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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd February 2010, 03:22 AM   #1
Loren42 is offline Loren42  United States
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Default Why no Bass?

I am frustrated with my speakers that i put a lot of time and learning into building and I still have a nagging problem of no bass with my system.

My design goals were to create a system with high SPL and extended frequency range. My amp is only about 50 WPC, so efficient speakers are pretty much a must. I use these for playing music mostly.

The speaker is a 3-way with a 15" JBL 2235H woofer, an Audax PR170M0 for the mid, and a Morel MDT-37 tweeter.

The mid and tweeter are in their own sub-cabinet. The 2235H is in a 6 cubic foot ported enclosure with two 3.95" diameter flared vents 6" long (tuned to 32 Hz).

I should see a flat response down to at least 35 Hz (according to LEAP and Bass Box Pro), but it dies at about 55 Hz.

Madisound designed the 3-way crossover using LEAP. It sounds great, except the lack of bass.

I did a 1 meter frequency plot on-axis and got this:

Click the image to open in full size.

Here is the mic stuck right into one of the ports:

Click the image to open in full size.

I am just baffled by the lack of bass and I would have though the JBL would kick butt in this department, but it doesn't and I can't seem to explain why.

Anyone have any ideas?
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Old 2nd February 2010, 03:27 AM   #2
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Descibe your room. What do they sound like outside?

dave

PS: those graphs look a lot like fuzzmeasure?
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Old 2nd February 2010, 03:35 AM   #3
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by planet10 View Post
Descibe your room. What do they sound like outside?

dave

PS: those graphs look a lot like fuzzmeasure?
Room is about 15' by 33' with a sloped ceiling. Room is a bit live as it contains a kitchen. I have not dragged the speaker outside (the bugger is heavy!!!).

I ran the tests with the speaker moved into the middle of the room facing a sofa with the mic stand in front of it about 1 meter away. I tried other arrangements and different volumes and get the same basic plots, so I think the measurements are correct. Well, they are at least consistent.

Yes, the tool is Fuzmeasure 3.2. Good catch!
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Old 2nd February 2010, 03:58 AM   #4
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Aounds like a NICE ROOM. 1 m is too close to get an accurate measure (actually in room, you move the mic or speaker, you should get a different response below the transition frequency). You need to be in the farfield.

What does the bass sound like?

dave
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Old 2nd February 2010, 04:08 AM   #5
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What do they sound like if you listen to just one at a time?

Sorry but I have to ask. First things first.
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Old 2nd February 2010, 04:21 AM   #6
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Good question Cal.
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Old 2nd February 2010, 04:32 AM   #7
cbdb is offline cbdb  Canada
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JBL 15"s should kick butt on LF (I owned a pair of JBL L201s? driven by a 85 watt amp and never had a lack of bass, even at partys with 150 people). A couple things you could check. If you havent already). Make sure the the speakers are wired in phase? (Swap + and - at one speaker and see if you get less bass). Make sure the pre and amp are putting out LF. (tone sweep?) Make sure you arnt measuring in a LF room mode null (move the mic around the whole room and try a few more measurements (or test it properly and take it outside). Try measuring 1 speaker at a time (to avoid acoustic phase cancelation between the 2 speakers, although this shouldnt matter if the mic is centered between the speakers)

Sorry reread your post and saw you were testing one speaker so disregard the phase swap etc.

Last edited by cbdb; 2nd February 2010 at 04:39 AM.
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Old 2nd February 2010, 05:18 AM   #8
kimbo is offline kimbo  Australia
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First thing I'd try is to hustle up someone elses amp, particularly if you can get your hands on a reputable one, as it is very easy to then eliminate this as the problem. I'm talking about frequency response/damping factor/speaker control etc. being the problem rather than total power. You should get plenty of bass with 50W.
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Old 2nd February 2010, 05:21 AM   #9
kevinkr is offline kevinkr  United States
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What amplifier source impedance was assumed when choosing the bass alignment and designing the cross-over? You might want to try inserting a small amount of series resistance between amp and speaker and see if the measured result changes- this will increase driver QES and thereby QTS. All of this assumes that the low cut filter if present on your amp is not turned on and the amplifier otherwise works properly.
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Last edited by kevinkr; 2nd February 2010 at 05:24 AM.
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Old 2nd February 2010, 05:44 AM   #10
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Are these 2235H brand new or have they been used for quite some time now?

Best regards Johan
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