed subwoofers just don’t sound as realistic. Any type of large boxy speaker cabinet just sounds different – although there are many different ways to build a great sounding speaker. Open baffle is more my cup of tea at the moment. I just prefer the sound they produce.
Open baffle speakers have the following sonic characteristics:
• Wide soundstage – orchestras sound BIG
• 3D imaging – instruments and vocals float in space
• Natural tone – no thumping bass or boxy colorations
• Space between instruments and vocals – there’s more ‘there’ there
I like traditional boxed speakers and have a great set in my bedroom but because of their limitations I listen to them less critically than I do open baffle.
Once setup properly, open baffle designs just let you enjoy music played thru your favorite full range drivers.
If you are interested in learning more about open baffle and full range drivers I highly recommend building an H-frame plus open baffle system. From one audiophile to another – one music lover to another – I predict you won’t be disappointed.