[strider]

Recently finished building my first pair of OB speakers. They are Hawthorne 15" Silver Iris drivers mounted in a 32" by 22" baffle. They've been running in for a couple of weeks now with no issues; time to start looking towards the next project!

Thinking about adding something to augment the bass. So far they seem slightly thin in the very low ranges. Bass detail is very good, output is sufficient (they don't "thump", but that's fine by me) but I feel my system could use a bit more presence in the low end. Reason for the post is to start a discussion about my system and see what other's experiences are.

The system: Source - Flac files from a PC, played through JRiver MC 18 into a DIY DAC based on a Burr Brown 1792 evaluation board. Pre - Aikido Octal running 12SN7 tubes, 2 pairs of outputs. Amp - PassDIY F5

Other equipment/tools: Rotel 120wpc into 8 ohm amp, miniDSP 2x4 crossover, measurement mic and associated equipment, REW.

Don't have: tons of money 

So far I've been looking at the Eminence Alpha 15A drivers in H frames. I'd like to build them as seperate cubes so I can move them around the room easier. Last speakers had bass modules that doubled as stands for monitors, and I didnt care for having the locations locked together. Also, with 2 little kids, I dont mind being able to drag them out of the way when not in use.

Any thoughts/experiences to share? Measure the current speakers and go from there? Two weeks of use too early to rely on measurements?
Like I said they are my first OB speakers, anything you could ad  would be great!

Thanks!
Ben

[mcgsxr]

Ben, good job on your first set of OB's, welcome to the club!

Even better job getting it done with little ones around the house, I too have experienced the pleasures of life with kids and large panels of mdf!

My own experience with bass augmentation for OB mains was varied.  I used a sealed 12 inch sub for a while, I used a different ported 12 inch sub for a while, I used a single 12 inch OB sub for a while, and eventually went for 2x12 OB sub biamped with my mains.

I built the bass drivers into the baffles, and would caution against it - I found the vibrations of the bass driver "smeared" the mids and highs from my main drivers (I used modded 8 inch Visaton b200's).  I did not want to use extra floor space though, so the compromise was one I had to live with.

The Alpha's you reference have a very positive history of being user friendly, and pretty good on OB.  There are other options (HA's own Augies clearly are an excellent choice too) including some from some of AC's own manufacturers.  There is a long thread on right now about some of the pro's of servo amps, you can review that if interested.

My own experiences never included measurements.  I recognize that this casts me out in many circles!  No matter, I tuned by ear, for my ears, and did not often have folks complain about the sound.  In fact, only 1 did, and I respect that he heard what he heard.

So, were it me, I would bang together some mdf baffles for a pair of Alpha's, biamp them with that Rotel, and see what comes of it.  Very cheap experimentation to be sure, since you already own the bass amp, and an Xover.

[Mijknarf]

Ben, I use separate H frame Eminence Alpha 15" units with my OBs to support the low end.  They are easy enough to build, but I didn't find much difference in sound regardless of where I positioned them in my room, thus, I made my OB baffle to fit on top of them.  I make an attempt to separate the vibrations coming from the H frame units by using a thick piece of granite and layers of cork/sorbothane between the two units which seems to work pretty well for me.  Simple pulls added to the H frames allows me to pull the units into/out of position fairly easily.  Good luck with your project.

[nicksgem10s]

Hi Ben,

I have dabbled a bit with open baffle speakers and really enjoy their sound.

I want to give you a strong recommendation to try to buy a pair or 15" Hawthorne Audio Augies.  You can build simple stand alone baffles for them.

I used the Rythmik Audio PEQ370 plate amps with the OB shelf circuit built in.  I hope that is the correct amp info as I am going from memory from a couple years back.

Incredibly satisfying bass performance with several different open baffle systems I have tried.

While they are not cheap I feel they are an excellent value.  Compared to some competitors products such as AE Dipole woofers the Hawthorne Audio Augies are a complete steal.

The fact that you are already using Hawthorne speakers seems to be a no brainer to me if you can swing the funds for the Augies.

Maybe you could sell the Rotel and repurpose the funds to buy the new drivers.  I think there may also be more affordable plate amp options that are still very good performers.  I think that Kiega may be the brand of the more affordable plate amps.

