Front horn loaded bass reflex

[panos29]

O.k after alot of reading in the literature and endless seraching and reading of old posts here, I decided to get started with a new project I got in my mind for a long time now.

So here it is, I was thinking of a loudspeaker design of a box around 50cm width 60-70cm height and 50-60cm depth, containing a woofer 12 or 15 inch loaded at the back with bass reflex(tuned at around 30-40Hz with chamber volume roughly 70 liters) and in the front with a horm with a cutoff around 130-200Hz. At the top of this there will be mounted a sectoral horn 811b with a compression driver (808-8b).

This project, silly at it seems will be my next project and I would like to ask for any proposals on a woofer candidate, preferably old alnico stuff or whatever JBL or even altec. Any help would be very appreciated!

[paragon]

A 4560 clone ?

[panos29]

Forget my ignorance but I am not very familiar with model numbers yet, but I will check this out later. To give a rough idea I have found 2 similar systems but alot bigger than what I had in mind though the general idea is the same, note that idea 2 is locally manufactured but did not yet had the chance to hear it.

[Zilch]

Greek design is "organic."

[panos29]

Yep, correct! very organic! LoL, so this is made of carbon fiber , containing an altec 515b and a TAD4002 on top. Notice the funny color!

[panos29]

So, any hint of the "right" woofer for this application I am talking about? I would also like to ask what are the desirable woofer parameters to look for ? I mean do I need a modern woofer that can perform well in comparatively small enclosure(but do not have the nice HF responce) or do I need an old type woofer with with very small Qts suitable for horn loading?
Please give me a hint so I can start the search or at least an answer suggesting that something like that is undoable so to abandon this and take a different path (suggest one!). I am open to any ideas for experimentation!

Thanks in advance,

Panos

[Earl K]

Hi Panos

- It sounds to me like you want to make a system similar to that of the web-page author from Vintage Audio Trader .
If I were you, I'd contact him ( Kevin, I think ) through his posted email address at that site .

- I'm also assuming you're familiar with volvotreters' Web Page . But there's the lik, in case you don't have it .

Woofer :
- I'm partial to most things JBL and would opt for a pair of their old 130A, 15" woofs for the 125hz straight horn.
If I had K145s available, I would try them.

- You might want to get a pair Altec 515 type bass drivers ( model would depend on what amplifier and type of impedance load you prefer ). Obviously these are harder to come by over in Europe and people like volvotreter end up settling for EVs (the EVM12L was his choice ).

- I'd forget about "porting" the back-chamber of that "cut-down" 4560 clone ( left pic, looks like an Exemplar ) . You'll need to "bite the bullet" and plan for some sort of sub to use below the Fc point of those midbass horns. Otherwise, you are just reinventing the Altec A7 ( why bother - just make those ). Even the A7 diehards ( with all the LF room-gain they can muster ) eventually admit they'd like more bass - then they seem to get Model 19s or add subs ( and dream of 2245h woofs inside the bottom portion of the A7 ) .

- HiMid should be a 2440/1 or 375 ( or equivalent - I like Altec 288-8K drivers ) on a @ 350hz Tractrix Flare with an axis-symmetric ( round ) horn flare.

- Tweeter needs to be efficient . There are quite a few choices, all dependant on your preference for output, pattern and maybe even diaphragm material-type ( I sort of like Mylar up in that UHF range , so B&C would be a logical choice for myself).

,,,, do I need a modern woofer,,,, ?

or do I need an old type woofer with with very small Qts suitable for horn loading?

My answer to that question is above. These are all low Qts transducers and some incorporate a "rising midband response" .

- Not yet mentioned is; take a look at JBLs' 2020 (12") midbass driver . Here' a ink to the page with a pdf product sheet .

[mikebake]

[QUOTE=Earl K]
- HiMid should be a 2440/1 or 375 ( or equivalent - I like Altec 288-8K drivers ) on a @ 350hz Tractrix Flare with an axis-symmetric ( round ) horn flare.
/QUOTE]

Kinda like Edgars salad bowl?

[Earl K]

Kinda like Edgars salad bowl?

Yes indeed, "kinda like" . I was assuming that Panos29 being located where he is, would want to spin his own bowls - hence the link to volvotreters site.

Now I realize after rereading his initial post that he intends to use his existing Altec 811/808 combo. Oh well .

[panos29]

Hmmmm, seems like I am in a dead end here, what I had in mind was a comparatively small system but from the answers till now, seems that my idea is more suited as mid bass without too much bottom end.
Pitty, i thought I could obtain some bass through bass reflexing and some midbass reinforcement around 130Hz or so from the front horn but obviously there is no driver with parameters to satisfy bass reflex simultaneously with horn loading in the front. Maybe I got to follow the model 19 path... Thanks for the informative answers anyway.

[Earl K]

i thought I could obtain some bass through bass reflexing and some midbass reinforcement around 130Hz or so from the front horn

You can;
(i) Bass reflex will extend the bass response downwards ( but not give you real gain )
(ii) Horn Loading the midrange gives acoustic gain - but just to those frequencies that the horn actually provides some proper loading for .

but obviously there is no driver with parameters to satisfy bass reflex simultaneously with horn loading in the front.

More or less that's true. A driver to satisfy both requirements would need a builtin response slope that actually "attenuates" the midband by 6 db per octave to conteract the 6 db increase of the horns' effect . To create that driver would be - a true exercise in design futility.

Here's a jpg that shows what happens when Bass Reflex and Horn Loading are combined.

- A person can expect the room to add a bit of low bass through room loading, but it won't be enough to avoid needing/wanting to EQ the system ( assuming of course a person isn't in FR denial ).

[BillC]

The gain from the horn decreases above 300Hz or so, at which point the rising frequency responce of the Altec 515 G is of great benifit. The same driver in a bass reflex enclosure has a rising frequency responce of about 5 db starting around 300Hz. Other drivers in this type of enclosure may not work nearly as well as the 515G.

Bill

[yggdrasil]

You might want to try to follow this link.

http://www3.ocn.ne.jp/~hanbei/eng-links.html

I did

Your physical demands is not far from this one http://audioheritage.org/vbulletin/s...ead.php?t=4950

[Cyclotronguy]

If anyone is interested I have JBL 4560 data aplently with either TAD 1601a or various 16 inch Altec drivers. Have MLSSA scans or in room RTA data.


Cyclotronguy

[Earl K]

Hi Cyclotronguy

- I'd love to see some jpgs of 4560s with the mentioned components .

- I want to see what room gain adds to its LF performance .

- Are your MLSSA files able to be saved as jpgs ?

- Do you know how to put photos/attachments into a post ?