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HF compression driver crossover questions


Tizman

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Hi All. 

 

This thread relates to whether or not a rule of thumb can be established for safely lowering crossover frequencies by increasing crossover slope and/or reducing the wattage specification of HF compression drivers.  I am currently stuck in a never ending search for a reasonably priced 1" throat compression driver that can be crossed over at 500 HZ, in a two way speaker system.  I have another thread in these forums that has progressed to the point where I have a few general questions about HF compression drivers and their crossover specifications.  I think that answers to these questions would be beneficial to anyone who finds themselves in a similar situation as myself.  The following are my questions:

 

1.  If a compression driver is specified as having a cross over at, for example, 1000 HZ @ 12 DB/octave @ 100 Watts, what would be an acceptable crossover frequency at 24 DB/octave?

 

2.  If this same compression driver is operated at, for example, 50 Watts maximum, would a 500 HZ @ 12 DB/octave be okay to protect the driver from damage?  If not, what might be a more acceptable safe wattage at this particular crossover frequency and slope?

 

3.  If, like myself, you use DIY SET tube amps of between 2 and 8 watts, and have no intention of ever exceeding 25 Watts (I have a DIY Aleph J in the works), what does the specification of 1000 HZ @ 12 DB @ 100 Watts mean to my choice of a 500 HZ crossover point at 2 Watts maximum, 8 Watts maximum, and 25 Watts maximum?  I am not sure what percentage of the wattage available in my amps will actually go to the HF compression drivers, but I would imagine that most would go to the bass bin.

 

There are some manufacturer's spec sheets that give a clue to what the answers might be, as is the case in the following two Radian spec sheets, but it seems that Radian is the exception when it comes to showing this specification.  Also, there is not a consistent change with respect to the rate of change in the crossover specifications for these two drivers.  For example, the specification sheet for the Radian 651PB/760PB/850PB shows 1200 HZ @ 12 DB and 500 HZ @ 24 DB at 50/60/75 Watts respectively, while the 450PB/465PB/475PB sheet shows 1200 HZ @ 12 DB and 800 HZ @ 24 DB at 25/35/35 Watts respectively.

http://www.usspeaker.com/radian 760pb-1.htm  

https://www.parts-express.com/pedocs/specs/manufacturer-specifications-44920.pdf

 

 

At the moment I am at the beginning of putting together a two way speaker system with Peavey FH-1 as bass bins (they were delivered earlier today), and Altec 511B as a HF horn with Renkus-Heinz SSD 1800-16 compression drivers.  I have a Behringer CX3400 on loan that has 24 DB/octave slopes, but I may go passive or choose a different active crossover when I get my own.  I also have Altec 811B horns, which I would like to combine with a DIY bass cab to create a two way.  I would also like to acquire either a Klipsch K510 or K401 in the future, and I will need 2" throat compression drivers for these horns, which will be used with either the bass bin portion of my La Scalas, the FH-1s, or the bin I build for the Altec 811Bs.  Having the above questions answered could, depending on the answers, greatly expand the choices of compression drivers that would be appropriate for these builds. 

 

Thank you in advance for any information/answers that you can provide to these questions.

 

Tiz  

 

 

 

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4 hours ago, Tizman said:

Hi All. 

 

This thread relates to whether or not a rule of thumb can be established for safely lowering crossover frequencies by increasing crossover slope and/or reducing the wattage specification of HF compression drivers.  I am currently stuck in a never ending search for a reasonably priced 1" throat compression driver that can be crossed over at 500 HZ, in a two way speaker system.  I have another thread in these forums that has progressed to the point where I have a few general questions about HF compression drivers and their crossover specifications.  I think that answers to these questions would be beneficial to anyone who finds themselves in a similar situation as myself.  The following are my questions:

 

1.  If a compression driver is specified as having a cross over at, for example, 1000 HZ @ 12 DB/octave @ 100 Watts, what would be an acceptable crossover frequency at 24 DB/octave?

