Ditto what fluid said (except with regard to Ap & 30% of Sd) plus you will find that two 10" drivers are sufficient. With 4 woofers you can probably reach <130 db. Thus you can reach 124 db with only two but in the home that is still more than you would need or want.
Don't make the woofer port holes any larger than they need to be. As you make them smaller, you will see the low end output dropping off. That is a little bit too small. Increase hole size until the loss in acoustic power is <.5 db and then check that the peak particle velocity is under 17 m/s. If these conditions obtain at the maximum anticipated SPL, then it doesn't matter what % of Sd your bandpass ports represent. However port size required to meet these conditions scales with SPL. At home levels you can get by with significantly smaller ports, which means less disturbance to the polar response due to the holes.
A disadvantage of going without midranges (just a tweeter and woofers) is that you lose a lot of one of the best features of the unity design. When drivers are fed offset through a bandpass chamber, there is an effective acoustical filter for those drivers -- any out of band distortions produced by the driver (which will be more than the amplifier's) get greatly reduced. With just woofers that are arranged to go high, any woofer distortion that falls in the midrange frequencies comes right through unattenuated and likely with higher gain than the desired woofer frequencies.
IMO, the reason to use a Unity is because you can have a multiway speaker that acts like a point source with smooth directivity. If you go with 2-way or 1-way you are giving up some multiway advantages.
IMO, the reason to use a Unity is because you can have a multiway speaker that acts like a point source with smooth directivity. If you go with 2-way or 1-way you are giving up some multiway advantages.
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But that only means that you design the natural bandpass of the horn to fit the crossover point you would like to have. I don't think that is specific to a 3-way design is it?
And in a 3-way you can use a 1" exit CD which typically have nicer top ends. You have to go to fairly high end 1.4 or 2" CD to get an equally nice top end and then you are still have breakup that starts a little sooner than on a 1" CD, which is irrelevant to the many of us that can no longer hear that high.
The other side of the coin is the highly attractive simplicity of a 2-way compared to a 3-way; just as much so in a Synergy as in a conventional speaker and many good sounding 2-way speakers exist, as do already a few 2-way Synergies.
I think the 2-way is most appropriate in a home environment where the maximum SPL is 10-15 db less than in a sound reinforcement application. In the home, where peaks are <120 db, the woofer cone motion is limited, limiting modulation distortion, and the voice coil remains in the linear region. If the woofer isn't generating a significant amount of distortion products, then acoustic low pass filtering of the woofer won't be missed.
Regardless of how many ways in the Synergy horn, you will want to hand off to a subwoofer at some point, except perhaps if your goal is 2 channel music instead of HT, and you are using vented 15" woofers. The higher you hand off to the subs, the lower the stress on the woofers and the woofer port, the easier the design, and the less you need a 3rd way in the horn.
In the 2-way Synergy, we aren't designing the woofers to go high so much as selecting a CD that can play low
I'm familiar with those projects and appreciate them as well as their limits. As I recall they used 2.5" and 3" FR drivers on tractrix horns that beam the HF, which may be OK if you only want one seat. Try the same thing on a constant directivity horn or in a larger room and you will see why compression drivers are needed. When the HF is more widely dispersed a small full range driver doesn't have enough [sensitivity*power handling] even with horn gain. A large format CD has almost 20 db advantage in sensitivity and another 6 or 12 db in power handling and doesn't strain in the HF to reach levels that are loud for the home but not excessively so.
A gentleman from the UK used a constant directivity horn with a pretty wide projection rather than tractrix (yes, beaming) and a 2" sb acoustics full range. Bushmaster comes to mind?
The 1" CD 3-way design many of you all take (including your very nice project!) also seems to be quite effective and should allow for greater output. I hardly listen above 80 db/1m nominal, so even with 20 dB crest factor that 120 dB output is lost on me. Compromises, compromises. I just look at the specs of a good 2" full range vs a 2" CD and it's hard to justify the CD for domestic use in a synergy, where the 300-500 hz output is so important.
One man's opinion with less empirical basis than yours.
So please take me with as many grains of salt as you deem fit. (And I mean that in the most sincere manner, no sarcasm)
The 1" CD 3-way design many of you all take (including your very nice project!) also seems to be quite effective and should allow for greater output. I hardly listen above 80 db/1m nominal, so even with 20 dB crest factor that 120 dB output is lost on me. Compromises, compromises. I just look at the specs of a good 2" full range vs a 2" CD and it's hard to justify the CD for domestic use in a synergy, where the 300-500 hz output is so important.
One man's opinion with less empirical basis than yours.
So please take me with as many grains of salt as you deem fit. (And I mean that in the most sincere manner, no sarcasm)
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I don't often listen a great deal louder than you but with my system I can listen at that level downstairs or in my office at the end of a long hall
But don't forget that 120 db with excursion at Xmax implies a fairly high level of THD in the bass. If you can hit 120 at Xmax, then you are also likely able to listen at normal levels with < 1% THD
But don't forget that 120 db with excursion at Xmax implies a fairly high level of THD in the bass. If you can hit 120 at Xmax, then you are also likely able to listen at normal levels with < 1% THD
Sensitivity for one? And the cone is probably heavier, so in the HF department you would not expect any improvement.
