Bass Horn Cabinet Coices?

Hello Speaker Gurus, I am in the planning stages of my first serious speaker project. All I really know about speakers at this point is how to hook them up and that I like horns. This brings me to the problem. I want to build some bass horns but don't know where to start. I can handle the woodworking ok, but I'm not sure about the design choice. I have some plans for a 15" Bass-Scoop rear horn loaded cabinet (AKA JBL 4530). It basically has the woofer at the top facing out and a 7 foot folded rear horn that empties out underneath. Problem here is the WAF as they are pretty big, 43"tall, 30" deep, and 26" across. I see a pair of yellow (I think) bass horns in the random photo's at the AK home page, which are basically just horns. I'm just really looking for ideas as I don't have a clue. I plan to use some EV SRO15's with a very low power amp (about 8watts per channel). If this should be in DIY maybe a Mod can move it. I just figured, ask the speaker nuts. Jay

I'm not sure but I think you are going to be hard pressed to find a bass horn with dimensions any less than what you've stated and still get good performance from it.

jaymanaa said:

Hello Speaker Gurus, I am in the planning stages of my first serious speaker project. All I really know about speakers at this point is how to hook them up and that I like horns. This brings me to the problem. I want to build some bass horns but don't know where to start. I can handle the woodworking ok, but I'm not sure about the design choice.

Click to expand...

My first inclination when presented with a question like this is to read all I can about the issue. I just went down to our bookshelves and see that we sell no less than 5 books related to speaker design (not counting the two I saw that were just for electrostatics!)...Designing, Building and Testing your own Speaker System by David Weems, Loudspeaker Design Cookbook, Vol. 7, by Vance Dickason, Speaker Building 201 by Ray Alden, Loudspeaker Recipes by Vance Dickason, and Audio Amateur Loudspeaker Projects from Audio Amateur Magazine. And this month's Audio Express magazine has a design for a transmission-line subwoofer that will fit (mostly) under a sofa! They have also had articles about lots of DIY enclosures, including some wild-looking horns...If I were contemplating building my own speakers now (I've done it in the past), I could be reading for months!

--Bob

You can take a tuba and make it half size... but it is no longer a tuba. It is then a baritone horn.

Long wavelengths take long horns to reproduce them... IF you are going to build a horn speaker. No matter how you fold, bend, or mutilate, them, roll them up into a ball, bass horns are still BIG. There is no other way, bass horns are big, physics being what it is and all that.

Many compromise on horn systems by using mid and tweeter horns, and bass reflex bass cabs. This can give great bass with cabinets in the 3 - 5 cubic feet range. My personal experience is that you don't really get smooth low bass from anything less than a 12" woofer. I like 15" woofers in 4.5 - 6 cft cabinets... most of the good 15's end up in ported boxes.

But that rear loaded horn is not a bad design. I had sent those (and other) plans to a fellow, and he built the Mogales 18" version which is even bigger. He is quite pleased with it.

The scoop is used by some bass guitarists, and it works fine for that. But it is used a lot for large outdoor PA systems. They place a bunch of them side by side, or stack four, the bottom two upside down, so that all four mouths are together. These are also used in clubs and on stage as part of PA systems. You can stack a mid horn and tweeter on top.

I have photos from a company who has these as part of a fine home stereo type speaker, the Air Partner (upside down scoop) and Air Scout. Another home stereo application of the scoop design is the BK-16 kit on page 63 of the current Madisound catalog. This is a small design with a more complex, long channel in the upper section, and they use a flat panel (as I describe further down) in the mouth of the horn.

http://www.madisound.com/cgi-bin/index.cgi?keywords=BK-16

http://www.madisound.com/cgi-bin/index.cgi?cart_id=5971460.10783&pid=1895

For the "scoop" designs it is NOT, repeat NOT necessary to put that curved ply section in the bottom of the mouth. It is neat looking, but a real pain to make. You can do as well acoustically with a flat panel put there at a 45 degree angle. Believe me, at those frequencies there is no auduble difference. In the third drawing below I have sketched in a gray line to show the substitute piece I use when making these.