 

2.  If this same compression driver is operated at, for example, 50 Watts maximum, would a 500 HZ @ 12 DB/octave be okay to protect the driver from damage?  If not, what might be a more acceptable safe wattage at this particular crossover frequency and slope?

 

3.  If, like myself, you use DIY SET tube amps of between 2 and 8 watts, and have no intention of ever exceeding 25 Watts (I have a DIY Aleph J in the works), what does the specification of 1000 HZ @ 12 DB @ 100 Watts mean to my choice of a 500 HZ crossover point at 2 Watts maximum, 8 Watts maximum, and 25 Watts maximum?  I am not sure what percentage of the wattage available in my amps will actually go to the HF compression drivers, but I would imagine that most would go to the bass bin.

 

There are some manufacturer's spec sheets that give a clue to what the answers might be, as is the case in the following two Radian spec sheets, but it seems that Radian is the exception when it comes to showing this specification.  Also, there is not a consistent change with respect to the rate of change in the crossover specifications for these two drivers.  For example, the specification sheet for the Radian 651PB/760PB/850PB shows 1200 HZ @ 12 DB and 500 HZ @ 24 DB at 50/60/75 Watts respectively, while the 450PB/465PB/475PB sheet shows 1200 HZ @ 12 DB and 800 HZ @ 24 DB at 25/35/35 Watts respectively.

http://www.usspeaker.com/radian 760pb-1.htm  

https://www.parts-express.com/pedocs/specs/manufacturer-specifications-44920.pdf

 

 

At the moment I am at the beginning of putting together a two way speaker system with Peavey FH-1 as bass bins (they were delivered earlier today), and Altec 500B as a HF horn with Renkus-Heinz SSD 1800-16 compression drivers.  I have a Behringer CX3400 on loan that has 24 DB/octave slopes, but I may go passive or choose a different active crossover when I get my own.  I also have Altec 800B horns, which I would like to combine with a DIY bass cab to create a two way.  I would also like to acquire either a Klipsch K510 or K401 in the future, and I will need 2" throat compression drivers for these horns, which will be used with either the bass bin portion of my La Scalas, the FH-1s, or the bin I build for the Altec 800Bs.  Having the above questions answered could, depending on the answers, greatly expand the choices of compression drivers that would be appropriate for these builds. 

 

Thank you in advance for any information/answers that you can provide to these questions.

 

Tiz  

 

 

 

First off do you mean 511b and 811b horns?  811b can't do 500 hz.

 

Since you are trying to squeeze a driver lower, likely lower in frequency where a passive crossover would be majorly affected by the resonant frequency of the driver, you would need significant compensation in the crossover to make the crossover work correctly with that resonant peak.  You don't do what you are trying by using a passive crossover in my opinion.  Also since you are down at the resonant frequency, your distortion will be higher and maybe unacceptable.

 

If you will be happy with the resonant area distortion and going active, the best you can do is to increase the slope to avoid over excursion and too low of a frequency from getting into the driver.  Another thing you aren't talking about is the response of the driver.  Most drivers are down significantly at the frequency extremes.  How will you manage that?

 

The power handling will go up and would need to be tested to be realistic but it does seem you will have a lot of compromises that you will require a speaker management system to overcome (eq and slope in particular) and if you are still talking passive, good luck with making your implementation sound good with passive.  Stay with biamp and a lot of processing power.

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I am aware that the 811B will only do 800 HZ.  It would be somewhat easier to find a driver that will do all the HF from 800 HZ and up, but choices are still limited, with most HF drivers being specified as over 1000 HZ.  The drivers frequency ratings are, as you mentioned, another relevant factor that I wasn't thinking about in my first post.  I suppose that is what explains the differences in the deratings of the Radian drivers used as examples above.  At any rate, if an active crossover is the only viable option, that will do.  My questions all relate to what is safe operating parameters for HF drivers run at lower crossover frequencies.  Distortion, while obviously a factor that needs to be considered, is not what I am asking about.  What constitutes acceptable levels of distortion is mostly a matter of personal opinion. Also, doesn't a typical quality compression driver have much less distortion than a regular cone driver?  If more distortion is created as a result of a lower than specified crossover frequency for a HF compression driver, would that distortion be more noticeable than the distortion created by running a horn loaded bass bin at a higher than specified crossover point?

