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[Guy Graham]

Guy,

1) 24 dB per octave crossovers have been available since the 1970s, and were used for Flash and Floodlight tops.
2) Crossover points in the 180-250 range were common because small mid-bass horns response drops off  below that range.
3) The OP has not been back since May 03, 2014, don't expect your query will be answered, but he wanted high efficiency for an off-grid application, an "Art Car" to be used at the Burning Man Festival, taking place Aug 25 - Sept 1, 2014.

Art

Thanks for correcting me Art - I'll have to be more careful in future about accepting information from supposed experts without question!

I still see a few Floodlight rigs going, but never with what I understood was the original matching bass cabinet. The sound quality has varied as much as the variety of subs I've seen used.

I assume what I was told about the old 21" & 24" Turbo sub drivers being very expensive to replace/recone is correct?

I did think I had read in threads both here and SF.net that some users were crossing over a fair bit lower than 180Hz, when using different processing to the original provided by Turbosound. Is that possible or another thing I've  misunderstood?

Many thanks for correcting my misinformation, Guy

Sent from my GT-I8160 using Tapatalk 2

[Ivan Beaver]

I assume what I was told about the old 21" & 24" Turbo sub drivers being very expensive to replace/recone is correct?

I heard a number of years ago I heard (but cannot confirm) that it around $600 to recone them.

They are very impressive looking drivers.  I have never reconed one.

I doubt that helps much-but is all I can offer

[Guy Graham]

Thanks for the info!

Out of interest, could you expand on what you describe as "impressive"?

Also just to clarify another area where my understanding may not be correct - is it not the case that a modern high-power 21" driver has TS parameters with a much greater Xmax than a much older driver such as the Turbosound sub in question?

Many thanks, Guy

Sent from my GT-I8160 using Tapatalk 2

[Ivan Beaver]

Thanks for the info!

Out of interest, could you expand on what you describe as "impressive"?

Also just to clarify another area where my understanding may not be correct - is it not the case that a modern high-power 21" driver has TS parameters with a much greater Xmax than a much older driver such as the Turbosound sub in question?

Many thanks, Guy

Sent from my GT-I8160 using Tapatalk 2

The magnet is REALLY large.

Just because a driver has more xmax does not mean it will work properly in a horn cabinet.

The Turbos are short horns-and don't work like a "normal horn".  So the parameters will be different.

Also just because a driver has a larger diameter does not mean that it will have a deeper low freq response.  In fact if you look at most of the 21" sub cabinets on the market you will find that the unprocessed response does not go very low.

[Art Welter]

I did think I had read in threads both here and SF.net that some users were crossing over a fair bit lower than 180Hz, when using different processing to the original provided by Turbosound. Is that possible or another thing I've  misunderstood?

Guy,

"Some users" do things that are simply wrong, crossing below a horn's Fc would be one of those things, even though it is very possible (and easy) to do.

Without seeing the measured raw response of the particular Turbosound cabinet, I really can't say whether 180 Hz is too low, but if the original crossover point was higher, there was a good reason for it.

Art

[Guy Graham]

The magnet is REALLY large.

Just because a driver has more xmax does not mean it will work properly in a horn cabinet.

The Turbos are short horns-and don't work like a "normal horn".  So the parameters will be different.

Also just because a driver has a larger diameter does not mean that it will have a deeper low freq response.  In fact if you look at most of the 21" sub cabinets on the market you will find that the unprocessed response does not go very low.

Ivan, I think I understand a bit better now...

The Turbo driver is impressive as it has a very large magnet and voice coil, so has good Bl - which is a more significant TS parameter in this case, compared with Xmax for example.

The "short horn" is compromised by the flare length. The benefit of acoustic pressure created by the sealed rear chamber is maximized by the capabilities of this driver.

Hence this design produces a substantial output and remains efficient. However it does so in a more compact box than a conventional horn design, so there must be a compromise here...

Apologies for throwing my work out and expecting others to go to the trouble of correcting it - I'll not be offended if you just suggest I go and study some more!

Thanks for your patience, Guy

Sent from my GT-I8160 using Tapatalk 2

[Ivan Beaver]

. However it does so in a more compact box than a conventional horn design, so there must be a compromise here...

The compromise is low freq extension.  In order to get low freq out of a horn it has to be long with a large mouth.  No way around that.

When the mouth is to small-the driver does not have a good "acoustical transformation" between the driver and the air.  So the response gets ragged down low.

When you add multiple horns together, they all "work together" to form a larger mouth, so the response "fills in" making it flatter to where it should be. 

While the actual response may go lower (but nowhere near as much as people would like to think), usually a Hz or 2, it is the fact that the "ragged response down low" fills in that makes people "think" it goes lower in multiples.  But in reality it is just smoother/flatter down to the cutoff.

HOWEVER it is my "understanding" that the "turbo device" does not work like a normal horn with regards to loading.

I remember reading back in the 80s that the engineers at Turbo sound had heard about the advantages of horns-but did not understand everything involved in how the concept worked.

So they came up with their own "idea", which was carried across to all of the products-just different sizes for different drivers.

I am just repeating what I remember and cannot comment on how well the "turbo device" works or doesn't work as I have only limited direct experience with them.

But I am not aware of other people who are using the same concepts to build bass horns.  Even in the DIY community that works real hard a copying designs that have been proven to work.  For example taking a "concept" and adding their own "twists" to it (different drivers-different horn flares-different throat loading etc)

[jason misterka]

We still have twenty of the TSW-721 boxes and use them often.

From a conversation I had with our Turbosound rep probably fifteen years ago, these subs were not designed to be used in a stack of less than six.  I use them in smaller stacks when necessary but understand that there are compromises  of course. 

There are better subs out there but these have great dimensions for truck packing in different sized truck boxes.  They are also very flexible with regard to stacking options for point source PA, and for making fun cardioid or endfire arrays.

We also cross them over at 80hz or 100hz now, since we don't have Floodlights anymore. Even crossed at 80hz they put out plenty of out-of-band information between 150-200 that often needs a little attention.

Downside is the repair.  Avoid whenever possible. Shipping those magnets to a reconer can be very expensive.  The good news is that in the last six months, Turbosound parts and service has become a real asset again and have had everything I have needed in stock in the US.  There were some dark days previously....

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