Help with this Altec mid-bass horn design please

[atilsley]

Hi audio friends

I'm wondering if you'd kindly look over the attached drawing.

I've designed this for a couple of reasons.

1. The measurements of the outside cabinet exactly meet my room restrictions.
2. I already have the Altec/GPA 416-8G woofers (8 ohm versions, brand new).
3. The design incorporates both bass reflex loading and front loading for efficiency.
4. The design picks up some other proven horns, eg the Altec 816 plus JBL similar versions (but these have quite weak bass below 80Hz)

http://www.greatplainsaudio.com/downloads/416_8C.pdf
New Page 2

I'm wondering what ideas people could add to make this work?

In particular -

1. desired flare rate. I'm using a standard 30 inch constant radius, as per flare on the Altec VOTT A5/7. The top and bottom sections are curved, the two side pieces are straight.
2. porting. I think I'll just suck it and see, using 3-4 smaller 3-inch ports, where I can close off and tune accordingly.
3. dampening. I'll start with fibre/wool filling for first attempt.

My target is for a good bass response from 70hz to 800Hz with approx 98-100dB, where these will be crossed over to an Altec 511 horn using Altec GPA 902 one-inch compression driver. Xover to be decided, but likely to be MiniDSP active to best tune the bass and give some EQ where needed down low. I will complement the horn with dual tapped bass horns from 30Hz to 100Hz later on.

Room size is largish...eg 25 feet x 20 feet, opeing to a larger dining area. Distance to listeing position is 19 feet.

Typical source is CD, driven by 300B SET...but as stated above, likely to run a separate SS amp suitable for the bass horn, eg Pass Labs F5, which I have sampled before and sounds great with the 416 in my existing large 620 cabinet.

Kind regards

Andrew

[more10]

If you really want to build cabs like these, use hornresp to simulate it. Free software by David McBean, countryman of yours. There is a thread at diyaudio about it, there are many guides on the internet.

I cannot find a BL value of your driver, that can be a problem.

[atilsley]

If you really want to build cabs like these, use hornresp to simulate it. Free software by David McBean, countryman of yours. There is a thread at diyaudio about it, there are many guides on the internet.

I cannot find a BL value of your driver, that can be a problem.

ok, thanks. what does BL stand for? Kindly

[more10]

http://en.wikipedia.org/wiki/Thiele/Small:

Bl - The product of magnet field strength in the voice coil gap and the length of wire in the magnetic field, in tesla-metres (T·m).

Usually you want a driver with high BL in a horn, that is with a strong magnet (and a gap to focus the magentic field) and enough windings on the voice coil. Typically above 20 for horn use.

[Carl_Huff]

Andrew,

I know that some here would consider what I am about to suggest to be heresy but here goes ...

I suggest that you take a look at the classic JBL 4560 'Perkins' cabinet. The 4560 has a flare that is very similar to that of the VOTTs yet is sized appropriate to the needs of the GPA 416 8C driver. The A7 cabinet is actually a little large for that driver. I have GPA 416 8C drivers as well as both the A7 and 4560 cabinets in my collection. The GPA 416 8C measures 3dB down at 60Hz (no EQ) in the 4560 cabinet which is in line with your requirements.


_____________
Best Regards,
Carl Huff

[atilsley]

Thanks Carl, more10

I've look considerably at the 4560....-3db at 60hz is appealing.

My main objective is bass slam/attack.

How does the 4560 perform in this regard?

Kindly

[atilsley]

Carl, I like this pic...similar to the 4560...but dressed up nicely for domestic.

See also pic of another JBL black horn I like.

[Lee in Montreal]

My main objective is bass slam/attack.

I am afraid that if it is what you are looking for, the 816 might not be the right choice. It is even not a mid bass cabinet, and I would consider it an upper bass/lower mid. The 4560 is more suitable for upperbass, but there's not much meat under 60-70Hz. Great for vocals though. If you want to have horn loaded mediums, and articulated bass down to 40Hz, then there's the 4550. But it is way bigger. It has 20cft for two woofers while the horn loads down to 140Hz if I am not mistaken. I think you might be interested by some A7, with a few improvements in cabinet rigidity. It has more volume for your bass than the 816 while the horn is basically similar.