The curved bottom piece is formed by first gluing in a piece of 1/4" ply and pushing it into a curve, lots of glue and screwing it into place with drywall screws. After that has driec, a second piece is laid on top of it using contact cement on both pieces. Some guys drill a few holes in the back and bottom and inject expanding foam in the airspace under the curved baffle.

The "scoop" or "rear loaded horn" is interesting in that it is a horn, but also a "transmission line". Undamped transmission lines have an up and down frequency response... looks like a sine wave. For the lowest frequencies the rear wave emerging from the horn mouth is in phase with the woofer's front wave. Other frequences are out of phase and cause a dip on response. So the trick with a transmission line is to "stuff the line" with sound absorbing material... long fiber wool, fiberglass (LAST RESORT), or my favorite, dacron poly fiberfill. This damping acts like a low pass filter. If you can kill off the higher out of phase frequencies, allowing only those lowest in phase notes, you can have all of the advantages and none of the disadvantages of the transmission line.

At still higher frequencies, the horn is not acting at all. The higher frequencies come from the front of the foward firing woofer.

So, stuff that section behind the woofer, the upward leading channel, and part of the downward channel leading to the mouth of the horn. You can make it stay up there with some staples, out of sight.

I'll attach a side view of a "rear loaded" or "scoop" cabinet. Aka JBL 4350, Eminence Scoop, Fane Scoop, and many other names. Who really invented the "scoop"? I don't know.

1st picture, the JBL 4350

Second picture will show up as a line drawing even though it looks black below.

Note the third picture has the diagonal drawn in.

Excerpts from an email to me by a scoop builder:

Hello Paul

If you will recall, you helped me with a horn project a while back, the jbl scoops. Just wanted to give you an update. I finally got around to working on this a bit, and wow, the results are very pleasing!

I built the mogale 18" version basically. This speaker is so loud! the 200 watt head that I'm using with it is more than enough.

Sounds great with standard tuning on my four strings.

I did a gig last weekend, used it with a 2x10 top cab, biamped, and WOW! The sound techs were all over me wanting to know what it was!

I'm going to build another one, better, more "craftsmanship" for my final unit.

Thanks again!

Lawrence

And another email:

Yes, I did bend that piece, just because I thought it would LOOK cooler...more SCOOPY! (I if you know what I mean).

And I did use the truck bed liner stuff on this one. I built the thing out of OSB, rather than plywood. I used APA floor underlayment grade. It's stronger and lighter than most plywoods, more economical too. The truck bed liner makes it look good too. I wonder if it doesn't damp the panels a little as well.

I stuffed exactly as you recommended.

Another happy camper! :thmbsp:

Also check out this:

http://www.pispeakers.com/catalog/product_info.php/products_id/121

It is the 8pi Thermionic... a two way horn system especially designed for tube amps such as yours.

Before you get sticker shock... that price on the link above is for the factory built units.

You can buy the kits quite reasonably, and the site owner will send you plans. Buy and cut your own wood.

http://www.pispeakers.com/catalog/product_info.php/products_id/112

I believe you used the terms "bass horns" and "WAF" in the same sentence.

Those cannot peacefully coexist. Many physicists, psychologists, philosophers, biologists, and anthropologists have studied the subject for the last half century, and have come to a remarkable and unanimous consensus, unknown in any other area of the arts and sciences: All domesticated females require invisible speakers.

I would respectfully suggest choosing a different speaker design, or choosing a different spouse (with the caveat that the above findings are absolute truth as we currently know it, so the second option really isn't one at all).

Theodoric is correct.

WAF = 1/Vb, where WAF (some use SAF, Spousal Approval Factor) is Wife Approval Factor, Vb is the volume of the box, litre's or cubic feet, it really makes little difference.

In general, WAF < 1 bears little chance of success, and a great chance of divorce.

WAF > 1 is considered borderline acceptable.

That being said, I have built speakers with WAF = .33 to WAF = .2 range and lived to tell about it.

