New DIY Mid High (90deg) - AKA PM90

[Peter Morris]

Re: New DIY Mid High

Jack,

Hidden, and pretty small ;^). The ribbed portion of the diaphragm probably is only contributing 50% to Sd.

Xmax on virtually all HF compression drivers is about the same, the winner in output is the driver with more Sd (cone/diaphragm) area, even with HF there is no replacement for displacement.

Smaller moving mass is a good thing from a distortion standpoint, a 4" diaphragm is too big (IMO) for clean HF reproduction, but a 3" diaphragm is OK, at least to my old ears.

If you compare Sd of a 3" dome diaphragm (easy to figure at PI r/squared) to the Sd of the annular ring diaphragms you can see why JBL "doubled up" on their D2, rather than use two diaphragms covering different frequency ranges.

Art

Wow …. I think we almost need to split this thread in half and have section dedicated to compression driver design.

---------------------------------------------

Art, you need to do the mathematics associated with the various designs, calculate Xmax, efficiencies, SPL etc.

In general, most compression drivers use similar clearances between the diaphragm and phase plug. If the clearance gets too large and the volume of air between diaphragm and phase plug gets too large there will be a secondary HF roll off in addition to the mass break-point.

The clearance determines how low and how much power it can take before the diaphragm hits the phase plug. As the frequency increases the diaphragms displacement reduces proportionally.

All things being equal - if you reduce the size of the diaphragm it just has move further to produce the same SPL. If we are talking about very high frequencies there is plenty of room to do this. The diaphragm does not have to be as large and will not hit the phase plug.

The trick is getting it to do this efficiently. You can reduce the diaphragm mass, raise the resonant frequency and increase the compression ratio. As you make the diaphragm smaller the voice coil sized is normally reduced and hence the power handling, but if the efficiency increase is more than the power handling loss, then you’re ahead. As the diaphragm becomes smaller it also becomes much stiffer and can be made thinner and lighter.

The trick with the BMS design is that they have been able to reduce the mass but maintain a reasonable VC size. JBL have now picked up on this with their new D2430K that you mentioned. It functions very much like a driver patented by Mr BMS (can’t remember his name). Their design is like the BMS 4599 that uses 2 diaphragms to cover the same frequency range.

I looked at the D2430 but it didn’t go low enough and the 4599 didn't high enough to be used with the 2 x 12” bent horn, hence the 4594 ... and it sounds wonderful.

Anyway … as I mentioned in an earlier thread; this approach using a small + large diaphragm avoids break up modes and reduces intermodulation distortion and the output is the sum of both drivers .

As you like EV compression drivers this is what they did with DH3A. It was “optimized for use as a super-tweeter component in professional sound reinforcement systems”. It used a 14:1 compression ratio as compared to the DH1A that used a 10:1 ratio (if my memory is correct). In the early EV MT4 manifold systems they used 4 x DH3As for the VHF and 4 x DH2As for the HF, Turbosound also used the DH3A in combination with a horn loaded 6.5” driver in their Flash and Flood light systems. There new Flashline and Flex also use this concept.

They did this to get better performance (in EV case I never liked the sound of the DH2A) …. and the logic for doing this is exactly the same as what BMS have done with the 4594, except BMS have combined them into one driver. Turbosound claim that on music this combination gives them a 6 dB advantage when compared to a large format compression driver.

You were also concerned about distortion - I won't go into detail but we tend not to hear 2nd harmonics that much because they are often masked, higher orders can be an issue as is IMD. The type and frequency of the distortion is important. This paper may be of interest - http://gedlee.com/downloads/Distortion_AES_I.pdf

 

[Mark DeArman]

Re: New DIY Mid High

Wow …. I think we almost need to split this thread in half and have section dedicated to compression driver design.

I think this forum is general needs a lot more thread splitting. We tend to bunch up a lot of really good topics into these mega threads. It's all up to us.