If I go back to open baffle in my next system I will likely use 4 of the Hawthorne Audio Augies.  They are excellent performers!

-Nick

[Mijknarf]

Hey Nick, I've often considered trying a pair of Augies in my H frames.  By chance have your ever compared them to the Eminence Alphas?  I wonder what kind of improvement it would be?

Thanks,
Jim 

[JohnR]

Measure the current speakers and go from there?

Sounds like a good idea

[Poultrygeist]

H-frame Alphas are versatile enough you can use them in a variety of different combinations. I've paired them with conventional full range box speakers, BL horns and OB tops. I now drive them with Yung class D plate amps.

[Guy 13]

Hi Ben and all Audio Circle members.

I own and use a pair of GR Research V1,
two pairs of (Modified) GR Research V2
and one pair of modified GR Research N3.

The V1 use the GR Research servo drivers (Two per side)
and the V2 use the Eminence Acoustinator, again two per side.

Of course the N3 needs a sub to complement.

Eminence Alphas or equivalent and
Dayton plate sub amplifiers are really affordable
and you can buy the Eminence and Dayton at Parts Express.

All easy to build, affordable and good performer.
I also found, like many Audio Circle members that the H frame does not need critical positioning.

I did not do the wood work, but I am sure any Home Depot
or equivalent can do it for you for free or minimum charge.

Good luck.

Guy 13

[unit]

Hi guys-I distribute the Bastanis speakers here in the U.S. and use the Mandala for my demo system. With the help of other qualified engineers, we came up with a modification of the standard Mandala-one that incorporates wings to help the low midrange fill in a bit more. With the wings folded back to 45 degrees the upper baffles are supported and can stand on their own. This allows the open baffle bass enclosure to be free-standing and not touch the upper baffles which we felt was a big benefit. The open-baffle bass now can truly keep up with the upper registers.



Bill at beautyofsound.com

[strider]

Thanks for all the responses everyone.

Poultrygeist - I've read through your posts about your build a couple of times and am especially glad you chimed in.

Nick - Mostly for cost considerations, I think I'm sticking with the Alphas assuming I do go ahead and build some subs. The Rotel I have wouldn't sell for enough to get too much further down the road. I think it retailed in the $700 range when it was new, which I think was late '90's.

Bill - While I'm certain those sound good, I think they may be a bit out of my league.....

Once I get some free time, I'm going to get the measurement equipment out and see what I am working with. Working things through in my head, I'm thinking that it wouldn't make much sense to run the Hawthornes full range. I'm expecting them to be down into the 50hz region in room; from Mr. King's site I see he measured H frame Alpha's as having a -3db point of 26hz. In terms of plan of attack, I'm thinking I'll measure the in room response of both speakers as a system with the mic in my usual listening position. Playing aroud with placement and listening, I feel I've got the speakers in a good place WRT soundstage, imaging and frequency response. Still debating whether it would be beneficial to measure each of the drivers independently of one another.

[Luigi]

Hi Strider

Here's an off-the-wall option for you, but it is cheap.

You have the PSIs, correct? Try changing the parallel crossover for a series one. Getting rid of the poxy components on the original board helps but better still is the change to an ARSXO type crossover. Just google it, and you will find the original Acoustic Reality Crossover. I've tried various implementations of this and all are good. In terms of safety, I've not yet blown up amps or drivers.

By getting rid of the caps, you'll notice an immediate improvement in bass strength and tonality. It's a real cheap upgrade too, because all you need to buy are a few good qual resistors, and a couple of foil-type inductors. Unlike the parallel crossover, using rubbish parts works ok as well, good for when you're dialing in the resistor value.

It's real easy to wire up, and you'll also notice slightly improved midrange clarity.

Downsides? Getting the right values for the resistors isnt easy, but as a hint, I'd take a very careful look at the resistor value on the standard parallel PSI crossover. It's a good place to start.

If that idea doesn't float your boat, you can always do what others have done and add a sub, but I'd strongly recommend an OB sub. Mine is a 4 foot long cylinder with a 15inch DIYCable driver in the top, and nothing in the bottom (like a U shaped baffle, in other words). Mine sits in the corner upright and is about an inch off the ground. The interior is filled with stuffing used in pillows. With a decent sized plate amp its a cheap way of adding solid bottom end.