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Don't use the Peavey drivers in the FH-1, very high distortion.  Use K-33s, an aftermarket equivalent or the Eminence driver touted for La Scalas here. 

I have done this, with 902-8Bs and 511Bs.  I set the crossover point at 1k for smooth response, not necessarily to protect the 902.  My crossover slopes are about 15 dB/octave.  The design creates about a 2 dB sag around 1 to 3k in the high pass section smoothing response and eliminating a need for an autoformer of other attenuation.   You are welcome to my crossover design and the Xover Pro design file to play with.  There are response curves on the forums for booth the FH-1 and 902/511B.  they are plenty accurate for design.  The outdoor measured response of my system is very close to the Xover Pro predicted response with a 1 dB peak at 1k. 

 

Cone (diaphragm?) travel increases at 12 dB/oct, so increasing the crossover slope to 24 dB from 12 should allow you to lower the crossover point one octave and prevent over excursion.  Thermal limits may come into play then, but thankfully, the energy in music is concentrated in the lower octaves.  However, be sure to observe the normal rule of setting the crossover point one octave above the actual horn cut-off, fc to maintain diaphragm loading. 

 

Search Peav-tec for more data and for user Sean Fogg for some of the raw data I used.  If you can come to Chattanooga, I can demo the speakers for you. 

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1 hour ago, Tizman said:

I am aware that the 811B will only do 800 HZ.  It would be somewhat easier to find a driver that will do all the HF from 800 HZ and up, but choices are still limited, with most HF drivers being specified as over 1000 HZ.  The drivers frequency ratings are, as you mentioned, anotner relevant factor that I wasn't thinking about in my first post.  I suppose that is what explains the differences in the deratings of the Radian drivers used as examples above.  At any rate, if an active crossover is the only viable option, that will do.  My questions all relate to what is safe operating parameters for HF drivers run at lower crossover frequencies.  Distortion, while obviously a factor that needs to be considered, is not what I am asking about.  What constitutes acceptable levels of distortion is mostly a matter of personal opinion. Also, doesn't a typical quality compression driver have much less distortion than a regular cone driver?  If more distortion is created as a result of a lower than specified crossover frequency for a HF compression driver, would that distortion be more noticeable than the distortion created by running a horn loaded bass bin at a higher than specified crossover point?

Distortion could be a sign of a driver operating out of the safe zone, hence you can't discard it when you are talking about extending a driver lower than comfortable, especially beyond resonant point.

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I read here on the forum over the years that several members are using the Faital Pro HF 200 with its factory spec'd 900 Hz minimum crossover frequency, installed in speakers with passive (and active) networks with lower crossover points.  I have not seen where anybody has questioned or critiqued those applications.

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All of the questions actually relate to how the driver is loaded by the horn.

 

The driver and the horn work together.

 

So ...

 

"If a compression driver is specified as having a cross over at, for example, 1000 HZ @ 12 DB/octave @ 100 Watts, what would be an acceptable crossover frequency at 24 DB/octave?"

 

Normally, one would expect to be able to go to 500Hz if you go from 12dB to 24dB -- but certainly not if you're using a horn with a Fc of 1000Hz. Do you see the problem?

 

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Thanks for the link and crossover design JohnA.  My primary