Okay, here I go making a blanket broad statement again... How many people can figure out how it relates to the phase response of your box ;-)

 

[Josh Ricci]

Re: New DIY Mid High

Don't forget that in regards to tweeter distortion the 3rd harmonic of 7kHz is 21kHz. I don't know about you guys but my hearing up past 17kHz isn't so good anymore. I tend not to worry about harmonic distortion above 5kHz too much and focus more on the midband and bottom of the HF drivers range. The BMS measurements look very good in that regard but I'd like to see some taken at more than the few volts that approximate 1w. A voltage corresponding to 20w would be very interesting in the 300-1kHz range.

 

[Art Welter]

Re: New DIY Mid High

1)Art, you need to do the mathematics associated with the various designs, calculate Xmax, efficiencies, SPL etc.
2)All things being equal - if you reduce the size of the diaphragm it just has move further to produce the same SPL. If we are talking about very high frequencies there is plenty of room to do this. The diaphragm does not have to be as large and will not hit the phase plug.
3)As you like EV compression drivers this is what they did with DH3A. It was “optimized for use as a super-tweeter component in professional sound reinforcement systems”. It used a 14:1 compression ratio as compared to the DH1A that used a 10:1 ratio (if my memory is correct). In the early EV MT4 manifold systems they used 4 x DH3As for the VHF and 4 x DH2As for the HF, Turbosound also used the DH3A in combination with a horn loaded 6.5” driver in their Flash and Flood light systems. There new Flashline and Flex also use this concept.
They did this to get better performance (in EV case I never liked the sound of the DH2A) …. and the logic for doing this is exactly the same as what BMS have done with the 4594, except BMS have combined them into one driver. Turbosound claim that on music this combination gives them a 6 dB advantage when compared to a large format compression driver.
4)You were also concerned about distortion - I won't go into detail but we tend not to hear 2nd harmonics that much because they are often masked, higher orders can be an issue as is IMD. The type and frequency of the distortion is important. This paper may be of interest - http://gedlee.com/downloads/Distort...ell use guitar and bass amps for PA :^). Art

 

[Peter Morris]

Re: New DIY Mid High

Peter,

1) I don't need to do the mathematics associated with the various designs, calculate Xmax, efficiencies, SPL, that info is already available from spec sheets, and besides, the recent SynTripP design does everything I want it to do ;^).
2) Correct, the smaller diaphragm will have to move further to produce the same VHF as a larger diaphragm, and consume more power doing such, therefore will burn up at a SPL lower than the larger diaphragm.
3) Although the DH3 was (is) a decent sounding tweeter, the EV MT4 suffered badly from air non-linearity, AKA "throat distortion", or "10 pounds of shit in a 5 pound bag". You will notice one of the main designers of the MT4, Dave Gunness, has not used multiple drivers on the same throat since those "bad old days". I bought a dozen or so dual manifolds for EVDH1AMT, managed to send them all back to EV for credit when I found that although they reduced comb filtering compared to two drivers on two horns, they also increased the hash factor greatly above about 10 watts total, yecchh.
4) I have had many "conversations" with Earl regarding that paper, to sum them up, the college kids he hired to listen to a short excerpt of "burning down the house" played on a variety of 4" diaphragm drivers with 10% (or more) distortion could not tell the difference between the distortion in various drivers. He did not use the raw, undistorted track as a comparison.

Having listened to recordings of lots of compression drivers at various drive levels, I know I can hear their distortion, whether even or odd order.
Air non-linearity distortion sounds bad, all drivers exhibit it when the throat SPL reaches around 160 dB, which for most drivers is way below their thermal limit.
Most designers aware of the problem tend to reduce compression ratios.
An easy to understand analogy: play music through a euphonic device like a guitar tube amp/speaker combo, the even order distortion does not sound bad, but it certainly does not sound "Hi Fi". If we were to believe Earl's white paper, we might as well use guitar and bass amps for PA :^).

Art

No, no, no … if the efficiencies are the same at a given frequency, the smaller diaphragm will move further (yes) but with the same input it will produce the same output. Provided there are no Xmax issues, there is no problem doing this.