Check out the Eminence Delta-12LF in a 3.3 cft ported cab.

http://www.partsexpress.com/pdf/290-416c.pdf

I posted some thoughts on bass horns back in this thread Jay and for the reasons I stated there, think you are on the wrong path considering bass horns unless you only want real horn loading down to about 80Hz. Even an 80Hz horn, ¼ space loaded (against a wall) requires a 4 square foot mouth and about a 2’ horn length – a big box that only goes from 80 to 500Hz or so.

If size and WAF is an issue (especially WAF), I feel the best coarse for a 97 to 100db efficient speaker is a 15” pro-style woofer in a large vented box crossing over to a horn at 500Hz or above.

On the woofer side, I have the most experience with the Altec 416 and 515 series woofers in boxes up to 9cu.ft. and in front horn cabinets like the A7. The 416 in a 9cu.ft./40Hz tuned box will give you an honest 99/100db from 40Hz up to whatever cross you need for your horn and sound damn nice doing it – not a horn but the speed, dynamics and sense of effortlessness is pretty horn like. You will have to pad down the horn to match the lower efficiency but this can actually work to your advantage as the padding circuit can include a horn EQ bypass cap that does an amazing job of taming the horn shout and extending frequency response.

I’m not too big a fan of the A7 approach that combines a small horn (100Hz?) with a vented box as I find these have a distinct ‘shelf’ in the bass with a soft low end and big hit above 100Hz or so. They sound fantastic with a horn sub (and in a HUGE room) but the right woofer in a large vented box just seems a better compromise for regular rooms and the usual spousal issues.

There are certainly drivers other than Altec 416’s that will do a great job here too and I’ve really liked some of the Eminence, JBL and EV’s I’ve heard in this configuration. You mentioned EV SRO15’s in your question – do you already have them and do you know the TS specs for them? (I couldn’t find anything).

If size and WAF is an issue (especially WAF), I feel the best coarse for a 97 to 100db efficient speaker is a 15” pro-style woofer in a large vented box crossing over to a horn at 500Hz or above.

I agree, Bill. There are many small subs, too, but they are all power hungry. They do the job by pure brute force from the amp... brute force Jay is not going to get from an 8w SET amp.

He needs high efficiency, but this can be had in many medium size ported boxes, too. The Eminence Delta-15, Gamma-15 (works nicely in 5cft), Delta-12LF, are all good ones to consider. When you look at these on the Parts Express site, click the "Project" tab. That will give you a pdf file you can save with box and port size, response information for the woofers in question.

Here's the specs I got from EV. I just had a long talk with the Missus, and she agreed that one wall in the living room was designated for audio equipment. So what do you guys think about these woofers? Will they reproduce 8 watts worth of bass efficiently? Thanks for the help, Jay

No Thiel/Small specs there Jay, without them you can't estimate response, cabinet parameters or efficiency.

Well I couldn't find any T/S ratings either I guess I'll resort to my highly scientific method of building something and seeing how it sounds. I think I'll try the JBL 4530 scoops, as I have detailed plans and instructions for building these. My room is 24 feet long with ten foot ceiling. If these don't work out with the 8 watts available, I can allways use them with something more powerful in the garage. :yes: Can anyone shed some light on what the EIA sensitivity rating in the specs means? Thanks, Jay

Have no idea about the "EIA sensitivity" rating. These are quite old speakers, huh? Without seeing some t/s parameters I don' know if they are suitable for horn enclosures.

Woofers that do work well in those scoop enclosures are 15" woofers such as JBL and EV pro woofers, Eminence Delta-15, Delta Pro-15, Gamma-15, Kappa-15, etc, Pyle PYM1555, PYM1578, PYM15128, and others. These are all high efficiencey woofers with SPL's in the 95-99 db range.

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ETA [whisper]This guy actually bought the wood and is building these things. I don't think his wife realizes what she is getting into. She will probably bring up the "D" word. Let's watch and see how this develops... its like watching a train wreck. [/whisper]

This thread goes to Phase 2 at

http://audiokarma.org/forums/showthread.php?t=76361&page=1&pp=15