But I'd start with the series crossover change; it makes a surprisingly noticeable and agreeable difference to the bass impact of the 15 inch driver, even with crappy crossover components.

[sfdoddsy]

I'd measure to see if you need a woofer, or a subwoofer.

If you need a woofer the dipole options suggested make sense.

If you need a subwoofer (ie below 50hz or so) i'd go sealed.

[Luigi]

Nothing wrong with sealed, but if you're OB on the top, why not on the bottom as well? The downside is it may cost you more, having to double up on drivers to get a similar effect.

Sealed and ported both load a room (which can transmit to the rest of the house) while OB bass doesn't.

Sure, you wont get the gut thumping bass for HT, but you will get the pleasant tonality that you also have from OB mids. I've had all three, won't be going back to sealed or ported, but that's just one opinion. If you want visceral bass you wont get it from OB without going large.

[JohnR]

I'm inclined to agree with Luigi. Bear in mind that once you have gone to having the subs separate from the mains, you have a lot of flexibility with placement, and that can mean very large gains in terms of (effective) output and reduced room effects. Here is one reason why, I'm interested to see results from anyone that does a similar experiment: http://www.hifizine.com/2012/03/on-dipole-subwoofer-placement/

[sfdoddsy]

For me the requirement is a balance between quality, quantity and practicality.

As John's experiments show, it is arguably easier to achieve quality of bass with dipole woofers.

But getting the quantity of quality bass is a different story.

On occasion I like to listen to music with significant deep bass (organ, big orchestral, reggae) loud.

And I find bass that measures with a slope downwards from 20Hz or so sounds most lifelike.

John's tests all show a roll-off in the true subwoofer regions. Whilst it certainly possibly to EQ a dipole woofer system to have true 20Hz extension (and mine sometimes are EQed that way), they are severely volume limited.

Unless you have magic woofers.



I've bottomed mine numerous times and blown one when I accidentally had the prepro on full range.

Of course you can add more dipole wooferage, but doubling to 4 x 12 a side is only going to add another 6dB and if you are bottoming your woofers already 6dB isn't going to mean much. You need to go to StigErk extremes to really have the headroom.

So to me it makes much more sense to bring in a big old-fashioned true subwoofer below 40Hz (I use a Velodyne HGS15 servo). Down that low qualitative differences are moot and I'm fairly sure dipole woofers that don't flap due to 20Hz signals sound better than those that do.

Of course if your musical choices don't require really deep powerful bass you'll be fine.

But if they do, I'd abandon dipole theory in favor of practicality.

[Poultrygeist]

I picked up these Yung class D plate amps to drive the H-frames and do they ever! These are the SD300's on sale at PE for $99. The class D's sound very clean and extract some nice detailed bass from the Alphas.

[Poultrygeist]

The H-frame Alphas will cover the lowest note on a double bass which is E at 42 Hz.

There is little music information below 42 Hz on most recordings.

[strider]

Six months later, and I finally have them knocked together. Still not finished, but they should at least be operative. They're pretty much the exact set up that MJK has described in his paper about bass response of open baffle speakers, Alpha 15A in a 16" square baffle with front and rear cavity depths of 7.5".

They're hooked up to an amp, but I need to figure out what I need to do to get my miniDSP working with a new computer. I much prefer sawdust to software, but hopefully this should be fairly painless. 

[4krow]

  So far, I have had good luck with the OB design by Decware(ZOB). It reaches down to about 40Hz. To augment when needed, I have used dual subs, sealed with a passive radiator. I have got them running, but the effect is just right for my taste. I am also using a Velodyne SMS-1 to EQ the subs.

[opnly bafld]

  So far, I have had good luck with the OB design by Decware(ZOB). It reaches down to about 40Hz. To augment when needed, I have used dual subs, sealed with a passive radiator. I have got them running, but the effect is just right for my taste. I am also using a Velodyne SMS-1 to EQ the subs.

Your solution should work well since the ZOB design does not produce true dipole (open baffle) bass.