Output = efficiency x power irrespective of the size of the diaphragm.

Efficiency (very simple explanation) is determined by the mass of the diaphragm and the strength of the motor pushing it.

There is a point of maximum efficiency in the mid band of the driver’s operation. In general this relates to the resonant frequency the driver. If you raise the resonate frequency you raise the frequency of where the maximum efficiency occurs.

The compression ratio of the driver also comes in to play. As with any electrical or mechanical system maximum efficiency occurs when the load impedance matches the impedance of the driving force. (i.e. the theoretical maximum efficiency is 50% ignoring some practical losses that occur.)

In this case this occurs when the voice coils impedance matches the acoustic impedance presented to the diaphragm. Without going in to detail this is where the compression ratio can play a part … and one of the reasons why I mentioned the DH3A – its uses a particularly high compression ratio to increase the efficiency a little. Personally I agree with you, I prefer the sound of drivers with a lower compression ratio, it was just what EV did at that time. It was optimised as a super tweeter and as such EV used a high compression ratio and resonate frequency.

To obtain maximum VHF output what you need to do it find the best compromise between cone & VC mass, Xmax, BL, resonant frequency, initial throat area and cone area. The resultant compromise will depend on the frequency range you want to cover.

All of this is in Keele’s paper that I posted above - in detail.

This is what I said regarding distortion – “I won't go into detail but we tend not to hear 2nd harmonics that much because they are often masked, higher orders can be an issue as is IMD. The type and frequency of the distortion is important. This paper may be of interest - http://gedlee.com/downloads/Distortion_AES_I.pdf”

As we all know MP3 uses data compression, and the compression is not lossless. The trick is to remove the bits / data we don’t need. If there is loud tone, we do not hear the softer frequencies either side, they are masked by the loud signal, the further the softer tone is away from the original, the softer it needs to be, to be masked by the loud tone.

The masking is not symmetrical. Frequencies higher than the loud tone are masked more than those below the tone.

This is one of the things they do to compress audio files (there are other tricks), remove quite a bit of the information we don't notice because of masking. It is also significant with regards to distortion. Second harmonics will be masked more than third harmonics of the same level. If the second harmonic is loud (e.g. an electric guitar) then of course you will hear it, and as you said second harmonics tend not to be that objectionable. ~~:smile:

 

[Roy Novio]

Re: New DIY Mid High

Been following this thread I would like to build a couple but those BMS drivers are expensive here, any plans on drawing up some plans or your design? I do some DJ work now and then,thanks!

 

[Peter Morris]

Re: New DIY Mid High

Been following this thread I would like to build a couple but those BMS drivers are expensive here, any plans on drawing up some plans or your design? I do some DJ work now and then,thanks!

Hi Roy,

Yes I’m happy to draw up some plans, but I must stress a few points.

· This is only a prototype - to test if the idea / design would work and look for improvements, especially through input from this forum (thx everyone so far)
· The BMS 4594ND is more or less a must.
· The compression driver needs to go down to about 600 Hz – 800 Hz and still maintain a very high output.
· The box will not work if the crossover point is above 800Hz
· HE version of the 4594 is not necessary
· A passive HF – VHF crossover could be used.
· An electronic crossover that can provide at least 3 PEQs per band is required.
· It will work without FIR processing.
· The HF horn needs a cut-off frequency around 400Hz or less.
· The horn should be an RCF HF950 or Eighteen Sound XT1464.
· Some slight modifications to the box design may be needed to accommodate the XT1464
· You will need some experience with Smaart, Systune to ensure that the results you are getting are optimum.

 

[Peter Morris]

Re: New DIY Mid High

Update,

Well I finally had an opportunity to see how they perform. They have now been used in 3 different applications - a function centre ball room on top of a single 21 inch sub, outside with your typical rock band, and a school for speeches and choirs reinforcement for about 700 people.

