Why no low bass!

[bhamvett]

I have a pair of Altec Lansing speakers with the 511-b\808-8a
horns and drivers.The woofers are 15" E\V and the crossovers
are the Altec N501-8A.These are very large speakers and cabinets.The speakers have no low bass.Is it the crossover.Or
is something else wrong.I even bought some brand new state
of the art 15" woofers and still no bass.What can I do to utilize
the 15" woofers and have some low bass? I love the speakers.
Thank's
Steve

[Mr. Widget]

Just be cause you have a big woofer and a big box there is no reason to expect low bass unless the woofer is designed for low bass and the cabinet is properly designed for that woofer and to achieve low bass.

I frequently see 12" and 15" mid bass woofers listed on eBay as subwoofers. You will have to give us more specific information about which woofers you have, how big the box actually is, what the port size is if any, etc.

It is very unlikely that it has anything to do with your crossover.

[bhamvett]

Mr.Widget,
Thank's for the quick reply.The cabinets are JBL.Separate
bass cabinet approx the size of a Klipsch horn.The cabinet
is open in front,with the woofer firing forward.The back of the
bass cabinet is sealed,no port.
They are the JBL 4560 cabinets:
http://www.lansingheritage.org/images/jbl/catalogs/1971-pro/page05.jpg.
Mine are identical.
Steve

[Mr. Widget]

That's your problem. The 4560 is not designed to produce low bass. It is designed to project mid bass deep into an audience. Used with the appropriate woofer it is also quite efficient. It will be difficult to find a sub that can keep up.

What is your application?

[Don McRitchie]

Hi Steve

If your bass cabinets are 4560's, they should be ported. The four slots that you can see on the front of the enclosure, above and below the bass horn flare are reflex slots. I'm not clear if you are saying that your cabinets do not have these slots or it you were not aware of their purpose.

Regardless, there is not much you can do to gain additional bass extension out of those cabinets, no matter what driver you use. If your cabinet is truly sealed, then restoring and tuning reflex slots will help, but the final system will still be noticeably bass shy.

This cabinet was designed around 1970, specifically for tour sound, with emphasis on midbass projection. Even in the early 70’s when it was first employed, it was used with separate bass bins to get any kind of bass extension. JBL was being extremely optimistic when they said there was usable bass to 50hz with this system. JBL used to define usable bass as –10db, which it rather unusable in my book.

I would suggest looking into a good sub as the best way to gain extension and still keep the sound of the 4560’s that you like.

[bhamvett]

Mine are the 4560's with the ports.You answered my question
perfectly.I am indeed using a dedicated subwoofer.I just
wondered why these huge cabinets and woofers would not
go any lower.I am using them in a stereo setup with a Acurus
DIA 100 amp.I am going back to separates soon,as I have a
Audio Research SP6-b pre-amp sitting on my shelf.The speakers
sound amazing.I just don't have them in a big enough room.
You guys really are great!
Thank's
Steve

[mikebake]

Hey Steve, I own/use/love these same cabinets; couple of observations for you;
Certain drivers will give you better low end in these cabs (and as previously pointed out, they were designed for midbass and up)
The 2226 had better low end than many others I've tried. Also, since they are fully horn loaded at 200hz and above, you can try cutting the response above 200 with an EQ. While somewhat defeating the purpose of the front horn, in a home application it can work fine, and subjectively you will now be getting low bass and still having a fairly efficient speaker.

[bhamvett]

Thank's for the reply.I will have to try an EQ!
I love your speakers.I bet they sound amazing.
Steve

[mikebake]

P.S. Don't boost the low end you are missing, cut the midbass.