Anyway, I did some more simulations with the Beyma and tried to input some more realistic numbers for Vtc, Ap1 an Atc. Obviously, things then indeed start to be tricky to get upto 1Khz. But as noted before, there is no need to play upto 1Khz anyway in a 2(ish)-way.
So I tied reading up on the BMS coax CD's. For instance the 4594 and 4593. According to some they seem to yield pretty good results, always referencing some other source without links, but I never found more than only half a line of text about them. What I also find confusing are the THD graphs in the datasheets. For the HF the 4594 2nd order THD is only down about 20dB (10%), the 4593 is almost 10dB better, but still about 3% THD. Actually the 4550 is not much better, it also shows about 3% THD. all at 1W, so at 110dB that is very loud indeed. On the other hand, the 4550 probably needs a 10dB boost HF, so the better distortion figures might even out in the end?
I recall at least one detailed build and discussion on AVS forum, a BMS4594 on a SEOS24.
As to THD, as you rightly note those graphs are at very high SPLs. My BMS4550 measured THD more than 50 db down at what was probably only 80 or 90 db.
I wouldn't worry about harmonic distortion at frequencies above half your upper hearing limit, where you need a lot of boost to compensate for controlled directivity, as you can't hear them.
One of the reasons that you see the SB Acoustics SB19 in a lot of my projects is because it's distortion performance is so darn good, especially considering it costs $20. In one of my tests, I measured the following:
1) an SB Acoustics SB19 ($20)
2) the inexpensive Celestion compression driver ($45 iirc)
3) a Dayton RS28 ($50)
The Dayton performed the worst. So bad that mine may be defective? It was really bad. Although the Celestion performed better above 2khz than the SB Acoustics, the SB19 was the best performer between 1000hz and 2000Hz. I believe the reason is because the SB has a surround. The Celestion is basically a mylar dome with no suspension. That allows for a very low MMS, for very high efficiency, but the surround on the SB19 allows for more xmax. So though the SB19 has less "SD" than the the Dayton or the Celestion, it has more xmax than the Celestion.
TLDR: check out 3/4" domes with a decent amount of xmax. They can perform very very nicely on waveguides. Don't bother with 1" domes; they're too large to work properly without a phase plug, IMHO.
Bushmeister, it was an SB65 in an XT1464 horn. Elliptical but not tractrix. XRK971 used the Faital LT142 horn which is tractix and beams a lot more. The tricky part of using the full range was avoiding cancellation nulls from the cone being larger that the horn entry. Bushmeister did a good job or fixing that. The SB65 has a rising response which helps compensate for the wider directivity. The driver has a lot of xmax (2.6mm) for a small driver which allowed it to get quite loud down to 500Hz in the horn. The two 8" woofers were the bottleneck in SPL. That being said it would not compete with a compression driver for SPL if you need or want it.
Compression drivers exit angles and phase plugs can have an effect on their directivity and some beam more than others despite the horn they are used in.
Yes if you need it that loud or powered by a small amp.
The THD graphs from BMS are quite hard to read in that they do not have a vertical scale listed so you have to guess. The level has also been raised by 10 or 20dB as indicated on the graph which isn't so helpful either. The thing that is good on those is how much lower the 3rd order THD is compared to the 2nd.
There is a project on one of the PA sites using a BMS coaxial in an XT1464 horn and two horn loaded 15" drivers. With an active crossover the response is very good. There are some measurements in the rephase thread from a member who has built one.
The level of output you need or want will set the type of drivers you can use, pick your favourite compromise
I have the parts for both fullrange and 1" compression driver but have not got round to building them yet, the line array jumped the queue.
Arguably, the sb65 almost behaves like a coaxial. The poly dustcap seems to "decouple" from the cone at high frequencies. This explains the rise from 10-20khz. Basically that powerful neodymium motor is only driving the dustcap at very high frequencies; it's decoupled from the aluminum cone. Nice engineering on the part of SB Acoustics!
I'm only aware of two other drivers that are as nice. The long discontinued thiel full range, and the full range from audiofrog.
to complete the comparison:
The bottom line of the table is from the data sheet. The DB reduction is from the roll off of the 12 db/octave high pass for which a 900 Hz XO is specified. At that reduction, the power applied to the CD with a 500 Hz XO is <= to that with a 900 Hz XO.
Faital Pro HF-148 Sensitivity (db) 109
XO freq DB reduction Pwr Ratio Max AES Pwr DB>1W Max Out
500 6.4 4.37 22.91 13.60 122.60
900 0 1 100 20.00 129.00
Chances are in home , even in a home theater, you will operate at least 12 db below the 122.6 db maximum and at that level you will have acceptably low distortion and have > 10 db advantage over the SB65. I think I would want the HF-148 or similar in my HT but the the SB65 would do well in a system for my home office.
Sorry the table formatting gets lost in posting/transtaltion
Tweeter measurements
Here are a few tweeter measurements in a synergy horn foam core model. My plan was to use the RS28A until it went NLA. I'm currently using the XT25TG30.
Here are a few tweeter measurements in a synergy horn foam core model. My plan was to use the RS28A until it went NLA. I'm currently using the XT25TG30.