They worked exactly as I had hoped. They are loud, clear, smooth with no harshness. They threw forever maintaining excellent tonal balance at a great distance.

The double 12” W style mid seems to work perfectly up to 800Hz as does the BMS 4594 for the rest of the spectrum.

A double 18 inch “no compromise” sub will not keep up with the DIY mid high.

I loaned them to a friend who used them for a small charity even to raise some money for the people affected by the recent bushfires. Five bands over the afternoon with very ordinary stage setup but a cost effective solution that maximized the donation $$.

In general people were amazed that so much sound could come out of such small speakers; it just didn’t look right. “Wow that’s amazing, so clear” was the typical comment.

More or less no EQ was needed other than 3 dB at 100Hz. I did however adjust some of my original settings before the show started. I will measure what I changed and try to polish things a little more.

In the meantime the Eighteen Sound XT1464 horns have arrived. I have done some quick comparisons to the RCF HF950. They behave slightly better and are about 2dB more efficient below 2 KHz. Even though the XT1464 was slightly better, given what you need to do to get a 1.4 inch throat horn of this size to provided 90 degree coverage, the RCF are excellent.

When I get an opportunity I will sketch up the design of this prototype.

 

[Roy Novio]

Re: New DIY Mid High

Thank you very much for that update, I do not have much exposure with Smaart and I am although a mobile DJ I am willing to learn my set up now is 2 way tops(SLA Pro) BFM and 2 T24 2X10" subs I use DCX and DEQ and off course analog amps QSC CX and Crest 7001 for sub duty. I plan on building a folded horn 21" subs good to 35 Hz - 100 Hz. I am willing to spend the money on the BMS HE if need be as I have heard a small clip of you speakers in beginning posts seems transparent the sound and excellent vocals to me from your video. I would like to build 4 tops and 2 initially, thanks Peter!~:-D~:grin:

 

[Peter Morris]

Re: New DIY Mid High

Thank you very much for that update, I do not have much exposure with Smaart and I am although a mobile DJ I am willing to learn my set up now is 2 way tops(SLA Pro) BFM and 2 T24 2X10" subs I use DCX and DEQ and off course analog amps QSC CX and Crest 7001 for sub duty. I plan on building a folded horn 21" subs good to 35 Hz - 100 Hz. I am willing to spend the money on the BMS HE if need be as I have heard a small clip of you speakers in beginning posts seems transparent the sound and excellent vocals to me from your video. I would like to build 4 tops and 2 initially, thanks Peter!~:-D~:grin:

What type of shows do you do - how many people and what type of music? You maybe surprized at how loud these thing go ... You may only need one pre side.

 

[Roy Novio]

Re: New DIY Mid High

Hi Peter, I do mostly weddings and small parties anywhere from 50- 320 which was done in a large auditorium (wedding) now the system that I have did not fair so well I need some flexibility for these larger shows my plan this spring was to build a large enough system to do a Miami Ultra show in a beach hotel did not get booked but I am looking at festivals here in the Tampa Bay area hopefully this summer. I want to build something bigger than BFM and with these I can probably operate 1 per side or 2 per side mid tops. I play anything from 50's 60's to todays top 40 including heavy bass Rap and Dubstep. Progressive House ( 45 Hz-180 Hz) I do not have a degree in sound engineering but I know what sounds good including flat response Funktion-One speakers (Res 4 and Res 5) Thanks!

 

[Peter Morris]

Re: New DIY Mid High

Hi Peter, I do mostly weddings and small parties anywhere from 50- 320 which was done in a large auditorium (wedding) now the system that I have did not fair so well I need some flexibility for these larger shows my plan this spring was to build a large enough system to do a Miami Ultra show in a beach hotel did not get booked but I am looking at festivals here in the Tampa Bay area hopefully this summer. I want to build something bigger than BFM and with these I can probably operate 1 per side or 2 per side mid tops. I play anything from 50's 60's to todays top 40 including heavy bass Rap and Dubstep. Progressive House ( 45 Hz-180 Hz) I do not have a degree in sound engineering but I know what sounds good including flat response Funktion-One speakers (Res 4 and Res 5) Thanks!