You can buy A7s for dirt cheap, and even get paid to move them out of people's home ;-) If you like what you hear, then build a better set.

[atilsley]

I am afraid that if it is what you are looking for, the 816 might not be the right choice. It is even not a mid bass cabinet, and I would consider it an upper bass/lower mid. The 4560 is more suitable for upperbass, but there's not much meat under 60-70Hz. Great for vocals though. If you want to have horn loaded mediums, and articulated bass down to 40Hz, then there's the 4550. But it is way bigger. It has 20cft for two woofers while the horn loads down to 140Hz if I am not mistaken. I think you might be interested by some A7, with a few improvements in cabinet rigidity. It has more volume for your bass than the 816 while the horn is basically similar.

You can buy A7s for dirt cheap, and even get paid to move them out of people's home ;-) If you like what you hear, then build a better set.

Thanks..I've also agonised over the A7/5...and this might be eventually decided upon...however, I just want to exhaust this mid-bass option in the first instance.

Remember, I did say I wasn't fussed over the low frequencies, as I will build some tapped horns to cater for the 40-100 range.

My main objective is horn loaded mid bass for slam and attack.

See attached a revised drawing of the 2360 where I've taken the horn flare out to the perimter of the cabinet, and increased the mouth by a few cm in both width and height. I'll need to keep the cabinet depth the same.

I think this tweak to the design will retain the worth of the front loading, while giving me another 40-50 liters of volume, which will improve the 60-80Hz area. For this to work, obviously I'd need to relocate the ports to one side, or a combination of 2 ports either side....which is do-able in my opinion. I also think the deisgn would look better, with the larger/cleaner horn exposed. A bit like the attached pic (although this Haigner bass horn is probably more like 65cm x 65cm....still, you get the idea.)

Kindly.

[atilsley]

Forgot to attach my drawing...

[Carl_Huff]

If you want to extend your horn loaded 4560 cabs and have the room I suggest that you build a pair of F-20 cabinets described in this thread ...

http://www.avsforum.com/t/1329971/lilmikes-cinema-f-20

I built a pair and have been very happy with them. They run strong between 20Hz and 80Hz.
______________
Best Regards,
Carl Huff

[atilsley]

If you want to extend your horn loaded 4560 cabs and have the room I suggest that you build a pair of F-20 cabinets described in this thread ...

http://www.avsforum.com/t/1329971/lilmikes-cinema-f-20

I built a pair and have been very happy with them. They run strong between 20Hz and 80Hz.
______________
Best Regards,
Carl Huff

Thanks Carl...I recall reading about your bass horn some time back...well done.

I've built the 38Hz and 30Hz smaller tapped horns from Volvotreter web site...plus a massive 20Hz model at 8 feet tall. I've built bass horns for GOTO, plus numerous Tannoy rear loaded horns, plus Lowther etc. All good fun.

Yours looks amazing....=/1 3dB 20-100Hz....that's excellent.

What sort of amp?

BTW, I've started on an open baffle 'horn' based on the Bert Dopenberg (of Oris fame) design...but I was going to build the half version, with x2 416's/side. My projec has stalled, because I want to ensure I get the best mid bass sound possible...hence me inquiring about the JBL and Altec variants.

See pic of the Oris open baffle....quite a startling looking design, I think. Bert thinks it's the best bass he's ever had. (Mine is the unfinished frame.)

Andrew

[atilsley]

Oh, here's some pics of my current rig (Altec 620 style cab with 511 horns), plus earlier horn setup from Stereolabs with Selenium drivers. Have also had Crites Cornscala's.

Before I borrowed my mate's 511s, I was using Paudio (JBL clone) horns, note silicone for dampening...drivers are 902's...plus U have brand new ones from GPA.

Andrew

[atilsley]

My amp is a 300B SET from Oz designer, Earle Weston...he has some nice products. See pic of my earler 2A3 PP amp also from Earle.

[more10]

I've built the 38Hz and 30Hz smaller tapped horns from Volvotreter web site...

Check out his midbass horns. Much longer than the ones you are talking about. The horn length decieds low end of the horn. It is the horn that gives you the slam, not the ports in the back chamber. A midbass horn is typically 1,5 meter (4,5 feet) long.