concern with a higher crossover point has to do with how  the bass bins I own will perform at this higher crossover point of 1000-1200 HZ.  It would appear that the FH1 would fare better than the La Scala bass bin, based upon what I have seen online, and assuming a driver swap in the FH1s to K-33 drivers.  So what's worse, running a bass bin meant to be crossed over at 500 HZ at 1000 HZ, or running an HF driver meant to be crossed over at 1000 HZ at 500 HZ?  It would seem that using the lower crossover point on the HF driver would be better, as indicated by Radian including that option in their spec sheet.  It seems that Radian specs the lower HF compression driver crossover based on their released frequency response figures for each driver.  I get the impression that pretty much all HF drivers are marketed/sold for pro PA use.  I will be using these drivers at fractions of the wattages they are intended for and this is why I'm asking the three questions in the first post of this thread.  By way of example, if an HF compression driver that is specified to be used at 1000 HZ @ 12 DB/octave @ 25 Watts is used at 500 HZ @ 12 DB/octave @ 5 Watts, would that result in excessive distortion?  5 Watts going to a HF driver of 110 DB/W/M efficiency would result in bleeding ears in my listening room.  I can pretty much guarantee that any HF driver I use of similar efficiency would rarely get more than 2 watts.  This is probably a lot more than is likely to happen in my situation.  A 2 Watt per channel amp, of which I have several, is just loud enough in my room with my La Scala speakers.  Two Watts total including the bass bins.

 

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Deang.  I do see the problem.  Makes sense.  Assuming the horn is properly loading the driver at a certain frequency, would it be okay to

use this lower frequency for the crossover?  Specifically, would the 511B properly load a compression driver at a 500 HZ crossover?

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On ‎12‎/‎18‎/‎2017 at 1:36 AM, Tizman said:

For example, the specification sheet for the Radian 651PB/760PB/850PB shows 1200 HZ @ 12 DB and 500 HZ @ 24 DB

The 2" Radian 651 used in a two-way system, crossover at 500 Hz, 24 db/oct. appears to need some upper high frequency boost. If you have an active crossover or an EQ, and REW or RTA for measuring your settings, then it may work for you. But with a passive network and no EQ, the 651 would probably be better as a midrange driver with a separate tweeter.

 

IMG_1137.JPG.53a27314f1c113189f906002dd89d47a.JPG

 

 

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2 hours ago, JohnA said:

It's difficult to find fc for the 511B, you might call Great Plains Audio, but from what I've seen, the fc is 500 Hz, or near to it.  I've not seen an Altec design that ran the crossover point on a 511B down to 500 Hz. 

Here's a FR plot from this site using an Altec 802 driver on three different horns, including the 811B (red trace) and 511B (green trace).  Looks good to me to cross at 500 Hz, or perhaps even lower.  I assume these are on-axis measurements, and that the loss of polar control/loading doesn't occur until ~350 Hz:

 

1.png

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I have some unused 802-8G drivers I should try. One fault with this driver design is the glue on the "Tangerine" phase plug can get brittle and lose adhesion, allowing the phase plug to make contact with the diaphragm, creating a crackling buzz at high SPL leading one to think the driver is blown. New glue on the phase plug fixes that problem.

 

IMG_9189.JPG.ddf615925bb8ee0e8e7a99100d3d7bb9.JPGIMG_9187.JPG.400774be1941aff725a9d5bc862f8226.JPG

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" Miss the chats -- how are you doing man? "

 

Been better, been worse. Trying to find a primary care quack, they don't like dealing with people that are knowledgeable and that can think (me).

 

Buried phone line is out, phone co does not want to repair, I have problems trying to use a cell (too small, hard to hear, etc). This also happened to a friend of mine, after a couple of months of the phone co abuse he ended up buying a cell.

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Thanks for the graphs, data and links.  It would appear that a 500 HZ crossover at 24 DB/octave on my 511B is a safe bet with the Renkus-Heinz SSD1800-16 that I have on hand.  Maybe 600 would allow for a little more safety margin if I use 12 DB/octave?  From memory, the GPA 902 are just over $200 each.  I'm going to use the R-H drivers for now, but the GPA 902s will probably be my next purchase.  It seems that the R-H driver is rated for 500 HZ with respect

to frequency range.

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11 hours ago, JohnA said:

It's difficult to find fc for the 511B, you might call Great Plains Audio, but from what I've seen, the fc is 500 Hz, or near to it.  I've not seen an Altec design that ran the crossover point on a 511B down to 500 Hz. 

 

I didn't have to look very hard...

 

 

Altec_9845_page01.jpg

Altec_9845_page02.jpg

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