FWIW - heavy bass Rap and Dubstep I suspect will require 2 double 18" "no compromise" subs per side to keep up with one DIY Mid-Hi. That's enough with 2 of mine per side to blur your vision if you get too close.

Started drawing up the plans - need to pull the box apart and measure things when a have some free time.

 

[Rob Timmerman]

Re: New DIY Mid High

Started drawing up the plans - need to pull the box apart and measure things when I have some free time.

I've found that photos with a ruler or tape measure in them are a great way of capturing dimensions (and can help with some of the "implied" dimensions)

 

[Ivan Beaver]

Re: New DIY Mid High

FWIW - heavy bass Rap and Dubstep I suspect will require 2 double 18" "no compromise" subs per side to keep up with one DIY Mid-Hi. That's enough with 2 of mine per side to blur your vision if you get too close.

Started drawing up the plans - need to pull the box apart and measure things when a have some free time.

It all depends on what the ratio of mid/hi to sub energy is. Different people like different amounts.

My experience is that after "adjusting by ear" a system (basically turning up the subs until it sounds "right"), and then measuring the system, the subs are in the range of 25-30dB louder than the full range cabinets for EDM style music.

So basically below 100Hzish it is 25-30 dB louder than above. Of course there is a big slope around 100Hz ish, so lets say above 300hz vs below 90Hz.

I know this sounds extreme-but I have done it a number of different times-with different people-on different systems in different places.

So as you can see-you need A WHOLE LOT more sub output than full range output-for that type of music-to be represented in the way the artists want it.

Of course many times people simply don't have enough sub to "outrun" the tops, so the ratio is lower and they just live with it.

But when "given the choice" a wide variety of people in the US like that.

I use that as a "starting point" for suggesting sub to top output range.

So for a top that is 130dB, you should be looking at sub outputs in the 155-160dB range-IF you are going to run the tops at full level.

And remember that the average level as read on a meter is going to be 10-15dB lower than the peak calculations.

 

[Simon Coffin]

Re: New DIY Mid High

Hey Peter

Once again, fantastic work. You have really done a great service to the community. Personally I find these types of projects to be fascinating opportunities to learn and experiment. The results are not always as desired, but the knowledge collected is worthwhile.

In this case it seems like you have put together an amazingly powerful cabinet if a capable double 18 sub cannot keep up. Although as Ivan points out, subs need significantly more output. But still, a home built top that outruns a capable sub and sounds good doing it is pretty impressive. Given the design I assumed that coherence would be good since there are minimal time arrival conflicts across the band and the summing that does occur in the crossover region is entirely constructive. This is something I mentioned earlier about the TW Audio T24N, since its sums so well, the tonal balance remains consistent even out to a fair distance. This makes the cabinet even more useful since fills are not necessary to restore intelligibility.

So count me in as a very interested potential builder.

Ciao
Simon

 

[Ivan Beaver]

Re: New DIY Mid High

Hey Peter



In this case it seems like you have put together an amazingly powerful cabinet if a capable double 18 sub cannot keep up. Although as Ivan points out, subs need significantly more output. But still, a home built top that outruns a capable sub and sounds good doing it is pretty impressive.

Having a top that outruns the subs is a GOOD thing. It just means that it will be that much cleaner-when it is loafing along.

Often times people look at it completely wrong.

With some of our high output cabinets people ask "How many subs does it take to keep up?". I tell them a suggestion and they say "I can't afford that many subs". WRONG

You DON't have to run the tops at full output all the time. The way you need to look at it is "How many subs does it take to do the job-and does the top have enough output to keep up?"

There is nothing wrong with having to much output. When you turn it down,it lasts longer and sounds better.

 

[Peter Morris]

Re: New DIY Mid High

It all depends on what the ratio of mid/hi to sub energy is. Different people like different amounts.

My experience is that after "adjusting by ear" a system (basically turning up the subs until it sounds "right"), and then measuring the system, the subs are in the range of 25-30dB louder than the full range cabinets for EDM style music.

So basically below 100Hzish it is 25-30 dB louder than above. Of course there is a big slope around 100Hz ish, so lets say above 300hz vs below 90Hz.

I know this sounds extreme-but I have done it a number of different times-with different people-on different systems in different places.

So as you can see-you need A WHOLE LOT more sub output than full range output-for that type of music-to be represented in the way the artists want it.

Of course many times people simply don't have enough sub to "outrun" the tops, so the ratio is lower and they just live with it.

But when "given the choice" a wide variety of people in the US like that.

I use that as a "starting point" for suggesting sub to top output range.

So for a top that is 130dB, you should be looking at sub outputs in the 155-160dB range-IF you are going to run the tops at full level.

And remember that the average level as read on a meter is going to be 10-15dB lower than the peak calculations.

I’m sure you're a 100% correct … but WOW that MUCH BASS! I knew you guys over the other side of the big pond like a lot of bass, but …. 30dB more !!!!

What I find interesting is that so many people argue for a flat frequency response, the flatter the better, yet they "hay-stack" the sub frequencies. I typically see 10dB or more.

Why do we like it that way? Wouldn’t it more logical to integrate the subs a little more smoothly? You would assume the original recordings already had right amount of LF so the DJ boys would only need a flat system.

When I voice this system with a measurement mic (earthworks M30), logically the tonal balance should exactly the same as my natural voice. To do that, I talk into a flat surface (eg. my iPad) so that I can hear the real timbre of my voice as it’s reflected from the surface.I then compare it to what I hear from the speakers. When they match, the frequency response is not flat. There is quite a bit of extra low frequency, but it sounds great on both music play back and live music.

In this case it’s not really taste. I have used an almost perfectly microphone – flat frequency response with no proximity effect and voiced the speaker so it sounded exactly like the original input. What my ears are telling me does not match what I’m measuring.

I think there are a lot of things happening regarding how we perceive sound particularly in relation to the early arrivals within the first 30ms.In this respect I really like some of the work that Raimonds Skuruls has done. http://aplaudio.com/conc2/ What I ended up with almost exactly matches what he suggests.

 

[Max Warasila]

Re: New DIY Mid High

Personally, and I'm still new to the whole thing so take this as you will, the system itself is tuned flat, but I allow for a heck of a lot of headroom. Just because the subs are equal to the tops doesn't mean the material they are sent has to remain that way.

Just preference, I'm likely to change it.

 

[Peter Morris]

Re: New DIY Mid High

Hey Peter

Once again, fantastic work. You have really done a great service to the community. Personally I find these types of projects to be fascinating opportunities to learn and experiment. The results are not always as desired, but the knowledge collected is worthwhile.

In this case it seems like you have put together an amazingly powerful cabinet if a capable double 18 sub cannot keep up. Although as Ivan points out, subs need significantly more output. But still, a home built top that outruns a capable sub and sounds good doing it is pretty impressive. Given the design I assumed that coherence would be good since there are minimal time arrival conflicts across the band and the summing that does occur in the crossover region is entirely constructive. This is something I mentioned earlier about the TW Audio T24N, since its sums so well, the tonal balance remains consistent even out to a fair distance. This makes the cabinet even more useful since fills are not necessary to restore intelligibility.

So count me in as a very interested potential builder.

Ciao
Simon

Hi Simon,

Firstly I should highlight that this box has only undergone a little bit of preliminary field testing.

Having said, that my first impression was that the coherence is excellent and the tonal balance remains consistent at a great distance. This is one of the things I first notice when we tried them outside. I don’t know what the T24N is like, but the DIY performed better than any box I have heard in that respect.

 

[Peter Morris]

Re: New DIY Mid High

Here are some dimensions and some more photographs.

Cheer Peter